In today’s Academic Minute, Dr. Jennifer Clack of the University of Cambridge reveals how recent discoveries are providing paleontologists with a better understanding of the development of early tetrapods.
Jennifer Clack is Professor and Curator of Vertebrate Paleontology at the University of Cambridge. She is currently working to reconstruct chroniosuchians, an enigmatic group of tetrapods from the Late Permian and Early Triassic periods. Her work has appeared in a number of peer-reviewed journals and in 2002 she published, Gaining Ground: The Origin and Evolution of Tetrapods.
Dr. Jennifer Clack, University of Cambridge – Early Tetrapod Development
The move onto land by vertebrates is one of the major events in evolution. In the Late Devonian period, about 365 million years ago, animals with limbs with digits (fingers and toes) called ‘tetrapods’, were evolving from their fish ancestors with fins. But the ones we know were predominantly aquatic, and a mass extinction seems to have wiped out most of these early pioneers.
For the next 20 or so million years, there is almost no evidence of limbed tetrapods in the fossil record. Very little is known about how, when, or under what circumstances, the key transition to land living was made.
Exciting finds made over the last few years have changed the picture quite dramatically, from one of sparsity to one of abundance. In southern Scotland, palaeontologists have discovered four sites whose ages span this gap in the fossil record. In one, a whole ecosystem changing through time has been revealed in a series of rock beds from a river. A large number of tetrapod fossils have been found from three of these levels. The fossils also include fish, arthropods (like millipedes), and plants. At another site, a sequence of vertical strata through this time period have given us tetrapods from five different levels from successive ages.
This new information should provide unprecedented information about the early evolution of life on land. Modern plant groups and modern members of the fish fauna also radiated during this time, and the ecosystems of today were born.