Conservatism in lizard vertebral number evolution is widespread but not universal

Meeting Abstract

51.4  Saturday, Jan. 5  Conservatism in lizard vertebral number evolution is widespread but not universal. BERGMANN, P.J.*; IRSCHICK, D.J.; University of Massachusetts Amherst; University of Massachusetts Amherst

We collected vertebral number data for a sample of 2402 lizards, representing 1045 species, or 27% of extant diversity. We mapped these data onto a supertree of the lizards, compiled from the literature. We analyzed vertebral numbers using ancestral reconstruction, correlation, and basic statistics to examine patterns of vertebral number evolution and interdependence of cervical, presacral, and caudal fractions of the vertebral column. Results indicate that the majority of lizard clades have maintained the ancestral condition, represented by Sphenodon. However, several clades have drastically deviated from this constrained pattern: the Chamaeleonidae have undergone column reduction, while the Anguimorpha, Serpentes, Amphisaenia, Gymnophthalmidae, Pygopodidae, and some Scincidae have evolved columns with many vertebrae. In these latter clades, elevated vertebral number correlates with increased interspecific variability in vertebral number. Further, there are high correlations between presacral vertebral number and caudal number, the presence of a sacrum, and hindlimb reduction. Therefore, body elongation and limb reduction are correlated, and the trunk and the tail are not evolving independently.

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