Handprints and the Human Experience

This post is going to be a bit different than the normal news reports, it’s more of a post for caregivers of young children. As a paleontologist, I study past life, and often try to imagine what different places may have looked like millions of years ago. Every so often, I have an experience that brings to light something from an ancient world and unites my random life events with those of an organism from long ago.

Usually, this occurs when I get to go fossil hunting. My life intersects with that of whatever creature whose bone I happen to pick up. It’s an incredible experience and feels a bit like time travel.

But recently, this occurred at home on a slow summer day. I believe that many caretakers of young kids will agree that some summer days move more slowly than others. It feels like every minute takes an hour and you’re just trying to make it to dinner. 

I was having one of those days when a question arose from my tiny co-habitant: “can I paint the bathtub?”

And of course I thought about having to clean up the whole thing afterwards. And the grout! Grout is so hard to clean. Even if the paint is ultra-washable. But instead of all of that I said, “Yes!” and off we went with the whole box of paint colors up to the bathroom where I dutifully placed globs of paint for strategic mixing around the tub. 

The tiny co-habitant climbed in and had a ball mixing the paint, painting their own body, and generally covering every inch of the tub (and the grout) in multiple colors. But something interesting occurred. 

My kid dipped her hands in the paint and started high-fiving the wall, leaving perfect, beautiful little hand prints as high as they could reach. After a few minutes, the bathtub looked like one of those caves with the handprint art.

Her beautiful little handprints.

That’s when it dawned on me. The people that helped the kids make that art in that cave so many thousands of years ago – maybe they were having a day where time ticked backwards and they were just trying to entertain the kids for a few minutes*. Maybe we haven’t changed all that much in the thousands of years since. Maybe the human experience is timeless.

And those little handprints are just so cute!

If you want to try it at home, I’d suggest Crayola Ultra-Washable fingerpaint (not an ad, just realistically very washable). It does stick to the grout though, so use at your own peril.

*Some caves, like [Cosquer Cave] in France have children’s handprints at a height of 8 feet off the ground (made either 27,000 years ago or 19,000 years ago). This implies that an adult picked them up to place those handprints, as ladders would not have fit in these cave chambers.

A handprint from Cosquer Cave. From Wikipedia.

Or [these] handprints symbolizing coming-of-age ceremonies from Mayan celebrations 1,200 years ago.

Handprints from Mayan celebrations. Photo courtesy of Sergio Grosjean.

Or [these], potentially the earliest cave art from 169,000-226,000 years ago in Tibet that may have been made by Neanderthals, Denisovans, or our own species.

Handprints from Tibet. Photo courtesy of D.D. Zhang et al. Science Bulletin.

The Tyrannosaur Controversy – Response!

Back in March, a [paper] was published that described evidence that T. rex may actually represent 3 species and not just 1. The authors used ratios of the length and circumference of the femur and also ratios of specific teeth diameters to define the differences between the 3 species. The authors of that paper named the new species Tyrannosaurus regina and Tyrannosaurus imperator

Specimens of T. rex showing the new species. According to the study, A and B are T. rex, C and D are T. regina, and E is T. imperator. Figure 1 from the original study.

That study ignited a ton of conversation and was widely published in different news outlets, almost as if the reign of the great Tyrannosaurus rex was at an end. However, from a scientific point of view, there were several questions that needed to be tested by other research groups in order to check if T. rex was actually 3 species or not. 

That study was officially [published] in July! The authors point out a few issues with the original work. They also re-did the analyses using a more thorough dataset and slightly different methods. Buckle up, this one is a doozy.

Firstly, the characteristics that the original study used to distinguish the 3 species do not actually separate all of the existing T. rex specimens – there is some overlap, making these characters difficult to use. 

Secondly, the original study did not use all of the information available for T. rex. There are 1850 traits that have been studied on Tyrannosaurus and its relatives that are available for use. Usually, new traits are added to the ones already available so that any new analyses use all of the data to get the most thorough answer. The original study based their species divisions on only the femur and tooth measurement traits.

Thirdly, the original study indicated that the amount of variation in the skeleton among the different Tyrannosaurus specimens was unusually large. When there’s a lot of variation, then it is more likely to be showing multiple species instead of just one. The new study compared the variation in Tyrannosaurus to that of 112 other species of theropods (including birds). They found a very typical amount of variation in Tyrannosaurus, not an unusually high amount.

Figure 4 from the new study shows that the variation in Tyrannosaurus (dashed line) is about average when compared to over 100 other therapods (yellow shading shows the range).

Fourthly, the tooth measurements from the original study were not consistently made. Some of the measurements were from teeth from the same side of the mouth, some from opposite sides, and sometimes no teeth were there so they measured the tooth socket instead. 

Lastly, the analysis the new study did showed that all of the information clustered all of the Tyrannosaurus specimens into 1 group, not 3. Part of the reason for that is the original study used a method in which you tell the analysis how many groups to look for, and then it usually shows you that many groups as a result. The new study did not define how many groups to look for, leaving it to the analysis to come up with the mathematically best answer (which was 1). 

Figure 3 a and c from the new study. A shows how the specimens clustered based on their femur measurements. The different colors correspond to the new species the original study categorized the specimens in (blue – T. rex, red – T. imperator, green – T. regina, purple – uncertain). The groups do not separate out the specimens by the species the original study indicated. C is the graph showing that the most likely number of groups is 1, not 3, for these measurements.

There were more discussion points in the new study than what I’ve listed here, but I hope that the case is pretty clear – Tyrannosaurus rex is a single species, not three.

An important point that the new study made is that half of the specimens in the original study came from private collections or commercial fossil companies. When specimens are sold to individuals or to companies, they become almost impossible to study. By doing this, the original study made it difficult to replicate their results. Replication is how we confirm conclusions in science, so if we cannot see the specimens, we cannot confirm a result. Specimens belong in museums or publicly accessible collections. 

You tell ’em, Indiana Jones!

Was Spinosaurus a Swimmer?

Spinosaurus has a long history of confusion and reanalysis behind it. Part of the reason that paleontologists can’t seem to make up their minds is because the first specimen was discovered in 1912 and promptly destroyed during World War II. New specimens were not discovered until the 1990s and 2000s.

What we knew about Spinosaurus from the 1912 specimens was that it was a large, carnivorous theropod with a sail on its back. The specimens uncovered in the 1990s were bits of the skull. It wasn’t until 2014 when more of the body was recovered in North Africa and we started to understand more about its proportions.

Spinosaurus reconstructions through time. Made by Nix Draws Stuff (Tumblr).

Even though we had first imagined a dinosaur similar in proportions to other large theropods (having long, muscular legs and more gracile arms), the new specimen showed a dinosaur with relatively equal length arms and legs, and a large sail on its back made out of the spines of the vertebrae.

But what did this mean for how Spinosaurus lived? Was it a terrestrial predator like T. rex? Did it sit idly by the water, waiting for unsuspecting aquatic prey? Or was it an active underwater predator?

A new [study] finally answers this question. Fully aquatic animals have bodies that usually have fins, noses that open at the top of their head instead of the front, and arms, legs, and tails that are more suited for swimming. But some animals that live mostly in the water do not show these obvious adaptations. Animals like hippos look more like other terrestrial animals. That is, until you look at their bones. Aquatic animals increase the amount of bone they develop in their limbs and ribs so that they have easier time sinking while swimming. It gives them more control over their position in the water.

The skeletons of a hippo and a dolphin.

With this information in mind, the authors measured bone density in the ribs and femur of hundreds of amniotes (animals that lay a shelled egg or give live birth). What they found was that Spinosaurus has bone density similar to other aquatic animals, meaning it likely spent a lot of time pursuing prey under water. Its close relatives, Baryonyx and Suchomimus, both of which are smaller than Spinosaurus and do not have a sail, showed an even more interesting result. Even though both Baryonyx and Suchomimus have similar looking bodies, Baryonyx’s bone density showed that it was likely an aquatic predator, whereas Suchomimus was terrestrial!

Spinosaurus (red), Baryonyx (yellow), and Suchomimus (green), to scale. Made by PaleoGeek.

The authors tested many more species of dinosaurs in their sample, and the spinosaurids seem to be the only aquatic non-avian dinosaurs. Many other amniotes return to the water, but most dinosaurs preferred to stay on land. Why this is, we are not yet sure. However, this study shows why it is so important to continue to look for fossils and to run large-scale analysis comparing animals across different groups and lifestyles.

The Tyrannosaur Controversy

Maybe you heard, but earlier this year a [study] came out that suggested splitting the iconic Tyrannosaurus rex into 3 species. Usually my posts just describe the study that is done and put it into context. In this case, I will start with the normal summary, but at the end I’ll add my take on it. I try to only discuss open access research (you don’t have to pay to access the paper), because I believe science should be accessible to everyone. This paper is not open access, but I do have a pdf – please just ask if you’d like a copy. You can always email the author on the paper for a copy as well. Scientists are happy to share the work they do!


Tyrannosaurus rex was a giant, meat-eating, theropod dinosaur from western North America during the Late Cretaceous.The authors noted that Tyrannosaurus rex existed in the fossil record for possibly 2 million years. This is a *long* time, long enough for that species to have split into multiple species. Other studies have shown that T. rex has 2 main body types: a robust form and a more gracile (thinner and longer bones) form. Some paleontologists have tried to investigate if these body types could be showing female vs. male forms, without much success. Others have wondered if they are tied to different ages, but that also didn’t work out.

Robust and gracile forms of Tyrannosaurus. From Pinterest.

These authors measured the circumference and length of the thigh bone. They used the measurements to run a few different statistical tests and compared the results to other large, closely related theropods. They found that Tyrannosaurus had much more variation than other theropods.

The authors also looked for other characteristics that differed between the body types and found that the gracile forms have 1 incisor-type tooth on their lower jaw and that the robust form could have 1 or 2 of these teeth.

Figure 3 from the paper, showing the single small incisor-like tooth on the right (labeled “1”), and the spaces for 2 small incisor-like teeth on the left (labeled “1” and “2”).

Using these and other types of evidence, the authors split Tyrannosaurus into 3 species: Tyrannosaurus rex (“Tyrant Lizard King,” robust with 1 incisor-type tooth), Tyrannosaurus imperator (“Tyrant Lizard Emperor,” robust with 2 incisor-type teeth), and Tyrannosaurus regina (“Tyrant Lizard Queen,” gracile with 1 incisor-type tooth). I find their choice of names very fitting.

My Take:

Recently, other dinosaurs have been split into multiple species based on differences in their bodies and on living in different places. It makes sense that a species would evolve when given millions of years of time, since that’s how evolution works. However, the data need to support the division. In this case, I am not sure the evidence they report is enough to justify dividing the species. I have more specific thoughts, but this blog is not the space to express them. I look forward to the debates about this.

A Sick Day for a Sauropod

We know a lot about how dinosaurs’ bodies worked because birds are dinosaurs. We can examine birds and how they function to better understand dinosaurs. This idea not only helps us understand how their bodies moved and behaved, but also how illness affected them.

That is what this [article] is about. Birds can get respiratory diseases (sickness in their lungs, throats, noses, and air sac system). One of the differences between birds and humans is that bird lungs are not just connected to their throats. Birds have a complicated set of other sacs connected to their lungs. The air flow through those sacs and into their lungs happens in a single direction, so every time the bird breaths in and out, fresh air is brought to the lungs. That’s not like what we, as mammals, have. Our air goes in and out of our lungs through the same passage, so every time we breath in, we have to breath in some air that was already in our lungs. Bird lungs are much more efficient than mammal lungs.

An animation showing how mammals, birds, and insects breath. Credit to Eleanor Lutz.

The flip side to this is that birds have more organ related to their breathing systems that can get sick. They can have illnesses in their lungs and air sacs. And as the air sacs carve spaces for themselves in the nearby bone, many illnesses in the air sacs can create illness in the bone. Sauropods, the long-necked dinosaurs, had the same system of air sacs invading bone in their bodies.

Figure 3 from the article showing the breathing system of this dinosaur. The human for scale is Dr. Anthony Fauci, “the exemplar of pandemic education and rationalism” in the words of the authors.

The authors describe a diplodocine (specimen MOR 7029) that had a deformation in the bones of the neck. Because those bones would have surrounded an air sac, it is likely that the dinosaur had an infection in the air sacs that caused the surrounding bone to react. The authors describe many respiratory diseases in birds that could have been the cause of this infection.

Figure 1 from the paper showing the neck of the specimen, and the deformed bones.

But because we are only able to analyze the bones, the authors tell us that it is hard to know exactly which disease caused this. They also say that the most likely cause was an infection from a fungus known from similar environments. We have fossils of that fungus from the Eocene, so it’s not too much of a stretch to assume it was around in the Mesozoic as well. The better understanding we have of birds, the more we can understand their extinct relatives.

The Ultimate Cave People

New fossil [findings] in a cave in France have made us rethink a decades-old idea in paleoanthropology. This information comes from the Grotte Mandrin cave in Mediterranean France, that contains sediments from 56,800 – 51,700 years before the present. These sediments are arranged in layers, just like all geologic strata, but because much of the sediment stays within the cave instead of being eroded away, they are able to preserve finer time intervals.

Figure 1 from the paper, showing the cave from outside and in.

Inside this cave, and in each layer, were teeth from “anatomically modern humans” (people like us) and Neanderthals, and stone tools of different kinds. Because of the difference in abilities between the two types of humans, the stone tools they produced look different.

The layers of the cave and the teeth and tools found in each. Image by Ludovic Slimak.

I want to pause here for a moment and talk further about Neanderthals. They get a bad reputation as being ‘inferior’ to modern humans because of the idea that modern humans outcompeted Neanderthals any time the two came into contact. The two species may have fought when they saw each other sometimes, but there’s also evidence of gene flow between the species, so their contact didn’t always end in a battle.

The fossil evidence in the Mandrin cave shows that modern humans and Neanderthals were living in the same cave at different times. Caves provide natural shelter from wind, rain, and animals, so it seems logical that people would want to stay in one. Because the alternating layers show a pattern of Neanderthal->Modern humans->Neanderthal->Modern humans staying in it, it tells us that this cave was an important ‘pit stop’ for modern humans migrating out of Africa and into Europe. And because there is this pattern of alternating species, it shows that the appearance of modern humans didn’t automatically mean doom for the Neanderthals.

So why did Neanderthals die out? Possibly changes in climate decreased their population (they were adapted to colder climates), and possibly modern humans were just intolerant to competition. More data, especially from caves, will help us find out.

A Fossil Oviraptor Embryo

In Late December 2021, an incredible discovery was [announced]. A new fossil embryo of an oviraptor dinosaur was found in China. We all know how rare fossils are in general, but articulated fossils (ones where the bones are still in life position), and articulated fossils INSIDE of eggs are even more rare.

The egg itself was actually discovered 20 years ago, but it wasn’t investigated until recently. Inside, paleontologists found a baby oviraptor. The egg is ~16cm long and the baby is ~23.5 cm long, so you can imagine that the little embryo is curled into a ball.

An image from the paper showing the fossil and interpretation.

The exact position of the embryo is really interesting. It has its head tucked between its legs with its back up against the bottom of the shell. This position is very similar to what embryonic chickens do when they are getting ready to hatch. Having their head tucked helps protect them when they are pushing the shell apart.

There are a few other dinosaur eggs that contain embryos, and with each one, we are getting a clearer picture of how baby dinosaurs grew in their eggs. It should not be a surprise that they seem very bird-like in their development, and not as similar to modern crocs.

This embryo sheds new light on the link between modern bird behavior and dinosaurs.

An artist rendition of the baby oviraptor. By Lida Xing.

A New Ankylosaur from Chile

In December 2021, a [study] was published describing a new, mostly complete ankylosaur from Chile. Complete skeletons are very rare in the fossil record, so this discovery is exciting for many reasons.

The new fossil is an ankylosaur, one of my favorite types of dinosaurs! I always used to say “an-KLEE-o-saur” when I was a kid, but I eventually learned that its “an-KY-lo-saur.” Ankylosaurs are spectacular. They’ve got armored backs and tails and heads and even eyelids (in some). They were basically walking, herbivorous tanks. And the lived all over the world.

Some of the global ankylosaur diversity. Image by paleontologist Dr. Victoria Arbour.

There are 2 general types of ankylosaurs: Nodosaurids (that do not sport a tail club) and Ankylosaurines (that have a tail weapon). The new ankylosaur, Stegouros (“roof tail”) elengassen (after an armored mythical creature of the local Aónik’enk people), had a unique tail weapon. It was a frond of flat plates coming off horizontally on each side, instead of a ball-like club. A big weapon for an animal only 2.5 meters long.

An image of Stegouros by Lucas Jaymez.

After a phylogenetic analysis, it seems this new ankylosaur did not belong to Ankylosaurinae or Nodosauridae, but rather to a third clade (group). The analysis joined Stegouros with Antarctopelta (from Antarctica) and Kunbarrasaurus (from Australia). These three dinosaurs, all from the southern hemisphere, had combinations of traits that look more like stegosaurs than ankylosaurs, and more ankylosaur-like traits. Stegosaurs are the sister taxon to ankylosaurs (the most closely related group), so it makes sense that these early ankylosaurs look a little more general.

We’ve learned a lot about ankylosaurs in the last decade and it’s exciting to see more material for this group.

A New Book for the New Year

Happy New Year! I am looking forward to many new blog posts this year, among other exciting projects I have been working on.

I am going to start this year’s blog posts with a big announcement I’ve been looking forward to making for a long time. The Mandarin version of She Found Fossils (寻找化石的她)is now available on Amazon!

I can’t begin to tell you how much harder it was to publish this version than the English and Spanish versions. In summary, we ended up needing not only a translator, but also an editor (thank you so much Dr. Juan Liu!), we had to find a new printing service because the one we used for the other languages would not produce physical books in Mandarin, and we needed multiple edits to the imagery due to the differences in printing quality. Suffice it to say, we’ve been hard at work for a long time on this version and it’s finally out.

Here’s to a New Year!

Meat Eating Sloths

Last Wednesday (Oct. 20) was International Sloth Day, so let’s talk about one of my favorite mammals. Today, sloths are adorable and slow tree-dwellers. They use their curved claws to passively hang from branches. There are 6 living species of sloths that are divided into Two-Toed and Three-Toed varieties based on the number of fingers (not toes).

Sloths move so slowly that moss can grow on their fur. That moss is eaten not only by the sloths, but also by a type of moth that eats only that moss. Their slow movement and algae covered fur help camouflage them in the trees. And even though sloths are not able to walk on the ground very well, they can swim, as can be seen in this clip from BBC’s Planet Earth II.

Sloths weren’t always so small and slow. During the Pleistocene (2.58 million – 11,700 years ago), they were giants. Megatherium, the giant ground sloth, was one of the largest land mammals to have existed, and measured 6m (20ft) in length. It lived in South America and was thought to be an herbivore, just like its modern relatives.

The burrowers | TwilightBeasts
Megatherium with a car and person for scale. (Image from here)

But, according to a [new study], not all extinct sloths were solely plant-eaters. The study examined the ratio of nitrogen isotopes in the hair of the extinct sloths Mylodon and Nothrotheriops and in several extant mammals. Nitrogen is an atom that is present in different food sources and in the proteins that make up our bodies. As animals eat different foods, different types of Nitrogen (different isotopes*) are used to make the necessary proteins. Measuring the amount of different isotopes of nitrogen in the proteins can tell us what kinds of foods animals were eating.

Dr. Julia Tejada, lead author on the study, sampling Nothrotheriops. Myolodon was a bit larger. (Photo by Julia Tejada)

The study found that Mylodon’s isotopes were more similar to present-day omnivores (animals that eat meat and plants) and that Nothrotheriops was most similar to present-day herbivores (animals that only eat plants). It’s really interesting to see how our ideas of the past can change with new analyses. And how diets, especially in extinct animals, can be more complicated than they seem.

If you’d like to read more about sloths – do an internet search for “sloths and avocados” and you’ll find information on how giant ground sloths helped spread avocados around Central America.

*Atoms are made of neutrons, protons, and electrons. Isotopes are atoms with different numbers of neutrons, but the same number of protons. For example, a nitrogen atom has 7 protons and usually 7 neutrons. A stable isotope of nitrogen will have 7 protons and 8 neutrons.