Shark or Ray? One Finny Fish, for Sure!

By Jim Brace-Thompson

It made the cover story for the March 19, 2021, issue of the journal Science. Therein, an international team led by vertebrate paleontologist Romain Vullo (University of Rennes, France) reported the discovery of one very strange creature, indeed.

Its remains were found in a rock quarry in northeast Mexico. There, workers split out layers of marine deposits of the Late Cretaceous Period some 93 million years old. Most of the rocks go for construction purposes, such as paving stones. But on one particular slab, an observant worker spotted something worth saving. Vullo and colleagues have determined it is a so-called planktivorous shark.

“Planki-what?” you may be asking.

This strange fossil shark, with a broad round head, was apparently a filter-feeder that sucked up plankton to sustain itself, much like today’s huge basking sharks. It sported a pair of fins that swept a full six-and-a-half feet, tip-to-tip, from its body. The closest existing creatures with such a body plan are filter-feeding devil and manta rays, which didn’t evolve for another 30 million years. Thus, scientists consider this a classic example of “convergent evolution” whereby similar body plans and living strategies independently evolve in creatures separated by time and space.

With its long sweeping fins, the critter—formally named Aquilolamna milarcae—has been dubbed an “eagle shark.” With fins exceeding the wing span of most eagles today, this shark would have cut an impressive outline flying through tropical waters of long, long ago as one finny fish, for sure!