Primate tarsal bones from Egerkingen, Switzerland, attributable to the middle Eocene adapiform Caenopithecus lemuroides.

Erik R Seiffert,Loïc Costeur,Doug M Boyer

doi:10.7717/peerj.1036

Erik R Seiffert, Loïc Costeur + Show 1 more

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https://doi.org/10.7717/peerj.1036

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Abstract

The middle Eocene species Caenopithecus lemuroides, known solely from the Egerkingen fissure fillings in Switzerland, was the first Paleogene fossil primate to be correctly identified as such (by Ludwig Rütimeyer in 1862), but has long been represented only by fragmentary mandibular and maxillary remains. More recent discoveries of adapiform fossils in other parts of the world have revealed Caenopithecus to be a biogeographic enigma, as it is potentially more closely related to Eocene adapiforms from Africa, Asia, and North America than it is to any known European forms. More anatomical evidence is needed, however, to provide robust tests of such phylogenetic hypotheses. Here we describe and analyze the first postcranial remains that can be attributed to C. lemuroides—an astragalus and three calcanei held in the collections of the Naturhistorisches Museum Basel that were likely recovered from Egerkingen over a century ago. Qualitative and multivariate morphometric analyses of these elements suggest that C. lemuroides was even more loris-like than European adapines such as Adapis and Leptadapis, and was not simply an adapine with an aberrant dentition. The astragalus of Caenopithecus is similar to that of younger Afradapis from the late Eocene of Egypt, and parsimony and Bayesian phylogenetic analyses that include the new tarsal data strongly support the placement of Afradapis and Caenopithecus as sister taxa to the exclusion of all other known adapiforms, thus implying that dispersal between Europe and Africa occurred during the middle Eocene. The new tarsal evidence, combined with previously known craniodental fossils, allows us to reconstruct C. lemuroides as having been an arboreal and highly folivorous 1.5–2.5 kg primate that likely moved slowly and deliberately with little or no capacity for acrobatic leaping, presumably maintaining consistent powerful grasps on branches in both above-branch and inverted postures.

Highlights

Caenopithecus is a phylogenetically and biogeographically enigmatic adapiform primate whose fossil record is restricted to middle Eocene (Lutetian, ∼43 Ma, MP13b) fissureHow to cite this article Seiffert et al (2015), Primate tarsal bones from Egerkingen, Switzerland, attributable to the middle Eocene adapiform Caenopithecus lemuroides
On the basis of articular compatibility of the astragalus (NMB En.270) with the calcaneus Naturhistorisches Museum Basel (NMB) Eh 719, as well as the similar size, color, preservation, and peculiar morphology of all three calcanei (i.e., NMB Eh 719, En.268, and En.269), we consider it highly probable that all of the tarsals described here belong to the same species, and so are likely to derive from the same fissure that Eh 719 was recovered from (i.e., fissure γ, where the two relatively large adapiforms C. lemuroides and Leptadapis priscus occur; note that Dagosto (1986), was unaware that remains of L. priscus have been recovered from fissure γ, and so thought that the much smaller species Microadapis sciureus was the only other option for attribution)
Using a more conservative metric, the minimum number of C. lemuroides individuals represented in the Egerkingen γ collection is six, while the minimum number of L. priscus individuals represented in Egerkingen γ collection is two

Summary

Introduction

Caenopithecus is a phylogenetically and biogeographically enigmatic adapiform primate whose fossil record is restricted to middle Eocene (Lutetian, ∼43 Ma, MP13b) fissureHow to cite this article Seiffert et al (2015), Primate tarsal bones from Egerkingen, Switzerland, attributable to the middle Eocene adapiform Caenopithecus lemuroides. Upper molars of the type and only species, Caenopithecus lemuroides, were described by Rutimeyer (1862), and later Stehlin (1916) described parts of the lower dentition, mandible, additional parts of the upper dentition, and the orbital region. These limited remains show that C. lemuroides was a relatively large adapiform—having second lower molars that are about the same length as those of the extant lemurids Eulemur fulvus and Prolemur simus (Kay et al, 2004)—and had a fused mandibular symphysis, large canine teeth, very small P2/2, simple P3−4/3−4, quadrate upper molars with distinct hypocones and mesostyles, and narrow lower molars with elongate crests and well-developed metastylids. Analysis of lower molar shearing crests suggests that C. lemuroides was a dedicated folivore (Kay et al, 2004)

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