Eostriatolamia: a Cretaceous shark classified by its teeth

Eostriatolamia is an extinct Cretaceous lamniform shark known mainly from fossil teeth. Its crowns have an archaic form and fewer tooth rows than the Cenozoic sand sharks with which it was once compared. Researchers have used large samples and statistical measurements to distinguish tooth morphologies across time, while a Cenomanian Canadian bonebed preserves an especially informative associated fauna. The genus belongs with other shark records in the ancient fish catalogue, though its full body remains unknown.

Quick facts

A genus separated by its tooth pattern

Eostriatolamia is a fossil lamniform shark genus established for Cretaceous teeth with an older-looking arrangement than the numerous reduced posterior rows of living sand tiger sharks. Its crowns may be tall and narrow, with a central cusp, smaller lateral cusplets and longitudinal folds. The exact appearance changes between front and side positions in the jaws. A single detached crown therefore cannot be compared fairly without asking where it may have sat.

Glickman and Averianov’s 1998 study compared measurements from 17 samples ranging from the Albian to Campanian. They used cluster and principal-component analyses to examine how tooth outlines varied through space and geological time. The authors recognised several named species and discussed possible synonymies. Their work was an attempt to make species comparisons more explicit than visual sorting alone, while still dealing with fossil species defined from incomplete samples rather than living populations.

A Canadian bonebed and a named species

A Cenomanian bonebed in Saskatchewan provides a different kind of evidence. Acid preparation yielded thousands of well-preserved chondrichthyan teeth among other vertebrate remains. Underwood and Cumbaa described E. paucicorrugata from this assemblage. They noted that its general tooth form resembles the living sand tiger Carcharias taurus, but the lack of numerous files of reduced posterior teeth supports keeping the fossil genus distinct.

The Canadian study also placed the shark within a local community of sharks, rays and other vertebrates. That tells us what else entered the same depositional system, not necessarily what Eostriatolamia ate. Sharp, narrow teeth are consistent with catching animal prey, but the fossil teeth do not name a regular prey species or show a specific hunting sequence.

Range and classification

Published Cretaceous records include samples from Europe, Central Asia and North America. Such a map combines several species and formations. It should not be read as one population travelling across the globe or a single shark species surviving unchanged through the entire interval. Age assignments also depend on the stratigraphy of each deposit, not on the genus name alone.

The family-level placement has varied. The 1998 paper treated Eostriatolamia as an odontaspidid, while later classifications have used different groupings, including Cretoxyrhinidae. These labels summarize competing ways of interpreting relationships among fossil sharks. The safest account specifies the study or classification being followed rather than presenting an older family assignment as timeless fact.

What a fossil tooth cannot show

Teeth document the cutting surfaces and, when tooth rows or varied samples are available, aspects of jaw position. They do not preserve the cartilage, fin proportions or skin of the shark. Comparisons with living lamniforms support a plausible general body plan, but exact length estimates from isolated crown height are unreliable without a validated relationship for the relevant species and tooth position.

The evidence for Eostriatolamia is therefore strongest at the level of dental anatomy, species comparisons and Cretaceous marine occurrence. Its full appearance remains a reconstruction. Other fossil fishes in the ancient fish catalogue show how the kind of preserved material shapes what can responsibly be said about an extinct animal.

Explore related evidence in the ancient fish catalogue.