Strange Symmetries #14: The Tooth About Baryonyx

A colored line drawing of Baryonyx, an extinct spinosaurid dinosaur. It has a long crocodile-like snout, a thick S-curved neck, enlarged curved claws on the first finger of its hands, webbed feet, and a tapering tail. The kinked "rosette" at the tip of its upper jaw has an uneven number of teeth, with six on the left side and seven on the right. it's depicted with a reddish-brown mottled colored scheme, with a bright yellow throat pouch.

Almost all toothed theropod dinosaurs had exactly four teeth on each of their premaxillary bones, the paired bones at the very tip of the upper snout.

A diagram of the various bones in the skull of Spinosaurus.
Spinosaurus skull by AS | Public domain

The semi-aquatic spinosaurids were an unusual exception to this with six or seven teeth per premaxilla – and one particular member of this lineage seems to have been just a little bit weirder.

Baryonyx walkeri lived during the early Cretaceous, around 130-125 million years ago, in what is now southeast England. About 9m long (~30′), it had distinctive enlarged curving claws on the first fingers of its hands, along with a long narrow snout with a “rosette” at the tip followed by a notch (a shape convergent with the jaws of modern pike conger eels).

And that premaxillary rosette had a strangely asymmetrical arrangement of teeth.

A closer view of the lineart for Baryonyx's premaxillary rosette. The six left teeth are indicated in pink, and the seven right teeth in dark green.

The left side had six teeth, and the right side had seven.

Why? We don’t know!

Baryonyx skull material is rare and fragmentary, so it’s unclear if this was actually a characteristic feature of the species or if the known asymmetric rosette just represents an unusual individual.

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