Didelphodon, AND

Ladevèze, Sandrine, 2007, Petrosal bones of metatherian mammals from the Late Palaeocene of Itaboraí (Brazil), and a cladistic analysis of petrosal features in metatherians, Zoological Journal of the Linnean Society 150 (1), pp. 85-115 : 105

DIDELPHODON AND PEDIOMYS

This clade is supported by five unambiguous and two ambiguous synapomorphies, and by a strong decay value (5 vs. a mean of 2).

Didelphodon and Pediomys exhibit a very large and deep fossa for the tensor tympani muscle on the anterolateral apex of the petrosal (11 0> 1, RI = 0.750), as does Pucadelphys , Andinodelphys , and the Petrosal Type II.

The presence of an undulated epitympanic wing of petrosal is autapomorphic of both taxa (13 0> 1, RI = 1.000) ( Wible et al., 2001).

The mastoid tympanic process is large vertical (24 1> 0, RI = 0.846) in both taxa, as in Vincelestes , Asiatherium , and Gurlin Tsav skull ( Rougier et al., 1998).

The fossa incudis and the epitympanic recess are separated by a distinct ridge (28 0> 1, RI = 0.500). A fossa incudis is a feature widely found in mammaliamorphs ( Rougier et al., 1996a), whereas an epitympanic recess is only found in multituberculates, Vincelestes , and therians ( Wible et al., 2001). The separation of both fossae is restricted to some metatherians (i.e. Didelphodon , Pediomys , borhyaenids, and most dasyurids).

The transverse sinus bifurcation occurs on the petrosal (34 0> 1, RI = 0.667), as it was observed in monotremes and didelphids.

The mastoid–squamosal fusion (55 0> 1, RI = 0/0) is an autapomorphy of stagodontids ( Wible et al., 2001).