Cimolodonta McKenna, 1975

Mao, Fang-Yuan, Wang, Yuan-Qing & Meng, Jin, 2016, New specimens of the multituberculate mammal Sphenopsalis from China: Implications for phylogeny and biology of taeniolabidoids, Acta Palaeontologica Polonica 61 (2), pp. 429-454 : 432-433

Suborder Cimolodonta McKenna, 1975 Superfamily Taeniolabidoidea Sloan and Van Valen, 1965

Families and genera included: Taeniolabididae Granger and Simpson, 1929 ( Taeniolabis Cope, 1882 , type genus; Catopsalis Cope, 1882 ). Lambdopsalidae Chow and Qi, 1978 , which we re-established in this study (see below) ( Lambdopsalis Chow and Qi, 1978 , type genus; Sphenopsalis Matthew, Granger, and Simpson, 1928 ). We tentatively consider Prionessus as family incertae sedis for the reason given in the following discussion. Following Kielan-Jaworowska et al. (2004), we also tentatively refer the poorly known Late Cretaceous Bubodens Wilson, 1987 to Taeniolabidoidea . Its general morphology is more Taeniolabis- like in having inflated tooth cusps that bear horizontal wear facets on cusp tips.

Emended diagnosis.—The combination of the following features distinguishes Taeniolabidoidea from other multituberculates: including the largest known North American and Asian multituberculates (skull length in the Paleocene Taeniolabis reaching 16 cm); dental formula 2.0.1-2.2/1.0.1.2; tooth with gigantoprismatic enamel (shared with all Cimolodonta except Ptilodontoidea); snout short and wide with anterior part of zygomatic arches directed transversely, resulting in a square-shaped skull; frontals small, pointed posteriorly, almost or completely excluded from the orbital rim; the frontal deeply inserted between the nasals; I2 and I3 singlecusped; small or no diastema between I2 and I3; I3 on the margin of the premaxilla; having only one upper premolar (except for one taxon); P4 with one main cusp row and one root, long diastema between I3 and premolars; P4 and p4 strongly reduced in proportion to enlarged, multicusped molars and triangular in lateral view; p4 without oblique ridges and not laterally compressed to be bladelike; M1 having three rows of cusps with the lingual one extending for nearly the whole length of the tooth and bearing 7–9 cusps or more.

Remarks.—The emended diagnosis is modified from that of Kielan-Jaworowska et al. (2004). Taeniolabidoidea as a subor- der was proposed and defined by Sloan and Van Valen (1965: 222) as: “including multituberculates in which the enamel of the lower incisor is restricted to the ventro-lateral surface of the tooth, producing a self-sharpening tooth similar to that of rodents. The shearing premolars are reduced in proportion to the molars in all included genera except Eucosmodon ”. Since the proposal, whether taeniolabidoids form a natural group has been a matter of debate for decades ( Clemens and Kielan-Jaworowska 1979; Kielan-Jaworowska 1974, 1980; Carlson and Krause 1985; Simmons 1993; Fox 1999, 2005; Kielan-Jaworowska and Hurum 2001; Kielan-Jaworowska et al. 2004). The complicated research history of the group may be reflected by the taxon name that is associated with multiple author names: “Superfamily Taeniolabidoidea ( Sloan and Van Valen 1965) , McKenna and Bell, 1997, Fox, 1999 ” ( Kielan-Jaworowska and Hurum 2001: 417).Since the work of Fox (1999), the taxonomy that Taeniolabidoidea include only a monotypic family Taeniolabididae Granger and Simpson, 1929 has been widely accepted ( Kielan-Jaworowska and Hurum 2001; Jaworowska et al. 2004; Fox 2005). The family includes mainly five genera: Taeniolabis Cope, 1882 (type genus), Catopsalis Cope, 1882 , Lambdopsalis Chow and Qi, 1978 , Prionessus Matthew and Granger, 1925 , and Sphenopsalis Matthew, Granger, and Simpson, 1929 . Kielan-Jaworowska et al. (2004) did not list all genera in the family for the reason that their work was intended to document only the Mesozoic taxa. These authors, however, tentatively assigned the poorly known Late Cretaceous Bubodens Wilson, 1987 to Taeniolabididae and provided by far the most up-todate diagnosis for the superfamily and family. In our understanding the diagnosis, expanded from Kielan-Jaworowska and Hurum (2001), should be applicable to the Paleogene genera. Fox (2005) analyzed and discussed seven characters in detail that were used in various studies, primarily Simmons (1993), to diagnose Taeniolabidoidea that included Taeniolabididae and species belonging to Eucosmodontidae , Sloanbaataridae , and Djadochtatheriidae . Fox (2005) concluded that Taeniolabidoidea as previously defined (i.e., Simmons 1993) were not monophyletic and noted that Taeniolabidoidea functions as a taxon redundant with its single included family, Taeniolabididae in Kielan-Jaworowska and Hurum (2001). However, because their manuscripts were probably completed roughly around the same time so that Kielan-Jaworowska et al. (2004) and Fox (2005) were unaware of each other’s work.

In light of the new specimens of Sphenopsalis , we are able to discuss some features that are relevant to the phylogenetic placement or taxonomy of Sphenopsalis and other taeniolabidoids. For instance, one of the diagnostic features used in the diagnosis for Taeniolabidoidea ( Kielan-Jaworowska et al. 2004: 331) was: “Share strong, self-sharpening incisors that have enamel limited to the outer surface with most Djadochtatherioidea and Eucosmodontidae .” As we will show below, this character does not seem to properly characterize Sphenopsalis and other Asian Paleocene taeniolabidoids. The focus of this study is to present the morphology of Sphenopsalis , assess its phylogenetic position, and re-establish the family Lambdopsalidae . A thorough review on the taxonomy and phylogenetic relationship of Taeniolabidoidea is beyond the scope of the present study. However, the new morphologic data and comparisons in the following sections allow us to clarify some features of taeniolabidoids that were unknown for taxa such as Sphenopsalis but were nonetheless used in the diagnosis of Taeniolabidoidea . With the re-establishment of Lambdopsalidae (see below) and the discussion on Taeniolabidoidea by Fox (2005), we hope that our emended diagnosis for Taeniolabidoidea can be justified.

Stratigraphic and geographic range.—Late Cretaceous and Paleocene of North America and Asia ( Fox 1989, 1997; Kielan-Jaworowska and Hurum 2001).