Thursday, July 21, 2011

Oldest Viviparous Squamata

The embryonic skeletons can be seen in 
side of their mother's remains. Photo
Credit: Susan Evans.

The lizard genus Yabeinosaurus Endo and Shikama 1942 was first described from Early Cretaceous deposits from the Jehol Group of northeastern China. Early interpretations suggested, Yabeinosaurus  was a small, weakly ossified lizard with gekkotan affinities. However, Evans et al. (2005) reported adults exceeded  300 mm snout–pelvis length, and lizard had a large, heavily ossified and strongly sculptured skull. Their results suggested Yabeinosaurus was close to the iguanian–scleroglossan dichotomy and they hypothesized that Yabeinosaurus may represent a relict species in the Jehol Biota, a survivor of the Pan-Laurasian lizard fauna of the Jurassic. Now, Wang and Evans (2011) document viviparity in Yabeinosaurus with the remains of a gravid female that contains more than 15 young with skeletal development that suggests they are near full term. Because Yabeinosaurus occupies a relatively basal position within crown-group squamates, they suggests that the anatomical and physiological preconditions for viviparity arose early within Squamata. It is the oldest terrestrial reptile known to give live birth, and it extends the evolution of viviparity to at least 120 million years ago. Yabeinosaurus probably lived on the banks of a stream and the remains were associated with hundreds of exquisitely preserved specimens of dinosaurs, fish, amphibians, reptiles, birds and mammals, plants and invertebrates.

Evans, S. E.; Wang, Y.; Li C. (2005). "The Early Cretaceous lizard genus Yabeinosaurus from China: resolving an enigma". Journal of Systematic Palaeontology 3 (4): 319–335. doi:10.1017/S1477201905001641.

Yuan Wang and Susan E. Evans. 2011. A gravid lizard from the Cretaceous of China and the early history of squamate viviparity. Naturwissenschaften

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