Aquilolamna milarcae: Cretaceous Plankton-Eating Shark Had Long, Wing-Like Fins
A new species of shark with hypertrophied, slender pectoral fins has been identified from the fossilized remains discovered in northern Mexico.
The newly-identified shark species, named Aquilolamna milarcae, swam in the Late Cretaceous oceans, approximately 93 million years ago.
“The complete specimen was found in 2012 in Vallecillo, Mexico, a locality yielding remarkably preserved fossils,” said lead author Dr. Romain Vullo from the University of Rennes and the CNRS and colleagues.
“This site, already famous for its many fossils of ammonites, bony fish and other marine reptiles, is most useful for documenting the evolution of oceanic animals.”
“Elasmobranchs are the highly successful group of cartilaginous fishes, including sharks, skates and rays,” the paleontologists said.
“They first appeared in Earth’s oceans roughly 380 million years ago and have since evolved to fill a diverse array of ecological roles.”
“Modern plankton-feeding elasmobranchs are characterized by two distantly related clades — those with a more ‘traditional’ shark-like body shape, such as whale and basking sharks, and those with the sleek, flattened bodies and winglike fins of Mobulidae rays.”
“Standing out among both living and fossil planktivorous (plankton-eating) sharks and rays, Aquilolamna milarcae resides somewhere in-between.”
Aquilolamna milarcae had many features similar to modern manta rays, notably long, slender fins and a mouth adapted to filter feeding, suggesting that it was planktivorous.
“It had a caudal fin with a well-developed superior lobe, typical of most pelagic sharks, such as whale sharks and tiger sharks,” Dr. Vullo said.
“Thus, its anatomical features thus give it a chimeric appearance that combines both sharks and rays.”
“With its large mouth and supposed very small teeth, it must have fed on plankton.”
Aquilolamna milarcae was a relatively slow swimmer, using both its long pectoral fins and tail to glide through the water while scooping up suspended plankton using its large, gaping mouth.
“Its body plan represents an unexpected evolutionary experimentation with underwater flight among sharks, more than 30 million years before the rise of Mobulidae rays, and shows that winglike pectoral fins have evolved independently in two distantly related clades of filter-feeding elasmobranches,” the researchers said.
The discovery of Aquilolamna milarcae is reported in a paper in the journal Science.
Romain Vullo et al. 2021. Manta-like planktivorous sharks in Late Cretaceous oceans. Science 371 (6535): 1253-1256; doi: 10.1126/science.abc1490