New Delhi, India

Scientists finally have an idea of what a shark that lived in the sea during the Cretaceous Period looked like. Till now, only its teeth had been available for study. The fish had large and rounded teeth, which it used to crush shelled creatures. Scientists have discovered its remains from limestone quarries in northeastern Mexico which is helping them understand what the fish looked like. One of the fossils, found in Nuevo León near the municipality of Vallecillo, shows the complete skeletal elements of the fish. 

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The predator was first discovered in the 18th century and its fossil records only consist of teeth since shark skeletons are made of cartilage, which means they do not fossilise well. The latest discovery also helps us place the genus Ptychodus on the shark evolutionary tree. Experts say it will help know more about the evolution of present-day sharks. The study on the shark has been published in the journal Proceedings of the Royal Society B: Biological Sciences. 

Species belonging to the Ptychodus genus lived 100 and 80 million years ago. As per a CNN report, the fossils were discovered in deposits dating back to approximately 93.9 to 91.85 million years ago. The size of the shark is now believed to be smaller than once thought. They possibly were 9.7 metres in length, as opposed to the size of a previous species known as Ptychodus mortoni which was estimated at 11.2 metres. 

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Why did it go extinct?

The six fossils found at the site, including the complete specimen, were studied and the study authors deduced that Ptychodus belonged to the order of sharks known as Lamniformes, or mackerel sharks. Notably, the extinct Otodus megalodon and the modern great white shark also belong to this group. The species of megamouth, sand, goblin and basking sharks, are also from the same family. 

As per the study, the shape of the shark's body and the location of the fin suggest that it might have been a predator and possibly hunted sea turtles and large ammonites. Previously, it was believed that it was simply a bottom dweller and fed only on molluscs found on the ocean floor. The authors say it being a predator might have played a role in its extinction since the shark was now competing with other Late Cretaceous marine predators for food.