Huge Cache of Pterosaur Eggs Discovered in China


This reconstruction image shows the species Hamipterus tianshanensis according to the discoveries in northwest China's Xinjiang Uygur Autonomous Region where more than 200 preserved eggs of pterosaurs were discovered. Illustration by Zhao Chuang

Flight is a hard thing to master. The vast majority of vertebrates can walk, swim or do both. But in the history of life on this planet, only three groups of backboned animals have ever evolved the ability to fly. Early bats acquired this skill roughly 52 million years ago. Feathered dinosaurs began to experiment with flight back in the Jurassic period. Incidentally, you probably know today's winged dinos as "birds."

Yet while birds and bats are still around, the animals that first pioneered vertebrate flight are long gone. That's because 228 million years ago, a flying clade of reptiles evolved. These were the pterosaurs. Though Hollywood often mislabels them as dinosaurs, they actually represented a separate, contemporaneous group.

Flying with Style

For more than 160 million years, dinosaurs and pterosaurs lived side-by-side. It was an exciting time to be an aeronaut. During their reign, the pterosaurs diversified like crazy. Some species would be comparable to sparrows in size. Others had wingspans of 36 feet (11 meters) or more, making them the largest flying animals of all time.

Then, 66 million years ago, the pterosaurs succumbed to the same mass extinction that wiped out all non-avian dinosaurs. Thanks to hard-working paleontologists, we've learned a great deal about these winged wonders. Nonetheless, there are still some large gaps in our knowledge.

One big mystery involves the early lives of young pterosaurs. The first confirmed dinosaur nest was unearthed in 1923. Since then, fossil hunters have excavated thousands of dino eggs at sites all over the world. Yet, pterosaur eggs are considerably rarer. None whatsoever were discovered until 2004, when two appeared in China and a third showed up in Argentina. In 2011, a fourth egg was found next to the skeleton of its presumed mother, an adult animal from the genus Darwinopterus. Three years later, another Argentinian egg emerged — along with five additional Chinese specimens.

A New Breakthrough

So, until very recently, the global scientific community hadn't found enough pterosaur eggs to fill a standard egg carton. But paleontologists just hit the motherload. In the December 2017 issue of the journal Science, a Chinese research team announced the discovery of a new site in China's Gobi Desert containing at least 215 pterosaur eggs. Sixteen preserved embryos were found there as well, along with some skeletons from hatchling, juvenile and adult pterosaurs.

These eggs are roughly 120 million years old and were laid by Hamipterus tianshanensis, a crested, toothy species with an 11-foot (3.3-meter) wingspan. Pterosaur experts are still trying to assess where it belongs on the family tree. One such authority is paleontologist David Hone, who told us in an email that Hamipterus' closest relatives were most likely "various groups of pterosaurs ... known for being ocean-going or at least coastal foragers." In terms of lifestyle, he says these animals would've behaved like today's gulls and albatrosses.

The newfound bounty of eggs was recovered by a team representing the Beijing-based Chinese Academy of Sciences (CAS). Most of the shelled treasures were embedded in a sandstone block that may be hiding even more clutches that have yet to be revealed.

One reason why this find is so spectacular has to do with the fragility of pterosaur eggshells. Like modern chickens, extinct dinosaurs laid hard-shelled eggs. Contrast these with the eggs of present-day snakes, whose shells are thin, soft, pliable and have the texture of old parchment. Pterosaur eggs resembled the latter, a fact confirmed by previous discoveries. Because their shells were so soft, these rare eggs tend to get squished flat by the forces of fossilization. Yet, the ones at this new Chinese site were preserved in three dimensions.

The more than 200 fossilized eggs in China is the largest pterosaur egg collection ever found.
Wang

Pterosaur Parenting

The discovery's implications are still open to debate. CAS paleontologist Xiaolin Wang was the lead author of the paper in the journal Science, which announced this big find. In it, he and his co-authors suggest that the site may have a lot to say about pterosaur parenting. As Wang and his colleagues point out, some of the embryos lack teeth and their wing bones seem underdeveloped. The paleontologists think this could mean that newly hatched Hamipterus could neither fly nor eat solid food. Thus, they would have had to depend upon their parents for protection and sustenance.

Other scientists have disagreed with that conclusion. In present-day reptiles, teeth are one of the last things embryos develop. So, while these developing pterosaurs were toothless, they still might have grown some chompers before hatching. Also, according to Michael Habib, a pterosaur specialist at the University of California, the fetal wings appear quite robust, meaning the newborns might've been able to start flying right away.

A point of consensus among paleontologists, though, is that pterosaurs probably didn't brood their eggs like present-day birds. For one thing, as Hone told us, the extinct reptiles "simply could not sit like birds" due to the anatomical differences. Also, while pterosaurs were coated with a strange, fuzzy material, they lacked feathers, which roosting avians use to keep their clutches nice and warm.

S. Christopher Bennett of Fort Hays State University in Kansas, another leading expert in modern pterosaur science, agrees. "There is no evidence, and no reason to think, that pterosaurs incubated their eggs," he said via email. "Rather they probably deposited them in sands, soils or vegetable matter like modern reptiles."

In the past, Bennett has championed the idea that at least some pterosaurs formed nesting groups "near environments suitable for the hatchlings to feed and grow safely." He says he feels the new Hamipterus site may lend some credence to that notion — a sentiment shared by Wang and his co-authors. "Careful excavation of [pterosaur egg deposits] could certainly provide evidence as to whether eggs were buried, and ... whether pterosaurs reused nesting sites year after year," Bennett adds.



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