Hundreds of newfound pterosaur eggs are giving scientists a peek into how the ancient fliers developed. These winged reptiles were not dinosaurs, but they lived alongside dinos. Some of the newly discovered eggs still contained the bones of tiny embryos. After studying those bones, researchers now think that the hatchlings might have been able to walk, although not yet fly.
A team of scientists uncovered at least 215 eggs. They came from a block of sandstone about 3 meters (10 feet) square. All of the eggs belonged to one species: Hamipterus tianshanensis. It lived in the early Cretaceous Period, some 120 million years ago, in what is now northwestern China. Xiaolin Wang of the Chinese Academy of Sciences in Beijing led the research team. As a vertebrate paleontologist, he studies the fossils of animals with backbones.
The eggs were a rare find. Researchers had found only a handful of pterosaur eggs before. Five came from the same site in China. Scientists unearthed two others in Argentina. And only one of these seven contained an embryo. Although flattened, it was rather well-preserved. Still, that early lone embryo gave scientists very little to work with as they initially tried to piece together details about the earliest stages of pterosaur (TAIR-oh-soar) development.
Unlike the hard-shelled eggs of dinosaurs, birds and crocodiles, the newfound eggs were soft. They had a thin outer shell, similar to those of modern-day lizards. This fragile shell also may explain why few fossils had survived.
Alexander Kellner is a vertebrate paleontologist. He works at Museu Nacional/Universidade Federal do Rio de Janeiro in Brazil. The new eggs did not come from a nesting site, he says. Instead, the eggs were jumbled and deformed. This suggests a flood likely washed them from their nests during an intense storm, Kellner says. Sand and other sediments in the water must have quickly buried them. “Otherwise,” he concludes, "they would have decomposed."
The researchers scanned the eggs using computerized tomography, or CT. This specialized type of X-ray imaging helped see inside the eggs. Being soft, most of the pterosaur eggs had flattened during burial and fossilization. But the block contained at least 16 partial embryos. And some of them were captured in 3-D.
Two of the best-preserved embryos revealed a tantalizing clue to pterosaur development, Kellner says. His team looked at a key part of a wing bone, called the deltopectoral (Del-toh-PEK-toh-rul) crest. Even in an embryo that the researchers think had been nearly ready to hatch, this bone had not been fully developed. But the embryo’s femur, or leg bone, was.
These features suggest that hatchlings could walk, the scientists say, but not yet fly. If so, the young creatures may have needed parental care for feeding, the researchers noted in their paper. It appeared December 1 in Science.
D. Charles Deeming is a vertebrate paleontologist at the University of Lincoln in England. He was not involved in the new study, although he wrote about it for the same journal. The walk-not-fly idea is interesting but no more than an educated hunch, he argues. There are not enough details to speculate about pterosaur behavior, he cautions. For example, he charges, no one can say for certain that the embryo in question was close to hatching. So it’s too early to say that it couldn’t fly at hatching. But as there were so many eggs, he says researchers certainly can get a better idea of the range of the animals’ sizes.
Kellner agrees that there are still many things his team does not know from the fossil eggs. That's why his group is continuing to study them along with other eggs found more recently at the same site. And the hunt is on for still more.
“Now that we know what they look like, we can go back and find more,” he says. “You just have to get your knees down and look.”
behavior The way something, often a person or other organism, acts towards others, or conducts itself.
birds Warm-blooded animals with wings that first showed up during the time of the dinosaurs. Birds are jacketed in feathers and produce young from the eggs they deposit in some sort of nest. Most birds fly, but throughout history there have been the occasional species that don’t.
computerized tomography (CT, for short). A special kind of X-ray scanning technology that produces cross-sectional views of the inside of a bone or body.
Cretaceous A geologic time period that included the end of the Age of Dinosaurs. It ran from roughly 145.5 million years ago until 65.5 million years ago.
development (in biology) The growth of an organism from conception through adulthood, often undergoing changes in chemistry, size and sometimes even shape
dinosaur A term that means terrible lizard. These ancient reptiles lived from about 250 million years ago to roughly 65 million years ago. All descended from egg-laying reptiles known as archosaurs. Their descendants eventually split into two lines
embryo The early stages of a developing organism, or animal with a backbone, consisting only one or a few cells. As an adjective, the term would be embryonic — and could be used to refer to the early stages or life of a system or technology.
femur In humans, the large bone in the upper leg. It is commonly known as the thighbone. In tetrapods (creatures with four limbs), it’s the large bone in the upper hind limbs.
fossil Any preserved remains or traces of ancient life. There are many different types of fossils: The bones and other body parts of dinosaurs are called “body fossils.” Things like footprints are called “trace fossils.” Even specimens of dinosaur poop are fossils. The process of forming fossils is called fossilization.
hatchling A young animal that recently emerged from its egg.
journal (in science) A publication in which scientists share their research findings with experts (and sometimes even the public). Some journals publish papers from all fields of science, technology, engineering and math, while others are specific to a single subject. The best journals are peer-reviewed: They send all submitted articles to outside experts to be read and critiqued.
lizard A type of reptile that typically walks on four legs, has a scaly body and a long tapering tail. Unlike most reptiles, lizards also typically have movable eyelids. Examples of lizards include the tuatara, chameleons, Komodo dragon, and Gila monster.
paleontologist A scientist who specializes in studying fossils, the remains of ancient organisms.
pterosaur Any of various extinct flying reptiles of the order Pterosauria. These animals lived 245 million years ago to 65 million years ago. Although not true dinosaurs, they lived during the reign of dinosaurs. Among members of this order were the pterodactyls of the Jurassic and Cretaceous periods, which were characterized by wings consisting of a flap of skin supported by the very long fourth digit on each forelimb.
range The full extent or distribution of something. For instance, a plant or animal’s range is the area over which it naturally exists.
reptile Cold-blooded vertebrate animals, whose skin is covered with scales or horny plates. Snakes, turtles, lizards and alligators are all reptiles.
sandstone A type of sedimentary rock. It formed as sand-size grains of mineral grit became compacted or glued together over time.
sediment Material (such as stones and sand) deposited by water, wind or glaciers.
species A group of similar organisms capable of producing offspring that can survive and reproduce.
vertebrate The group of animals with a brain, two eyes, and a stiff nerve cord or backbone running down the back. This group includes amphibians, reptiles, birds, mammals and most fish.
X-ray A type of radiation analogous to gamma rays, but having somewhat lower energy.
Journal: X. Wang et al. Egg accumulation with 3D embryos provides insight into the life history of a pterosaur. Science. Vol. 358, December 1, 2017, p. 1197. doi: 10.1126/science.aan2329.
Journal: D.C. Deeming. How pterosaurs bred. Science. Vol. 358, December 1, 2017, p. 1124. doi: 10.1126/science.aao6493.