Eomorphippus neilopdykei, Wyss & Flynn & Croft, 2018

Wyss, André R., Flynn, John J. & Croft, Darin A., 2018, New Paleogene Notohippids and Leontiniids (Toxodontia; Notoungulata; Mammalia) from the Early Oligocene Tinguiririca Fauna of the Andean Main Range, Central Chile, American Museum Novitates 2018 (3903), pp. 1-44 : 14-17

Eomorphippus neilopdykei , species novum

Figure 2

HOLOTYPE: SGOPV 2855 , pair of mandibles preserving at least one representative of each lower tooth locus except the canine and p1.

PARATYPE: SGOPV 3071 , a right mandible bearing five or more teeth, apparently m2 and more anterior loci, but only partially prepared .

TYPE LOCALITY: As for Eomorphippus bondi .

AGE: As for Eomorphippus bondi .

ETYMOLOGY: In recognition of Neil Opdyke, for his pioneering research on paleoclimate and plate tectonics, and career-long support of integrative studies of vertebrate paleontology and geology. He fondly recalls serving as a “pack animal” while he was an undergraduate field assistant for Keith Runcorn, making it especially appropriate to name a fossil evoking a “beast of burden” in his honor.

DIAGNOSIS: As for E. obscurus and E. bondi , but differing from those species mainly in much smaller size.

DESCRIPTION: Eomorphippus neilopdykei , identified as “notohippid new taxon B” by Wyss et al. (1994) and as “undescribed taxon B” by Flynn et al. (2003), is currently known only from lower teeth. E. neilopdykei is nearly identical in all comparable morphological details to E. bondi , except that it is much smaller at only slightly greater than half the size of the latter species.

LOWER DENTITION: The partial rami of the fused pair of mandibles making up the holotype have been mildly deformed by tectonic compression, but the teeth are uncracked and otherwise show no evidence of distortion. The left ramus is broken ventral to p2; the portion of the specimen posterior to this disruption has been shifted medially. Slight dorsoventral compression and dislocation of the symphysis has resulted in a pronounced postmortem splaying of the lower incisors. Mensural data are provided in table 1 .

All six lower incisors are preserved. They are chisel shaped and closely spaced, increasing slightly in size from i1–3. Deformation of the specimen has obscured the original arrangement (transverse vs. arcuate) of the incisors. Cingula are absent lingually and labially. The lingual faces of the incisors of SGOPV 3071 bear a subtle, centrally placed ridge, a more subdued version of the condition described for E. obscurus by Simpson (1967). The most striking feature of the incisors in SGOPV 3071 is their strong degree of hypsodonty, with enamel covering the teeth both lingually and labially to levels well below the alveolar border. Breakage of the anterodorsal edge of the symphysis exposes deep portions of the roots of the right incisors, but even here enamel is present.

The canines and p1 are not preserved. The second premolar is better preserved on the left side. It is a simple tooth, dominated by an anterior cusp from which two short, straight crests originate, one trailing posteriorly, and the other anterolabially. The latter terminates at the tip of the strong protoconid ridge. A strong, anteriorly inclined concavity occurs behind the protoconid ridge.

The third premolar (preserved in its entirety on the left side, but consisting of only the talonid portion on the right) is substantially larger and more complex than p2. Reflecting the tooth’s greater length, the median crest is essentially bicrescentic. Both crescents originate from the well-elevated metaconid, the anterior one (convex labially) terminating in a small but distinct, posteromedially projecting paralophid. The anterior end of the posterior crescent joins the metaconid; its posterior end curves medially, encircling the faint indications of an entoconid. The trough behind the protoconid ridge is deeper, more vertical, and more angular than the corresponding structure on p2.

The last premolar represents the next logical step in the progressive molarization of the posterior premolars. It is well preserved on both sides of the specimen. Apart from its smaller size, the clearest distinctions between this tooth and the molars are its relatively short talonid and its connection of the cristid obliqua directly to the metaconid (rather than to the center of the metalophid). The latter condition results in a deeper divide between the trigonid and talonid labially on p4 relative to the molars. The paralophid is well formed, defining a broad trigonid abrasion surface anteriorly. The entoconid is fully developed, wear having reduced it to an anteroposteriorly broad entolophid. Only a small cleft remains separating the entolophid from the metaconid anteriorly, while only a small indentation marks the merger of the entolophid and hypolophid posteriorly.

The molars are all highly similar in form. Only m1 is preserved on the left side, while all three molars occur on the right, although the posterior half of the m3 talonid was lost to an errant rock-saw cut. The first molar is worn to the point that the trigonid and talonid have melded into a single unified occlusal wear surface, divided only slightly by the elevated remnants of the metaconid. The para- and metalophids of m2–3 are separated by a narrow, vertical cleft. A small fossettid is present immediately behind the trigonid on m2, the apparent result of the anterior margin of the entolophid having worn to the level where it coalesces with the remainder of the talonid (i.e., the anterolingual part of the entolophid contacts the posterior part of the metaconid). A deep, lingually opening pocket sets the rear of the entolophid apart from the medially curving hypolophid. The preserved cross section of the m3 talonid reflects the markedly greater length and straighter form of this structure than on m1–2.

DISCuSSION: Despite the scant material currently referable to E. neilopdykei , its diminutive size readily distinguishes it from the most similar species, E. obscurus and E. bondi . Nearly every morphological detail of the lower dentition in E. neilopdykei matches that of E. obscurus and E. bondi , except that E. neilopdykei is much smaller. We are unaware of additional material from Patagonia or the Chilean Andes that is referable to E. neilopdykei or that represents any other taxon with which it might be confused.

Figures

FIGURE 2. Left and right mandibles of holotype of Eomorphippus neilopdykei, SGOPV 2855, preserving Ri1–3, p2–m3 (m3 inadvertently trimmed during preparation), Li1-3, p2–m1, in A, occlusal and B, ventral views. Note hypsodonty of incisors.