In the Atlantic Coastal Plain, a day's collecting of Cretaceous material normally yields an array of 'sand tiger' teeth. Certain tooth-designs (usually those figured in various publications) are readily identified, but others can be problematic -- most of us tend to group all these teeth as 'sand tigers', or separate the obvious goblin shark teeth. The latter become more ambiguous if Eocene material (ie Striatolamia) contamination is present. There will be no attempt to differentiate all Eocene from Cretaceous material, but the key used for Scapanorhynchus can be applied when Striatolamia is present.

Step 0: Remove Serratolamna serrata

The post-collecting rapid sorting of specimens is often less than perfect -- review the batch to insure that the asymmetrical shoulders of Serratolamna serrata (or other inadvertent errors) are not present in the sample.

Step 1: Segregating Scapanorhynchus

In my experience, most of the 'sand tiger'-type teeth tend to be from Scapanorhynchus. These teeth show a characteristic not present in other taxa -- the lingual striations extend onto the neck (Cappetta 1987: 93 and Kent 1994: 47). More accurately, two fine ridges on the neck merge near the crown and map directly to the striations on the cusp. This characteristic is strongly present in the anterior teeth; in the laterals, it becomes less definitive distally. Only rarely are these ridges as well expressed as in figure , but even in worn teeth they can be seen (with a hand lens) on lateral portions of the neck. Although this sorting detail is primarily useful for the anteriors and the first few upper laterals, these positions are the most commonly collected.

Step 2: Separating Carcharias

The remaining teeth should be relatively small (in both quantity and size), often making it difficult to determine which teeth belong together. This step is selecting teeth with a smooth lingual crown face, C. samhammeri; these teeth should be broader and have nearly no basal labial overhang (Fig. -left).

Step 3: Eostriatolamia vs Odontaspis

At this point, the lingual crown faces are all folded (difficult to see in images). This step requires the evaluation of the lower labial margin of the crown -- does it significantly extend beyond the root (Odontaspis, Fig. -right) or not (Eostriatolamia, Fig. -center). [I find that viewing the basal perspective can be particularly useful in differentiating the salience of this bulge.] In addition, the neck of Eostriatolamia tends to be wider (Fig. ).

Step 4: Odontaspis hardingi vs aculeatus

Two small tooth-designs, each with striated crowns fall into this group. In one, the primary lateral cusplet is relatively short and triangular and the secondary much reduced (Fig. ). In the other, the cusplets are longer and narrower (Fig. ). These two tooth groupings compare well with Cappetta & Case's (1975a) descriptions of Odontaspis hardingi and "Hypotodus" aculeatus respectively.

Conclusion

The above decision tree was developed while sorting Late Cretaceous material from North Carolina during 2007. In 2010, Eostriatolamia replaced Carcharias as the genus for the holmdelensis on the website. After the teeth were separated into groups, those groups were compared with Cappetta & Case (1975) yielding the proposed identifications. I have made no attempt to validate the specific names they erected or compare them with earlier Cretaceous fossil taxa from other areas.
Particularly useful with this methodology, root lobes don't need to be complete and cusplets are generally irrelevant (except with Odontaspis). Undoubtedly, continued use by myself or others may expose faults / exceptions in this method -- caveats will be added when encountered.

Cited References