Cretoxyrhina agassizensis ( Underwood and Cumbaa, 2010 ) Newbrey & Siversson & Cook & Fotheringham & Sanchez, 2015

Newbrey, Michael G., Siversson, Mikael, Cook, Todd D., Fotheringham, Allison M. & Sanchez, Rebecca L., 2015, Vertebral morphology, dentition, age, growth, and ecology of the large lamniform shark Cardabiodon ricki, Acta Palaeontologica Polonica 60 (4), pp. 877-897 : 882

Cretoxyrhina agassizensis ( Underwood and Cumbaa, 2010) comb. nov.

Holotype: SMNH P2989.144, tooth from Bainbridge River Bonebed , Royal Saskatchewan Museum locality number 63E09-0003, Belle Fourche Member , Ashville Formation (“middle” to late Cenomanian benthic foraminiferal Verneuilinoides perplexus Zone ), Pasquia Hills region, Saskatchewan, Canada.

Referred material. —WAM 13.6.2 ( Fig. 3B ), WAM 95.7.29– 32, 34, 36, 37 ( Siverson 1996: pl. 1: 1–6, 9, 10, 13–18; the colour of the teeth in figs. 7, 8, 11, 12 indicates that they may not originate from the basal Haycock Marl); late Cenomanian or early Turonian, Western Australia.

Emended diagnosis.— Cretoxyrhina agassizensis ( Underwood and Cumbaa, 2010) can be diagnosed as a species with a very slender cusp in anterior teeth in the juvenile to sub-adult stage (broader at the same height in the older Cretoxyrhina denticulata ( Glikman, 1957) and the younger Cretoxyrhina mantelli ), presence of cusplets with a sharp apex on many of the lateroposterior teeth (not rounded as is commonly the case in topotypic Cretoxyrhina denticulata ) and the lack of complete cutting edges on small juvenile anterior teeth. The labial face of the cusp is increasingly more constricted basally in anterior teeth with decreasing age of the individual.

Remarks.—The tooth WAM 13.6.2 from the basal Haycock Marl, lower Murchison River area, Western Australia (Fig.

B) is inseparable from anterior teeth of Telodontaspis agassizensis Underwood and Cumbaa, 2010 . The narrow median furrows along the lower part of the basal face of the root ( Fig.

B 2) is a common feature in early Cretoxyrhina ( Siverson and Lindgren 2005: fig. 2I 2, P 2; Siverson et al. 2013: fig. 5Z, D’, 7R, B’; Underwood and Cumbaa 2010: pl. 5: 5, misidentified as a Roulletia tooth). Similar furrows are present on the holotype of T. agassizensis ( Underwood and Cumbaa 2010) described from the Belle Fourche Member (probably the late middle Cenomanian Acanthoceras amphibolum Zone ) of the Ashville Formation, Saskatchewan, Canada. The nominal Telodontaspis co-occurs with larger, typical Cretoxyrhina at its type locality and in the basal Haycock Marl

(compare Siverson 1996: pl. 1: 5, 6 with Underwood and Cumbaa 2010: pl. 6: 16, 17 and Fig. 3B 1 with Underwood and Cumbaa 2010: pl. 6: 27). The gradual transition in basal constriction of the labial face of the cusp in anterior teeth from a “ Telodontaspis ” morphology ( Fig. 3B 1 ); Underwood and Cumbaa (2010: pl. 6: 27) via a “juvenile” Cretoxyrhina -stage ( Siverson 1996: pl. 1: 9) to the sub-adult or adult stage ( Siverson 1996: pl. 1: 15) and the identical furrows on the basal face of the root in the two nominal taxa, indicate that the generic names denominate different ontogenetic stages in a single species. Synonymy is likewise indicated by the fact that Telodontaspis has not been shown to occur in deposits lacking typical, larger Cretoxyrhina teeth.As indicated by Siverson et al. (2013), the ontogenetic heterodonty is very marked in Cretoxyrhina and it appears that Underwood and Cumbaa (2010) underestimated the degree of ontogenetic heterodonty during the first few years in individuals of this genus. The earliest occurrence of this species is in the Belle Fourche Member of the Ashville Formation (described as Cretoxyrhina denticulata , Telodontaspis agassizensis , and Roulletia canadensis [the “A3” in the reconstructed dentition of the latter species] by Underwood and Cumbaa 2010) whereas the youngest occurrence is in the early middle Turonian of the Fairport Member of the Carlile Shale (described as Cretoxyrhina mantelli by Siverson and Lindgren 2005). A sample of middle Cenomanian Cretoxyrhina from the uppermost Gearle Siltstone at CY Creek, Giralia Anticline (type stratum for Cardabiodon ricki ) includes anterior teeth of Cretoxyrhina agassizensis - type and lateroposterior teeth of Cretoxyrhina denticulata - type (cusplets present on all lateroposterior teeth and commonly rounded) and it is possible if not likely that the two species are chrono-segments of a single lineage (i.e., the early to early middle Cenomanian Cretoxyrhina denticulata followed by the late middle Cenomanian to early middle Turonian Cretoxyrhina agassizensis ).

Stratigraphic and geographic range.—The late middle Cenomanian to early middle Turonian, United States, Canada, and Australia.

Figures

Fig. 3. Isolated, small juvenile teeth of Cardabiodon ricki Siverson, 1999 (WAM 13.6.1: lp7–9?) (A) and Cretoxyrhina agassizensis (Underwood and Cumbaa, 2010) (WAM 13.6.2: a2?) (B) from the basal (0.1 m) of the Haycock Marl, Pillawarra Plateau, Western Australia, late Cenomanian or early Turonian. In labial (A1, A2) and lingual (B1, B2) views.

Fig. 2. Schematic drawing of a hypothetical shark centrum in hemisected view showing potential criteria used for age determination.

Fig. 1. Early Late Cretaceous map (90 Ma; PLATES Program 2009) showing locations of fossil localities (late Cenomanian to middle Turonian) yielding Cardabiodon spp. (see Cook et al. 2010). UALVP 49430 from Canada is likely a transitional morphotype between Cardabiodon ricki and Cardabiodon venator.