Mammalia, Multituberculata) from Near Calgary, Southwestern Alberta, Canada
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Canadian Journal of Earth Sciences First mammal from the Willow Creek Formation: a new, early Paleocene ptilodontid (Mammalia, Multituberculata) from near Calgary, southwestern Alberta, Canada Journal: Canadian Journal of Earth Sciences Manuscript ID cjes-2020-0151.R2 Manuscript Type: Article Date Submitted by the 26-Jan-2021 Author: Complete List of Authors: Scott, Craig S.; Royal Tyrrell Museum of Palaeontology, Preservation and Research Keyword: Multituberculate,Draft Paleocene, Puercan, Alberta, Willow Creek Formation Is the invited manuscript for consideration in a Special Not applicable (regular submission) Issue? : © The Author(s) or their Institution(s) Page 1 of 58 Canadian Journal of Earth Sciences 1 First mammal from the Willow Creek Formation: a new, early Paleocene ptilodontid 2 (Mammalia, Multituberculata) from near Calgary, southwestern Alberta, Canada 3 4 Craig S. Scott 5 6 Royal Tyrrell Museum of Palaeontology, P. O. Box 7500, Drumheller, Alberta, T0J 0Y0, 7 CANADA 8 Ph: 403-820-6219 9 Fax: 403-823-7131 10 [email protected] 11 Draft 12 13 14 15 16 17 18 19 20 21 22 23 1 © The Author(s) or their Institution(s) Classification: Protected A Canadian Journal of Earth Sciences Page 2 of 58 24 First mammal from the Willow Creek Formation: a new, early Paleocene ptilodontid 25 (Mammalia, Multituberculata) from near Calgary, southwestern Alberta, Canada 26 27 Craig S. Scott 28 29 Abstract: 30 Although multituberculates are among the best-represented mammals of the Late Cretaceous and 31 early Paleogene in North America, their evolution during the first several tens to hundreds of 32 thousands of years following the Cretaceous-Paleogene (K-Pg) impact event is largely obscure. 33 A better understanding of the early Paleogene record of multituberculates is crucial, for their 34 dominance in early Paleocene mammalianDraft faunas is unquestionably a result of rapid evolution 35 during the immediate post-impact interval, and they accordingly played an important role in the 36 evolution of mammalian communities more generally. I report on a new multituberculate from 37 the early Paleocene of southwestern Alberta, in rocks of the Willow Creek Formation, the first 38 such occurrence in this otherwise poorly known unit. The new multituberculate, Aenigmamys 39 aries, most closely resembles the ptilodontid Kimbetohia campi in comparable parts of the 40 dentition, and sheds light on the early evolution of Ptilodontidae, one of the major cimolodontan 41 families that diversified during the Paleocene. The presence of Aenigmamys in mammalian 42 faunas that lived soon after the K-Pg boundary implies a still-deeper evolutionary history for 43 Ptilodontidae that may have extended into the Late Cretaceous. Aenigmamys is part of a new 44 mammalian fauna from southwestern Alberta, the taxonomic composition of which includes a 45 diversity of multituberculates, cimolestans, primates, and condylarths. The fauna correlates with 46 those of middle Puercan age from other parts of the Western Interior of North America, and its 2 © The Author(s) or their Institution(s) Classification: Protected A Page 3 of 58 Canadian Journal of Earth Sciences 47 high taxonomic diversity further corroborates previous hypotheses that multituberculate 48 recovery–and mammalian recovery more generally–occurred relatively quickly after the K-Pg 49 extinction event. 50 51 Keywords: Multituberculata, Ptilodontidae, Puercan, Paleocene, Alberta 52 53 Résumé: 54 55 56 Introduction 57 The fossilized remains of mammals thatDraft lived during the first several hundred thousand years 58 after the Cretaceous-Paleogene (K-Pg) impact event, during the Puercan North American Land 59 Mammal Age (NALMA), are known almost exclusively from localities in the Western Interior of 60 North America (Cifelli et al. 2004; Lofgren et al. 2004). While this record is the most nearly 61 complete of anywhere in the world, much of what is known about mammalian faunal recovery 62 following the extinction event comes from but a handful of key localities, and although the 63 number and quality of localities have improved considerably in recent years (e.g., Fox et al. 64 2014; Dahlberg et al. 2016; Fuentes et al. 2019; Lyson et al. 2019;), the record overall remains 65 poor when compared to those from the preceding Lancian and succeeding Torrejonian 66 NALMAs. A better understanding of this record is important, as the K-Pg mass extinction 67 induced both a reorganization of terrestrial ecosystems and significant biotic turnover, and set the 68 stage for adaptive radiations in several major vertebrate clades. Although debate continues over 69 the timing and tempo of their diversification after the extinction event, there is little argument 3 © The Author(s) or their Institution(s) Classification: Protected A Canadian Journal of Earth Sciences Page 4 of 58 70 that among the beneficiaries of the selective nature of extinctions at the K-Pg boundary were 71 early Paleocene mammals (see, e.g., dos Reis et al. 2012; O’Leary et al. 2013; Beck and Lee 72 2014; Halliday et al. 2016, 2017; Fuentes et al. 2019). The demise of all non-avian dinosaurs 73 opened a significant number of previously occupied ecological niches, allowing mammals to 74 flourish during the Cenozoic (Archibald 1982; Archibald and Lofgren 1990; Lofgren 1995; 75 Clemens 2002; Archibald and Rose 2005; Wilson 2014; Sprain et al. 2015; Smith et al. 2018). 76 Of the mammals that survived the extinction, multituberculates are among the best 77 represented and best studied. Estimates of extinction and origination rates prior to and after the 78 impact vary (e.g., Archibald and Lofgren 1990; Wilson et al. 2012; Wilson 2014; Pires et al. 79 2018), but multituberculates generally achieved a modest level of taxonomic diversity during the 80 later parts of the Cretaceous, experiencedDraft reduced origination and diversification at the 81 extinction event (and the elimination of several higher-level taxa), and briefly radiated during the 82 early Paleogene before finally going extinct in the late Eocene (Krause 1986: fig. 1; Weil and 83 Krause 2008; Pires et al. 2018). Multituberculate survival across the K-Pg boundary–inferred 84 primarily from well-sampled, fossiliferous sections in northeastern Montana and southwestern 85 Saskatchewan–appears to have been restricted primarily to species of Mesodma Jepsen, 1940 and 86 Cimexomys Sloan and Van Valen 1965, and at least two additional neoplagiaulacids 87 (Parectypodus Jepsen, 1930 and Neoplagiaulax Lemoine, 1882 have been identified from a few 88 Lancian localities; Archibald 1982; Storer 1994). These Late Cretaceous survivors co-occur in 89 the early Puercan with several supposed immigrant multituberculates in local faunas (e.g., the 90 eucosmodontid Stygimys Sloan and Van Valen, 1965 and the taeniolabidoid Valenopsalis 91 Williamson et al., 2016). Because of the density of their fossil record, multituberculates have 92 figured importantly in understanding mammalian evolution during the first several hundred 4 © The Author(s) or their Institution(s) Classification: Protected A Page 5 of 58 Canadian Journal of Earth Sciences 93 thousand years following the K-Pg extinction (e.g., Wilson et al. 2012; Wilson 2014; Pires et al. 94 2018). 95 I report herein on a new multituberculate from the Willow Creek Formation of 96 southwestern Alberta, a rock unit that has until relatively recently been regarded as poorly 97 fossiliferous, particularly the upper, Paleocene part. The new multituberculate, Aenigmamys 98 aries gen. et sp. nov., sheds light on the early evolution of Ptilodontidae, one of the major 99 cimolodontan families that diversified during the Paleocene (Weil and Krause 2008). The 100 specimens are noteworthy for their excellent preservation, with much of the dentition known 101 from articulated remains. Aenigmamys is part of a newly discovered mammalian local fauna that 102 existed in southwestern Alberta during the Puercan NALMA; this fauna is taxonomically 103 diverse, further corroborating previous hypothesesDraft that multituberculate recovery–and 104 mammalian recovery more generally–occurred relatively quickly after the K-Pg extinction event 105 (e.g., Archibald 1982; Johnston and Fox 1984; O’Leary et al. 2013; Wilson 2013, 2014; Halliday 106 et al. 2016; Pires et al. 2018). 107 108 Geological setting and locality 109 Geological Setting and Formational Nomenclature: Specimens described in this paper were 110 collected at outcrops of the Willow Creek Formation south of Calgary and east of Okotoks in 111 southwestern Alberta (Fig. 1). The formation, together with the laterally equivalent Scollard and 112 Coalspur formations of the central Plains and central Foothills, respectively, forms the upper 113 parts of an eastward-thinning clastic wedge of primarily fluvial sediments that were deposited in 114 the foreland basin during the latest parts of the Cretaceous and early parts of the Paleocene 115 (Jerzykiewicz 1997: figs. 1, 2; Hamblin 2010: fig. 1). The Willow Creek Formation was first 5 © The Author(s) or their Institution(s) Classification: Protected A Canadian Journal of Earth Sciences Page 6 of 58 116 described by Dawson (1883) for rocks exposed on Willow Creek south of Calgary; Williams and 117 Dyer (1930) defined the type section based on exposures at the mouth of the creek east of Fort 118 McLeod. The formation forms a strongly asymmetrical wedge that becomes thicker westwards, 119 from approximately 320 m in the plains to in excess of 1000 m in the southwestern corner of the