Gomphodontosuchus brasiliensis
Creators: name: Desojo, Julia B.
name: Ezcurra, Martín D.
name: Kischlat, Edio E.
Publisher: name: Zenodo
Year: 2012
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Reptilia
Therapsida
Traversodontidae
Gomphodontosuchus
Gomphodontosuchus brasiliensis

description: Aetobarbakinoides brasiliensis gen. et sp. nov.
Figures 3–17
Stagonolepis robertsoni Agassiz, 1844; Lucas & Heckert (2001)
Etymology. The generic name (long-legged aetosaur form) is derived from the Greek word aetobarbakina (longlegged buzzard, vulgar name of the falconiform Buteo rufinus) and the Latin word oides (form); in allusion to the elongated humerus and tibia in relation to the axial skeleton and the Greek word aetos (eagle), which refers to the name Aetosaurus (eagle reptile). The specific name is derived from the country Brazil from which the holotype specimen was discovered.
Holotype. CPE2 168, partial postcranium including cervical vertebra 5 or 6 with its corresponding right and left proximal end of ribs, articulated series including cervical 9 and dorsals 1-9, one almost complete left cervical rib 9 and some fragmentary dorsal ribs, one anterior caudal vertebra, right scapula, right humerus, probable distal end of right femur, right tibia, right distal tarsal IV, proximal half of right metatarsal I, right metatarsals II-III, right metatarsal IV lacking its proximal end, proximal half of metatarsal V, right pedal phalanx IV-1, anterior and middorsal paramedian osteoderms, and some associated paramedian osteoderms.
Diagnosis. Medium-sized aetosaur (around 2 meters in total length) distinct from other archosaurs by the following combination of characters (autapomorphies indicated by an asterisk): cervical vertebrae with prezygapophyses widely laterally extended through most of the anterior edge of the diapophysis* and with hyposphene; midcervical vertebrae with anterior articular facet width more than 1.2 times wider than the posterior one* and without ventral keel; anterior and mid-dorsal vertebrae without lateral fossa in the centrum, and postzygapophyses mainly posteriorly projected; anterior caudal vertebrae with extremely anteroposteriorly short prezygapophyses*; elongated humerus and tibia in relation to axial skeleton (including humerus with a length/transverse width at midlength ratio greater than 12)*. The paramedian osteoderms of Aetobarbakinoides present a radial ornamentation composed of grooves and pits and with a weakly raised anterior bar. This osteoderm morphology is also exhibited by Paratypothorax and Rioarribasuchus, but Aetobarbakinoides differs from these taxa in the presence of proportionally transversely narrower and strongly ventrally flexed paramedian osteoderms.
Locality and horizon. Inhamandá, close to the city of Sao Pedro do Sul, center of the Rio Grande do Sul State, southern Brazil (Fig. 1). Sequence 2 of the Santa Maria Supersequence (Hyperodapedon Assemblage Zone) (late Carnian-earliest Norian, 231.4-225.9 Mya, Late Triassic; Langer et al. 2007; Martinez et al. 2011) (Fig. 2).
Biostratigraphical setting. The predominant lithofacies at the Inhamandá 1 locality is non-laminated to finely laminated reddish mudstones, with some sandy inclusions (Zerfass et al. 2003). From this locality were also collected the rhynchosaurs Hyperodapedon huenei and Hyperodapedon mariensis and the holotype of “ Aetosauroides subsulcatus ” (MCP13a-b-PV: currently considered a junior synonym of Aetosauroides scagliai; Desojo and Ezcurra 2011) (Langer et al. 2007). The Inhamandá 1 locality is situated in the Acme Zone of the Hyperodapedon Assemblage Zone, which was correlated with the lower levels of the Argentinean Ischigualasto Formation of late Carnian-early Norian age (Langer et al. 2007). The Santa Maria Hyperodapedon Acme Zone also contains the following known species: the rhynchosaurs Hyperodapedon sanjuanensis and Hyperodapedon sp., the proterochampsid Rhadinosuchus gracilis, the pseudosuchians Aetosauroides scagliai and Rauisuchus tiradentes, the cynodonts Therioherpeton cargnini, Prozostrodon brasiliensis, and Gomphodontosuchus brasiliensis, the parareptile Candelaria barbouri, the dinosaurs Staurikosaurus pricei, “ Teyuwasu barberenai ”, and Saturnalia tupiniquim (Langer 2005; Langer et al., 2007; Desojo and Ezcurra, 2011).
A recent study on the chronostratigraphy of the Ischigualasto Formation indicates that the rhynchosaur biozone (Scaphonyx - Exaeretodon - Herrerasaurus biozone) and the younger Exaeretodon biozone (in which Hyperodapedon and Herrerasaurus are not recorded) can be constrained between 231.4 and 225.9 Ma (Martinez et al. 2011). The age of the boundary between both biozones of the Ischigualasto Formation cannot be confidently assessed. In the Santa Maria 2 Sequence most localities have Hyperodapedon - Exaeretodon associations and in the cases in which a locality only possesses Exaeretodon (e.g. the Sacisaurus site; Langer et al. 2007) we cannot assign it unambiguously to the Exaeretodon biozone because the assessment will be based on negative evidence. Accordingly, we have decided to consider here that the entire Hyperodapedon Assemblage Zone is constrained between the 231.4 and 225.9 Ma (Fig. 2).
Description. The length of the preserved dorsal centra of Aetobarbakinoides is very similar to those of the holotype of Aetosauroides (PVL 2073) and a statistical analysis does not recover a significant difference between the size of both specimens (p<0.05) (see below). Accordingly, we estimate that Aetobarbakinoides had a similar body size to that of PVL 2073, with a total length of 2 meters (Desojo & Ezcurra 2011). The absence of open neurocentral sutures in the available vertebrae suggests that CPE2 168 was not a juvenile individual at the time of death of the animal (Irmis 2007).
Cervical rib 9
Length 108 Anteroposterior depth of tubercle 5 Dorsoventral heigth of tubercle 6 Traverse width of proximal end (25) Paramedian dorsal osteoderm 8
Maximum width of anterior margin 58 Maximum width of posterior margin 68 Maximum length at mid-width 34 Scapula
Length 85* Proximal transverse width 20 Proximal anteroposterior depth 50 Distal transverse width 6.5* Distal anteroposterior depth 28* Humerus
Length 138.2 Proximal transverse width 51 Proximal anteroposterior depth 21 Perimeter at mid-legth 36 Distal transverse width 45* Distal anteroposterior depth 17 Tibia
Length 131.4* Distal transverse width 37 Distal anteroposterior depth 23 Distal tarsal IV
Anteroposterior length 13 Transverse width 14.5 Dorsoventral height 7.5 Metatarsal I
Length 28* Proximal transverse width 11 Proximal dorsoventral depth 14 Permimeter at mid-length 22 Metatarsal II
Length 44 Proximal transverse width 14 Proximal dorsoventral depth 9 Permimeter at mid-length 23 Distal transverse width 16 Distal dorsoventral depth 10 Metatarsal III
Length 50 Proximal transverse width 12 Proximal dorsoventral depth 8 Permimeter at mid-length 22 Distal transverse width 14 Distal dorsoventral depth 12 Metatarsal IV
Length 36* Proximal transverse width 12 Proximal dorsoventral depth 6 Distal transverse width 13 Distal dorsoventral depth 10
continued next page Metatarsal V
Length 13* Proximal transverse width 14 Proximal dorsoventral depth 15 Pedal phalanx IV-1
Length 17 Proximal transverse width 12 Proximal dorsoventral depth 10 Permimeter at mid-length 22 Distal transverse width 10 Distal dorsoventral depth 7 The overall preservation of the specimen is very good (e.g. cervical and dorsal vertebrae and right pedal elements), but some bones have suffered some degree of distortion (e.g. caudal vertebra, right scapula, humerus, and tibia) and others are weathered and crushed (e.g. some paramedian osteoderms).
Cervical vertebrae. Two cervical vertebrae are preserved in the holotype of Aetobarbakinoides (Figs. 3, 4). A mid-cervical probably corresponds to the fifth or sixth vertebra of the series based on the position of the parapophyses, which are positioned slightly below the mid-height of the vertebral centrum. This vertebra is amphicoelous and the length of the centrum is slightly lower than the height of the anterior articular facet, with a ratio of 0.97 between them. This ratio resembles those of the mid-cervical vertebrae of most aetosaurs, including Typothorax (C6: 0.74: Long & Murry 1995: fig. 102a), Stagonolepis robertsoni (C6?: 0.84, Walker 1961: fig. 7g), Sierritasuchus (anterior or mid-cervical: 0.93, Parker et al. 2008: fig. 2f), and Desmatosuchus spurensis (C5: 0.93; Parker 2003; 2008). In Neoaetosauroides this ratio (C5: 0.45, PVL 5698) is even lower than in other aetosaurs and in Aetosauroides the centrum length is longer than the height of the anterior articular facet (C5: 1.16, PVL 2059). The lateral surface of the centrum of Aetobarbakinoides is concave and lacks a well-rimmed fossa (Fig. 3 C–D), as occurs in Neoaetosauroides (PVL 5698), Stagonolepis robertsoni (NHMUK R4784), Desmatosuchus spurensis (Parker 2008), and Sierritasuchus (Parker et al. 2008). By contrast, well-rimmed lateral fossae are present in the centra of the entire presacral region of Aetosauroides (PVL 2059, 2073; MCP 13-a-b-PV; Desojo & Ezcurra 2011). The cervical centrum of Aetobarbakinoides is constricted at mid-length in ventral view (Fig. 3 F). The ventral surface of the centrum completely lacks a median keel, resembling the condition observed in Desmatosuchus spurensis (Parker 2008), but contrasting with the sharp keels present in the cervical vertebrae of Aetosauroides (PVL 2059), Neoaetosauroides (PVL 5698), Stagonolepis robertsoni (Walker 1961: fig. 7f), and Typothorax (Long & Murry 1995: fig. 102c). The anterior articular facet of Aetobarbakinoides is 1.35 times transversely wider than the posterior one and also more ventrally extended (Fig. 3 A). The presence of an anterior articular facet wider than the posterior one is a condition also observed, but in a lesser degree, in Desmatosuchus spurensis (Parker 2008). In some specimens of Typothorax (e.g. TTU P-9214; Martz 2002) the latter condition is also present but lesser developed than in Aetobarbakinoides, whereas in others the articular facets are sub-equal in width (e.g. AMNH 7634; Long & Murry 1995: fig. 102). In specimens of Aetosauroides (PVL 2059), Neoaetosauroides (PVL 5698), Stagonolepis (S. robertsoni: Walker 1961), and Sierritasuchus (Parker 2008: fig. 2) the anterior and posterior articular facets are always sub-equal in width. The outline of the anterior and posterior articular facets is circular in Aetobarbakinoides, resembling the condition of Stagonolepis (S. robertsoni: Walker 1961) and Sierritasuchus (Parker et al. 2008). By contrast, in Neoaetosauroides (Desojo & Baez 2005) and Typothorax (Martz 2002) these facets are oval, with a transverse main axis, and in Desmatosuchus spurensis are sub-rectangular (Parker 2008). The parapophyses are situated at the anterior margin of the centrum and are placed on a very low peduncle. The articular facet of the parapophysis is oval, being dorsoventrally taller than anteroposteriorly long (Fig. 3 E).
Most of the neural arch is preserved, but only the base of the neural spine is available (Fig. 3 D). The preserved portion of the neural arch is higher than the centrum. The pedicles of the neural arch are parallel to each other and directly ventrally projected. Their lateral borders are slightly concave in anterior or posterior view. The neural canal is sub-quadrangular and its height is around two times lower than the height of the anterior articular surface of the centrum. A complete right diapophysis and the base of the left diapophysis are preserved. The diapophyses are dorsolaterally projected and short (Fig. 3 C). The distal articular surface is rounded and with an oval outline, and an oblique main axis, in which the upper portion is the anterodorsal. An anterior and a posterior infradiapophyseal lamina (sensu Salgado et al. 1997) are present below each diapophysis, as also occurs in Aetosauroides (PVL 2059) and, at least, in the posterior cervical vertebrae of Stagonolepis robertsoni (NHMUK 4784) and Desmatosuchus spurensis (Parker 2008). By contrast, the available cervical vertebrae of Neoaetosauroides do not present infradiapophyseal laminae (Desojo & Báez 2005). These laminae are well-preserved in the right side of the mid-cervical of Aetobarbakinoides and bound a central infradiapophyseal fossa. The diapophysis of Aetobarbakinoides is connected with the postzygapophysis through a sharp and well-developed postzygodiapophyseal lamina, only preserved in the right side of the element (Fig. 3 C). The latter lamina and the posterior infradiapophyseal lamina bound a shallow and wide posterior infradiapophyseal fossa, resembling the condition of Aetosauroides (PVL 2059), Stagonolepis robertsoni (NHMUK 4784), and Desmatosuchus spurensis (Parker 2008). The anterior infradiapophyseal fossa is absent. Only the base of the right prezygapophysis of the mid-cervical of Aetobarbakinoides is preserved. It has an oblique main axis with a dorsolateral upper end. The prezygapophysis is transversely wide at its base, being extended through most of the anterior edge of the diapophysis (Fig. 3: leprz). In contrast, in other known aetosaurs the prezygapophyses are more medially restricted than in Aetobarbakinoides, as occurs in Aetosauroides (PVL 2059), Neoaetosauroides (PVL 5698), Typothorax (TTU P-9214), Desmatosuchus spurensis (Parker 2008), and Stagonolepis robertsoni (NHMUK 4784). Between the prezygapophyses exists a moderately deep and circular pre-spinal fossa, which is not dorsally extended along the neural spine. The postzygapophyses are anteroposteriorly short and slightly upturned. The articular facets are ventrolaterally oriented and with an oval outline, being transversely wider than anteroposteriorly long. Both postzygapophyses are connected at their mediodistal corner by a horizontal lamina which forms the dorsal border of the neural canal and defines a U-shaped hyposphene (Fig. 3 B). Directly above and between both postzygapophyses exists a deep post-spinal fossa. This fossa is dorsally extended on the posterior surface of the base of the neural spine as far as is preserved and at this region the fossa is laterally bounded by sharp spinopostzygapophyseal laminae, as also occurs in Desmatosuchus spurensis (Parker 2008). The base of the neural spine is only preserved and the available portion indicates that it was anteroposteriorly short. A shallow depression is present laterally to the base of the neural spine, but the deep circular pit found within it in some pseudosuchians is absent.
The neural arch of the last cervical vertebra is preserved, lacking the left pedicle, prezygapophyses, left diapophysis, and the distal end of the neural spine (Fig. 4, 5 A, C). The right diapophysis is almost completely obscured by matrix and a cervical rib. The base of the right pedicle is available, but with a broken distal end. Only the base of the postzygadiapophyseal lamina is preserved. The postzygapophyses are anteroposteriorly short and the right one is mostly obscured by matrix and dorsal paramedian osteoderms. The left postzygapophysis lacks its distal end, but its preserved overall morphology resembles that of the above described cervical. A deep post-spinal fossa is present between both postzygapophyses and is extended dorsally on the neural spine. This fossa is co-laterally delimited by a pair of spinopostzygapophyseal laminae, resembling the condition exhibited by the cervicals of Desmatosuchus spurensis (Parker 2008). The presence of a hyposphene cannot be determined. The preserved portion of the neural spine is taller than anteroposteriorly long. An incipient depression is present lateral to the base of the neural spine and posteriorly displaced from the mid-length of the neural arch.
Dorsal Vertebrae. An articulated series of nine complete anterior and middle dorsal vertebrae are preserved in the holotype of Aetobarbakinoides (Figs. 4–8). The dorsal vertebrae are moderately tall, with the neural arch ranging between 1.65 to 2.05 times higher than the centrum height along the preserved series, resembling the ratios observed in Desmatosuchus spurensis (Parker 2008) and Typothorax (TTU P-9214). By contrast, in the neural arches of the posterior dorsal vertebrae of Stagonolepis (S. robertsoni: Walker 1961) this ratio is slightly lower than three times and in Aetosauroides (PVL 2073; MCP 13a-b-PV; Desojo & Ezcurra 2011), the holotype of Calyptosuchus wellesi (Long & Murry 1995:fig. 75), and a putative Polish specimen of Stagonolepis robertsoni (sensu Lucas et al. 2007; ZPAL AbIII 502/67) the neural arch is three times higher than the centrum height. The centra of the dorsal vertebrae of Aetobarbakinoides are amphicoelous and subequal or slightly longer than their anterior articular facet height, with a ratio ranging from 1.04-1.1 in the first through third dorsals and 1.22-1.39 in the fourth through ninth dorsals. A similar condition is observed in the anterior dorsals of Typothorax (1.15: Martz 2002) and Desmatosuchus spurensis (0.95-1.42: Parker 2003, 2008) and the middle dorsals of Stagonolepis robertsoni (0.97: Walker 1961: fig. 7k). In contrast, in the anterior and middle dorsals of Aetosauroides (1.5: PVL 2073) and anterior dorsals of Stagonolepis robertsoni (1.45: NHMUK R4784; Walker 1961: fig. 7i) and Sierritasuchus (1.46: Parker et al. 2008: fig. 2g) the centrum is proportionally longer, being 1.45-1.5 longer than high. In ventral view, the centra are moderately transversely compressed at mid-length, acquiring an overall spool-shape. The ventral surface is convex and smooth, without a longitudinal keel or groove. The anterior and posterior articular facets are usually taller than wide, contrasting with the middle dorsals of Aetosauroides in which they are as tall as wide (Desojo & Ezcurra 2011). However, in the ninth dorsal of Aetobarbakinoides the articular facets are wider than tall, as occurs in the posterior dorsals of Aetosauroides (Desojo & Ezcurra 2011). None of the available dorsal centra do exhibit lateral fossae. These fossae are also absent in Stagonolepis robertsoni (Walker 1961; ZPAL AbIII 502/67), Calyptosuchus wellesi (Long & Murry 1995), Typothorax coccinarum (Martz, 2002), Tecovasuchus chatterjeei (Martz & Small 2006), and Neoaetosauroides (PVL 3525). In contrast, Aetosauroides exhibits an oval shallow lateral fossa in the presacral vertebral centra (Desojo & Ezcurra 2011).
In the available dorsal series of Aetobarbakinoides the infradiapophyseal laminae are incipient or completely absent. A very faint posterior infradiapophyseal lamina is present in the middle dorsals (e.g. D9) (Fig. 8). Conversely, better developed infradiapophyseal laminae are present in the dorsal vertebrae of Aetosauroides (Desojo & Ezcurra 2011), Stagonolepis robertsoni (NHMUK R4784), Desmatosuchus spurensis (Parker 2008), and Typothorax coccinarum (Martz 2002). The infradiapophyseal laminae are absent in Neoaetosauroides (PVL 3525) and the Polish Stagonolepis (ZPAL AbIII 502/67). No traces of anterior infradiapophyseal fossae are observed, resembling the condition of Aetosauroides (Desojo & Ezcurra 2011). In the first through eighth dorsals the central and posterior infradiapophyseal fossae are absent in Aetobarbakinoides (Figs. 5–7), but incipient central and posterior infradiapophyseal fossae are present in the ninth dorsal. The latter contrasts with the well-defined central and posterior infradiapophyseal fossae observed in Aetosauroides (Desojo & Ezcurra 2011). As occurs in Aetosauroides, in Aetobarbakinoides the transverse processes are anteriorly displaced from the mid-length point of the neural arch. In the first through eighth dorsals, the transverse processes are dorsolaterally projected, but they are directly laterally oriented in the ninth dorsal. The transverse processes are sub-rectangular in dorsal view, which is the same condition observed in Stagonolepis robertsoni (NHMUK R4784), Neoaetosauroides (PVL 3525), and Desmatosuchus spurensis (Parker, 2008). In contrast, in Aetosauroides the transverse processes are trapezoideal in dorsal view (PVL 2073, MCP 13-a-b-PV; Desojo & Ezcurra 2011).
The prezygapophyses are very anteroposteriorly short, without a well-developed pedicle, and with dorsomedially oriented articular facets, resembling the condition of Aetosauroides (PVL 2073; MCP 13-a-b-PV), Stagonolepis (S. robertsoni: Walker 1961), and Typothorax (Martz 2002). In dorsal 9 of Aetobarbakinoides the right prezygapophysis is complete and well exposed, exhibiting a sub-rectangular articular facet with a transverse main axis (Fig. 9). The postzygapophyses are longer than the prezygapophyses, but they do not reach the mid-length of the subsequent vertebra, resembling the condition of Typothorax (Martz 2002). The postzygapophyses of the dorsal vertebrae of Aetosauroides (Desojo & Ezcurra 2011) and Stagonolepis (S. robertsoni: Walker 1961) extend posteriorly up to the mid-length of the subsequent neural arch. Conversely, in Desmatosuchus spurensis (Parker 2008) and the Polish Stagonolepis robertsoni (ZPAL AbIII 502/67) the postzygapophyses are extremely posteriorly short. An anteriorly shallow median notch separates the postzygapophyses of the dorsal vertebrae of Aetobarbakinoides. This median notch is deeper in Stagonolepis (S. robertsoni: Walker 1961) than in Aetobarbakinoides. In Aetosauroides the postzygapophyses are posterolaterally projected, resulting in strongly divergent apophyses with an even transversely wider median notch than in Stagonolepis robertsoni in dorsal view (Desojo & Ezcurra 2011). In the first through eighth dorsals of Aetobarbakinoides the postzygapophyses exhibit a lateral triangular projection, resulting in an oval articular facet with a transverse main axis in ventral view (Figs. 5–7). In contrast, in the ninth dorsal this lateral projection is lacking and the lateral margin of the postzygapophyses is slightly convex and consequently the articular facets are circular (Fig. 8). A well-developed Y-shaped hyposphene is present in all the available dorsal vertebrae of Aetobarbakinoides in which this region is exposed, as also occurs in Desmatosuchus spurensis (Parker 2008). In contrast, in Aetosauroides these structures are completely absent (PVL 2073; MCP 13-a-b-PV). The postzygadiapophyseal lamina is well-developed in all the preserved dorsal vertebrae, resembling the condition present in Aetosauroides (Desojo & Ezcurra 2011). At both sides of the neural spine of all preserved dorsals, a deep and circular pit is present at the posterior level of the transverse process (Fig. 8: dlp). This condition is widely observed among pseudosuchians (e.g. Batrachotomus: Gower & Schoch 2009), but absent in Aetosauroides (PVL 2073; MCP 13-a-b-PV) and still unreported in other aetosaurs.
The neural spines of the first through eighth dorsals of Aetobarbakinoides are dorsally directed (Figs. 4–7), as also occurs in Desmatosuchus spurensis (Parker 2008), the Polish Stagonolepis robertsoni (ZPAL AbIII 502/67), and Calyptosuchus wellesi (Long & Murry 1995). However, in the ninth dorsal the neural spine is anterodorsally projected, resembling the anterior and middle dorsals of Aetosauroides (PVL 2073; MCP 13-a-b-PV), and posterior dorsals of Stagonolepis (S. robertsoni: Walker 1961) and Typothorax (Martz 2002). In the first through eighth dorsals of Aetobarbakinoides the neural spine is taller than anteroposteriorly long, but in the ninth dorsal the neural spine is as tall as long (Fig. 8), resembling the morphological change observed along the dorsal series of Aetosauroides (PVL 2073). The distal end of the neural spine of the fifth, sixth, and ninth dorsals are moderately expanded transversely into spine-tables, resembling the condition of the Aetosauroides specimens PVL 2073 and PVL 2052, Stagonolepis robertsoni (NHMUK R4784), and Calyptosuchus wellesi (Long & Murry 1995). In contrast, better transversely developed spine tables are present in Desmatosuchus spurensis (Parker 2008), Longosuchus (Sawin 1947), and Typothorax (Martz 2002). The spine tables of Aetobarbakinoides are drop-shaped in dorsal view, with the widest end anteriorly positioned. This condition resembles that of the drop-shaped spine tables of Sierritasuchus (Parker et al. 2008) and Stagonolepis (S. robertsoni: Walker 1961), but contrasts with the oval spine tables of the entire dorsal series of Aetosauroides (PVL 2073) and the sub-rectangular ones of Typothorax (Martz 2002). In Desmatosuchus spurensis a strong variation in shape of the spine table is observed through the dorsal and caudal series, ranging from sub-rectangular in anteriormost dorsals, oval in more posterior anterior dorsals, drop-shaped with a posteriorly positioned main transverse axis in middle dorsals, drop-shaped with an anteriorly positioned main transverse axis in posterior dorsals, and oval to circular in anterior caudals (Parker 2008). The post-spinal fossae are moderately deep, sub-triangular, and do not extend dorsally into the neural spine. Unfortunately, the presence of pre-spinal fossae cannot be confirmed.
Neoaetosauroides PVL 3525 5.86 Aetosauroides PVL 2052 6.4 Stagonolepis robertsoni Walker, 1961 6.5 “ Argentinosuchus ” PVL 2091 6.53 Aetosauroides PVSJ 326 6.68 Typothorax NMMNH P-12964 6.74 Typothorax UCMP 34240 7.99 Longosuchus TMM 31185-84 8.00 Aetosauroides PVL 2073 9.2 Aetobarbakinoides CPE2 168> 12.22 Type of analysis p-value
One-way Kruskal– Wallis axial size 0.631 (NS) One-way Kruskal– Wallis C/H 0.005075 (S) One-way Kruskal– Wallis C/T 0.06555 (NS) Spearman’s correlation C/H-T 0.17971 (NS) Caudal vertebra. One posterior proximal caudal vertebra is preserved (Fig. 9). It lacks the left transverse process and postzygapophysis and presents some degree of post-mortem distortion, which is particularly evident in the posterior articular facet of the centrum (Fig. 9 C). It is interpreted as a caudal vertebra because of its short transverse process, elongated centrum, and the strongly lateroventrally oriented articular facet of the postzygapophysis. The centrum is amphicoelous and longer than the available presacral vertebrae, about 1.56 times longer than the anterior articular facet. The proportion of the centrum of Aetobarbakinoides resembles the moderately elongated centra of the posterior proximal caudals of Aetosauroides (PVL 2073), Aetosaurus (SMNS 11837), and Stagonolepis (S. robertsoni: Walker 1961), but contrasts with the proportionally shorter anterior caudals of Desmatosuchus spurensis (Parker 2008: fig. 15, 16). The caudal centrum is more transversely compressed at mid-length than in the preserved presacral vertebrae. The ventral surface of the centrum is convex and does not present a ventral groove or keel, as occurs in other aetosaurs (Fig. 9 E). The lateral surface of the centrum is slightly concave but does not present a well-rimmed fossa, as is the case of Aetosauroides (PVSJ 326) and other aetosaurs. Although the anterior and posterior articular facets are heavily distorted they are taller than wide (Fig. 9 B, C).
The neural arch is 1.42 higher than the anterior articular facet of the centrum, a ratio which resembles that of the anterior caudals of Aetosauroides (PVL 2073) and Stagonolepis (S. robertsoni: Walker 1961). In contrast, in Desmatosuchus spurensis this ratio is lower than 1.17 in the anterior caudal vertebrae (Parker 2008). The right transverse process is short, sub-rectangular in dorsal view, and strongly anterolaterally projected. However, the unusual orientation of the transverse process is here considered a dubious natural feature because of the strong post-mortem distortion present in the element. A low and wide lamina connects the posterior end of the base of the transverse process with the posterodorsal corner of the centrum, as occurs in Aetosauroides (PVL 2073). The transverse process is not connected with the postzygapophysis by a lamina. At both sides of the anterior exit of the neural canal there is a slightly concave surface directly below the prezygapophyses. An incipient circular depression is present at both sides of the base of the neural spine, which is in the same position as the pits present in the dorsal vertebrae. The prezygapophyses are short, almost lacking a peduncle, and do not project beyond the anterior level of the anterior articular facet of the centrum. This condition contrasts with the proportionally longer prezygapophyses of the caudals of other aetosaurs (e.g. Aetosauroides: PVL 2073; Stagonolepis robertsoni: Walker 1961; Desmatosuchus spurensis: Parker 2008). The articular facets of the prezygapophyses are dorsomedially oriented and oval in outline with a transverse main axis. A small and shallow pre-spinal fossa is observed at the base of the neural spine and between both prezygapophyses. The postzygapophysis is slightly elongated and projected beyond the posterior level of the posterior articular facet of the centrum, resembling the condition of Aetosauroides (PVL 2073) and Stagonolepis (S. robertsoni: Walker 1961). In contrast, in Desmatosuchus spurensis the postzygapophyses are posteriorly extended up to the same level of the posterior articular surface of the centrum (Parker 2008). The articular facet of the postzygapophysis is longer than wide and strongly lateroventrally oriented. A well-developed and sharp spinopostzygapophyseal lamina is present, which bounds a deep post-spinal fossa. No hypophene or hypantrum are observable in the caudals, resembling the pattern of Desmatosuchus spurensis (Parker 2008). The neural spine is slightly higher than long and presents a spine-table at its distal end (Fig. 9 D). The spine table is drop-shaped in dorsal view with its widest end being anteriorly positioned, as occurs in dorsal 9. In contrast, in the proximal caudals of Aetosauroides (PVL 2073) and Desmatosuchus spurensis (Parker 2008) the spine-tables are oval or circular in dorsal view.
Cervical and dorsal ribs. The proximal ends of the two cervical ribs, which are preserved in articulation with the available middle cervical vertebra, are present. Although fragmentary, the preserved portions of these ribs evidence a stout morphology. The right cervical rib corresponding to cervical 9 is completely preserved, being two times longer than the maximum height of this vertebra (Fig. 5 E). It has a bicipitous head with a sub-rectangular capitulum two times longer than the tuberculum. The articular facet of the capitulum is oval. The shaft is straight and presents an oval cross-section. At the distal end of the rib the shaft becomes more anteroposteriorly flattened. Several dorsal ribs are preserved, but most of them are only represented by parts of their shafts. The proximal ends are bicipitous and the shafts elongated, with a circular cross-section at the proximal end of the shaft which gradually flattens distally towards an oval cross-section.
Osteoderms. Fragments of at least eight dorsal paramedian osteoderms and an almost complete right dorsal paramedian osteoderm corresponding to the eighth dorsal vertebra are preserved (Figs. 4–7, 10). The eighth paramedian osteoderm is sub-rectangular in dorsal view, about 1.96 times transversely wider than anteroposteriorly long (Fig. 10 B, C). In posterior view, this osteoderm possesses a strong ventral inflexion at mid-width between the flat medial and lateral portions, as occurs in desmatosuchines and typothoracisines (Parker 2007). The preserved osteoderms are proportionally dorsoventrally thin, as is typical for aetosaurs but contrasting with the thicker dorsal osteoderms of Koilamasuchus (Ezcurra et al., 2010), Erythrosuchus (Gower 2003), Euparkeria (cast of SAM-PK- 5867), doswelliids (e.g. Doswellia, Tarjadia, Archeopelta; Weems 1980; Arcucci & Marsicano 1998; Desojo et al. 2011), Chanaresuchus (PVL 6244), phytosaurs (e.g. Parasuchus, Smilosuchus gregorii; ISI R42; UCMP 26699), “rauisuchians” (e.g. Prestosuchus, Batrachotomus; UFRGS 156; Gower & Schoch 2009), Revueltosaurus (Parker et al. 2005), Gracilisuchus (PULR 08), and crocodylomorphs (e.g. Terrestrisuchus; NHMUK P. 79/1). The eighth paramedian dorsal osteoderm presents an unornamented transverse anterior articular bar. This anterior bar is restricted to the anterior-most region of the osteoderm and becomes anteroposteriorly longer towards the lateral edge of the osteoderm, as occurs in other aetosaurs (e.g. Aetosauroides: MCP 13-a-b-PV). The anterior margin of the osteoderm is slightly convex, whereas the posterior margin is slightly concave. The medial margin is completely straight and the lateral one is slightly damaged and the shape of its border cannot be confidently assessed.
The overall ornamentation of the dorsal paramedian osteoderms consists of irregular circular pits, grooves, and ridges with a radial pattern originated from a low eminence (Fig. 10). A radial pattern of ornamentation is also present in Aetosauroides scagliai (e.g. PVL 2059, 2073; MCP 13-a-b-PV) (Fig. 4 E–F), Neoaetosauroides (Bonaparte 1971), Aetosaurus (Schoch 2007), Lucasuchus, Paratypothorax (Long & Murry 1995), Coahomasuchus (Heckert & Lucas 1999), Stagonolepis robertsoni (NHMUK R4788), and Calyptosuchus wellesi (Long & Murry 1995). In contrast, a reticular pattern is observed in Typothorax (Long & Ballew 1985), Redondasuchus (Heckert et al. 1996), and Chilenosuchus (Desojo 2003) and a random distribution (sensu Long & Ballew 1985) is exhibited by Desmatosuchus smalli, Desmatosuchus spurensis, Longosuchus, and Acaenasuchus (Long & Ballew 1985; Parker 2005, 2008; Parker & Martz 2010). Although an overall radial ornamentation, in the eighth paramedian dorsal osteoderm of Aetobarbakinoides the portion medial to the dorsal eminence presents a reticular ornamentation, as occurs in some paramedian osteoderms of Aetosauroides (PVL 2073) as well as Calyptosuchus and Paratypothorax (Long and Ballew 1985). The dorsal eminence of the eighth dorsal paramedian osteoderm of Aetobarbakinoides is incipient, as also occurs in Typothorax and Redondasuchus (Long & Ballew 1985; Heckert et al. 1996). By contrast, other aetosaurs (e.g. Stagonolepis robertsoni: NHMUK R4788; Calyptosuchus wellesi: Long & Murry 1995; Aetosaurus: Schoch 2007; Acaenasuchus: Long & Murry, 1995; Paratypothorax: Long & Murry 1995; Aetosauroides scagliai: PVL 2059, 2073; Desmatosuchus spurensis: Parker 2008; Neoaetosauroides: Bonaparte 1971; Coahomasuchus: Heckert & Lucas 1999) present stouter eminences in the mid-dorsal paramedian osteoderms.
Scapula. A right scapula lacking the distal end of the scapular blade and anteroventral portion of the proximal end is preserved (Fig. 11). The scapular blade is wide in lateral view, slightly medially bowed, and presents a sharper anterior margin than the thicker posterior one. The distal-most preserved portion of the scapular blade only presents the beginning of the distal anteroposterior expansion. The lateral surface of the scapular blade is convex and the medial one is straight. The scapular blade becomes gradually thinner towards its distal end (Fig. 11 D). The proximal end is well anteroposteriorly expanded, with a low acromial process (Fig. 11 A, B). This process is not distinctly differentiated from the scapular blade, resembling Aetosaurus (SMNS 5770 S-2), Neoaetosauroides (PVL 3525), Typothorax (Long & Murry 1995: fig. 105), and Longosuchus (TMM 31185-84a). In contrast, in Aetosauroides (PVL 2073) these structures form a distinct gently obtuse angle. In Aetobarbakinoides the sub-acromial tuberosity is thick and well laterally developed. However, in Aetosauroides (PVL 2073), Neoaetosauroides (PVL 3525), and Longosuchus (TMM 31185-84a) the sub-acromial tuberosity is much sharper. The sub-acromial tuberosity of Aetobarbakinoides distally delimits a moderately deep sub-acromial depression, as occurs in Neoaetosauroides (PVL 3525), but contrast with the shallower anteroposterior groove of Aetosauroides (PVL 2073). The remaining portion of the scapular proximal end, anterior to the supraglenoid lip, is concave. The supraglenoid lip is a well laterally projected process, resembling the condition of other aetosaurs such as Aetosauroides (PVL 2073). In contrast, in Neoaetosauroides the supraglenoid tuberosity is poorly developed. Below it, the scapular portion of the glenoid fossa is posterolaterally oriented and is more transversely constricted proximally. A sharp edge rises distally from the supraglenoid lip and ends at the base of the scapular blade, delimiting the concave lateral and convex posterior surfaces of the proximal end of the bone, respectively. The medial surface of the proximal end of the scapula is biconvex, with a concave median longitudinal depression (Fig. 11 B). The posterior convexity is wider than the anterior one. The preserved ventral portion, for contact with the coracoid, is gently convex.
Humerus. A right humerus, lacking the distal ectepicondyle, is preserved (Fig. 12). Both proximal and distal ends of the bone are distinctly transversely expanded with respect to the shaft (Fig. 12 E, F). The humeral head is well-defined and presents a convex proximal articular surface. The greater (= lateral) tuberosity is well differentiated from the head and globous, contrasting with the less developed greater tuberosity observed in Aetosauroides (PVL 2052, 2073; PVSJ 326), Neoaetosauroides (PVL 3525), Stagonolepis (S. robertsoni: Walker 1961), and Typothorax (Martz 2002). Nevertheless, in the holotype of “ Argentinosuchus bonapartei ” [PVL 2091: Argentinosuchus was considered as a nomen dubium, representing an indeterminate aetosaur by Desojo & Ezcurra (2011)] and a referred specimen of Longosuchus (TMM 31185-84) this tuberosity resembles the condition of Aetobarbakinoides. At the lateroventral corner of the humeral head of Aetobarbakinoides a rounded and low tuberosity is present (Fig. 12: lvt), which is less developed in Aetosauroides (PVL 2073). A second dome-shaped tuberosity is situated on the dorsal margin of the humeral head, slightly laterally displaced from the mid-width of the element (Fig. 12: dt). Both tuberosities are similar in size (Fig. 12 E). However, in Aetosauroides the ventrolateral tuberosity is less developed than the dorsal one (PVL 2073). The morphology of the internal tuberosity cannot be determined because this region is not well-preserved. The deltopectoral crest is directly ventrally projected sub-triangular in medial view (Fig. 12 D), resembling the condition of other pseudosuchians (e.g. Batrachotomus: Gower & Schoch 2009; Aetosauroides: PVL 2073). The ventral surface of the proximal end of the humerus is concave, whereas the dorsal one is slightly convex (Fig. 12 E).
Below the proximal end of the bone, the humeral shaft is straight and with a circular cross-section. The shaft is proportionally elongated in relation to the entire length of the bone, with a length-transverse width of the shaft at mid-length greater than 12.22. In contrast, this ratio is lower in other aetosaurs, such as Longosuchus (TMM 31185-84), Aetosauroides (PVL 2052, 2073; PVSJ 326), “ Argentinosuchus ” (PVL 2091), Neoaetosauroides (PVL 3525), Typothorax (NMMNH P-12964, UCMP 34240, Martz 2002), and Stagonolepis (S. robertsoni: Walker 1961). At the distal end of the bone, the entepicondyle and ectepicondyle are well separated by a median groove which opens onto the ventral surface (Fig. 12 F). The entepicondyle is globous and with a strongly convex distal articular surface. A shallow sub-triangular depression is present on the dorsal surface of the distal end of the bone. A deep wide groove is present directly above the ectepicondyle, which is bounded by a sharp dorsal ridge and a more rounded ventral edge. The same condition is present in other aetosaurs, such as Aetosauroides (PVL 2073; PVSJ 326), Neoaetosauroides (PVL 3525), and Stagonolepis (S. robertsoni: Walker 1961).
Femur?. A fragment of bone was attached to the proximal end of the preserved tibia (Fig. 13 A–C). Because this fragment preserves a condyle like structure and in addition to its preserved position, we infer that it could be the distal end of the right femur. However, because of the fragmentary condition of the bone and heavy damage no further useful information is available from this element.
Tibia. The right tibia is almost complete, but preserves a strongly damaged proximal end and displaced proximal and distal halves due to a diagonal break close to its mid-length (Fig. 13 D–H). The tibia of Aetobarbakinoides presents a moderately gracile morphology (total length/transverse width at mid-length ratio 6.44), a ratio which falls within the intraspecific variation observed in Aetosauroides (PVL 2073: 8.43; PVL 2052: 6.14) and Typothorax (Martz 2002, TTU P-9214: 6.55; Heckert et al. 2010: 4.63). The tibia is posteriorly curved in lateral or medial views (Figs. 12 E, G). The proximal end is well transversely expanded but we lack evidence of an anteroposterior expansion. In Aetosauroides an anteroposterior expansion of the proximal end of the bone is observed (PVL 2073). The shaft is oval in cross-section at the mid-length of the bone, with a major transverse axis. The distal end of the bone is transversely expanded but in a lesser degree than the proximal end, as occurs in other aetosaurs (e.g. PVL 2073; PVL 3525; Walker 1961; Long & Murry 1995). The anterior surface of the distal end of the bone is strongly convex and the posterior one is almost planar (Fig. 13 H). A rounded diagonal tuberosity extends from the anteromedial corner of the distal end towards the mid-length of the bone. The medial and lateral surfaces of the distal ends are also convex. The medial surface is continuous with the posterior and anterior ones, but the lateral surface is separated from the posterior one by a distinct posteromedial longitudinal edge. The distal expansion of the bone is mainly medially oriented, which results in a globous condyle for articulation with the tibial facet of the astragalus. This condyle is more distally extended than the medial facet for reception of the calcaneum, as usually occurs in crurotarsal archosaurs (Sereno 1991). The distal-most tip of the astragalar condyle is posteriorly displaced. The facet for reception of the calcaneum is slightly concave and posteriorly projected as a sub-triangular lip in lateral view. The distal end is only incipiently expanded anteroposteriorly.
Distal tarsal. A probable right distal tarsal 4 is the only tarsal element preserved of Aetobarbakinoides (Figs. 14–15). The element presents a sub-triangular outline in dorsal view, in which the straight medial margin is the anteroposteriorly deepest and the convex lateral margin is more anteroposteriorly reduced (Fig. 15 A). The ventral surface of the bone is pointed, for articulation with the metatarsal IV and V, and the lowest point is situated at the centre of the bone (Fig. 15 B). In lateral and dorsal views the bone is pyramidal in shape (Fig. 15 A, C). The surface for articulation with the metatarsal V is ventrolaterally oriented and slightly convex (Fig. 15).
Pes. All the bones of the right metatarsus are available, but only the metatarsals II and III are completely preserved (Figs. 14, 16). In contrast, the metatarsals I and V lack their distal ends and the metatarsal IV lacks its proximal end. The metatarsus is robust and composed by well separated bones, in which the metatarsals II and III are the most robust elements, as usually occurs in non-ornithodiran archosauriforms (Sereno 1991).
The metatarsal I of Aetobarbakinoides is gracile, resembling the condition of Aetosaurus (Schoch 2007), but contrasting with the more robust elements of Neoaetosauroides (PVL 3525), Aetosauroides (PVL 2052), Stagonolepis (S. robertsoni: Walker 1961), and Typothorax (Heckert et al. 2010). The bone preserves a well transversely expanded proximal end, mainly in lateral direction. The proximal articular facet is saddle-shaped, being bounded by anterior and posterior lips, and a squared outline in proximal view. The shaft is slightly laterally curved and straight in anterior view. The shaft is oval in cross-section, with a posterolaterally to anteromedially diagonal main axis.
The metatarsal II is a robust bone, even more robust than that observed in Neoaetosauroides (PVL 3525), and Aetosaurus (Schoch 2007). The proximal end of the bone is only slightly transversely expanded, contrasting with the strong expansion observed in Neoaetosauroides (PVL 3525), Aetosaurus (Schoch 2007), Stagonolepis (S. robertsoni: Walker 1961), and Typothorax (Heckert et al. 2010). The proximal articular facet is slightly concave and oval, with a transverse main axis. The anterior margin of the proximal end is strongly convex whereas the posterior one is only slightly convex. The shaft is straight with an anteroposteriorly depressed oval cross-section. The distal end is as transversely expanded as the proximal end and presents a well-developed ginglymous articulation. The medial collateral fossa is completely absent and the lateral one is circular and very deep. The dorsal extensor groove is semilunate is shape and very deep. This groove is distally limited by the distal articular surface of the bone. The distal condyles are separated by a shallow median depression distally and ventrally. The medial condyle is more ventrally projected than the lateral one. The lateral collateral groove opens distally resulting in a notched lateral margin of the lateral distal condyle. The distal end of the bone is asymmetric in anterior view, in which the medial condyle is more projected beyond the main axis of the bone than the lateral condyle. The dorsal margin of the distal articular surface is straight and the medial margin of the medial distal condyle is convex, with its most medially projected region posteriorly displaced.
The metatarsal III is longer and more gracile than the metatarsal II, as occurs in Aetosauroides (PVL 2052), Aetosaurus (Schoch 2007), and Neoaetosauroides (PVL 3525). In contrast, in Stagonolepis robertsoni the metatarsals II and III are subequal in length (Walker 1961). The proximal end of the bone is only slightly expanded laterally in anterior view, but anteroposteriorly expanded in lateral view with respect to the shaft. The degree of expansion of the proximal end is lesser than that observed in Neoaetosauroides (PVL 3525), Aetosaurus (Schoch 2007), Stagonolepis (S. robertsoni: Walker 1961), and Typothorax (Heckert et al. 2010). The proximal end presents a concave proximal articular surface, which has a semi-oval outline in proximal view. The anterior and posterior surfaces of the proximal end are strongly convex, whereas the medial one is slightly convex and the lateral is straight exhibiting a facet for the reception of the metatarsal IV. The shaft is straight and with a circular cross-section. The anterior surface of the shaft is almost planar and the other ones are slightly convex. The distal end of the bone is more transversely expanded and robust than the proximal end. The anterior surface of the distal end presents a deep extensor groove semilunate in shape. As occurs in the metatarsal II, the lateral collateral fossa is only present and is well-defined but shallow. The distal articular surface is ginglymous and sub-rectangular in distal view. In anterior view the distal end is slightly asymmetric with a lateral condyle more distally projected than the medial one, but in distal view the medial condyle is more ventrally projected than the lateral one.
The distal end and a probable fragmentary shaft of the metatarsal IV are preserved. The available portion of the shaft is straight and presents a semi-oval cross-section, in which the planar margin is probably the anterior surface. The distal end of the metatarsal IV is more asymmetric in anterior view than in the metatarsals II and III, with a lateral condyle more distally projected than the medial one. The dorsal extensor groove is shallower than in the more medial metatarsals. As is the case in the metatarsals II and III, only the lateral collateral fossa is present in the metatarsal IV. This fossa is shallow, resembling the condition of the metatarsal III, but contrasting with the deeper fossa observed in the metatarsal II. The distal articular surface is ginglymous and smaller than those from the metatarsals II and III, as occurs in Neoaetosauroides (PVL 3525), but contrasting with the sub-equal distal ends observed in Stagonolepis (S. robertsoni: Walker 1961). This surface is sub-rectangular in distal view and the medial condyle is incipiently more ventrally extended than the lateral one, in a lesser degree than the condition observed in the metatarsal III.
The proximal half of the metatarsal V presents the characteristic hook-shape present in archosauromorphs, as the result of a medial projection. The proximal articular surface is proximomedially oriented and heart-shaped in proximal view, with the notch being laterally oriented. The medial three-quarters of the proximal articular surface are concave and the lateral quarter is slightly convex. The articular surface is laterally bounded by a raised and proximally directed lip, in which the notch is present. The lateral surface is planar and directly below the proximal end of the bone a faint longitudinal groove is present. This groove confers a semi-lunate shape to the cross-section of the bone. The anterior surface presents a depression directly below the proximal articular surface and it is medially opened. Below it, the anterior surface is convex.
The single available pedal phalanx of Aetobarbakinoides is interpreted to be the first element of the fourth digit because of its robust morphology and the strong asymmetry observed in its proximal articular surface, which matches with the morphology observed in the distal end of the metatarsal IV (Figs. 14, 16–17). The proximal end is dorsoventrally higher than the distal one, but both extremes present sub-equal transverse widths. The proximal articular surface is semi-oval, with a straight ventral margin. The main axis of the proximal articular surface is rotated in an angle of about 10º with respect to the main axis of the distal end. The proximoventral lip is much more proximally extended than the proximodorsal one. The phalanx presents a transverse compression at mid-length. The posterior surface of the shaft is planar and the anterior one is convex. The distal end of the phalanx is asymmetric with a distinct trochlea, in which the medial condyle is more distally extended than the lateral one. The collateral fossae are circular, shallow, and present at both sides of the distal end of the bone. In distal view, the condyles are separated by a ventral groove and the medial condyle is more ventrally projected than the lateral one.
description: Published as part of Desojo, Julia B., Ezcurra, Martín D. & Kischlat, Edio E., 2012, A new aetosaur genus (Archosauria: Pseudosuchia) from the early Late Triassic of southern Brazil, pp. 1-33 in Zootaxa 3166 on pages 3-25, DOI: 10.5281/zenodo.279748