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Live birth reptile fossil discovered is oldest yet

A fossil capturing the live birth of an ancient reptile provides an evolutionary link between marine reptiles and their land ancestors.

By Gabrielle Levy
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Live birth reptile fossil discovered is oldest yet
Color coding indicates: black, maternal vertebral column, including neural and haemal spines; blue, maternal pelvis and hind flipper; green, maternal ribs and gastralia. Embryos 1 and 2 are in orange and yellow, respectively, whereas neonate 1 is in red. Scale bar is 1 cm. Abbreviations: i-v, metatarsals; 4, fourth distal tarsal; a, astragalus; c, calcaneum; cr, caudal rib; cv, caudal vertebra; d, dentary; fe, femur; fi, fibula; h, haemal spine; il, ilium; is, ischium; pb, pubis; pm, premaxilla; sr, sacral rib; sv, sacral vertebra; and ti, tibia. See fig. S2 for a high resolution image. (Credit: Plos One)

HEFEI, China, Feb. 13 (UPI) -- A newly discovered fossil is the earliest specimen of a reptile giving head-first birth to live offspring.

The Chaohusaurus mother apparently died in labor some 248 million years ago in the Mesozoci period, along with her three babies. The fossil, with the mother and three babies -- one out of her body, one half-emerged from her pelvis, and a third still inside -- is about 10 million years older than other reptile embryo fossils.

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Researchers already knew that ichthyosaurs -- giant sea predators and descendants of the Chaohusaurus -- carried live embryos, not eggs. And one previously uncovered fossil from the Jurassic period (between 145 and 201 million years ago), a Stenopterygius ichthyosaur preserved showing tail-first birth.

But while most air-breathing marine creatures born live are birthed tail-first so that newborns don't suffocate during labor, land creatures and some early whales, which evolved from land mammals, give birth to newborns head-first.

Until the discovery of this fossil, researchers thought live birth evolved in marine reptiles after they moved into the sea. But according to Ryosuke Motani, the lead author of a study, published this week in the journal PLOS ONE, the new fossil counters previous assumptions by linking marine reptiles with their land-based relatives.

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

[PLOS ONE] [Live Science]

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