An ancient shark’s weird fins helped it glide like a manta ray

Thirty million years before manta rays began gracefully gliding through ocean waters, a shark with fantastically elongated fins gave such underwater flight a go, researchers report in the March 19 Science.

A quarry worker unearthed the fossil of the strange shark, now dubbed Aquilolamna milarcae, in 2012 from a rock layer in northeastern Mexico dating to about 93 million years ago. The shark’s most distinctive feature is the long curving fins that swoop out from its sides. Spanning nearly 2 meters from tip to tip, the fins’ length rivals the wingspan of bald eagles. Nicknamed eagle shark by researchers, A. milarcae may have used the fins to stabilize itself or propel itself in a manta ray–like fashion.

The eagle shark’s broad, rounded head, long jaws and small teeth hint that it may have been a filter feeder, sucking in floating plankton from seawater. Its torpedo-shaped body and high tail fin suggest the shark was an active swimmer, although not a particularly fast one, say vertebrate paleontologist Romain Vullo of the University of Rennes in France and colleagues.

A. milarcae may have been a member of a highly diverse group of sharks that includes extinct megalodons as well as modern great whites and filter-feeding basking sharks (SN: 8/2/18). Although that group once dominated the seas, many of its members became extinct after an asteroid struck Earth about 66 million years ago.