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Did egg-laying lead to the dinosaurs' demise?

New research suggests that dinosaurs' reproduction through egg-laying may have been a fatal weakness.

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A close-up of a near-perfect fossil named Scionyx Samnitcus, shows muscles, intestines, teeth and even traces of windpipe. This species is believed to be related to the powerful flesh-eater Tyrannosaurus Rex and the Velociraptor. A new study suggests that dinosaurs' egg-laying ways may have lead to their extinction.

Stefano Rellandini / Reuters

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Dinosaurs' egg-laying may have left them vulnerable to extinction when disaster struck.

The bigger the egg, the thicker the shell, but growing embryos need access to outside air. Therefore, egg size is necessarily limited.

Because of this fixed egg size, huge adult dinos began their lives as tiny babies. For example, Titanosaur newborns were 2,500 times smaller than their parents who at full-size weighed-in at 4 tons. In comparison, elephant calves are only 25 times smaller than their parents.

A new study attempted to explain this size discrepancy and its repercussions. Through modeling, a team of researchers lead by Daryl Codron, a zoologist at the University of Zurich in Switzerland determined that there weren't many small or mid-sized adult dinosaurs because they would have been forced to compete with growing youngsters for food. In other words, competition forced them to grow big.

The paper suggests that dinosaurs, except for birds, were too large to survive the asteroid that hit Earth about 65 million years ago. On the other hand, birds and mammals survived because they did not have the same size limitations. Their young were not born with as much growing left to do. In addition, mammals did not need to compete with other species for food at birth, relying instead on their mothers' milk for sustenance.

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