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smithsonian contributions to paleobiology • number 101

The Neogene Record 

of Northern South American 

Native Ungulates

Juan D. Carrillo, Eli Amson, Carlos Jaramillo, 

Rodolfo Sánchez, Luis Quiroz, Carlos Cuartas, 

Aldo F. Rincón, and Marcelo R. Sánchez-Villagra
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smithsonian contributions to paleobiology • number 101

The Neogene Record 

of Northern South American 

Native Ungulates

Juan D. Carrillo, Eli Amson, Carlos Jaramillo, 

Rodolfo Sánchez, Luis Quiroz, Carlos Cuartas, 

Aldo F. Rincón, and Marcelo R. Sánchez-Villagra

WASHINGTON D.C.

2018
ABSTRACT

Carrillo, Juan D., Eli Amson, Carlos Jaramillo, Rodolfo Sánchez, Luis Quiroz, Carlos Cuartas, Aldo F. Rincón, and Marcelo 

R. Sánchez-Villagra. The Neogene Record of Northern South American Native Ungulates. Smithsonian Contributions to 

Paleobiology, number 101, viii + 67 pages, 35 figures, 13 tables, 2018.—South America was isolated during most of the 

Cenozoic, and it was home to an endemic fauna. The South American Native Ungulates (SANUs) exhibited high taxonomical, morphological, and ecological diversity and were widely distributed on the continent. However, most SANU fossil 

records come from high latitudes. This sampling bias challenges the study of their diversity dynamics and biogeography 

during important tectonic and biotic events, such as the Great American Biotic Interchange, the faunal exchange between 

North and South America after the formation of the Isthmus of Panama. We describe new SANU remains from the Neogene 

of the Cocinetas (northern Colombia) and Falcón (northwestern Venezuela) Basins. In the Cocinetas Basin, the middle 

Miocene fauna of the Castilletes Formation includes Hilarcotherium miyou sp. nov. (Astrapotheriidae), cf. Huilatherium

(Leontiniidae), and Lambdaconus cf. L. colombianus (Proterotheriidae). The late Pliocene fauna of the Ware Formation 

includes a Toxodontinae indet. and the putative oldest record of Camelidae in South America. In the Falcón Basin, the 

Pliocene/Pleistocene faunas of the Codore and San Gregorio Formations include Falcontoxodon aguilerai gen. et sp. nov. and 

Proterotheriidae indet. We provide a phylogenetic analysis for Astrapotheriidae and Toxodontidae. The new data document 

a low-latitude provinciality within some SANU clades (e.g., Astrapotheriidae, Leontiniidae) during the middle Miocene. This 

contrasts with the wide latitudinal distribution of clades of other mammals recorded in the fauna, including the sparassodont 

Lycopsis padillai, the sloth Hyperleptus?, and the proterotheriid Lambdaconus cf. L. colombianus. The Pliocene/Pleistocene 

tropical faunas from northern South America are characterized by the predominance of native taxa despite their proximity 

to the Isthmus of Panama (fully emerged by that time). Only one North American ungulate herbivore immigrant is present, 

a cf. Camelidae indet. The Pliocene and early Pleistocene faunas suggest that environmental changes and biotic interactions 

affected the diversity dynamics and biogeographic patterns of SANUs during the Great American Biotic Interchange.

Cover image: Detail from Figure 34, life reconstruction of the Ware Formation faunal assemblage, Cocinetas Basin, Colombia, by Stjepan Lukac.

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Library of Congress Cataloging-in-Publication Data

Names: Carrillo, Juan D. (Juan David), 1987– author. | Smithsonian Institution Scholarly Press, issuing body.

Title: The Neogene record of northern South American Native Ungulates / Juan D. Carrillo [and seven others].

Other titles: Smithsonian contributions to paleobiology ; no. 101. 0081-0266

Description: Washington, D.C. : Smithsonian Institution Scholarly Press, 2018. | Series: Smithsonian contributions to paleobiology ISSN 0081-0266 ; number 101 | Includes bibliographical references. | Compilation copyright 2018 Smithsonian 

Institution

Identifiers: LCCN 2018007367

Subjects: LCSH: Ungulates, Fossil—South America. | Paleontology—South America.

Classification: LCC QE882.U2 C37 2018 | DDC 569/.62098—dc23 | SUDOC SI 1.30:101

LC record available at https://lccn.loc.gov/2018007367

ISSN: 1943-6688 (online); 0081-0266 (print)

ZooBank registration: 5 July 2018 (LSID urn:lsid:zoobank.org:pub:E42FF7D0-4DCB-40EF-9843-BF9F7481AD40)

Publication date (online): 27 July 2018

Ó The paper used in this publication meets the minimum requirements of the American National Standard for Permanence 

of Paper for Printed Library Materials Z39.48–1992.
Contents

LIST OF FIGURES v

LIST OF TABLES vii

INTRODUCTION 1

Astrapotheria 3

Notoungulata 4

Litopterna 4

Study Sites 4

Cocinetas Basin 4

Falcón Basin 5

The Great American Biotic Interchange 7

MATERIALS AND METHODS 7

Abbreviations 7

Comparative Anatomical Descriptions 8

Astrapotheriidae 8

Leontiniidae 9

Toxodontidae 9

Proterotheriidae 9

Camelidae 9

Phylogenetic Analyses 9

Astrapotheriidae 9

Toxodontidae 9

Body Mass Estimations 9

Chronostratigraphic Framework 11

RESULTS 11

Systematic Paleontology 11

Astrapotheria Lydekker, 1884 11

Astrapotheriidae Ameghino, 1887 11

Uruguaytheriinae Kraglievich, 1928, sensu Vallejo-Pareja et al. (2015) 11

Hilarcotherium Vallejo-Pareja et al., 2015 11

Hilarcotherium miyou sp. nov. 11

Hilarcotherium cf. H. miyou 15

Body Mass Estimation 23

Phylogenetic Analysis of Astrapotheriidae 23
i v • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

Notoungulata Roth, 1903 24

Toxodontia Owen, 1853 24

Leontiniidae Ameghino, 1895 24

cf. Huilatherium Villarroel and Guerrero, 1985 24

Toxodontidae (Gervais, 1847) 25

Toxodontinae (Trouessart, 1898) 25

Falcontoxodon gen. nov. 25

Falcontoxodon aguilerai sp. nov. 25

Falcontoxodon aff. F. aguilerai 32

Falcontoxodon sp. 32

Toxodontinae indet. 34

Body Mass Estimation 37

Phylogenetic Analysis of Toxodontidae 37

Litopterna (Ameghino, 1889) 42

Proterotheriidae (Ameghino, 1887) 42

Lambdaconus (Ameghino, 1897) 42

Lambdaconus cf. L. colombianus (Hoffstetter and Soria, 1986) 

comb. nov. 42

Proterotheriidae indet. 43

Artiodactyla (Owen, 1848) 44

Camelidae (Gray, 1821) 44

cf. Camelidae indet. 44

Chronostratigraphy of the Falcón Basin 47

DISCUSSION 47

Astrapotheriidae 47

Toxodontidae 50

Miocene Fauna 54

Pliocene/Pleistocene Faunas 56

CONCLUSION 59

ACKNOWLEDGMENTS 59

REFERENCES 61
Figures

1. Geologic time scale of the Cenozoic illustrating the South 

American Land Mammal Ages and the chronology of the 

Cocinetas and Falcón Basins 2

2. Geographic location of the Cocinetas and Falcón Basins 5

3. Geographic and stratigraphic occurrence of South American Native 

Ungulates in the Cocinetas Basin 8

4. Geographic and stratigraphic occurrence of South American native 

ungulates in the Falcón Basin 10

5. Mandible of Hilarcotherium miyou sp. nov. (Astrapotheriidae) 12

6. Upper fourth premolar and mandibular symphysis of 

Hilarcotherium miyou sp. nov. 13

7. Mandible of Xenastrapotherium christi (Astrapotheriidae) 15

8. Bivariate plots of dental measurements of Uruguaytheriinae 16

9. Basicranium and vertebrae of Hilarcotherium cf. H. miyou and 

selected astrapotheres for comparison 17

10. Scapulae and humeri of Hilarcotherium cf. H. miyou and selected 

astrapotheres for comparison 21

11. Antebrachial bones of Hilarcotherium cf. H. miyou and selected 

astrapotheres for comparison 22

12. Hypothesis of phylogenetic relationships within Astrapotheriidae 24

13. Right m3 of Leontiniidae 25

14. Skull of Falcontoxodon aguilerai gen. et sp. nov. (Toxodontidae) 26

15. Holotype of Gyrinodon quassus (Toxodontidae) 27

16. Mandible of Falcontoxodon aguilerai gen. et sp. nov. 28

17. Partial skull of Falcontoxodon aff. F. aguilerai 33

18. Partial mandibles of Falcontoxodon sp. 35

19. Right foot of Nesodon imbricatus (Toxodontidae) 36

20. Toxodontid astragali 37

21. Astragalar morphospace in toxodontids 38

22. Toxodontid calcanei and metatarsals 38

23. Upper molars of Toxodontinae indet. from the Ware Formation 39

24. Hypothesis of phylogenetic relationships within Toxodontidae 41

25. Dental remains of Proterotheriidae (Litopterna) from the 

Cocinetas Basin 43
v i • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

26. Postcrania of Proterotheriidae (Litopterna) from Ware and Codore 

Formations 45

27. Right m1 or m2 of Camelidae indet. (Artiodactyla) from the Ware 

Formation 46

28. Urumaco West chronostratigraphy 48

29. Urumaco East chronostratigraphy 49

30. Life reconstruction of fauna from the Castilletes Formation 55

31. Key of the reconstruction shown in Figure 30 55

32. Life reconstruction of fauna from the San Gregorio Formation 57

33. Key of the reconstruction shown in Figure 32 57

34. Life reconstruction of fauna from the Ware Formation 58

35. Key of the reconstruction shown in Figure 34 58
Tables

1. Mammals from the Cocinetas Basin 6

2. Mammals from the Falcón Basin 6

3. Dental measurements of Hilarcotherium miyou sp. nov. 

and Hilarcotherium cf. H. miyou from Castilletes Formation 14

4. Postcranial measurements of Astrapotheriidae 18

5. Body mass estimates of astrapotheres 23

6. Dental measurements of Falcontoxodon 30

7. Astragalar measurements of toxodontids 36

8. Measurements of calcaneus and metatarsals of toxodontids 39

9. Cranial and mandibular measurements of Falcontoxodon 

aguilerai sp. nov. 40

10. Body mass estimates for Falcontoxodon aguilerai sp. nov. 40

11. Postcranial measurements of the Proterotheriidae indet. specimens 

of the Ware Formation 46

12. Chronostratigraphic data for composite Urumaco East and West sections 50

13. Biochronology of the Cocinetas and Falcón Basins 51

INTRODUCTION

South America was isolated during most of the Cenozoic Era and was home to a 

highly endemic fauna (Simpson, 1980; Wilf et al., 2013). This isolation was punctuated 

with dispersal events that introduced novel clades into the continent (Croft, 2012), such 

as the hystricognath rodents during the middle Eocene (ca. 41 million years ago [mya];

Antoine et al., 2012) and platyrrhine monkeys during the late Eocene (Bond et al., 2015) 

(Figure 1), migrations referred to as the Trans-Atlantic Dispersal Interval (TADI; Croft, 

2016). The isolation of South America’s mammal fauna ceased during the late Neogene 

after the formation of the Isthmus of Panama, which facilitated a faunal exchange with 

North America known as the Great American Biotic Interchange (Figure 1).

Among mammals, the South American Native Ungulates (“SANUs”; Welker et al., 

2015) are an important faunal element of the Cenozoic in the continent, with an extensive fossil record that extends from the early Paleocene (ca. 64 mya, Tiupampan South 

American Land Mammal Age [SALMA]; Gelfo et al., 2009; Woodburne et al., 2014a) to 

late Pleistocene (ca. 11–7 kya, Cione et al., 2003; ca. 11–13 kya, Barnosky and Lindsey, 

2010). The SANUs are recorded along a wide latitudinal range in South America reaching central and southern North America at least by late Pleistocene times (Lundelius 

et al., 2013). The SANUs exhibit a high taxonomic diversity, wide body mass range, and 

different degrees of hypsodonty (Madden, 2015; Bond, 2016; Gomes-Rodrigues et al., 

2017).

Phylogenetic relationships among SANUs, and of SANUs to other placentals, have 

long been a subject of debate. The SANUs include the clades Litopterna, Notoungulata, Astrapotheria, Xenungulata and Pyrotheria, which have been hypothesized to be 

monophyletic (classified in Meridiungulata; McKenna, 1975; McKenna and Bell, 1997) 

or polyphyletic (O’Leary et al., 2013); and for some SANU clades, different affinities 

within placentals are proposed (Billet and Martin, 2011; Kramarz and Bond, 2014; 

Buckley, 2015; Welker et al., 2015; Westbury et al., 2017). Phylogenetic hypotheses 

include affinities of Litopterna and other closely related SANUs with an extinct group of 

North American ungulates known as Mioclaenideae, based on morphological evidence 

The Neogene Record of Northern South 

American Native Ungulates

Juan D. Carrillo,1,2* Eli Amson,3 Carlos Jaramillo,2

Rodolfo Sánchez,4 Luis Quiroz,5 Carlos Cuartas,2

Aldo F. Rincón,6 and Marcelo R. Sánchez-Villagra1

1 Paläontologisches Institut und Museum, Universität Zürich, Karl-Schmid-Strasse 4, 8006 

Zurich, Switzerland. Present address: Department 

of Biological and Environmental Sciences, University of Gothenburg, Carl Skottsbergs gata 22B, 

SE 405 30, Gothenburg, Sweden.

2 Smithsonian Tropical Research Institute, 

Apartado 0843-03092, Balboa, Ancon, Panama.

3 Humboldt-Universität, AG Morphologie und 

Formengeschichte, Bild Wissen Gestaltung ein 

interdisziplinäres Labor & Institut für Biologie, 

Philippstrasse 12/13, D-10115, Berlin, Germany.

4 Museo Paleontológico de la Alcaldía de Urumaco, Falcón, Venezuela.

5 Department of Geological Sciences, University 

of Saskatchewan, Saskatoon, Saskatchewan S7N 

5E2, Canada.

6 Departamento de Física y Geociencias, Universidad del Norte, Km. 5 Vía Puerto Colombia, Barranquilla, Colombia.

* Correspondence: juan.david.carillo@gu.se

Manuscript received 24 July 2017; accepted 

22 September 2017.
2 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY
NUMBER 101 • 3

FIGURE 1. (Opposite page) Geologic timescale of the Cenozoic Era illustrating the South American Land Mammal Ages (SALMAs), the 

chronology of the Cocinetas and Falcón Basins, the first appearance datums (FADs) of some South American clades, and the Cenozoic 

events of faunal exchange (Croft, 2016): TADI (Trans-Atlantic Dispersal Interval), the Great American Biotic Interchange, including 

the main dispersal events (GABI 1–4). The FAD of Litopterna is a minimum age, and the clade could be present since the Tiupampan 

SALMA (Muizon and Cifelli, 2000). The chronology of the latter follows Woodburne (2010): GABI 1 = ca. 2.4–2.6 mya, GABI 2 = ca. 

1.8 mya, GABI 3 = ca. 0.8–1.0 mya, GABI 4 = ca. 0.125 mya.

(Cifelli, 1983; Muizon and Cifelli, 2000). Using postcranial data, 

Horovitz (2004) analyzed the relationships of SANUs with several other placentals and found no support for their monophyly. 

The SANUs were split between two separate clades of Holarctic ungulates (“Condylarthra”), one comprising Litopterna and 

Notoungulata and another comprising Astrapotheria. Using 

craniodental characters, Billet (2010, 2011) included Pyrotheria within Notoungulata and found this clade to be sister to 

Astrapotheria rather than Litopterna.

O’Leary et al. (2013) combined morphological characters 

and molecular sequences to evaluate the phylogenetic relationships within Placentalia, represented by 86 extinct and living 

species. According to this phylogeny, representatives of Notoungulata and Xenungulata are within Afrotheria, whereas representatives of Litopterna are within Laurasiatheria. In contrast, 

Welker et al. (2015) and Buckley (2015) used alpha 1 and 2 collagen chains to address the phylogenetic relationship of Notoungulata and Litopterna. Their results support the conclusion that 

Notoungulata and Litopterna form a clade as sister taxon to 

Perissodactyla, within Laurasiatheria. The close relationship of 

Litopterna with Perissodactyla is also supported by mitogenomic 

data (Westbury et al., 2017). Carrillo and Asher (2017) combined amino acid, collagen sequences, and morphological characters into a dataset including 182 fossil and living taxa in order 

to evaluate the relationship of Notoungulata and other SANUs 

within placentals. Their results yielded a limited number of possible phylogenetic relationships, but did not arbitrate between 

potential affinities with Afrotheria and Laurasiatheria.

Astrapotheria

Astrapotheria is a clade of SANUs recorded from the early 

Eocene (Itaboraian SALMA; Soria and Powell, 1981; Soria, 1987; 

Kramarz and Bond, 2013; Woodburne et al., 2014a,b; Kramarz 

et al., 2017) to the middle Miocene (12.76–13.6 mya, Laventan 

SALMA; Johnson, 1984; Johnson and Madden, 1997; Goillot 

et al., 2011; Vallejo-Pareja et al., 2015). The clade had a large 

body mass range between ~60 kg (Albertogaudrya; Vizcaíno 

et al., 2012) and ~4117 kg (Parastrapotherium herculeum?; 

Kramarz and Bond, 2011). Astrapotheres are characterized by 

canines developed as tusks, flattened astragalus, and calcaneus 

with secondary ectal facet and enlarged peroneal tubercle (Cifelli, 1993; Weston et al., 2004). In the more derived taxa the 

nasals are retracted, indicating the presence of a proboscis (Scott, 

1937; Johnson, 1984; Johnson and Madden, 1997). Scott (1937) 

suggested amphibious habits for astrapotheres. Taphonomic evidence supports semiaquatic habits (Scott, 1937; Johnson, 1984; 

Marshall et al., 1990; Weston et al. 2004), and microanatomical 

features of long bones could support specializations to graviportality and semiaquatic habits in astrapotheres (Houssaye et al., 

2016).

According to Cifelli (1993) two main clades are recognized 

within Astrapotheria: Trygonostylopidae and Astrapotheriidae. 

The latter comprises two clades: Astrapotheriinae, consisting 

of the southern taxa Astrapotherium and Astrapothericulus, 

and Uruguaytheriinae, which is composed of Uruguaytherium, 

Granastrapotherium, Xenastrapotherium and Hilarcotherium.

The Uruguaytheriinae is supported by dental characters such as 

the absence of hypoflexid, absence of pillar in the lower molars, 

and absence of a labial cingulum (Johnson and Madden, 1997; 

Kramarz and Bond, 2009, 2011; Vallejo-Pareja et al., 2015).

Among Uruguaytheriinae, Uruguaytherium beaulieui is the 

oldest described taxon, being the sister taxa to the rest of the 

clade, and recorded in Uruguay but without precise provenance 

or known age (Kraglievich, 1928; Kramarz and Bond, 2011; 

Vallejo-Pareja et al., 2015). The earliest record of Uruguaytheriinae is a P4 of an undetermined genus collected in Alto Río Beu, 

near Santa Rosa, Ucayali, Peru (?late Oligocene; Antoine et al., 

2016). Additional Uruguaytheriinae specimens are recorded in 

the early middle Miocene (Colloncuran SALMA) fauna of Cerdas, Bolivia (Croft et al., 2016). A Neotropical clade within 

Uruguaytheriinae comprises Hilarcotherium castanedaii, Granastrapotherium snorki, and five species of Xenastrapotherium

(X. kraglievichi, X. aequatorialis, X. chaparralensis, X. amazonense, X. christi) (Kraglievich, 1928; Stehlin, 1928; Cabrera, 

1929; Johnson and Madden, 1997; Vallejo-Pareja et al., 2015). 

Hilarcotherium is recorded in La Victoria Formation (middle 

Miocene), in the upper Magdalena valley, Colombia (VallejoPareja et al., 2015). Granastrapotherium and Xenastrapotherium co-occurred in the middle Miocene (Laventan SALMA) 

faunas of La Venta and Fitzcarrald (Johnson and Madden, 1997; 

Goillot et al., 2011). Xenastrapotherium is widely distributed 

geographically and stratigraphically. It is recorded in Colombia, 

Venezuela, Ecuador, Brazil, and Peru, in sediments ranging from 

early to middle late Miocene in age (Goillot et al., 2011; Antoine 

et al., 2016).
4 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

Notoungulata

Notoungulata is a clade of SANUs with a high taxonomic 

diversity that includes more than 140 genera and 13 families 

(Croft, 1999), large morphological disparity (Giannini and 

García-López, 2014; Bond, 2016), and diverse dental eruption patterns, degrees of hypsodonty (Madden, 2015; GomesRodrigues et al., 2017) and inferred diets (MacFadden, 2005; 

Croft and Weinstein, 2008; Townsend and Croft, 2008). 

Notoungulata is monophyletic (Roth, 1903; Cifelli, 1993; Billet, 2010, 2011) and is recorded during most of the Cenozoic 

in South America, from the early Paleocene (ca. 64 mya Tiupampan) (Muizon and Cifelli, 2000; Gelfo et al., 2009; Woodburne et al., 2014a) to the late Pleistocene (Cione et al., 2003; 

Barnosky and Lindsey, 2010). Together with Typotheria, Toxodontia is one of the main clades of Notoungulata. Toxodontia 

includes, among others, the clades Leontiniidae and Toxodontidae (Billet, 2011).

Leontiniidae are part of a clade within Toxodontia that also 

includes some Notohippidae and Toxodontidae (Cifelli, 1993; 

Billet, 2011). Leontiniidae are known from the late Eocene 

(Mustersan SALMA) (Bond and López, 1995; Ribeiro et al., 

2010) to the middle Miocene (Laventan) (Villarroel and Colwell Danis, 1997). It attained its greater diversity during the late 

Oligocene (Deseadan SALMA) (Shockey et al., 2012; Cerdeño 

and Vera, 2015). Leontiniids have a medium-to-large body mass 

among Toxodontia. They are characterized by having mesodont 

(see Mones, 1982) cheek teeth and a tendency to form tusk-like 

incisors (Shockey et al., 2012). In the Miocene, leontiniids were 

widespread. They are represented by Colpodon from the various localities in central Patagonia, Argentina (Colhuehuapian 

SALMA; ca. 20.0–20.2 mya) and Laguna del Laja, Chile (early 

Miocene; ca. 19.5–19.8 mya) (Ré et al., 2010; Ribeiro et al., 

2010; Shockey et al., 2012), and Huilatherium from La Venta, 

Colombia (Laventan) (Villarroel and Colwell Danis, 1997). 

The phylogenetic relationships within Leontiniidae are not fully 

resolved, but the Miocene taxa Colpodon and Huilatherium are 

hypothesized to belong to the same clade (Shockey et al., 2012; 

Cerdeño and Vera, 2015).

Toxodontidae is a clade of medium-to-large herbivores characterized by a specialized anterior dentition, ever-growing tusks, 

and hypsodont molars (Madden, 1997). Toxodonts were widespread in South America from the late Oligocene to late Pleistocene (Deseadan through Lujanian SALMAs) (Nasif et al., 2000). 

Within Toxodontidae two clades are recognized: Nesodontinae 

and Toxodontinae (Nasif et al., 2000; Forasiepi et al., 2015; 

Bonini et al., 2017a). Nesodontinae consists of early middle Miocene (“Pinturan” and Santacrucian SALMA) toxodontids from 

southern South America, whereas Toxodontinae comprises middle Miocene to late Pleistocene (Santacrucian through Lujanian) 

taxa widely distributed on the continent (Forasiepi et al., 2015). 

Toxodontinae representatives reached Central (Webb and Perrigo, 1984; Lucas et al., 1997; Lucas, 2014) and North America 

(~30°N) (Lundelius et al., 2013) during the late Pleistocene as 

part of the Great American Biotic Interchange (see below).

Litopterna

Litopterna is a diverse clade of SANUs recorded in South 

America from at least the late Paleocene (Peligran SALMA 

[Gelfo et al., 2009], although possibly they were present since 

the Tiupampan SALMA [Muizon and Cifelli, 2000]), to the late 

Pleistocene (Bond et al., 2001). Several clades are recognized 

within Litopterna: Protolipternidae, Notonychopidae, Adianthidae, Macraucheniidae, and Proterotheriidae (Cifelli, 1983, 

1993; Schmidt, 2015; Forasiepi et al., 2016). The Sparnotheriodontidae has been variably treated as “Condylarthra” (Cifelli, 

1983, 1993) or as a member of Litopterna (Soria, 2001).

Proterotheriids were small to medium-sized cursorial 

herbivores. They show different types of dentition, including 

brachyodont, mesodont, and protohypsodont (Soria, 2001; 

Villafañe et al., 2012; Schmidt, 2015). They are characterized 

by a reduction of the digits II and IV, acquiring a functional 

monodactyly (Cifelli and Villarroel, 1997; Ubilla et al., 2011; 

Schmidt, 2015). Proterotheriidae had a wide latitudinal distribution, and it is recorded from the early Eocene (Itaboraian) 

to the late Pleistocene (Bonaerian–Lujanian). It attained its 

maximum diversity during the Miocene (Santacrucian through 

Huayquerian SALMAs) (Bond et al., 2001; Villafañe et al., 

2006; Scherer et al., 2009; Ubilla et al., 2011; Schmidt, 2015).

There are three main clades recognized within Proterotheriidae: Anisolambdinae, Megadolodinae, and Proterotheriinae; only the latter two are recorded in the Neogene (Cifelli, 

1983; Cifelli and Villarroel, 1997; Soria, 2001; Villafañe et al., 

2006). The Megadolodinae is known from the La Venta fauna 

(middle Miocene; Laventan) of Colombia (McKenna, 1956; 

Cifelli and Villarroel, 1997) and the Urumaco Formation (late 

Miocene) of Venezuela (Carlini et al., 2006b). The Proterotheriinae is recorded from the late Oligocene to the late Pleistocene (Deseadan through Lujanian) (Villafañe et al., 2006). They 

have a wide distribution (including northern South America) and 

reach their highest diversity during the Miocene (Santacrucian 

through Huayquerian) (Cifelli and Guerrero, 1997; Villafañe 

et al., 2006; Schmidt, 2011, 2015).

Study Sites

Cocinetas Basin

The Cocinetas Basin is located in the eastern Guajira Peninsula, in northern Colombia (Figure 2). The Neogene stratigraphy of the basin was revised by Moreno et al. (2015). The 

terrestrial mammal assemblages were collected from both the 

Castilletes and Ware Formations. The Castilletes Formation 

was deposited in a shallow marine to fluvio-deltaic environment 

and has been dated as 16.7–14.2 mya based on 87Sr/86Sr isotope 
NUMBER 101 • 5

chronostratigraphy and macroinvertebrate biostratigraphy 

(late early to early middle Miocene, upper Burdigalian–Langhian; Santacrucian/Colloncuran SALMAs; Hendy et al., 2015; 

Moreno et al., 2015). The Ware Formation is dominated by fluvio-deltaic environment deposits at the base and shoreface and 

nearshore deposits at the top. It is dated as 3.4–2.78 mya based 

on 87Sr/86Sr isotope chronostratigraphy and macroinvertebrate 

biostratigraphy (late Pliocene, Piacenzan, Chapadmalalan/Marplatan SALMAs; (Hendy et al., 2015; Moreno et al., 2015).

The terrestrial mammalian fauna of the Castilletes Formation includes a sparassodont, a sloth, astrapotheres, litopterns, 

and notoungulates (Table 1; Amson et al., 2016; Suarez et al., 

2016). The Castilletes Formation also records other terrestrial 

and marine fossils such as mollusks, echinoderms, arthropods, 

sharks, rays, bony fishes, snakes, turtles, crocodiles, cetaceans, 

and plants (Aguilera et al., 2013b; Cadena and Jaramillo, 2015a, 

2015b; Hendy et al., 2015; Moreno et al., 2015; Moreno-Bernal 

et al., 2016; Aguirre-Fernández et al., 2017a). The mammalian 

fauna of the Ware Formation is characterized by an assemblage 

of sloths, cingulates, rodents, toxodontids, a procyonid, and a 

camelid (Table 1), the last two being immigrants from North 

America (Forasiepi et al., 2014; Moreno et al., 2015; Amson 

et al., 2016; Moreno-Bernal et al., 2016; Pérez et al., 2017). The 

Ware Formation also records crocodiles (Moreno-Bernal et al., 

2016), turtles, bony fishes, fossil wood, and a diverse marine 

assemblage (Aguilera et al., 2013a; Hendy et al., 2015; Jaramillo 

et al., 2015; Moreno et al., 2015).

Falcón Basin

The Falcón Basin in northwestern Venezuela (Figure 2) has a 

long history of paleontological and geological studies (SánchezVillagra, 2010). The Urumaco sequence includes seven geological formations: Agua Clara, Cerro Pelado, Querales, Socorro, 

Urumaco, Codore and San Gregorio (Quiroz and Jaramillo, 

2010). Four of these formations have reports of fossil mammals: 

Socorro, Urumaco, Codore (Sánchez-Villagra et al., 2010, and 

references therein), and San Gregorio (Table 2), which together 

extend from the middle Miocene to the late Pliocene (Quiroz and 

Jaramillo, 2010).

The Urumaco Formation is characterized by diverse faunal associations in terrestrial, estuarine, and marine environments of late Miocene age (Sánchez-Villagra and Aguilera, 

2006; Quiroz and Jaramillo, 2010). The terrestrial mammal 

fauna of Urumaco includes giant rodents (Sánchez-Villagra 

et al., 2003; Horovitz et al., 2006, 2010; Geiger et al., 2013; 

Carrillo and Sánchez-Villagra, 2015) as well as a high diversity 

of sloths (Carlini et al., 2006a, 2006c, 2008a; Rincón et al., 

2015). Coprolites of fossil vertebrates (including terrestrial 

mammals) are also recorded (Dentzien-Dias et al., 2018). The 

described SANUs include the megadolodine litoptern Bounodus enigmaticus (Carlini et al., 2006b) and a toxodontine 

incertae sedis (Bond et al., 2006). Linares (2004) provided a 

list of SANUs, none of which have been described (see Bond 

and Gelfo, 2010).

FIGURE 2. Geographic location of 

Cocinetas and Falcón Basins in Colombia and Venezuela, respectively.
6 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

TABLE 1. Mammals from the Cocinetas Basin. BM = Body mass in kg. A dash (-) indicates data not available.

Clade Subclade Taxon BM Reference

Castilletes Formation

Sparassodonta Borhyaenoidea Lycopsis padillai ~22 Suarez et al. (2016)

Xenarthra Megatherioidea Hyperleptus? - Amson et al. (2016)

Glyptodontidae Glyptodontidae indet. - Moreno et al. (2015)

Pampatheriidae Pampatheriidae indet. - Moreno et al. (2015)

Astrapotheria Uruguaytheriinae Hilarcotherium miyou n. sp. ~6,456 This work

Notoungulata Leontiniidae cf. Huilatherium - This work

Litopterna Proterotheriidae Lambdaconus cf. L. colombianus - This work

Ware Formation

Xenarthra Lestodontini Gen. et sp. nov. - Amson et al. (2016)

Scelidotheriinae Gen. et sp. indet. - Amson et al. (2016)

Megalonychidae Gen. et sp. nov. - Amson et al. (2016)

Megatheriinae Pliomegatherium lelongi ~2,417 Amson et al. (2016)

Nothrotheriinae cf. Nothrotherium ~41 Amson et al. (2016)

Glyptodontidae Glyptodontidae indet. - Moreno et al. (2015)

Pampatheriidae Pampatheriidae indet. - Moreno et al. (2015)

Rodentia Caviomorpha Hydrochoeropsis? wayuu ~24 Pérez et al. (2017)

Caviomorpha Erethizontidae indet. - Moreno et al. (2015)

Notoungulata Toxodontidae Toxodontinae indet. - This work

Artiodactyla Camelidae Camelidae indet. - This work

Carnivora Procyonidae Chapalmalania sp. - Forasiepi et al. (2014)

Litopterna Proterotheriidae Proterotheriidae indet. - This work

TABLE 2. Mammals from the Falcón Basin.

Clade Subclade Taxon Reference

Codore Formation

Notoungulata Toxodontidae Falcontoxodon aguilerai n. sp.a This work

Litopterna Proterotheriidae Proterotheriidae indet. This work

Xenarthra Glyptodontidae Boreostemma pliocena Carlini et al. (2008)

Pampatheriidae Indet. Carlini, pers comm.b

San Gregorio Formation

Carnivora Procyonidae Cyonasua sp. Forasiepi et al. (2014)

Notoungulata Toxodontidae Falcontoxodon sp. This work

Rodentia Caviomorpha cf. Caviodon Vucetich et al. (2010)

Hydrochoeropsis? wayuu Vucetich et al. (2010); Pérez et al. (2017)

Marisela gregoriana Vucetich et al. (2010)

Neoepiblema sp. Vucetich et al. (2010)

Xenarthra Dasypodidae Pliodasypus vergelianus Castro et al. (2014)

Glyptodontidae Boreostemma? sp. nov. Zurita et al. (2011)

Megatheriinae aff. Proeremotherium Carlini, pers comm.

Pampatheriidae Indet. Carlini, pers comm.

a Body mass = 796 kg.

b A. A. Carlini, Museo de La Plata, personal communication.
NUMBER 101 • 7

The Codore Formation is early Pliocene in age. It is divided 

into three formal members: El Jebe, Chiguaje, and Algodones. 

The El Jebe and Algodones Members were deposited in a fluvial environment, whereas the Chiguaje Member represents a 

marine transgression (Quiroz and Jaramillo, 2010) and records 

cetaceans (Aguirre-Fernández et al., 2017a; 2017b). The terrestrial mammal fauna from Codore includes the glyptodon 

Boreostemma pliocena from the El Jebe Member (Carlini et al., 

2008b) and a pampathere (A. A. Carlini, Museo de La Plata, 

personal communication).

The San Gregorio Formation is late Pliocene–early Pleistocene in age (Quiroz and Jaramillo, 2010). Fossil mammals come 

from the Vergel Member at the base of the San Gregorio and 

consist of caviomorph rodents (Vucetich et al., 2010), cingulates (Zurita et al., 2011; Castro et al., 2014), and a procyonid 

(Forasiepi et al., 2014).

The Great American Biotic Interchange

The Great American Biotic Interchange (GABI) is one of the 

greatest events of biotic exchange at a continental scale (Marshall et al., 1982; Webb, 1985, 1991). The traditional interpretation places the onset of the GABI ca. 3 mya, with some early 

mammal migrations (“heralds”) during the late Miocene from 

South to North America by ca. 9 mya and from North to South 

America by ca. 7 mya (Webb, 2006; Woodburne, 2010; Leigh 

et al., 2014; Cione et al., 2015; O’Dea et al., 2016). Other studies 

using dated molecular phylogenies across a wide range of taxa 

in addition to mammals indicate that an important part of the 

interchange predated ca. 3 mya (Koepfli et al., 2007; Cody et 

al., 2010; Eizirik, 2012; Leite et al., 2014; Bacon et al., 2015; 

Stange et al., 2018).

The mammalian fossil record in South America shows that 

although the first immigrations are recorded during the late 

Miocene (ca.10–7 mya), the number of GABI participants rapidly increases after ca. 5–3 mya and this trend continues during 

the Pleistocene (Carrillo et al., 2015). Dated molecular phylogenies suggest a similar pattern for birds (Weir et al., 2009). 

For mammals, the core of the GABI is composed of a series 

of major migration “waves” during the Pleistocene (2.5–0.012 

mya) (Woodburne, 2010). Climatic and environmental changes 

possibly influenced migration patterns during the Pleistocene 

(Webb, 1991; Bacon et al., 2016). Additional data on tropical paleoenvironments and paleofaunas from the Pliocene and 

Pleistocene are needed to test this hypothesis (Jaramillo, 2018).

The Neotropical fossil record is essential to reach a better 

understanding of the diversity dynamics and paleobiogeography 

during the GABI (Jaramillo, 2018). However, there is a fossil 

sampling bias in the continent, as our knowledge of the tropics 

is very scant when compared with that of the temperate faunas 

(Carrillo et al., 2015). The new findings from the Cocinetas and 

Falcón Basins serve to characterize changes of mammal assemblages in northern South America just before and during the 

GABI.

MATERIALS AND METHODS

We took standard linear measurements with a caliper to 

the nearest 0.1 mm, and with a metric tape for large elements 

(> 15 cm). For orientation of the dentition we follow Smith and 

Dodson (2003), where the four cardinal directions are mesial, 

distal, lingual, and labial (buccal). We follow the recommendations of Bengtson (1988) for the use of open nomenclature. The 

chronology of SALMAs follows Flynn and Swisher (1995), Madden et al. (1997), Cione and Tonni (1999, 2001), Tonni (2009), 

Kramarz et al. (2010), Shockey et al. (2012), Tomassini et al. 

(2013), and Woodburne et al. (2014a,b). Three-dimensional surface models of selected specimens of the described material are 

available in MorphoMuseuM (Carrillo et al., 2018a). Additional 

supplementary material is available from the Dryad Digital 

Repository (Carrillo et al., 2018b).

Abbreviations

Institutions

AMU-CURS Alcaldía del Municipio de Urumaco, Colección Urumaco Rodolfo Sánchez, Venezuela

IGM Museo Geológico José Royo y Gómez, 

Servicio Geológico Colombiano, Bogotá, 

Colombia

MACN Museo Argentino de Ciencias Naturales, 

Buenos Aires, Argentina

MLP Museo de La Plata, La Plata, Argentina

MNHN Muséum national d’Histoire naturelle, Paris, 

France

MUN Mapuka Museum, Universidad del Norte, 

Barranquilla, Colombia

NHMUK Natural History Museum, London, UK

NMB Naturhistorisches Museum Basel, Basel, 

Switzerland

PIMUZ Paläontologisches Institut und Museum Universität Zürich, Zurich, Switzerland

STRI Smithsonian Tropical Research Institute, 

Panama

UNEFM-CIAAP Universidad Nacional Experimental Francisco de Miranda, Centro de Investigaciones 

Antropológicas, Arqueológicas y Paleontológicas, Coro, Venezuela

YPM Yale Peabody Museum, New Haven, Conn., 

USA

Other Abbreviations

C, c upper canine, lower canine

I, i upper incisor, lower incisor

M, m upper molar, lower molar

mya million years ago

P, p upper premolar, lower premolar

SALMA South American Land Mammal Age

SANU South American native ungulate
8 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

Comparative Anatomical Descriptions

Astrapotheriidae

The astrapothere material described here comes from the 

Castilletes Formation, in the Guajira Department, northern 

Colombia (Figure 3). Dental morphology and terminology follow Johnson (1984). We took craniodental measurements for 

astrapotheres following Johnson and Madden (1997) and VallejoPareja et al. (2015). The craniodental material is described in 

comparison with other Uruguaytheriinae sensu Vallejo-Pareja 

et al. (2015), and postcranial elements are compared with 

FIGURE 3. Geographic and stratigraphic occurrence of South American Native Ungulates (SANUs) in the Cocinetas Basin. (a) Map 

showing locations of fossiliferous localities with SANUs; (b) stratigraphic profile of the Castilletes Formation indicating the stratigraphic 

position of each locality; (c) stratigraphic profile of the Ware Formation indicating the stratigraphic position of each locality; both profiles are modified from Moreno et al. (2015); (d) landscape view at the Police Station locality (for scale, note two people standing at top 

of bluff); photo by Christian Ziegler.
NUMBER 101 • 9

astrapotheres whose postcranial anatomy is best known, in particular Astrapotherium and Parastrapotherium (Riggs, 1935; 

Scott, 1937).

Leontiniidae

The leontiniid molar comes from the Castilletes Formation 

(Figure 3); for its description, we considered recent systematic 

works on leontiniids (e.g., Villarroel and Colwell Danis, 1997; 

Shockey et al., 2012; Cerdeño and Vera, 2015). Dental terminology follows Ribeiro et al. (2010).

Toxodontidae

The toxodontid material described here comes from the 

Algodones Member of the Codore Formation and the Vergel Member of the San Gregorio Formation (Figure 4). Dental 

morphology and terminology follow Madden (1990, 1997). 

Craniodental material is described in comparison with other 

Toxodontinae sensu Nasif et al. (2000) and Forasiepi et al. 

(2015). Postcranial elements are described in comparison with 

toxodontids whose postcranial elements are best known, in particular Nesodon imbricatus and Toxodon platensis.

For the toxodontid foot bones, we measured the length and 

width of the calcaneus and tarsals. For the astragalus, we took 

nine measurements following Tsubamoto (2014), and we used 

these measurements in a Principal Component Analysis (PCA) to 

explore astragalar variation in toxodontids.

Proterotheriidae

The proterotheriid material described here comes from 

the Castilletes and Ware Formations in the Cocinetas Basin, 

and the Algodones Member of the Codore Formation in the 

Falcón Basin (Figures 3–4). Dental terminology follows Soria 

(2001) and Schmidt (2015). Dental and postcranial remains 

are described in comparison with recent systematic works on 

Proterotheriidae (Cifelli and Villarroel, 1997; Scherer et al., 

2009; Schmidt, 2015). Postcranial measurements were taken 

following Schmidt (2013).

Camelidae

The camelid molar comes from the Ware Formation 

(Figure 3). Dental terminology follows Scherer et al. (2007) and 

Rincón et al. (2012). We follow Scherer (2013) and Gasparini 

et al. (2017) for the taxonomy of South American camelids.

Phylogenetic Analyses

Astrapotheriidae

We conducted a phylogenetic analysis using maximum 

parsimony. The analysis included 17 taxa and 64 characters; 

61 characters were ordered and three unordered, following 

Vallejo-Pareja et al. (2015). Studies on simulated and empirical data showed that parsimony analyses with ordered states 

perform better when using characters that form morphoclines 

(Grand et al., 2013). Taxa included are Eoastrapostylops as 

the outgroup (Kramarz et al., 2017), and 16 astrapotheriids. 

We used the matrix presented by Vallejo-Pareja et al. (2015), 

and we added Xenastrapotherium kraglievichi, Xenastrapotherium christi, and the new Uruguaytheriinae from the Castilletes 

Formation. We excluded Xenastrapotherium aequatorialis, 

Xenastrapotherium chaparralensis, and Xenastrapotherium 

amazonense, because they are known only from fragmentary 

elements. We analyzed the character matrix with the program 

PAUP* 4.0 (Swofford, 2002). We used equally weighted characters, excluded uninformative characters, treated gaps as 

missing, and treated taxa with multiple states as polymorphic. 

We did a search using the branch-and-bound algorithm with 

a furthest addition sequence. A normal bootstrap resampling 

was performed, with 1000 replications. We provide the character–taxon matrix in supplementary materials (Carrillo et al., 

2018b: appdx. 3).

Toxodontidae

We performed a maximum parsimony analysis on 28 

notoungulate taxa and 59 morphological characters with 

PAUP* 4.0 (Swofford, 2002). We used the matrix presented by 

Forasiepi et al. (2015) and modified by Bonini et al. (2017a). We 

added Piauhytherium as described by Guérin and Faure (2013), 

and the new toxodontine from Codore Formation. We included 

Xotodon cristatus and Xotodon major as coded by Bonini et al. 

(2017a,b). We excluded uninformative characters, treated gaps 

as missing, and treated taxa with multiple states as polymorphic. Forasiepi et al. (2015) performed a phylogenetic analysis 

using implied and equal weights. In order to be comparable, 

we also used equally weighted characters and implied weighting 

with a concavity constant (k) value of 3. The implied weighting 

weights characters against homoplasy and improves the resampling metrics associated with the quality of the results (Goloboff 

et al., 2008; Goloboff, 2014). We did a heuristic search with 

a starting tree obtained via stepwise addition using the closest 

addition sequences and tree bisection reconnection (TBR), saving ten trees per round. A normal bootstrap resampling was 

performed, with 1000 replications. We provide the character–

taxon matrix in supplementary materials (Carrillo et al., 2018b: 

appdx. 4).

Body Mass Estimations

To estimate the body mass in toxodonts, we used the 

multivariate regression functions proposed by Mendoza et al. 

(2006), based on craniodental measurements of living ungulates. For astrapotheres, we used the bivariate regression equation of the second lower molar length (m2) for non-selenodont 
1 0 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

FIGURE 4. Geographic and stratigraphic occurrence of Falcontoxodon gen. nov. and Proterotheriidae: (a) location and (b) stratigraphic profile of localities from the Codore and San Gregorio Formations where specimens of Falcontoxodon and Proterotheriidae 

were found (Fm. = formation; Mbr. = member.); (c) landscape view in Norte Casa Chiguaje locality, of the Vergel Member, San 

Gregorio Formation; (d) artistic reconstruction of a toxodontid by Jorge González (modified from Sánchez-Villagra et al., 2010).
NUMBER 101 • 1 1

ungulates from Damuth (1990: tbl. 16.9), and the equation of 

the humerus length (H2) for all ungulates from Scott (1990: 

tbl. 16.7).

Chronostratigraphic Framework

The Neogene sequence of the Falcón Basin is one of the 

thickest and best exposed sedimentary sequences in the Neotropics, with more than 7 kilometers of stratigraphic thickness 

cropping out. Most of the sequence is highly fossiliferous and we 

expect that the paleontological exploration of this large region 

will continue for many decades to come. To help this and future 

studies in the region, we established a chronology for the region 

based on an extensive literature review, as this region has had 

many biostratigraphic studies over the past few decades. Most 

of these studies, especially in the western region, have been correlated to Bolli’s zonal schemes in Trinidad (Bolli et al., 1994), 

which is the base for the biostratigraphy of tropical latitudes in 

the Americas. Furthermore, we include in supplementary materials (Carrillo et al., 2018b: appdx. 1), the lithological description 

of ten stratigraphic sections that encompass the entire Neogene 

sequence and could be used as a stratigraphic reference for future 

paleontological research.

RESULTS

Systematic Paleontology

Astrapotheria Lydekker, 1884

Astrapotheriidae Ameghino, 1887

Uruguaytheriinae Kraglievich, 1928, 

sensu Vallejo-Pareja et al. (2015)

Hilarcotherium Vallejo-Pareja et al., 2015

Type Species. Hilarcotherium castanedaii Vallejo-Pareja 

et al., 2015.

Hilarcotherium miyou sp. nov.

FIGURES 5, 6

Diagnosis. H. miyou differs from H. castanedaii in 

having lower canines, oval in cross section and implanted horizontally in lateral view; the absence of lingual cingulid in the 

lower molars; the absence of an anteroligual pocket in P4; and 

the absence of lingual cingulum in M2.

Etymology. The species is named after the word 

“miyo’u,” which means big or large in Wayuunaiki (Captain 

and Captain, 2005), the language of the Wayuu community that 

inhabits in the Guajira Department.

Holotype. Specimen IGMp 881327, partial mandible 

with left ramus bearing left m3, m2, canines, and alveoli for the 

incisors. Fragment of the left condylar process, right M2 and 

distal portion of femur.

Referred Material. MUN-STRI 34216, fragmentary skull with portion of the occipitals, palatines, and left upper 

canine, associated P4 and M2, and fragmentary mandibular 

symphysis with the base of the lower canines and alveoli for left 

i3?, i2, and i1 and right i1 and i2. MUN-STRI 38073, left P4 and 

upper molar fragments.

Type Locality and Horizon. Patajau, Castilletes 

Formation. The holotype, MUN-STRI 34216 and MUNSTRI 38073 come from STRI locality 470058; 11.95062°N, 

71.32370°W (Figure 3).

Description. The specimens are referred to Uruguaytheriinae based on the well-developed mesiolingual pocket in the 

upper molars, the absence of labial cingulum in upper molars, 

and the absence of hypoflexid and pillars in the lower molars 

(Johnson and Madden, 1997; Kramarz and Bond, 2009, 2011; 

Vallejo-Pareja et al., 2015; Croft et al., 2016). The material is 

further referred to Hilarcotherium based on the presence of 

three lower incisors, and the presence of a lingual cingulum in P4 

(Figure 6; Vallejo-Pareja et al., 2015).

The width of the mandible (measured as the mediolateral 

width between the labial margin of the canines) of H. miyou

is comparable to that of H. castanedaii and Granastrapotherium snorki, and larger than that of Xenastrapotherium christi

(Table 3; Vallejo-Pareja et al., 2015). The symphysis is wide 

(Figure 5b) as in H. castanedaii (Vallejo-Pareja et al., 2015: fig. 

4b) and X. christi (Figure 7b), and unlike G. snorki, where the 

symphysis is very narrow due to the absence of lower incisors 

(Johnson and Madden, 1997: fig. 22.5). In IGMp 881327 the 

most anterior portion of the mandible is not well preserved, 

but it is possible to identify at least three alveoli for the incisors, which are interpreted as the right and left i1 and the left i2 

(Figure 5c). It is not possible to assess with confidence the size of 

the alveoli and the presence of i3. The alveoli size of lower incisors is a variable character in other uruguaytheriinae taxa (e.g., 

Xenastrapotherium kraglievichi; Johnson and Madden, 1997), 

and its significance as a diagnostic character needs to be further 

evaluated. MUN-STRI 34216 preserves the most anterior portion of the mandibular symphysis, which preserves four alveoli 

for the incisors, the base of the left i2, and the base of the left 

lower canine (Figure 6c,d). The incisors of uruguaytheriines are 

single rooted (Vallejo-Pareja et al., 2015: fig. 4f,g), and therefore 

the alveoli of MUN-STRI 34216 are interpreted as left i1, i2, i3 

and right i1, i2 (Figure 6c,d). The alveolus of the right i3 and the 

right lower canine were not preserved.

The incisor alveoli of H. miyou are slightly larger (Table 3) 

than in H. castanedaii (Vallejo-Pareja et al., 2015). Xenastrapotherium has only two lower incisors. Johnson and Madden (1997) noted that in some specimens of X. kraglievichi, the 

lower incisors’ alveoli were very small, “indicating that the lower 

incisors are either variably developed or may have worn out and 
1 2 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

FIGURE 5. Mandible of Hilarcotherium miyou sp. nov. (Uruguaytheriinae, Astrapotheria) (holotype, IGMp 881327): (a) left lateral 

view; (b) occlusal view; (c) anterior view of symphysis indicating alveoli for incisors; (d) detail of dentition in occlusal view; (e) photograph and drawing of upper second molar (M2) in occlusal view.
NUMBER 101 • 1 3

been shed” (Johnson and Madden, 1997:360). There is intraspecific variation in the size of the incisors. This seems to be 

the case also in H. miyou (Figure 5c) and X. christi (Figure 7b), 

whose incisors have very small alveoli. G. snorki has no lower 

incisors (Johnson and Madden, 1997; Pardo-Jaramillo, 2010). 

The lower canines of H. miyou are oval in cross section, whereas 

in H. castanedaii they are triangular. In H. miyou the canines are 

implanted horizontally in lateral view and curved labially, unlike 

H. castanedaii, which has canines with a diagonal implantation 

in lateral view. Based on size differences and morphology of the 

canines, Johnson and Madden (1997) inferred sexual dimorphism in Granastrapotherium, with the larger (male?) morphotype having longer and nearly straight lower canines, and the 

smaller (female?) morphotype having shorter and more curved 

lower canines (Johnson and Madden, 1997).

Specimen IGMp 881327 preserves the left m2 and m3, and 

the root of m1, which is biradiculated, as in all astrapotheres 

(Figure 5d). They lack a hypoflexid, as is the case in Hilarcotherium castanedaii, Uruguaytherium beaulieui, and Xenastrapotherium aequatorialis. In G. snorki “the hypoflexid is indicated 

as a faint indentation opposite to the metalophid” (Johnson and 

Madden, 1997:371). In X. christi the hypoflexid is located opposite to the metalophid (Figure 7c,d), whereas in X. kraglievichi

it is opposite to the paraflexid (Johnson and Madden, 1997). 

The m2 crown is undamaged in IGMp 881327 and is 40% 

larger than the m2 of H. castanedaii (Figure 8a; Vallejo-Pareja 

FIGURE 6. Upper fourth premolar (P4; MUN-STRI 

38073) and mandibular symphysis (MUN-STRI 34216) 

of Hilarcotherium miyou sp. nov. (a) P4 in occlusal view; 

(b) P4 in lingual view; (c) mandibular symphysis in occlusal view; (d) drawing of mandibular symphysis showing 

canine and alveoli of incisors. The gray shading represents the base of the teeth.
1 4 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

et al., 2015). The entoflexid is deeper linguo-labially in occlusal 

view than the paraflexid (Figure 5d), a feature related to wear 

and observed in other Uruguaytheriinae (Vallejo-Pareja et al., 

2015). H. miyou has no lingual cingulid, unlike H. castanedaii, 

X. christi, and X. aequatorialis (Johnson and Madden, 1997; 

Vallejo-Pareja et al., 2015).

The P4 (MUN-STRI 34216 and MUN-STRI 38073) has a 

well-defined paracone fold, unlike G. snorki. The P4 of H. miyou

shares with that of H. castanedaii the absence of a hypocone 

and the presence of a lingual cingulum (Vallejo-Pareja et al., 

2015); however, in H. miyou the cingulum is continuous. Two 

M2 are referred to H. miyou (IGMp 881327 and MUN-STRI 

TABLE 3. Dental measurements (mm) of Hilarcotherium miyou sp. nov. and Hilarcotherium cf. H. miyou from Castilletes Formation. 

Features: C, upper canine; i, lower incisor; m, lower molar; M, upper molar; p, lower premolar; P, upper premolar. Measurements follow Johnson and Madden (1997).

Taxon Specimen Feature Side Measurement Value

H. miyou IGMp881327 C Left Maximum diameter 64.0

Transverse diameter 45.8

C Right Maximum diameter 65.7

Transverse diameter 48.4

p4a Left Length 28.8

Width 22.2

m1a Left Length 52.6

Width 28.2

m2 Left Length 81.8

Width 28.8

m3b Left Length 79.9

Width 27.9

M2 Right Length 71.7

Width 59.8

Mandible Left Depth at m2 104.5

Mandible Left Thickness at m2 78.2

Mandible Width between the labial margin of lower canines 125

MUN-STRI 34216 i1a Left Anteroposterior length 21.0

Transverse length 11.0

i2a Left Anteroposterior length 18.0

Transverse length 8.4

i3a Left Anteroposterior length 19.8

Transverse length 14.5

H. cf. H. miyou MUN-STRI 16778 P4a Left Length 31.8

Width 40.7

M1b Left Length 59.2

Width 65.4

M2b Left Length 71.2

Width 76.7

M3b Left Length 73.6

Width 60.1

a Measured at the alveolus.

b Tooth crown incomplete.
NUMBER 101 • 1 5

34216), and these display a nearly quadrangular contour and the 

Y-shaped median valley, characteristic of the M2 in astrapotheriids (Figure 5e). They lack a labial cingulum, which is present in 

X. chaparralensis (Johnson and Madden, 1997). H. miyou has 

a well-defined mesiolingual pocket, parastyle, and paracone fold 

(Figure 5e). There is no evidence of a lingual cingulum, as in 

G. snorki, and unlike H. castanedaii and other Uruguaytheriinae 

(Vallejo-Pareja et al., 2015).

Hilarcotherium cf. H. miyou

Referred Material. MUN-STRI 16777, almost 

complete left humerus, left radius with unfused and missing distal epiphysis, vertebral centrum, distal tibia and associated bone 

fragments. MUN-STRI 16778, left and right upper tooth rows 

highly fragmented bearing P4-M3. MUN-STRI 16779, lower 

canine. MUN-STRI 16785, three fragmentary caudal vertebrae. 

MUN-STRI 34212, patella. MUN-STRI 34217, sacrum, fragment of acetabulum, and thoracic vertebra. MUN-STRI 34221, 

atlas, almost complete left radius, metapodial, molar fragment, 

rib fragments and a fragment of a neural arch. MUN-STRI 34222, 

proximal portion of left humerus. MUN-STRI 34223, almost 

complete left ulna, distal epiphysis of left humerus, distal portion 

of left scapula, ribs, and vertebrae fragments. MUN-STRI 34225, 

distal portion of scapula. MUN-STRI 34229, partial right femur, 

tibia, and fibula. MUN-STRI 34292, patella. MUN-STRI 34310, 

distal portion of femur. MUN-STRI 36644, posterior portion of 

basicranium (cast PIMUZ A/V 5292). MUN-STRI 37384, dorsal portion of left scapula. MUN-STRI 37765, dorsal portion of 

scapula, partial radius and lunar. MUN-STRI 37390, distal tibia.

Locality and Horizon. Castilletes Formation. 

MUN-STRI 16777, 16778, 16779, 16785, 34217, 34221, 

34222, 34223, 34225, 34229, 34310, 36644, 37384, and 

37390 come from Patajau, STRI locality 390094; 11.9465°N, 

71.3255°W. MUN-STRI 37765 comes from STRI locality 130024; 11.9348°N, 71.3344°W. MUN-STRI 34212 

comes from Patajau west, STRI locality 290632; 11.9458°N, 

71.3299°W. MUN-STRI 34292 comes from Makaraipao, STRI 

locality 930093; 11.9089°N, 71.3401°W (Figure 3).

Description. The isolated distal fragment of a canine 

(MUN-STRI 16779) has an oval wear facet that forms an acute 

chisel-like shape. MUN-STRI 16778 is a left upper tooth row 

with P4–M3. It is fractured, and not much can be discerned 

about crown morphology, although it is possible to clearly 

identify each tooth in situ. MUN-STRI 16778 has no P3, as in 

Hilarcotherium (Vallejo-Pareja et al., 2015) and Granastrapotherium, and unlike Xenastrapotherium (Johnson and Madden, 

1997). The partial basicranium (MUN-STRI 36644) preserves 

FIGURE 7. Mandible of Xenastrapotherium christi (Uruguaytheriinae, Astrapotheria) (NMB Aa21): (a) left lateral view; (b) dorsal view 

of symphysis showing the alveoli of canines and incisors; (c) left dentition in occlusal view; (d) drawing and dental features of dentition 

in occlusal view. Photos from NMB provided by L. Costeur.
1 6 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

FIGURE 8. Bivariate plots with dental and mandible 

measurements of Uruguaytheriinae (Astrapotheria): 

(a) second lower molar (m2) mesiodistal length 

(MDL) vs. labiolingual width (LLW). In G. snorki

and X. kraglievichi, the dot represents the mean and 

the bars the standard deviation provided by Johnson 

and Madden (1997); (b) second upper molar (M2) 

MDL vs. LLW. The values of G. snorki and X. kraglievichi are shown as explained in (a); (c) depth of 

the mandible at the level of m2 vs. m2 MDL.
NUMBER 101 • 1 7

the occipital condyles and part of the basioccipital and exoccipital (Figure 9a,b). The occipital condyles are large, measuring 85.5 mm in dorsoventral height, and the maximum width 

between the condyles is 153.5 mm. The foramen magnum is 

larger than in H. castanedaii (Vallejo-Pareja et al., 2015). It is 

almost circular, as in Astrapotherium (Scott, 1928). The foramen 

magnum’s mediolateral width measures 54.7 mm and its dorsoventral height is 52.4 mm. In contrast, the foramen magnum in 

Astraponotus is considerably wider than high (Kramarz et al., 

2011). The median notch at the dorsal margin of the foramen 

magnum is not as clearly differentiated as in Astraponotus

(Kramarz et al., 2011). The exoccipital has a distinct process 

dorsal to the foramen magnum (Figure 9a,b).

The atlas (MUN-STRI 34221) preserves the cranial articular 

foveae, caudal articular surfaces, the neural and ventral arches, 

part of the transverse processes, and the transverse foramina 

(Figure 9c,d). It is comparable in size to that of Parastrapotherium herculeum? (Table 4; Figure 9e,f). The transverse process 

is wide as in Astrapotherium and Parastrapotherium. The cranial articular foveae for the occipital condyles are large, deeply 

FIGURE 9. Basicranium and vertebrae of Hilarcotherium cf. H. miyou from the Castilletes 

Formation, and selected astrapotheres for comparison. Hilarcotherium cf. H. miyou basicranium (MUN-STRI 36644) in (a) caudal view, 

and (b) left lateral view. Hilarcotherium cf. 

H. miyou atlas (MUN-STRI 34221) in (c) cranial view, and (d) caudal view. Parastrapotherium herculeum? (MNHN COL 6) atlas, from 

the Colhuehuapian of Argentina in (e) cranial 

view, and (f) caudal view. (g) Hilarcotherium

cf. H. miyou thoracic vertebra (MUN-STRI 

34217) in caudal view; (h) Parastrapotherium

sp. thoracic vertebra (MNHN DES 112) from 

the Deseadan of Argentina in caudal view.
1 8 

• SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY TABLE 4. Postcranial measurements (cm) of Astrapotheriidae. An asterisk (*) indicates estimated value. For the humerus, the acronym used by Scott (1990) is in parentheses. A dash (-) indicates measurement could not be taken in the specimen. Measurement Data by taxon and specimen H. cf. H. miyou P. herculeum? Atlas MUN-STRI 34221 MNHN COL 6 Anteroposterior length 15.6* 16.5 Dorsoventral height 12.9* 14.8 Mediolateral width 26.2* 27.4 H. cf. H. miyou Parastrapotherium sp. Caudal vertebra MUN-STRI 34217 MNHN DES 112 Dorsoventral height of centra 7.65 6.27 Anteroposterior length of centra 5.95 5.19

Mediolateral width of centra 9.64 8.72

H. cf. H. miyou

Scapula MUN-STRI 34384 MUN-STRI 37765

Dorsoventral width at distal end 10.28 -Mediolateral thickness at distal end - 12.0*

H. cf. H. miyou P. herculeum?

Humerus MUN-STRI 16777 MNHN COL 127

Length from head (H1) 65.0 -Length from external tuberosity (H2) 67.5 -Transverse diameter of the distal articulation surface (H4)

18.25 10.68

Transverse epicondylar diameter (H5) 25.5* 19.0*Transverse diameter of the diaphysis below the deltoid process (H7)

9.1* -

Anteroposterior diameter of the diaphysis below the deltoid process (H8) 13.1* -
NUMBER 101

• 1 9

Measurement Data by taxon and specimen

H. cf. H. miyou P. hombergi Parastrapotherium sp. P. herculeum?

Ulna MUN-STRI 34223 MNHN DES 985 MNHN DES 1013 MNHN COL 128

Length - 4.60 6.00 6.10

Median width of diaphysis 5.06 6.55 8.79 8.10

Olecranon height 6.34* 7.49 12.41 12.78

Olecranon thickness - 6.60 9.31 9.17

Length of the trochlear notch 10.94 10.15 13.72 13.73*

Width at distal epiphysis - 8.46 6.92 -Thickness at distal epiphysis - 6.92 - -

H. cf. H. miyou P. holmbergi Parastrapotherium sp.

Radius MUN-STRI 16777 MUN-STRI 34221 MUN-STRI 37765 MNHN DES 989 MNHN DES 1013 MNHN COL 129

Length 40.0 - - 33.5 43.5 -Width at proximal end 11.70 11.61 - 8.60 11.82 8.43

Thickness at proximal end 7.70 6.71 6.6* 5.27 6.95 5.28

Median width of diaphysis 5.72 4.34 - 5.18 8.71 -Width at distal epiphysis 11.77 - 12.0* 9.00 11.07 -

Thickness at distal epiphysis 9.07 - 7.5* 5.57 8.14 -

H. cf. H. miyou P. holmbergi Parastrapotherium sp.

Femur MUN-STRI 34310 MUN-STRI 34229 MNHN DES 988 MNHN DES 1017

Length from head - 104.0* - -

Length from greater trochanter - 98.0* - -Median width of diaphysis 11.05 13.94* 9.52* -Width at epicondyles 15.5* - - 17.2

TABLE 4. (Continued)
2 0 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

concave, widely separated dorsally, and more proximate ventrally (Figure 9c), as in Astrapotherium (Scott, 1928, 1937) and 

Parastrapotherium (Figure 9e). The neural canal is circular in 

anterior and posterior view. The ventral side of the ventral arch 

is convex. The caudal articular surface is oval and nearly flat. 

The posterior opening of the large arterial foramen opens posteroventrally (Figure 9d), as in Astrapotherium (Scott, 1928). 

The thoracic vertebra (MUN-STRI 34217) preserves the centrum 

and a small fragment of the neural arch (Figure 9g). The centrum 

forms a triangle with rounded corners in anterior view, with the 

widest border on the dorsal side, as in Parastrapotherium. It has 

an oval articular surface for the rib on the dorsolateral edge of 

the centrum, also present in Parastrapotherium (Figure 9g,h).

The sacrum (MUN-STRI 34217) preserves three fused vertebrae of total length 26.8 cm. It is likely that the sacrum was 

formed by more vertebrae, given that in Astrapotherium it consists of four and probably five vertebrae (Scott, 1937). In anterior view the vertebral centrum is oval, but in the most caudal 

vertebra the centrum is strongly compressed dorsoventrally. The 

neural arches of the vertebrae are fused, forming a continuous 

plate. The transverse processes are also fused, and one sacral 

foramen is observed.

Three partial scapulae were recovered; they all represent the 

most dorsal portion of the scapula (Figure 10a,b). The scapula 

of astrapotheres is narrow anteroposteriorly, and does not have 

the bladelike appearance seen in most terrestrial mammals. In 

Astrapotherium, it narrows dorsally, but is wider anteroposteriorly than in the scapulae referred to Hilarcotherium cf. 

H. miyou, forming a more quadrangular end (Figure 10a,c; 

Scott, 1928, 1937). In Hilarcotherium cf. H. miyou, the dorsal 

end seems more bulbous. The fragmentary scapulae of Hilarcotherium cf. H. miyou show a spine that is wide and well developed 

laterally (Figure 10a,b), as in Astrapotherium and Parastrapotherium (Loomis, 1914).

One almost complete humerus (MUN-STRI 16777; Figure 10e–h) is large and comparable in size to G. snorki (Johnson and Madden, 1997: tbl. 22.6). The associated radius with 

unfused distal epiphysis (see below) indicates that this individual was not skeletally mature. The humerus is larger and more 

robust than in H. castanedaii, A. magnum, and P. herculeum? 

(Figure 10e–m; Table 4). The head is large and projects posteriorly to the plane of the shaft (Figure 10g), as in H. castanedaii and A. magnum (Scott, 1928, 1937; Vallejo-Pareja et al., 

2015). The greater tubercle extends more proximally than the 

lesser tubercle (Figure 10e,i), as in H. castanedaii and A. magnum. The bicipital groove is broad and shallow, more than in 

H. castanedaii and A. magnum. The shaft is proportionally slender, but it has an elongated and marked delto-pectoral crest, 

which extends up to about two-thirds of the humeral length, 

as in Parastrapotherium (Loomis, 1914). The supinator crest is 

small and narrow. The radial fossa is large and deep, with no 

foramen (Figure 10e–f), as in H. castanedaii and A. magnum

(Scott, 1928, 1937; Vallejo-Pareja et al. 2015). The capitulum is 

rounded and extends less distally than the trochlea, as in H. castanedaii and A. magnum (Figure 10e,j). The medial epicondyle 

is well developed as in H. castanedaii and unlike in A. magnum

(Vallejo-Pareja et al., 2015).

An almost complete ulna (MUN-STRI 34223) was recovered and lacks only its most distal portion (Figure 11a–d). The 

shaft is anteroposteriorly deeper than mediolaterally wide. The 

olecranon is short and robust, as in Parastrapotherium (Figure

11a–f; Loomis, 1914). In anterior view, the olecranon projects 

more medially than the plane of the shaft (Figure 11a), but in lateral view the olecranon and the shaft are on the same plane (Figure 11c), as in Parastrapotherium (Figure 11e,f) and A. magnum

(Scott, 1937). The length of the trochlear notch is similar to that 

in P. holmbergi, but smaller than in P. herculeum? (Table 4). The 

trochlear notch forms a semicircle in lateral view (Figure 11c). 

The coronoid process is large and is almost perpendicular to the 

axis of the shaft (Figure 11c,d), whereas in Parastrapotherium it 

is more oblique (Figure 11f). Distal and lateral to the coronoid 

process is the radial notch (Figure 11b), as in Parastrapotherium

(Figure 11e).

Remains of several Hilarcotherium cf. H. miyou radii were 

recovered from Castilletes. The most complete (MUN-STRI 

16777; Figure 11g,h) is from a juvenile, as determined from the 

unfused and missing distal epiphysis. It is comparable in size to 

the large specimens of Parastrapotherium (Table 4). The proximal end is wider than the shaft (Figure 11g–j) as in Astrapotherium and Parastrapotherium (Figure 11k,l). The articular surface 

FIGURE 10. (Opposite) Scapulae and humeri of Hilarcotherium cf. H. miyou from the Castilletes Formation, and selected astrapotheres 

for comparison. Hilarcotherium cf. H. miyou scapulae, (a) MUN-STRI 38384 in lateral view; (b) MUN-STRI 34223 in anterior or posterior view; left scapula of Astrapotherium magnum from the Santa Cruz Formation, Argentina (YPM PU 15255) in (c) lateral view and 

(d) posterior view. Hilarcotherium cf. H. miyou left humerus (MUN-STRI 16777), (e) anterior view; (f) schematic drawing in anterior 

view; (g) medial view; (h) posterior view. Hilarcotherium cf. H. miyou partial humeri, (i) proximal portion of left humerus (MUN-STRI 

34222); Hilarcotherium cf. H. miyou distal epiphysis of left humerus (MUN-STRI 34223), (j) anterior view and (k) posterior view. Left 

humerus of Astrapotherium magnum (YPM PU 15255) in (l) anterior and (m) posterior view.
NUMBER 101 • 2 1
2 2 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

for the humerus is divided into two sections, the medial is concave and the lateral is saddle-shape, as in A. magnum (Scott, 

1928, 1937). The anterior border of the proximal epiphysis 

is more proximal than the posterior one. The shaft is slightly 

curved (Figure 11g,h).

Two fragmentary femora were recovered from Castilletes. 

MUN-STRI 34229 is almost complete but badly preserved, 

and no details from the epiphyses can be observed. MUNSTRI 34310 preserves part of the shaft and the distal epiphysis. The median and lateral epicondyles project distally to the 

same level, and the articulation surface for the patella seems 

narrower than in A. magnum (Scott, 1937). The patella (MUNSTRI 34212) is oval and elongated proximodistally, narrowing 

at its distal end, as in A. magnum (Scott, 1937). It measures 

FIGURE 11. Antebrachial bones of Hilarcotherium cf. H. miyou from the Castilletes Formation, and selected astrapotheres for comparison. Hilarcotherium cf. H. miyou left ulna (MUN-STRI 34223), (a) anterior view; (b) schematic drawing in anterior view; (c) lateral 

view; (d) medial view. Left ulna of Parastrapotherium holmbergi (MNHN DES 985) from the Deseadan of Argentina in (e) anterior and 

(f) lateral view. Left radius of Hilarcotherium cf. H. miyou (MUN-STRI 16777), (g) anterior, and (h) posterior view. MUN-STRI 34221, 

(i) anterior, and (j) posterior view. Left radius of Parastrapotherium holmbergi (MNHN DES 989) in (k) anterior and (l) posterior view.
NUMBER 101 • 2 3

15 cm in length. It is curved in lateral view, with a convex anterior border. The articular facet is quadrangular and measures 

8.5 cm proximodistally and 6.2 cm mediolaterally. MUN-STRI 

16777 includes a partial distal left tibia. The shaft is trihedral 

in cross section. The medial malleolus is broad, very similar to 

the condition of the tibiae reported from the Castillo Formation (Weston et al., 2004). MUN-STRI 34229 also includes a 

fibula, which is slender and straight, as in A. magnum (Riggs, 

1935; Scott, 1937).

Body Mass Estimation

The body mass estimate from the m2 length of the holotype of H. miyou is ~6456.6 kg (Table 5). Previous studies used 

the m1–m3 length to estimate the body mass in astrapotheres 

(Johnson and Madden, 1997; Kramarz and Bond, 2011; VallejoPareja et al., 2015). For other taxa, including the uruguaytheriines H. castanedaii, G. snorki, and X. kraglievichi, the body 

mass estimates from the m2 length are similar to those obtained 

from the m1–m3 length in the same specimen (Table 5), suggesting that if the lower molar row length could be measured in 

H. miyou, it would yield an estimate similar to the m2 length. 

The length of proximal limb bones is highly correlated with body 

mass in ungulates (Scott, 1990). The humerus length of a specimen tentatively referred to Hilarcotherium cf. H. miyou (MUNSTRI 16777) yields an estimate of ~4985.0 kg (Table 5), 23% 

less than the value obtained from the m2 length in H. miyou. For 

G. snorki the difference was observe to be 23% more (Table 5).

Phylogenetic Analysis of Astrapotheriidae

The cladistic analysis resulted in 10 most parsimonious trees of 128 steps, with a consistency index of 0.680 and 

retention index of 0.759. Ten characters were parsimony uninformative. The strict consensus (Figure 12) differs from the 

topologies presented by Vallejo-Pareja et al. (2015; fig. 6) in the 

TABLE 5. Body mass (BM) estimates of astrapotheres (in kg). % PE = percent of error. The estimations from the m2 length and the 

m1–m3 length use equations of non-selenodont ungulates (Damuth, 1990). For m2 length, log(BM) = 2.98 * log(m2 length) + 1.11, 

with r2

 = 0.97 and % PE = 30.61. For m1–m3 length, log(BM) = 3.03 * log(m1–m3 length) − 0.39; with r2 = 0.96 and % PE = 37.19. 

Estimates from the humerus length follow the equation of all ungulates for H2 in Scott (1990): log(BM) = 3.4026 * log(H2) − 2.513; 

with r2

 = 0.9196 and % PE = 29.

Taxon Specimen(s) Length Estimated BM BM+PE BM−PE

BM estimates from m2 length

Hilarcotherium miyou IGMp 881327 81.8 mm 6,456.6 8,433.0 4,480.2

Hilarcotherium castanedaii a IGM p881231 48.8 mm 1,385.1 1,809.1 961.1

Granastrapotherium snorki b mean of 9 specimens 66.5 mm 3,483.4 4,549.7 2,417.2

Xenastrapotherium kraglievichi MLP 12-96 49.3 mm 1,427.9 1,864.9 990.8

Parastrapotherium martiale MACN A 52604 66.9 mm 3,546.3 4,631.8 2,460.7

Astrapotherium giganteum MACN-A 3274-3278 64.6 mm 3,195.2 4,173.2 2,217.1

BM estimates from m1–m3 length

Hilarcotherium castanedaii a IGM p881231 140.2 mm 1,302.7 1,787.1 818.2

Granastrapotherium snorki b UCMP 40017 187.5 mm 3,141.9 4,310.4 1,973.4

Xenastrapotherium kraglievichi c MLP 12-96 141 mm 1,324.7 1,817.4 832.1

Parastrapotherium martiale c MACN A 52604 194 mm 3,483.7 4,779.3 2,188.1

Astrapotherium giganteumc MACN-A 3274-3278 196 mm 3,593.7 4,930.1 2,257.2

BM estimates from humerus length

Hilarcotherium castanedaii a IGM p881231 45.5 cm 1,306.5 1,685.4 817.7

Hilarcotherium cf. H. miyou MUN-STRI 16777 70 cm 4,985.0 6,430.7 3,120.1

Granastrapotherium snorki b UCMP 40192 65.5 cm 4,501.1 5,806.4 2,817.3

Astrapotherium magnumb FMNH 14251 52.3 cm 2,096.5 2,704.4 1,312.2

a Reported by Vallejo-Pareja et al. (2015).

b Reported by Johnson and Madden (1997).

c Reported by Kramarz and Bond (2011).
2 4 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

position of Comahuetherium, and the relationships of northern 

Uruguaytheriinae. In the strict consensus, Comahuetherium, 

Parastrapotherium, and the clades Astrapotheriinae and Uruguaytheriinae form a polytomy (Figure 12), whereas VallejoPareja et al. (2015) recovered Comahuetherium as the sister 

taxon of a clade including Parastrapotherium, Astrapotheriinae 

and Uruguaytheriinae.

We recovered the main clades previously recognized 

within Astrapotheriidae. The Astrapotheriinae (Astrapotherium, Astrapothericulus) clade has a bootstrap value of 0.79 

and is supported by four unambiguous synapomorphies that 

concern the molars: deep hypoflexid (character state 0 of character 26; 26[0]), the presence of a lingual cingulid (30[1]), a 

rounded hypocone (40[0]), and an ephemeral median fossette 

(44[1]). The Uruguaytheriinae clade has a bootstrap value of 

0.64 and is supported by two unambiguous synapomorphies: 

the absence of molar hypoflexid (26[2]) and the absence of 

labial cingulum in the molars (27[0]). The Uruguaytheriinae 

from northern South America (Hilarcotherium, Granastrapotherium, and Xenastrapotherium) form a clade supported by 

one unambiguous synapomorphy, the presence of a superficial 

paraflexid on the lower molars (28[1]). Finally, X. kraglievichi

and X. christi form a clade supported unambiguously by the 

absence of i3 (3[1]) and the presence of a superficial hypoflexid (26[1]). Within the 10 most parsimonious trees obtained, 

H. miyou is recovered as the sister taxon of H. castanedaii in 

one, as the sister taxon of G. snorki in five, and as the sister 

taxon of a (Xenastrapotherium, Granastrapotherium) clade in 

four. The inclusion of additional taxa and more complete material is necessary to futher test the monophyly of the two Hilarcotherium species.

Notoungulata Roth, 1903

Toxodontia Owen, 1853

Leontiniidae Ameghino, 1895

cf. Huilatherium Villarroel and Guerrero, 1985

Type Species. Huilatherium pluripicatum Villarroel and 

Guerrero, 1985.

Referred Material. MUN-STRI 34312 right m3 

(cast PIMUZ A/V 5290).

FIGURE 12. Hypothesis of phylogenetic relationships within Astrapotheriidae. Time-calibrated topology of the strict consensus resulting from the analysis with PAUP* 4.0. Bootstrap values higher than 0.50 are indicated for several nodes. Blue tint = Astrapotheriinae; 

red tint = Uruguaytheriinae. Letters below time line (mya) denote SALMAs (from left to right): I = Itaboraian; R = Riochican; S = 

Sapoan; V = Vacan; B = Barrancan; M = Mustersan; T = Tinguirican; D = Deseadan; C = Colhuehuapian, P = “Pinturan”; S = Santacrucian; O = Colloncuran; L = Laventan.
NUMBER 101 • 2 5

Locality and Horizon. MUN-STRI 34312 comes 

from Patajau, Castilletes Formation, STRI locality 340094; 

11.9465°N, 71.3255°W (Figure 3).

Description. The isolated tooth is interpreted as an m3 

because of its elongate talonid that narrows distally (Figure 13a). 

It is protohypsodont (rooted teeth, crown height <50% of mesiodistal length; Pérez and Vucetich, 2012), with a mesiodistal 

length of 40.4 mm and labiolingual width of 14.5 mm, approximately 30% smaller than the m3 of H. pluripicatum (Villarroel 

and Colwell Danis, 1997: tbl. 19.4). The crown height measured 

at the labial side is 14.4 mm, yielding a hypsodonty index of 0.4, 

although this value may be an underestimation for this animal, 

as the appearance of the ento-hypoconulid as a fossettid indicates high wear in the specimen (Figure 13 a,b; see below).

The paralophid is wide and perpendicular to the mesiodistal 

axis of the crown. The trigonid lingual groove is well developed 

and straight, projecting from the lingual to the labial side of the 

crown. The metalophid is wider than in H. pluripicatum and it 

is oblique. The meta-entoconid fold is well developed and projects linguomesially, as in H. pluripicatum (Figure 13a). It has a 

posterior fossettid, which is rounded and not U-shaped, as in 

H. pluripicatum (Figure 13a,b). Due to wear, the ento-hypoconid 

fold appears as a fossettid between the entoconid and the hypoconulid (Figure 13a). According to Villarroel and Colwell Danis 

(1997), in H. pluripicatum the ento-hypoconid fold (treated as 

“entoflexid” by these authors) appears as a “large rounded pit” 

with extensive wear. The hypoconulid is large and almost parallel to the mesiodistal axis of the tooth, as in H. pluripicatum

(Villarroel and Colwell Danis, 1997). There are neither lingual 

nor labial cingulids (Figure 13c,d). In H. pluripicatum and 

Colpodon distinctus, the labial cingulid is absent, and the lingual 

cingulid is present but reduced (Villarroel and Colwell Danis, 

1997; Ribeiro et al., 2010). In Henricofilholia the labial and lingual cingulids are variably developed (Ribeiro et al., 2010), and 

Martinmiguelia, Scarritia, Elmerriggsia and Gualta have both 

lingual and labial cingulids (Ubilla et al., 1994; Bond and López, 

1995; Ribeiro et al., 2010; Shockey et al., 2012; Cerdeño and 

Vera, 2015).

Toxodontidae (Gervais, 1847)

Toxodontinae (Trouessart, 1898)

Falcontoxodon gen. nov.

Type Species. Falcontoxodon aguilerai sp. nov.

Diagnosis. As for the type and only species.

Falcontoxodon aguilerai sp. nov.

FIGURES 14, 16

Etymology. The genus name is for the Falcón state in 

Venezuela, where the holotype was found. The species name is 

after Orangel Aguilera, in recognition of his lifetime contribution to paleontology in Venezuela.

FIGURE 13. Leontiniidae (Notoungulata) right m3: (a) cf. Huilatherium

(MUN-STRI 34312) in occlusal view; 

(b) H. pluripicatum (UCMP 40280), 

modified from Villarroel and Colwell 

Danis (1997); (c) MUN-STRI 34312 

in lingual and (d) labial view.
2 6 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

FIGURE 14. Skull of Falcontoxodon aguilerai gen. et sp. nov. (Toxodontidae, Notoungulata) (holotype, AMU-CURS 765): (a) left 

lateral view; (b) ventral view; (c) detail of the upper left dentition in occlusal view; (d) schematic drawing of dentition: distribution of 

enamel is shown by thick lines; (e) right I2 in mesiolingual view.
NUMBER 101 • 2 7

Holotype. AMU-CURS 765, fairly complete skull with 

left I1 and P3–M3 and right P3–M1 in situ, and associated right 

I2, M2, and M3. Alveoli of the other teeth are preserved. Mandible with complete dentition excepting left i2 and right i1, i2.

Referred Material. AMU-CURS 70, left m3.

Type Locality and Horizon. The holotype and 

AMU-CURS 70 were collected in the Algodones Member, Codore 

Formation, Urumaco, Falcón State, Venezuela. 11°17′39.8′′N 

070°14′15.6′′W (Figure 4a,b).

Diagnosis. The dental formula is i 2/3, c 1/0, p 4/4, 

m 3/3. Mandibular symphysis reaches the level of m1–m2. 

Comparable in size to Pericotoxodon, larger than Nesodon and 

Xotodon, and smaller than Toxodon and Mixotoxodon. Upper 

molars have simple enamel lingual fold. Well-defined protoloph 

lingual column present only in M3. It differs from Gyrinodon

in the sigmoid shape of the zygomatic arch in lateral view, the 

broad metaloph, and the absence of a ventral extension of the 

dentary. It differs from Mixotoxodon in having a short diastema 

posterior to i3, lingual enamel band of m1 restricted between the 

anterior fold and the hypoconulid, a less developed lower molar 

anterior fold, and less procumbent lower incisors. It differs from 

Trigodonops in the absence of a labial groove in p3 and p4. It differs from Piauhytherium in having a long nasal and the presence 

of an upper canine. It differs from Pericotoxodon in the position 

of the infraorbital foramen, widely separated from the zygomatic 

arch, the absence of I3, the upper molars with a simple enamel 

fold, and the absence of a ventral extension of the horizontal 

ramus of the mandible. It differs from Andinotoxodon in the 

presence of p1, absence of lingual enamel in the lower premolars, and in having a labiolingually narrower entolophid. It differs from Hoffstetterius in the presence of the upper canine and 

P1, and the absence of a mandibular ventral extension. It differs 

from Paratrigodon and Trigodon in the presence of P1 and lingual enamel in P3 and P4. It differs from Calchaquitherium in 

the rounded angle of the posteroventral border of the vertical 

ramus of the mandible, the incisors being at the same level as the 

cheek teeth, and the absence of a median symphyseal labial keel.

Description. The skull is pyriform in ventral view (Figure 14b), and the nasal is long as in most toxodontids (Forasiepi 

et al., 2015). The premaxilla is not expanded laterally, as in most 

Toxodontinae except for Toxodon (Owen, 1840) and Hoffstetterius (Saint-André, 1993). The infraorbital foramen is distant 

FIGURE 15. Gyrinodon quassus (Toxodontidae, Notoungulata) (holotype, NHMUK PV M 13158): (a) right partial mandible in lateral view; (b) top, right partial mandible in occlusal view; bottom, schematic drawing of m1–m3: distribution 

of enamel is shown by thick lines; (c) right I2 in labial view; (d) cross section of M1or M2. Photos by Lucie Goodayle; 

courtesy of Natural History Museum, London.
2 8 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

FIGURE 16. Mandible of Falcontoxodon aguilerai gen. et sp. nov. (holotype, AMU-CURS 765): (a) left lateral view; (b) dorsal 

view; (c) detail of dentition and symphysis in occlusal view; (d) schematic drawing of left dentition: distribution of enamel is 

shown by thick lines.
NUMBER 101 • 2 9

from the zygomatic arch (Figure 14a), as in Adinotherium, Nonotherium, Nesodon, Palyeidodon, Hoffstetterius, Gyrinodon, and 

Toxodon, and unlike Pericotoxodon, Posnanskytherium, Trigodon, Piauhytherium, Paratrigodon, and Xotodon in which the 

infraorbital foramen is in close proximity to the zygomatic arch 

(Madden, 1997; Guérin and Faure, 2013; Forasiepi et al., 2015). 

The zygomatic arch is sigmoid (Figure 14a), unlike the condition 

in Gyrinodon, Toxodon, Hoffstetterius, Palyeidodon, and Trigodon, and the root of the zygomatic process of the squamosal is 

located dorsal to the M3 (Figure 14a,b), as in most toxodontids 

except for Posnanskytherium, in which it is positioned dorsal to 

the M2 (Madden, 1997).

The palate is widest at the level of M3 and narrows toward 

P1. Anterior to P1 the palate is elongate and the lateral borders are parallel (Figure 14b). The I1 is approximately oval in 

cross section, similar to Calchaquitherium (Nasif et al., 2000). 

The I2 is developed as a tusk. It has enamel only on the labial 

side of the crown (Figure 14e), as in Gyrinodon (Figure 15c). 

The I3 is absent, unlike in Pericotoxodon, Trigodon, Pisanodon, Palyeidodon, and Nesodon. There is a diastema of 

51 mm between I2 and C (Figure 14b), and a shorter diastema 

between C and P1 (Figure 14d), as in Pericotoxodon (Madden, 

1997). The upper canine is greatly reduced, as shown by the 

size of the alveolus, with a diameter of approximately 7 mm 

(Table 6).

The upper and lower cheek teeth are hypselenodont (rootless) as in most toxodontids (Forasiepi et al., 2015). Only the 

alveoli of P1 and P2 are preserved. The P3 does not have a lingual enamel fold, but one is present in P4 (Figure 14d), as in 

Mixotoxodon and Piauhytherium (Van Frank, 1957; Guérin and 

Faure, 2013). The P4, and in a lesser degree the P3, are elongate mesiolabially, resulting in teardrop shape in cross section 

(Figure 14d), similar to Pericotoxodon and Mixotoxodon (Van 

Frank, 1957; Madden, 1997). In occlusal view, there is a broad 

labial enamel band that reaches the mesiolabial corner, and a 

second enamel band in the mesiolingual portion of the P3–P4 

(Figure 14d) as in Pericotoxodon and Mixotoxodon. Madden 

(1997) noted that this band is obliterated in advanced stages of 

wear in Pericotoxodon.

The upper molars have a simple, persistent primary lingual 

enamel fold, which separates the protoloph from the metaloph 

(Figure 14d; see also Madden, 1990; 1997), as observed in 

individuals of Pericotoxodon with an advanced stage of dental 

wear (Madden, 1997: fig. 21.5), as well as in Andinotoxodon

(Madden, 1990), Mixotoxodon (Laurito, 1993), Piauhytherium

(Guérin and Faure, 2013), and Gyrinodon (Figure 15d). The 

protoloph does not support a lingual column in M1 and M2, 

but one is present in M3 (Figure 14d). In contrast, the lingual 

column is present in all molars in Pericotoxodon (Madden, 

1997), and it is absent in Mixotoxodon (Laurito, 1993) and 

Andinotoxodon (Madden, 1990). The metaloph is broad and 

does not taper distally, as in most specimens of Pericotoxodon

(Madden, 1997).

The horizontal ramus of the mandible of Falcontoxodon

does not have a ventral extension (Figure 16a), in contrast to 

the presence of this feature in Pericotoxodon (Madden, 1997) 

and Gyrinodon (Figure 15a). The vertical ramus is wide and has 

a rounded caudoventral border (no distinct angular process), in 

contrast with the right-angle border of Pericotoxodon and Calchaquitherium (Madden, 1997; Nasif et al., 2000). The coronoid 

process is at the same level as the condyle, as in Mixotoxodon

(Van Frank, 1957). There is no median symphyseal labial keel, 

unlike in Nesodon and Calchaquitherium (Nasif et al., 2000; 

Forasiepi et al., 2015). The symphysis extends caudally up to 

the level of m1–m2 (Figure 16b), in contrast to Trigodonops, 

Piauhytherium, Mixotoxodon, and Gyrinodon where it extends 

until the p4–m1.

The i1 is triangular in cross section, with a broad labial 

enamel band and a narrow lingual band, as in Mixotoxodon

(Van Frank, 1957; Laurito, 1993). Only the alveolus of i2 is preserved. The i3 is tusk-like, with broad labial and lingual enamel 

bands (Figure 16c). There is a short diastema between i3 and p1. 

The c is absent, as in Mixotoxodon, Calchaquiterium, Paratrigodon, Trigodon, and Piauhytherium (Guérin and Faure, 2013; 

Forasiepi et al., 2015). Only the alveoli of p1 and p2 are preserved. The p3 and p4 are approximately rectangular in cross 

section. There is no labial groove in p3 but one is present in p4 

(Figure 16d), similar to Mixotoxodon (Van Frank, 1957), and 

unlike Trigodonops and Piauhytherium, which have a marked 

labial groove in both p3 and p4 (Paula Couto, 1979; Guérin and 

Faure, 2013).

The lower molars are bicrescentic and ever growing, with 

a well-defined labial enamel fold (Figure 16c,d). The m1 has a 

lingual enamel band between the anterior fold and the hypoconulid (Figure 15d). In contrast, the lingual enamel of the m1 

of Mixotoxodon is between the meta-entoconid fold and the 

hypoconulid (Van Frank, 1957; Rincón, 2011). The m1 and m2 

have a shallow mesial fold at the same level as the labial fold, as 

in Mixotoxodon and Gyrinodon (Hopwood, 1928; Van Frank, 

1957). The meta-entoconid and ento-hypoconulid folds are well 

defined in m1, but in the m2 the meta-entoconid fold is shallow, 

as in Mixotoxodon (Van Frank, 1957). In contrast, in the m2 of 

Gyrinodon the ento-hypoconulid and meta-entoconid folds are 

well defined (Hopwood, 1928). The m2 and m3 have a lingual 

enamel band between the anterior fold and the hypoconulid, as 

in all Toxodontinae (Forasiepi et al., 2015). The m3 has metaentoconid and ento-hypoconulid folds, both absent in Calchaquitherium (Nasif et al., 2000). The ento-hypoconulid fold is 

present, but open, similar to Mixotoxodon and Gyrinodon. An 

open ento-hypoconulid fold is correlated with increasing mesiodistal crown length, a feature that appears as the tooth grows 

and is worn away (Madden, 1997).
3 0 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

TABLE 6. Dental measurements of Falcontoxodon (in mm). An asterisk (*) indicates tooth crown incomplete; double asterisk (**) 

indicates specimen measured at the alveolus.

Taxon Specimen Feature Side Measurement Value

Falcontoxodon aguilerai AMU-CURS 765 I1 Left Maximum length 16

Maximum width 25

I2 Left Maximum length 24

Maximum width 35

C Left Maximum length** 7

Maximum width** 6

Right Maximum length** 7

Maximum width** 6

P1 Left Maximum length** 13

Maximum width** 16

P2 Left Maximum length 19

Maximum width 19

Right Maximum length 19

Maximum width 19

P3 Left Maximum length 22

Maximum width 24

Right Maximum length 22

Maximum width 25

P4 Left Maximum length 30

Maximum width 29

Right Maximum length 29

Maximum width 30

M1 Left Ectoloph length 45

Maximum length 55

Right Ectoloph length 49

Maximum length 36

M2 Left Ectoloph length 50

Maximum width 44

Right Ectoloph length 51

Maximum width 45

M3 Left Ectoloph length 63

Maximum width 41

Right Ectoloph length 64

Maximum width 41

Diastema I2–C Left Length 51

Right Length 51

Upper molar row Left Length 150

i1 Left Length 21

Width 17

i3 Left Length 39

Width 25
NUMBER 101 • 3 1

Taxon Specimen Feature Side Measurement Value

Right Length 40

Width 24

p1 Left Length** 14

Width** 9

p2 Left Length** 19

Width** 22

p3 Left Length 22

Width 16

Right Length 22

Width 16

m1 Left Length 42

Talonid width 17

Right Length 43

Talonid width 21

m2 Left Length 42

Trigonid width 18

Talonid width 15

Right Length 41

Trigonid width 18

Talonid width 15

m3 Left Length 59

Trigonid width 17

Talonid width 11

Right Length 59

Trigonid width 17

Talonid width 12

Lower molar row Left Length 14.6

Right Length 14.5

AMU-CURS 70 m3 Left Length 49.9

Trigonid width 13.4

Talonid width 9.2

Falcontoxodon aff. F. aguilerai AMU-CURS 585 C Right Maximum length 21.6

Maximum width 15.6

P2 Left Maximum length 14.9

Maximum width 16.7

P3 Left Maximum length 16.3

Maximum width 18.0

P4 Left Maximum length 26.0

Maximum width 21.5

M1 Left Ectoloph length 44.4

Maximum width 23.5

TABLE 6. (Continued)
3 2 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

Falcontoxodon aff. F. aguilerai

Referred Material. AMU-CURS 585, maxilla with 

left M3–P2 and right I2.

Locality and Horizon. Norte Casa Chiguaje, Vergel Member, San Gregorio Formation, Urumaco, Falcón State, 

Venezuela. 11°17′52.5′′N 070°14′11.1′′W (Figure 4a,b).

Description In AMU-CURS 585 the skull is pyriform in ventral view and the infraorbital foramen is separated 

from the zygomatic arch (Figure 17a,b), as in F. aguilerai. Only 

the zygomatic process of the maxilla is preserved, which is dorsal to the M3. The I3 and C are absent, as in Hoffstetterius, 

Posnanskytherium, Paratrigodon, and some specimens of Toxodon (Forasiepi et al., 2015). In F. aguilerai the I3 is absent and 

the C is greatly reduced. The P1 is absent, unlike in F. aguilerai, 

and as in Hoffstetterius, Trigodon, and Paratrigodon (SaintAndré, 1993; Forasiepi et al., 2015). There is a large diastema 

between the I2 and P2 (Figure 17b). The P2 is nearly square in 

cross section, it does not have a lingual fold or fossette, and 

it shows enamel bands on the labial and mesiolingual sides 

(Figure 17c,d).

In AMU-CURS 585 the lingual enamel fold is absent in P3 

but present in P4, and there are labial and mesiolingual enamel 

bands in P3 and P4. These features are also seen in the P3–P4 

of F. aguilerai. In addition, the upper molars of AMU-CURS 

585 have a simple lingual fold, and the protoloph supports a 

lingual column only in M3, as in F. aguilerai. However, AMUCURS 585 differs from F. aguilerai in the absence of C and P1. 

These characters suggest that AMU-CURS 585 represents a 

closely related but different taxon from F. aguilerai. However, 

in the absence of more complete material, we prefer to refer 

AMU-CURS 585 to Falcontoxodon aff. F. aguilerai, following the recommendations for open nomenclature of Bengtson 

(1988).

Falcontoxodon sp.

Referred Material. AMU-CURS 69, partial left 

mandible with m1–m3 (cast PIMUZ A/V 5285). AMU-CURS 

77, upper right I2, right P2, right P3 and unidentified left upper 

tooth. AMU-CURS 270, partial right mandible with m3 (cast 

PIMUZ A/V 4786). AMU-CURS 542, right astragalus, metatarsals III–IV, and two phalanges (cast PIMUZ A/V 5287). 

AMU-CURS 544, mandibular symphysis and four isolated 

lower teeth fragments. AMU-CURS 548, left M1/M2. AMUCURS 562, left metatarsal IV and metatarsals II–III. AMUCURS 563, distal portion of humerus. AMU-CURS 570, upper 

right I2 fragment, two unidentified upper premolars and seven 

Taxon Specimen Feature Side Measurement Value

M2 Left Ectoloph length 47.2

Maximum width 22.6

M3 Left Ectoloph length 54.6

Maximum width 25.1

Diastema Right Length 88.0

Upper molar row Left Length 115.9

Falcontoxodon sp. AMU-CURS 69 m1 Left Length* 34.4

Talonid width 12.0

m2 Left Length 36.1

Trigonid width 13.3

Talonid width 11.4

m3 Left Length 48.3

Trigonid width 12.7

Talonid width* 9.3

Lower molar row Left Length 119.0

AMU-CURS 270 m3 Left Length 44.5

Trigonid width 13.0

Talonid width 8.7

TABLE 6. (Continued)
FIGURE 17. Partial skull of Falcontoxodon aff. F. aguilerai (AMU-CURS 585): (a) left lateral view; (b) ventral view; (c) detail 

of the upper left dentition in occlusal view; (d) schematic drawing of dentition: distribution of enamel is shown by thick lines.
3 4 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

teeth fragments. AMU-CURS 738, left calcaneus and three 

phalanges. AMU-CURS 739, partial m1/m2. AMU-CURS 741, 

right upper I2.

Locality and Horizon. Norte Casa Chiguaje, Vergel Member, San Gregorio Formation, Urumaco, Falcón State, 

Venezuela. 11°17′52.5′′N 070°14′11.1′′W (Figure 4a,b).

Description. In AMU-CURS 69 the m1 is not complete, but it shows lingual enamel extending mesially, reaching the meta-entoconid fold, as seen in F. aguilerai and in 

contrast to Mixotoxodon, where the lingual enamel does not 

extend mesially beyond the meta-entoconid fold. The lingual 

enamel of m2 does not extend distally to the hypoconulid, as 

in most Toxodontinae (Forasiepi et al., 2015). The m2 has a 

marked ento-hypoconulid fold and shallow meta-entoconid 

fold (Figure 18b), as in Mixotoxodon (Van Frank, 1957; Laurito, 1993; Rincón, 2011) and F. aguilerai. The m2 of AMUCURS 69 differs from that of F. aguilerai, Gyrinodon, and 

Mixotoxodon in the presence of a mesial fossettid and distal 

fossettids (Figure 17b).

The m3 of AMU-CURS 69 and 270 have lingual enamel 

between the mesial fold and the hypoconulid. They show an open 

ento-hypoconulid fold, similar to the condition in F. aguilerai, Gyrinodon (Hopwood, 1928), and Mixotoxodon (Van 

Frank, 1957; Laurito, 1993; Rincón, 2011). The m3 of AMUCURS 270 shows mesial, accessory, and distal fossettids (Figure 18g). Madden (1997) noted that during life the lower 

molar enamel folds can become isolated, forming fossettids, 

and eventually obliterate in individuals with advanced wear. 

In Pericotoxodon the ento-hypoconulid fold first becomes isolated and eventually wears away completely, and in an even 

more advanced stage the meta-entoconid fold becomes isolated as a fossettid.

Several isolated foot bones were recovered in the San Gregorio Formation. Among toxodontids, foot anatomy is best 

known for the Santacrucian Nesodon imbricatus (Figure 19) 

and Adinotherium ovinum (Scott, 1912), and for the Pleistocene Toxodon platensis (Owen, 1840). The right astragalus 

(AMU-CURS 542) from San Gregorio is comparable in size to 

that of Nesodon, larger than in Adinotherium, and smaller than 

in Toxodon (Table 7). AMU-CURS 542 has a shallow trochlear 

groove (Figure 20a), which is deeper in Nesodon (Figure 20c), 

and shallower in Toxodon (Figure 20e). The neck is very short 

(Figure 20a), similar to Toxodon (Figure 20e), and somewhat 

less defined than in Nesodon (Figure 20c). The medial tibial 

facet is expanded medially, forming a tuberosity (Figure 20a), 

which is absent in Nesodon (Figure 20c) and less developed 

in Toxodon (Figure 20e). In plantar view, the sustentacular 

and navicular facets are connected (Figure 20b), whereas in 

Nesodon and Toxodon they are separate (Figure 20d, f). The 

navicular facet is larger than the sustentacular facet, as in other 

toxodontids. In Nesodon, the navicular facet reaches the distal plane and it can be observed in dorsal view (Figure 20c), 

whereas in AMU-CURS 542 and Toxodon, it is restricted to 

the plantar plane. The ectal facet is concave and elongate. The 

PCA of toxodontid astragalar measurements (Table 7) roughly 

differentiates the four taxa, Adinotherium, Nesodon, Toxodon, 

and Falcontoxodon (Figure 21a). They are mainly separated 

along the PC1, which correlates with size, with the smaller 

Adinotherium toward the negative values, the larger Toxodon

toward the positive values, and Nesodon and Falcontoxodon

in between.

The left calcaneus of Falcontoxodon (AMU-CURS 738) is 

of comparable length but wider, and somewhat more robust, 

than the calcanei of Nesodon. It is smaller than the calcaneus of Toxodon (Table 8; Figure 22a–h). In Falcontoxodon

the cuboid facet is wider than in Nesodon. The ectal facet is 

approximately perpendicular to the fibular facet, and the sustentacular facet is inclined anteromedially (Figure 22a). AMUCURS 542 and 562 include tarsals consisting of a fragment of 

metatarsal II, and complete metatarsals III (Figure 22i–k) and 

metatarsal IV (Figure 22 l–n). Overall, they are comparable in 

length and width to those of Nesodon, and much smaller than 

in Toxodon (Table 8).

Toxodontinae indet.

Referred Material. MUN-STRI 13103, lower 

molar fragment. MUN-STRI 13118, upper molar fragment. 

MUN-STRI 34153, upper molar fragment. MUN-STRI 34168, 

lower molar fragment. MUN-STRI 34178, molar fragments. 

MUN-STRI 34184, molar fragments. MUN-STRI 34189, 

lower molar fragment. MUN-STRI 34353, lower incisor fragment. MUN-STRI 37507, lower molar fragment; MUN-STRI 

37561, lower molar fragment; MUN-STRI 44459, partial palate with I3.

Locality and Horizon Ware Formation, Police 

Station. MUN-STRI 13103 and MUN-STRI 13118 come 

from STRI locality 390020; MUN-STRI 34153 and MUNSTRI 34168 come from STRI locality 470061; MUN-STRI 

34178, MUN-STRI 34184, MUN-STRI 34189, MUNSTRI 34353 and MUN-STRI 44459 come from STRI locality 470060; MUN-STRI 37507 comes from STRI locality 

470062; MUN-STRI 37561 comes from STRI locality 

470059; (Figure 3).

Description. The isolated teeth are upper molars 

(Figure 23). The enamel is not well preserved (Figure 23b). 

They have a simple primary lingual enamel fold, which separates the protoloph from the metaloph (Figure 23a), as in 

Falcontoxodon, some specimens of Pericotoxodon with an 

advanced stage of dental wear (Madden, 1997), Andinotoxodon (Madden, 1990), Mixotoxodon (Laurito, 1993), Piauhytherium (Guérin and Faure, 2013), and Gyrinodon (Figure

15d). The protoloph does not support a lingual column (Figure

23a); the metaloph is broad and does not taper distally, as in 

Falcontoxodon and most specimens of Pericotoxodon (Madden, 1997).
NUMBER 101 • 3 5

FIGURE 18. Partial mandibles of Falcontoxodon sp.: (a) left mandible (AMU-CURS 69), in occlusal view; (b) schematic drawing of m2 

and m3 of AMU-CURS 69: distribution of enamel is shown by thick lines; (c) AMU-CURS 69 in lateral view; (d) AMU-CURS 69 in 

medial view; (e) left partial mandible (AMU-CURS 270) in lateral view; (f) AMU-CURS 270 in occlusal view; (g) schematic drawing of 

the m3 of AMU-CURS 270: distribution of enamel is shown by thick lines.
3 6 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

FIGURE 19. Right foot 

(without phalanges) of Nesodon imbricatus (Toxodontidae) (MNHN F SCZ 212) 

from the Santa Cruz Formation (Santacrucian SALMA) 

in Argentina: (a) articulated 

right foot in dorsal view; (b) 

schematic drawing of foot.

TABLE 7. Astragalar measurements (mm) of toxodontids. Measurements follow those of Tsubamoto (2014: fig. 1). Li1 = transverse 

width of the tibial trochlea; Li2 = proximodistal length of the lateral trochlear ridge of the tibial trochlea; Li3 = proximodistal length of 

the medial trochlear ridge of the tibial trochlea; Li4 = transverse width of the astragalus; Li5 = proximodistal length of the astragalus; 

Li6 = proximodistal length of the central part of the tibial trochlea; Li7 = transverse width between the medial and lateral trochlear 

ridges of the tibial trochlea; Li8 = dorsoventral thickness of the lateral part of the astragalus; Li9 = dorsoventral thickness of the medial 

part of the astragalus. Measurements are shown in Figure 21b.

Taxon Specimen Li1 Li2 Li3 Li4 Li5 Li6 Li7 Li8 Li9

Adinotherium sp. MLP 67-XII-8-1 18.0 21.6 20.9 24.2 27.0 17.0 14.7 14.6 21.3

MLP 67-XII-8-2 23.8 33.6 29.7 32.8 34.4 24.8 20.3 24.2 34.4

Nesodon imbricatus MNHN SCZ 1902-6 34.08 45.1 43.81 54.13 56.79 35.27 27.69 33.5 43.08

MNHN SCZ 30 35.62 42.31 43.25 47.1 48.25 32.07 26.19 30.08 35.17

NHM UK M 96594 32 41.3 41.5 48.9 48.8 35.1 25 28.3 42.4

NHM UK M5475 31.9 41.9 41.6 49.3 48.2 34.5 27.9 22.7 37.7

Toxodon platensis MNHN PAM 284 58.33 67.22 60.72 83.68 66.55 48.3 53.01 36.44 59.03

NHM UK M 5486 63 69.4 58.1 86.6 67.2 50.4 56 36 56.1

Falcontoxodon sp. AMU-CURS 542 40.3 45.2 44.1 60.9 51.3 36.7 34 31.2 38.1
NUMBER 101 • 3 7

FIGURE 20. Toxodontid astragali: (a) Falcontoxodon sp. 

(gen. nov.), right astragalus (AMU-CURS 542) in dorsal 

view; (b) AMU-CURS 542 in plantar view; (c) schematic 

drawing of AMU-CURS 542 in dorsal view; (d) schematic 

drawing of AMU-CURS 542 in plantar view; (e) Nesodon imbricatus, right astragalus (MNHN F SCZ 212) in 

dorsal and (f) plantar view; (g) Toxodon platensis, right 

astragalus (MNHN PAM 284) in dorsal and (h) plantar 

view.

Body Mass Estimation

The different craniodental measurements (Table 9) yielded 

body mass estimates for F. aguilerai that range from 616 to 1075 

kg (Table 10). The arithmetic mean is 796 kg. The mean minimum estimate, taking into account the percentage of error, is 735 

kg, and the maximum is 946 kg.

Phylogenetic Analysis of Toxodontidae

The parsimony analysis with extended implied weighting resulted in nine most parsimonious trees of 268 steps, with 

a consistency index of 0.507 and retention index of 0.641. In 

the strict consensus (Figure 24a), the clade Toxodontidae has a 

bootstrap value of 0.62 and is supported by two unambiguous 
3 8 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

FIGURE 21. Astragalar morphospace in selected toxodontids: 

(a) bivariate plot of the first two principal components of the 

PCA; (b) linear measurements follow Tsubamoto (2014).

FIGURE 22. Toxodontid calcanei and metatarsals. Left calcaneus 

of Falcontoxodon sp. (gen. nov.) (AMU-CURS 738): (a) photograph and (b) schematic drawing in dorsal view; (c) plantar 

view. Left calcaneus of Nesodon imbricatus (MNHN SCZ 30): 

(d) photograph and (e) schematic drawing in dorsal view; 

(f) plantar view. Right calcaneus of Toxodon platensis (MHMUK 

PV M 5486): (g) photograph and (h) schematic drawing in dorsal 

view. Metatarsals of Falcontoxodon sp. (gen. nov.) (AMU-CURS 

542). Left metatarsal III: (i) plantar view; (j) photograph and (k) 

schematic drawing in dorsal view. Left metatarsal IV: (l) plantar 

view; (m) photograph and (n) schematic drawing in dorsal view.
NUMBER 101 • 3 9

synapomorphies: i1 that is triangular in cross section (36[1]) 

and lingual enamel of i3 that is narrower than the labial enamel 

(40[3]). Proadinotherium is hypothesized as being the sister 

taxon of all the other toxodontids (Figure 24a). The Nesodontinae comprises Adinotherium and Nesodon (Figure 24a), and 

is supported by one unambiguous synapomorphy, the symphysis without a well-differentiated chin angle (16[0]). The clade 

Toxodontinae has a bootstrap value of 0.96 (Figure 24a) and is 

supported by ten unambiguous synapomorphies: short sagittal 

crest (4[1]), hypselodont cheek teeth (19[2]), molars without 

fossettes (29[1]), M1–M2 with distal groove/fossette smooth or 

absent (31[1]), M3 with groove smooth or absent (32[1]), lingual enamel extending distally to the posterior groove (33[1]), 

the mesial fold of m1–m2 at the same level as the labial fold 

(49[1]), m1 with lingual enamel between the anterior fold and 

the hypoconulid (55[1]), lingual enamel of m2 restricted between 

the mesial fold and the hypoconulid (56[1]), and lingual enamel 

of m3 reaching the level of the hypoconulid (57[1]).

TABLE 8. Measurements (in mm) of the calcaneus and metatarsals of toxodontids. Mt = Metatarsal. A dash (-) indicates data not 

available.

Taxon Specimen Element Length Distal width Proximal width

Falcontoxodon sp. AMU-CURS 542 Mt IV 93 39 39.5

Mt III 70.6 29.7 27.6

AMU-CURS 562 Mt IV 91.4 46.8 39.8

Mt III - 42.7 -

Mt II - 32 -

AMU-CURS 738 Calcaneus 88.8 46.7 46.4

Nesodon imbricatus MNHN SCZ 30 Mt IV 77.3 28.8 32

Mt III 82.8 29.9 29.7

Calcaneus 87.9 34.3 40

MNHN SCZ 212 Mt IV 78.9 27 31.7

Mt III 83.7 28.9 25

Calcaneus 82.7 31 35.3

NHM UK M96586 Calcaneus 88.2 33.6 38

NHM UK M96585 Calcaneus 87.9 32.3 43.2

Toxodon platensis NHM UK M 5487 Mt III 160 78.8 72.7

NHM UK M 5486 Calcaneus 133 67.2 73.9

FIGURE 23. Toxodontinae indet. left M1 or M2 from 

Ware Formation. (a) Occlusal and (b) lingual view.
4 0 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

TABLE 9. Cranial and mandibular measurements (mm) of Falcontoxodon aguilerai sp. nov. (holotype, AMU-CURS 765).

Variable Acronym Definition Value Reference

Lower premolar row length LPRL Measured along the base of the teeth 96 Janis (1990)

Lower molar row length LMRL Measured along the base of the teeth 148 Janis (1990)

Anterior jaw length AJL Measured from the boundary between p4 and m1 to the base of i1 164 Janis (1990)

Posterior jaw length PJL Measured as the horizontal distance from the back of the condyle 

to distal border of m3

150 Janis (1990)

Depth of mandibular angle DMA Measured from the top of the condyle to the deepest point of the 

mandibular angle

344 Janis (1990)

Maximum width of mandibular angle WMA Measured from the junction of the distal part of m3 with the dentary to the most distant point on the mandibular angle199 Janis (1990)

Length of coronoid process JD Measured as the vertical distance from the base of the condyle to 

the tip of the coronoid process

35 Mendoza et al. 

(2006)

Length of ridge for masseteric 

attachment

MFL Measured from the posterior portion of the glenoid to the most 

anterior extent of the scar for the origin of the masseter muscle

190 Janis (1990)

Posterior skull length PSL Measured from the occipital condyle to the distal edge of M3 240 Janis (1990)

Depth of face under orbit SD Measured from the boundary between premolar and molar tooth 

rows to the nearest point of the orbit

125 Mendoza et al. 

(2006)

Muzzle width MZW Measured between the most lateral points between the maxilla and 

premaxilla contact

100 Janis (1990)

Basicranial length BCL Measured from the ventral edge of the foramen magnum to the 

point of the basicranium where a change in angulation occurs 

between the basicranium and the palate

235 Janis (1990)

Total jaw length TJL TJL = PJL + LMRL + AJL 462 Janis (1990)

Total skull length TSL TSL = PSL + LMRL + AJL 552 Janis (1990)

TABLE 10. Body mass (BM) estimates (kg) for Falcontoxodon aguilerai sp. nov. (holotype, AMU-CURS 765) using the multivariate 

regression functions from Mendoza et al. (2006). RPE = range of PE; PE = Percent of error. See Table 9 for definitions of acronyms used 

in the equations.

Algorithm 

or statistic Equation Adj. R2 % RPE

mid % 

PE BM

BM + 

mid PE

BM − 

mid PE

2.1 ln BM = −1.602 * ln(LMRL) + 2,791 * ln(SLML) + 0.576 * ln(JLB) + 1.005 * ln(JMA) + 2.402

0.99 13.5–15 14.25 616 704 607

2.2 ln BM = −1.352 * ln(LMRL) + 2.434 * ln(SLML) + 0.587 *

ln(JLB) + 0.866 * ln(JMA) + 0.263 * ln(JMC) + 1.890

0.99 13.5–15 14.25 674 770 578

2.3 ln BM = −1.366 * ln(LMRL) + 2.421 * ln(SLML) + 0.542 * ln(JLB) + 1.017 * ln(JMA) + 0.716 * ln(JMC) – 0.509 * ln(JMB) + 2.006

0.99 13.5–15 14.25 608 695 521

3.1 ln BM = 1.119 * ln(LMRL) + 0.210 * ln(LPRL) + 0.730 *

ln(JMA) + 0.637 * ln(JMC) + 0.181 * ln(JD) + 0.619

0.98 21–25 23 1,075 1,322 1,018

3.2 ln BM = 1.0 * ln(LMRL) + 0.176 * ln(LPRL) + 0.823 * ln(JMA) 

+ 0.968 * ln(JMC) + 0.167 * ln(JD) − 0.331 * ln(JMB) 

+ 0.573

0.98 21–25 23 1,006 1,237 952

Mean 796 946 735
NUMBER 101 • 4 1

Palyeidodon is the first taxon to diverge within Toxodontinae, followed by Hyperoxotodon (Figure 24a). The remaining Toxodontinae are divided into two main clades: nodes 44 

and 46. Node 44 is supported unambiguously by a P2 without 

groove or fossette (25[1]). It comprises two clades: nodes 38 

and 43 (Figure 24a). Node 38 comprises two groups: one (node 

34) consists of (Calchaquitherium [Xotodon major, Xotodon 

cristatus]) and it is supported unambiguously by a mandibular 

symphysis with a median ventral keel (15[1]), upraised mandibular symphysis and lower incisors (18[2]), smooth or absent 

labial groove in p2–m4 (45[1]), and a smooth or absent entohypoconulid fold in m3 (53[1]). The second group (node 37) 

consists of (Pisanodon [Pericotoxodon (Paratrigodon, Trigodon)]), and is supported unambiguously by the presence of I3 

(22[0]), the absence of enamel in P1 (24[1]) and upper molars 

with median crista and an incipient median valley (30[1]). Node 

43 comprises two groups (Figure 24a). One includes Nonotherium and Posnanskytherium and it is supported by a very concave ectoloph (34[1]). The second group (node 42) consists of 

(Andinotoxodon [Hoffstetterius, Ocnerotherium, (Toxodon, 

Dinotoxodon)]), and is supported by a straight alveolar border 

of the symphysis (14[1]).

Within Toxodontinae, node 46 (Figure 24a) groups the 

clade (Piauhytherium [Mixotoxodon, Falcontoxodon, Gyrinodon]), which is supported by a rounded posteroventral border 

of the vertical mandibular ramus (12[0]), mandibular symphysis without a well-differentiated angle (16[0]), absence of lower 

canines (41[1]) and absence of lingual enamel in p2–p4 (44[2]). 

FIGURE 24. Hypothesis of phylogenetic relationships within Toxodontidae. (a) Time calibrated topology of the most parsimonious 

tree resulting from an analysis with PAUP using implied weighting (k = 3). Bootstrap values higher than 0.50 are indicated for several 

nodes. Numbers within circles designate nodes discussed in the text. Blue shading = Nesodontinae, red shading = Toxodontinae. Letters 

below time line (mya) denote SALMAs (from left to right): V = Vacan; B = Barrancan; M = Mustersan; T = Tinguirican; D = Deseadan; 

C = Colhuehuapian; P = “Pinturan”; S = Santacrucian; O = Colloncuran; L = Laventan; Y = Mayoan; Ch = Chasicoan; H = Huayquerian; E = Montehermosan; A = Chapadmalalan; R = Marplatan; N = Ensenadan. (b) Strict consensus of the 12 most parsimonious 

trees resulting from the analysis of the same data matrix but without using character weighting. Bootstrap values higher than 0.50 are 

indicated for several nodes.
4 2 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

The Venezuelan toxodontids form a clade (node 45; Figure 24a) 

supported by a smooth or absent ento-hypoconulid fold in m3 

(53[1]) and the presence of a deep and narrow labial groove in 

the molars (54[2]).

The analysis using equal weights yielded 193 most parsimonious trees of 264 steps, with a consistency index of 0.515 

and retention index of 0.652. In the strict consensus (Figure 24b), Toxodontinae has a bootstrap value of 0.85, and 

is supported by the following unambiguous synapomorphies: 

short sagittal crest (4[1]), mandibular symphysis with smooth 

chin angle (16[1]), euhypsodont cheek teeth (19[2]), molars 

without fossettes (29[1]), upper molars without a groove, or if 

present being smooth (31[1] and 32[1]), lingual enamel in M3 

extending distally to the distal groove (33[1]), the mesial fold 

in m1–m2 at the same level as labial fold (49[1]), the lingual 

enamel of m1 (55[1]) and m2 (56[1]) between the mesial fold 

and the hypoconulid, and the lingual enamel of m3 reaching 

the level of the hypoconulid (57[1]). In this analysis Nesodontinae was not recovered as monophyletic (Figure 24b). Within 

Toxodontinae, Palyeidodon is the first taxon to diverge, followed by Hyperoxotodon. The remaining taxa form a clade 

which is not well resolved. It includes the clades (Xotodon cristatus, Xotodon major), (Toxodon, Dinotoxodon) and (Trigodon, Paratrigodon) in a polytomy with the other toxodontinaes 

(Figure 24b).

Litopterna (Ameghino, 1889)

Proterotheriidae (Ameghino, 1887)

Lambdaconus (Ameghino, 1897)

Type Species. Lambdaconus suinus (Ameghino, 1897).

Lambdaconus cf. L. colombianus

(Hoffstetter and Soria, 1986) comb. nov.

=Neodolodus colombianus (Hoffstetter and Soria, 1986) by original designation.

=Prothoatherium colombianus (Cifelli and Guerrero, 1989) comb. nov.

Referred Material. MUN-STRI 16716, a left dentary with the alveolus of p3 and m2, and the p4, m1 and m3 (cast 

PIMUZ A/V 5291).

Locality and Horizon. Makaraipao, Castilletes 

Formation. STRI locality 930093; 11.9089°N, 71.3401°W (Figure 3).

Description. The partial mandible preserves part of 

the alveolus of p3, the p4, m1, the alveolus of m2, and a fragment of m3 (Figure 25a–d). The teeth are brachyodont, bicrescentic, and very low crowned (Figure 25a), as in Lambdaconus 

colombianus (Hoffstetter and Soria, 1986; Cifelli and Guerrero, 

1989). The cheek teeth have four roots (Figure 25b,d). The 

lophs are not well defined (Figure 25b) due to the low crown 

height and wear, as in L. colombianus (Cifelli and Guerrero, 

1989).

Lambdaconus colombianus was described by Hoffstetter 

and Soria (1989) on the basis of a partial mandible with worn 

lower dentition. These authors considered that the taxon represented a new genus and species (Neodolodus colombianus), 

and referred it to Didolodontidae. Cifelli and Guerrero (1989) 

transferred the taxon to Prothoatherium (Proterotheriidae, 

Litopterna) and assigned the new combination of Prothoatherium colombianus. Prothoatherium was named by Ameghino 

(1902), who recognized two species and later added a third 

one (Ameghino, 1904). Soria (2001) did not recognize Prothoatherium as valid, and transferred one species to Lambdaconus (L. lacerum) and established the other two as synonyms of 

Paramacrauchenia scammata (=Prothoatherium scammatum

[partim] and Prothoatherium plicatum) and Paramacrauchenia inexpectata (=Prothoatherium scammatum [partim]). Soria 

died in 1989, and his dissertation (published posthumously in 

2001) made no mention of Lambdaconus (=Prothoatherium) 

colombianus.

Based on the descriptions of Hoffstetter and Soria (1986) 

and Cifelli and Guerrero (1989), we consider that L. colombianus belongs to Lambdaconus and not to Paramacrauchenia. 

L. colombianus shows some diagnostic characters of Lambdaconus as revised by Soria (2001), including the following: 

m1–m3 without paraconid and with entoconid (Hoffstetter and 

Soria, 1986; Cifelli and Guerrero, 1989), P4–M3 with metaconule, and M3 with a reduced hypocone (Cifelli and Guerrero, 

1989). In contrast, in Paramacrauchenia the P4 does not have a 

metaconule, in the M1–M2 the metaconule is reduced and associated with the hypocone, and the M3 does not have a hypocone 

(Soria, 2001).

In Lambdaconus cf. L. colombianus (MUN-STRI 16716), 

the p4 is molariform and narrows mesially in occlusal view (Figure 25d). It measures 12.4 mm in mesiodistal length and 8.5 mm 

in labiolingual width. The ectoflexid is shallow and the paraconid is reduced (Figure 25d). There is no evidence of labial or 

lingual cingula (Figure 25a,c), which are present in L. colombianus and poorly developed or absent in L. lacerum (Cifelli and 

Guerrero, 1989; Soria, 2001; Kramarz and Bond, 2005). The 

p4 has a hypoconulid, unlike in Megadolodus where it is absent 

(Cifelli and Villarroel, 1997). The p4 and m1 have a welldeveloped hypoconid, and the metaflexid and entoflexid are 

present (Figure 25d).

The m1 measures 13.5 mm in mesiodistal length and 9.8 

mm in labiolingual width. The protoconid and metaconid are 

well developed, as in L. colombianus (Hoffstetter and Soria, 

1986). The paraconid is present, unlike in Prolicaphrium and 

Megadolodus (Cifelli and Guerrero, 1997; Cifelli and Villarroel, 1997). The ectoflexid is deep and the hypoconid is well 
NUMBER 101 • 4 3

developed, with a marked crescent shape, as in L. colombianus

(Hoffstetter and Soria, 1986). The entoconid and hypoconulid 

are undifferentiated, due to wear (Figure 25d). The alveolus of 

the m2 accommodates four roots (Figure 25b,d). The crown 

of the m3 is broken, missing distal and mesiolingual portions 

(Figure 25d). It measures 97 mm in labiolingual width, and it 

has a deep ectoflexid. MUN-STRI 16716 differs from Megadolodus (McKenna, 1956; Cifelli and Villarroel, 1997) in having 

less bunodont and more rectangular molars, having a paraconid, 

and lacking cingula.

Proterotheriidae indet.

Referred Material. MUN-STRI 13119, diaphysis 

and distal epiphysis of left humerus. MUN-STRI 13120, right 

ulna. MUN-STRI 13121, left metacarpal III. MUN-STRI 16289, 

fragment of lower molar. MUN-STRI 19544, right calcaneus. 

MUN-STRI 34170, M1/M2. MUN-STRI 34185, partial mandible with fragment of left m2. MUN-STRI 34348, distal fragment 

of metapodial. MUN-STRI 34372, diaphysis and distal epiphysis 

of left humerus. MUN-STRI 34641, left M2. MUN-STRI 37753, 

FIGURE 25. Proterotheriidae (Litopterna) from the Cocinetas Basin. 

Lambdaconus cf. L. colombianus, left 

dentary (MUN-STRI 16716) from the 

Castilletes Formation: (a) lingual, (b) 

occlusal, and (c) labial views; (d) schematic drawing of dentition in occlusal view. Proterotheriidae indet. from 

the Ware Formation. Left M1 or M2 

(MUN-STRI 34170) in occlusal view: 

(e) photograph and (f) schematic drawing. Fragment of right lower molar 

(MUN-STRI 16289) in (g) occlusal 

and (h) labial views.
4 4 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

metapodial. AMU-CURS 745, epiphysis of metacarpal III. AMUCURS 746, left metacarpal III.

Locality and Horizon. Police Station, Ware Formation; 11.8487°N, 71.3243°W. MUN-STRI 13119, 13120, 

13121 come from STRI locality 390020. MUN-STRI 19544 

comes from STRI locality 390018. MUN-STRI 16289 comes 

from STRI locality 430052. MUN-STRI 34170, MUN-STRI 

34185, MUN-STRI 34348 and MUN-STRI 34641 come from 

STRI locality 470060. MUN-STRI 34372 comes from STRI 

locality 470061. MUN-STRI 37753 comes from STRI locality 

470062. AMU-CURS 745 and 746 come from the Algodones 

Member, Codore Formation, 11°17′39.8′′N, 70°14′15.6′′W.

Description. The upper molar (MUN-STRI 34170) 

is brachyodont and quadrangular in occlusal view, suggesting 

that it represents an M1 or M2 (or a molarized P4). The M3 

in proterotheriids has a distinctive outline in occlusal view; for 

example, in Brachytherium it is trapezoidal (Schmidt, 2015), 

and in Villarroelia it is more triangular (Cifelli and Guerrero, 

1997). It has a mesiodistal length of 10.4 mm and a labiolingual 

width of 10.6 mm (Figure 25e). MUN-STRI 34170 is referred to 

a Proterotheriidae indet. based on its size, the bunoselenodont 

(Janis, 2000: fig. 7.2) condition and the position of the hypocone 

posterior to the paracone (Schmidt, 2013).

MUN-STRI 34170 differs from the megadolodine Bounodus enigmaticus (Carlini et al., 2006b) in having a more developed protocone, and the paracone positioned less mesially. The 

mesiolingual border of the crown is broken, and the presence of 

the mesiolingual cingulum cannot be evaluated. The protocone 

is the largest cusp (Figure 25f), as in Brachytherium (Schmidt, 

2015). The hypocone is broken, but it appears to have been 

separated from the protocone by a distolingual groove, as in 

Brachytherium, Proterotherium, and Prothoatherium (Cifelli 

and Guerrero, 1989; Schmidt, 2015). The paraconule is not 

connected with the protocone by a loph, as it is in the Proterotheriinae (Schmidt, 2013). The metaconule is also an isolated 

cusp, as in Prothoatherium (Cifelli and Guerrero, 1989), and it 

is not reduced as in Neolicaphrium (Ubilla et al., 2011), or connected to the protocone, as in Prolicaphrium (Cifelli and Guerrero, 1997). The metaconule is located distal to the paraconule 

and mesiolingual to the hypocone (Figure 25f). MUN-STRI 

34170 has three labial styles (Figure 25f), as in the Protherotheriinae (Schmidt, 2013). The mesostyle is well developed, as in 

Villarroelia (Cifelli and Guerrero, 1997), and as opposed to the 

reduced condition seen in Neobrachytherium (Schmidt, 2015). 

The paracone and metacone labial folds are well developed as 

in Brachytherium and Proterotherium, and unlike Neobrachytherium and Thoatheriopsis (Villafañe et al., 2012; Schmidt, 

2015).

The lower molar fragment (MUN-STRI 16289) measures 

8.2 mm in labiolingual width and 8.9 mm in crown height on 

the labial side. It preserves the mesial portion of the crown, with 

well-defined paralophid and metalophid (Figure 25g). The protoconid and paraconid are well developed, and the metaflexid and 

ectoflexid are deep (Figure 25g,h). This lower molar fragment 

preserves only the mesio-labial root, which is long and narrow 

(Figure 25h).

The proterotheriid humerus (MUN-STRI 34372) preserves 

part of the diaphysis and the distal epiphysis (Figure 26a–c). 

The capitulum is rounded and projects less distally than the 

trochlea (Figure 26a). The medial and lateral epicondyles are 

weakly developed. There is a supratrochlear foramen. The 

olecranon fossa is a fenestra (Figure 26c), as in Prothoatherium and Proterotherium (Cifelli and Guerrero, 1989). The 

diaphysis is mediolaterally compressed, as in other proterotheriids (Cifelli and Guerrero, 1989). The proximal portion of 

the diaphysis (at the level of the deltoid tuberosity) has the 

greatest anteroposterior depth, which decreases distally (Figure 26b) (Table 11).

The ulna (MUN-STRI 13120) is fairly complete, missing 

only a portion of the olecranon and a distal portion (Figure

26d–f; Table 11). The diaphysis is narrow and nearly straight. 

The anconeal process is not well developed, but projects laterally 

(Figure 26d). The coronoid process is small and projects distomedially (Figure 26d). The preserved portion of the olecranon is 

in the same plane as the shaft (Figure 26d,f).

The calcaneus (MUN-STRI 19544) has an elongate shape, 

with the distal portion broader than the body (Figure 26g,h). 

The body is not lateromedially compressed, as in Neolicaphrium (Scherer et al., 2009). The ectal facet is oval and located 

in the midline of the body (Figure 26g), as in Neolicaphrium. 

The sustentacular facet is also oval and elongated posteroventrally (Figure 26g), as in Neolicaphrium (Scherer et al., 2009). 

The metatarsals III from the Ware (MUN-STRI 13121; Figure

26i,j) and Codore (AMU-CURS 746; Figure 26k,l) Formations 

are very similar. The diaphysis is straight and long (Table 11). 

The distal epiphysis has a well-defined median keel.

Artiodactyla (Owen, 1848)

Camelidae (Gray, 1821)

cf. Camelidae indet.

Referred Material. MUN-STRI 34380 (cast 

PIMUZ A/V 5289), right m1 or m2.

Locality and Horizon. Police Station, Ware 

Formation. STRI locality 470060. 11.8487°N, 71.3243°W 

(Figure 3).

Description. The tooth measures 15.2 mm in mesiodistal length and 8.9 mm in labiolingual width. The crown height 

at the labial side is 10.4 mm, yielding a hypsodonty index of 0.7; 

this is a minimum value because the tooth is worn. The molar is 

bicrescentic and the talonid is approximately the same size as the 

trigonid (Figure 27a). The trigonid and talonid fossae are deep, 

semilunar, and elongated mesiodistally (Figure 27b), as in Hemiauchenia (Scherer et al., 2007). The protoconid and hypoconid 

are well developed, the labial lophids are V-shaped, but the labial 

edge is not as defined as in Palaeolama (Scherer et al., 2007). The 
NUMBER 101 • 4 5

FIGURE 26. Proterotheriidae (Litopterna) postcrania from 

Ware and Codore Formations. Left humerus (MUN-STRI 

34372): (a) anterior, (b) medial, and (c) posterior view. 

Right ulna (MUN-STRI 13120): (d) anterior, (e) medial, 

and (f) posterior view. Right calcaneus (MUN-STRI 

19544): (g) dorsal and (h) plantar view. Left metacarpal III 

(MUN-STRI 13121): (i) anterior and (j) posterior view. 

Left metacarpal III (AMU-CURS 746): (k) anterior and 

(l) posterior view.
4 6 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

TABLE 11. Postcranial measurements (mm) of the Proterotheriidae indet. specimens of the Ware Formation; width = mediolateral; 

thickness = anteroposterior; a dash (–) indicates measurement could not be taken in the specimen.

Humerus Ulna Calcaneus Metacarpal III

Measurement MUN-STRI 13119 MUN-STRI 13120 MUN-STRI 19544 MUN-STRI 13121 AMU-CURS 746

Diaphysis width 12.6 10.1 – 9.8 15.9

Diaphysis thickness 18.3 12.0 – – –

Distal width 29.0 (Epiphysis)

20.6 (Trochlea)

– – 11.8 21.2

Lateral epicondyle thickness 16.7 – – – –

Medial epicondyle thickness 18.2 – – – –

Sigmoid cavity height – 18.2 – – –

Olecranon thickness – 14.0 – – –

Olecranon width – 8.7 – – –

Total length – – 53.9 70.1 89.3

Maximum width – – 19.2 – –

Maximum thickness – – 14.8 – –

Proximal width – – – 12.6 19.9

Proximal thickness – – – 11.1 –

FIGURE 27. cf. Camelidae indet. (Artiodactyla) 

from the Ware Formation. Right m1 or m2 

(MUN-STRI 34380): (a) photograph and (b) 

schematic drawing in occlusal view; (c) labial 

and (d) lingual views.
NUMBER 101 • 4 7

most mesial portion of the crown is broken and the presence of 

the proto- and parastylid (“llama buttress”) cannot be evaluated 

(Figure 27a). South American camelids are thought to belong to 

the clade Lamini (Scherer, 2013), and the presence of a “llama 

buttress” has been proposed as a synapomorphy of the clade 

(Harrison, 1985; Webb and Meachen, 2004). However, Scherer 

(2013) noticed that the development of proto- and parastylid 

is highly variable in South American camelids. Despite being 

in an advanced wear stage, MUN-STRI 34380 differs from the 

lower molars of cervoids in being more hypsodont, and it differs 

from derived protoceratids (Synthetoceratines) in having a more 

developed metastylid. Finally, the Camelinae (sensu Webb and 

Meachen, 2004) is in need of systematic revision, and diagnostic 

characters for different taxa must be reevaluated on the basis 

of genomic and morphological data recovered from fossil taxa 

(Heintzman et al., 2015).

Chronostratigraphy of the Falcón Basin

The Falcón Basin is divided between a western and an 

eastern sector. For each of the sectors, author L. Quiroz did 

an extensive stratigraphic study and described several stratigraphic sequences to produce a composite sequence of both 

regions (Quiroz and Jaramillo, 2010) (Figures 28, 29). Seven 

sections were measured and described in western Urumaco, 

producing a composite sequence that is 8.75 km thick (Figure 28), and in eastern Urumaco three sections were measured 

and described, producing a composite sequence that is 2.25 km 

thick (Figure 29).

We provide a detailed description of each section, including its geographic position, in appendix 1 of the supplementary materials (Carrillo et al., 2018b). The biostratigraphic 

record of foraminifera in the Urumaco region (both western 

and eastern) has been extensively studied, and correlated to 

Bolli’s biostratigraphic schemes from Trinidad (Renz, 1948; 

Bermudez and Bolli, 1969; Blow, 1969; Díaz de Gamero 

1977a,b, 1985a,b, 1989, 1996; Díaz de Gamero et al., 1988; 

Díaz de Gamero and Linares, 1989; Wozniak and Wozniak, 

1987; Guerra and Mederos, 1988; Rey, 1990; Hambalek, 

1993; Bolli et al., 1994; Pérez et al., 2016). For a detailed 

description of the key studies, see appendix 2 in supplementary 

materials (Carrillo et al., 2018b). The age of the Querales Formation is further supported by nannoplankton (Pérez et al., 

2016). The foraminiferal ages of the Urumaco Formation 

are also supported by vertebrates (Linares, 2004; Sánchez-Villagra, 2006; Sánchez-Villagra and Aguilera, 2006). A sample 

from the lower member of the Urumaco Formation (Urumaco 

West section, Figure 28) was analyzed for nannoplankton and 

yielded a flora that includes Coccolithus pelagicus, Discoaster 

deflandrei, Sphenolithus abies, and Sphenolithus moriformis.

This association corresponds to Nannoplankton Zone NN7, 

which is equivalent to Planktonic Zone N14, early Tortonian 

(Figure 28). Herrera (2008) studied the magnetic stratigraphy 

of the Urumaco Formation at the same locality of our Urumaco West section. Herrera identified the top of Chron C4 

Ar2r within the Urumaco Formation at meter 6693 of our section (Figure 28). Overall, the top boundaries of the formations 

in the Urumaco region, both East and West, are well dated and 

summarized in Table 12 and Figures 28 and 29.

To estimate the age of the stratigraphic horizons where the 

fossil mammals are recorded in the Falcón and Cocinetas Basins, 

we used the age model presented by Hendy et al. (2015) for the 

Jimol and Castilletes Formations in the Cocinetas Basin. We followed the chronostratigraphic framework described above for 

the Codore and San Gregorio Formations in the Falcón Basin. 

The stratigraphic occurrence and age of each specimen are summarized in Table 13.

DISCUSSION

Astrapotheriidae

The clade Uruguaytheriinae is registered in low and middle 

latitudes (<23°S; Goillot et al., 2011; Vallejo-Pareja et al., 2015; 

Croft et al., 2016), with the exception of Uruguaytherium, the 

most basal Uruguaytheriinae, whose precise provenance and age 

are unknown. The oldest record of Uruguaytheriinae comes from 

the bank of Río Beu, near the Santa Rosa locality in Peru, and it 

is interpreted to be late Oligocene in age (Antoine et al., 2016). 

The time-calibrated tree (Figure 12) is also consistent with the 

origin of Uruguaytheriinae in the late Oligocene. Given the current evidence, it is unclear whether the clade’s origin took place in 

low or high latitudes, and more complete material from the late 

Oligocene deposits should help to clarify this issue. In any event, 

the middle Miocene (Laventan) uruguaytheriine taxa are the last 

occurring astrapotheres (Johnson and Madden, 1997; Goillot 

et al., 2011) (Figure 12).

The interrelationships of northern Uruguaytheriinae are not 

well resolved (Figure 12). Hilarcotherium is known only from 

Colombia, and its biochron extends from the upper Burdigalian–

Langhian (Santacrucian/Colloncuran; 16.7–14.2 mya; Moreno 

et al., 2015) to the Serravallian (?Laventan; Vallejo-Pareja et al., 

2015). Granastrapotherium is a monospecific genus and Xenastrapotherium includes five species; some were described from 

fragmentary remains without associated upper and lower dentition, and more complete specimens are needed to evaluate their 

validity.

Postcranial elements of Uruguaytheriinae are rare, and their 

intra- and interspecific variation has not been studied. Isolated 

postcranial elements are common in the Castilletes fauna. They 

are not associated with dental remains and we tentatively refer 

them to Hilarcotherium cf. H. miyou, as this is the only astrapotherid taxon recognized for the Castilletes Formation. All the 

postcranial elements are large, and given the size of H. miyou, it 

is plausible that they belong to this taxon. The material described 
4 8 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

FIGURE 28. Urumaco western sequence chronostratigraphy. Composite section corresponds to several outcrop sections measured in 

western Urumaco, Venezuela, and described in Quiroz and Jaramillo (2010); scale bar values are total thickness (m). A detailed description of each individual section and its geographic position is given in supplementary materials by Carrillo et al. (2018b: appdx. 1). The 

ages (mya) are derived from multiple foraminiferal, nannoplankton, and magnetic stratigraphic studies (Renz, 1948; Bermudez and 

Bolli, 1969; Blow, 1969; Díaz de Gamero 1977a,b, 1985a,b, 1989, 1996; Díaz de Gamero et al., 1988; Díaz de Gamero and Linares, 

1989; Wozniak and Wozniak, 1987; Guerra and Mederos, 1988; Rey, 1990; Hambalek, 1993; Bolli et al., 1994; Pérez et al., 2016).
NUMBER 101 • 4 9

FIGURE 29. Chronostratigraphy of Falcón State east of Urumaco town. Composite section corresponds to several outcrop sections 

measured in eastern Urumaco. Formation ages are derived from multiple foraminiferal, nannoplankton, and magnetic stratigraphic 

studies (see text and Figure 28 for references).
5 0 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

TABLE 12. Chronostratigraphic data for composite Urumaco East and West sections. Numerical ages follow Gradstein et al. (2012). Reported ages (mya) are for the top of each section.

Datum (event top) Composite section (M) Age (mya)

Codore Algodones 8,285 1.81

Codore Chiguaje 7,935 3.6

Codore Jebe 7,886 5.33

Urumaco 7,403 6.8

Top C4 Ar2r 6,693.6 8.1

Socorro 5,338 12.4

Querales 3,130 14.5

Cerro Pelado 2,704 16

Agua Clara 631 17.5

Coro 2,185 0.4

La Vela 1,838 1.81

Caujarao Tara 1,025 5.6

Caujarao Mataruca 710 8.6

Caujarao Muaco 538 9.6

here will serve as a basis to compare the postcranial morphology 

of uruguaytheriine and non-uruguaytheriine astrapotheres in 

order to assess possible paleobiological differences or phylogenetically informative characters.

The dental measurements and associated body mass estimates of H. miyou (Figure 8; Tables 3, 5) indicate that it is one of 

the largest astrapotheres, comparable in size to G. snorki, Parastrapotherium martiale (Deseadan–Colhuehuapian SALMAs), 

and Parastrapotherium herculeum? (Colhuehuapian; Kramarz 

and Bond, 2008, 2010, 2011). Few studies have addressed the 

estimation of body mass in astrapotheres, and the congruence 

between estimates from dental and postcranial measurements 

has not been studied. Previously reported body mass estimations in astrapotheres used only dental and craniomandibular 

measurements. The m2 length yields an estimate of ~6,456.6 

kg for H. miyou, notably larger than H. castanedaii (~1,303 

kg; Vallejo-Pareja et al., 2015) and X. kraglievichi (~1,238.7–

1,324.7 kg; Johnson and Madden, 1997; Kramarz and Bond, 

2011). It is possible that the dental measurements overestimate 

the body mass of astrapotheres (Kramarz and Bond, 2011). The 

best known astrapotheriid is Astrapotherium magnum from the 

Santa Cruz Formation (Santacrucian SALMA) in Patagonia, 

which is known by almost complete skeletons with skulls and 

associated postcranial remains (Scott, 1928, 1937). The mean 

body mass estimate for A. magnum using bivariate and multivariate regression equations from craniomandibular measurements 

is ~921.3 kg (Cassini et al., 2012), much smaller than the mean 

estimate of ~1,824.5 kg using the m1–m3 length (Kramarz and 

Bond, 2011). Similarly, the mean estimate for G. snorki using 

craniomandibular measurements reported by Johnson and Madden (1997; table 22.8) is ~1,126.1 kg, whereas the estimate using 

the m1–m3 length is ~3,141.9 kg.

Proximal limb bones are considered better estimators of 

body mass because they are weight-bearing elements and subject to greater biomechanical constraints (Scott, 1990). Body 

mass estimates using the humeral length (Table 5) yield similar 

values to the estimates from dental measurements in H. castanedaii (~1,306.5 kg; Vallejo-Pareja et al., 2015), but this was not 

the case in G. snorki (~4,501.1 kg) and A. magnum (~2,096.5 

kg), where the humeral estimates were larger than estimates 

from craniodental measurements. The estimate for the Hilarcotherium cf. H. miyou humerus from Castilletes (MUN-STRI 

16777) was approximatedly 4,985.0 kg, 23% smaller than 

the estimate for H. miyou using the m2 length (Table 5). It is 

worth mentioning that the humerus of the former was associated with a radius that indicated the individual was a juvenile. 

These results emphasize the need for a comparative study on 

the relative proportions and scaling of teeth and limb bones in 

astrapotheres to choose an adequate living analog to estimate 

body mass in this group.

Toxodontidae

The obtained phylogenetic hypothesis for Toxodontidae differs from the ones presented by Forasiepi et al. (2015: fig. 11) 

and Bonini et al. (2017a: fig. 6) mainly in the position of several 

taxa within Toxodontinae. The clades (Paratrigodon, Trigodon) 

and (Toxodon, Dinotoxodon) are recovered also in Forasiepi 
NUMBER 101

• 5 1

TABLE 13. Biochronology of the Cocinetas and Falcón Basins. For Cocinetas, the age model of Hendy et al. (2015) used a linear regression of the stratigraphic position and the 87Sr/86Sr isotopes ages for the upper part of the Jimol and the Castilletes Formations. The regression function is y = −0.0058x + 16.722, where y is the age in mya

and x is the stratigraphic meter. The original equation cannot be applied for the Ware Formation due to an unconformity between the Castilletes and Ware Formations (Moreno et al., 2015). For the Ware Formation, a mean age of 3.2 mya was estimated for the shell bed at the top of the formation (Hendy et al., 2015; Moreno et al., 

2015). This shell bed is 17–20 m above the stratigraphic horizons where the vertebrates were recovered. Assuming the same sedimentation rate for the Jimol, Castilletes, and Ware Formations, we used the regression equation presented by Hendy et al. (2015) to estimate the age of the horizons of fossil vertebrates from the Ware Formation. Using the age of 3.2 mya obtained for the horizon at stratigraphic meter 22, we calculated that 3.2 = −0.0058 * 22 + intercept, and we obtained a regression function for the Ware formation of y = −0.0058x + 3.0724. Abbreviations: SM = Stratigraphic meter; Lat = latitude; Lon = longitude.

Basin Clade Subclade Taxon Specimen ID Formation Locality

Section 

ID Lat. Long. SM

SM 

composite 

section

Age 

(mya)

Falcón Notoungulata Toxodontidae Falcontoxodon 

aguilerai

AMU-CURS 765 Codore Codore Algodones NA 11.29 −70.24 2,530 8,257 1.96

AMU-CURS 70 Codore Codore Algodones NA 11.29 −70.24 2,530 8,257 1.96

Litopterna Proterotheriidae Proterotheriidae 

indet.

AMU-CURS 745 Codore Codore Algodones NA 11.29 −70.24 2,530 8,257 1.96

AMU-CURS 746 Codore Codore Algodones NA 11.29 −70.24 2,530 8,257 1.96

Xenarthra Glyptodontidae Boreostemma 

pliocena

AMU-CURS 158 Codore Road to Tío Gregorio NA 11.26 −70.29 2,530 8,257 1.96

Notoungulata Toxodontidae Falcontoxodon aff. F.

aguilerai

AMU-CURS 585 San Gregorio Norte Casa Chiguaje NA 11.29 −70.24 4 8,291 1.78

Falcontoxodon sp. AMU-CURS 69 San Gregorio Norte Casa Chiguaje NA 11.29 −70.24 7 8,294 1.79

AMU-CURS 77 San Gregorio Norte Casa Chiguaje NA 11.29 −70.24 7 8,294 1.79AMU-CURS 270 San Gregorio Norte Casa Chiguaje NA 11.29 −70.24 7 8,294 1.79AMU-CURS 542 San Gregorio Norte Casa Chiguaje NA 11.29 −70.24 7 8,294 1.79AMU-CURS 544 San Gregorio Norte Casa Chiguaje NA 11.29 −70.24 7 8,294 1.79AMU-CURS 548 San Gregorio Norte Casa Chiguaje NA 11.29 −70.24 7 8,294 1.79AMU-CURS 562 San Gregorio Norte Casa Chiguaje NA 11.29 −70.24 7 8,294 1.79AMU-CURS 563 San Gregorio Norte Casa Chiguaje NA 11.29 −70.24 7 8,294 1.79AMU-CURS 570 San Gregorio Norte Casa Chiguaje NA 11.29 −70.24 7 8,294 1.79AMU-CURS 738 San Gregorio Norte Casa Chiguaje NA 11.29 −70.24 7 8,294 1.79AMU-CURS 739 San Gregorio Norte Casa Chiguaje NA 11.29 −70.24 7 8,294 1.79AMU-CURS 741 San Gregorio Norte Casa Chiguaje NA 11.29 −70.24 7 8,294 1.79

Carnivora Procyonidae Cyonasua sp. AMU-CURS 224 San Gregorio Norte Casa Chiguaje NA 11.29 −70.23 5 8,292 1.78Rodentia Caviomorpha cf. Caviodon UNEFM-VF-53 San Gregorio Norte Casa Chiguaje NA 11.29 −70.24 5 8,292 1.78

Hydrochoeropsis? 

wayuu

UNEFM-VF-50 San Gregorio Norte Casa Chiguaje NA 11.29 −70.24 5 8,292 1.78

(Continued)
5 2 

• SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY Basin Clade Subclade Taxon Specimen ID Formation Locality Section ID Lat. Long. SM SM composite section Age (mya) UNEFM-VF-51 San Gregorio Norte Casa Chiguaje NA 11.29 −70.24 5 8,292 1.78 UNEFM-VF-52 San Gregorio Norte Casa Chiguaje NA 11.29 −70.24 5 8,292 1.78 Marisela gregoriana UNEFM-VF-55 San Gregorio Norte Casa Chiguaje NA 11.29 −70.24 5 8,292 1.78 Neoepiblema sp. UNEFM-VF-54 San Gregorio Norte Casa Chiguaje NA 11.29 −70.24 5 8,292 1.78 Xenarthra Dasypodidae Pliodasypus vergelianus AMU-CURS 192 San Gregorio Norte Casa Chiguaje NA 11.28 −70.24 5 8,292 1.78 Coci- netas Sparasso- donta Borhyaenoidea Lycopsis padillai MUN-STRI 34113 Castilletes STRI 390093 170514 11.91 −71.34 128 280 15.1 Xenarthra Megatheroidea Hyperleptus? MUN-STRI 37413 Castilletes STRI 130024 430103 11.93 −71.33 80 80 16.3 Astrapotheria Uruguaythe- riinae Hilarcotherium miyou IGMp 881327 Castilletes STRI 470058 430103 11.95 −71.32 28 28 16.6 MUN-STRI 34216 Castilletes STRI 470058 430103 11.95 −71.32 28 28 16.6 Hilarcotherium cf. 

H. miyou

MUN-STRI 16778 Castilletes STRI 390094 430103 11.95 −71.33 46 46 16.5

MUN-STRI 34229 Castilletes STRI 390094 430103 11.95 −71.33 46 46 16.5

MUN-STRI 34223 Castilletes STRI 390094 430103 11.95 −71.33 46 46 16.5

MUN-STRI 34222 Castilletes STRI 390094 430103 11.95 −71.33 46 46 16.5

MUN-STRI 34221 Castilletes STRI 390094 430103 11.95 −71.33 46 46 16.5

MUN-STRI 34217 Castilletes STRI 390094 430103 11.95 −71.33 46 46 16.5

MUN-STRI 16777 Castilletes STRI 390094 430103 11.95 −71.33 46 46 16.5

MUN-STRI 34212 Castilletes STRI 290632 430103 11.95 −71.33 28 28 16.6

MUN-STRI 37384 Castilletes STRI 390094 430103 11.95 −71.33 46 46 16.5

MUN-STRI 37765 Castilletes STRI 130024 430103 11.93 −71.33 80 80 16.3

MUN-STRI 34225 Castilletes STRI 390094 430103 11.95 −71.33 46 46 16.5

MUN-STRI 34310 Castilletes STRI 390094 430103 11.95 −71.33 46 46 16.5

MUN-STRI 36644 Castilletes STRI 390094 430103 11.95 −71.33 46 46 16.5

MUN-STRI 37390 Castilletes STRI 390094 430103 11.95 −71.33 46 46 16.5

MUN-STRI 34292 Castilletes STRI 390093 170514 11.91 −71.34 128 280 15.1

MUN-STRI 16779 Castilletes STRI 390094 430103 11.95 −71.33 46 46 16.5

MUN-STRI 16785 Castilletes STRI 390094 430103 11.95 −71.33 46 46 16.5

TABLE 13. (Continued)
NUMBER 101

• 5 3

Basin Clade Subclade Taxon Specimen ID Formation Locality

Section 

ID Lat. Long. SM

SM 

composite 

section

Age 

(mya)

Notoungulata Leontinidae cf. Huilatherium MUN-STRI 34312 Castilletes STRI 390094 430103 11.95 −71.33 46 46 16.5

Litopterna Proterotheriidae Lambdaconus cf. 

L. colombianus

MUN-STRI 16716 Castilletes STRI 390093 170514 11.91 −71.34 128 280 15.1

Xenarthra Lestodontini Lestodontini gen. 

et sp. nov.

MUN-STRI 36643 Ware STRI 470060 430052 11.85 −71.32 4 NA 3.05MUN-STRI 20424 Ware STRI 390023 430052 11.85 −71.32 3.5 NA 3.05MUN-STRI 34353 Ware STRI 470060 430052 11.85 −71.32 4 NA 3.05

Scelidotheriinae Scelidotheriinae gen. 

et sp. indet.

MUN-STRI 16535 Ware STRI 390025 430052 11.85 −71.32 4.5 NA 3.05

Megalonychidae Megalonychidae gen. et sp. nov. MUN-STRI 16601 Ware STRI 390077 430052 11.85 −71.32 1.7 NA 3.06

MUN-STRI 34226 Ware STRI 470060 430052 11.85 −71.32 4 NA 3.05

Megatheriinae Pliomegatherium 

lelongi

MUN-STRI 36685 Ware STRI 390024 430052 11.85 −71.32 4.5 NA 3.05MUN-STRI 19747 Ware STRI 390017 430052 11.85 −71.33 5 NA 3.04MUN-STRI 20446 Ware STRI 390026 430052 11.85 −71.33 5 NA 3.04

Nothrotheriinae cf. Nothrotherium MUN-STRI 12924 Ware STRI 390024 430052 11.85 −71.32 4.5 NA 3.05

Rodentia Caviomorpha Hydrochoeropsis? 

wayuu

MUN-STRI 12846 Ware STRI 390017 430052 11.85 −71.33 5 NA 3.04MUN-STRI 37602 Ware STRI 470062 430052 11.85 −71.32 5 NA 3.04MUN-STRI 16233 Ware STRI 430052 430052 11.85 −71.32 5 NA 3.04MUN-STRI 16438 Ware STRI 430052 430052 11.85 −71.32 5 NA 3.04MUN-STRI 34315 Ware STRI 470062 430052 11.85 −71.32 5 NA 3.04

Notoungulata Toxodontidae Toxodontidae indet. MUN-STRI 37507 Ware STRI 470062 430052 11.85 −71.32 5 NA 3.04

MUN-STRI 37561 Ware STRI 470059 430052 11.85 −71.32 2 NA 3.06

Artiodactyla Camelidae Camelidae indet. MUN-STRI 34380 Ware STRI 470060 430052 11.85 −71.32 4 NA 3.05Carnivora Procyonidae Chapalmalania sp. MUN-STRI 34114 Ware STRI 470061 430052 11.85 −71.32 4.3 NA 3.05Litopterna Proterotheriidae Proterotheriidae 

indet.

MUN-STRI 34170 Ware STRI 470060 430052 11.85 −71.32 4 NA 3.05MUN-STRI 13378 Ware STRI 390023 430052 11.85 −71.32 3.5 NA 3.05MUN-STRI 13121 Ware STRI 390020 430052 11.85 −71.32 5 NA 3.04MUN-STRI 19544 Ware STRI 390018 430052 11.85 −71.32 4.5 NA 3.05MUN-STRI 13119 Ware STRI 390020 430052 11.85 −71.32 5 NA 3.04MUN-STRI 13120 Ware STRI 390020 430052 11.85 −71.32 5 NA 3.04MUN-STRI 16289 Ware STRI 430052 430052 11.85 −71.32 5 NA 3.04

TABLE 13. (Continued)
5 4 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

et al. (2015) and Bonini et al. (2017a) topologies but their positions are different in the cladograms. Concerning the toxodontinaes from northern South America, the main difference in our 

result is that the toxodontids recorded in Venezuela (Mixotoxodon, Gyrinodon, and Falcontoxodon) form a monophyletic 

group (node 45) and belong to a clade that also includes Piauhytherium (node 46; Figure 24a).

Bond et al. (2006) described a specimen of Toxodontinae 

(UNEFM-CIAAP 616) from the middle member of the Urumaco Formation consisting of a partial mandibular ramus with 

m1–m3. The specimen UNEFM-CIAAP 616 shows unique characters not seen in combination in other toxodontids. Some of 

these characters are also seen in Falcontoxodon: a broad trigonid with a lingual enamel-less contour, a weakly developed 

meta-entoconid fold in m2, and an open labial enamel fold. The 

morphology of the lower molar folds can be affected by wear, 

as noticed in Pericotoxodon (Madden, 1997). The UNEFMCIAAP 616 differs from Falcontoxodon in having a weakly 

developed meta-entoconid fold in m1, and a better developed 

ento-hypoconulid fold in m2 than in m1. The fragmentary 

nature of UNEFM-CIAAP 616 impedes the precise assessment 

of its phylogenetic affinities (Bond et al., 2006). More complete 

toxodontid material from the Urumaco Formation may confirm 

or refute whether the clade that includes Gyrinodon, Falcontoxodon and Mixotoxodon was present in the region since the 

late Miocene.

The type of Gyrinodon quassus (NHMUK PV M13158) 

was collected in La Puerta Formation (middle to late Miocene) (Gonzalez de Juana et al., 1980), western Buchivacoa, 

Falcón, Venezuela. Additional material from Acre, Brazil, has 

been referred to this taxon (Bond et al., 2006; Sánchez-Villagra 

et al., 2010). Mixotoxodon larensis is recorded in late Pleistocene 

sediments of tropical localities of South and Central America 

(between 15°S and 18°N) (Rincón, 2011). Mixotoxodon is the 

only toxodontid that migrated to Central and North America 

during the GABI (Webb and Perrigo, 1984; Laurito, 1993; Lucas 

et al., 1997; Cisneros, 2005; Lucas, 2008, 2014; Lundelius 

et al., 2013).

The estimated body mass of approximately 796 kg for 

Falcontoxodon aguilerai is comparable to that of Pericotoxodon platignathus (~798 kg, Madden, 1997), larger than estimates for Nesodon taweretus (~550 kg, Forasiepi et al., 2015), 

Nesodon imbricatus (~637 kg, Cassini et al., 2012; ~250–300 

kg, Croft, 2016), and Xotodon sp. (mean = 626 kg, standard 

deviation [sd] = 59 kg; Elissamburu, 2012), and smaller than 

Toxodon platensis (mean = 1,642 kg, geometric mean = 1,187 

kg, Fariña et al., 1998), Trigodon (mean = 1,809 kg, sd = 508 

kg) and Mixotoxodon larensis (mean = 3,797 kg, sd = 1,296 

kg, Elissamburu, 2012). With a sample size of six taxa, Elissamburu (2012) estimated a body mass range for toxodontids 

of 104–3,797 kg. Falcontoxodon shows an intermediate body 

mass among Toxodontinae, and did not reach the large sizes of 

the Pleistocene taxa.

Miocene Fauna

Of the seven mammalian taxa currently recognized for the 

assemblage of the Castilletes Formation in the Cocinetas Basin 

(Table 1), three are SANUs. The taxa previously described for 

this assemblage are the sparassodont Lycopsis padillai (Suarez 

et al., 2016) and the megatherioid sloth Hyperleptus? (Amson 

et al., 2016). Althought the taxonomic status of Hyperleptus? 

needs to be confirmed with more complete material, the current evidence suggests that these two taxa belong to genera 

that show a wide latitudinal range and are also recorded at 

higher latitudes in the Santacrucian fauna (Kay et al., 2012). 

The SANUs from the Castilletes Formation (Lambdaconus cf. 

L. colombianus, H. miyou, and cf. Huilatherium) have affinities 

with taxa also recorded in the Laventan fauna of the Magdalena 

valley in Colombia (Cifelli and Guerrero, 1989; Villarroel and 

Colwell Danis, 1997; Vallejo-Pareja et al., 2015). The records of 

these taxa in Castilletes expand their temporal and geographical 

distribution.

With the referral of Lambdaconus (=Prothoatherium) 

colombianus to Lambdaconus, the biochron of this genus now 

spans from the Deseadan to the Laventan SALMAs (Soria, 

2001; Cifelli and Guerrero, 1989). In low latitudes, Lambdaconus is recorded in middle Miocene deposits (Santacrucian 

and Laventan SALMAs), whereas in high latitudes it is represented by three species recorded in Oligocene and early middle 

Miocene deposits of the Sarmiento and Pinturas Formations 

(Deseadan, Colhuehuapian SALMAs, and “Pinturan”) (Soria, 

2001; Kramarz and Bond, 2005). L. colombianus and Megadolodus molariformes are two small proterotheriids recorded 

in La Venta and originally referred to Didolodontidae (McKenna, 1956; Hoffstetter and Soria, 1986). However, additional 

material was used to hypothesize assignation to Proterotheriidae (Cifelli and Guerrero, 1989; Cifelli and Villarroel, 1997). 

The distinctiveness of Megadolodus warranted the recognition 

of a distinct clade within Proterotheriidae, the Megadolodinae 

(Cifelli and Villarroel, 1997). This clade also includes Bounodus enigmaticus from the Urumaco Formation (Carlini et al., 

2006b). A systematic revision of Proterotheriidae including the 

middle Miocene taxa from low latitudes is necessary to clarify 

the phylogenetic relationships and paleobiogeography of tropical proterotheriids.

The deposition of the Castilletes Formation represents a 

shallow marine to fluvio-deltaic environment with transgressive sequences (Hendy et al., 2015; Moreno et al., 2015). The 

localities where the mammal remains were collected show a 

strong fluvial influence (Moreno et al., 2015), as indicated by 

the diverse assemblage of crocodiles (Moreno-Bernal et al., 

2016) and turtles (Cadena and Jaramillo, 2015a). The mammal record is in agreement with this paleoenvironmental reconstruction (Figures 30, 31). The astrapothere remains from the 

Castilletes Formation were collected from muddy sediments 

and were often associated with freshwater “invertebrates” 
NUMBER 101 • 5 5

FIGURE 30. Life reconstruction of the Castilletes Formation faunal assemblage, Cocinetas Basin, Colombia. Artist: Stjepan Lukac.

FIGURE 31. Key of the reconstruction shown in Figure 30. 1. Hilarcotherium miyou n. sp. (Astrapotheriidae). 2. Lycopsis padillai (Borhyaenoidea). 3. Hyperleptus? (Megatherioidea). 4. cf. Huilatherium (Leontiniidae). 5. Boidae indet. (Squamata). 6. Lambdaconus cf. L. colombianus (Proterotheriidae). 7. Gavialoidea indet. (Crocodilia). 8. Pampatheriidae indet. 9. Glyptodontidae indet. 

10. Mourasuchus sp. (Crocodilia). 11. Chelonoidis sp. (Testudines). 12. Purussaurus sp. (Crocodilia). 13. Podocnemidae (Testudines). 

14. Chelus colombiana (Testudines).
5 6 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

(Moreno et al., 2015). Astrapotheres are commonly reported 

to occur in sediments representing stream channels (Riggs, 

1935; Scott, 1937; Marshall et al., 1990), and in association 

with aquatic fauna (Sánchez-Villagra et al., 2004). The bone 

microstructure (studied in Parastrapotherium) is similar to that 

of graviportal taxa, and it is possible that astrapotheres were 

specialized for graviportality and semiaquatic habits (Houssaye 

et al., 2016). Based on the body mass and skeletal adaptations 

of L. colombianus, Cifelli and Guerrero (1989) inferred cursorial and forest-dwelling habits for this species.

Pliocene/Pleistocene Faunas

The toxodontid and proterotheriid material from the Codore 

Formation comes from the upper part of the Algodones Member 

(Figure 4b), 30 stratigraphic meters below the contact with the 

San Gregorio Formation. At the moment, the mammal fauna of 

the Codore Formation includes four taxa (Table 2). The glyptodont Boreostemma pliocena is recorded in the lower member 

(El Jebe) of the Codore Formation (Carlini et al., 2008b). When 

compared with the better known underlying Urumaco Formation (Sánchez-Villagra and Aguilera, 2006) and even the San 

Gregorio Formation (Table 2), the mammal diversity of Codore 

is modest. This is due to undersampling, and further efforts will 

increase the diversity of this unit (Carlini, 2010).

The San Gregorio fauna includes macro and micro mammals (e.g., rodents; Table 2). Small vertebrates have not been 

recovered in the Urumaco Formation, the fauna of which is 

mostly characterized by large crocodiles, turtles, and xenarthrans. However, in San Gregorio the lithology favors the preservation of small vertebrates, and it promises for the late Pliocene/

early Pleistocene to offer a more complete picture of the faunal 

assemblage in the Falcón Basin (Figures 32, 33). The age of San 

Gregorio overlaps with two GABI migration pulses (GABI 2 

and 3; Figure 1) (Woodburne, 2010). Paleontological and molecular evidence shows that GABI significantly increased during the 

early Pleistocene (Woodburne, 2010; Bacon et al., 2015; Carrillo 

et al., 2015). However, in San Gregorio so far only one of the ten 

described mammalian taxa is an immigrant from North America, 

the procyonid Cyonasua (Forasiepi et al., 2014). The age of San 

Gregorio corresponds to the Ensenadan SALMA (Figure 28), of 

which the type locality is located in La Plata county (~34° S) in 

Argentina (Cione et al., 2015). In southern South America, this 

time interval is characterized by the presence of several clades of 

Holarctic origin (e.g., Cervidae, Ursidae, Tapiridae, Felidae, and 

Gomphotheriidae; Cione et al., 2015), which contrasts with the 

pattern observed in the Falcón Basin.

A similar pattern is observed in the mammalian fauna of 

the Ware Formation, in the Cocinetas Basin, which is slightly 

older than San Gregorio and close to the first GABI migration 

pulse (GABI 1; Figure 1) (Woodburne, 2010; Moreno et al., 

2015). Despite its close proximity to the Isthmus of Panama, 

of the 13 taxa recorded for the Ware fauna (Table 1), only two 

are migrants from North America, the procyonid Chapalmalania

(Forasiepi et al., 2014) and a camelid. The latter is arguably 

the oldest well-dated record of Camelidae in South America, 

although the record of Hemiauchenia reported by Gasparini 

et al. (2017) from Chapadmalalan deposits in Argentina could be 

older, as it comes from a locality assignable to the Gauss Chron 

(3.55–2.59 mya). Hendy et al. (2015) reported a mean age of 

3.2 mya (range from 3.40 to 2.78 mya) calculated from 87Sr/86Sr 

ratios for the shell bed at the top of the formation (Figure 3), 

which is 16 stratigraphic meters above where the camelid was 

collected. Macroinvertebrate biostratigraphy also yielded a Piacenzian age for the Ware Formation (Hendy et al., 2015; Moreno 

et al., 2015).

The oldest record of Camelidae in South America has been 

a problematic point in the understanding of the paleobiogeography of this group during GABI (Scherer, 2013; Gasparini 

et al., 2017). The most recent evidence suggests that the putative 

oldest camelid record in the continent is Chapadmalalan (Gasparini et al., 2017). The Chapadmalalan record is from the Buenos 

Aires province in Argentina (~36°S; Gasparini et al., 2017), more 

than 5,000 km south from the Isthmus of Panama. The camelid 

record from Ware supports a minimum age of ca. 3.2 mya for 

the arrival of camelids in South America, as would be expected 

given its proximity to the Isthmus. Unfortunately, the material 

available does not permit us to evaluate whether it belongs to the 

Lamini, like the other South American camelids (Scherer, 2013; 

Gasparini et al., 2017), or to the group of camelids that inhabited the Central American tropics beginning in the early Miocene 

(Rincón et al., 2012).

The mammalian fauna of the Ware Formation is characterized by a high diversity of herbivores (Figures 34, 35), which 

includes at least five different taxa of sloths (Amson et al., 2016), 

as well as cingulates, caviomorph rodents (Moreno et al., 2015; 

Pérez et al., 2016), a toxodont, a proterotheriid, and a camelid 

(Table 1). The diversity and wide body mass range of herbivores 

from the Ware Formation suggest that they occupied different 

ecological niches, and that there was enough vegetation cover 

to sustain a complex herbivorous community. Other vertebrates 

from the assemblage, such as crocodiles, turtles, and freshwater 

fishes (Aguilera et al., 2013a,b; Moreno et al., 2015; MorenoBernal et al., 2016), are indicative of the fluvial influence in the 

region during the late Pliocene. A provenance study of the Ware 

Formation indicates that the sediments were derived mostly from 

local sources within the Guajira peninsula ranges and the water 

was probably derived by local precipitation (Pérez-Consuegra 

et al., 2018). Today, the Guajira peninsula is dominated by a dry 

landscape with low rainfall (less than 500 mm of mean annual 

precipitation), high seasonality, xerophytic vegetation, and lack 

of large rivers (Pabón-Caicedo et al., 2001).

The Pliocene climate prior to the increase of the Northern Hemisphere glaciations was characterized by warmer mean 

annual temperatures than the preindustrial conditions, higher 

levels of CO2

 (>400 ppm), and reduced meridional and vertical 

ocean temperature gradients than today (Pagani et al., 2010). We 

hypothesize that the change in the landscape in the Cocinetas and 

Falcón Basins relates to the increase of the Northern Hemisphere 
FIGURE 32. (Top) Life reconstruction of the San Gregorio Formation faunal assemblage, Falcón Basin, Venezuela. Artist: Stjepan Lukac.

FIGURE 33. (Bottom) Key of the reconstruction shown in Figure 32. 1. Cyonasua (Procyonidae). 2. Tupinambis sp. (Squamata). 3. Boreostemma? sp. (Glyptodontidae). 4. Neoepiblema (Neoepiblemidae). 5. Hydrochoeropsis? wayuu (Caviidae). 6. Pliodasypus vergelianus

(Dasypodidae). 7. Pampatheriidae. 8. aff. Proeremotherium (Megatheriinae). 9. Marisela gregoriana (Octodontoidea). 10. Falcontoxodon

sp. (Toxodontidae). 11. cf. Caviodon (Caviidae). 12. Characiformes indet. 13. Loricariidae indet. (Siluriformes). 14. Crocodylus falconensis

(Crocodilia). 15. Potamotrygonidae indet. (Myliobatiformes). 16, Doradidae indet. (Siluriformes). 17, Podocnemidae indet. (Testudines).
FIGURE 34. (Top) Life reconstruction of the Ware Formation faunal assemblage, Cocinetas Basin, Colombia. Artist: Stjepan Lukac.

FIGURE 35. (Bottom) Key of the reconstruction shown in Figure 34. 1. Pliomegatherium lelongi (Megatheriinae). 2. cf. Nothrotherium (Nothrotheriinae). 3. Camelidae indet. 4. Proterotheriidae indet. 5. Hydrochoeropsis? wayuu (Caviidae). 6. Podocnemidae indet. (Testudines). 7. Crocodylus (Crocodylidae). 8. Chapalmalania sp. (Procyonidae). 9. Toxodontinae indet. 10. Lestodontini gen. et sp. nov. 11. Pampatheriidae indet. 12. Glyptodontidae indet. 13. Erethizontidae indet. 14. Megalonychidae gen. et sp. nov. 15. Scelidotheriinae gen. et sp. indet.
NUMBER 101 • 5 9

glaciations in the Pliocene (ca. 2.7 mya), which was mainly controlled by a decrease of the atmospheric CO2

 (Lunt et al., 2008). 

During the early Pliocene (ca. 4–5 mya) the CO2

 concentration 

ranged from ~390 to 280 ppm, and CO2

 atmospheric levels progressively decreased from 5 to 0.5 mya (Pagani et al., 2010). 

Global rainfall is higher at the Intertropical Convergence Zone 

(ITCZ), a tropical belt of clouds. The ITCZ migrates seasonally between the boreal and austral summers toward the warmer 

hemisphere, and its position is linked to the atmospheric energy 

transport (Schneider et al., 2014). The increase of ice cover in 

the Northern Hemisphere during the Pliocene could have caused 

the ITCZ to migrate toward a more southern position. For 

example, Holocene sediments from the Cariaco Basin (coast of 

north central Venezuela) indicate a southward ITCZ migration 

during time intervals when the high northern latitudes cooled 

(Schneider et al., 2014: fig. 6). A southward migration of the 

ITCZ would have reduced the amount of rainfall in northwestern South America, producing the landscape change observed in 

the Cocinetas and Falcón Basins.

CONCLUSION

We describe new material of SANUs from the Neogene 

deposits of the Cocinetas and Falcón Basins, in northern South 

America, a region less represented in the fossil record than the 

southern portion of the continent. The middle Miocene deposits 

of the Castilletes Formation in the Cocinetas Basin are characterized by the presence of a large uruguaytheriine astrapothere 

(Hilarcotherium miyou sp. nov.), the leontiniid cf. Huilatherium, 

and the proterotheriid Lambdaconus cf. L. colombianus. All of 

the above have affinities with taxa that are otherwise recorded in 

the Laventan fauna of the Magdalena valley, Colombia. Lambdaconus cf. L. colombianus and other members of the mammalian 

fauna (the sparassodont Lycopsis padillai and the sloth Hyperleptus?), belong to groups with a wide latitudinal distribution 

across the continent, whereas Hilarcotherium and Huilatherium

are restricted to low latitudes. Hilarcotherium miyou is one of 

the largest astrapotheres, with an estimated body mass of about 

6,456.6 kg, although estimations based on dental measurements 

in astrapotheres should be taken with caution. Astrapothere 

postcranial elements are common in the Castilletes Formation 

and found in association with freshwater “invertebrates.”

We describe a new species of Toxodontinae (Falcontoxodon 

aguilerai gen. et sp. nov.), the holotype of which was found in 

the Codore Formation, and we refer some dental and postcranial 

remains from the San Gregorio Formation to the same genus. 

F. aguilerai shows an intermediate body mass among Toxodontinae, with an estimate of ~796 kg. The new material allows us to 

recognize a tropical clade within Toxodontinae that includes the 

Venezuelan toxodonts recorded from the Miocene (Gyrinodon) 

to the Pleistocene (Falcontoxodon and Mixotoxodon). Mixotoxodon is the only toxodont that migrated to Central and North 

America as part of the GABI. The Pliocene/Pleistocene faunas of 

Codore and San Gregorio Formations in the Falcón Basin and 

Ware Formation in the Cocinetas Basin are characterized by a 

predominance of South American native taxa in spite of their 

age and proximity to the Isthmus of Panama. This suggests that 

biotic interactions and biogeography influenced the timing and 

distribution of migrations in northern South America during the 

interchange.

The North American immigrants include procyonids and 

the putative oldest record of Camelidae in South America, which 

was recovered in the Ware Formation and has a minimum age 

of ca. 3.2 mya, based on 87Sr/86Sr ratios and macroinvertebrate 

biostratigraphy.

ACKNOWLEDGMENTS

Our gratitude goes to all the other members of the different 

field efforts in the Cocinetas and Falcón Basins. In particular, J. 

D. Carrillo-Briceño, T. M. Scheyer, A. Wegmann, G. AguirreFernández (PIMUZ), A. A. Carlini (MLP), A. Hendy (Natural 

History Museum of Los Angeles County), A. Reyes, D. Gutiérrez, and the students from the University of Zurich for the 2013 

field projects in Falcón. The González family kindly provided 

access to collect in their land. We thank the authorities at the 

Instituto del Patrimonio Cultural of the República Bolivariana 

de Venezuela and the Alcaldía Municipio de Urumaco for their 

generous support.

For fieldwork in Cocinetas, we are grateful to J. W. MorenoBernal, C. Montes, and J. Escobar (Universidad del Norte, 

Colombia); M. C. Vallejo (Sam Houston State University); 

F. Moreno (Univesity of Rochester); C. Martinez (Cornell University); A. Hendy (NHMLA); J. D. Carrillo-Briceño (PIMUZ); 

J. Luque (University of Alberta, Canada); C. Suarez and 

K. Jimenez (MLP); E. Cadena (Yachay Tech University, Ecuador); G. Ballén (University of Sao Paulo, Brazil); A. Cárdenas 

(Universidad Eafit, Colombia); and N. Pérez-Consuegra (Syracuse 

University). The constant help of L. Londoño (STRI) is also 

acknowledged.

We thank Carlos Rosero for managing all the logistics in 

the field in Colombia. We also extend thanks to the communities 

of Warpana, Patajau, Aulechit, Nazareth, Wososopo, Sillamana, 

Paraguachon, La Flor de la Guajira, and Ipapura, as well as to 

the Colombian National Police (Castilletes base) and the Colombian Army. We express special thanks to our drivers, Grillo, 

Lalo, and Medardo.

We thank M. L. Parra and the Centro de Investigaciones 

Paleontológicas in Villa de Leyva for the preparation of the 

specimens from the Cocinetas Basin. We thank J. E. Arenas, 

M. Pardo-Jaramillo (Servicio Geológico Colombiano), J. Escobar 

(Universidad del Norte), L. Costeur (NMB), G. Billet (MNHN), 

P. Brewer (NHMUK), A. Kramarz, S. Alvarez (MACN), M. Reguero, 

A. Scarano (MLP), G. Ojeda (UNEFM-CIAAP), and H. Moreno 

(Museo de Ciencias, Caracas) for allowing access to the collections 

under their care.
6 0 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

We are grateful to J. D. Carrillo-Briceño, T. M. Scheyer 

(PIMUZ), C. Pimiento (Museum für Naturkunde, Germany), A. 

A. Carlini (MLP), A. Forasiepi (Instituto Argentino de Nivología, 

Glaciología y Ciencias Ambientales [IANIGLA], CCT-CONICET, Argentina), R. Salas-Gismondi, J. W. Moreno-Bernal (Universidad del Norte), G. Billet (MNHN), R. J. Asher (University 

of Cambridge), M. Pardo (Servicio Geológico Colombiano), and 

the Evolutionary Morphology and Palaeobiology of Vertebrates 

group in Zurich for valuable advice.

Graphic reconstructions of the faunas (Figures 30–35) 

were made by S. Lukac. C. Ziegler shot the photo in Figure 3d; 

L. Goodayle took the photos shown in Figure 15, which were 

provided by the NHMUK; G. Billet (MNHN) provided pictures 

from the YPM collections (Figure 10c,d,l,m); and L. Costeur 

(NMB) provided pictures of X. christi in Figure 7a,b,c.

Our research was supported by Swiss National Fund 

P1ZHP3_165068 to J. D. Carrillo and by SNF 31003A-149605 

and 31003A-169395 to M. R. Sánchez-Villagra. E. Amson was 

granted a short-term postdoctoral fellowship by STRI and was 

subsequently funded by the Alexander von Humboldt Foundation. The Swiss National Science Foundation, the Smithsonian 

Institution, the National Geographic Society, the Anders Foundation, Gregory D. and Jennifer Walston Johnson, Universidad 

del Norte, and the National Science Foundation (Grant EAR 

0957679) also helped to support this work.

We thank D. Croft and an anonymous reviewer for their 

comments that improved the manuscript, as well as G. Minkiewicz, C. Doran, and M. McQuoid-Greason for editorial 

assistance.
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SUMMARY OF REQUIREMENTS FOR SMITHSONIAN CONTRIBUTIONS SERIES

For comprehensive guidelines and specifications, visit https://scholarlypress.si.edu.

ABSTRACTS must not exceed 300 words.

TEXT must be prepared in a recent version of Microsoft Word; use a Times font in 12 point for regular text; be double 

spaced; and have 1" margins.

REQUIRED ELEMENTS are title page, abstract, table of contents, main text, and references.

FIGURES must be numbered sequentially (1, 2, 3, etc.) in the order called out; have components lettered consistently 

(in size, font, and style) and described in captions; include a scale bar or scale description, if appropriate; include any 

legends in or on figures rather than in captions. Figures must be original and must be submitted as individual TIF or 

EPS files.

FIGURE FILES must meet all required specifications in the Digital Art Preparation Guide. Color images should be 

requested only if required.

TAXONOMIC KEYS in natural history manuscripts should use the aligned-couplet form for zoology. If cross referencing 

is required between key and text, do not include page references within the key, but number the keyed-out taxa, using the 

same numbers with their corresponding heads in the text.

SYNONYMY IN ZOOLOGY must use the short form (taxon, author, year:page), with full reference at the end of the 

manuscript under “References.”

REFERENCES should be in alphabetical order, and in chronological order for same-author entries. Each reference should be 

cited at least once in main text. Complete bibliographic information must be included in all citations. Examples of the most 

common types of citations can be found at SISP’s website under Resources/Guidelines.