Tooth morphology on shark evolution across mass extinction



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Tooth morphology on shark evolution across mass extinction

The Cretaceous-Paleogene mass extinction was a dramatic reduction in the number of living species on Earth, which occurred about 65.95 million years ago, which led to the disappearance of about 80% of existing marine and continental species.

This extinction led to the disappearance of approximately 80% of Cretaceous plant and animal species including dinosaurs. The cause of the extinction at the end of the Cretaceous period could be traced back to the impact of an asteroid in the Gulf of Mexico 66 million years ago and the consequent environmental changes of that event.

In the past, several hypotheses have been formulated to explain this mass extinction. Researchers Gerta Keller, Thierry Adatte, Wolfgang Stinnesbeck, Mario Rebolledo-Vieyra, Jaime Urrutia Fucugauchi, Utz Kramar and Doris Stüben believe that the impact of the meteorite occurred at least 300,000 years before the extinction of the dinosaurs.

According to them, the demise of the great reptiles was caused by an incredibly violent series of volcanic eruptions in the Deccan, a region of India. These huge eruptions would have caused those climatic upheavals that led to mass extinction.

The enormous amount of gas, and other substances emitted by volcanoes, would almost certainly have caused the effects that paleontologists can now observe in sedimentary rocks dating back to about 65 million years ago. The research Tooth morphology elucidates shark evolution across the end-Cretaceous mass extinction, published on the PLoS biology, explained: "Sharks (Selachimorpha) are iconic marine predators that have survived multiple mass extinctions over geologic time.

Their prolific fossil record is represented mainly by isolated shed teeth, which provide the basis for reconstructing deep time diversity changes affecting different selachimorph clades. By contrast, corresponding shifts in shark ecology, as measured through morphological disparity, have received comparatively limited analytical attention.

Here, we use a geometric morphometric approach to comprehensively examine tooth morphologies in multiple shark lineages traversing the catastrophic end-Cretaceous mass extinction-this event terminated the Mesozoic Era 66 million years ago.

Our results show that selachimorphs maintained virtually static levels of dental disparity in most of their constituent clades across the Cretaceous- Paleogene i nterval. Nevertheless, selective extinctions did impact apex predator species characterized by triangular blade-like teeth.

This is particularly evident among lamniforms, which included the dominant Cretaceous anacoracids. Conversely, other groups, such as carcharhiniforms and orectolobiforms, experienced disparity modifications, while heterodontiforms, hexanchiforms, squaliforms, squatiniforms, and † synechodontiforms were not overtly affected.

Finally, while some lamniform lineages disappeared, others underwent postextinction disparity increases, especially odontaspidids, which are typified by narrow-cusped teeth adapted for feeding on fishes. Notably, this increase coincides with the early Paleogene radiation of teleosts as a possible prey source, and the geographic relocation of disparity sampling spots, perhaps indicating a regionally disjunct extinction recovery.

Ultimately, our study reveals a complex morphological response to the end-Cretaceous mass extinction and highlights an event that influenced the evolution of modern sharks."