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Fossil Shows Triassic-Era Sea Creature Gave Birth On Land

Fossil of Chaohusaurus reveals a baby inside its mother (orange) and another stuck in her pelvis (yellow). Ryosuke Motani/UC-Davis hide caption

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Ryosuke Motani/UC-Davis

Fossil of Chaohusaurus reveals a baby inside its mother (orange) and another stuck in her pelvis (yellow).

Ryosuke Motani/UC-Davis

An extraordinary find of a fossil of 250-million-year-old air-breathing sea creature shows that it must have given birth on land, not in the sea as long assumed.

The fossil is of a mother chaohusaurus, which is believed to be a genus of ichthyosaur, who died giving birth. It shows the baby birthing headfirst.

From earlier fossil finds, scientists already knew that these Triassic-era predators gave live birth, but what they didn't know was whether the earliest ichthyosaurs, who evolved from land-dwelling cousins, gave birth headfirst, like land mammals, or tail-first, like modern whales and dolphins do, an evolutionary adaptation to avoid suffocating the offspring underwater.

And, according to a statement from researchers, who published in the latest edition of PLOS ONE, the fossil (which shows three neonates in the womb, one in the process of being born) shows a head-first birth, so "live births in ichthyosaurs may have taken place on land, instead of in the water, as some studies have previously suggested," according to Ryosuke Motani, a prehistoric marine reptile expert at the University of California, Davis who led the study.

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Motani tells LiveScience: "This land-style of giving birth is only possible if they inherited it from their land ancestors. ... They wouldn't do it if live birth evolved in water."

National Geographic writes:

"[New] research reveals that over the evolutionary trajectory of reproduction, reptiles veered back and forth between the two strategies before settling on egg-laying. Live birth in reptiles seems to have evolved more than 100 times in history. But there are many gaps in scientific knowledge surrounding the phenomenon in ancient sea reptiles."