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.

Trilobite Eggs

Last week, a new [fossil] was unveiled. This one comes from the oceans of the Ordovician period (around 450 million years ago) and it’s a trilobite.

(Above: Trilobites from Dinopedia and Pinterest)

Trilobites are extinct arthropods (spiders, insects, millipedes, centipedes, crabs, lobsters, scorpions and more). They only lived during the Paleozoic Era (542-251 million years ago), but they had around 17,000 species (there’s only 5,400 species of mammals)! Trilobites came in a huge variety of shapes and sizes. Some of them were over 70 cm long and some were only 1 cm long.

The largest trilobites. From here.

The name “trilobite” comes from the three lobes that make up its body – the two side lobes (pleural lobes) and the central lobe. Note: they are not named for their cephalon (head), thorax, and pygidial (butt) lobes.

2 ways to divide a trilobite.

Since arthropods shed their exoskeletons to grow, we have many fossils of the same species, showing how an individual develops.

A growth series of a single species of trilobite. From here.

This new fossil shows something egg-straordinary. It has eggs preserved with it! The eggs are located under the cephalon of the trilobite. Even though trilobite eggs have been found before, they’ve never been found with an adult trilobite!

Figure 1a, d, and e from the paper showing the fossil and the eggs underneath the cephalon.

From this we understand that trilobites carried their eggs outside of their body, but tucked underneath their heads. Not on [kite strings] like other extinct arthropods.

Tyrannosaurs: Babies and Growth!

The middle of March brought new information about Tyrannosaurs.

We start with a [paper] by Schweitzer and others in the journal Science. These authors discovered a special type of bone on the inside of a thigh bone (a femur) of a Tyrannosaurus rex. This type of bone is only found today in birds. This makes sense because birds are a type of dinosaur, the only ones to make it through the extinction at the end of the Cretaceous Period.

cladogram

Evolutionary tree of Archosauria (crocodiles, birds, their common ancestor and all of its descendants). Birds, on the far right, are theropod dinosaurs. Drawings by Scott Hartman.

This bone is super special because in birds, it’s only found in FEMALE birds that are in the process of forming or laying eggs. This type of bone is called Medullary Bone and it forms because the calcium that is needed for the mom to make eggshells is taken from her bones. Calcium is the component in eggshells that forms the outer, hard, protective layer.

MedBone3

Figure 1 from the paper. MB is medullary bone, CB is cortical bone (the outside layer of bone), and ELB is dividing bone layer. Left is a chicken, right is Tyrannosaurus rex.

This medullary bone forms to help move the calcium from the bones to the eggshells so it is only present while the eggs are being formed and laid. Once egg laying is done, the bone is almost instantly reabsorbed. This means that if we find this bone in dinosaurs, we can tell that they are female dinosaurs and that they were able to make eggs at the time they died. This gives us a whole new window into dinosaur life!

pregnant-t-rex

Pregnant versus not pregnant female Tyrannosaurus rex.

Next, a [paper] by Brusatte and others in the journal PNAS. These authors describe a newly found tyrannosaur from Uzbekistan.

uzbekistan-map

Uzbekistan is the middle pink country.

This new tyrannosaur, named Timurlengia eutica, is important because it is from the early Late Cretaceous, a time that we did not have any tyrannosaurs for before. Timurlengia fills in a large time gap and can help answer questions about how quickly tyrannosaurs went from being small animals, like Dilong, to large ones, like Tyrannosaurus rex.

dilongtrex size
Dilong on the left, Tyrannosaurus rex on the right.

What the authors found is that this new species is still small to medium sized even though it is more closely related to the largest tyrannosaurs. This means that tyrannosaurs went from being small to medium sized animals to really big, much faster than we had thought and begins to fill in information we did not have before.

TyranoTree

Figure 3 from the paper. Tyrannosaur tree of life with the time periods on the bottom. Timurlengia is in red in the middle.