Ctenohystrica HUCHON et al., 2000

Flynn, Lawrence J., Jacobs, Louis L., Kimura, Yuri & Lindsay, Everett H., 2019, Rodent Suborders, Fossil Imprint 75 (3 - 4), pp. 292-298 : 294

Suborder Ctenohystrica HUCHON et al., 2000

The large division Ctenohystrica of Huchon et al. (2000) has endured scrutiny and subsequent analyses and is a useful group, distinct from the extant squirrel-like and mouse-like family clusters. Suborder Ctenohystrica (see Appendix) includes the Hystricognathi TULLBERG, 1899 (infraordinal rank) plus two family-level outgroups, Ctenodactylidae and Diatomyidae . The latter two show the plesiomorphic sciurognathous rodent jaw structure, which would occur in basal members of the suborder. The hystricognathous jaw structure is derived with respect to sciurognathy, and while characterizing Hystricognathi , by far the majority of Ctenohystrica , that character state evolved within the suborder after its origin. Following McKenna and Bell (1997) the Hystricognathi are considered an infraorder containing families Hystricidae , Erethizontidae , Thryonomyidae , Petromuridae , Bathyergidae , various extinct phiomorphs of Africa, and diverse South American families derived from a Paleogene hystricognath radiation ( Rowe et al. 2010). The South American families within Hystricognathi are the monophyletic Caviomorpha WOOD, 1955 , a taxon comparable to the Caviida of Bryant and McKenna (1995).

All ctenohystricans are hystricomorphous (with an enlarged infraorbital foramen accommodating passage of a portion of the masseter muscle), but hystricomorphy occurs outside the suborder. Ctenohystrican families other than the ctenodactylids and diatomyids are hystricognathous. All are also derived in the enamel microstructure of their enlarged gnawing incisors. The enamel has a highly organized system of interlocking prisms referred to as multiserial enamel, with decussating prisms forming adjacent enamel bands that are several prisms thick. This organized system is derived with respect to the pauciserial enamel character state, which occurs in earlier Paleogene rodents ( Wahlert 1968). The multiserial character state occurs outside this suborder as a homoplasy only in Pedetidae (see below).

Cheek tooth features typical of Ctenohystrica include presence of a hypocone in upper molars and deciduous 4 th premolar, and rectangular lower cheek teeth, primitively with a hypoconulid. In most lineages, the cuspate cheek teeth become lophodont, and some become high crowned. Several closely related but independent hystricognath lineages suppress replacement of deciduous premolars, so that the adult dentition is DP4/4, M1–3/1–3.