Shark diversity was not affected when dinosaurs were wiped out in a global disaster
The selective extinction of apex predators suggests a shift towards more generalist diets.
A global catastrophe 66 million years ago resulted in the extinction of all non-avian dinosaurs and large marine reptiles like mosasaurs and plesiosaurs. But what happened to the sharks? According to a study on shark teeth published on August 10e in the open access journal PLOS Biology by Mohamad Bazzi of Uppsala University and colleagues, the diversity of shark teeth remained relatively constant throughout the mass extinction event at the end of the Cretaceous.
Researchers analyzed the morphology of 1,239 fossil shark teeth, including species in eight extant orders and one now extinct order. The teeth cover a period of 27 million years, from the late Cretaceous 83.6 million years ago to the early Paleogene 56 million years ago, across the so-called K-Pg border which has ended the age of dinosaurs.
Scientists found that shark dental diversity already declined before the K-Pg limit, but remained relatively constant during the mass extinction event itself. Some groups of apex predators, particularly those with triangular blade-shaped teeth, experienced selective extinctions during the period studied, which may have been linked to the extinction of their prey species.
However, other lines of sharks increased their dental diversity after the K-Pg limit. For example, sharks in the Odontaspididae family, which have narrow, cuspid teeth adapted to feed on fish, showed an increase in diversity that coincided with the rapid diversification of finfish in the early Paleogene. The authors suggest that this pattern of selective extinctions may reflect an ecological shift from specialized tetrapod predators to more general diets of bony fish.
This study is the first global study of dental morphology in multiple groups of sharks at the end of the Cretaceous mass extinction event, and indicates that the K-Pg limit was not as dramatic for sharks, as it This was the case for most of the other vertebrate lineages.
Reference: “Tooth morphology elucidates shark evolution across the end-Cretaceous mass extinction” by Mohamad Bazzi, Nicolás E. Campione, Per E. Ahlberg, Henning Blom and Benjamin P. Kear, August 10, 2021, PLoS Biology.
DOI: 10.1371 / journal.pbio.3001108
Funding: This work was supported by the Royal Swedish Academy of Sciences (GS2017-0018) in MB, and a Wallenberg Fellowship from the Knut and Alice Wallenberg Foundation at PEABPK also recognizes funding from a project grant from the Swedish Council of research (2020-3423), and NEC is funded by an Early Career Research Grant from the Australian Research Council (DE190101423). Funders played no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.