Fossil experts have uncovered remarkable insights into a massive prehistoric shark species by discovering complete skeletons of the creatures.
The findings, unearthed in small quarries in north-eastern Mexico over the past decade, pertain to Ptychodus – a creature that inhabited the seas between approximately 105 million and 75 million years ago.
While Ptychodus fossils had been found previously, their cartilage-based bones made mineralisation difficult, resulting in mostly isolated teeth, which were notably large and unusual.
As a consequence, accurately determining Ptychodus' appearance and its place on the evolutionary tree had been challenging.
Dr. Romain Vullo, lead author of the research from the University of Rennes, remarked, “Its overall appearance has remained a puzzle due to the scarcity of comprehensive material over nearly two centuries. The discovery of new specimens from Vallecillo, elucidating the body shape and anatomy of this extinct shark, resolves this mystery.”
Documented in the journal Proceedings of the Royal Society B, Vullo and colleagues analysed six Ptychodus specimens dating back about 93 million years. One specimen, complete with almost all skeletal elements, teeth, preserved muscle remains, and a body outline with fins, provided a comprehensive view of Ptychodus. Three other specimens were nearly complete, including a juvenile measuring just over 56 cm, while the remaining two were incomplete skeletons.
The preserved features, including fin skeletal anatomy, enabled a fresh analysis of Ptychodus' evolutionary position. The study suggests Ptychodus belonged to the mackerel shark group, which includes the extinct megalodon and the modern
Ptychodus is inferred to have been a fast swimmer, with a diet primarily comprising sea turtles and ammonites rather than bottom-dwelling creatures like clams, as previously thought.
Dr. Vullo commented, “Ptychodus was previously likened to benthic sharks like the modern nurse shark, but now we know it resembled the porbeagle shark, a fast-swimming pelagic species.” The fossils indicate Ptychodus may have reached a maximum length of about 9.7 meters, smaller than previously estimated.
The study also suggests Ptychodus may have faced extinction due to competition with other predators, such as large aquatic reptiles, that fed on similar prey.
Patrick Jambura, a fossil fish expert at the University of Vienna, emphasised the importance of these findings, given the significant threat of extinction facing many sharks and rays today. He said, “Ptychodus serves as a warning, illustrating the potential fate of large apex predators like the white shark if we don't reconsider our actions.”
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