A remarkable 250 million-year-old Chinese fossil is already changing scientists’ understanding of evolution.
The fossil is of a long-necked marine animal called an archosauromorph, and shows an embryo inside its mother, which is clear evidence for live birth. This is the first evidence for live birth in an animal group previously thought to have exclusively laid eggs.
“This new specimen from China rewrites our understanding of the evolution of reproductive systems,” Chris Organ, a professor from Montana State University, said in a press statement. “We identified that Dinocephalosaurus, a distant ancestor of crocodiles, determined the sex of its babies genetically, like mammals and birds.”
Archosautomorphs lived around 247 to 237 million years ago and ate fish in shallow seas in what is now southern China. The discovery suggests that much of what scientists knew about how sexual reproduction and birth evolved could be incorrect.
The small embryo reptile inside the mother is an example of the same species and does not appear to have been swallowed.
“This combination of live birth and genotypic sex determination seems to have been necessary for animals such as Dinocephalosaurus to become aquatic,” Dr. Mike Benton, a professor from the University of Bristol involved in the research, said in a press statement. “It’s great to see such an important step forward in our understanding of the evolution of a major group coming from a chance fossil find in a Chinese field.”
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