By Will Dunham
WASHINGTON (Reuters) – About 93 million years ago, a bizarre plankton-eating shark unlike any other known marine animal slipped through the sea in present-day northeastern Mexico with strange elongated wing-like fins that made its body wider than it had long been .
Scientists on Thursday announced the discovery of an almost complete fossil of the shark, called Aquilolamna milarcae, which lived in the Cretaceous during a time when dinosaurs ruled the country.
Its unusual proportions – a 1.9-meter fin pan and a 1.65-meter head-to-tail length – amaze scientists.
Aquilolamna’s name means ‘eagle shark’, a wink to its slender pectoral fins, which ‘acted primarily as an effective stabilizer’, according to 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, strange. Yes, it is the only shark that is wider than long,” says Vullo, associated with Geosciences Rennes, a research unit in which the University of Rennes and France’s National Center for Scientific Research (CNRS).
“Aquilolamna is indeed a perfect example of an extinct creature that reveals an unexpected new morphology. It strongly suggests that other outstanding body shapes and morphological adaptations may have existed throughout the evolutionary history of sharks,” Vullo said.
Like all sharks and the related skates and rays, Aquilolamna has a cartilaginous skeleton. It had the familiar torpedo-shaped body and tail of a shark, but the pectoral fins were completely unique. According to the researchers, it appears that Aquilolamna was a slow-swimming shark fed by plankton by plankton, as the plankton-eating whale sharks and pit sharks do today.
The fossil excavated in the state of Nuevo Leon in Mexico did not reveal the filter mechanism of Aquilolamna for food.
Rays like the manta ray, with their flattened bodies and large pectoral fins fused to the head, swim through the water as if they were flying through the air. It looks like Aquilolamna has done something similar.
“While the movement of manta rays is like a flight underwater, with fluttering movements of their powerful pectoral fins, the long slender pectoral fins of Aquilolamna acted rather than the wings of a glider or glider,” Vullo said.
Aquilolamna lived in the open ocean at a time when the sea was populated with marine reptiles, squid family with large shells called ammonites, various bonefish and large sharks. The largest predator in its ecosystem was a shark called Cretoxyrhina, which was 6 meters long.
The fish group that includes sharks appeared about 380 million years ago, long before the dinosaurs.
Aquilolamna is not the only unusual shark that has swum the earth’s oceans. Sharks and their relatives have taken many shapes and sizes – including a prehistoric name called Helicoprion with a mouth like a spiral saw, another prehistoric name called Stethacanthus with a dorsal fin shaped like an ironing board, and the strange gnome and sawfish of today. Sharks.
(Reporting by Will Dunham, Editing by Rosalba O’Brien)