Chaohusaurus Fossil Shows Oldest Live Reptile Birth

Feb 14, 2014 by Sci-News.com

A team of paleontologists led by Dr Guan-bao Chen of Anhui Geological Museum, China, says a newly discovered fossil of a Mesozoic ichthyosaur reveals the earliest live reptile birth.

248-million-years-old fossil of the ichthyosaur Chaohusaurus. Image credit: Motani R et al.

248-million-years-old fossil of the ichthyosaur Chaohusaurus. Image credit: Motani R et al.

Recent excavations in south Majiashan, Anhui, China, yielded more than 80 new ichthyosaur skeletons. Among the specimens was a partial skeleton that contained embryos.

According to Dr Chen and colleagues, the fossil belongs to the ichthyosaur Chaohusaurus, which is the oldest of Mesozoic marine reptiles.

This viviparous creature lived around 248 million years ago. It had a lizard-like appearance and was one of the smallest ichthyosaurs (up to 1.8 m long).

The new fossil was associated with three embryos and neonates: one inside the mother, another exiting the pelvis-with half the body still inside the mother-and the third outside of the mother.

The headfirst birth posture of the second embryo indicates that live births in ichthyosaurs may have taken place on land, instead of in the water, as some studies have previously suggested.

Chaohusaurus specimen with three embryos. 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. 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. Scale bar is 1 cm. Image credit: Motani R et al.

Chaohusaurus specimen with three embryos. 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. 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. Scale bar is 1 cm. Image credit: Motani R et al.

“The study reports the oldest vertebrate fossil to capture the ‘moment’ of live-birth, with a baby emerging from the pelvis of its mother. The 248-million-year old fossil of an ichthyosaur suggests that live-bearing evolved on land and not in the sea,” said Dr Ryosuke Motani from the University of California, Davis, the first author of a paper published in the journal PLoS ONE.

The Chaohusaurus fossil may also contain the oldest fossil embryos of Mesozoic marine reptile, about 10 million years older than those indicated on previous records.

“Live births in land reptiles may have appeared much earlier than previously thought,” the scientists said.

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Motani R et al. 2014. Terrestrial Origin of Viviparity in Mesozoic Marine Reptiles Indicated by Early Triassic Embryonic Fossils. PLoS ONE 9 (2): e88640; doi: 10.1371/journal.pone.0088640