Comment to “Primates in the Eocene” by Gingerich (2012)

Abstract

In his recent article BPrimates in the Eocene^, Gingerich (2012) presented a broad review of Eocene primate radiations and their place in the primate evolutionary tree, with a particular focus on Adapoidea. While synthetic reviews of early primate evolution are always welcome additions to the literature, within his larger analysis Gingerich (2012) specifically discussed two issues that deserve special comment, the first relating to the evolution of grooming claws within Adapoidea and the second relating to his phylogenetic interpretation of Darwinius and Adapoidea within the order Primates, which was supposedly based on a modification of our own final matrix inMaiolino et al. (2012). Unfortunately, as we will demonstrate below, in both cases the interpretations of Gingerich (2012) are unlikely to be correct. First, Gingerich (2012) characterises the morphology of Notharctus pedal distal phalanges as Bambiguous^. In fact, there is very little ambiguity involved. The analyses provided in Maiolino et al. (2012) demonstrate quite conclusively, both metrically and visually, that pedal distal phalanges bearing grooming claws are readily separated from other unguis forms (ungulae=nails, falculae=non-primate claws, and tegulae= claw-like ungues of callitrichins and aye-ayes) on the basis of facet-shaft angle (FSA), volar feature length (VFL), and other distinctive measures. Univariate and multivariate analyses including FSA and VFL clearly indicate that Notharctus tenebrosus possessed a grooming claw on pedal digit II (Maiolino et al. 2012). To illustrate this point further, a simple bivariate plot of FSA and VFL divided by total phalanx length (TPL) from 512 primate pedal distal phalanges shows the stark distinction between grooming claw and ungula-bearing distal phalanges (Fig. 1). Strepsirrhine and tarsier phalanges that bear grooming claws are well-separated from ungulaand tegula-bearing forms (Fig. 1, dotted line within convex hull surrounding all grooming claws). On the basis of FSA and VFL/TPL, Fig. 1 indicates that Notharctus venticolis (UM 102287), Cantius nuniensis (UM 102193), and Notharctus tenebrosus (AMNH 143612_3 and AMNH 129382) bore grooming claws, confirming the results of Maiolino et al. (2012) for Notharctus tenebrosus and extending them to notharctid pedal morphology, more generally. We note that Gingerich (2012) provides no compelling evidence to the contrary, and the discriminant analyses mentioned by Gingerich (2012) (see also von Koenigswald et al. (2012)) exclude FSA, VFL, VFL/TPL, and other distinctive measures. Until our results are contradicted by a proper study including diagnostic features such as FSA, VFL, and VFL/TPL, the analyses in Maiolino et al. (2012) remain the most comprehensive performed thus far and strongly Electronic supplementary material The online version of this article (doi:10.1007/s12549-015-0184-1) contains supplementary material, which is available to authorized users.