The fossil shark Ptychodus was first identified 190 years ago, but over the past centuries of paleontological research it has been difficult to get a comprehensive look at the ancient fish. Until now. In a paper published Last week in the Proceedings of the Royal Society B, a team of researchers described an exceptionally well-preserved specimen Ptychodus, petrified from the nose to the tip of the tail.
In their research, the paleontologists analyzed six almost complete ones Ptychodus Specimens excavated in Vallecillo, Mexico, in the last decade. The specimens show the skeletal components of the sharks as well as their preserved body outlines. The team used the fossils to uncover new information about shark anatomy and their place in the shark family tree.
“This new study provides crucial information about affinities [evolutionary relations] and the paleoecology of Ptychodus” said Romain Vullo, a paleontologist at the University of Rennes in France and lead author of the study, in an email to Gizmodo. “So far, this Cretaceous shark was only known from isolated teeth [sets of teeth]and some skeletal elements such as vertebrae.”
“The complete specimens from Mexico show this Ptychodus “was a fast-swimming open-water shark (similar in shape to the living porbeagle shark) that probably fed primarily on ammonites and sea turtles using its gnashing jaws,” Vullo added.
In 2021, Vullo was the lead author of an article describing the following Aquilolamna milarcaeA Bizarre looking lamniform shark from the Cretaceous period which was excavated in the same area of eastern Mexico. In the current publication, the team also classified Ptychodus as a lamniform shark – a mackerel shark – and assume that the animal’s extinction may have been due to competition with it Mosasauran extinct group of giant marine reptiles.
But the reality may be more complicated, as Tyler Greenfield, a paleontologist at the University of Wyoming, explained to Gizmodo. Instead of being a mackerel shark, Greenfield suggests Ptychodus belongs to a completely different category.
“Sharks of the order Lamniformes have specific patterns in the size and shape of the teeth, the cavities in the jaw that hold the rows of teeth, and the cartilage structures inside the vertebrae Ptychodus has not,” Greenfield, who is not affiliated with the new newspaper, wrote in an email. “These features were overlooked by the authors of the new work and instead used certain features of the skull and jaw that are not unique to lamniforms for classification Ptychodus.”
Greenfield added that based on similarities between Ptychodus and both Squalicorax And Ptychocorax (two more species of ancient sharks), including the shark family Ptychodus and that which includes the latter two species should be placed in a separate order, Anacoraciformes or Crow Sharks.
“Anacoraciformes was named by other authors before me, but it has not been used as validly since then, nor did it include ptychodontids until now,” Greenfield said, adding that the teeth built to crush armored prey probably would have evolved outside of Lamniformes. “Overall, my hypothesis aims to provide a more accurate picture of the relationships and diversity of prehistoric sharks,” Greenfield said.
One might assume that such immaculately preserved fossils would clarify, rather than complicate, aspects of the shark’s phylogeny. But regardless of how the dust settles Ptychodus‘ classification, it is refreshing – and indeed incredibly fortunate – that paleontologists have such well-preserved specimens to use in making their decisions.
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