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Fossil Shows Triassic-Era Sea Creature Gave Birth On Land

Fossil of <em>Chaohusaurus</em> reveals a baby inside its mother (orange) and another stuck in her pelvis (yellow).
Ryosuke Motani
Fossil of Chaohusaurus reveals a baby inside its mother (orange) and another stuck in her pelvis (yellow).

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 , 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 , 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.

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."

Copyright 2020 NPR. To see more, visit https://www.npr.org.

Scott Neuman is a reporter and editor, working mainly on breaking news for NPR's digital and radio platforms.