Shark fossil shows a creature with wing-like fins

Researchers have discovered a new shark species that has been named Aquilolamna milarcae. The shark swam in the oceans during the Late Cretaceous about 93 million years ago. Scientists discovered a complete fossilized specimen in 2012 in Vallecillo, Mexico. That particular location has yielded remarkably well-preserved fossils in the past.

The site is famous for its well-preserved bony fish, marine reptiles, and ammonites. Scientists say that the Aquilolamna milarcae belongs to Lamniformes, an order of sharks in the subclass Elasmobranchii. That subclass was highly successful and includes sharks, skates, and rays. Creatures in that class first appeared in the oceans about 380 million years ago and have evolved to fulfill a wide range of roles.

The creature is believed to have eaten plankton and modern plankton-feeding elasmobranchs are characterized by creatures with a more traditional shark body shape like whales and basking sharks as well as those with flattened bodies and wing-like fins, such as Mobulidae rays. What's so interesting about the Aquilolamna milarcaefossil is that it shows a creature that was distinctly in the middle of both of those groups.

It had many common features with modern manta rays, specifically long thin fins and a mouth adapted for filter feeding. Its specially adapted mouth suggests it fed on plankton. The creature also had a caudal fin and well-developed superior lobe, typical of pelagic sharks like whale sharks and Tiger sharks.

The fascinating design of the creature has anatomical features that are a combination of both sharks and rays. Scientists believe the creature would have been a relatively slow swimmer using the long pectoral fins to glide through the water and scoop up suspended plankton using its largemouth. Paleontologists also note that the creature shows that pectoral fins that work like wings evolved independently into distantly related types of filter-feeding elasmobranches.