美考古学家发现某爬行动物出生时的化石

An ichthyosaur（鱼龙） fossil may show the earliest live birth from an ancient Mesozoic marine¹ reptile², according to a study published February 12, 2014 in PLOS ONE by Ryosuke Motani from the University of California, Davis, and colleagues. Ichthyosaurs were giant marine reptiles³ that evolved from land reptiles and moved to the water. Scientists report a new fossil specimen⁴ that belongs to Chaohusaurus (Reptilia, Ichthyopterygia), the oldest of Mesozoic marine reptiles that lived approximately 248 million years ago. The partial skeleton was recovered in China and may show a live birth. The maternal⁵ skeleton was associated with three embryos⁷ 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 posture⁸ of the second embryo⁶ indicates that live births in ichthyosaurs may have taken place on land, instead of in the water, as some studies have previously⁹ suggested.   The new specimen may contain the oldest fossil embryos of Mesozoic marine reptile, about 10 million years older than those indicated on previous records. The authors also suggest that live births in land reptiles may have appeared much earlier than previously thought.   Dr. Motani added, "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."