A 245-million-year-old pregnant reptile has overturned long-held theories about why birds lay eggs.
A fossil discovered in China, of a long-necked marine species known as Dinocephalosaurus, clearly contains an embryo, which, equally clearly, was destined for live birth.
This is highly significant because Dinocephalosaurus was an archosauromorph – a large clade that includes dinosaurs, crocodiles and birds. Until now, all species within this group were thought to be egg layers.
Among lizards and snakes in other lineage groups, live birth has evolved independently at least 115 times. The fact that it has never been seen among archosauromorphs led evolutionary biologists to assume it was constrained by an unknown mechanism.
But Dinocephalosaurus, described in Nature Communications by a team led by Jun Liu at Hefei University of Technology in China, upends that theory.
“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,” the researchers report.