Pterosaur Eggs and Nests

Last week, a [paper] was published that described an amazing fossil find. In China, in sediments dating to the Early Cretaceous, the authors found over 200 pterosaur eggs! Remember, pterosaurs are flying reptiles that lived alongside the dinosaurs, but are not dinosaurs themselves. Based on an adult specimen found with the eggs, the authors identified the fossils as Hamipterus tianshanensis.

A reconstruction of Hamipterus by C. Zhao.

These pterosaur eggs are preserved in 3 dimensions, which is a rare thing on its own. The authors used CT scanning and very careful preparation to look inside many of the eggs. Out of the 200-ish eggs, 16 of them had parts of embryos. The rest were filled with sediment, which potentially helped them stay in 3 dimensions as they became fossils.

Figure 2A from the paper showing the eggs and some adult bones.

The embryos all showed different levels of development, meaning that they were different ages (and that they were laid at different times). This tells us that many adult pterosaurs were nesting together and laying their eggs around the same time. The embryos also showed that their legs were more developed than their arms, even in embryos that were close to hatching. This tells us that these baby pterosaurs could not fly when they first hatched, but they could probably walk around. Because they couldn’t fly, their parents probably had to take care of them until they learned how to fly.

The authors think a storm came through while the pterosaurs were nesting and washed the eggs and some adults into a nearby lake. There might be more eggs under the first layer, so there might be more to find out from this wonderful find.

A Tiny Pterosaur

This week, an [article] was published about a new pterosaur specimen. The specimen was found in British Columbia, Canada and is from the Late Cretaceous (around 83-76 million years ago). The specimen includes a humerus and some vertebrae.

Fig 1 map

Figure 1 from the paper showing the location of the new specimen.

Pterosaurs are among my favorite animals. They were one of three vertebrate groups that was able to fly. They have a huge diversity in head shapes, feeding styles, and body sizes.

Pterosaur diversity sergey krasovskiy

Pterosaur diversity by S. Krasovskiy.

Pterosaurs share many flight-related features with birds, like hollow bones, long arms, fusion of many of their bones, but they fly in a completely different way. Birds have long arms with fused hands at the end and asymmetrical feathers that allow them to create lift. Pterosaurs also have long arms, but instead of fusing their hands, they extend and embiggen their ring finger. Instead of feathers, pterosaurs had a skin membrane that extended from their hips (or ankles in some) to the tip of their ring finger. In comparison, bats also use a skin membrane, but they have all of their fingers in the membrane instead of just one.

wing comparison

These are all different solutions to being able to fly.

This new specimen of pterosaur is known to be an azhdarchid because of features in its bones. Another famous azhdarchid pterosaur is Quetzalcoatlus, which had the height of a giraffe and the wingspan of a Cessna airplane.

Queztal Mark Witton

Quetzalcoatlus with a giraffe for scale. By M. Witton.

Now, the interesting thing about this pterosaur is that it’s very small. Most pterosaur fossils from the Late Cretaceous are very large (like Quetzalcoatlus), even though they started out very small in the Triassic and Jurassic. This new specimen is comparably tiny, with a wingspan of only 1.5 meters. And it’s not a baby. Based on microscopic features of the bones, the authors think this specimen is a late-stage juvenile (like a teenager) or a sub-adult.

pterosaur cat Fig 6

Figure 6 from the paper showing the new pterosaur with a cat for scale.

Why is that important? Remember how I said that birds and pterosaurs are very similar. When you have animals that have similar habits and habitats, they tend to compete for resources, like foods and shelter. There is a hypothesis (a testable scientific idea) that pterosaurs had to get really large because birds out-competed them at smaller sizes. This new specimen shows that small pterosaurs still existed during the Late Cretaceous. The authors also note that since we don’t find baby pterosaurs in the Late Cretaceous, that maybe small pterosaurs existed, but weren’t fossilized.