Biology and Evolutionary History of Mesosaurs, the Oldest Known Aquatic Reptiles
Mesosaurs are among the most amazing extinct animals; they are the oldest known reptiles that developed aquatic adaptations, although how terrestrial their ancestors had become remains to be established; they are the only known vertebrates from Gondwana at the Early Permian and they are represented by thousands of well preserved and almost complete skeletons. Mesosaurs were capable of inhabiting cold and salty water bodies resulting from the drought of an originally large inland sea that extended over what is now South America and Africa.
So far, mesosaurs are the only tetrapods known from a depauperate ecosystem that included pygocephalomorph crustaceans, algal and microbial mats, and the still unidentified producers of the trace fossil Chondrites. Recently, the discovery of well-preserved mesosaur embryos curled as if within an egg, and one pregnant female yielded clues about early amniote reproductive biology. The fact that mesosaurs may have developed extended embryo retention along with the apparent absence of a mineralized egg-shell may explain the large gap in the fossil record of early amniotic eggs for the first 90 million years of their evolution.
More basic remaining gaps in our knowledge of mesosaurs include taxonomic questions. For instance, how many nominal mesosaur taxa are valid? What are the affinities of mesosaurs?
These interesting aspects of mesosaur biology, along with a reappraisal of their diet and aquatic adaptations, as well as the analysis of the taxonomic problems that are still unresolved justify a Research Topic on mesosaurs in Frontiers in Earth Science. The aim of this proposal is to contrast earlier hypotheses about this taxon and contrast it to recent or new hypotheses that stem from the new data produced in the last few years.
We seek contributions from recognized specialists of early amniote evolution, comparative anatomy and reproductive strategies of extant reptiles, and mesosaurs. We believe that this collection of papers will be useful for a wide range of researches, from those working on paleoecology of basal tetrapods to those focusing on various aspects of vertebrate evolution or paleobiology.
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International Journal of Pure and Applied Zoology