The North American fossil record includes tooth-designs attributed to:

In general, the functional morphology of the Squalicorax dentition-design is most similar to that of Galeocerdo -- dignathic heterodonty of a multi-purpose cutting-like design. Tooth-design spans a broader range, reflecting designs seen in the upper files of various Recent Carcharhinus and Sphyrna taxa. The more primitive Squalicorax tooth-designs tend to have narrower and more: distally inclined cusps, differentiated heels and bilobate roots. In younger taxa, the cusps broaden and become more erect, the heels less defined and root lobes less differentiated. The most "advanced" design is reflected by S. pristodontus; in this species, the bilobate root-design is largely lost and the root is labio-lingually compressed. The cusp is broader, the heel weakly differentiated and the serrations much stronger, a design similar to the upper teeth of the bull and dusky shark.

Despite the large study-sets and extensive research by both Siverson and Shimada in recent years, neither author has tendered a Squalicorax dentition-set or even proposed a means of distinguishing upper and lower teeth. This 'safety-net' of ambiguity is equally problematic as the overlooked/under appreciated characteristics as expressed by Siverson et al (2007). These key characteristics include:

Western Atlantic (Campanian-Maastrichtian)

Collecting the Atlantic coastal plain is limited to upper Late Cretaceous sediments and yields three tooth-designs; Squalicorax "kaupi" is the most common and cf "bassanii" the least.

Squalicorax "kaupi". Most commonly in this area, small Squalicorax teeth with a notched distal edge are referred to this species. As included herein, the mesial edge should smoothly extend to the lateral margin of the root and the serrations be of equal size. In the accompanying images, three specimens reflect variations of unknown importance, figure displays an deep distal notch with an enlarged first serration of the heel, figure reflects a mesial edge which falls short of the root margin and figure depicts a "kaupi"-like tooth with a mesial heel. (Note the difference in the above definition for "kaupi" from the one provided by ME for specimens from the chalk.)

Squalicorax "pristodontus". This tooth-design is generally viewed as a large Squalicorax with homogeneous serrations which lacks a strong distal notch. The lateral margins of the crown extend to or may bulge beyond the root which appears more massive than in "kaupi". Smaller teeth are more problematic in that ontogenetic variations may prove less definitive. Queried below (Fig. & ) is a specimen which includes erect distal and basally curved mesial (this may only be an artifact of the lack of wear) serrations.

Squalicorax cf "bassanii". The below images (Fig. - ) are of a tooth-design referred to in the Eastern US as S. bassanii and are similar in size and shape to "kaupi" but with a mesial 'heel'; the distal heel is rather elongated and rather than the homogeneous serrations of "kaupi" & "pristodontus", those above the mesial heel are enlarged and often ragged. Based on Gemmellaro's (1920) illustrations, the distal heel (mammellone) of S. bassanii is much shorter than seen in cf bassanii and the 'hump' of the mesial edge more pronounced.
Mikael Siverson (pers coms, 1999) reviewed images of NC specimens and noted:

".. occasionally get the mesial notch on anteriors in S. kaupi (from which S. bassanii is most likely derived) as well. True S. bassanii teeth have the mesial notch IN COMBINATION with a very marked increase in labiolingual thickness of the tooth.... I strongly suspect ... belong to another, similar looking anacoracid, more closely related to S. yangaensis (DARTEVILLE & CASIER, 1943). In true S. bassanii the cusp and the neck are broader and the basal edge of the root is less scalloped."

Figures in Darteville & Casier (1943) show differences as well between cf "bassanii" and yangaensis. In the former, the mesial heel is stronger, the distal more elongated and the 'hump' more accentuated; in addition, the mesial serrations of the latter appear more gradational, lacking the ragged appearance of cf "bassanii". It would appear that the crowns of these NC specimens fail to compare well with either option although they could be a regional variation of either.

Inland Sea (Albian-Campanian)

The Smoky Hill chalk of Kansas yields teeth from a number of anacoracid species. This fauna is currently under study by Mikael Siverson, but certain observations are possible.

Squalicorax cf "falcatus" teeth are small to medium in size, and tend to increase in size from the bottom to the top of the Smoky Hill Chalk. The teeth are generally triangular in side view, with the crowns of the anterior teeth narrow and erect. The lateral and posterior teeth have lower crowns that are inclined distally. The angle of the cusp is acute to obtuse, and all cutting edges are finely serrated. The root is intermediate in length and bilobate, without a nutrient groove.

Squalicorax "kaupi" teeth are found only in the upper 1/4 of the Smoky Hill Chalk (early Campanian). These teeth are usually larger than S. cf "falcatus", and may be 2 cm tall or larger. They have a high crown with a very inflated and convex mesial cutting edge. The distal edge of the tooth is nearly vertical. The serrations are generally coarser than those found on S. cf "falcatus" teeth and may be compound (small serrations on larger ones). The root is large, bilobate and without a nutrient groove.

Teeth from an as yet unnamed paleoanacoracid species are also found in the lower one-third (late Coniacian) of the Smoky Hill chalk. These teeth are characterized as being small (10 mm or less in height), with low crowns and shallow roots. Proportionately, their length is always greater than their height. One feature that distinguishes them from small specimens of Squalicorax is the distinctly smooth and rounded distal cusp.

Texas (Albian-Campanian)

The Cretaceous of Texas has a diverse group of anacoracids as reported by Welton & Farish (1993), Cappetta & Case (1999) and Siverson et al (2007). In addition to taxa currently reported from the Inland Sea, these more southerly waters include Squalicorax baharijensis, S. pawpawensis, S. priscoserratus and at least one undescribed species. Ed Swiatovy provided and Mikael Siverson identified examples included below. The pawpawensis tooth-design is more common and includes a broader neck and more gradationally mesial serrations. S. priscoserratus teeth have a narrow neck and more homogeneous serrations of the mesial edge, which may range from nearly smooth to coarse.

Aknowledgements

We'd like to thank individuals that helped-out and/or provided specimens used in this page -- Tom Caggiano, Howie Cohn, Pieter De Schutter, Kim Greene, Gary Grimsley and Ed Swiatovy, Most importantly is the decade of comments, suggestions and identifications provided by Mikael Siverson.

Selected References