As stated by Dr Marcello Ruta from the University of Lincoln and Professor Matthew Wills from the University of Bath, the diversity of fish and early tetrapods limbs were equally subtle, despite the vast differences of their overall body plan. It was previously believed that the evolution of early vertebrates with legs – collectively known as tetrapods – also increased the diversity of anatomy within the group.
This is a common assumption about evolution, which states that new features tend to trigger the rapid diversification and anatomical experimentation to fill the previously empty niches. In the case of early tetrapods, this relates to the possibilities of life on land.
According to Wills, legs had to fulfil two new functions: supporting the weight of the animal on land, and helping them to navigate the terrain. This dual requirement likely restrained the variability of early legs, limiting the possibilities of forms they could take.