Neoreomys huilensis Fields 1957
Creators: name: Urrea-Barreto, Francisco J.
name: Link, Andrés
name: Carrillo, Juan D.
name: Vanegas, Andrés
name: Perdomo, César A.
name: Cooke, Siobhán B.
name: Tallman, Melissa
name: Pérez, María E.
Publisher: name: Zenodo
Year: 2023
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Mammalia
Rodentia
Dasyproctidae
Neoreomys
Neoreomys huilensis

description: Neoreomys huilensis Fields, 1957
Neoreomys huilensis Fields, 1957: 376-380.
“ Neoreomys ” huilensis – Walton 1997: 396.
HOLOTYPE. — UCMP 37973, incomplete left dentary bone with p4 to m3 and the base of the incisor.
REFERRED SPECIMENS. — FMNH PM 54708, left mandibular fragment with dp4 to recently erupted m3 and the base of the incisor. — IGM 183327, rigth mandibular fragment with m1-m3. — IGM 183683, rigth mandibular fragment with p4 to m2 (although Walton considered it as m1-m3). — KU-I-11, right mandibular fragment with m2 and m3. — KU-I-18, right mandibular fragment with m1. — LA 4292, fragmentary M3?. — LA 4300, right mandibular fragment with dp4, m1, recently erupted m2 and base of the incisor. — LA 5561, left mandibular fragment with p4 to m3. — LA 5562, mandibular fragment bearing m1 with negligible wear. — VPPLT 134, isolated left m3. — YMS-Y3, left mandibular fragment with m1 to m3.
STRATIGRAPHIC AND GEOGRAPHIC PROVENANCE. — The holotype (UCMP 37973) comes from the Lone Tree Locality, at the Monkey Beds, in the Cerbatana Beds, Villavieja Formation. — FMNH PM 54708 comes from the Monkey Beds, Villavieja Formation. — KU-I-8 and KU-I-11 come from the El Dinde Locality (3°16’48”N, 75°11’52”W), Tatacoa Beds, La Victoria Formation. — IGM 183327 and IGM 183683 come from the Tatacoa Beds, La Victoria Formation. — LA 4292 comes from the Monkey Beds, Villavieja Formation. — LA 4300 and LA 5561 come from “Duke Locality” (3°16’48”N, 75°11’45”W), Tatacoa Beds, La Victoria Formation. — LA 5562 comes from an unknown locality in the La Victoria Formation. — VPPLT 134 comes from the Km 121 Locality (3°19’29”N, 75°10’55”W), Tatacoa Beds, La Victoria Formation. — YMS-Y3, La Venta, unknown provenance.
REVISED DIAGNOSIS. — Cavioid rodent diagnosed by the following unique combination of characters: nearly 50% smaller than Neoreomys australis and N. pinturensis; cheek teeth high-crowned with the formation of roots, similar to N. pinturensis but lower than N. australis; mesial flexid on the anterior wall of the lower molars more persistent than in N. australis and Luantus, but less persistent than in Asteromys.
REMARKS
In addition to the holotype (UCMP 37973, Fig. 3 A-C), the three specimens illustrated in Walton (1997: fig. 24.1.G and 24.3.A-C; FMANH PM 54708, IGM 183327 and IGM 183683) had an associated provenance in her work, but there was no data on each specimen’s anatomy. IGM 183683 (a right mandibular fragment with p4-m2) is the largest specimen among the material assigned to “ Neoreomys ” huilensis by Walton (1997). Unfortunately, we were unable to locate this specimen for this review, and the collection number is currently assigned to a sloth Pseudoprepotherium (pers. comm. R. Kay 2021). Thus, it can only be compared and measured from Walton’s publication (Walton 1997: fig. 24.3.C). We assigned IGM 183683 (as described by Walton 1997) to N. huilensis, given that its occlusal morphology resembles that of the other specimens here described. Nonetheless, size variation within our sample is not high enough to consider two taxa within it (even including IGM 183683; seeTable 1), bearing in mind the wide variability in size observed in other species of the genus (see Table 2).
DESCRIPTION AND COMPARISONS
The sample consists mainly of dentary bones and lower cheek teeth; an isolated upper molar (LA 4292), was recently found and here referred to as Neoreomys huilensis by its size and morphological pattern (similar to the other Neoreomys species; see description below).
Dentary
The dentary bones are fragmentary; most of the sample consists of pieces of the corpus, and even in the most complete ones (e.g., Fig. 3 A-I), most anterior and posterior portions were lost. The lateral wall, anteriorly to the p4, has a mental foramen close to the dorsal margin of the diastema that opens dorsolaterally (Fig. 3E, H) as in N. australis and Dasyprocta (the dentary of Mesoprocta, UF 26915 is deteriorated so the presence of a mental foramen cannot be confirmed; Croft et al. 2011a: fig. 4). The notch for the insertion of the tendon of the masseter medialis pars infraorbitalis muscle (nMpi) is below m1 and develops without forming a shelf around the notch (Fig. 3B, E, H). The nMpi is connected to the masseteric crest, which arises below the m1-m2. The horizontal crest is better observed in FMNH PM 54708 (Fig. 3H) as a low and broad ridge, similar to N. australis. On the medial side, the incisor is posteriorly extended at the level of the m3 (Fig. 3C, F, I). The incisor is slender, and the enamel face is less flattened than in N. australis. On LA 4300 (Fig. 3F), the chin seems to be at the level of the dp4/p4 and is not exposed on its lateral side, probably because it is broken. The mandibular foramen (MaF) is only observed in the most complete specimen (Fig. 3I) and is ventrally placed to the retromolar fossa, as in N. australis. The pterygoid fossa is shallow, like that of N. australis. The only dentary bone fragment assigned to N. pinturensis is broken and significantly deteriorated, so its morphology cannot be evaluated.
Lower cheek teeth
Almost all cheek teeth except for dp4 are tetralophodont with transverse and wide crests (Fig. 3A, D, G, J, L-Q). They are high-crowned with the formation of roots (i.e., protohypsodont sensu Mones 1982; hypsodont sensu Janis & Fortelius 1988), similar to N. pinturensis, but lower-crowned compared to N. australis at the same stage of wear (sensu Kramarz 2006a). The mesial and distal walls are convex, while the lingual margin is straight. The enamel layer is continuous and thick around the entire crown, so it is the one that delimits flexids and fossetids. The hypoflexid has the shape of a narrow “V” (as in the other species of Neoreomys), with straight borders, and reaches up to the transverse midpoint of the crown in occlusal view. Molars lack cementum in juvenile and adult ontogenetic stages (no known specimens in senile stages) as in N. pinturensis, while in N. australis it presents cementum only in senile ontogenetic stages.The lingual flexids become transversely elongated fossetids, more persistent than in N.australis, Mesoprocta, and Dasyprocta.
Deciduous premolar (dp4)
The dp4 is pentalofodont, mesiodistally longer (Fig. 3D, G), and lower-crowned than the other teeth (Fig. 3E, F, H, I). It has two big roots (mesial and distal) as in the dp4 of N. australis (e.g., MPEF-PV 1636), and other cavioids such as Asteromys, Luantus, Phanomys, or Eocardia (Kramarz 2006b; Pérez 2010; Pérez et al. 2012). The anterolophid is labiolingually short with a rounded mesial border, and the neolophid is long and straight. Between them is a small and round fossetid. From the protoconid area, lingually arises the metalophulid II and distally an oblique ectolophid. Between the neolophid and metalophulid II is a straight and labio-lingually very long labial flexid. A lingual spur of the ectolophid and a labial widening lingual portion of the metalophulid II could represent a mesolophid’s lingual and labial portions. A central S-shaped fossetid separates these two structures. The hypoconid area is a little more lingual with respect to the protoconid area. The hypolophid is straight, and the posterolophid is long and distally convex. The hypoflexid is similar to that of other lower teeth, with the shape of a narrow “V”, and its apex faces the hypolophid. The posteroflexid is thin, slightly convex, and still lingually open on LA 4300. This general morphology is similar to the dp4 of some specimens of Dasyprocta (e.g., FMNH 69559, FMNH 95792). In FMNH PM 54708 (Fig. 3 G-I), the crown is more worn, the enamel layer is narrower than in the dp4 of LA 4300 specimen (Fig. 3 D-F) and is entirely absent on the mesiolingual border. The hypoflexid closes and forms an hypofossetid. The lingual flexids are closed, and there are four small lingual fossetids that were about to disappear with wear; among them, the mesial and distal fossetids are transversally elongated, and the two central ones are subcircular (Fig. 3G). Among the reviewed specimens of N. australis with dp4, the specimen MPM-PV 19179 shows a similar (or even younger) ontogenetic stage to that of LA 4300 but with a higher degree of wear (Vizcaíno et al. 2022: fig. 9A). So far, no dp4 has been recognized for N. pinturensis (Kramarz 2006a) and Mesoprocta (Croft et al. 2011a).
Premolar (p4)
Only two sample specimens preserve their p4 (UCMP 37973 and LA 5561; Fig. 3 A-C, J-K). The mesial and lingual margins of the crown are straight, whereas the distal border is slightly convex. On the mesial wall of both specimens is a straight metalophulid I. This lophid comprises a lingual and a labial portion, nearly joined in the holotype (UCMP 37973; Fig. 3A) and recently connected in the other specimen (LA 5561; Fig. 3J), forming a fossetid. This could result from merging a mesial flexid with the lingual anteroflexid that probably closes in the early stages of wear as occurs in N. australis (e.g., AMNH DPV 97727). The second crest in position (metalophulid II) converges with the metalophulid I in the metaconid area. The protoconid area and an oblique ectolophid form a labially convex region that is continuous with the hypolophid. The hypoconid area and the posterolophid form the transversally longest lophid that is as wide as the hypolophid. The mesoflexid is still lingually open, very narrow, and much deeper in the lingual wall than the metaflexid, which is almost closed. In the holotype (Fig. 3A), the metaflexid and the hypoflexid are merged, splitting the occlusal surface completely. The meta- and hypoflexid separate at a slightly advanced wear stage (LA5561; Fig. 3J).
Lower molars
In the most juvenile specimens (Fig. 3 D-I), the molars present a mesial flexid (flexid or notch between the protoconid and metalophulid I that disappears with wear) that has merged to the anteroflexid/anterofossetid, as in the p4 of the holotype (Fig. 3A). The mesial flexid is more persistent in N. huilensis than in N. australis and Luantus propheticus (e.g., Kramarz 2006b: fig. 3G), but more ephemeral than in Asteromys punctus. In the youngest individual (LA 4300; Fig. 3D), this mesial flexid has closed at the m1, forming part of the anterofossetid; but in the m2, it remains mesially open. Likewise, in the other juvenile specimen (FMNH PM 54708; Fig. 3G), the mesial flexid is closed in m1 and m2 but remains mesially open in m3. The protoconid + ectolophid area and the hypolophid form an oblique and wide lophid (e.g., m2 inFig. 3D). From the metaconid area arises a wide lingual portion of the second lophid in position (m 2 in Fig. 3D). At early stages of wear the hypoflexid and metaflexid merge as an extended flexid that splits the occlusal surface (m1 or m 2 in Fig. 3D, G, P; m 3 in Fig. 3A, D, G, J, N, Q), and the meso- and metaflexid are lingually open (Fig. 3D, G). The posterolophid is oblique and linguolabially short (m 2 in Fig. 3D; m 3 in Fig. 3A, G, J, Q).
At more advanced stages of wear (Fig. 3A, J, L, M, O), the metaflexid becomes wholly separated from the hypoflexid. Generally, the metaflexid closes lingually before the mesoflexid; however, this is variable, like the condition observed in N. australis or Luantus. Thus, three elongated and narrow fossetids are formed. Some molars (m 2-3, Fig. 3J) have an anterofossetid that splits into two smaller ones (labial and lingual). This variable condition is also observed in some specimens of N. australis, Luantus propheticus, and Asteromys. The hypoflexid is extended to less than half of the transverse occlusal area, and its apex is opposite to the hypolophid. The second crest in position (metalophulid II) is transversely long (Fig. 3D, G), as in N. pinturensis. The extension of the ectolophid and the second crest in position is variable in the cheek teeth of N. australis, both in the same dental series and among different specimens (see Kramarz 2006a). In the m3, the metaflexid remains lingually open and shows a noticeable reduction in the length of the posterolophid (Fig. 3A, J, N, Q).
Upper cheek teeth
The tooth described here is the first upper molar described for Neoreomys huilensis. A left upper molar, probably an M3, LA 4292 (Fig. 3 R-T), displays a pentalophodont pattern as in N. australis and N. pinturensis. Although the mesial and labial walls of the tooth are broken, the enamel appears to be continuous around the crown, and lacks cement. The tooth is high-crowned, and the hypoflexus is still open, but the base of the root is broken. At this stage of wear, the labial flexi/fossettes persist. In occlusal view, the hypoflexus is continuous with the parafossette (as in N. australis and N. pinturensis), the mesoflexus and metaflexus are labially open, and this latter is extended and narrow. The posterofossette is rounded, broad, and shallower than the others (Fig. 3R). The labial flexi is closed at the tooth base, the hypoflexus and parafossette are separated, and the para, meso, and meta fossettes are small and rounded (Fig. 3T). The mesiodistal length (even though the mesial border is broken) is greater than the transverse width (Table 1). Compared to other Neoreomys species in similar wear stages, the tooth is smaller, and the crests are relatively wider. The anteroloph is mesially broken. The protoloph is long and widens on the labial side. The third crest in position (mesoloph?) is long and straight. The metaloph is wide and relatively long and is attached to the posterloph. This posteroloph is shorter and narrower than the others.
description: Published as part of Urrea-Barreto, Francisco J., Link, Andrés, Carrillo, Juan D., Vanegas, Andrés, Perdomo, César A., Cooke, Siobhán B., Tallman, Melissa & Pérez, María E., 2023, Systematic revision of Neoreomys huilensis Fields, 1957 (Rodentia, Hystricognathi) from the Middle Miocene of La Venta (Villavieja, Colombia), pp. 721-737 in Geodiversitas 45 (25) on pages 728-730, DOI: 10.5252/geodiversitas2023v45a25, http://zenodo.org/record/10421982