By Will Dunham
WASHINGTON (Reuters) – About 93 million years ago, a bizarre plankton-eating shark in the form of unlike any other known sea creature slid through the sea in what is now northeastern Mexico, with strangely elongated wing-like fins that made its body wider than it was long. .
Scientists on Thursday announced the discovery of a nearly complete shark fossil called Aquilolamna milarcae that lived during the Cretaceous Period when dinosaurs ruled the land.
The unusual proportions – a fin span of about 6-1 / 4 feet (1.9 meters) and a length from head to tail of about 5-1 / 2 feet (1.65 meters) – left the scientists in amazement.
Aquilolamna’s name means “eagle shark,” a nod to its slender pectoral fins, which “primarily acted as an effective stabilizer,” said vertebrate paleontologist Romain Vullo, lead author of the study published in the journal Science.
“Many adjectives can be used to describe this shark: unusual, unique, extraordinary, bizarre, weird. Yes, it is the only shark that is wider than it is long,” said Vullo, of Geosciences Rennes, a research unit where the University of Rennes and the French National Center for Scientific Research (CNRS).
“Aquilolamna is indeed a perfect example of an extinct creature revealing an unexpected new morphology. This strongly suggests that other excellent body shapes and morphological adaptations have existed throughout the evolutionary history of sharks,” Vullo said.
Like all sharks and the accompanying skates and rays, Aquilolamna had a cartilaginous skeleton. It had the familiar torpedo-shaped body and tail of a shark, but its pectoral fins were completely unique. The researchers said Aquilolamna appears to be a slow-swimming shark that fed on plankton through filter feeding, as plankton-eating whale sharks and basking sharks do today.
The fossil, excavated in Mexico’s Nuevo Leon state, did not reveal Aquilolamna’s filtering mechanism for eating.
Rays like the manta ray, with their flattened bodies and large pectoral fins fused all the way to the head, swim through the water as if flying through the air. Aquilolamna appears to have done something similar.
“While the locomotion of manta rays is like underwater flight, with the flapping movements of their powerful pectoral fins, Aquilolamna’s long, slender pectoral fins acted more like the wings of a glider or glider,” said Vullo.
Aquilolamna lived in the open ocean at a time when the seas were populated with marine reptiles, squid relatives with large shells called ammonites, various bony fish and large sharks. The largest predator in its ecosystem was a shark called Cretoxyrhina, which was 20 feet long.
The fish group that includes sharks appeared about 380 million years ago, long before the dinosaurs.
Aquilolamna isn’t the only unusual shark to have swum Earth’s oceans. Sharks and their close relatives have taken on many shapes and sizes – including a prehistoric one called Helicoprion with a mouth like a spiral saw, another prehistoric one called Stethacanthus with a dorsal fin in the shape of an ironing board, and today’s strange goblin and sawfish sharks.
(Reporting by Will Dunham, Edited by Rosalba O’Brien)