Lerista skinks and the evolution of limb loss
The Australian scincid clade Lerista (Scincidae) provides perhaps the best available model for studying limb reduction in squamates (lizards and snakes), comprising more than 75 species.
Among extant tetrapods, Lerista is exceptional in comprising a large number of closely-related species displaying prodigious variability of body form; several species possessing well-developed, pentadactyl limbs resemble typical non-fossorial scincids in body proportions, while many other species exhibit varying degrees of limb reduction and body elongation, including two that are highly elongate and entirely limbless.
Inferred phylogeny reveals extraordinary evolutionary mutability of limb morphology in Lerista. Ancestral state reconstructions indicate at least ten independent reductions in the number of digits from a pentadactyl condition.
An estimated age of 13.4 million years for Lerista entails that limb reduction has occurred not only repeatedly, but also very rapidly. At the highest rate, complete loss of digits from a pentadactyl condition is estimated to have occurred within 3.6 million years.
A relatively recent research about the phylogeny and evolution of Lerista, hypothesizes that an increase in the extent of seasonally dry and arid habitats coincident with the origination of the genus would have facilitated limb reduction and body elongation by furnishing an environment conducive to the adoption of fossorial habit.
The photo shows a Pilbara Flame-tailed Slider orRedtail Lerista, Lerista flammicauda, endemic to West Australia and found only in the Pilbara shrublands and the Western Australian Mulga shrublands.
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Photo credit: ©Jordan Vos
Locality: The Pilbara, Western Australia