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Mesosaurs from Early Permian gave birth to live young



From: Ben Creisler
bcreisler@gmail.com


OK--not a dinosaur item, but of possible interest to some DML members.
This adds to evidence that viviparity repeatedly evolved in different
groups of extinct marine reptiles, notably the Mesozoic groups
sauropterygians, ichthyosaurs, and mosasaurs:


Graciela Piñeiro, Jorge Ferigolo, Melitta Meneghel & Michel Laurin (2012)
The oldest known amniotic embryos suggest viviparity in mesosaurs.
Historical Biology: An International Journal of Paleobiology (advance
online publication)
DOI:10.1080/08912963.2012.662230
http://www.tandfonline.com/doi/abs/10.1080/08912963.2012.662230

The earliest undisputed crown-group amniotes date back to the Late
Carboniferous, but the fossil record of amniotic eggs and embryos is
very sparse, with the oldest described examples being from the
Triassic. Here, we report exceptional, well-preserved amniotic
mesosaur embryos from the Early Permian of Uruguay and Brazil. These
embryos provide the earliest direct evidence of reproductive biology
in Paleozoic amniotes. The absence of a recognisable eggshell and the
occurrence of a partially articulated, but well-preserved embryo
within an adult individual suggest that mesosaurs were viviparous or
that they laid eggs in advanced stages of development. Our finds
represent the only known documentation of amniotic embryos in the
Paleozoic and the earliest known case of viviparity, thus extending
the record of these reproductive strategies by 90 and 60 Ma,
respectively.