Zoological Journal of the Linnean Society, 2015. With figures A new taeniolabidoid multituberculate (Mammalia) from the middle Puercan of the Nacimiento Formation, New Mexico, and a revision of taeniolabidoid systematics and phylogeny THOMAS E. WILLIAMSON1*, STEPHEN L. BRUSATTE2, ROSS SECORD3 and SARAH SHELLEY2 1New Mexico Museum of Natural History and Science, 1801 Mountain Road, NW, Albuquerque, NM 87104-1375, USA 2School of GeoSciences, University of Edinburgh, Grant Institute, James Hutton Road, Edinburgh EH9 3FE, UK 3University of Nebraska, Department of Earth and Atmospheric Sciences, 200 Bessey Hall, Lincoln, NE 68588-0340, USA Received 11 March 2015; revised 24 July 2015; accepted for publication 31 July 2015 Multituberculates were amongst the most abundant and taxonomically diverse mammals of the late Mesozoic and the Palaeocene, reaching their zenith in diversity and body size in the Palaeocene. Taeniolabidoidea, the topic of this paper, includes the largest known multituberculates, which possess highly complex cheek teeth adapted for herbivory. A new specimen from the early Palaeocene (middle Puercan; biochron Pu2) of the Nacimiento Forma- tion, New Mexico represents a new large-bodied taeniolabidoid genus and species, Kimbetopsalis simmonsae.A phylogenetic analysis to examine the relationships within Taeniolabidoidea that includes new information from Kimbetopsalis gen. et sp. nov. and gen. nov. and from new specimens of Catopsalis fissidens, first described here, and data from all other described North American and Asian taeniolabidoids. This analysis indicates that Catopsalis is nonmonophyletic and justifies our transfer of the basal-most taeniolabidoid ‘Catopsalis’ joyneri to a new genus, Valenopsalis. Kimbetopsalis and Taeniolabis form a clade (Taeniolabididae), as do the Asian Lambdopsalis, Sphenopsalis, and possibly also Prionessus (Lambdopsalidae). Taeniolabidoids underwent a modest taxonomic ra- diation during the early Palaeocene of North America and underwent a dramatic increase in body size, with Taeniolabis taoensis possibly exceeding 100 kg. Taeniolabidoids appear to have gone extinct in North America by the late Palaeocene but the appearance of lambdopsalids in the late Palaeocene of Asia suggests that they dispersed from North America in the early to middle Palaeocene. © 2015 The Linnean Society of London, Zoological Journal of the Linnean Society, 2015 doi: 10.1111/zoj.12336 ADDITIONAL KEYWORDS: body size – dispersal – ecological recovery – mammalian radiation – multituberculata – palaeobiogeography – Palaeocene – San Juan Basin – Taeniolabididae – Taeniolabidoidea. INTRODUCTION diated yet again in the post-extinction world of the Palaeocene, and then rapidly dropped in diversity in Multituberculates were a diverse group of mammals the late Palaeocene and early Eocene as more modern that thrived alongside dinosaurs during much of the groups of mammals (particularly the anatomically and Mesozoic, survived the end-Cretaceous extinction, ra- ecologically similar rodents) spread across the globe (Krause, 1986; Kielan-Jaworowska, Cifelli & Luo, 2004; Weil & Krause, 2008). Multituberculates reached their *Corresponding author. E-mail: [email protected] peak in species diversity, body size, and morphologi- [Version of Record, published online 5 October 2015] cal disparity in the early Palaeocene, within a few © 2015 The Linnean Society of London, Zoological Journal of the Linnean Society, 2015 1 2 T. E. WILLIAMSON ET AL. million years of the non-avian dinosaur extinction (Weil We here describe a peculiar new taeniolabidoid from & Krause, 2008; Wilson et al., 2012). Some of the the early Palaeocene of the San Juan Basin of New most distinctive multituberculates flourishing during Mexico, USA. This is the first new taeniolabidoid taxon this time were the taeniolabidoids. Taeniolabidoids at- to be described in nearly 20 years, and the first to be tained the largest sizes of any multituberculates and described from New Mexico – one of the world’s premier were characterized by a short rostrum, reduced pre- localities for early Palaeocene mammal fossils – since molars, a pair of gliriform incisors separated from cheek 1884. We establish the validity of this species, compare teeth by a long diastema, and enormous molars with it with other taeniolabidoids, and use this as a jumping- a high number of cusps, all of which permitted an off point for a systematic revision of the group, based unusual herbivorous diet. These taeniolabidoids – in- on a species-level phylogenetic analysis. We then use cluding such familiar taxa as Taeniolabis and Catopsalis the results of this analysis to clarify the taxonomy of – were amongst the most aberrant and specialized Taeniolabidoidea and ingroup clades, provide an updated mammals of the early Palaeocene, a time when ter- list of all valid species, designate a new genus name restrial ecosystems were being dramatically re- for a problematic species of ‘Catopsalis’ that is now shaped and mammals were beginning their march to strongly supported as a basal taeniolabidoid, and discuss dominance. evolutionary trends in diversification, body size, and The first taeniolabidoids were discovered during the biogeography across taeniolabidoid history. geological surveys of western North America during the 1880s, around the same time that multituberculates MATERIAL AND METHODS were recognized as a distinct group of extinct mammals INSTITUTIONAL ABBREVIATIONS (Cope, 1884, 1888a; Marsh, 1889a, b). Taeniolabidoids AMNH, American Museum of Natural History, New are common components of Palaeocene faunas of the York, USA; NMMNH, New Mexico Museum of Natural western USA and are now also known from Asia. Some History and Science, Albuquerque, USA; SDSM, South species are important index taxa in defining the mam- Dakota School of Mines, Rapid City, South Dakota, USA; malian biochronological timescale (Lofgren et al., 2004; SPSM, St. Paul Science Museum, Minnesota, USA; UCM, Ting et al., 2011) and taeniolabidoids have played a University of Colorado, Boulder, USA; UM, University key role in understanding patterns of extinction and of Michigan, Ann Arbor, USA; UMVP, University of Min- survivorship, and changes in mammalian body size and nesota Vertebrate Paleontology, Minneapolis, USA; dietary habits across the Cretaceous–Palaeogene bounda- USNM, United States National Museum, Washington ry (e.g. Archibald, 1983; Wilson et al., 2012; Wilson, D.C., USA; UW, University of Wyoming, Laramie, USA. 2013, 2014). Although taeniolabidoids have been known for some ANATOMICAL ABBREVIATIONS 130 years, their phylogenetic relationships are still poorly understood and their taxonomy is in need of revi- I2, second upper incisor; L, length; M, upper molar; sion. It is widely accepted that genera such as m, lower molar; P, upper premolar; W, width; cusp Taeniolabis, Catopsalis, and Sphenopsalis form an ana- formula following the pattern established by Simpson tomically and palaeobiologically distinctive taeniolabidoid (1929), counting the buccal row first and the lingual clade (e.g. Rougier, Novacek & Dashzeveg, 1997; row last. Kielan-Jaworowska et al., 2004; Mao, Wang & Meng, 2015), but the number of valid species in this clade SYSTEMATIC PALAEONTOLOGY and their detailed ingroup relationships are the subject MAMMALIA LINNAEUS, 1758 of debate. A pioneering phylogenetic analysis by MULTITUBERCULATA COPE, 1884 Simmons & Miao (1986) found the characteristic North TAENIOLABIDOIDEA SLOAN &VAN VALEN, 1965 American genus Catopsalis to be a nonmonophyletic array of several diagnostic species, some constituting TAENIOLABIDIDAE GRANGER &SIMPSON, 1929 a paraphyletic grade of basal taeniolabidoids, and others KIMBETOPSALIS SIMMONSAE GEN. ET SP. NOV. forming a polytomy with Taeniolabis and a clade of (FIGS 1, 2, TABLES 1 AND 2) Asian taxa. Over the following three decades, several (http://zoobank.org/ new taeniolabidoid specimens have been discovered, urn:lsid:zoobank.org:pub:9E9F07C3-D042- which promise to provide insight into the evolution of 4E8F-862A-279072E04035) large body size and high dental complexity in this clade Holotype (e.g. Simmons, 1987; Buckley, 1995; Lucas, Williamson NMMNH P-69902 from locality L-9181. & Middleton, 1997; Meng, Zhai & Wyss, 1998; Mao, Wang & Meng, 2015). These have yet to be synthe- Type locality and horizon sized into a comprehensive phylogenetic analysis and The specimen was discovered in the lower Palaeocene systematic revision of the group. part of the Nacimiento Formation of the San Juan Basin © 2015 The Linnean Society of London, Zoological Journal of the Linnean Society, 2015 REVISION OF TAENIOLABIDOIDEA 3 Figure 1. Holotype of Kimbetopsalis simmonsae gen. et sp. nov., NMMNH P-69902. A, dorsal view of partial skull roof; B–C, dorsal view of portion of braincase and base of right zygomatic arch in dorsal (B) and ventral (C) views. of northwestern New Mexico, in the west flank of occurrence of Taeniolabis defines the beginning of the Kimbeto Wash, at locality 11 of Williamson (1996: Pu3 Interval Zone (Archibald et al., 1987; Lofgren et al., fig. 18). It is from Fossil Horizon A and within the 2004). Although it does not in itself support a Pu2 age Hemithlaeus kowalevskianus – Taeniolabis taoensis for the locality, the absence of Taeniolabis is further Biozone (H-T Zone) (Williamson, 1996). The verte- evidence that the west flank of Kimbeto Wash is not brate fauna from this horizon is considered part of the Pu3 in age (a time when other large taeniolabidids are type faunas of the middle Puercan