Pozomys ucayaliensis, Boivin, 2017
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publication ID |
https://doi.org/ 10.26879/742 |
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publication LSID |
lsid:zoobank.org:pub:540D23AA-F705-4A05-8E10-FADAD3356D9C |
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persistent identifier |
https://treatment.plazi.org/id/E38E9E2A-6303-4278-888F-0F8FC05C5010 |
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taxon LSID |
lsid:zoobank.org:act:E38E9E2A-6303-4278-888F-0F8FC05C5010 |
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treatment provided by |
Felipe |
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scientific name |
Pozomys ucayaliensis |
| status |
sp. nov. |
Pozomys ucayaliensis sp. nov.
Figure 6.1-6 View FIGURE 6 , Appendix 3
zoobank.org/ E38E9E2A-6303-4278-888F-0F8FC05C5010
2016 Canaanimys sp. Antoine et al., Supplementary data, p. 9.
2016 Cachiyacuy cf. kummeli Antoine et al. , Supplementary data, p. 9.
2016 Chinchilloidea indet. Antoine et al., Supplementary data, p. 9.
2017 Canaanimys sp. Antoine et al., Supplementary data, p. 9.
2017 Cachiyacuy cf. kummeli Antoine et al. , Supplementary data, p. 9.
2017 Chinchilloidea indet. Antoine et al., Supplementary data, p. 9.
Etymology. Refers to the Ucayali River, which is a major tributary of the Amazon River flowing near Contamana, Peru.
Holotype. MUSM 2833 , right M2. Deposited in the Museo de Historia Natural de la Universidad Nacional Mayor de San Marcos, Lima, Peru.
Referred material. In addition to the holotype ( MUSM 2833) MUSM 2821, left p4 ( Figure 6.2 View FIGURE 6 ); MUSM 2820, fragmentary right p4; MUSM 2822, right mandibular fragment bearing m1 and m2 ( Figure 6.1, 6.5-6 View FIGURE 6 ); MUSM 2833, right M2 ( Figure 6.4 View FIGURE 6 ); MUSM 2819, fragmentary right M3 ( Figure 6.3 View FIGURE 6 ).
Type Locality. Contamana CTA-29, Loreto Department, Peru.
Formation and age. Pozo Formation, lower member, late middle Eocene ( Antoine et al., 2016).
Diagnosis. Tiny rodent characterized by tetralophodont p4s and lower molars. Pozomys differs from Eoincamys in having no posterior arm of the protoconid (or very reduced one) on p4, and less oblique transverse cristids on the lower molars. Differs from Cachiyacuy and Canaanimys in having a residual metaloph, which can be merged with the metacone-posteroloph complex on upper molars. Differs from Cachiyacuy , Eoespina / Eosachacui and Incamys in having a metalophulid I more or less disconnected to the protoconid on lower molars. Its teeth tend to be taeniodont, contrary to Eoespina / Eosachacui and most teeth of Cachiyacuy . Differs from Incamys in being lower-crowned and in showing a similar thickness of the enamel layer on the mesial and distal flanks of the hypoflexus. Differs from Platypittamys and Deseadomys in having a p4 with a hypolophid. Differs from Galileomys and Paulacoutomys in having a very thin lateral crest, which does not reaches the masseteric crest below the m1 on mandible.
Description. The nearly complete p4 (MUSM 2821; Figure 6.2 View FIGURE 6 ) is moderately eroded, and shows rounded corners. The shape of this premolar is characterized by a talonid, which is nearly twice wider than the trigonid. Despite of the wear, the four main cuspids (metaconid, entoconid, protoconid, and hypoconid) are well-recognizable, as they are well-defined. Although the tooth is slightly broken mesially (it lacks the enamel), the metaconid and protoconid appear well-separated and connected mesially by a transverse and straight metalophulid I. The rounded protoconid seems to display a short posterior arm, which is in connection and in line with a strongly oblique ectolophid. The hypolophid is also oblique and in line with the ectolophid. These two cristids form a distolingualmesiolabial directed central and diagonal cristid, which links the entoconid and protoconid (its posterior arm?). Lingually, the mesostylid is faintly visible to indistinct and linked to a short and low posterior arm of the metaconid. The second transverse cristid is short, straight, and strikingly labiodistally directed. This second transverse cristid is lingually linked to the posterior arm of the metaconid-mesostylid complex, and labially to the ectolophid, and as such it could represent a neomesolophid rather than a metalophulid II. Labiodistally, the hypoconid is massive but crestiform (mesiodistally pinched), and bears a noticeably long labial outgrowth. Distolabially, the hypoconid is entirely merged with the strong posterolophid. This latter cristid runs lingually and connects to a short, well-marked, and high posterior arm of the entoconid. A very short, low, and thin anterior arm of the hypoconid is faintly linked to the hypolophid (the tooth is almost taeniodont). Therefore, the distal metafossettid is almost confluent with the hypoflexid, which exhibits a wide labial aperture. The fragment of p4 (MUSM 2820) is less eroded than the former one described above. This tooth fragment does not present any second transverse cristid. A thin and deep furrow separates the mesostylid from the metaconid.
MUSM 2822 is a mandibular fragment preserving m1 and m2 ( Figure 6.1, 6.5-6 View FIGURE 6 ). Labially, the broken masseteric crest is posteroventrally directed. It is widely prominent and reduced at its anterior tip, which probably ends below the premolar (p4). The part of the ascending ramus, which runs toward the coronoid process, begins below the m2. That mandibular fragment shows neither horizontal crest nor lateral crest nor notch for the insertion of the tendon of the zygomatico-mandibularis pars infraorbitalis. The m1 has a trigonid narrower than the talonid, whereas the trigonid is roughly as wide as the talonid on m2. Although the occlusal surface of the molars is worn, their cuspids are still well-recognizable, notably on m2. Both teeth are tetralophodont. The metalophulid I is very thin in its labial part and it is clearly separate from the protoconid by a wide notch on m2. On both molars, the posterior arm of the metaconid is long and reaches a well-defined mesostylid. The latter is well-separated from the entoconid. The short second transverse cristid is straight and complete but constricted in its middle part, which suggests that it could result from the coalescence of two cristids (lingually, a neomesolophid, and labially, a posterior arm of the protoconid). On m1, the pinching of the second cristid is labially located, which would indicate that the neomesolophid is dominant, whereas the two cristids are equal in length on m2. The hypolophid is strong and straight transversely. The second transverse cristid and hypolophid are parallel and mesiodistally close in position. Both isolate a labiolingually long and mesiodistally narrow furrow-like mesoflexid. The ectolophid, longitudinal, is short due to the advanced stage of wear. The anterior arm of the hypoconid, poorly developed (faintly visible and very low), separates the metaflexid from the hypoflexid. Yet, given the weak development and low elevation of the anterior arm of the hypoconid, we can describe this dental pattern as “pseudo-taeniodont.” The hypoconid is crestiform (mesiodistally pinched), with a long and labially oriented outgrowth. This outgrowth and the distal flank of the protoconid isolate a narrow and nearly transverse hypoflexid (notably on m2). Lingually, on both teeth, the entoconid does not develop an anterior arm, and thus the furrow-like mesoflexid remains open lingually. The metaflexid is lingually open on m1 but closed on m2.
MUSM 2833 ( Figure 6.4 View FIGURE 6 ) is slightly wider than long. The hypocone is reduced compared to the protocone, and displaced labially like on some M3s and M2s. This specimen has interstitial facets on its mesial and distal margins, which allows us to identify it as a M2. The protocone, massive and slightly oblique, displays a short but thick posterior outgrowth. Connected to the protocone, the anteroloph runs labially. It ends its course at the mesial base of the paracone, without connecting to it, thereby letting the paraflexus faintly open labially. The paracone is large and rounded, and much more differentiated than the metacone (nearly indistinct and subsumed within the posteroloph). From the paracone, the oblique labial protoloph runs distolingually and joins the mure-anterior arm of the hypocone complex, subparallel to the protoloph. The lingual protoloph is lacking, and thus the hypoflexus connects the paraflexus, thereby illustrating a full taeniodont pattern. Labially, at mid-distance between the paracone and metacone-posteroloph, the mesostyle is strong and well-defined, but only connected to the metacone-posteroloph complex by a strong longitudinal crest (posterior arm of the mesostyle and/or anterior arm of the metacone). The central transverse crest between the mesostyle and the mesial extremity of the anterior arm of the hypocone is sinuous, indicating that this crest could be a composite crest, including a short mesolophular spur and a long mesoloph. Distolabially, the posteroloph shows a distinct mesiodistal enlargement, thus suggesting the presence of a residual metaloph, backwardly oriented and merged with the posteroloph. The metaflexus is the unique flexus entirely closed labially.
The fragmentary MUSM 2819 ( Figure 6.3 View FIGURE 6 ) is subpentalophodont and non-taeniodont, with a rounded labial margin and a hypocone more labial than the protocone, which indicates that the specimen is a M3. The protoloph is slightly oblique, close and parallel to the anteroloph (narrow paraflexus). Although broken labiomesially, these two mesial crests seem not to be linked labially. The metacone is small, slightly more lingual than the paracone, and merged to the posteroloph. The mesostyle is almost as large as the paracone and isolated on the labial margin. Neither a posterior arm of the paracone nor an anterior arm of the metacone is developed, and the mesoflexus and metaflexus remain open labially. The hypocone displays a strong and sagittal anterior arm. It connects to the protoloph via a strong mure, although almost undifferentiated. The central transverse crest consists of two disjoint crests: lingually, a short mesolophule and labially, a long mesoloph stemming from the mesostyle. A short metaloph, stemming from the metacone, runs mesiolingually toward the labial extremity of the mesolophule, without being connected to it. Distolingually, the posteroloph is faintly connected to the hypocone, and a shallow notch separates both structures.
Comparisons. The size of these specimens is comparable to that of Cachiyacuy kummeli , Canaanimys maquiensis , Eoespina woodi / Eosachacui lavocati , and Eoincamys ameghinoi Frailey and Campbell, 2004 . On the lateral view of the MUSM 2822 mandible ( Figure 6.5 View FIGURE 6 ), the general disposition and strong development of the masseteric crest on the dentary is found in all Paleogene caviomorphs for which the mandible is known (e.g., Eobranisamys , Andemys Bertrand et al., 2012 , Platypittamys Wood, 1949 , Scotamys Loomis, 1914 , Cephalomys Ameghino, 1897 , Branisamys , Incamys Hoffstetter and Lavocat, 1970 , Sallamys , Migraveramus Patterson and Wood, 1982 , Paulacoutomys Vucetich et al., 1993 , Galileomys Vucetich and Kramarz, 2003 , Acarechimys Patterson, 1965 (in Patterson and Wood, 1982), Leucokephalos Vucetich et al., 2015 , Loncolicu Vucetich et al., 2015 , and Llitun Vucetich et al., 2015 ). Contrary to MUSM 2822, Galileomys and Paulacoutomys develop a very thin lateral crest, stemming from the ascending ramus, and almost reaching the masseteric crest below the m1. The lower molars of Pozomys ucayaliensis nov. gen. et sp. display an association of characters that can be found in Canaanimys and/or in Eoincamys ( Frailey and Campbell, 2004) . The molars of the MUSM 2822 mandible show a metalophulid I that tends to be disconnected to the protoconid, a configuration which can be observed in lower molars of Eoincamys and Canaanimys . As on the m2 of MUSM 2822, the m1s and m2s of Eoincamys pascuali clearly show an interrupted metalophulid I, which is separate from the protoconid by a large notch. In Eoincamys ameghinoi and Canaanimys maquiensis , this feature is more variable: the metalophulid I can show the same configuration than the m2 of MUSM 2822 and Eoincamys pascuali (on LACM 149435 [in Frailey and Campbell, 2004, p. 114] and MUSM 1893, 2788-2789 [in Antoine et al., 2012, figure 2x], respectively), but also it can be complete in linking the metaconid to the protoconid (on LACM 143435 [in Frailey and Campbell, 2004, p. 114] and MUSM 2787, 2790-2791, respectively). In Eoincamys , the second transverse cristid is almost limited to its lingual part (neomesolophid), which tends to be disconnected to a very short, spur-like posterior arm of the protoconid. In Canaanimys , the second transverse cristid is either complete or discontinuous (split into two or three parts). The molars of the MUSM 2822 mandible are characterized by a pseudo-taeniodont pattern, like in some lower molars of Canaanimys (MUSM 1892 and 1893; in Antoine et al., 2012, figure 2w-x). This is also observed on a tooth of Eoincamys ameghinoi (LACM 149442; in Frailey and Campbell, 2004, p. 114). In contrast, Eoincamys pascuali has more taeniodont lower molars. Contrary to the m1-2 of P. ucayaliensis and Canaanimys , the transverse cristids of the lower molars are more oblique in Eoincamys : the hypolophid is slightly oblique and tends to be aligned with an oblique ectolophid along with the posterior arm of the protoconid. The ectolophid is oblique in Eoincamys and Canaanimys , contrary to P. ucayaliensis . The p4 of P. ucayaliensis also resembles that of Eoincamys in showing a rounded crown outline and a reduced second cristid; yet, the posterior arm of the protoconid is more developed in Eoincamys than in P. ucayaliensis (small or absent). A reduced second cristid is also found in Draconomys Vucetich et al., 2015 , Leucokephalos , Platypittamys , Deseadomys Wood and Patterson, 1959 , and Incamys . As for Eoincamys , the p4 of P. ucayaliensis is relatively shorter with respect to the p4 of Draconomys , Leucokephalos , Platypittamys , Deseadomys , and Incamys ( Wood, 1949; Wood and Patterson, 1959; Hoffstetter and Lavocat, 1970; Lavocat, 1976; Vucetich et al., 2010, 2015). Besides, the MUSM 2821 p4 ( Figure 6.2 View FIGURE 6 ) differs from Platypittamys and Deseadomys in the presence of a hypolophid. Although being taeniodont, the M2 of P. ucayaliensis is very distinct from that of Eoincamys or Canaanimys . Indeed, there is a prominent outgrowth of the protocone on M 1–2 in C. maquiensis , which is less developed in P. ucayaliensis . On MUSM 2833 (and MUSM 2819) of P. ucayaliensis , the mesoloph is still linked to the mesolophular spur of the anterior arm of the hypocone, while the mesoloph tends to have no lingual connection with the anterior arm of the hypocone in E. ameghinoi (i.e., absence of the mesolophular spur) and the mesoloph is backwardly directed and connected with the posteroloph in E. pascuali . Finally, the MUSM 2833 M2 ( Figure 6.4 View FIGURE 6 ) of P. ucayaliensis shows a posteroloph with a distinct mesiodistal enlargement, which probably corresponds to a residual metaloph fused with the posteroloph. On the contrary, there is no metaloph in Eoincamys . In Canaanimys , there is a metaloph, but the latter is longer than in MUSM 2833 and lingually connected to the third transverse crest. However, Canaanimys can have reduced metaloph but only on M3. A reduced metaloph on MUSM 2833 can be documented in Eoespina / Eosachacui and Incamys . Contrary to MUSM 2833 and Incamys , Eoespina / Eosachacui displays no taeniodont or pseudo-taeniodont molars. MUSM 2833 shows a slight oblique (diagonal) alignment of the protoloph with the mure and the anterior arm of the hypocone, as in Incamys (and Eoincamys ). Contrary to MUSM 2833, upper molars of Incamys and Eoincamys can have a third transverse crest lingually free or connected to the posteroloph. MUSM 2833 ( P. ucayaliensis ) is lower-crowned than in Incamys , with equally thick enamel layer on the mesial and distal flanks of the hypoflexus (characteristic of most chinchilloids; Kramarz et al., 2013). Indeed, the leading edges are thicker than the trailing edges in Incamys and most chinchilloids ( Kramarz et al., 2013; Vucetich et al., 2015). MUSM 2833 differs from all aforementioned taxa in having a shorter protoloph and third transverse crest. In sum, this material from CTA-29 is attributed to a new genus and species following this particular association of dental traits. Despite its non-taeniodont pattern, the MUSM 2819 M3 ( Figure 6.3 View FIGURE 6 ) is tentatively attributed to this new taxon.
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