Eoespina sp.

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 : 12-13

Eoespina sp.

Figure 5.12 , Appendix 3

2016 Cachiyacuy aff. kummeli Antoine et al. , Supplementary data, p. 5.

2017 Cachiyacuy aff. kummeli Antoine et al. , Supplementary data, p. 9.

Referred material. MUSM 2655, right M2 ( Figure 5.12 ).

Locality. Contamana CTA-51, Loreto Department, Peru.

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

Description. The M2 (MUSM 2655; Figure 5.12 ) is worn but all its occlusal structure is well-recognizable, with a subquadrate outline. The hypocone is slightly displaced labially and smaller than the protocone, thereby indicating that this tetralophodont tooth is a M2. The transverse crests (anteroloph, protoloph, third transverse crest, and posteroloph) are subparallel, with a slightly oblique protoloph. Both the anteroloph and posteroloph are massive and strongly connected to the lingual and labial cusps. The tooth is not taeniodont. The mure is short and almost longitudinal. Labially, there is a large mesostyle, twinned with the metacone and strongly connected to the lingually thinning third transverse crest (therefore interpreted as a mesoloph). A deep and narrow notch separates the mesostyle from the paracone, and thus the mesoflexus remains open labially. The mesoflexus is particularly narrow due to the close proximity of the mesoloph with the protoloph. Labially, the metacone is virtually indistinct and entirely incorporated within the labial posteroloph. The mesial enamel edge of the posteroloph expends mesially, and forms an enamel platform-like surface. This structure might correspond to a relic of the metaloph. The paraflexus and the posteriormost flexus (fused meta- and posteroflexus) are close lingually. The hypoflexus is mesiodistally constricted but remains open.

Comparisons. This specimen has a size comparable to that of teeth of Cachiyacuy kummeli , Canaanimys maquiensis , Eoespina woodi Frailey and Campbell, 2004 , and Eosachacui lavocati Frailey and Campbell, 2004 . Except for Canaanimys , the concerned upper molars have a pattern close to that of MUSM 2655: non-taeniodont and with a metaloph reduced or absent. In Eosallamys , upper molars are non-taeniodont but their metaloph is still present and long. The subquadrate occlusal outline of MUSM 2655 and the strong connections of the anteroloph and posteroloph to the labial cusps, respectively, better match the conditions found in Eoespina . Given the scarcity the available material, we provisionally assign this tooth to Eoespina sp.

Remarks. Following Frailey and Campbell (2004), Eoespina woodi and Eosachacui lavocati , both found at Santa Rosa, are two close taxa sharing many similarities. This is particularly shown in their brachydonty, non-taeniodonty, subquadrate upper molars with rounded corners, and pentalophodont/ tetralophodont upper molars with a very reduced or absent metaloph. Frailey and Campbell (2004, p. 88–91) described seven characters distinguishing both taxa. However, these characters are not found in all specimens referred to each taxon and can result from an intraspecific variation. A taxonomic revision of both taxa would hence be required, notably in considering their possible synonymy. According to Frailey and Campbell (2004, p. 88– 91):

1. Eoespina is slightly smaller than Eosachacui . However, the size range of its dental variation matches that of Eosachacui ;

2. Contrary to Eoespina , upper molars of Eosachacui often display additional spurs or cuspules in their metaflexus. However, this addition of enamel structures is only limited to three specimens (LACM 143292, 143387, and 143401; Frailey and Campbell, 2004, p. 128);

3. In Eosachacui , the deflections of the protoloph are less severe than those observed in Eoespina . These deflections of the protoloph in Eosachacui probably correspond to the obliquity of the protoloph, which is more pronounced (strongly oblique) and tends to be in line with the mure. However, some upper molars of Eosachacui have a transverse protoloph (LACM 143387 and 143388; Frailey and Campbell, 2004, p. 128), while this crest can be slightly oblique in Eoespina (e.g., LACM 143286 and 149436; Frailey and Campbell, 2004, p. 124–125);

4. Contrary to Eosachacui , lower molars of Eoespina display accessory cristulids and cuspids in their anteroflexid. Nevertheless, one lower molar of Eosachacui shows these secondary structures (LACM 143325; Frailey and Campbell, 2004, p. 129). Interestingly, the presence or absence of these structures is also observed in Cachiyacuy contamanensis , but that remains very variable;

5. In lower molars of Eoespina , the second transverse cristid (named “metalophid” by Frailey and Campbell, 2004, p.91) is not uniform either in height or thickness. Indeed, the second transverse cristid appears as a combination of two cristids (i.e., neomesolophid and posterior arm of the protoconid), more or less developed depending on the specimens. From our personal observation of the Santa Rosa specimens figured in Frailey and Campbell (2004, p. 124–130), this apparent composite second cristid in Eoespina is also found in lower molars of Eosachacui ;

6. The second transverse cristid and hypolophid (named “protolophid” in Frailey and Campbell, 2004, p. 91) are mesiodistally closer in Eosachacui than in Eoespina . However, in both genera, these two cristids are variably spaced, which implies a variation of the shape and size of the flexids (anteroflexid and mesoflexid); and

7. Finally, in lower molars of Eosachacui , the hypolophid is transverse or slightly backwardly directed, while it is transverse or slightly forwardly directed in Eoespina . However, as noticed by Frailey and Campbell (2004, p. 91), this character is highly variable.

cf. Eoespina sp.

Figure 4.17 , Appendix 3

Referred material. MUSM 1913 (in Antoine et al., 2012, figure 2f’) and 2802 ( Figure 4.17 ), left M2s; MUSM 1912, right M2 (in Antoine et al., 2012, figure 2e’).

Locality. Contamana CTA-27, Loreto Department, Peru.

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

Description. Only three minute upper molars can be referred to cf. Eoespina sp. (MUSM 1912, 1913, and 2802; in Antoine et al., 2012, figure 2e’-f’; Figure 4.17 ). They have a rounded crown outline in occlusal view. These teeth are primarily tetralophodont with strong and long third transverse crest, antero-, proto-, and posteroloph (no metaloph). The cusps are still well-defined. There is no parastyle. Mesially, a strong anteroloph runs from the protocone to the mesiolabial aspect of the paracone. The teeth are not taeniodont and display a short and longitudinal mure, which is slightly situated lingually to the medial axis of the crown. There is a strong but short anterior arm of the hypocone that connects the mure. The hypocone is more labial and reduced with respect to the protocone. The metacone is mesiodistally elongated and slightly more lingual than the paracone, and it is merged with a strong mesostyle. The paracone and mesostyle are only separate by a narrow but deep notch, and the mesoflexus remains open labially as a result. A strong and continuous third transverse crest runs from the mesial extremity of the anterior arm of the hypocone to the mesostyle. The protoloph and third transverse crest are nearly parallel. On the distolabial region of MUSM 1913 (in Antoine et al., 2012, figure 2f’), it may occur a vestigial metaloph, very low, short, backwardly directed, and practically subsumed within the posteroloph. On all teeth, the hypoflexus is narrow and somewhat constricted lingually.

Comparison. Teeth of this taxon are slightly smaller than those of Canaanimys maquiensis . These three diminutive upper molars from CTA-27 exhibit a tetralophodont/non-taeniodont pattern, with strong and long third transverse crest, antero-, proto-, and posteroloph (no metaloph or very reduced), as it can be observed in “? Vallehermosomys merlinae Vucetich et al., 2010 ,” Sallamys Hoffstetter and Lavocat, 1970 or Eoespina / Eosachacui . The general morphology of these upper teeth from CTA-27, with notably a strong and long posterior arm of the paracone and a rounded crown outline, recall upper molars of E. woodi / E. lavocati . However, these specimens from CTA-27 differ from E. woodi / E. lavocati in having slightly more transverse upper molars, usually characterized by less inflated labial cusps. These upper molars have a longer and more mesially positioned third transverse crest contrary to the condition observed on the M3 of? Vallehermosomys merlinae . Indeed, the latter displays a wider mesoflexus, and displays a third transverse crest that is clearly more displaced distally and close to the posteroloph. These upper molars from CTA-27 also differ from those of Sallamys in being lower-crowned, and in having a stronger third transverse crest, which always connects to the anterior arm of the hypocone.

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.