Different drivers of diversification for body elongation and limb reduction in convergently snake-like lizards

This dataset includes numbers of digits, phalanges, and presacral
vertebrae for 1386 species of squamate reptiles gathered from the
literature. Each species also has clade and habitat classifications. From
the manuscript: Convergence is the evolution of similar phenotypes often
due to similar selective pressures or constraints limiting evolutionary
options. Snake-like morphologies, characterized by elongated bodies and
reduced limbs, have evolved repeatedly among vertebrates, including
numerous times in squamate reptiles (lizards and snakes). It has been
suggested that elongation facilitates locomotion through substrates while
limb reduction typically occurs in clade-specific patterns, but this has
not been tested. We compared the fit of a series of habitat-specific and
clade-specific models for the evolution of digits, phalanges. and trunk
vertebrae in lizards. We found that species inhabiting fossorial and
cluttered habitats differed in numbers of vertebrae, digits, and phalanges
from species in other habitats. A model with habitat-specific rates fit
best for vertebral evolution, with sand swimmers, litter dwellers, and
burrowers having higher rates of vertebral evolution than non-fossorial
taxa. However, we found digits and phalanges evolved in a clade-specific
manner, with higher rates of limb evolution in certain clades. This
suggests that limb reduction in snake-like lizards is dictated by
clade-specific constraints. In contrast, fossoriality appears to relax
functional constraints on vertebral number, facilitating body form
diversification. These results suggest that the relaxation of constraints
may be an additional mechanism for convergent evolution.