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Live birth in an archosauromorph reptile
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Journal Article
Live birth in an archosauromorph reptile
2017
Overview
Live birth has evolved many times independently in vertebrates, such as mammals and diverse groups of lizards and snakes. However, live birth is unknown in the major clade Archosauromorpha, a group that first evolved some 260 million years ago and is represented today by birds and crocodilians. Here we report the discovery of a pregnant long-necked marine reptile (
Dinocephalosaurus
) from the Middle Triassic (∼245 million years ago) of southwest China showing live birth in archosauromorphs. Our discovery pushes back evidence of reproductive biology in the clade by roughly 50 million years, and shows that there is no fundamental reason that archosauromorphs could not achieve live birth. Our phylogenetic models indicate that
Dinocephalosaurus
determined the sex of their offspring by sex chromosomes rather than by environmental temperature like crocodilians. Our results provide crucial evidence for genotypic sex determination facilitating land-water transitions in amniotes.
Although live birth evolved repeatedly in other clades, it has not been found in archosauromorphs, the group including modern birds and crocodilians. Here, the authors describe a fossilized pregnant
Dinocephalosaurus
from ∼245 million years ago, providing evidence of live birth in archosauromorphs.
