Eobranisamys javierpradoi, , MUSM, 2842

Boivin, M, Marivaux, L, Orliac, MJ, Pujos, F, Salas-Gismondi, R, Tejada-Lara, JV & Antoine, P, 2017, Late middle Eocene caviomorph rodents from Contamana, Peruvian Amazonia, Palaeontologia Electronica 16 (7), pp. 1-50 : 7-9

Eobranisamys javierpradoi sp. nov.

Figure 4.7-8 , Appendix 3

zoobank.org/ 54337122-7076-48E5-81CC-83D8A1435825

2012 Eobranisamys sp. Antoine et al., p. 1321–1322. 2016 Eobranisamys sp. Antoine et al., Supplementary data, p. 7.

2017 Eobranisamys sp. Antoine et al., Supplementary data, p. 9.

Etymology. In honour of Javier Prado, who founded the “Museo de Historia Natural, Universidad Mayor de San Marcos” in Lima, Peru, in 1918.

Holotype. MUSM 1897 , left M1 (in Antoine et al., 2012, figure 2b’). 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 1897 ) MUSM 2795 , left m1 or m2; MUSM 1898 , right fragmentary m2 (in Antoine et al., 2012, figure 2c’); MUSM 1899 , left m3 (in Antoine et al., 2012, figure 2d’); MUSM 2796 , right m3; MUSM 2797 , right dP4 ( Figure 4.7 ); MUSM 1896 (in Antoine et al., 2012, figure 2a’) and 2798, left P4s; MUSM 2799 , right M1 or M2; MUSM 2800 , left M1; MUSM 2801 , left M3 ( Figure 4.8 ).

Type locality. Contamana CTA-27, Loreto Department, Peru.

Formation and age. Pozo Formation, lower member, late middle Eocene ( Antoine et al., 2012, 2016).

Diagnosis. Smallest species of Eobranisamys (about half the size of E. romeropittmanae and 20% smaller than E. riverai ), showing sharper crests, more salient cusps, and longer M3 with a less rounded occlusal outline than other referred species.

Description. The lower molars are tetralophodont (in Antoine et al., 2012, figure 2c’–d’). Mesially, there is no trace of anterocingulid at the base of the crowns. On MUSM 1899 (m3; in Antoine et al., 2012, figure 2d’), the protoconid is the largest cuspid of the tooth. On MUSM 1899 and 2795 (m1 or 2; in Antoine et al., 2012, figure 2c’), the metaconid is situated more mesially than the protoconid, with a strong and high posterior arm. The protoconid and metaconid are connected by a strong and complete metalophulid I. On m3, the second transverse cristid is strong and complete. Labially, this cristid starts from a well-defined and oblique (distolingually oriented) posterior arm of the protoconid, then it makes an angle and runs lingually to reach the distal extremity of a long posterior arm of the metaconid. The same is true on m1-2s. On MUSM 1898 (in Antoine et al., 2012, figure 2c’), a noticeable angulation in the middle of this cristid could correspond to the junction of two cristids. Furthermore, on this tooth, the lingual connection of this second cristid could be a mesostylid. So, the question remains as to whether this second cristid is a complete metalophulid II or a combination of two cristids, i.e., a short posterior arm of the protoconid and a lingual neomesolophid. The metalophulid I and second transverse cristid are well-separated, and isolate a broad and oval anterofossettid. The ectolophid is very short, medial (at the center of the tooth), and fully or roughly longitudinal. There is no mesoconid. The hypoconid and entoconid are labiolingually opposed. The hypolophid, strong and oblique (slightly forwardly oriented), connects to both a thin, oblique and moderately long consists of two cristulids. The hypoconid is mesiodistally compressed. The posterolophid on m2 and m3 is massive but short. It is clearly separate from the entoconid on MUSM 1898 and 1899; it reaches the base of that cuspid on MUSM 2796. In any case, the posteroflexid remains open lingually.

Many upper teeth are referable to this taxon: one dP4, two P4s, and nine molars.

The dP4 (MUSM 2797; Figure 4.7 ) is damaged and highly worn. It is subrectangular, with a mesiodistal long axis. Only the mesiodistally elongated mesostyle is clearly distinct on the labial margin. The mesostyle is mesially separate from the paracone but distally connected to the metacone. The dP4 is pentalophodont and taeniodont (absence of lingual protoloph). The anteroloph is markedly curved, strongly connected to the protocone, and runs labially to reach and connect to the paracone mesiolabially. The mure, oblique and aligned with the anterior arm of the hypocone, reaches mesially the short and transverse protoloph. The third transverse crest, interrupted labially and not reaching the mesostyle, is identified as a mesolophule. There are two accessory enamel crestules: one on the mesolophule and one on the anterior arm of the hypocone. The metacone is crestiform (mesiodistally elongated) and connected to the posteroloph distolabially. The metaloph, connected labially to the metacone, runs lingually and bends distally near the midline of the crown to link the posteroloph.

The P4s are oval in occlusal view, with a tetralophodont pattern (MUSM 1896 and 2798; in Antoine et al., 2012, figure 2a’). The paracone and metacone are twinned on MUSM 1896, whereas they are less connected on MUSM 2798. The protocone is mesiodistally developed and lingually opposed to the labial paracone-metacone complex. There is a minute hypocone (distinct on MUSM 2798; broken on MUSM 1896), located distolabially to the protocone. These two lingual cusps, also twinned, form a protocone-hypocone complex. The paracone-metacone and protocone-hypocone complexes, associated with long and strongly developed posteroloph and anteroloph, design a circular enamel wall on the entire crown margin. On MUSM 1896 (in Antoine et al., 2012, figure 2a’), there is only a small depression on this wall, located mesially, at the level of the anterolophparacone junction. This depression is absent on MUSM 2798. The protoloph is short and limited to its labial part. There is no lingual protoloph: the tooth is taeniodont. The hypocone has an oblique anterior arm ending near the center of the tooth. This hypocone arm extends labially via a straight and long third transverse crest (mesolophule on MUSM 1896 and mesolophule/mesoloph? on MUSM 2798). There is a tiny enamel spur mesiolingually directed at the junction between the hypocone arm and the third transverse crest.

The M1s referred here to Eobranisamys (MUSM 1897 and 2800; in Antoine et al., 2012, figure 2b’) are subquadrate, while the M3 (MUSM 2801; Figure 4.8 ) is smaller and shows a more rounded occlusal outline. On all upper molars, the protocone appears mesiodistally opposed to the hypocone. However, the hypocone is more reduced with respect to the protocone on M3 than on M1. There is no significant difference of crown height with upper molars of other rodent species from CTA-27. All upper molars are fully pentalophodont. The main cusps are sometimes faintly visible, but still distinct. These upper molars are fully taeniodont. The paraflexus is merged with the hypoflexus to form a continuous labiolingual groove, without any vestige of lingual protoloph. The protocone is slightly labiolingually pinched and connected to a strong anteroloph. This mesial transverse crest runs labially and connects to a well-defined parastyle. There is no connection between the parastyle and the paracone, even if they are very close on MUSM 2799 (where the paraflexus is almost completely labially closed). The hypocone is slightly labiolingually pinched. Its anterior arm is strong and frequently runs labiomesially to join the lingual extremity of the interrupted protoloph. Thus, the mure is present but rather indistinct except on MUSM 2800 where it is long and mesiolabially oriented. The third transverse crest is strongly connected to a well-defined and isolated mesostyle. This crest is a composite of either equally developed mesolophule and mesoloph (MUSM 2800), or of a long mesoloph with a short spur-like mesolophule (MUSM 1897 and 2801; in Antoine et al., 2012, figure 2b’). In addition, the mesostyle is separate from the paracone and metacone by two notches (the posterior arm of the paracone and anterior arm of the metacone are absent or weakly developed). On all upper molars, the metacone is labiolingually compressed and oblique. The metaloph is strong but short and backwardly directed in its lingual end, and it is variably connected to the medial part of the posteroloph (i.e., from slightly [MUSM 2800 and 2801] to strongly [MUSM 1897] connected). With such a configuration, the lingual part of the posteroflexus is confluent with the metaflexus. The metaloph and posteroloph isolate a small and oval posterofossette (the remaining labial part of the posteroflexus). The posteroloph is low compared to other transverse crests, and it links the distal aspects of the hypocone and of the metacone. In addition, the posteroloph bears a labial secondary crestule on M3 ( Figure 4.8 ).

Comparisons. This new species of Eobranisamys is roughly similar in size to the sympatric Cachiyacuy contamanensis . The transverse crests and cristids are well-marked and slightly higher than in molars of species referred to Cachiyacuy or Canaanimys . Teeth studied here display features reminiscent of those of Eobranisamys and Branisamys Hoffstetter and Lavocat, 1970 (especially upper molars; Lavocat, 1976; Frailey and Campbell, 2004). This is particularly shown in the development of a taeniodont and pentalophodont pattern, characterized by the presence of a strong third transverse crest, and a strong and well-defined metaloph, which is transverse and connected to the posteroloph. As in Eobranisamys romeropittmanae and E. riverai , the teeth of E. javierpradoi nov. sp. are much lower crowned than teeth of Branisamys . However, E. javierpradoi differs substantially from E. romeropittmanae in being about half the size, and from E. riverai in being 20% smaller, and in showing sharper crests and more salient cusps. Besides, E. romeropittmanae and E. riverai tend to have M3 shorter and with a more rounded occlusal outline than E. javierpradoi .

Figures

FIGURE 4. Scanning electron microscope images (in occlusal view) of fossil caviomorph teeth from CTA-27. Cachiyacuy contamanensis (1-6), Eobranisamys javierpradoi sp. nov. (7-8), Cachiyacuy kummeli (9-13), Canaanimys maquiensis (13-16) and cf. Eoespina sp. (17). 1, right m3 (MUSM 2713); 2, right m2 (MUSM 1914); 3, right m2 (MUSM 1915); 4, right p4 (MUSM 2678); 5, fragmentary right dp4 (MUSM 2670); 6, left M3 (MUSM 2758); 7, right dP4 (MUSM 2797); 8, fragmentary left M3 (MUSM 2801); 9, left dp4 (MUSM 2762); 10, left p4 (MUSM 2766); 11, right m3 (MUSM 2780, reversed); 12, left M1 (MUSM 2785); 13, left M2 (MUSM 2786); 14, fragmentary right M3 (MUSM 2794); 15, right M3 (MUSM 2793); 16, left M3 (MUSM 2792, reversed); 17, fragmentary left M2 (MUSM 2802). Top scale for 1-13, bottom scale for 14-17.

FIGURE 5. Scanning electron microscope images (in occlusal view) of fossil caviomorph teeth from CTA-47 (1-4), CTA-51 (5-12), CTA-73 (13-14) and CTA-66 (15-16).?Canaanimys sp. (1-2),?Cachiyacuy kummeli (3), Caviomorpha indet. 1 (4), Cachiyacuy cf. contamanensis 1 (5-7), Caviomorpha indet 2 (8-10), Cachiyacuy cf. kummeli (11), Eoespina sp. (12), Caviomorpha indet 3 (13), Caviomorpha indet 4 (14) and Eobranisamys sp. (15-16). 1, fragmentary right dp4 (MUSM 2645); 2, fragmentary left lower molar (MUSM 2646); 3, fragmentary left dP4 (MUSM 2648); 4, fragmentary right lower molar (MUSM 2647); 5, fragmentary right dp4 (MUSM 2651, reversed); 6, left m1 (MUSM 2652); 7, left m3 (MUSM 2653); 8, fragmentary right lower molar (MUSM 2656); 9, fragmentary left dP4 (MUSM 2657); 10, fragmentary left upper molar (MUSM 2658); 11, fragmentary left M1 (MUSM 2654); 12, right M2 (MUSM 2655); 13, fragmentary right lower molar (MUSM 2659); 14, fragmentary left upper molar (MUSM 2660); 15, fragmentary left upper molar? (MUSM 2841); 16, fragmentary left upper molar (MUSM 2842). Top scale for 1-12, bottom scale for 13-16.

FIGURE 6. Scanning electron microscope images of fossil caviomorph teeth from CTA-29. Pozomys ucayaliensis gen. et sp. nov. (1-6), Cachiyacuy cf. contamanensis 2 (7-12), Caviomorpha indet. 5 (13), Caviomorpha indet. 6 (14) and Cavioidea or Chinchilloidea indet. (15-17). 1, right m1-2, occlusal view (MUSM 2822); 2, left p4, occlusal view (MUSM 2821, reversed); 3, fragmentary right M3, occlusal view (MUSM 2819); 4, right M2, occlusal view (MUSM 2833); 5, right m1-2, labial view (MUSM 2822); 6, right m1-2, lingual view (MUSM 2822); 7, left dp4, occlusal view (MUSM 2825); 8, right m1, occlusal view (MUSM 2827, reversed); 9, right dP4, occlusal view (MUSM 2828, reversed); 10, left M1, occlusal view (MUSM 2831); 11, right M2, occlusal view (MUSM 2563, reversed); 12, fragmentary left M2, occlusal view (MUSM 2832); 13, right dp4, occlusal view (MUSM 2838); 14, fragmentary right upper molar, occlusal view (MUSM 2839); 15, right m2, occlusal view (MUSM 2835); 16, right dp4, occlusal view (MUSM 2834); 17, fragmentary right upper molar, occlusal view (MUSM 2836, reversed).

FIGURE 7. Morphological variation of the p4 (in occlusal view) of Cachiyacuy contamanensis from CTA-27. 1, MUSM 2674; 2, MUSM 2676; 3, MUSM 2677; 4, MUSM 1879; 5, MUSM 2678. Original computerized schemas (1-5) by Myriam Boivin.

FIGURE 8. Morphological variation of the lower molars (in occlusal view) of Cachiyacuy contamanensis from CTA-27. 1, MUSM 1878; 2, MUSM 2704; 3, MUSM 2684; 4, MUSM 2708; 5, MUSM 2692; 6, MUSM 2701; 7, MUSM 2714; 8, MUSM 2689; 9, MUSM 1915; 10, MUSM 1914. Original computerized schemas (1-10) by Myriam Boivin.