Tooth morphology elucidates shark evolution across the end-Cretaceous mass extinction

Area of Science:

• Paleontology
• Marine Biology
• Evolutionary Biology

Background:

• Sharks (Selachimorpha) possess a rich fossil record primarily from shed teeth, crucial for understanding deep-time diversity.
• Morphological disparity of shark teeth offers insights into ecological shifts, yet this aspect has been under-analyzed across major extinction events.

Purpose of the Study:

• To investigate changes in shark tooth morphology and ecological disparity across the Cretaceous-Paleogene (K-Pg) mass extinction event.
• To analyze how different shark lineages (clades) responded morphologically to this catastrophic environmental change 66 million years ago.

Main Methods:

• Employed a geometric morphometric approach to comprehensively study tooth morphologies.
• Examined multiple shark lineages, focusing on those that survived or were impacted by the K-Pg extinction.

Main Results:

• Most shark clades exhibited static dental disparity across the K-Pg boundary.
• Apex predators with blade-like teeth, particularly certain lamniforms (e.g., anacoracids), faced selective extinction.
• Some lineages, like odontaspidids (with narrow-cusped teeth), increased disparity post-extinction, coinciding with teleost radiation.

Conclusions:

• The end-Cretaceous mass extinction caused complex morphological responses in sharks, not uniform extinction.
• Selective extinctions and subsequent adaptive radiations, like that of odontaspidids, significantly influenced the evolutionary trajectory of modern shark groups.
• Ecological factors, such as the rise of teleost fishes, may have driven post-extinction morphological diversification in sharks.