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[1] Reisz RR, Müller J. Molecular timescales and the fossil record: a paleontological perspective. Trends Genet. 2004 May20(5):237-41. DOI: 10.1016/j.tig.2004.03.007 [2] S. Sumida, K. Martin , Eds., Amniote Origins: Completing the Transition to Land (Academic Press, London, 1997).PubMed ID15109777
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P.806 left column: "The conquest of dry land by vertebrate animals began with the evolution of the first four-legged, amphibious animals ∼360 million years ago (primary sources 1, 2). Amniotes originated ∼50 million years later (primary source 1) 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 (refs 3–6). 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 amniotes." P.806 right column top paragraph: "Soon after their origin, Amniota split into two major lineages: the mammal-line amniotes (Synapsida) and the bird-line amniotes (Reptilia). Phylogenetic inference from living animals (see the figure) suggests that amniote egg laying evolved no later than in the last common ancestor of mammals and birds, ∼310 million years ago (primary source 1). Both animal groups have a cleidoic egg, although this has been lost in mammals more derived than monotremes. It is highly unlikely that this complex egg structure evolved more than once (primary source 2). Paleontologists have inferred egg laying on dry land from skeletal indicators of full terrestriality—such as well-developed limb joints—in tetrapods close to the mammal-bird split (primary source 2)." |