This project addresses the fish-tetrapod transition, by which a group of fishes evolved the ability to live permanently on land and gave rise to the tetrapods or backboned land animals - the group to which we ourselves belong. This transition took place during the Devonian period, which lasted from 419 to 359 million years ago. It was a very important event, producing an entirely new kind of animal that changed the character of land ecosystems forever: today there are more than 30 000 tetrapod species, inhabiting all environments from the tropics to the high arctic. The fossil record of skeletons shows tetrapods first appearing around 375 million years ago. In slightly older rocks from 385-380 million years ago we find so-called elpistostegalians - intermediate forms that look quite similar to tetrapods but still have fins rather than legs. This looks like a straightforward picture of the fish-tetrapod transition captured by the fossil record, but the fossil footprint record shows something quite different: the oldest known fossil tetrapod footprints and trackways are about 390 million years old. However, the dominant evolutionary scenario for the fish-tetrapod transition - the one presented in popular media - shows tetrapods evolving from elpistostegalians in an aquatic setting, and fails to take proper account of the footprint data. There is also a more general failure to place the early tetrapods in a well-defined ecological context.
Our project addresses these problems. We are undertaking fieldwork at Devonian tetrapod localities in Ireland, Latvia and Greenland, gathering data that encompass tetrapod body fossils, tetrapod trackways, non-tetrapod body fossils and trackways (arthropod as well as vertebrate), plants, and the sediments themselves. Techniques used to study the material include synchrotron microtomography (which allows us to image the fossils in three dimensions inside the rock) and isotope geochemistry (which can be applied to the sediment, to determine environmental conditions, or to the fossils themselves, to investigate their environmental preferences or the preservation of their tissues). Trackways are recorded using optical scanning, which captures three-dimensional surfaces. We aim to understand not just the tetrapods themselves, but their environmental and ecological associations, so that we can make sense of the fish-tetrapod transition in an ecosystem context as well as a series of evolutionary events.
