Necrocarcinus siouxensis Feldmann, Awotua & Welshenbaugh, 1976

Guinot, Danièle, Vega, Francisco J. & Van Bakel, Barry W. M., 2008, Cenomanocarcinidae n. fam., a new Cretaceous podotreme family (Crustacea, Decapoda, Brachyura, Raninoidia), with comments on related families, Geodiversitas 30 (4), pp. 681-719 : 681-719

Necrocarcinus siouxensis Feldmann, Awotua & Welshenbaugh, 1976

Necrocarcinus siouxensis Feldmann, Awotua & Welshenbaugh, 1976: 986 , pl. 1.

Remarks

Necrocarcinus siouxensis , from the Maastrichtian of North Dakota, known from a unique specimen with a fairly well-preserved venter, illustrates the difficulty in placing crabs which have been included in the Necrocarcinidae . Necrocarcinus siouxensis was considered to be of uncertain position according to Fraaye (1994: 264, fig. 1), not referable to Necrocarcinus according to Bishop & Williams (1991: 452), who suggested either a species of Cenomanocarcinus or of a new genus, and was finally assigned to Cenomanocarcinus by Schweitzer et al. (2003a: 36-39, table 1) and Crawford et al. (2006: 5). Possible affinities with the Podotremata were hinted at by Guinot & Quenette (2005: 329) and Guinot & Breton (2006: 616), but undeniable features are absent.

The reconstruction of the venter by Feldmann et al. (1976: pl. 1, fig. 5) is puzzling. The region between the legs regarded as thoracic by Feldmann et al. (1976) does not fit with any known sternal plate ( Guinot & Quenette 2005: 329). It could, alternatively, represent a wide and long abdomen, which completely fills the sterno-abdominal depression and is maintained by the pereiopods. We interpret this venter to be a composite.The posterior two-thirds correspond to the (slightly displaced) abdomen, probably that of a female, which entirely covers the space between the coxae and is rather long (the telson reaching the level of the cheliped coxae); the anterior portion corresponds to the sternum (anterior sternites and triangle between the mxp3). Necrocarcinus siouxensis exhibits a tricarinate carapace

with the characteristic “H”pattern, pediform mxp3 as in Cenomanocarcinus , and probably a similar venter. However, the shape of the longitudinal branchial ridges, the absence of a hepatic transverse ridge and the presence of huge orbits in N. siouxensis (60% of the maximum width of the carapace versus 30% in Cenomanocarcinus species according to Schweitzer et al. 2003a: 37, 38) warrant its separation from Cenomanocarcinus . We cannot determine its generic attribution at present. Placement with the raninoid stock is the most probable hypothesis; however, its family assignment remains doubtful.