Journal of Paleontology, 92(5), 2018, p. 896–910 Copyright © 2018, The Paleontological Society 0022-3360/18/0088-0906 doi: 10.1017/jpa.2018.2


A new, diminutive species of Catopsalis (Mammalia, Multituberculata, Taeniolabidoidea) from the early Paleocene of southwestern Alberta, Canada


Craig S. Scott,1 Anne Weil,2 and Jessica M. Theodor3


1Royal Tyrrell Museum of Palaeontology, P.O. Box 7500, Drumheller, Alberta, Canada T0J 0Y0 ⟨craig.scott@gov.ab.ca⟩ 2Oklahoma State University Center for Health Sciences, Department of Anatomy and Cell Biology, Oklahoma State University, Tulsa, Oklahoma,


USA 74107-1898 ⟨anne.weil@okstate.edu⟩ 3Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada T2N 1N4 ⟨jtheodor@ucalgary.ca⟩


Abstract.—Multituberculates were among the most taxonomically diverse mammals of the early Paleocene, having survived the catastrophic Cretaceous-Paleogene mass extinction and radiating soon thereafter. Although their evolution during the early Paleocene saw the advent of increasingly specialized dentitions, multituberculates generally remained small, rarely exceeding body sizes greater than those of extant rabbits. A conspicuous exception is the Taeniolabidoidea, a primarily North American clade whose members include the largest multituberculates yet discovered. Taeniolabidoidea includes several genera, with one of these, Catopsalis, being speciose and geographically wide ranging. Until recently, the chronological succession of Catopsalis appeared to document a trend of increasing body size. We report here on a new species of Catopsalis from the early Paleocene of Alberta that violates this trend and suggests that the evolutionary history of Catopsalis is considerably more complex. Catopsalis kakwa new species is not only the smallest species of Catopsalis, but is the smallest taeniolabidoid so far discovered, with an estimated body mass between 400 g and 660 g. In contrast to previous studies, we used recently proposed regressions based on lower cheek tooth row length to estimate body masses for North American taeniolabidoids. Our results propose more modest body mass estimates, particularly for the largest taeniolabidoids. The occurrence of C. kakwa n. sp. in the late early Paleocene implies either a significant ghost lineage, or reversal of several characters, including body size, during the latter part of the early Paleocene; the more likely of these scenarios must await a better understanding of the phylogenetic position of C. kakwa n. sp.


UUID: http://zoobank.org/66d85345-49b8-4a46-ba6e-a4d4369cb3e0 urn:lsid:zoobank.org:pub:AF7A5659-9068-4F2F-A6EC-5522A2BBA4CB


Introduction


The Taeniolabidoidea is a clade of multituberculates known from the Late Cretaceous to Eocene of North America and eastern Asia (e.g., Cope, 1882, 1884; Matthew and Granger, 1925; Russell, 1926; Matthew et al., 1928; Granger and Simpson, 1929; Gazin, 1939; Sloan and Van Valen, 1965; Chow and Qi, 1978; Middleton, 1982; Johnston and Fox, 1984; Wilson, 1987; Miao, 1988; Simmons, 1987; Buckley, 1995; Lucas et al., 1997; Williamson et al., 2015), and includes the largest multi- tuberculates so far discovered, e.g., Taeniolabis taoensis (Cope, 1882) from the early Paleocene of New Mexico, thought to have approached the size of extant beavers (Weil andKrause, 2008, but see also Williamson et al., 2015 for a contrasting opinion). The taxonomic composition of Taeniolabidoidea has varied, but results of recent studies suggest that the superfamily minimally contains four North American genera (Valenopsalis Williamson et al., 2015, Catopsalis Cope, 1882, Kimbetopsalis Williamson et al., 2015, and Taeniolabis Cope, 1882), all from the early Paleocene to earliest late Paleocene, aswell as two genera fromthe late Paleocene of eastern Asia (Sphenopsalis Matthew, Granger,


and Simpson, 1928 and Lambdopsalis Chow and Qi, 1978). A third eastern Asian genus, Prionessus Matthew and Granger, 1925, has traditionally been considered a taeniolabidoid, but we consider this referral doubtful (contra, e.g., Xu et al., 2015). Among the currently recognized taeniolabidoid genera,


Catopsalis is by far the most speciose, with six nominal species that collectively span the latest Cretaceous through earliest late Paleocene (see summary by Williamson et al., 2015). Until relatively recently, the chronological succession of the various species of Catopsalis appeared to document what has been interpreted as fairly straightforward evolutionary trends of increasing body size (as inferred from molar length), an increase in the length of the upper and lower first molar (M1/m1) relative to the second molar (M2/m2), and an overall reduction in the size of the upper and lower fourth premolar (P4/p4) (Kielan- Jaworowska and Sloan, 1979; Middleton, 1982). The discovery of specimens of the size of C. foliatus Cope, 1882 in putative Late Cretaceous deposits (C. johnstoni Fox, 1989, but see Lucas et al., 1997), and even more so, the discovery of a species of the size of C. calgariensis Russell, 1926 in the middle to late Puercan (C. waddleae Buckley, 1995) muddies the waters, and


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