Monthly Archives: May 2019

Episode 121: Cave Dwelling Animals

This week let’s learn about some animals that live in caves!

The dipluran Haplocampa:

Oilbirds and their big black eyes:

A swiftlet:

The angel cave fish that can walk on its fins like a salamander walks on its feet:

Leptodirus, carrying around some air in its abdomen in case it needs some air:

The cave robber spider and its teeny hooked feet:

The devils hole pupfish:

Show transcript:

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

Way back in episode 27 we learned about some animals that live deep in caves. Cave dwelling animals are always interesting because of the way they’ve adapted to an unusual environment, so let’s learn about some of them!

We’ll start with an invertebrate. Diplurans are common animals that are related to insects but aren’t insects. They live all over the world, with hundreds of species known to science, but most people have never seen one because of where they live. They like moist, dark areas like soil, dead leaves, and caves. They’re also small, usually only a few millimeters long, although a few species grow larger, up to two inches long, or five cm.

Diplurans have long bodies with a number of segments, six legs, long antennae, and a pair of tail appendages called cerci. Depending on the species, the cerci may just be a pair of straight filaments like an extra pair of antennae, or they may look like pincers. Diplurans with pincer-like cerci use them to help capture prey, while ones with antennae-like cerci eat fungi and plant material.

Diplurans also don’t have eyes. They don’t need eyes because they live underground where there’s little or no light. A lot of species are pale in color or lack pigment completely.

Diplurans have been around for something like 350 million years, although we don’t have very many fossil diplurans. But recently, a new species of dipluran was discovered in North America that has raised some interesting questions.

Vancouver Island is a large island on the west coast of Canada, near the city of Vancouver. It’s prone to earthquakes and contains a lot of caves, and last summer, in June of 2018, a party of cavers and scientists explored two of the caves and found a new dipluran, which has been named Haplocampa wagnelli. This dipluran is chunkier than most other known diplurans, with shorter antennae, which researchers think points to a more primitive body plan. Since the dipluran is so different from most other diplurans known, and because the caves where it was found were under a thick ice sheet until around 18,000 years ago, researchers are trying to figure out if it found its way into the caves after the ice sheet melted or if it survived in the caves while they were buried under ice.

Haplocampa seems to be most closely related to a few diplurans found in Asia. Asia was connected to western North America during the Pleistocene when sea levels were much lower, since so much of the world’s water was frozen, so it’s possible the ancestors of Haplocampa migrated from Asia after the ice sheets started to melt but before the Bering Land Bridge was completely submerged. Possibly its eggs were accidentally transported by birds who foraged in leaf litter where its ancestor lived.

A lot of animals that live in caves are only found in one particular cave system. This happens when a species of animal that lives near a cave moves into the cave, either full-time or part-time. As its descendants grow up, they become more and more adapted to cave life, until eventually they couldn’t live outside of the cave. Since there’s no way for them to travel from one cave system to another, they are confined to that single cave. And since caves are largely difficult for humans to explore, that means there are lots and lots and lots of animals unknown to science living out their quiet lives deep within caves where humans have never visited. Every so often a group of adventurous and brave scientists explore a cave and discover new animals, usually with the help of experienced cavers.

Animals that are endemic to a specific cave system are rare to start with and vulnerable to any changes in the cave environment. The Tumbling Creek cave snail is only found in a single stream in Tumbling Creek Cave in Missouri, in the United States. It lives its whole life in the water and is only about 2 millimeters in size, with a pale yellowish shell. When it was first discovered in 1971 it was common. Thirty years later, researchers could only find about forty of the snails due to water pollution.

Caves aren’t very friendly environments. Most of the animals that live in caves are very small as a result. Lots of insects and spiders live in caves, some snails, lots of fish, lots of crustaceans that live in fresh water, like crawdads and amphipods, and some salamanders. But the only mammals and birds that live in caves leave the cave to hunt or forage outside of it, like bats. There just isn’t enough food inside a typical cave to sustain a population of larger animals.

So what do cave animals eat? Obviously they eat each other, but without plants a cave system is definitely lacking in organic matter that can sustain populations of animals. Nutrients enter a cave primarily in two ways. Water flowing into a cave brings nutrients from outside, and animals that mainly live outside but sleep in caves also bring nutrients in. In the case of animals, their poop is a major source of organic material, with dead animals also contributing to the cave’s ecosystem. Bats in particular support a lot of cave animals with their poop, which is called guano, but bears, hyenas, and various other animals, birds, and insects also spend time in caves, either to sleep or to hibernate, and bring nutrients in from outside in one way or another.

There are two birds that spend time in caves, and I’m going to talk about both of them briefly even though technically they don’t live in caves, because they’re so interesting. Both birds are nocturnal and can echolocate like bats. The oilbird lives in parts of northern South America and is related to nightjars. I have a whole episode planned about nightjars and their relatives, but the oilbird is the only one that echolocates (as far as we know). The other bird that echolocates is the swiftlet.

The oilbird nests in caves and also roosts in caves during the day, then flies out at night and eats fruit. Some oilbirds roost in trees during the day instead. Its wings have evolved to allow it to hover and to navigate through tight areas, which helps it fly through caves. It sees well in darkness, with eyes that are arranged more like those of deep-sea fish rather than typical bird eyes.

Several species of swiflet echolocate. These are the birds that make their nests from saliva, and which humans gather to make bird’s nest soup from. They mostly live in Asia. They nest in caves and roost in caves at night, then fly out during the day to catch insects.

Researchers don’t know a lot yet about either bird’s echolocation. It’s audible to human ears, unlike most bat echolocating, and some researchers think it’s less sophisticated than bats’. It’s always possible there are other birds that echolocate, but we don’t know about them yet because maybe we can’t hear their echolocating.

This is what oilbirds sound like. The clicking noises are the echolocation calls.

[oilbird calls]

Cave fish are especially interesting. There isn’t one kind of cave fish but hundreds, mostly evolved from ordinary fish species that ended up in a cave’s water system and stayed. Sometimes the species of fish that gave rise to cave fish are still around, living outside the cave, but most cave fish species have evolved so much that they’re no longer very closely related to their outside ancestors.

Cave fish are considered extremophiles and they tend to have similar characteristics. They usually have no pigment, no scales, and often have no eyes at all, or tiny eyes that no longer function. They’re usually only a few inches long, or maybe 10 cm, and have low metabolic rates. They typically eat anything they can find.

Some cave fish have evolved in unusual ways to better fit their specific habitats. The cave angel fish lives in a single large cave system in Thailand, in fast-moving water. It’s about an inch long, or not quite 3 cm, and gets its name from its four broad fins, which look feathery like angel wings.

It was discovered in 1985 but it wasn’t until 2016 that researchers verified a persistent rumor about the fish, which is that it can WALK on its fins. It has a robust pelvis and vertebral column, and strong fin muscles that allow it to climb rocks to navigate waterfalls.

Other fish navigate waterfalls and other obstacles by squirming and wriggling, using their fins to push them along. But the cave angel fish walks like a salamander. Scientists are studying the way it walks to learn more about how the ancestors of four-legged animals evolved.

The largest cave dwelling animal is the blind cave eel, which grows up to 16 inches long, or 40 cm, although it’s very slender. Since it appears pink due to a lack of pigment in its skin and it has no eyes or fins, it looks a lot like a really long worm. But it’s actually a fish. Not much is known about it, but it’s widespread throughout western Australia and is sometimes found in wells. It lives in caves or underground waterways that are connected to the ocean.

The first insect that was recognized as living only in caves is a beetle called Leptodirus hochenwartii. It was discovered in 1831 deep in a cave in Slovenia, and researchers of the time found it so intriguing that they invented a whole new discipline to study it and other cave animals, known as biospeleology.

Leptodirus has some interesting adaptations to cave living. It has no wings and no eyes, its antennae and legs are long, but the real surprise is its body. Its head is small and the thorax, the middle section of an insect, is slender. But the abdomen is relatively large and round, and the insect uses it to store moist air. Caves tend to be humid environments and Leptodirus has evolved to need plenty of moisture in the air it breathes. But some parts of a cave can be dry, so not only does Leptodirus keep a supply of breathable air in its abdomen, its antennae can sense humidity levels with a receptor called the Hamann organ.

Some spiders live in caves and like other cave dwellers, they’ve evolved to look strange compared to ordinary spiders. The cave robber spider was only discovered in 2010 in a few caves in Oregon. Researchers suspect there are more species of cave robber spider in other cave systems that haven’t been explored yet by scientists.

The cave robber spider is so different from other spiders that it’s been placed in its own family, Trogloraptoridae, which means cave robber. It has hook-like claws on the ends of its legs which it probably uses to capture prey. It spins small, simple webs on the roofs of caves and researchers think it probably hangs upside down from its web and grabs its prey as it passes by. But since no one knows what the cave robber spider eats, it’s anyone’s guess. Researchers have even tried raising the spider in captivity to learn more about it, but it wouldn’t eat any of the insects or other small invertebrates it was offered as food. It starved to death without ever eating anything, so it’s possible it only eats specific prey. It’s a yellowish-brown spider with two rows of teeth, called serrula in spiders, which researchers say is unique among spiders.

It’s also pretty big for a cave dweller. Its body is up to 10 millimeters long, or about a third of an inch, and it has a legspan of about 3 inches, or 7.6 cm. But it’s very shy and rare, and of course it’s not going to hurt you. It literally wouldn’t even hurt a fly to keep itself from starving.

One of the scientists who discovered the spider and is studying it, Charles Griswold, points out that there are stories in the area of giant spiders living in caves. He suggests the cave robber spider might be the source of the stories, since a three inch spider looks much bigger when it’s hanging down from the roof of a cave right in your face, with hooked claws.

Let’s finish with a remarkable cave fish known as the devil’s hole pupfish. Devil’s hole is a geothermal pool inside a cavern in the Amargosa Desert in Nevada, which is in the southwestern United States. It’s not far from Death Valley. The cavern is more than 500 feet deep, or 150 meters, with water that stays at about 92 degrees Fahrenheit, or 33 degrees Celsius. There’s a single small opening into the cavern at the surface, which geologists estimate opened about 60,000 years ago. The cavern and cave system are more than half a million years old.

The geothermal pool is home to the devils hole pupfish, which is barely an inch long, or 25 millimeters, and looks pretty ordinary. It mostly stays around the opening to the surface, where there’s a limestone shelf just below the water’s surface that measures about 6 ½ by 13 feet, or 2 by 4 meters. While the pupfish does swim deeper into the cavern at times, it mostly eats algae that live on and around the shelf, and tiny animals that live within the algae. It also depends on the shelf for laying eggs and spawning.

So the shelf is really important. But it’s also really small and close to the surface. It can only support so many pupfish, so the average devil’s hole pupfish population is about 200 or 300 fish, although this fluctuates naturally depending on many factors. In the 1960s, a farming corporation drilled wells in the area and pumped water out for irrigation, and the water in devil’s hole started to drop and drop. Devil’s hole is part of Death Valley National Monument, and conservationists were well aware of how fragile the pupfish’s environment was. As the water level dropped, threatening to expose the limestone shelf that the pupfish depended on for their entire lives, conservation groups sued to stop the pumping of groundwater in the area. After a series of court cases that went all the way up to the Supreme Court, the water rights were acknowledged to be part of the national monument status. Pumping of groundwater was limited and the pupfish was saved.

The water level in devil’s hole is monitored daily, which has led to a lot of information about how the water is affected by seismic events. Earthquakes as far away as Alaska, Japan, and South America have all affected the water level.

Researchers aren’t sure how long the pupfish have lived in devil’s hole. Some researchers think they’ve been there for 20,000 years, others think it’s more like a few hundred. Researchers aren’t sure how such a small population of fish has stayed healthy for so long, since such a restricted number of individuals should be so inbred they’re no longer viable. The most recent genetic analysis of the pupfish suggests they became isolated from other pupfish species in the area less than a thousand years ago. But if that’s the case, no one’s sure how they got into devil’s hole in the first place. Flooding of the area hasn’t happened in the last thousand years.

Because the pupfish’s habitat is so fragile, the U.S. Fish and Wildlife Service has moved some of the fish into captive populations that mimic the fish’s original habitat. It’s nice to think that these tiny silvery-blue fish with big eyes have so many people working to keep them safe.

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

Thanks for listening!

Episode 120: Hybrid Animals

If you’re a subscriber on Patreon, you may recognize some of the information in this episode, but I’ve updated it and added a whole bunch. Thanks to Pranav for the topic suggestion!

A cama, llama/camel hybrid:

A swoose, swan/goose hybrid:

Motty the Asian/African elephant hybrid and his mother:

A zorse, zebra/horse hybrid:

Show transcript:

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

This week we’ve got another listener suggestion. Pranav really really wants me to do an episode about hybrid animals, but I’ve been dragging my feet on it because I actually already did an episode on the topic back in 2017—but only for Patreon subscribers. It wasn’t my best episode so for various reasons I’d decided not to unlock it. But Pranav really really wants to learn about hybrids! So I’ve taken part of the Patreon episode and added a lot of newer information to it to bring it up to date and make it more interesting.

The term for an animal with parents of different species is hybrid. Crossbreed is also a common term, although technically a crossbred animal is one with parents of the same species but different breeds, like a labradoodle is a crossbreed of a Labrador and a poodle. Both parents are domestic dogs.

A mule, on the other hand, is a hybrid between a horse and a donkey, specifically a mare and a jack, which is what a male donkey is called. The offspring of a stallion and a lady donkey, known as a jenny, is a hinny.

So why can a horse and a donkey breed while, for instance, a possum and a rat can’t? The two species must belong to the same family, and with very few exceptions, they must also belong to the same genus. The genus is indicated in an animal’s scientific name. Equus caballus is a horse and Equus africanus is a donkey, while a Labrador and a poodle are both Canis familiaris, or Canis lupus familiaris depending on who you ask. The Virginia opossum is Didelphis virginiana while the brown rat is Rattus norvegicus. They’re not even slightly related, although superficially they look alike.

If the hybrid’s parents are from species with different numbers of chromosomes, hybrid males will almost always be sterile. You can’t cross two mules to get more mules, for instance, because male mules can’t make babies. Female mules are sometimes fertile but very rarely conceive. Horses have 64 chromosomes while donkeys have 62. Mules end up with 63. Hinnies are much rarer than mules because if the female of a pair of related species has fewer pairs of chromosomes than the male, it’s less likely that any offspring will result.

More closely related species can have fertile offspring. Killer bees, for instance, are hybrids of a European honeybee and an African honeybee. The two are actually subspecies of the honeybee, Apis mellifera, so it’s less like creating a hybrid and more like crossing a Labrador and a poodle to get an adorable happy pup with curly hair. It seemed like a really good idea. The result was supposed to be a tropical bee that would produce more honey. What actually happened was killer bees. Which do actually kill people. Hundreds of people, in fact, since they escaped into the wild in 1957 and started spreading throughout the Americas.

When animals hybridize even though they aren’t of the same genus, it’s called an intergeneric hybrid. That’s the case with sheep and goats. While sheep and goats are related on the subfamily level, they belong to separate genuses. Sheep have 54 chromosomes while goats have 60. That’s enough of a difference that most hybrid babies don’t survive long enough to be born alive, but it does happen occasionally. Usually the babies have 57 chromosomes, and sometimes the babies survive and even prove to be fertile when crossed with either a goat or a sheep. So that’s weird.

Just because someone wants to find out what you get when you cross, say, a sheep and a goat, doesn’t mean the sheep and goat in question are willing to make that effort. The less closely related the two animals are, the less interested they are in mating. Occasionally hybrids are produced by artificial insemination, or rarely by genetic manipulation of embryos, although genetic manipulation technically results in a chimera, not a hybrid.

Another intergeneric hybrid is a cross between a male camel and a female llama. In this case it’s accomplished by artificial insemination and has only produced a handful of living babies, called camas. Researchers were hoping to produce a camel-sized animal with a llama’s more cooperative temperament, but camas turn out to act like camels. So basically they’re just camels that aren’t as big or strong as camels.

In the 1970s, Chester Zoo in Cheshire in the UK kept a female Asian elephant and a male African elephant together in the same enclosure. The pair mated but no one thought they could produce a hybrid calf, since Asian elephants and African elephants aren’t that closely related. They’re another pair of animals that don’t share a genus. But a calf named Mottie was born in 1978. Surprise!

Many hybrids resemble one or the other of their parents. Motty was a fascinating blend of both. He had five toenails on his forefeet and four on the hind feet like his mom. African savannah elephants like his dad have four front toenails and three hind toenails. But he had longer legs and bigger ears than an Asian elephant. His trunk was wrinkled like his dad’s, but had only one digit at the tip like his mom’s. African elephants have two digits at the tip of their trunks. Even the shape of Motty’s head and back were a mixture of his parents’ characteristics.

So why would anyone want to cross species to get a hybrid? I mean, you might end up with killer bees.

A lot of times hybrids show what is known as hybrid vigor. This is more common in hybrid plants, but some hybrid animals combine the best features of their parents. Mules, for instance, have more stamina than horses and are stronger than donkeys. A hybrid of a domestic cow and an American bison is called a beefalo, which is bred to produce leaner meat in an animal that is better for the environment than a cow but easier to handle than a bison. But a lot of times, hybrids are the result of human ignorance, such as keeping related animals together without realizing babies might result, or human curiosity. We just want to see what might happen.

Unfortunately, for every healthy mule-like hybrid, there’s an unhealthy, malformed, or stillborn animal from parents who should have never produced offspring. Motty the elephant was premature and died of infection when he was only eleven days old, probably because his immune system was weakened due to his hybridized genetics.

Lions, tigers, leopards, and other big cats can all interbreed, but the resulting babies sometimes have unusual health issues. When a male lion and a female tiger breed, the resulting babies are known as ligers, and ligers are enormous. They’re much bigger and heavier than both their parents. This sounds neat, but it happens because of a genetic anomaly that means the animals just grow and grow much faster and longer than a normal tiger or lion cub. This puts stress on the body and can lead to health problems. Ligers can sometimes weigh over 1200 pounds, or over 550 kg, and grow up to 12 feet long, or 3.6 meters, bigger than a full-grown tiger or lion. The offspring of a puma and a leopard, often called a pumapard, has the opposite problem, with cubs usually inheriting a form of dwarfism. The cubs are only half the size of the parents.

The savannah cat is now accepted as a domestic cat breed by some organizations, but it was first developed in 1986 by crossing a female domestic cat and a male serval. The serval is a wild cat from Africa with large ears, long legs, and a spotted and striped coat pattern. It’s a little larger than a domestic cat and is sometimes kept as an exotic pet, although it’s not domesticated. The hybrid babies inherited their mother’s domesticated nature and turned out to be mostly sociable with humans, although some are less tame. But while Savannah cats are pretty, the kittens of a serval and domestic cat are often stillborn or premature, and many male offspring are infertile. Savannah cats are also prone to certain health issues, especially heart problems. Some areas have banned savannah cats since they’re not considered fully domesticated.

The more closely related the parents, the more likely a hybrid baby will result, and the more likely it will be healthy. Many wolf-like canids can and do easily hybridize with other wolf-like canids, since they have 78 chromosomes in the same arrangement and are closely related. Offspring are usually fertile. The wolf-like canids include wolves, domestic dogs, coyotes, jackals, and dholes. Where the ranges of these various species overlap in the wild, hybrids are not uncommon. But canids that are less closely related to the wolf-like canids, like foxes and raccoon dogs, can’t and don’t hybridize with their cousins.

Some whales will hybridize in the wild, including the fin whale and the blue whale, which are closely related. Dolphins of different species sometimes hybridize when they’re kept together in captivity, such as the false killer whale and the bottlenose dolphin. The resulting babies don’t usually live very long. Occasionally dolphins also hybridize in the wild too. In 2017 a hybrid baby of a rough-toothed dolphin and a melon-headed whale, which is actually a species of dolphin, was spotted off the coast of Hawaii. Researchers were able to get a small tissue sample from the young hybrid to DNA test, which confirmed its parentage. The melon-headed whale mother was also spotted with her calf in a pod of rough-toothed dolphins.

Birds also sometimes hybridize in the wild. This happens occasionally where the range of two closely related species overlap. Since the resulting babies may look very different from both their parents, this makes bird-watching even more challenging. Some warbler species hybridize so often that the hybrid offspring are well-known to birders, such as Brewster’s warbler and Lawrence’s warbler. These two birds are both offspring of a golden-winged warbler and a blue-winged warbler mate, with the appearance different depending on which traits the babies inherit from which parent.

Occasionally a domestic chicken will mate with a wild pheasant and produce babies, since chickens and pheasants are related. Very rarely, a swan and goose will mate and produce babies, although the babies don’t usually survive very long. One swan-goose hybrid that did survive was hatched in 2004 in Dorset in the UK, with a mute swan mother and a domestic goose father. The baby was referred to as a swoose and it was the only of the offspring to survive. It looks like a goose but with a longer, more swan-like neck and head.

If you’ve listened to episode 25, part one of the humans episode, you’ll recall that human DNA contains traces of DNA from our extinct cousins, including Neandertals. If Neandertals were still around, we could undoubtedly produce hybrids with them. But what about our living cousins, the other great apes? Humans are closely related to chimpanzees, but could a human produce a hybrid with a chimp? It’s possible but very unlikely. We belong to different genuses and have different numbers of chromosomes, not to mention the enormous ethical issues involved.

Let’s finish up with my favorite hybrid animal, the zebroid. This is a term for any hybrid where one parent is a zebra and the other parent is a horse, a donkey, or a pony, which also leads to the terms zorse, zedonk, and zony. These all crack me up, especially zedonk.

Zebroids are usually at least partially striped, frequently on the legs and neck but sometimes all over. The mane may stand up like a zebra’s or fall over the neck like a horse’s. The zebroid is adorable because of the stripes, but it’s also ornery and can be aggressive. There goes my dream of having a stripy horse.

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

Thanks for listening!

Episode 119: Before the Dinosaurs

What kinds of animals lived before dinosaurs evolved? What did they evolve into? Let’s find out!

Dimetrodon! Not a dinosaur! Not even actually a reptile:

Cotylorhynchus had a teeny head. I am not even exaggerating:

Moschops had a big thick skull:

Lisowicia was the size of an elephant but looked like…well, not like an elephant:

Show transcript:

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

Lots of people know about dinosaurs. Dinosaurs are really interesting. But do you know what animals lived before dinosaurs evolved? Let’s find out.

If you’ve heard of dimetrodon, you may think it’s just another dinosaur. It’s the animal that looks sort of like a huge lizard with a sail-like frill down its back. But not only was dimetrodon not a dinosaur, it went extinct 40 million years before the first dinosaur evolved.

Dimetrodon lived almost 300 million years ago and was a synapsid. Synapsid is a catchall term for a group of animals with both reptilian and mammalian characteristics, also sometimes called proto-mammals. The term synapsid also includes mammals, so yes, you are related to dimetrodon verrrrrrry distantly. You are more closely related to dimetrodon than you are to any dinosaur, let’s put it that way.  Dimetrodon was an early synapsid, which are referred to as pelycosaurs.

The largest species of dimetrodon grew up to 15 feet long, or 4.6 meters, with some probably growing even larger. It had serrated teeth, a long tail, short legs, and a massive sail on its back. The sail is formed from neural spines, which are basically just really long prongs of bone growing from the vertebrae. The spines were connected with webbing, although possibly not all the way to the tip of the spines. Ever since the first fossil remains of dimetrodon were discovered in 1878, scientists have been trying to figure out what the sail was for.

For a long time the most popular theory was that the sail helped with thermoregulation. That is, it helped dimetrodon stay warm in cool weather and cool in warm weather by absorbing sunshine or releasing heat, depending on where dimetrodon was. If dimetrodon was chilly, it would angle its body so that lots of sunlight reached its sail, but if dimetrodon was hot, it would find a patch of shade or turn its body so that minimal sunlight reached its sail, allowing the blood vessels covering the sail to release heat into the atmosphere.

This is a pretty good guess, since many modern animals use something similar to help regulate body temperature. That’s why African elephants have such large ears. But more recent studies of dimetrodon’s sail show that it didn’t have a lot of blood vessels, as it would if it was for thermoregulation. These days paleontologists suggest the sails may have mostly been for display. Different species had differently shaped sails, and there’s some evidence that male and female dimetrodons of the same species may have had differently shaped sails too. It’s possible the sails were brightly colored or patterned during the breeding season.

But dimetrodon wasn’t the only early synapsid with a sail. Secodontosaurus had one too and resembled dimetrodon in many ways, including having a long tail and short legs. But where dimetrodon was chunky with a massive skull, secodontosaurus was much more slender with long, narrow jaws. It may have eaten fish. It probably grew up to nine feet long, or 2.7 meters, and it lived around 275 million years ago. It was related to dimetrodon, but paleontologists aren’t sure how closely it was related.

The largest pelycosaur, or early synapsid, was cotylorhynchus [ko-tillo-rinkus], which lived around 275 million years ago in what is now North America. It was a weird-looking animal. Weird, weird weird. Seriously, it was very strange. It grew to almost twenty feet long, or 6 meters, with a barrel-shaped body, great big legs, and a long tail. But its neck was very short and its head was tiny.

Some researchers think cotylorhynchus lived in the water. Its forefeet may have been paddle-shaped. It ate plants, which is why its body was so big, since it needed room to hold lots of plants while they digested. It may have dug for roots as well, since its forefeet had long claws. Weird as it was, if you think of it as shaped sort of like a giant tortoise, its small head and big body make more sense.

Dimetrodon and other pelycosaurs lived in the early Permian era. By the mid-Permian, a group of synapsids called therapsids started evolving to become more mammal-like. The legs of therapsids were positioned more beneath the body instead of sprouting out from the sides, which is the difference between a dog’s body and a lizard’s body. This allowed therapsids to run more efficiently and breathe more efficiently when moving fast.

We know that at least some of these early therapsids had fur because paleontologists have found coprolites, which as you recall are fossilized poops, with fur embedded in them. Since this was long before mammals evolved, it had to be therapsids with fur. In fact, it was the therapsids that eventually evolved into mammals, so technically you are also a therapsid.

Therapsids were probably warm-blooded and probably had whiskers. But they wouldn’t have looked like mammals today. They probably resembled reptiles in a lot of ways, especially early therapsids. The tails of many therapsids would have looked like reptile tails, long, thick, and pointed. The heads would have looked much more like a lizard head than a mammal head, with no external ears.

Some therapsids would have looked really weird. For instance, moschops [mo-shops], which lived around 260 million years ago in what is now southern Africa. Moschops was a type of therapsid that ate plants, and it was massively built. It was around 8 feet long, or 2.5 meters, and had a thick skull and short snout with strong jaw muscles. The back sloped downward from the shoulders to a short tail. Its relatively short legs were sturdy to hold up the weight of the broad and massive body. The front legs were much farther apart than the hind legs. Its teeth were strong but not sharp; instead, they had chisel-like edges that helped it bite through tough vegetation.

Moschops had such a thick skull that many researchers think it fought other moschopses by butting heads. The small brain was extremely well protected by a skull that was as much as 6 inches thick, or 15 cm, and new research shows that the head was usually held forward instead of up. This makes sense in a grazing animal, and would also make sense if males were butting heads to impress potential mates, or if individuals fought over territory or food. If moschops did butt heads, it’s possible that it lived in groups with a certain amount of social organization.

Toward the end of the Permian, a group of therapsids called dicynodonts became widespread and lived well into the Triassic era. Dicynodonts were probably warm-blooded, probably had fur or hair, and some may have had feet that were more paw-like than reptilian, with fleshy pads. But while all these features are mammalian, most dicynodonts had a horny beak like a turtle and either no teeth at all, or only a pair of teeth in the front of the jaw that grew like tusks. Some paleontologists think only males had these tusks. Most dicynodonts were herbivorous and some dug burrows.

About 250 million years ago, there was a mass extinction event called the Permian-Triassic extinction, or sometimes just the Great Dying. Researchers aren’t sure what caused it, but like the later extinction that ended the dinosaurs, it may have been caused initially by a massive meteor impact that sent the earth’s climate into a tailspin. 96% of all marine species went extinct and 70% of land animals. This was the event that led to the rise of the dinosaurs ultimately. But some therapsids survived.

The biggest dicynodont evolved after the great dying and it was the size of an elephant. Lisowicia lived in what is now Poland around 230 million years ago, but it was probably more widespread than that sounds. We only have a single specimen of lisowicia that was discovered in south Poland in 2008. It probably stood 8 ½ feet high, or 2.6 meters. All four of its legs were positioned under the body like modern mammals, whereas most dicynodonts were similar to moschops, where the hind legs were under the body and the forelegs were more widely spaced and sprawling. But it probably didn’t look much like a modern mammal beyond that. Its head would probably have looked quite reptilian since it had a horny beak like other dicynodonts. Its tail was short.

Dicynodonts went extinct by the late Triassic, but the related cynodonts persisted. Cynodonts are the direct ancestors of mammals. You are definitely also considered a cynodont. The first cynodonts evolved in the late Permian and had a lot of traits that are still retained by mammals, such as fur, whiskers, warm-bloodedness, and teeth that are differentiated into different types like molars and incisors. They also developed what’s called a secondary palate, or as we call it, the roof of the mouth. All mammals still have this feature, which allows us to breathe and chew at the same time. But cynodonts also still probably laid eggs. Eventually cynodonts developed into monotremes like the platypus and echidna, which many researchers consider to retain many cynodont features.

Probably the largest cynodont was cynognathus, which lived around 240 million years ago. Cynognathus was a predator that grew almost four feet long, or 1.2 meters, not counting its long tail. It was widespread throughout the southern hemisphere, with cynognathus fossils of various species found in modern-day southern Africa, South America, and Antarctica. It had already evolved the secondary palate, and its head and jaws were both long and wide, with sharp teeth.

Because cynodonts lived alongside dinosaurs for millions of years, they evolved into animals that were generally quite small, no larger than a rat, and frequently nocturnal. But they were still incredibly successful, spreading out across the world and evolving into animals that looked more and more like mammals that we’d recognize today. The haramiyids were probably insectivores and lived in trees, with some species able to glide like flying squirrels or the colugo. Many cynodonts lived in large shared burrows, suggesting increasingly complex social behavior.

But not all early mammals were tiny and ran away from dinosaurs. Repenomamus [re-penno-may-mus] lived around 125 million years ago and grew over three feet long, or 1 meter. In shape, it somewhat resembled a badger with a long tail. We know it ate small animals, including hatchling dinosaurs, because fossil remains of a baby psittacosaurus [sit-acko-saurus] was found in the stomach area of a fossil repenomamus. The psittacosaurus remains were in chunks, which suggests that repenomamus had bitten it into pieces to swallow it.

Repenomamus was considered a Eutriconodont, a type of early mammal, but the eutriconodonts went extinct at about the same time as the dinosaurs.

But by then, the therapsids were fully evolved into what we have termed mammals. And they were poised to take over. Or, I should say, we mammals were poised to take over. And we have.

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

Thanks for listening!

Episode 118: The Hummingbird

This week’s episode is about the world’s tiniest birds, the hummingbird! Thanks to Tara for the suggestion!

The bee hummingbird:

The giant hummingbird:

The giant giant hummingbird:

If you’re interested in my little side project, Real Life Cooking Podcast, here’s the URL (or you can just search for it in your regular podcast app):

Show transcript:

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

This week is another listener suggestion, this one from Tara! Tara’s favorite bird is the hummingbird, and I can’t believe I didn’t know that before she texted me, because I’ve known Tara for a long long time and in fact she is married to my brother. Tara, I hope you are ready for hummingbird-themed birthday gifts for the rest of your life!

The smallest birds in the world are hummingbirds, but not all hummingbirds are the smallest birds in the world. If that makes sense. The very smallest hummingbird, and definitely the smallest bird alive today and possibly alive ever, is the bee hummingbird.

The bee hummingbird is literally the size of a bee. Males are slightly smaller than females and barely grow more than two inches long, or 5.5 cm, from the tip of its long bill to the end of its tail. It weighs less than an ounce, or 2 grams. A penny weighs more than this bird does.

The bee hummingbird lives in Cuba and parts of the West Indies. Males are iridescent green and blue while females are more green and gray. During the breeding season, in spring and early summer, males also have red or pink spots on the head and throat.

Just like other birds, the bee hummingbird builds a nest and lays one or two eggs. The female takes care of the eggs and babies by herself. But her nest is so incredibly small! It’s barely an inch across, or 2.5 cm, lined with soft items like dandelion fluff and cobwebs. And the bee hummingbird’s eggs are the size of peas. I have some peas in my lunch today. Peas are really small. Can you imagine the smallness of an egg the size of a pea, and the smallness of the baby that hatches from the egg? I just died. I literally just died because it’s so cute and tiny I can’t stand it. Don’t worry, I came back to life to finish telling you about hummingbirds.

The largest hummingbird is called the giant hummingbird. It’s just over 9 inches long, or 23 cm, which sounds enormous, especially compared to the bee hummingbird. But keep in mind that its long bill is included in that length, so if you go by actual body size it’s only about the size of a sparrow. It has relatively long, pointed wings and sometimes actually glides instead of flapping its wings, which is practically unheard-of among hummingbirds. The giant hummingbird lives in the Andes Mountains in western South America, with some populations even living in high altitudes where the air is thinner. You know the so-called Nazca lines, the giant geoglyphs created by the ancient Nazca people that are shaped like animals? One of the geoglyphs is a hummingbird that’s 305 feet long, or 93 meters. It’s based on the giant hummingbird that lives in the area, so I guess you could say it’s a GIANT giant hummingbird.

*rimshot!* [it’s actually called a sting, and I played this one myself. Years of drum lessons have finally paid off!]

All hummingbirds are specialized to eat nectar from flowers. A hummingbird has a long, slender bill that can reach down into a flower to get at the nectar. In the process, the hummingbird gets pollen on its feathers that it then transfers to the next flowers it visits, helping pollinate the flowers. So the hummingbird gets a good meal and the flowers get pollinated, so everyone wins. Some hummingbird species have co-evolved with certain plant species so that only the bird can reach the nectar and only the bird can pollinate the flowers.

But the hummingbird’s bill isn’t a straw. It can open its bill just like other birds, and in fact hummingbirds eat a lot of tiny insects they find while foraging for nectar. They need to eat insects because while nectar provides a ton of energy, since it’s mostly just sugar, it doesn’t supply many nutrients. The upper part of the bill is much longer than the lower part, and the lower bill actually fits tightly inside the upper bill. That’s why it looks like a hummingbird’s bill is a tiny needle-like tube, since even if the bird has its mouth open it’s hard to tell.

A hummingbird actually uses its tongue to lap up nectar. The hummingbird’s tongue is extremely long, up to twice the length of the bill, and has a forked end. The tongue also contains grooves. When a hummingbird puts its bill into a flower, it sticks its tongue out and laps up the nectar rapidly, something like 13 licks a second. The nectar travels up the grooves into the bird’s mouth.

If you were wondering, a mother hummingbird feeds her babies nectar and tiny insects. Also, the reason hummingbirds use so much spiderweb silk in their nests is because it will expand as the babies grow. I’m sorry, I just died again. Give me a second to stop dying of cute. A baby hummingbird grows quickly and some species learn to fly at only two weeks old, although the mother bird continues to feed the babies for a little longer.

Hummingbirds move fast, which is why they need all that energy from nectar. Their energy needs are incredibly high. When a hummingbird flies, its metabolic rate increases to the highest ever measured in an animal that’s not an insect. Its heart can beat over 1,200 times per minute and it may breathe 250 times per minute. At night, or if there’s not a lot of food around, the hummingbird’s metabolism slows dramatically and the bird enters a state called torpor. Its body temperature falls, its heartrate can drop to only 50 beats per minute—which is on the slow side for a human—and its breathing rate drops too. Torpor is basically a very short hibernation where the bird will sleep deeply until morning or until it needs to go out and find more food. Even so, a hummingbird can lose up to 10% of its body weight overnight as its body burns fat reserves to keep it alive.

So that makes it all the more amazing that some species of hummingbird migrate long distances, including over the ocean. All hummingbird species are native to the Americas, but many species that spend the summer in North America migrate south to spend winter in Central America or Mexico. Some species in South America migrate north to winter in warmer areas too. The rufous hummingbird migrates from Alaska to Mexico, about 3,900 miles, or almost 6,300 km, and then it migrates back up the western coast of North America in spring.

The hummingbird doesn’t fly like other birds. It flaps its wings in a figure 8 motion that provides lift, which allows it to hover. Its wings beat incredibly quickly, up to 80 times a second. Even the slowest-moving hummingbird, the giant hummingbird, beats its wings 12 times a second. I don’t know about you, but I’m pretty sure I can’t do anything 12 times a second except maybe flutter my eyelashes, and even then my eyelids would get tired after a few seconds. Also, that’s not going to help me fly. Not even if I wear really long false eyelashes.

The hummingbird gets its name from the humming sound its wings make as they beat so incredibly fast. But the hummingbird’s feathers also make other sounds as the bird flies. In some species of hummingbird, the male grows special feathers that vibrate as he flies and make a whistling or chirping sound. This helps females find a male and helps the male defend his territory by announcing his presence to other males.

Oh, you didn’t know hummingbirds were territorial? They sure are. They may be tiny and pretty, but they’re fierce too. A male will chase other males away from his flowers, even stabbing other males with his long bill.

My aunt likes to tell a story of a cat she had years and years ago who liked to go into her garden and lie in the sun. One day the cat leaped at what my aunt thought was a bee. The cat stopped with a startled look on his face and opened his mouth. A hummingbird backed up out of the cat’s mouth and flew away and the cat never bothered a bird or a bee again, since the hummingbird’s beak had stabbed him in the back of the throat.

Needless to say, the hummingbird is the only bird that can fly backwards.

It’s one thing to think, “Oh, hummingbirds are so small” but it’s another thing to see a hummingbird in the wild and really understand how small they are. When I’m out birdwatching I almost always mistake hummingbirds for bees when I first see one. The hummingbird is so small, in fact, that it’s eaten by some larger insects, like the preying mantis, and by larger spiders. Anything that will eat an insect will eat a hummingbird, and that includes some other birds.

Fortunately, the hummingbird is so fast that it can usually get away from predators. It can fly up to 30 mph, or 48 km per hour. Its tail feathers also come out easily and grow back quickly, so anything that grabs it by the tail is probably just going to end up with a few feathers to eat.

The hummingbird flies so quickly through dense vegetation that its brain processes images in a different way from other birds so it doesn’t run into things. It has excellent vision, too, since it finds flowers by sight.

You can attract hummingbirds to your garden by planting flowers they like, such as bee balm, hollyhocks, petunias, trumpet vine, and lots more. You can also put out hummingbird feeders that you fill with imitation nectar. It’s important to keep the feeders cleaned, since the nectar will spoil after a while, mold will grow inside the feeder, and insects may get into the nectar and drown. Also make sure to hang the feeder where the birds will be safe from predators like cats and snakes.

Some of you may have heard that I’ve started a little side project, another podcast called Real Life Cooking where I share recipes and explain how to make them. So as a sort of crossover event, I’ll give you a recipe for making hummingbird nectar.

You don’t need anything expensive, just plain tapwater and plain white sugar. Use one part sugar to four parts water. So if you use one cup of water, add ¼ c sugar. Put them together in a small pot on the stove and heat the water, stirring occasionally, until the water is boiling. Let it boil for about a minute, then remove it from the heat and let it cool to room temperature. Once it’s cool, you can pour it into your hummingbird feeder. Don’t add red food coloring or any kind of flavoring, and don’t use any sugar except regular white sugar. Brown sugar and natural-colored sugars can contain iron, which is toxic to hummingbirds. If the feeder you use isn’t attracting hummingbirds, you can tie a red ribbon around it to make hummingbirds notice it. Make sure to change out the nectar every couple of days so it won’t go bad.

Sugar-water sounds like a horrible thing to feed a wild animal, but it’s exactly what hummingbirds need and what they eat naturally.

Hummingbirds are such unusual birds that it’s hard to imagine what they’re related to. There are birds that resemble hummingbirds in some ways, especially the sunbird that lives in Africa, parts of Asia, and Australia. But the hummingbird and the sunbird aren’t related. They just share a very specific ecological niche, which has resulted in similarities due to convergent evolution.

No, the hummingbird is most closely related to the swift! Not closely related, of course, because the two started evolving separately as much as 42 million years ago. The first ancestral hummingbird is found in the fossil record in South America around 22 million years ago, where they spread throughout the Americas and evolved into the hundreds of species we have today. In the Andes Mountains alone, there are 140 species of hummingbird and researchers keep finding new ones. The blue-throated hillstar was only discovered in 2017, for instance, since it lives in a very small area of the Andes in Ecuador and is very rare.

Researchers keep finding out more about hummingbirds, too. The black Jacobin hummingbird from the mountains of eastern Brazil makes complex sounds that are so high-pitched that the researchers have to record them using equipment developed to record bat calls. So who knows what else we’ll learn about hummingbirds next? I can definitely see why they’d be anyone’s favorite bird.

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

Thanks for listening!