Limbs of the earliest four-legged vertebrates, dating back more than 360 million years, were no more structurally diverse than the fins of their aquatic ancestors, reveals a new study.
The new finding overturns long-held views that the origin of vertebrates with legs, known as tetrapods, triggered an increase in the anatomical diversity of their skeletons.
The research found that fish and early tetrapods developed similar levels of anatomical diversity within their fins and limbs, despite the fact that their skeletons were constructed in very different ways.
It is generally expected that when organisms evolve new features, or 'key innovations,' that enable them to exploit new environments, the rate of evolution and diversification will speed up.
The evolution of limbs was thought to have opened up a whole new realm of possibilities for tetrapods, so the scientists set out to examine just how substantial the evolutionary transition from fish to tetrapods really was by analysing a variety of different fin and limb skeletons from the fossil record.
This is believed to have happened with the evolution of birds from dinosaurs and, most iconically of all, in the transition from finned aquatic fish to limbed tetrapods.
The study has been published in Palaentology.