Evolution and extinction risks of sharks, rays, and skates

Sharks, skates, and rays (Elasmobranchii) form together with chimaeras (Holocephali) the last extant members of cartilaginous fish (class Chondrichthyes), an ancient group of jawed vertebrates that has been around for more than 400 million years and survived all five mass extinctions. During their evolution, they developed a diverse set of morphological and biological traits allowing them to cope with changes in their environment and to become important predators in a variety of different ecological occuppying top positions in food-webs. Today, the biodiversity on our planet is experiencing an anthropogenically driven extinction event, with extinction levels very similar to past mass extinctions. Despite being well-adapted predators, this new mass extinction event doesnt spare sharks, rays, and skates, with an estimated one third of all species already being threatened according to the IUCN Red List. Extinction of only a few species of this evolutionary distinctive clade can cause significant pruning of the tree of life with subsequent loss of millions of years of evolutionary history. Although being a versatile group, the mechanisms how elasmobranchs have coped with past mass extinctions, the drivers for the evolution of morphological traits and the correlated body plans, the tempo and timing of morphological trait evolution, whether appearance changes occurred regularly over time or were increased during times of extinction events, and how biological traits like body size have developed during their evolution, are not fully understood yet. To answer these questions, multidisciplinary approaches are necessary, in which various phylogenetic methods, molecular clock and other approaches for dating origins and evolutionary events as well as morphological data comprising skeletal and dental traits are combined with morphospace methods to estimate the relationships of taxa, duration of individual evolutionary lineages, lineage specific rates, divergence rates, evolutionary diversifications, fossilization and life history traits within a single coherent phylogenetic time tree. This time tree will be crucial for our understanding of the evolutionary history of elasmobranchs and the evolution of biological traits, which have helped elasmobranch fishes to become top predators of todays seas. Furthermore, the newfound understanding of the role of different biological traits on the survival and longevity of elasmobranchs in deep time can serve as basis, on which extinction risks and conservation priorities of distinct elasmobranch groups can be formulated within a strict evolutionary framework towards maintaining their morphological diversity and evolutionary history, and therefore ensuring the continued existence of this group in the future. Univ.-Prof Dr. J. Kriwet, J. Türtscher, MSc and P.L. Jambura, MSc of the University of Vienna with support of Dr. G. Naylor (Univ. Florida, Gainesville, U.S.A.) und Dr. G. Marramà (Univ. Turin, Italien) will conduct this project.