Spalacotheriidae Marsh, 1887

Tsubamoto, Takehisa, Rougier, Guillermo W., Isaji, Shinji, Manabe, Makoto & Forasiepi, Analía M., 2004, New Early Cretaceous spalacotheriid “ symmetrodont ” mammal from Japan, Acta Palaeontologica Polonica 49 (3), pp. 329-346 : 332

Family Spalacotheriidae Marsh, 1887

Type genus: Spalacotherium Owen, 1854 (including Peralestes Owen, 1871 ).

Included genera.— Spalacotheroides Patterson, 1955 ; Symmetrodontoides Fox, 1976 ; Spalacotheridium Cifelli, 1990 ; Shalbaatar Nessov, 1997 ; Spalacolestes Cifelli and Madsen, 1999 ; Symmetrolestes gen. nov. Tsubamoto and Rougier.

Revised diagnosis.—Acute−angled “symmetrodonts” which differ from other “symmetrodonts” in having a strong pterygoid crest of the dentary, broad and erect coronoid process, laterally deflected posteroinferior border of dentary, buccal alveolar margin of dentary much lower than lingual margin, continuous prevallum and postvallum shearing crest, high crown (twice as or more than the mesio−distal length), reduced talonid on lower molariforms, and continuous or almost continuous buccal and lingual cingulids on lower molariforms (the last character is lost in Spalacotheroides ). Also characteristic of the family is the presence of upper molariforms with reduced, or very small, stylocones, and two roots strongly mesiodistally compressed. Differs from more basal zhangheotheriids in the presence of complete shearing surfaces on the para− and protocristids, taller crowns, and more complete cingulids.

Comment on taxa content and synonymy.—Many workers (e.g., Simpson 1928, 1929; Clemens, 1963; Cassiliano and Clemens 1979; Prothero 1981; Hu et al. 1997, 1998; McKenna and Bell 1997; Sigogneau−Russell and Ensom 1998; Averianov 2002) consider Peralestes to be a junior synonym of Spalacotherium . Sigogneau−Russell (1991) described Microderson from the Lower Cretaceous of Morocco and assigned it to Spalacotheriidae . However, Sigogneau−Russell and Ensom (1998) and Averianov (2002) excluded Microderson from Spalacotheriidae . Averianov (2002) considered Microderson to be a stem−group zatherian, a group that includes peramurans and tribosphenidans ( McKenna and Bell 1997). Hu et al. (1997) described Zhangheotherium from the Lower Cretaceous of China, and assigned it to Spalacotheriidae . However, Cifelli and Madsen (1999), Rougier et al. (2001), Rougier, Ji, and Novacek (2003), and Averianov (2002) suggested that Zhangheotherium seems to be a sister taxon of Spalacotheriidae . We follow here this concept of Spalacotheriidae . Nessov (1997) described Shalbaatar from the Upper Cretaceous of Uzbekistan and assigned it to the Multituberculata . However, Averianov (2002) has considered Shalbaatar to be a spalacotheriid. Bonaparte (1990) described Brandonia from the Upper Cretaceous of Argentina and with doubts assigned it to Spalacotheriidae . Later, Bonaparte (1994) and Averianov (2002) consider Brandonia to be a dryolestoid.