Cachiyacuy kummeli

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 : 30

? Cachiyacuy kummeli

Figure 5.3 , Appendix 3

2016? Canaanimys sp. Antoine et al., Supplementary data, p. 5.

2017? Canaanimys sp. Antoine et al., Supplementary data, p. 9.

Referred material. MUSM 2648, fragmentary left dP4 ( Figure 5.3 ).

Locality. Contamana CTA-47, Loreto Department, Peru.

Formation and age. Pozo Formation, lower member, late middle Eocene ( Antoine et al., 2016). This is the lowermost locality having yielded rodents in the Quebrada Cachiyacu section of Contamana ( Antoine et al., 2016).

Description. MUSM 2648 ( Figure 5.3 ) is a labial fragment of a brachydont upper tooth. Due to the trapezoidal shape of the occlusal outline, this is identified as a dP4. The paracone is clearly visible because it is the largest cusp of the tooth. In its mediolabial part, the anteroloph bears a tiny and backwardly directed spur that reaches a second spur linked to the protoloph. There is a lingual connection between the anteroloph and the protoloph due to wear. Because of the important thickness of that link, it may be expected that this dP4 did not exhibit a taeniodont pattern when it was pristine. There is a very thin and low crestule, distally placed to the protoloph, and labially linked to a minute cusp. These structures are too small and anteriorly placed to be identified as the main central transverse crest and mesostyle, given that these latters are well-defined and situated just posteriorly. As such, they appear to be accessory dental traits. With the advanced degree of wear, it is difficult to know if the lingual end of that secondary crestule is free or linked to the central transverse crest. The latter, running labiodistally from the junction between the mure and the mesial extremity of the anterior arm of the hypocone to the mesostyle, corresponds to a mesolophule. Due to wear, the enamel of the distal flank of the mesolophule reaches one of the last distal crests, a configuration which forms a wide enamel plate rather than a metaflexus. The dentine part of the apparent fourth crest is wide and slightly excavated, which suggests that it might include both a metaloph and a posteroloph. The metaflexus is strongly reduced and limited to a very small and faintly visible fossette.

Comparisons. MUSM 2648 ( Figure 5.3 ) has a size close to that of Cachiyacuy kummeli , Canaanimys maquiensis , Eoespina woodi , and Eosachacui lavocati ( Frailey and Campbell, 2004) . In Antoine et al. (2016, 2017), this tooth was attributed to? Canaanimys on the basis of a different interpretation of dental homologies from that proposed here (see description). Topographically, the third apparent transverse crest was originally interpreted as a metaloph (with a configuration as that observed on upper molars of Canaanimys [i.e., oriented anteriorly]), while here it is interpreted as a mesoloph. Likewise, the posteriormost crest, which was originally interpreted as a posteroloph, might be a fusion of the metaloph with the posteroloph instead. Finally, the central tiny crestule is reinterpreted here as a neostructure instead of a mesoloph. If our current interpretations regarding the homologies are correct, this pattern characterized by a metaloph associated with the posteroloph is reminiscent of that found in Cachiyacuy contamanensis . Moreover, Cachiyacuy is the only genus that often displays a central crestule (more or less long) and/or cusp between the protoloph and the third transverse crest on dP4 (MUSM 1874, 2717, 2720, and 2721; in Antoine et al., 2012, figure 2e) and on upper molars (MUSM 1871 and 2742; in Antoine et al., 2012, figure 2b). On these teeth, the accessory crestule and/or cusp is on the distal wall of the paracone and protoloph, except on two teeth: on MUSM 2717, the accessory cusp is neither on the wall of the paracone nor on that of the mesostyle but is located on the opening of the mesoflexus, while on MUSM 1874, the accessory crestule and cusp are closer to the central transverse crest, like on MUSM 2648. To summarise, MUSM 2648 has more affinities with the upper molars of C. kummeli .

Figures

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.