The pterosaurs were an order of flying reptiles that went extinct some 66 million years ago. They were not actually dinosaurs, but they went extinct at the same time. Along with bats and birds, they are the only vertebrates to truly fly. And though these creatures lorded over the skies for around 162 million years, only a handful of pterosaur egg fossils have ever been unearthed. And of those, paleontologists have just six three-dimensional eggs — that is, eggs not completely flattened by millions of years of being crushed under younger sediments.
But now, we have a pterosaur egg extravaganza. According to the new research, a site in China’s Turpan-Hami Basin in Xinjiang has coughed up 215 beautiful, pliable and miraculously three-dimensional eggs — 16 of which contain embryonic remains. The researchers also suspect there could be as many as 300 more eggs within the same sandstone block. No wonder Xiaolin Wang, the study’s lead author and a paleontologist at the Chinese Academy of Sciences, said the discovery could be described as a sort of “pterosaur Eden.”
Aside from breaking records, Unwin said there are practical reasons for why having more eggs is better. “When you have a really unique find, you basically can’t do anything to it because that’s all you’ve got.” But now that we have literally hundreds of eggs to work with, we have more options — such as cutting different eggs into cross-sections to study growth rates.
What’s more, the egg treasure trove also boasts skeletons from what appear to be hatchlings, juveniles and adults. This, too, is an embarrassment of riches, because it means scientists now have more information about how pterosaurs progressed from egg to adult than ever before.
“This is by far the most exciting discovery that I know of,” said Alexander Kellner, co-author of the new study and paleontologist at the National Museum of the Federal University of Rio de Janeiro in Brazil.
And Kellner isn’t some newbie to pterosaur discoveries. He’s been studying these ancient animals for more than 30 years and has personally been a part of naming or describing more than 20 species. This includes the species in question, Hamipterus tianshanensis, which Kellner, Wang, and a team of their colleagues discovered in 2014.
Probably a fish-eater, H. tianshanensis inhabited hot and dry environments but would have buried its eggs in the sand and vegetation found on the shores of lakes or rivers. This is also likely why so many eggs have been found together. Kellner suspects recent storms caused torrential flooding which unearthed the eggs and washed them into the fossil record, along with other, older pterosaurs that fell victim to the deluge.
While all four of the outside researchers contacted for this story seemed genuinely wowed by the team’s findings, they did not agree with all of the conclusions the study’s authors drew from the fossils.
The paper says that H. tianshanensis hatchlings wouldn’t have been able to fly immediately because several of the eggs the team examined showed wing bones that were less developed than expected. This may have meant that baby pterosaurs would have spent some time on the ground hunting insects and generally trying not to be eaten before learning how to take wing. Kellner even speculated that the pterosaur females and maybe even males would have stuck around to feed the hatchlings to help get them through such a precarious stage.
Michael Habib, a paleontologist at the University of Southern California, said the authors make a good argument but that it doesn’t necessarily prove the young pterosaurs were flightless.
“It is important to note that while the wings were less mature than the bones of the thighs in some respects, the wing bones are still much more robust than the bones of the hind limbs,” Habib said.
Furthermore, he said, bone shape and structure are integral to strength, which means it’s possible for a comparatively underdeveloped bone to in fact be stronger than one that is seemingly more developed.
Unwin is similarly unconvinced that the hatchlings were grounded. For starters, he said, the embryos in question were likely only halfway done growing, so they would have developed more before they hatched out. Furthermore, none of these embryos have their teeth yet, and if pterosaurs are similar to other reptile groups in development — as most experts agree they are — then lack of teeth is a pretty good indicator that they weren’t fully baked, so to speak.
Unwin said this makes the find even more important because all of the pterosaur embryos that have been discovered thus far have been late-stage and nearly ready to hatch.
“And while it’s wonderful to have those, they’re not much different from hatchlings really,” he said. “So I think these new embryonic finds are really exciting because with these, we can begin to reconstruct the embryonic development of pterosaurs inside the egg. I just think it’ll take time to do that.”
Hundreds of pterosaur eggs in one place is impressive, but Unwin said we’d need more evidence to demonstrate another suggestion in the paper: that this species of pterosaur was a communal nester, like penguins. Instead, Unwin thinks it more likely that a bunch of female pterosaurs simply laid their eggs in the same general area, much like female sea turtles returning to the same beaches year after year.
Luis Chiappe, a paleontologist at the Natural History Museum of Los Angeles County, said this paper is probably just the tip of the iceberg and that a site like this could sustain a decade or more of research.
“Pterosaurs are incredibly diverse, not just in the shape but also in sizes,” said Chiappe, who was part of a team that reported a 100-million-year-old pterosaur egg in central Argentina in 2004.
Pterosaurs ran the gamut from the gigantic, aircraftlike Quetzalcoatlus all the way down to animals about the size of a sparrow, such as Nemicolopterus. Some had the long, pointy snouts we typically associate with the flying reptiles. Others boasted wild and crazy crests, which may have been used to attract the opposite sex, as has been suggested with H. tianshanensis. And still other pterosaur species had short, squat skulls more like that of a frog, Chiappe said. (Albeit, a very scary frog.)
Pterosaurs were the very first animals with backbones to master powered flight, Kellner said. How they did what they did, and did it for as long as they did, is just one of the mysteries he and his colleagues hope to solve.