The idea of a shark with similar characteristics to stingrays may seem like something appropriate for a low-budget sci-fi movie. However, paleontologists have reported discovering such a creature in the Cretaceous period rock of Mexico. This strange shark combines a streamlined body with expansive wing-like fins, an ancient creature unlike anything ever found before in the fossil record.
In 2012, an unknown quarry worker found a strange set of bones in 95-million-year-old rock layers near Vallecillo, Mexico, says Romain Vullo, a paleontologist at the Karlsruhe State Museum in Germany. The fossil caught the attention of local paleontologist Margarito González González, who collected it and prepared it by cutting rocks from the preserved skeleton. Photos of the shark began to make waves at paleontological conferences, and the specimen was described in a study published today in the journal. Sciences.
Called Aquilolamna milarcae, the six-foot-long fossil represents a filter-feeding species of shark like no other previously known. “My first thought when I saw the fossil was that this unique morphology is totally new and unknown among sharks,” says Vullo, lead author of the new study. Most of the time, fossil sharks are identified by their teeth and the occasional part of the spine. Finding a complete skeleton, and one so rare, presents a rare opportunity to study the anatomy of this ancient swimmer.
Although there are no teeth Aquilolamna Vullo and his colleagues propose that it belongs to the same family of sharks that includes the great white, shortfin and basking sharks. However, the broad head and long wing-shaped fins hint that it was not a hunter. Aquilolamna It was more likely to filter feed, opening its mouth to sift plankton and other small organisms out of the water.
A prehistoric rarity
Aquilolamna It appears to combine characteristics of both sharks and stingrays, the latter of which would not evolve until millions of years later. The body of Aquilolamna It is long and tube-shaped, similar to many sharks that navigate the oceans today. But the expanded pectoral fins are reminiscent of stingrays and devil’s rays, forming broad underwater wings.
This would do Aquilolamna one of the oldest known animals that moves through “underwater flight”, slowly flapping its fins like live stingrays. “Aquilolamna may have been swimming relatively slowly with slight movements of its tail fin [tail fin] and the long pectoral fins acted primarily as an effective stabilizer, ”says Vullo.
This type of body plan is completely unexpected for sharks, says Kenshu Shimada, a professor of paleobiology at DePaul University in Chicago. The oldest sharks from before the time of the dinosaurs had a wide variety of different body shapes, but by the Cretaceous period, they were thought to have evolved into much more modern shapes.
Aquilolamna It could be evidence that a wide variety of strange sharks continued to exist for much longer than previously thought. “The proposed body shape and filter feeding lifestyle in the new study are quite compelling,” says Shimada.
Shark or something else entirely?
But not all experts are convinced that this new creature was a manta-like shark. “There are many unusual features described by these authors, and I have some reservations about some of their interpretations, so I would be excited to see more research on this remarkable new fossil,” says Allison Bronson, a paleontologist at Humboldt State University of California.
While the impressions of the skin of Aquilolamna are mentioned in the new study, they are not shown in enough detail for outside experts to determine whether the tissue is really fossilized skin or some other material that resembles skin, such as a bacterial mat. And while this fish likely fed by sifting plankton or other small morsels from the water column, it may have had tiny, pointed teeth similar to modern filter-feeding sharks like the basking shark and megamouth. These teeth can be used to determine the evolutionary relationships of these sharks, but none were found with the new fossil.
“It’s really unfortunate that no teeth were preserved in the specimen that could have allowed the researchers to determine the exact taxonomic affinity of the new shark,” says Shimada.
The idea that this animal was a shark and a filter feeder probably needs to be confirmed by future findings and further analysis. If this interpretation is correct, Aquilolamna it was straining the seas for plankton long before its modern relatives evolved to do the same. Perhaps this shark represents a particular way of filtering food that evolved before the mass extinction at the end of the Cretaceous period that killed roughly 75 percent of all marine species. Other filter feeders, including the ancestors of megamouth, whale, and basking sharks, evolved after the world’s oceans recovered.
Yes Aquilolamna it was in fact a strange relative of basking sharks, there were probably even stranger sharks or sea creatures that paleontologists have yet to discover. “The fossil record for sharks and rays is good” in terms of time periods covered, says Vullo, but “the body shape of many extinct species remains enigmatic.” Perhaps some teeth that paleontologists have already found belonged to oddly shaped animals.
Even the famous giant shark Otodus megalodon It has only been described from teeth and vertebrae (megalodon means “big tooth” in Greek), leading to various interpretations of what the animal might have been like. Exceptional fossils, such as that of Aquilolamna, hint that many fossil sharks may have been much weirder than scientists expected.
“When we have the opportunity to discover complete skeletons in locations like Vellecillo,” says Vullo, “we can have some surprises.”