Isurolamna: a Paleogene shark recognised by its tooth rows

Isurolamna is an extinct lamniform shark known chiefly from isolated teeth and tooth series in Paleogene marine deposits. Its diagnostic challenge is pronounced heterodonty: front teeth can be narrow and isuroid in shape, while lateral teeth become broader and resemble those of other mackerel sharks. A series from one locality is therefore more informative than a single crown. The genus adds a tooth-based case study to the ancient fish catalogue.

Quick facts

A genus created to sort a complicated tooth record

Henri Cappetta established Isurolamna in 1976 while revising Paleogene lamniform teeth. Earlier specimens had been placed in broad combinations under names such as Lamna and Odontaspis. The new genus grouped teeth with a distinctive combination of crown and root features, but the record remains dominated by isolated material.

This matters because a shark does not carry one repeated tooth shape. Front, intermediate and lateral positions may differ, and the upper and lower jaws can add further variation. When those positions are collected separately, the same species may appear to be several forms; when deposits mix species, different animals can be mistaken for a single dental series.

Heterodonty across the jaw

Anterior and anterolateral teeth attributed to Isurolamna tend to have slender, high central cusps. Their roots are robust, and the crown can curve in profile. Farther back, lateral teeth become broader and more triangular, with distal inclination and, in some species, paired accessory cusplets. The Kyiv material described in 2023 illustrates this contrast with seven teeth assigned to I. affinis from Vyshhorod: three anterior, one anterolateral and three lateral teeth.

The authors measured the anterior crowns at roughly 16–17 millimetres high and described lateral crowns with a different outline and root geometry. Those dimensions refer to the particular specimens, not a standard size for every Isurolamna. The same study synonymised the older name Oxyrhina biflena with I. affinis, showing how revision can change the names attached to historic collections.

Species distinctions also rely on which positions are represented. The Kyiv authors considered their teeth most similar to I. affinis, while noting differences from I. inflata and larger teeth assigned to I. bajarunasi. They also warned that similar teeth such as Anomotodon could be mixed in the sample. A species label is strongest when several positions and diagnostic characters agree.

What can be inferred about the animal?

The cutting edges and pointed crowns are compatible with capturing fish and other mobile prey. That is a functional reading of the teeth, not a record of a particular meal. The genus is not represented by a complete skeleton in the material discussed here, so fin proportions, body length, reproduction and colour cannot be read directly from its teeth.

Estimating length from one tooth requires a validated relationship between a known tooth position and body size in a sufficiently close analogue. Because tooth position and species identification can both be uncertain, a single crown does not yield a precise total length for Isurolamna. A drawing may use the general shape of a lamniform shark, but its full outline remains comparative reconstruction.

The genus is most useful when the teeth are treated as a positional series rather than as isolated labels. That approach helps distinguish genuine taxonomic differences from the ordinary variation within one jaw, while leaving body features that the fossils do not preserve unresolved.

Explore related evidence in the ancient fish catalogue.