11. Evaluating the Mitten-Gliding Hypothesis for Paromomyidae and Micromomyidae (Mammalia, “Plesiadapiformes”) Using Comparative Functional Morphology of New Paleogene Skeletons

Teeth of primate-like mammals from the Paleogene (“plesiadapiforms”) have been known for at least 130 years (Gervais, 1877). These fossil taxa are generally recognized as being closely related, but not monophyletic (e.g., Gingerich, 1976; Szalay et al., 1987; Beard, 1993a; Silcox, 2001; Bloch and Boyer, 2002a; Bloch et al., 2007) and we maintain that view here. Thus “plesiadapiforms” are referred to with quotation marks throughout the text to reflect that status. Vertebrate paleontologists have struggled to understand the nature of the phylogenetic relationship of “plesiadapiforms” to the extant and extinct members of crown group Primates [= Euprimates (Hoffstetter, 1977)], since Plesiadapis was first described by Gervais in 1877 (e.g., Lemoine, 1887; Stehlin, 1916; Teilhardde-Chardin, 1922; Gidley, 1923; Simpson, 1935; Russell, 1959; Simons, 1972; Szalay, 1973; Gingerich, 1975, 1976; Szalay et al., 1975; MacPhee et al., 1983; Gunnell, 1989; Kay et al., 1990; Beard, 1993a; Silcox, 2001; Bloch and Boyer, 2002a). The strongest support for a close relationship between “plesiadapiforms” and Euprimates, specifically, has historically come from the excellent fossil record of teeth known for “plesiadapiforms,” first in Europe and then in North America (e.g., Gidley, 1923). Cranial and postcranial fossils were relatively rare and fragmentary initially, such that the first researchers were unable to evaluate the presence of non-dental euprimate features in “plesiadapiforms.” As nondental fossils of “plesiadapiforms” were recovered there was some disagreement as to whether they suggested treeshrew or euprimate affinities. A humerus from the San Juan Basin (at the time attributed to Nothodectes) was figured by Gregory (1920) and interpreted to fit the “tupaioid” pattern. Later, a crushed skull and additional postcranial material associated with that specimen (and now referred to Nannodectes gidleyi Gingerich) was interpreted by Simpson (1935) as being similar to both lemurs and treeshrews. An implication of this acknowledged similarity was that Nannodectes spent time in the trees, as expected for the early forebears of 11. Evaluating the Mitten-Gliding Hypothesis for Paromomyidae and Micromomyidae (Mammalia, “Plesiadapiformes”) Using Comparative Functional Morphology of New Paleogene Skeletons