A look into the mouth of sharks

Classically, diversification of fish is thought to involve an onshore-offshore gradient; i.e., species originate on nearshore environments and later expand offshore in their evolutionary history. Sharks are a group of cartilaginous fish (Chondrichthyes) with a global distribution in the marine realm and, less commonly, in freshwater. Previous studies could not clearly confirm the classic „onshore-offshore“ diversification gradient.

HaiIn the current paper (López-Romero et al. 2023 Communications Biology, DOI: 10.1038/s42003-023-04882-3) Prof. Dr. Böhmer collaborated with researchers from Austria, France and the UK to quantitatively study the shape of the mandibles of 90 different shark species. The results reveal that there two „hotspots“ of lower jaw morphological evolution in sharks: In both reef and deep-sea sharks, the range of mandibular shapes is greater and the rate of evolution is higher than in species living in other habitats. Thus, sharks represent an exception to the classic „onshore-offshore“ diversification gradient.

Another result of the current study is the finding that the shape of the lower jaw correlates with the main feeding mode of sharks. For example, fish-eating species are relatively variable in their morphology, while large predators or even filter-feeding sharks have a very specific lower jaw shape. Overall, this confirms that the mandibular shape in extinct sharks can be used as a proxy for the type of food.

Press release Kiel University: Jaw shapes of various shark species provide insight into evolutionary biology

Press release University of Vienna: Jaw shapes of 90 shark species show: Evolution driven by habitat

References:

López-Romero FA, Stumpf S, Kamminga P, Böhmer C, Pradel A, Brazeau MD and Kriwet J (2023) Shark mandible evolution reveals patterns of trophic and habitat-mediated diversification. Communications Biology. DOI: 10.1038/s42003-023-04882-3