An enigma’: scientists finally learn what giant prehistoric shark looked like

Fossil experts have reported gaining unprecedented insights into a type of enormous prehistoric shark after finding complete skeletons of the creatures.

In the last decade, they discovered the specimens in small quarries in northeastern Mexico. These specimens are of Ptychodus, a creature that roamed the seas from around 105 million to 75 million years ago.

Previously, Ptychodus fossils, primarily consisting of isolated, huge, and unusual teeth, had been found. Since its bones were made of cartilage, which does not mineralize well, it was challenging to determine precisely what Ptychodus looked like and its position on the evolutionary family tree.

Dr. Romain Vullo, the first author of the research from the University of Rennes, said, “Its general appearance has remained a mystery until now due to the lack of more complete material for almost two centuries.”

“The new specimens from Vallecillo have revealed the body shape and anatomy of this extinct shark, solving this enigma,” he added.

Prof. Michael I. Coates from the University of Chicago, who did not participate in the study, described the new fossils as superb.

“Ptychodus has always been a classic example of teeth in search of a body,” he commented. “And now we have it, with detailed analyses of where it fits in the shark family tree and a good attempt at understanding its ecomorphology – how it integrated into the marine ecosystems of the late Cretaceous.”

Writing in the journal Proceedings of the Royal Society B, Vullo and his colleagues discuss their study of six Ptychodus specimens, dating from about 93 million years ago.

One of these was a complete specimen providing a side view of Ptychodus, including almost all its skeletal elements as well as teeth, preserved muscle remains, and a body outline with all its fins.

Three more of the specimens were almost complete, including a juvenile that measured just over 56 cm in length, while the other two specimens were incomplete or partial skeletons.

The team noted that the plethora of features preserved within the specimens, including the fin skeletal anatomy, allowed them to conduct a new analysis of where Ptychodus ranks on the evolutionary family tree.

Their findings classify Ptychodus as a type of mackerel shark, a group that also includes the extinct gigantic shark Megalodon and the contemporary great white shark.

Furthermore, the researchers pointed out that Ptychodus’ overall body shape and proportions, along with specific features like the size, shape, and position of its fins and its thick vertebral column, suggest that it was fast-swimming. Its massive, pavement-like teeth also support earlier conclusions that it fed on shelled creatures.

The findings indicate that Ptychodus likely hunted prey in open water, feeding on creatures such as sea turtles and ammonites, rather than sea-floor dwellers like clams, as previously thought.

Vullo explained that Ptychodus was once generally believed to resemble benthic sharks like the modern nurse shark, but we now understand it more closely resembled the extant porbeagle shark, a fast-swimming pelagic type.

Although Ptychodus may have been the largest shark ever to subsist on such a diet, the new fossils suggest its maximum length was about 9.7 meters—larger than today’s great white shark but smaller than previously estimated lengths of over 10 meters.

The study also suggests that the extinction of Ptychodus could have been due to competition with other large marine predators that fed on similar prey.

Patrick L. Jambura, a fossil fish expert at the University of Vienna who did not participate in the study but works closely with three of the authors, emphasized the significance of these findings. He noted that more than a third of all sharks and rays today are threatened with extinction.

“Ptychodus offers us a mirror reflecting what could happen to large apex predators like the white shark if we, their main competitors, do not reconsider our actions,” he remarked.

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