Tag Archives: humans

Episode 236: Updates 4 and a Mystery Snake!



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It’s our fourth annual updates and corrections episode! I’ve already had to make a correction to this episode!

Further reading:

Cassowary, a rare emu-like bird, attacks and kills Florida man, officials say

The dog Bunny’s Facebook page

3D printed replicas reveal swimming capabilities of ancient cephalopods

Enormous ancient fish discovered by accident

A rare observation of a vampire bat adopting an unrelated pup

Pandemic paleo: A wayward skull, at-home fossil analyses, a first for Antarctic amphibians

Neanderthals and Homo sapiens used identical Nubian technology

Entire genome from Pestera Muierii 1 sequenced

Animal Species Named from Photos

Cryptophidion, named from photos:

The sunbeam snake showing off that iridescence:

Show transcript:

Welcome to Strange Animals Podcast. I’m your host, Kate Shaw.

 

It’s our fourth annual updates and corrections episode, and to keep it especially interesting we’ll also learn about a mystery snake. Make sure to check the show notes for lots of links if you want to learn more about these updates.

 

First, we have a small correction from episode 222. G emailed with a link about a Florida man who was killed by a cassowary in 2019, so cassowaries continue to be dangerous.

 

We also have a correction from episode 188, about the hyena. I called hyenas canids at one point, and although they resemble canids like dogs and wolves, they’re not canids at all. In fact, they’re more closely related to cats than dogs. Thanks to Bal for the correction!

 

In response to the talking animals episode, Merike told about a dog who uses computer buttons to communicate. The dog is called Bunny and she’s completely adorable. I’ll link to her facebook page. I have my doubts that she’s actually communicating the way it looks like she is. She’s obviously a clever dog but I don’t think she understands the English language so well that she can choose verbs like “is” from her list of words. I think she’s probably mostly taking unconscious cues from her owner. But I would be happy to be proven wrong.

 

Following up from our recent deep-sea squid episode, a team of paleontologists studying ancient cephalopods 3-D printed some replicas of what the animals would have looked like while alive. Then they took the models into a swimming pool and other water sources to study how their shells affected the way they could move through the water. They discovered that a type of cephalopod with a straight shell, called an orthocone, probably mostly moved up and down in the water to find food and could have moved extremely fast in an upward or downward direction. A type of cephalopod with a spiral shaped shell, called a torticone, also spun slightly as it moved around. The same team has previously worked with 3-D models of ammonoids, which we talked about in episode 86. The models don’t just look like the living animals, they have the same center of balance and other details, worked out mathematically.

 

Speaking of ancient animals, a collector in London bought a fossil found in Morocco thinking it was part of a pterodactyl skull. When the collector asked a palaeontologist to identify it, it turned out to be a fossilized coelacanth lung. The collector donated the fossil for further study, and the palaeontologist, David Martill, worked with a Brazilian coelacanth expert, Paulo Brito, to examine the fossil.

 

The fossil dates to the Cretaceous, about 66 million years ago, and is bigger than any coelacanth lung ever found. Modern coelacanths grow a little over six feet long at most, or 2 meters, but the estimated length of this Coelacanth is some 16 ½ feet, or 5 meters. The fossil is being donated to a university in Morocco.

 

We talked about vampire bats way back in episode 11, and I love bats and especially vampire bats so I try to keep an eye on new findings about them. Everyone thinks vampire bats are scary and creepy, but they’re actually social, friendly animals who don’t mean to spread rabies and other diseases to the animals they bite. It just happens.

 

Vampire bats live in colonies and researchers have long known that if a female dies, her close relations will often take care of her surviving baby. Now we have evidence that at least sometimes, the adoptive mother isn’t necessarily related to the birth mother. It’s from a recently published article based on a study done in 2019.

 

A team researching how unrelated vampire bats form social bonds captured 23 common vampire bats from three different colonies and put them together in a new roost where their interactions could be recorded by surveillance cameras. One particular pair of females, nicknamed Lilith and BD, became good friends. They groomed each other frequently and shared food. If you remember from episode 11, vampire bats share food by regurgitating some of the blood they drank earlier so the other bat can lap it up. Since vampire bats can starve to death in only a few nights if they can’t find blood, having friends who will share food is important.

 

During the study, Lilith gave birth to a baby, but shortly afterwards she started getting sick. She had trouble getting enough food and couldn’t groom or take care of her baby as well as a mother bat should. Her friend BD helped out, grooming the baby, sharing food with Lilith, and eventually even nursing the baby when Lilith got too sick to produce milk. After Lilith died, BD adopted the baby as though it was her own. By the time the study ended, BD was still caring for the baby bat.

 

We talked about spiders in the Antarctic in episode 221, and mentioned that Antarctica hasn’t always been a frozen wasteland of ice and snow. In a new study of fossils found in Antarctica, published in May of 2021, the first Antarctic amphibian skull has been identified. It lived in the early Triassic, not long after the end-Permian mass extinction 252 million years ago. It’s been named Micropholis stowi and is a new species of temnospondyl that was previously only known from South Africa. The skull, along with other fossils from four individuals, was discovered in the Transantarctic Mountains in 2017 and 2018, and the research team studied them from home during the 2020 pandemic lockdowns.

 

In news about humans and our extinct close relations, a new finding shows that Neanderthals and humans used the same type of tools. Researchers studied a child’s tooth and some stone tools, all found in a cave in the mountains of Palestine, and determined that the tooth was from a Neanderthal child, not a human. The tooth was discovered in 1928 but was in a private collection until recently, so no one had been able to study it before now. The tools are a specific type developed in Africa that have only been found associated with humans before. Not only that, but until this finding, there was no evidence that Neandertals ever lived so far south.

 

The child is estimated to have been about nine or ten years old, which is the age when you’re likely to lose a baby tooth as your adult teeth start growing in. I like to think about the child sitting next to their Mom or Dad, who were either creating new tools or using ones they’d already made to do something like cut up food for that evening’s dinner. Maybe the child was supposed to be helping, and they were, but they had a loose tooth and kept giving it a twist now and then, trying to get it to come out. Then, finally, out it popped and bounced onto the cave floor, where it was lost for the next 60,000 years.

 

Researchers have just announced that they’ve sequenced the genetic profile of a woman who lived in what is now Romania about 35,000 years ago. Judging from her skull shape and what is known about ancient humans in Europe, the team had assumed she would be rather restricted in her genetic diversity but that she would show more Neanderthal ancestry than modern humans have. Instead, they were surprised to find that the woman had much more genetic diversity than modern humans but no more Neanderthal genes than most human populations have these days.

 

This was a surprise because modern humans whose prehistoric ancestors migrated out of Africa show much less genetic diversity than modern humans whose ancestors stayed in Africa until modern times. Researchers have always thought there was a genetic bottleneck at some point during or not long after groups of humans migrated out of Africa around 80,000 years ago. Lots of suggestions have been made about what might have caused the bottleneck, including disease, natural disaster, or just the general hardship of living somewhere where humans had never lived before. A genetic bottleneck happens when a limited number of individuals survive long enough to reproduce—in other words, in this case, if so many people die before they have children that there are hardly any children left to grow up and have children of their own. To show in the general population as it does, the bottleneck has to be widespread.

 

Now researchers think the genetic bottleneck happened much later than 80,000 years ago, probably during the last ice age. Humans living in Europe and Asia, where the ice age was severe, would have had trouble finding food and staying warm.

 

I’m getting close to finishing the Strange Animals Podcast book, which I’ll talk about a little more in our Q&A episode later this week. It’s a collection of the best mystery animals we’ve covered on the podcast, along with some new mystery animals, and I’m working hard to update my research. If you remember back in episode 83, about mystery big cats, we discussed the Barbary lion, which was thought to be an extinct subspecies of lion that might not actually be extinct. Well, when I looked into it to see if any new information had turned up, I found more than I expected. I rewrote those paragraphs from episode 83 and I’ll read them here as an update:

 

Lions live mostly in Africa these days, but were once common throughout southern Asia and even parts of southern Europe. There even used to be a species called the American lion, which once lived throughout North and South America. It only went extinct around 11,000 years ago. The American lion is the largest species of lion ever known, about a quarter larger than modern African lions. It probably stood almost 4 feet tall at the shoulder, or 1.2 meters. Rock art and pieces of skin preserved in South American caves indicate that its coat was reddish instead of golden. It lived in open grasslands like modern lions and even in cold areas.

 

Much more recently, the Barbary lion lived in northern Africa until it was hunted to extinction in the area. The Barbary lion was the one that battled gladiators in ancient Rome and was hunted by pharaohs in ancient Egypt. It was a big lion with a dark mane, and was thought to be a separate subspecies of lion until genetic analysis revealed in 2006 that it wasn’t actually different from Panthera leo leo.

 

The last wild Barbary lion was sighted in 1956, but the forest where it was seen was destroyed two years later. The lions in a few zoos, especially in Ethiopia and Morocco, are descended from Barbary lions kept in royal menageries for centuries.

 

Lions are well known to live on the savanna despite the term king of the jungle, but they do occasionally live in open forests and sometimes in actual jungles. In 2012 a lioness was spotted in a protected rainforest in Ethiopia, and locals say the lions pass through the reserve every year during the dry season. That rainforest is also one of the few places left in the world where wild coffee plants grow. So, you know, extra reason to keep it as safe as possible.

 

Finally, we’ll finish with a mystery snake. In 1968, during the Vietnam War, the United States Naval Medical Research Unit discovered a small snake in central Vietnam. It was unusual enough that they decided to save it for snake experts to look at later, but things don’t always go to plan during wartime. The specimen disappeared somewhere along the line. Fortunately, there were photographs.

 

The photos eventually made their way to some biologists, and in 1994 a paper describing the snake as a new species was published by Wallach and Jones. They based their description on the photos, which were good enough that they could determine details like the number of scales on the head and jaw. They named it Cryptophidion annamense and suggested it was a burrowing snake based on its characteristics.

 

Other biologists thought Cryptophidion wasn’t a new species of snake at all. In 1996 a pair of scientists published a paper arguing that it was just a sunbeam snake. The sunbeam snake is native to Southeast Asia, including Vietnam, and can grow over 4 feet long, or 1.3 meters. It’s chocolate-brown or purplish-brown but has iridescent scales that give it a rainbow sheen in sunshine. It’s a constricting snake, meaning it squeezes the breath out of its prey to kill it, but it only eats small animals like frogs, mice, and other snakes. It’s nocturnal and spends a lot of its time burrowing in mud to find food.

 

Wallach and Jones, along with other scientists, argued that there were too many differences between the sunbeam snake and Cryptophidion for them to be the same species. But without a physical specimen to examine, no one can say for sure if the snake is new to science or not. If you live in or near Vietnam and find snakes interesting, you might be the one to solve this mystery.

 

You can find Strange Animals Podcast online at strangeanimalspodcast.blubrry.net. That’s blueberry without any E’s. If you have questions, comments, or suggestions for future episodes, email us at strangeanimalspodcast@gmail.com. If you like the podcast and want to help us out, leave us a rating and review on Apple Podcasts or just tell a friend. We also have a Patreon at patreon.com/strangeanimalspodcast if you’d like to support us that way.

 

Thanks for listening!


Episode 124: Updates 2 and a new human



It’s our second updates and corrections episode! Thanks to everyone who sent in corrections and suggestions for this one! It’s not as comprehensive as I’d have liked, but there’s lots of interesting stuff in here. Stick around to the end to learn about a new species of human recently discovered on the island of Luzon.

The triple-hybrid warbler:

Further reading:

New species of ancient human discovered in the Philippines: Homo luzonensis

Show transcript:

Welcome to Strange Animals Podcast. I’m your host, Kate Shaw.

Yes, it’s our second updates episode, but don’t worry, it won’t be boring!

First, a few corrections. In episode 45 I talked about monotreme, marsupial, and placental mammals, and Tara points out that the placenta and bag of waters are different things. I got them mixed up in the episode. The bag of waters is also called the amniotic sac, which protects and cushions the growing baby inside with special amniotic fluid. The placenta is an organ attached to the lining of the womb, with the bag of waters inside the placenta. The umbilical cord connects the baby to the placenta, which supplies it with all its needs, including oxygen since obviously it can’t breathe yet.

Next, I covered this correction in in episode 111 too, but Judith points out that the picture I had in episode 93 of the Queen Alexandra’s birdwing butterfly was actually of an atlas moth. I’ve corrected the picture and if you want to learn more about the atlas moth, you can listen to episode 111.

Next, Pranav pointed out that in the last updates episode I said that the only bears from Africa went extinct around 3 million years ago–but the Atlas bear survived in Africa until the late 19th century. The Atlas bear was a subspecies of brown bear that lived in the Atlas Mountains in northern Africa, and I totally can’t believe I missed that when I was researching the nandi bear last year!

Finally, ever since episode 66 people have been emailing me about Tyrannosaurus rex, specifically my claim that it was the biggest land carnivore ever. I don’t remember where I found that information but it may or may not be the case, depending on how you’re defining biggest. Biggest could mean heaviest, tallest, longest, or some combination of features pertaining to size.

Then again, in 1991 a T rex was discovered in Canada, but it was so big and heavy and in such hard stone that it took decades to excavate and prepare so that it can be studied. And it turns out to be the biggest T rex ever found. It’s also a remarkably complete fossil, with over 70% of its skeleton remaining.

The T rex is nicknamed Scotty and was discovered in Saskatchewan. It lived about 68 million years ago, and turns out to not only be the biggest T rex found so far, it was probably the oldest. Paleontologists estimate it was over 30 years old when it died. It was 43 feet long, or 13 meters. This makes it bigger than the previously largest T rex found, Sue, who was 40 feet long, or 12.3 meters. Scotty also appears to be the heaviest of all the T rexes found, although estimates of its weight vary a lot. Of course some researchers debate Scotty’s size, since obviously it’s impossible to really know how big or heavy a living dinosaur was by just looking at its fossils. But Scotty was definitely at least a little bigger than Sue.

Scotty is on display at the Royal Saskatchewan Museum in Canada.

Way back in episode 12, I talked about snakes that were supposed to make noises of one kind or another. Many snakes do make sounds, but overall they’re usually very quiet animals. A snake called the bushmaster viper that lives in parts of Central America has long been rumored to sing like a bird. The bushmaster can grow up to ten feet long, or 3 meters, and its venom can be deadly to humans.

Recently, researchers discovered the source of the bushmaster’s supposed song. It’s not a snake singing. It’s not a bird singing. It’s not even a single animal–it’s two, both of them tree frogs. One of the frogs is new to science, the other is a little-known frog related to the new one.

I tried so hard to find audio of this frog, and I’m very bitter to report that I had no luck. The closest I could find was not great audio of this frog, whose name I forgot to write down, which I think is related to the new frogs.

[frog sound]

Now let’s do some quick, short updates, mostly from recent articles I’ve happened across while researching other things.

A triple-hybrid warbler, its mother a golden-winged/blue-winged hybrid (also called a Brewster’s warbler) and its father a warbler from a different genus, chestnut-sided, was sighted in May of 2018 by a birder in Pennsylvania. Lowell Burket noticed it had characteristics of both a blue-winged and a golden-winged warbler but sang like a chestnut-sided warbler. He contacted the Cornell Evolutionary Biology Lab about the bird with photos and video of it, and they sent a researcher, David Toews, out to look at it. Toews caught the bird, measured it, and took a blood sample for analysis. I think a listener told me about this article but I didn’t write down who, so thank you, mystery person.

Red-fronted lemurs chew on certain types of millipedes and rub the chewed-up millipedes on their tails and their butts. They also eat some of the millipedes. Researchers think the millipedes secrete a substance called benzoquinone, which acts as an insect repellant and may also help the lemurs get rid of intestinal parasites. Other animals rub crushed millipedes on their bodies for the same reasons.

A recent study of saber-toothed cat fossils show that many of the animals with injuries to their jaws and teeth that would have kept them from hunting properly survived on softer foods like meat and fat. Researchers think the injured cats were provided with food by other cats, which suggests they were social animals. The study examined micro-abrasions on the cats’ teeth that give researchers clues about what kinds of food the animals ate.

Simon sent me an article about a 228 million year old fossil turtle, Eorhynchochelys [ay-oh-rink-ah-keel-us]. It was definitely a turtle but it didn’t have a shell. Instead, its ribs were wide, which gave its body a turtle-like shape. Turtle shells actually evolved from widened ribs like these. Researchers are especially interested because Eorhynchochelys had a beak like modern turtles, while the other ancient turtle we know of had a partial shell but no beak. This gives researchers a better idea of how turtles evolved. Oh, and in case you were wondering, Eorhynchochelys grew over six feet long, or over 1.8 meters.

The elephant bird, featured in episode 51, was a giant flightless bird that lived in Madagascar. Recently new research about elephant birds has revealed some interesting information. For one thing, we now know what the biggest bird that ever lived was. It’s called Vorombe titan and grew nearly ten feet tall, or 3 meters, and weighed up to 1,800 lbs, or 800 kg. It was first discovered in 1894 but not recognized as its own species until 2018.

There’s also some evidence that at least some elephant bird species may have been nocturnal with extremely poor vision. This is the case with the kiwi bird, which is related to the elephant bird. Brain reconstruction studies of two species of elephant bird reveal that the part of its brain that processed vision was very small. It resembles the kiwi’s brain, in fact. One of the species studied had a larger area of the brain that processed smell, which researchers hypothesize may mean it lived in forested areas.

Another study of the elephant bird bones show evidence that the birds were killed and eaten by humans. But the bones date to more than 10,000 years ago. Humans supposedly didn’t live in Madagascar until 4,000 years ago at the earliest. So not only is there now evidence that people colonized the island 6,000 years earlier than previously thought, researchers now want to find out why elephant birds and humans coexisted on the island for some 9,000 years before the elephant bird went extinct. Hopefully archaeologists can uncover more information about the earliest people to arrive on Madagascar, which may help us learn more about how they interacted with the elephant bird and other extinct animals of the island.

Speaking of humans, humans evolved in Africa and until very recently, evolutionarily speaking, that’s where we all lived. Scientists rely on fossils, archaeological materials, and studies of ancient DNA to determine when and where humans spread beyond Africa. But at the moment, the DNA that researchers have studied doesn’t overlap entirely with what we’ve learned from the other sources. Basically this means that there are big chunks of data we still need to find to get a better picture of where our ancestors traveled. Part of the problem is that DNA preserves best in cold, dry areas, so most of the viable DNA recovered is from middle Eurasia. Fortunately, DNA technology is becoming more and more refined every year.

This brings us to a suggestion by Nicholas, who told me about a newly discovered hominin called Homo luzonensis. Homo luzonensis lived on an island called Luzon in the Philippines at least 50,000 years ago. It wasn’t a direct ancestor to Homo sapiens but was one of our cousins, although we don’t know yet how closely related.

No one thought humans could reach the island of Luzon until relatively recent times, because of how remote it is and because it hadn’t been connected to the mainland for the last 2 ½ million years. But when Homo floresiensis was discovered in 2004 on the island of Flores in Indonesia, which you may remember from episode 26, suddenly scientists got interested in other islands. Researchers knew there had been human settlements on Luzon 25,000 years ago, but no one had bothered to search for older settlements. In 2007 a team of paleoanthropologists returned to the island and found a foot bone that looked human. In 2011 and 2015 the team found some teeth and more bones from at least three different individuals.

We don’t know a whole lot about the Luzon humans yet. The discoveries are still too new. The Luzon hominins have a combination of features that are unique, a mixture of traits that appear more modern and traits that are seen in more ancient hominins. They’re also smaller in stature than modern humans, closer to the size of the Flores people. Homo luzonensis apparently used stone tools since researchers have found animal bones that show cut marks from butchering.

Researchers are starting to put together a picture of South Asia in ancient times, 50,000 years ago and more, and it’s becoming clear that there were a surprising number of hominins in the area. It’s also becoming clear that hominins lived in the area a lot longer ago than we thought. Researchers have found stone tools on the island of Sulawesi that date back at least 118,000 years. Even on Luzon, in 2018 researchers found stone tools and rhinoceros bones with butcher marks that date back over 700,000 years ago. We don’t know who those people were or if they were the ancestors of the Luzon people. We just know that they liked to eat rhino meat, which is one data point.

You can find Strange Animals Podcast online at strangeanimalspodcast.com. We’re on Twitter at strangebeasties and have a facebook page at facebook.com/strangeanimalspodcast. If you have questions, comments, or suggestions for future episodes, email us at strangeanimalspodcast@gmail.com. We also have a Patreon if you’d like to support us that way.

Thanks for listening!


Episode 103: Trace Fossils



You may know what fossils are (I hope), but have you heard of trace fossils? You have now!

A giant ground sloth footprint with a human footprint inside it, made some 11,000 years ago:

Climactichnites:

A “devil’s corkscrew”:

A Paleocastor fossil found at the bottom of its fossilized burrow:

Stromatolite:

Coprolites:

Gastroliths found with a Psittacosaurus:

Show transcript:

Welcome to Strange Animals Podcast. I’m your host, Kate Shaw.

This week we’re going back in time to look at fossils, but these aren’t regular fossils. They’re called trace fossils, or ichnofossils. Instead of fossilized bones and other body parts, trace fossils are records of where organisms were and what they were doing.

Fossil footprints are one of the most common trace fossils. We have lots of dinosaur footprints, and from them we know that dinosaurs held their tails off the ground, that some dinosaurs traveled in herds with the young in the middle, and things like that. A fossil footprint is formed when an animal steps in soft mud or sand, usually near water, and the resulting footprints were covered with sediment which then dried, protecting the footprints. If the footprints continued to be protected from water and other processes that might wipe them out, over the years more and more sediment was deposited on top, eventually compacting it so that pressure and chemical reactions within the sediment turned it to stone. This is why we sometimes have two impressions of the same footprints: the actual footprints and a cast of the footprints made by the sediment that filled them initially.

The White Sands National Monument in New Mexico has so many footprints of so many animals around what was once a lake that it’s referred to as a megatrack. Seriously, we’re talking hundreds of thousands of footprints. In 2014 a team studying the tracks found a set of ancient human footprints, the first ones found in the park. But while the tracks were well preserved, the team couldn’t pinpoint how old they were. They invited other researchers to come examine the prints to help date them.

In 2016 a British paleontologist named Matthew Bennett came to examine the prints, but while he was there, he took a look at some giant ground sloth prints nearby. And when he did, he made an amazing discovery. There was a sloth footprint with a human footprint on top of it, actually within the sloth’s footprint. The sloth’s print was 20 inches long, or almost 51 cm. And after that, the next sloth footprint also had a human footprint in it. And after that another. And another. And another. Ten sloth footprints in a row had human footprints inside.

Since the tracks were made in sandy lake mud and both tracks were reasonably clear, the researchers determined that the tracks were probably left on the same day. In other words, the human was probably trailing the sloth.

But that’s not all. Bennett and the other scientists at the site followed the tracks of both sloth and human and found marks where the sloth turned around and reared on its hind legs to face the approaching human. And there are more human prints that approach at a different angle—not just human prints, but prints that suggest the human was actually tip-toeing.

The most likely explanation is that the humans were hunting the sloth, with one human getting its attention while a second crept up behind it. But we don’t know for sure. One odd thing is that the human trailing the sloth actually had to stretch to step inside each sloth print. Even small giant ground sloths were enormous, nine or ten feet long, or about three meters, with long curved claws. Ground sloths were plant-eaters that used their claws to strip leaves from branches and dig giant burrows, but the claws made formidable weapons too. It’s possible that the ancient human was just amusing himself by stepping exactly in the sloth’s prints.

Since this initial finding, researchers have found more sites where sloths appear to have turned to face an aggressor, possibly humans. The age determined for the prints, around 11,000 years old, corresponds with the time that giant ground sloths went extinct in North America. Researchers have long suspected that humans hunted them to extinction, and now we may have some direct evidence that this happened.

But fossil footprints aren’t just of big animals. Small squidgy ones leave footprints too, or trails that show where an animal traveled even if it didn’t actually have feet. For instance, 510 million years ago, during the Cambrian period, a creature lived along the shores of a shallow sea and left tracks that have been found in North America. The fossil tracks are called Climactichnites and while we don’t know what animal actually left them, paleontologists have determined that there were two species and that they were probably slug-like in appearance, possibly an early mollusk, since modern slugs and their relatives sometimes leave similar tracks. We even have some body prints of the stationary animal, and some of them were 27 inches long, or 69 cm.

Similarly, fossilized burrows are considered trace fossils. But often fossilized burrows don’t actually look like holes in the ground. Instead, the burrow has filled up with soil that then fossilizes, leaving the shape of the burrow behind in a rock that looks different from the surrounding rock. And these can be remarkably difficult to identify in some cases.

Back in 1891, a rancher in Nebraska showed a visiting geologist some weird formations he’d found. The geologist, Erwin Barbour, didn’t know what they were. He and the rancher dubbed the formations “devil’s corkscrews,” and probably had a laugh. But the formations did look like corkscrews—but they were enormous, taller than a full-grown man and always situated straight up and down. Some were as long as ten feet, or three meters.

Barbour suggested that the corkscrews were freshwater sponges, since the prevailing belief was that the area had once been a lake. Other scientists thought they might be the remains of fossilized tree or other plant roots. And a couple of people thought they might be fossilized burrows of an unknown rodent.

Those people were right, of course, but at the time, no one knew for sure. And if the corkscrews were burrows, what made them?

The mystery was solved when fossils of a beaver relative called Paleocastor was found at the bottom of one of the corkscrews. Unlike modern beavers, it wasn’t an aquatic rodent but a burrowing one, and it lived around 25 million years ago. Once the Paleocastor fossil was discovered, it was clear that the marks noted on some of the corkscrews, which had been interpreted as scratch marks from claws, were actually tooth marks. They perfectly matched Paleocastor’s teeth, which meant the beaver excavated its corkscrew-shaped burrow by chewing through the dirt instead of digging through it.

So why did Paleocastor dig burrows with such an odd shape? The answer may lie in another fossil found not in the bottom of the burrow but stuck in the corkscrews. Zodiolestes was an extinct weasel relative. Possibly it had gone down the burrow while hunting beavers, become stuck in the tight corkscrew turns in the tunnels, and died.

More recent research shows that Paleocastor burrows were frequently connected to one another with side passages, sometimes hundreds of burrows joined together like the burrows and tunnels of modern prairie dogs. This suggests that Paleocastor was a sociable animal that lived in colonies.

As it happened, Dr. Barbour had been right about one thing. The area where the devil’s corkscrews were initially found had once been a lake. His mistake was not realizing that the structures had been dug into the ground where the lake had once been.

Some of the oldest fossils known are trace fossils called stromatolites. These are stones that were formed by microbes. Early life consisted of microbial mats, colonies of microorganisms like bacteria that grow on surfaces that are either submerged or just tend to stay damp. Microbial mats are still around today, often growing in extreme environments like hot springs and hypersaline lakes. When microbial mats grow on a sea or lake floor, they tend to build upwards, forming columns or even reefs that rise out of the mud and toward the light. But while stromatolites are formed by bacteria, they’re not formed of bacteria. Instead, the stones are formed from grains of sand and other sediments that were trapped and cemented together within the mats, which forms a thin layer of limestone. The layers grow over time, giving stromatolites a banded or striped pattern. But it can be really hard to tell them apart from regular old non-stromatolite rocks that also happen to have a banded pattern. Geologists spend a lot of time studying stromatolites and suspected stromatolites to find out more about them. Microbial mats evolved almost 3.5 billion years ago and it’s possible they were around as much as 4 billion years ago. The earth is about 4.5 billion years old, if you were wondering.

But let’s return to more modern times, with animals and fish and things. Another trace fossil is one I’ve mentioned here a few times, the coprolite. A coprolite is a fossilized poop. Most of the original organic material has been mineralized, preserving it. Coprolites are valuable since paleontologists can cut them open to find out what the animal was eating, if it had intestinal parasites, and lots of other information. Coprolites are also frankly hilarious. Did you know that if you become a scientist whose area of study is coprolites, you’re called a paleoscatologist?

We’ve also talked about gastroliths before. Gastroliths are small stones swallowed by an animal to help digest its food. The stones especially help grind up plant material, which eventually causes the stones to become smooth. Lots of animals use gastroliths for digestion, including birds that eat plants, crocodiles and alligators, seals and sea lions, although they may swallow them by accident, and many dinosaurs, especially sauropods. We know sauropods swallowed stones to help in digestion, because we’ve found gastroliths associated with sauropod fossils.

Other trace fossils include marks an animal may have made during its life, like those tooth marks preserved in the devil’s corkscrews. Skin imprints, or fur or feather imprints, are also trace fossils but are incredibly rare. Sometimes a skin imprint remains in place around an animal’s fossilized body parts, which gives paleontologists incredible insight into what an animal looked like while it was alive. That’s how we know a lot of dinosaurs had feathers. Root cavities are trace fossils too, caused not by animals but by plant roots that burrow into the soil but rot away, leaving a hole that fills with dirt and later fossilizes in the shape of the original roots. There’s even a type of trace fossil called a urolite, which was caused when an animal urinated and the urine stream left marks on soft ground.

Since trace fossils are usually hard to match up with the animal that made them, trace fossils are given scientific names of their own. This allows scientists to refer to them without guessing at what made them, and it reduces confusion.

Trace fossils are remains of biological activity. But animals and plants aren’t the only things that can move soft soil. Cracks in dried-out mud are sometimes fossilized, as are ripple marks from water and little dimples made by raindrops or bubbles. Geologists use these fossilized moments in time to help determine how the rock strata have been shifted by geologic forces. They know that a rock that shows ripple marks was once flat, so if it’s been tipped up sideways or deformed into a curve, they can determine what forces were at work on the rocks over the centuries.

It’s not all that uncommon to find these non-biological traces alongside trace fossils and body fossils. I’ve seen big flat rocks that show the bottom of a shallow sea, with ripple marks, the tracks of tiny animals that trundled around looking for food in the sandy mud, and the occasional fossil like a bryozoan or fragment of shell. It’s the closest thing we have to photographs of prehistoric times.

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