A Sauropod Footprint with a Skin Impression

This week, a new [paper] was published that described the largest sauropod footprint ever found from the Early Cretaceous (146-100 millions of years ago) of Korea. The footprint is more than 50cm (20 inches) in diameter!

The authors found something very rare inside the footprint: a dinosaur skin impression. That’s the equivalent of leaving a palm print on wet cement, like on the Hollywood Walk of Fame.

Mickey Mouse’s hand and footprints on the Hollywood Walk of Fame. From Pinterest.

The impression preserves interlocked hexagons that have a range of sizes. They seem to get smaller on the outsides of the impression.

Figure 2A from the paper showing the footprint on the left and a close up of the skin impression on the right.

The authors analyzed the sediment around the footprint to try and understand why skin impressions are so rare. They found that these impressions were left in on a muddy surface that had dried enough to preserve the impression. That muddy surface had to stay dry afterwards, and not get covered over by water. If more flooding had occurred, the print would have disappeared. The muddy surface also had to be covered by a thin layer of bacteria in order to hold the mud together. The combination of these conditions allowed the footprint and skin impression to stay preserved. These conditions can be hard to find in the same place and time, meaning that more dinosaur skin impressions could still be rare in the future.

A New Look for Sinosauropteryx

Last week, a [paper] came out discussing the color patterns on the theropod dinosaur Sinosauropteryx. This dinosaur was a small-bodied meat eating dinosaur from the Cretaceous (133-120 million years ago) of China.

Figure 1 from the paper showing one of the specimens of Sinosauropteryx.

The authors took photos of 2 specimens of Sinosauropteryx under special lighting conditions. This helped them see the feathers that surround the skeletons. Feathers that had color in them are preserved more easily than feathers without color. So looking at the fossils helps us understand how colors were distributed on the animal. Artists then made reconstructions to show how the colors appeared on the dinosaur. They found that Sinosauropteryx had a striped tail, a bandit mask around its eyes, and a brown back with a white belly.

Figure 2A from the paper showing the color reconstruction on Sinosauropteryx.

The authors also wanted to test what the colors could tell us about what kind of habitat Sinosauropteryx lived in. Animals that live in open habitats (like deserts or grasslands) usually have darker colors on their back and lighter colors on their bellies. This helps break up their body shape so that predators have a harder time seeing them. Animals that live in closed habitats (like forests) usually are darker everywhere and have fewer areas with lighter colors. Think of the color differences between an antelope that lives in the grasslands, and an okapi that lives in the rainforest.

An antelope on the left showing coloration for open habitats. An okapi on the right showing coloration for closed habitats. Okapi from here.

To do this, the authors 3D printed models of the dinosaur and photographed it twice: once when it was fully sunny and once when it was completely cloudy. The full sun imitates the open habitat and the cloudy day imitates the closed habitat. They found that the shadows cast on the model on the sunny day match the color distribution found on the fossils. This means that Sinosauropteryx lived in open habitats.

Figure 2B from the paper showing how the open habitat where Sinosauropteryx lived and its coloration.

It probably used its bandit mask to reduce the sunlight entering its eyes. The striped tail, dark color on its back and light color on its belly helped camouflage it in open habitats, making it harder for predators to see it, and making it harder for prey to see it coming. This study shows us how new techniques can help us answer questions about how dinosaurs lived.

Crab-Eating Hadrosaurs

Last week, a [paper] was published that described some fossil poops. That’s right, poops! When a poop fossilizes, it’s called a coprolite (‘copro’ for poop and ‘lite’ for stone).

A coprolite. From Wikipedia.

These coprolites came from Grand Staircase-Escalante National Monument in Utah and they date back to around 76-74 million years ago. The coprolites contain decayed wood bits that had been chewed up before swallowing. Of the dinosaurs known from this area and time, it is most likely that hadrosaurs were responsible for creating the poops. Hadrosaurs have specialized teeth that are really good at crushing and breaking tough vegetation to make it easier to digest. Instead of having a single row of teeth, hadrosaurs unite dozens of teeth into a thick collection of teeth (called a dental battery). All of the teeth work together to create a large, flat surface for grinding.

A dental battery with one tooth outlined in white. At the top of the battery, there is a flat surface for grinding. Photo by V. Williams.

The hadrosaur coprolites had more than just plants and decayed wood, though. They also contained bits of crab shell! And it wasn’t only 1 coprolite that had crab shell in it. Several different coprolites from different areas and different times had crab shell in them. This means that it wasn’t an accidental swallowing of a crab, but rather, that the hadrosaurs were eating them on purpose.

Figure 2b from the article showing the coprolite.

How can we be so sure though? We know how wide a hadrosaur mouth was and we know how big the crabs were. It turns out, the crabs would have taken up a large portion (20-60%) of the hadrosaur’s mouth! If the dinosaur didn’t want to eat the crab, it would have noticed it and spit it out. The authors think that during times where plant matter was harder to find, these dinosaurs would eat the decaying logs that crabs also ate. As the dinosaurs munched away on the wood, they’d eat the crabs as well, providing a good source of protein.

My own reconstruction of a hadrosaur, Maiasaura finding a crab. Drawing found on Pinterest. Log photo by C. Perrin. Crab photo by The Daily Dot.

This study shows us that even though we think teeth are specialized for one type of food, animals might eat a larger variety of items that we thought.

Cretaceous Hell Ants

At the beginning of September, a [paper] was published that described a new species of ant. Not just any ant! A hell ant from the Cretaceous. That was preserved in amber from Burma.

A photo of the hell ant in amber. The authors called the new species Linguamyrmex vladi.

This group of ants is extinct and known only from the Cretaceous (specifically around 98 million years ago). The amber is see-through, so the authors took high-resolution images of the ant through the amber. They also CT scanned it.

Figure 3 from the paper showing a reconstruction of the ant.

They found that this ant had a large horn coming off the head and a scythe-like jaw. A scythe is a curved metal tool for cutting tall grasses. It’s also what Death carries around.

Death, holding its scythe. From here.

These jaws were used to pin and pierce soft larvae, but could not be used to chew their prey. Instead, the authors think that after piercing the prey, the jaws would funnel blood down into the bend of the jaw, and then small hairs and suction would direct the blood into the ant’s mouth. This ant sucked blood like a vampire!

Figure 4 from the paper showing the hell ant and its prey.

Lastly, the CT analysis showed that the jaws are denser than the rest of the head. This analysis also showed that the increased density was due to metals in the jaw. These ants absorbed metals from their environment and used them to make their jaws stronger. It’s too bad that this group is extinct – it would have made for a killer nature show!

An Exceptional Fossil Insect

Cockroaches are known for surviving multiple extinction events on Earth. They evolved around the Carboniferous Period (360-300 million years ago) and modern versions appear in the fossil record in the middle of the Mesozoic Era.

A Madagascar hissing cockroach. From National Geographic Kids.

Now imagine if a cockroach evolved long, grasping arms, and giant eyes for hunting prey. That’s pretty terrifying, right? Well, that’s basically what a praying mantis is*.

A praying mantis. If you think about it, a praying mantis is really the insect form of a carnivorous giraffe. A carnivorous giraffe with knife hands. Photo from Wikipedia.

Today, praying mantises hunt prey by ambushing animals as they come close. Mantises are normally camouflaged to blend in with their surroundings. When a particularly tasty insect comes by, they attack! They have a single pair of arms they use for catching and holding prey (called raptorial arms). Each arm has a set of spikes that help hold the prey in place. But did they always use one pair of arms for this job?

Figure 1 from the article showing the fossil in the center. On the left, the different body parts are colored (eyes are dark blue, head is yellow, body and arms are the other colors). On the right is a close up of the second set of arms.

A new 110 million-ear-old [fossil] from Brazil shows us a different idea. This exceptionally preserved mantis shows a pair of wings, the head, part of the first body segment, and the first two pairs of arms.

The interesting thing is that both the first and the second pairs of arms have spikes on them. Since these spikes are used to catch and hold prey in modern mantises, we know that this fossil mantis was probably using its second pair of arms to help hold prey. This fossil shows us that extinct mantises may have hunted a little differently than what we see today.

A couple of praying mantis showing their colors. Photo by I. Siwanowicz.

*To be clear, mantises did not evolve from cockroaches. Both mantises and cockroaches evolved from an ancestor that looked more like a cockroach.