The Mystery of the Upside-down Ankylosaurs

Many ankylosaurs, the armored dinosaurs, have been found upside down when they’ve been discovered, especially when they’ve been found in river beds or marine sediments. Researchers have had different ideas as to why this might be the case.

An anklosaur. From here.

A new [study] tested several hypotheses to figure out which is the most likely to explain the upside-down fossils. The authors tested 4 hypotheses. The first was the ankylosaurs were just clumsy and would fall down hills and land upside down. This idea is hard to test, and seems unlikely, so the authors moved on.

Turtles can actually flip themselves over when they’re on their backs (though it’s nice to have help from a friend). Ankylosaurs would not have been so successful if they could not do the same.

The second hypothesis was that predators would flip the ankylosaurs over and eat them, leaving the remains to be preserved upside-down. The authors examined 36 ankylosaur specimens and only found 1 with any tooth marks on it. They rejected this hypothesis, since it did not seem that the upside-down ankylosaurs were eaten.

A picture of an ankylosaur being threatened by a T. rex. By Eldar Zakirov.

The third hypothesis was that dead ankylosaurs would wash into a river. Once there, it would start to decompose. The process of decomposition releases a lot of gas, which gets trapped inside the body of the animal, causing it to float. The armor on the back of an ankylosaur would weight more than the gas-filled belly, and the whole dinosaur would flip upside-down. Eventually it would settle to the bottom and be preserved upside-down. To test this, the authors created computer models of a bloated ankylosaur and a bloated nodosaur (an ankylosaur with no tail club). They found that the nodosaur would tip very easily and would flip over more readily. The ankylosaur had a more difficult time flipping over.

Figure 3 from the paper showing the bloated ankylosaur and nodosaur. The plus and diamond symbols are place markers for the computer simulations to test how easily they would flip over.

The last hypothesis was that the ankylosaurs would roll over as the decomposed on land. The authors tested this by examining road-kill armadillos and by watching 22 armadillos decompose in a more controlled setting. They did not find support for this hypothesis as the armadillos were equally likely to be found on their sides, stomachs, and backs.

Armadillos are pretty cute.

The authors concluded that the most likely scenario is that the ankylosaurs would get washed into a stream or into the ocean, bloat from decomposition, and roll over as they floated along. Once the gases escaped, they’d sink to the bottom and get fossilized. This study took it upon itself to test a long-standing idea that had never been tested. Now we have a better notion for how ankylosaurs were preserved and more about their biology.

A Fossil Fight

A couple of weeks ago, 2 articles were published by different research groups about a species of arachnids. Arachnids are the group that contains spiders, scorpions, ticks, mites, harvestmen, and a couple other groups. They all have 8 legs, 2 body segments, and 2 other pairs of appendages that serve a lot of different functions.

The diversity of arachnids. From Encyclopedia Britannica.

The articles focused on 4 specimens of a new species, called Chimerarachnae yingi. ‘Chimera’ means ‘a mixed animal’, ‘arachnae’ refers to the arachnid group, and ‘yingi’ is in honor of the person who found the specimens. All 4 specimens were found in amber in Myanmar and date back to the mid-Cretaceous (around 100 million years ago).

One of the specimens used in the studies. From Wang et al. 2018 (the first group).

Each research group looked at the specimens and ran an analysis of evolutionary relationships to see where this new species fits in. [One research group] found that this species is more closely related to spiders. [The other research group] found that it’s more closely related to an extinct group of arachnids called Urareneida.

The different positions the new species takes. The first study showed that it was closer to spiders (in blue) and the second showed that it was a Uraraneid (in red).

But why the difference? It seems the combination of traits that Chimerarachnae has makes it difficult to clearly place into the tree of arachnids. When analyses are run in slightly different ways, its position moves around. Hopefully more specimens can help clear this up in the future.

NASA and the Lower Cretaceous

The National Aeronautics and Space Administration (NASA) usually has their eyes on the sky, but this week, a [paper] came out that described a fossil found at their Maryland Space Flight Center.

Figure 1 from the paper showing the location of the NASA Goddard Space Flight Center (NASA/GSFC) in Maryland. The different shades of grey indicate different rocks.

Ray Stanford was dropping off his wife, Sheila, back at NASA after having lunch together, when Ray spotted an interesting rock. As an amateur paleontologist, Ray went to investigate. He noticed this rock had a 12-inch-long footprint preserved on it and called on a few professionals to help excavate it. That was back in 2012, and this week, the paper describing this fossil has been published.

The rock slab is 8 feet (almost 2.5 meters) long and 3 feet (almost a 1 meter) wide and shows almost 70 tracks of different animals. The rock is from the Lower Cretaceous (142-96 million years ago) and preserves footprints from theropod, ankylosaurian, and sauropod dinosaurs, and pterosaurs.

Figure 3 from the paper showing the slab on top and the interpretation of the footprints below. The big, purple sauropod print is what Ray had spotted.

But the real stars of this slab are the mammal tracks. Cretaceous mammal tracks are extremely rare, and this slab seems to preserve 26 tracks made by mammals. That’s an incredible amount!

Figure 6A from the paper showing a close up of the mammal footprints on the slab.

Without any body fossils, it is hard to pinpoint exactly what species made these tracks, but further studies and new discoveries could eventually help to figure this out. What this slab does indicate is that Maryland had a very diverse set of animals living there at the beginning of the Cretaceous.

Cheetahs, Ears, and High-Speed Chases

I’m back! I spent the last two weeks of December and a lot of January finishing and sending out She Found Fossils, the [book] about women in paleontology that Abby West, Amy Gardiner, and I wrote. I also went to the annual Society of Integrative and Comparative Biology conference in San Francisco and learned a ton. Now hopefully I can get back to a once-a-week schedule for this blog.

Last week, a [paper] was published that looked at the ears of cheetahs and their cat relatives. Cheetahs are the fastest land animal of today. They’ve got spots and face stripes and little manes when they’re babies.

A cheetah with her cub. From BBC.

Cheetahs are specialized in running at high speeds to chase down small antelopes. Their whole bodies are adapted for running: they have deep chests for bigger lungs and more oxygen flow, flexible backs to make their strides longer, long tails that they use to turn, and their claws don’t fully retract so that they can grip the ground better. All of these traits help them run down their prey.

But when did cheetahs get so fast? This new study looks at their inner ears. The inner ear doesn’t help us with hearing, instead it tells us how quickly and in what direction our heads are moving. It also works with the visual system in the brain to help stabilize the head so that what we see stays steady instead of blurry.

The parts of the ear. The inner ear has is the portion that deals with balance and head movement. From here.

This paper used CT scanning to look at the inner ear of cheetahs, other large cats (like lions and pumas), and 1 species of fossil cheetah. By analyzing the size of the different parts, the authors figured out how much each cat was adapted to high speed running. The bigger the components of the inner ear, the better the cat would be at keeping vision stable at high speeds.

The inner ear of the extinct (middle) and modern (lower) cheetah. You can see how the modern cheetah has wider and larger components than the extinct cheetah. Illustration by M. Grohé.

The authors found that the modern cheetah has larger inner ear components than the fossil cheetah. This means that the fossil cheetah was probably not specialized for high speed running, and that high-speed chasing has evolved more recently in modern cheetahs.

A smiling cheetah. From the Caters News Agency.

Top 5 Cool Fossil Animal Posts of 2017

Ok friends. I posted a lot in 2017 (37 times!) so in trying to narrow down the top posts this year, I thought about narrowing it down to just dinosaurs, but that didn’t seem fair. So, in order of appearance, here are the top 5 cool fossil animals posts of 2017:


February 2017: [Bulbasaurus] a small-sized adult dicynodont from the Permian, which was named for its bulbous nose.

Bulbasaurus by M. Celesky

May 2017: [Zuul] the most complete North American ankylosaur ever found. Its head is covered in horns, giving it the appearance of Zuul, from Ghostbusters.

Zuul and Zuul. Left by D. Dufault.

July 2017: [Coronodon] a whale from the Oligocene whose teeth had many bumps for filter feeding.

Coronodon by A. Gennari.

September 2017: And speaking of filter feeding – [Morturneria] a plesiosaur from Antarctica with a ton of tiny teeth that it used as a sieve.

Morturneria by S.J.G.

December 2017: The trove of [pterosaur eggs], some with embryos, from the Early Cretaceous that tell us a lot about the growth of pterosaur babies and the nesting habits of the adults.

The pterosaur eggs.

Honorable mention: The ongoing dinosaur tree debate [1] [2], which isn’t a cool fossil animal, but could completely change how we think about (the coolest) fossil animals.

Note #1: between the holidays and traveling to a conference, I will not be back for a while. But fear not, DrNeurosaurus will return in February 2018.

Note #2: Our book SHE FOUND FOSSILS is available! Check here for details: She Found Fossils

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 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.

The Giant Extinct Otter and its Giant Bite

Last week, an [article] was published that talked about the biting ability of the extinct giant otter, Siamogale melilutra. The [discovery] of this otter in south-western China was published in January of this year. It lived during the Miocene (23-5.3 million years ago). Siamogale weighed about 50 kg (110 pounds) and is the largest otter to have been found.

A reconstruction of Siamogale by M. Antón.

Living otters have a range of sizes from 4 kg (9 pounds) to 45 kg (100 pounds). They live all over the world in fresh and marine waters. And they’re really cute.

Otters holding hands. From Wikipedia.

This new paper compared the jaw mechanics of all of the living otters. Jaw mechanics include things like how much force the jaw can handle, muscle volumes, jaw stiffness, and how efficient the jaw is when biting. The authors used the jaw mechanics information from the living species to calculate the mechanics of Siamogale. Then the authors made CT scans of all of the skulls and tested the mechanics using computer software.

Figure 4 from the paper showing the computer models for the Giant River Otter and Siamogale. Red areas have higher stress, blue areas have less stress.

They found that Siamogale had a jaw 6 times stiffer than any of the living otters! This means that Siamogale had a super powerful bite. It probably used this powerful bite to eat foods like clams that have to be cracked open to enjoy. Some of the living otters use tools to help them crack the shells. Other living otters use their powerful bite. Siamogale’s super powerful bite probably let them eat foods that other animals at the time couldn’t eat.

The Dinosaur Tree Debate Continues

This week, a [reply] to the new [dinosaur tree] from March was published. You might recall that the March paper found a new set of relationships for dinosaurs. Ornithischians and theropods were found as closest relatives, forming the group Ornithoscelida, and sauropods and a group of early dinosaurs formed another group.

Evolutionary tree of dinosaurs published in March. Made by me.

The reply paper itself is only 1 page long. The authors looked at all of the characters used in the March analysis and rewrote them based on their own examination of the fossils. They also added a few more dinosaurs that were in important places in the tree.

Evolutionary tree of dinosaurs given by this new analysis. Made by me.

The authors ran their updated characters in a new evolutionary relationship analysis. The analysis gave them the standard evolutionary tree for dinosaurs. Theropods and sauropods are closest relatives, forming the saurischians, and ornithiscians are their own group.

You might think – ok, problem solved! But in fact, the authors ran a statistical analysis on their tree to see how many changes would need to be made to find the March tree. This analysis shows that only a few would have to be made to get from their tree to the March tree. This means that the trees are not very different, statistically speaking.

Another possibility. Made by me.

The authors also found that another tree is almost equally possible – one where sauropods and ornithischians are closest relatives and the theropods are their own group! WOW! What we know for sure is that early dinosaurs from each group looked very alike and so working out how they are all related to each other is going to take more research.

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.