The idea of a shark with manta-ray-like characteristics may seem appropriate for a low-budget science film. Yet paleontologists report that they discovered just such a creature in the rock of the Cretaceous period of Mexico. This strange shark combines a streamlined body with outstretched wing-like fins, an ancient creature found nothing but in the fossil record.
In 2012, an unknown quarryman found a strange set of bones in 95-million-year-old rock formations near Vallecillo, Mexico, says Romain Vullo, a paleontologist at the Karlsruhe State Museum in Germany. The fossil came to the attention of local paleontologist Margarito González González, who collected and prepared it by cutting off the rock from the preserved skeleton. Photographs of the shark began to wave at paleontological conferences and the monster was described in a study published in the journal today. Science.
Name Aquilolamna milarcae, the six-foot-long fossil represents a type of shark that feeds filters, unlike what was previously known. “My first thought about seeing the fossil was that this unique morphology is completely new and unknown among sharks,” says Vullo, the lead author of the new study. Most of the time, fossil sharks are identified by teeth and occasionally a piece of spine. Finding a complete skeleton, and one that is so strange, offers a rare opportunity to study the anatomy of this ancient swimmer.
Although no teeth of Aquilolamna found, Vullo and colleagues suggest that it belongs to the same shark family that includes great white, mako and bowl sharks. The broad head and long, wing-like fins indicate, however, that it was not a hunter. Aquilolamna was probably a filter feed, which opened its mouth to sift plankton and other small organisms out of the water.
A prehistoric strangeness
Aquilolamna seems to combine the properties of both sharks and manta rays, the latter of which would only develop millions of years later. The body of Aquilolamna is long and tubular, similar to many sharks that sail through the oceans today. But the elaborate pectoral fins are reminiscent of manta rays and devil rays, forming broad underwater wings.
It would make Aquilolamna one of the oldest known animals that moved by means of an ‘underwater flight’, and clapped slowly like the living manta rays with its fins. ‘Aquilolamna may have swum relatively slowly with slight movements of its tail fin [tail fin] and the long pectoral fins acted mainly as an effective stabilizer, ‘says Vullo.
This kind of body plan is completely unexpected for sharks, says Kenshu Shimada, a professor of paleobiology at DePaul University in Chicago. Older sharks from before the time of the dinosaurs had a wide variety of body shapes, but in the Cretaceous they were thought to have evolved into much more modern shapes.
Aquilolamna may be proof that a wide variety of alien sharks have persisted for much longer than previously thought. “The proposed body shape and filter feeding style in the new study is very convincing,” says Shimada.
Shark or something else?
But not all experts are convinced that this new creature was a rooster of manta. “There are many unusual features described by these authors, and I have some doubts about some of their interpretations, so I would be excited to see further research into this new, remarkable fossil,” says Allison Bronson, a paleontologist from Humboldt State. University of California.
While skin impressions of Aquilolamna mentioned in the new study, it is not shown enough for outside experts to determine if the tissue is really a fossilized skin or another material that looks like a bacterial mat. And although this fish is probably fed by sifting plankton or other small pieces out of the water column, it may have had small, pointed teeth, similar to modern sharks such as filter sharks and megamonds. These teeth can be used to determine the evolutionary ratios of these sharks, but nothing has been found with the new fossil.
“It’s really unfortunate that no teeth have been preserved in the sample that have allowed researchers to determine the exact taxonomic affinity of the new shark,” says Shimada.
The idea that this animal is a shark and a filter feeder should probably be confirmed by future finds and additional analyzes. If this interpretation is correct, Aquilolamna was testing the sea for plankton long before its modern relatives developed to do the same. Perhaps this shark is one specific way of filtering feed that evolved before the mass extinction at the end of the Cretaceous, which killed about 75 percent of all marine species. Other filter feeds, including the ancestors of megamouth, whale and cow sharks, evolved after the world’s oceans receded.
As Aquilolamna was indeed a strange relative of the shark, there were probably even more strange sharks or marine animals that paleontologists had not yet discovered. “The fossil record of sharks and rays is good” in terms of periods, says Vullo, but “the body shape of many extinct species remains enigmatic.” Perhaps some teeth that paleontologists have already found belong to strangely shaped animals.
Even the famous giant shark Otodus megalodon was only described from teeth and vertebrae – megalodon means ‘big tooth’ in Greek – which led to differing interpretations of what the animal might look like. Exceptional fossils, such as those of Aquilolamna, suggests that many fossil sharks may have been much stranger than scientists ever expected.
“If we have the opportunity to discover complete skeletons in places like Vellecillo,” says Vullo, “we may have some surprises.”