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. 2021 Feb 24;8(2):210050.
doi: 10.1098/rsos.210050.

Earliest Palaeocene purgatoriids and the initial radiation of stem primates

Gregory P Wilson Mantilla  1   2 , Stephen G B Chester  3   4   5 , William A Clemens  6   7 , Jason R Moore  8 , Courtney J Sprain  9 , Brody T Hovatter  10 , William S Mitchell  11 , Wade W Mans  12 , Roland Mundil  13 , Paul R Renne  14   13
Affiliations

Earliest Palaeocene purgatoriids and the initial radiation of stem primates

Gregory P Wilson Mantilla et al. R Soc Open Sci. .

Abstract

Plesiadapiform mammals, as stem primates, are key to understanding the evolutionary and ecological origins of Pan-Primates and Euarchonta. The Purgatoriidae, as the geologically oldest and most primitive known plesiadapiforms and one of the oldest known placental groups, are also central to the evolutionary radiation of placentals and the Cretaceous-Palaeogene biotic recovery on land. Here, we report new dental fossils of Purgatorius from early Palaeocene (early Puercan) age deposits in northeastern Montana that represent the earliest dated occurrences of plesiadapiforms. We constrain the age of these earliest purgatoriids to magnetochron C29R and most likely to within 105-139 thousand years post-K/Pg boundary. Given the occurrence of at least two species, Purgatorius janisae and a new species, at the locality, we provide the strongest support to date that purgatoriids and, by extension, Pan-Primates, Euarchonta and Placentalia probably originated by the Late Cretaceous. Within 1 million years of their arrival in northeastern Montana, plesiadapiforms outstripped archaic ungulates in numerical abundance and dominated the arboreal omnivore-frugivore niche in mammalian local faunas.

Keywords: Cretaceous–Palaeogene boundary; Purgatoriidae; frugivory; plesiadapiforms; primates.

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Figures

Figure 1.
Figure 1.
(a) Location map showing the study area in northeastern Montana, USA. Fort Peck Reservoir is shown in grey. Circles show locations of localities discussed here including Harley's Point and Garbani Channel. The location of the Hell Creek type section, Flag Butte, is also shown. (b) Stratigraphy of a composite section compiled from the most proximal outcrops to Harley's Point locality (shown in electronic supplementary material, figure S1b). Ages shown were determined in [26], for details see the electronic supplementary material.
Figure 2.
Figure 2.
Purgatorius from Harley's Point (Pu1) and Garbani Channel (Pu3) localities of northeastern Montana, USA. Images are three-dimensional surface renderings derived from µCT scans: P. janisae in stereo occlusal, buccal, lingual, mesial and distal views (a,e,f,i,j) UCMP 150018, right m1 and (b,g,h,k,l) UCMP 192398, left m3; P. mckeeveri sp. nov. in stereo occlusal, buccal and lingual views (c,d,m) UCMP 157977 (holotype), incomplete right dentary with p4–m2, (n,q,t) UCMP 111586, incomplete left dentary with m1–2, (o,w,x) UCMP 189505, incomplete left dentary with m2–3 and in stereo occlusal, buccal, lingual, mesial and distal views (p,r,s,u,v) UCMP 150021, left m2; and Purgatorius cf. P. mckeeveri in stereo occlusal, buccal and lingual views (y,aa,bb) UCMP 150019, right M2, and (z,cc,dd) UCMP 150020, right M2.
Figure 3.
Figure 3.
Taxonomic diversity and dental morphospace of early Palaeocene plesiadapiforms versus archaic ungulates. (a) Species richness and (b) relative abundances of plesiadapiforms (stars) and archaic ungulates (plus signs) in mammalian local faunas from northeastern Montana, USA. Data are from [12,28,30] and are provided in the electronic supplementary material. (c) PC1 versus PC2 plot of two-dimensional geometric morphometric analysis of lower molars illustrating dental morphospace occupancy of Lancian and early Puercan (Pu1) therians from northeastern Montana with additional plesiadapiforms from later in the Puercan (Pu3) and the early Torrejonian (To1) NALMA subintervals. Purgatorius ceratops (cer) = ?Pu1; P. janisae (jan) and P. mckeeveri (mck) = Pu1 and Pu3; and P. unio (uni) and Ursolestes perpetior (Urs) = Pu3. Data are from [31] and this study. The specimen list is provided in the electronic supplementary material.
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