Cachiyacuy contamanensis Antoine et al., 2012

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 : 19-24

Cachiyacuy contamanensis Antoine et al., 2012

Figures 4.1-6 , 7 , 8 , Appendix 3

Referred material. In addition to the holotype ( MUSM 1871 , right M2; in Antoine et al., 2012, figure 2b) - MUSM 2661–2667 , left dp4s ; MUSM 1880 (in Antoine et al., 2012, figure 2k) and MUSM 2668–2673 ( Figure 4.5 ), right dp4s ; MUSM 2674– 2675 ( Figure 7.1 ), left p4s ; MUSM 1879 (in Antoine et al., 2012, figure 2j, Figure 7.4 ) and 2676–2678 ( Figures 4.4 , 7.2-3, 7.5 ), right p4s ; MUSM 2679– 2682 , left m1s ; MUSM 1878 (in Antoine et al., 2012, figure 2i, Figure 8.1 ) and 2683–2694 ( Figure 8.3, 8.5, 8.8 ), right m1s ; MUSM 2695–2703 ( Figure 8.6 ), left m2s ; MUSM 1877 (in Antoine et al., 2012, figure 2h), 1914–1915 ( Figures 4.2-3 , 8.9 -10) and 2704–2710 ( Figure 8.2, 8.4 ), right m2s ; MUSM 2711 , left m3 ; MUSM 1876 (in Antoine et al., 2012, figure 2g) and 2712–2714, right m3s ( Figures 4.1 , 8.7 ) ; MUSM 1875 , dP3 or P3 (in Antoine et al., 2012, figure 2f) ; MUSM 1874 (in Antoine et al., 2012, figure 2e) and 2715–2717, left dP4s ; MUSM 2718–2723 , right dP4s ; MUSM 2724 , left P4 ; MUSM 1873 (in Antoine et al., 2012, figure 2d) and 2725–2729, right P4s ; MUSM 1872 (in Antoine et al., 2012, figure 2c) and 2730–2738, left M1s ; MUSM 2739–2746 , right M1s ; MUSM 2747–2750 , left M2s ; MUSM 2751–2757 , right M2s ; MUSM 2758–2761 , left M3s ( Figure 4.6 ) ; MUSM 1870 , right M3 (in Antoine et al., 2012, figure 2a) .

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

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

Diagnosis sensu Antoine et al. (2012, p. 1321). Cachiyacuy contamanensis (body mass estimated at 80–120 g) is ~30% larger than C. kummeli . Differs from C. kummeli in having upper molars with labial cusps and styles generally more marked and lower molars sometimes developing accessory enamel crests.

Description. The dp4 is about twice as long as wide, and it has a talonid wider than the trigonid ( Antoine et al., 2012, figure 2k; Figure 4.5 ). The main cuspids are easily recognizable, but the protoconid and metaconid are slightly smaller than the hypoconid and entoconid. There is neither distinct anteroconid on the metalophulid I nor hypoconulid on the posterolophid. The mesial margin of the crown is rounded and formed by a curved metalophulid I. This cristid links the metaconid to the protoconid. The protoconid develops a short posterior arm, which extends lingually. The latter can reach the labial base of the metaconid (= metalophulid II) or not (MUSM 2663, 2665, 2670 [ Figure 4.5 ], and 2673). Another cristid, stemming from the metaconid or its posterior arm, can participate to the formation of the second transverse cristid (MUSM 2663, 2665, and 2673). The mesostylid is well-developed and nearly as large as the protoconid. The mesostylid can be lingually isolated between the entoconid and metaconid or connected to the metaconid notably at a late wear stage (MUSM 2663, 2670, and 2669). Centrally, there is a mesolophid situated between the mesostylid and the distal ectolophid. The mesolophid is not strongly connected to these structures and can also be reduced (MUSM 2670; Figure 4.5 ). The majority of dp4s shows a long mesial ectolophid, mesially longitudinally oriented, and distally linguodistally directed. It connects the protoconid to the mesolophid and the distal ectolophid. However, on some dp4s (MUSM 1880, 2464, and 2671), it appears composed of different structures. On MUSM 2464 and 2671 for instance, there are two cristulids: one is linguodistally directed, stemming from the mesolophid-distal ectolophid junction, and another one is longitudinal, separate from the first and the protoconid by tiny notches. On MUSM 1880, the second cristulid (longitudinal one) is also found while the first (linguodistally directed) corresponds here to a large cuspid displaying anterior and posterior arms. That cuspid may be interpreted as a neomesoconid-like cuspid. Accessory enamel wrinkles occur between the second transverse cristid and the mesolophid on most dp4s. The distal ectolophid is very short and links the hypolophid to the mesolophid labially. The hypoconid and entoconid are labiolingually opposed and linked together by a long transverse hypolophid, which connects a short and thin anterior arm of the hypoconid. On two dp4s (MUSM 2670 [ Figure 4.5 ] and 2671), the anterior arm of the hypoconid is low in its middle part and thus appears composed of two cristulids: a mesial one from the ectolophid and a distal one from the hypoconid. The distal margin of the crown is circular and formed by a strong posterolophid, which can be connected to the posterior arm of the entoconid. The posterolophid and hypolophid isolate a broad metaflexid/metafossettid.

The p4s differs substantially from dp 4 in having a talonid significantly wider than the trigonid, and in being as long as large (in Antoine et al., 2012, figure 2j; Figure 4.4 ). The main cuspids are equally sized and salient. Mesially, the metalophulid I is well-elevated and labiolingually straight. The second transverse cristid is complete and continuous on the most specimens (but most are worn). It extends from the protoconid to the mesostylid, which is faintly distinct, being merged with the posterior arm of the metaconid. Two p4s (MUSM 1879 [in Antoine et al., 2012, figure 2j; Figure 7.4 ] and 2678 [ Figures 4.4 , 7.5 ]) show a complex pattern of the second transverse cristid. On these p4s, this cristid is divided into three parts: two labial and a lingual one. The more mesial and labial part, stemming from the protoconid, corresponds to the posterior arm of the protoconid. The second labial part is more reduced, notably on MUSM 1879, and may be a residual branch of the mesolophid (labial part) because it is connected to a distinct but low mesoconid (on MUSM 2678), which occupies a more central position than on dp4. The homology of the lingual part stemming from an isolated mesostylid is more obscure (probably a neomesolophid). From its cuspid connections, its position and shape, the continuous second transverse cristid of other p4s (e.g., MUSM 2674, Figure 7.1 ) is probably a fusion of the first labial part with the lingual one found in MUSM 1879 ( Figure 7.4 ) and 2678 ( Figures 4.4 , 7.5 ). MUSM 2678 is very particular because it shows a very low cristulid (a neostructure?) between the hypolophid and the second cristid. It appears divided with a lingual part lingually connected to a small cuspid (neostructure too?) and a labial part that reaches the base of the ectolophid. Two other p4s (MUSM 2676 [ Figure 7.2 ] and 2677 [ Figure 7.3 ]) display fragments of that cristulid. On all p4s, the hypolophid is complete and joins the short and thin anterior arm of the hypoconid. The posterolophid is strongly developed and connects a strong and short posterior arm of the entoconid. There is no trace of hypoconulid.

The lower molars (m1–3) share the same dental structure (in Antoine et al., 2012, figure 2g-i; Figure 4.1-3 ). The m1s are clearly smaller than m2s, and m3s are of the same size or smaller than m2s. The m3s are characteristic in having a small entoconid, which is more labial in position to the metaconid and in showing a distal expansion of the posterolophid ( Figure 4.1 ). The occlusal pattern is similar from m1 to m3 and strongly reminiscent of that of p4. Molars differ from p4s in being much more quadrate, and in showing a strong development of the posterior arm of the metaconid (metastylar fold), which is directed to a small but well distinct mesostylid. The posterior arm of the metaconid and mesostylid are connected (twinned) or separated by a tiny and shallow notch. In contrast, a deep and narrow furrow usually separates the mesostylid from the entoconid. Mesially, at the base of the crown, there is no trace of anterocingulid. The metaconid and protoconid are labiolingually opposed and linked by a straight and welltrenchant metalophulid I. The second transverse cristid is somewhat difficult to describe inasmuch as it appears highly variable ( Figure 8 ). On some teeth, this cristid is formed by a posterior arm of the protoconid, which is connected to the mesostylid or the posterior arm of the metaconid (= metalophulid II; Figure 8.5 ). However, the posterior arm of the protoconid can also be short in some cases ( Figure 8.2, 8.7-8 ). On some other molars ( Figure 8.1, 8.3, 8.9 -10), like on p4s, it may appear as a composite of two cristids that merge together: one being a short posterior arm of the protoconid (lingually directed), and the other being a short cristid stemming from the mesostylid (labially directed, = neomesolophid). These two cristids can be often disjoined ( Figure 8.7-8 ). On some molars, there is a neomesolophid and no posterior arm of the protoconid or a very short one (e.g., MUSM 2708, Figure 8.4 ). In many cases, a longitudinal accessory enamel cristulid may occur, joining the second transverse cristid to the metalophulid I ( Figure 8.3, 8.9 -10). Like on p4s, some lower molars (MUSM 1914, 1915, 2689, 2692, 2701, 2708, and 2714; Figures 4.2-3 , 8.5 -10) display an accessory “third” transverse cristulid and/or a small lingual cuspid, (neostructures?). In MUSM 1914 ( Figures 4.2 , 8.10 ), that “third” cristulid is long but interrupted. Its lingual part is connected to the small lingual cuspid and remains labially free. Its shorter labial part is labially linked to the hypolophid. Also on this tooth occurs a short longitudinal enamel wrinkle that bridges the second and third transverse cristids. On two lower molars (MUSM 1915 [ Figures 4.3 , 8.9 ] and 2689 [ Figure 8.8 ]), there is a fragment of cristulid that could be the labial part of a mesolophid. On MUSM 1915, there are two labial cristulids situated between the second transverse cristid and the hypolophid, one stemming from the ectolophid (but without mesoconid) and the other from the hypolophid. The first might be a fragment of the mesolophid. On MUSM 2689, there is a short cristulid distolabially directed, linked to the lingual part of the second transverse cristid and labially free. It might be a fragment of the mesolophid or the “third” transverse cristulid. On all molars, the hypoconid and entoconid are labiolingually opposed and linked by a long and straight hypolophid, which connects labially a short, but strong anterior arm of the hypoconid (absence of taeniodont pattern). Many lower molars have a minute mesoconid, located directly mesial to the labial extremity of the hypolophid. On these lower molars, there is no trace of mesolophid stemming from the mesoconid. The entoconid can display anterior and posterior arms. When it is present, the anterior arm of the entoconid is thin and faintly visible, contrary to the posterior arm (usually stronger, except on MUSM 2708 [ Figure 8.4 ]). The hypoconid is slightly mesiodistally compressed. A strong and curved posterolophid connects the hypoconulid but not the posterior arm of the entoconid, which is separate from the posterolophid by a narrow and shallow notch. However, in some teeth showing an advanced degree of wear, the posterolophid can be connected to the posterior arm of the entoconid. The anteroflexid and metaflexid are wide.

As for the lower dentition, all the dental loci are documented for the upper dentition.

Only one specimen of DP3 is available (MUSM 1875; in Antoine et al., 2012, figure 2f). It is a single-rooted, peg-like tooth, with a circular outline. On the occlusal surface, there are two crests and two cusps. The higher crest connects both cusps.

We identify as dP4s trapezoidal teeth that show their labial crown margin longer than their lingual one (in Antoine et al., 2012, figure 2e). These teeth are brachydont and exhibit a pentalophodont pattern with transverse crests that are moderately elevated. The main cusps (protocone, hypocone, paracone, and metacone) remain well-defined. The anteroloph is oblique, directed mesiolabially. Lingually, it connects the mesial border of the protocone, and labially, a distinct parastyle. The parastyle is slightly mesiolingual to the paracone and separate from it by a narrow but deep notch (paraflexus labially open). The labial protoloph is long, oblique, and parallel to the anteroloph, and it connects a short lingual protoloph (= posterior arm of the protocone). As such, the internal sinus (hypoflexus) remains separate from the paraflexus (absence of taeniodont pattern). The protocone is slightly pinched labiolingually and somewhat oblique in position. On some dP4s (MUSM 2720 and 2721), a secondary cusp is present on the distal wall of the paracone. On MUSM 2717, that accessory cusp is neither on the wall of the paracone nor on that of the mesostyle but it is located on the opening of the mesoflexus. On all dP4s, the hypocone is slightly labial to the protocone. Both cusps are equally sized. The hypocone displays a strong, long, and oblique anterior arm, which extends mesially (via a short but complete mure) to join the confluence between the lingual protoloph and the lingual extremity of the labial protoloph. This entire complex delimits the hypoflexus, which appears narrow and deep. The third transverse crest usually connects the mesial extremity of the anterior arm of the hypocone to a strong mesostyle, but this crest often appears as a composite crest including a mesolophule and a mesoloph. The mesolophule is always long, while the mesoloph (when present) is short and either connected or not to the mesolophule. Otherwise, in most specimens, the mesolophule displays in its lingual part a small but well-defined enamel swelling (accessory neocusp). On MUSM 1874 (in Antoine et al., 2012, figure 2e), a tiny accessory cusp is present and twinned to the mesostyle. This accessory cusp displays a short crestule that runs lingually between the protoloph and the central transverse crest, and ends without connection. On all dP4s, the mesostyle is mesiodistally enlarged and often twinned with the metacone. The metacone is distally positioned with respect to the hypocone. These two distal cusps are linked by a strong and complete posteroloph. The fourth transverse crest is a metaloph, which shows a variable development. It is either long, stemming from the metacone (MUSM 1874; in Antoine et al., 2012, figure 2e), or disconnected to that cusp and usually very reduced or even absent (MUSM 2716 and 2718). Generally, the lingual extremity of the metaloph does not reach the anterior arm of the hypocone. It remains free lingually or linked to the mesolophule and/or the posteroloph via thin, short, and longitudinal accessory enamel crestules. On MUSM 2719, there are three structures (crestules and cusps) on the most distal flexus (confluence of the metaflexus and posteroflexus), which may correspond at least in part to the metaloph. One of these structures is labially and lingually connected to the posteroloph, which forms a small and rounded fossette.

In occlusal view, the crown outline of the P4s is oval- to heart-shaped (mesiodistal compression), and as such, these teeth are clearly distinguishable from the dP4s (in Antoine et al., 2012, figure 2d). The anteroloph shows the same connexions (labially with the parastyle and lingually with the protocone) as it does in the dP4s. It is continuous but can be divided in two parts. Its labial part is slightly less elevated than the other transverse crests. Its lingual one is more elevated and corresponds to a long anterior arm of the protocone. The protocone is mesially canted and labiolingually pinched. It develops a long and lingual posterior outgrowth, which is backwardly directed. This outgrowth connects a minute and crestiform hypocone, and entirely closes the hypoflexus lingually as a result. As on dP4s, P4s exhibit the same arrangement of the anterior arm of the hypocone, which connects the protoloph via a complete longitudinal mure. The metacone is crestiform and mesiodistally elongated. Labially, there is a minute and isolated mesostyle, which is separate from the paracone to the metacone. The third transverse crest can be complete: it connects the mesostyle to the mesial extremity of the anterior arm of the hypocone. On MUSM 1873 (in Antoine et al., 2012, figure 2d), the third transverse crest shows a break in its middle part and thus, corresponds to the combination of a mesoloph and a mesolophule. On two specimens (MUSM 2724 and 2725), the third transverse crest is reduced: it lacks its lingual connection with the anterior arm of the hypocone (= mesoloph; MUSM 2724), or its labial one with the mesostyle (= mesolophule; MUSM 2725). On MUSM 2726, the third transverse crest is entirely lacking. When it is present (MUSM 1873 and 2727), a short metaloph, stemming from the metacone, runs lingually. On MUSM 2727, the metaloph is lingually free, while it is connected to the posteroloph via a very short and longitudinal accessory enamel crestule on MUSM 1873 (in Antoine et al., 2012, figure 2d).

The upper molar proportions are similar to those observed for the lower molars (in Antoine et al., 2012, figure 2a–c; Figure 4.6 ). The upper molars (M1–3) share the same dental structure. M1s are significantly smaller than M2s, and M3s appear roughly equal in size to M2s. However, M3s differ substantially from M2s in having a hypocone strongly displaced labially. As for the dP4s, the upper molars are brachydont, fully pentalophodont, and non-taeniodont. On pristine teeth, the five transverse crests (anteroloph, protoloph, mesolophule/mesoloph, metaloph, and posteroloph) are thin and moderately elevated, and the main cusps and styles are well-defined. There is no conule. Lingually, the protocone is massive and slightly labiolingually compressed. It displays a short posterior arm (= lingual protoloph), which connects the long and transverse labial protoloph (absence of taeniodont pattern). The lingual branch of the protoloph is often grooved in its middle part and thus, appears composed of two crestules: a mesial one from the hypocone, and a distal one from the protoloph-mure junction. On M1s, the hypocone is distal and as large as the protocone. On M2s, the hypocone is slightly smaller and also slightly displaced labially. Except on some M3s, the upper molars bear a strong and longitudinal mure, which connects the anterior arm of the hypocone to the protoloph lingually. On the three molar loci, the third transverse crest, strongly developed, links the anterior arm of the hypocone to a strong and well-defined mesostyle, situated in the labialmost margin of the crown. As for dP4s and P4s, this crest seems to be formed by the union of a mesoloph and a mesolophule. The mesoloph is often long, while the mesolophule can be either long, reduced (spur), or absent. The mesostyle is usually remote from the metacone except on five molars (among less worn upper molars; MUSM 2739, 2740, 2744, 2750, and 2759) where it is close but still separated by a narrow and shallow notch. The metaloph is usually present and well-developed, but it can also be reduced, interrupted, or absent on M1–3. It is usually strong on M1s and M2s and reduced on M3s. On M1–2s, the metaloph runs lingually (slightly oblique on M2s) but remains without lingual connection. Accessory, thin and short enamel crestules may lingually connect the metaloph either to the posteroloph or/and to the third transverse crest. On M3s, the metaloph is associated with other crestules stemming from accessory cusps on the posteroloph ( Figure 4.6 ). The hypoflexus is narrow, and its lingual aperture is somewhat mesiodistally constricted. The paraflexus and mesoflexus remain open labially. When the mesostyle and metacone are very close, the metaflexus appears almost labially closed. When the metaloph is lingually connected to the posteroloph, the posteroflexus is divided into two parts: a labial one, which is delimited by the metaloph and posteroloph, and a lingual one, which is delimited by the metaloph, the anterior arm of the hypoconid and lingual end of the posteroloph.

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.