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Reproduction in Early Amniotes

From: Ben Creisler

A new paper that may be of interest, with a discussion of Mesosaurus:

P. Martin Sander (2012)
Reproduction in Early Amniotes.
Science 337(6096): 806-808
DOI: 10.1126/science.1224301

The conquest of dry land by vertebrate animals began with the
evolution of the first four-legged, amphibious animals ~360 million
years ago. Amniotes originated ~50 million years later  and have since
become the most diverse clade of land-living vertebrates, including
mammals, turtles, lizards, snakes, crocodiles, and birds. Evolutionary
changes in reproduction were crucial for the move from the sea via
swamps to dry land. However, the reproductive structures and early
life stages of amniotes fossilize poorly. Exceptional insights into
early amniote reproduction are offered by recent fossil discoveries.
The fact that these fossils come from ancient seas and lakes and not
from dry land helps to explain the paradox that there is an older
fossil record for live-bearing amniotes than for egg laying in