ResearchEagle Shark Flew Through the Ocean 93 Million Years Ago
19 March 2021
Scientists discover fossil of hitherto unknown plankton eater in Mexico
New insights into the history of shark evolution are offered by the fossil of a hitherto unknown primeval fish. It was discovered in a quarry in Mexico by a European-Mexican paleontological team, of which Prof. Dr Wolfgang Stinnesbeck from Heidelberg University is a member. The find is a type of shark from the Cretaceous Period. The planktivorous “eagle shark” called Aquilolamna milarcae had huge, wing-like pectoral fins with which it – like present-day manta rays – “flew” through the Cretaceous seas 93 million years ago.
During its lifetime the fish had a pectoral fin width of 1.9 metres although it was only 1.7 metres long. On the basis of this extraordinary physique, the researchers underline that the newly discovered primeval fish had a variable swimming technique. It could not only use its pectoral fins to fly like a manta ray but also – like other sharks – swim by kicking its forked tail fins. The broad mouth, which the researchers believe may have had tiny teeth, was situated at the end of the blunt head. “It’s very likely that the shark was planktivorous, like modern-day whale sharks or manta rays,” suspects Prof. Stinnesbeck from the Institute of Earth Sciences at Heidelberg University.
The primeval fish enables new insights into the history of shark evolution. With respect to the creature’s build, which was unknown to date with these fish, the scientists speak of an “unexpected evolutionary experiment”. Wing-like pectoral fins in combination with a nutrition-filtering way of living had so far only been known in the case of manta rays and their kinship, which did not make an appearance in the earth’s history until 30 million years later. The current investigations show that, in the course of evolution, there have evidently been two separate cases of “underwater flight” using pectoral fins – by planktivorous sharks and rays. While they do it in different ways, the result is the same: the fish fly through the oceans in order to filter plankton out of the water.
The “eagle shark” fossil was found in a platy limestone quarry near the northeast Mexican town of Vallecillo. It contains numerous fossils that supply a unique snapshot of the habitat of the open ocean 93 million years ago, including turtles, sharks and marine saurians. Ammonite fossils were also found, which belong to the class of cephalopods and played an important role in determining the age of the newly discovered fossil shark. Scientists from Heidelberg University have been investigating the Vallecillo fossil storage site for many years and have already discovered a host of excellently preserved fish and marine reptiles.
Other scientists involved, besides Prof. Stinnesbeck and his team, were from the universities of Rennes (France) and Bonn, the Jura Museum Eichstätt of the Bavarian Natural History Collections, the State Museum of Natural History Karlsruhe and the Museo del Desierto in Mexico. The project was funded by the German Research Foundation. The results were published in the journal “Science”.
R. Vullo, E. Frey, C. Ifrim, A. González González, E.S. Stinnesbeck, W. Stinnesbeck (2021): Manta-like planktivorous sharks in Late Cretaceous oceans. Science