With the skull shape of an early tetrapod, but proportions like a fish, an exceptionally well-preserved braincase fossil of the species Ventastega curonica from the Late Devonian of Latvia is described in the today's issue of Nature.
The evolution from fish to land vertebrates occurred during the Late Devonian, about 360 to 380 million years ago, and required many changes in physiology. Over the last two decades, researchers have begun to piece together how this transition might have occurred, but a full understanding is hindered by the fragmentary nature of the fossil record.
A team of researchers from Uppsala University, University Museum of Zoology, Cambridge, University of Latvia, and the Natural History Museum of Latvia now describe a skull, braincase, shoulder girdle and partial pelvis of Ventastega, discovered in deposits in Latvia. The fossil is complete enough to allow the whole skull and parts of the limb girdles to be reconstructed, providing a picture of what an animal from this crucial evolutionary period looked like.
Ventastega is the most primitive Devonian tetrapod represented by extensive remains. Ventastega falls into the morphological gap between Tiktaalik and Acanthostega, with a tetrapod-like lower jaw, but retaining more fish-like fangs among other features. The findings also point to changes in skull shape during the transition - the eyes and snout became larger, but the skull overall began to shrink.
Seeming like an evolutionary half-way point between the lobe-finned fish (such as Tiktaalik roseae) and primitive tetrapods such as Acanthostega and Ichthyostega, the discovery reveals that these animals diversified much earlier than previously thought, and helps reconstruct the sequence of events that took place during this transition.