About 380 million years ago, during the Devonian period, a group of fishes evolved limbs and began to leave the water.
This move was a tremendous success; all back-boned land animals, or 'tetrapods', (amphibians, reptiles, birds, and mammals including humans) that have ever lived can ultimately trace their ancestry to these fishes.
Figure 1. Painting of what Elginerpeton may have looked like. This is modelled partly on the more complete Devonian tetrapods Ichthyostega and Acanthostega, and gives a good general impression of what these animals looked like.
However, until recently, this important event was very poorly understood. It is only during the past decade that new fossil discoveries have started to give a clear picture of the move from water to land. We now know that the earliest tetrapods retained fish-like tail fins and probably spent most, if not all, of their time in the water (see the above illustration). They may have evolved limbs in order to move more effectively through shallow and weed-choked waters, and the real move onto land may have begun after they had acquired the ability to walk.
Figure 2. Lower jaw fragment of Elginerpeton. The scale bar is 1 centimetre.
Per Ahlberg has discovered two of the earliest known tetrapods, and is now studying their fossils. Elginerpeton comes from a site in Scotland, and dates to the middle of the Late Devonian; it is the earliest known tetrapod. The fossils are fragmentary, but Elginerpeton seems to have been quite large (about one and a half metres long) and adapted for swimming rather than walking.
Figure 3. Skull reconstruction of Ventastega. The scale bar is 2 centimetres. Image provided courtesy of the Royal Society of London,
which retains copyright.
Ventastega from Latvia is a little later, dating to the end of the Late Devonian. However, it appears less specialized and may be closer to the ancestry of the later tetrapods.
This project is part of the Systematics and Evolution Research Theme.
For further information contact:
Dr Per E Ahlberg
Department of Palaeontology
The Natural History Museum
Cromwell Road
London SW7 5BD UK
Tel: +44 (0) 171 938 9528 Fax: +44 (0) 171 938 9277
Email: pea@nhm.ac.uk
