The eagle shark sailed the waters of the Gulf of Mexico 93 million years ago

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A group of scientists reconstructs the steps of a hitherto unknown species from a fossil found in 2012 in Vallecillo, in northeast Mexico.

An animal that today might seem unimaginable plowed the waters of North America about 93 million years ago. “When you take a first look at this specimen, you realize that you are looking at something extraordinary and completely new,” says Romain Vullo, an academic at the University of Rennes, one of the discoverers of the first and only specimen of Aquilolamna milarcae

The commonly called eagle shark had two huge pectoral fins, more similar to those of a stingray: the “wings” that give it its colloquial name. The fossil was found in 2012 in Vallecillo, a small community in the Mexican state of Nuevo León., but it was until just over a week ago that the new species was documented in the prestigious journal Science.

“Its proportions are unique,” explains the paleontologist, “and it gives us a lot of information about the ancient morphological diversity of sharks.” The Aquilolamna was a shark wider than it was long, measuring 1.9 meters from side to side and 1.6 meters in length. Its discovery dates from the mid- Cretaceous, a geological period that began 145 million years ago and ended about 66 million years ago. “He’s a bit older than a T. Rex,” says Vullo.

The fossil of 'Aquilolamna milarcae' found in Vallecillo, Mexico.
The fossil of ‘Aquilolamna milarcae’ found in Vallecillo, Mexico. WOLFGANG STINNESBECK / AFP

The reconstructions that a team of European scientists has made allow us to know some aspects of the life of these animals. The Aquilolamna had long fins but did not use them like stingrays, which move them up and down. His were practically immobile and he used them as a paraglider to help him steady himself. It carried like a small submarine plane, pushed slowly by its tail fin, on the back of its body.

Vullo, who has been interested in sharks since childhood, laughs when he comments that the most threatening thing about the eagle shark is probably its name. Its slow swim, flattened head, and small teeth indicate that it was not a predator that hunted other species. The researchers’ hypothesis is that it fed on plankton.

The discovery is exceptional, Vullo points out because the most common thing in shark paleontology is to find teeth because their skeletons are cartilaginous and they are not so hard as to withstand the passage of millions of years. In the case of Aquilolamna it is the opposite. The fossil of his body is very well preserved, but he has no teeth in his mouth. That detail has been the most complicated part of the research because the teeth are key to knowing with greater certainty how it fed and to classify it compared to other sharks. There are other enigmatic parts of its anatomy such as whether or not it had a dorsal or pelvic fin, which was not identified when it was unearthed.

To imagine its habitat you have to think about what the world was like during the Cretaceous. About 90 million years ago, the water level was much higher than today because it was a very warm period and there was no ice at the poles, says the scientist. The sea was between 150 and 200 meters higher than today and North America was split into two islands. The western part was bounded by the Rocky Mountains and the eastern side by the Appalachian Mountains. Between the two pieces of land, there was an inland sea that stretched from the Arctic, passed through the center of present-day Canada and down to the Gulf of Mexico.

Vallecillo, which is now an extensive semi-desert plain in the northeast of the country, was a coastal plain and became a site that has preserved an ocean ecosystem. It was quite far from the coast that Mexico had during the Cretaceous. The eagle shark probably spent most of its time in the middle of the ocean and swam to the reefs near the shore.

“In the proto-Gulf of Mexico there was a very rich ecosystem,” says Vullo. When the animals died, the corpses went to the bottom, which was favorable to preserving their skeletons due to the absence of scavengers and sea currents. “It was a fairly calm ocean floor with very little activity, the sediment was very fine,” he explains.

That is the secret that Vallecillo has gained international fame as an exceptional site. It was in the same area that the Mauriciosaurus Fernandezi was found in 2011, a fossil of a marine reptile that was baptized six years later in honor of Mauricio Fernández, a millionaire businessman and local politician who is seeking a fourth term as mayor of San Pedro Garza. García, the richest municipality in Nuevo León and all of Mexico.

“I never expected to find such a ‘crazy’ and incredible species,” confesses Vullo, who believes there will be more discoveries in Vallecillo. “You have to wait and cross your fingers,” he adds. Now, the team seeks to find out if the teeth that have been found in the area corresponding to the Aquilolamna and, if we are lucky, find another specimen that will keep company and help to discover more characteristics of the enigmatic eagle shark.

Source: EL PAÍS 

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