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Selected Journal & Book Covers from SBS Faculty

"Developmental Morphology of Limb Reduction in Hemiergis (Squamata: Scincidae): Chondrogenesis, Osteogenesis, and Heterochrony. Journal of Morphology"

Michael D. Shapiro

Abstract


Digit loss is a common theme in tetrapod evolution that may involve changes in several developmental processes. The skink genusHemiergisprovides an ideal model to study these processes in closely related taxa: within three Western AustralianHemiergisspecies, digit quantity ranges between two and five. For three consecutive reproductive seasons, gravid females ofHemiergiswere collected in the field and their embryos prepared for histological analysis of limb skeletal development (chondrogenesis and osteogenesis). Comparative studies of skeletal developmental morphology demonstrate that limbs with fewer than five digits do not result from a simple truncation of a putative ancestral (five-digit) developmental program. The developmental and adult morphologies in two-, three-, and four-digitHemiergisare neither predicted nor explained by a simple model of heterochrony involving either chondrogenesis or osteogenesis. In postnatalHemiergis, digit number and relative limb length do not correlate in a simple linear fashion. Instead, limb size and digit reduction may correlate with substrate conditions and burrowing behavior