A new species of shark with hypertrophy, slender pectoral fins has been identified from the fossilized remains discovered in northern Mexico.
Life reconstruction of Aquilolamna milarcae. Image credit: Oscar Sanisidro.
The newly identified shark species, called Aquilolamna milarcae, swam about 93 million years ago in the late Cretaceous oceans.
“The complete sample was found in 2012 in Vallecillo, Mexico, an area that produces remarkably well-preserved fossils,” said lead author Dr. Romain Vullo, of the University of Rennes and the CNRS and colleagues said.
“This site, already known for its many fossils of ammonites, bony fish and other marine reptiles, is the best to document the evolution of oceanic animals.”
Aquilolamna milarcae belongs to Lamniformes, an order of sharks in the subclass Elasmobranchii.
“Elasmobranchs are the most successful group of cartilaginous fish, including sharks, skaters and rays,” said paleontologists.
“They first appeared in Earth’s oceans about 380 million years ago and have since evolved to fulfill a variety of ecological roles.”
“Modern plankton-feeding elasmobranches are characterized by two distance-related clays – those with a more ‘traditional’ shark-like body shape, such as whale and pit sharks, and those with the smooth, flat bodies and wing-like fins of Mobulidae rays.”
“Standing out between living and fossil planktors (plankton-eating) sharks and rays, Aquilolamna milarcae live somewhere in between. ”
Fossil of Aquilolamna milarcae found in the limestone of Vallecillo, Mexico. Image credit: Wolfgang Stinnesbeck.
Aquilolamna milarcae has many characteristics similar to modern manta rays, especially long, thin fins and a mouth adapted to feed filter, indicating that it was planktivorous.
“It had a finch with a well-developed superior lobe, typical of most pelagic sharks, such as whale sharks and tiger sharks,” said Dr. Vullo said.
“Its anatomical features thus give it a chimeric appearance that combines sharks and rays.”
“With its large mouth and supposedly very small teeth, it must have fed on plankton.”
Aquilolamna milarcae was a relatively slow swimmer, using both his long pectoral fins and tail to glide through the water while scooping up hanging plankton using his large, gaping mouth.
“His body plan represents an unexpected evolutionary experiment with underwater flight under sharks, more than 30 million years before the rise of Mobulidae rays, and shows that wing-like pectoral fins developed independently in two closely related clusters of filter-feeding elastomeric branches,” the researchers said. . said.
The discovery of Aquilolamna milarcae is reported in a paper in the journal Science.
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Romain Vullo et al. 2021. Manta-like planktivorous sharks in late-Cretaceous oceans. Science 371 (6535): 1253-1256; doi: 10.1126 / science.abc1490