• body size;
  • dispersal;
  • ecological recovery;
  • mammalian radiation;
  • multituberculata;
  • palaeobiogeography;
  • Palaeocene;
  • San Juan Basin;
  • Taeniolabididae;
  • Taeniolabidoidea

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 Formation, 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 ‘Catopsalisjoyneri 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 radiation 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.