A ‘giant’ purgatoriid (Plesiadapiformes) from the Paleocene of Montana, USA: mosaic evolution in the earliest primates

Abstract

Ursolestes perpetior gen. et sp. nov. is a large purgatoriid plesiadapiform primate from the middle/late Puercan (earliest Paleocene) Simpson Quarry, Montana, USA. It differs from Purgatorius Van Valen and Sloan, 1965, the only other known purgatoriid and the oldest discovered primate, in its substantially larger body size as inferred from the dimensions of the known parts of its dentition, while resembling Purgatorius in possessing a large lower canine, unreduced p1, and in the upper molars, a protocone twist and weakly developed postprotocone fold; moreover, the m3 of U. perpetior possesses an expanded, plesiadapiform-like posterior lobe of the talonid that supports the hypoconulid. The large lower canine and the greater development of trenchant molar crests suggest that U. perpetior was more insectivorous, differing appreciably from the omnivorous niche long hypothesized for Purgatorius and purportedly marking the insectivore-primate transition. Hence, U. perpetior adds significant new knowledge regarding the breadth of the adaptive zone occupied by purgatoriids in their position at the very beginnings of primate evolution.

The evolutionary radiation of plesiadapiforms

“…F) are of early Paleocene age (Fox & Scott, ), implying that there is no unambiguous direct evidence that primates ever overlapped in time with non‐avian dinosaurs. However, since there is now a range of purgatoriid morphologies known from early Paleocene deposits (Fox & Scott, ; Fox, Scott, & Buckley, ; Scott, Fox, & Redman, ), it seems likely that the group originated close to the K‐Pg boundary (Silcox, ; Fox et al, ). Purgatoriids generally come out at the base of the primate tree, without special relationships to any other family, excepting possibly Micromomyidae (Bloch et al, ; Silcox, , ; Silcox et al, ; Chester et al, ).…”

“…This has particularly been argued for P. pinecreeensis , which is apparently lower‐crowned with more swollen molar cusps than other species of the genus (Scott et al, ). The only other genus in the family, Ursolestes , is notably larger (944 g) and has been interpreted to exhibit more shearing potential (Fox et al, ). This could imply some measure of folivory, (but probably not insectivory, since no modern primate at that body mass is predominantly insectivorous) (Kay, ).…”

Contextualising primate origins – an ecomorphological framework

“…The earliest most primitive putative plesiadapiform taxa ( Pandemonium , Purgatorius , Ursolestes ) are from the earliest Palaeocene of North America and Canada (Clemens, ; Fox et al. , ), although another primitive‐looking plesiadapiform ( Asioplesiadapis ) is known from the early Eocene of China (Fu et al. ), implying the existence of less derived plesiadapiforms on that continent as well (Silcox, ).…”

“…Plesiadapiforms are currently known from North America, Europe, Asia, and possibly Africa, but with a strong emphasis on North America and Western Europe (Silcox, 2008;Fleagle, 2013). The earliest most primitive putative plesiadapiform taxa (Pandemonium, Purgatorius, Ursolestes) are from the earliest Palaeocene of North America and Canada (Clemens, 2004;Fox et al 2014Fox et al , 2015, although another primitive-looking plesiadapiform (Asioplesiadapis) is known from the early Eocene of China (Fu et al 2002), implying the existence of less derived plesiadapiforms on that continent as well (Silcox, 2008). The results of optimisation of areas of origins over phylogenies can vary substantially depending on dataset, phylogeny, and method of analysis .…”

A new species of the basal plesiadapiform Purgatorius (Mammalia, Primates) from the early Paleocene Ravenscrag Formation, Cypress Hills, southwest Saskatchewan, Canada: further taxonomic and dietary diversity in the earliest primates

“…These features of the dentition have been thought to reflect the results of an adaptive shift from reliance on insects as a primary food resource toward a greater incorporation of plant tissues, such as fruit and seeds, in the diet (Szalay 1968(Szalay , 1969Kay and Cartmill 1977;Silcox and Gunnell 2008). The timing of this shift is uncertain: traditionally, it has been thought to occur soon after the K-Pg extinction horizon, but with increased knowledge of the diversity of primitive plesiadapiforms and the ghost lineages that this diversity requires, it seems likely to have already begun in the Late Cretaceous (Clemens 2004;Fox 2011;Fox and Scott 2011;Fox et al, 2015). Moreover, the recent discovery of several isolated, possible plesiadapiform tarsals from the early Paleocene of Montana suggests that the change from an insectivorous to a more omnivorous diet may have occurred concurrently with adaptation to an arboreal environment (Chester et al 2015) D r a f t For many years, the record of the earliest and most basal plesiadapiforms consisted only of Purgatorius unio Van Valen and Sloan, 1965, based on a small sample of isolated teeth from the late Puercan (Pu3) Purgatory Hill locality of Montana.…”