Unravelling the stem and early evolution of elasmobranchs

This project focuses on the oldest ancestors (stem members) of living cartilaginous fishes, i.e., sharks, rays and skates (the elasmobranchs). They are among the oldest surviving vertebrates with one of the most exceptional evolutionary histories. Potential ancestors of these cartilaginous fishes possibly originated more than 350 million years ago. Subsequently, sharks, rays and skates seemingly underwent various diversifications that eventually led to the rise of the living groups ca. 200 million years ago. But from then on, their diversity declined, which continued until today. Decades of conflicting hypotheses and interpretations about the ancestors of sharks, rays and skates and their relations to the more recent members hampered the full understanding of the evolutionary history of this long-lived and diverse group of cartilaginous fishes. Although this study mainly focuses on fossil sharks, rays and skates, revealing their early evolution also provides a better understanding of how current sharks, rays and skates fit into the long and complex history of these marine predators. The main goal of this project thus is to identify the earliest ancestors of todays sharks, rays and skates based on skeletal and tooth features by comparing these with those of recent groups. Reconstructing the interrelationships of the ancient ancestors and living groups of sharks, rays and skates is also central to the research planned. Establishing the relationships to identify the common ancestor of living elasmobranchs is essential for exploring the timeframes of origin and initial diversification. This will help to gain an in-depth understanding of their early evolutionary history leading to their ultimate success. Tooth characters are employed here for the first time to clarify the connection between the oldest ancestors of recent groups and their descendants. The integration of general features (morphological traits) and microstructural characteristics (histological traits) to reconstruct the evolution of sharks, rays and skates is another major novelty of this study. The first robust and comprehensive evolutionary tree including a wide range of both putative ancestors and their descendants of recent members of sharks, rays and skates is the main outcome expected for the present project. Overall, this research will enhance our understanding of the evolution of marine vertebrates, deepens our knowledge of a key group of aquatic predators, which are important for maintaining the health of marine environments, and introduces an innovative approach for integrating morphological and histological data based on both skeletons and teeth in palaeontological investigations. The project will be conducted by Dr. M. Amadori (senior postdoc, PI; University of Vienna, Austria) in co-operation with Prof. Dr. J. Kriwet (University of Vienna, Austria), Dr. E. Villalobos-Segura (University of Vienna, Austria), and Prof. Dr. G. Cuny (Claude Bernard University Lyon 1, France).