While the title of this article implies that it will focus on animals that have gone extinct only within the last 100 years, it won’t. It will actually showcase a number of animals that have gone extinct over the last 15,000 years, and longer. The animals featured start out with relatively recent extinctions, such as the Carolina Parakeet, and the European Lion, and work their way back in time.

The animals to be highlighted include the largest eagle to have ever existed, the Haast’s Eagle, one of the largest birds to have ever existed, the Elephant Bird, and an armadillo relative that grew to be the size of a car. As well as examples of convergent evolution, such as the American Cheetah. And also examples of animals related to those still in the world but that lived in regions and climates not associated with the animals nowadays, and that were much larger or possessed different qualities + occupied different ecological niches.

So, yeah, there’s no focus on just 10 extinct animals of the last 100 years, but rather on the before as well. Enjoy the article.

10 Extinct Animals Of The Last 100 Years, & Before – List

Carolina Parakeet (Conuropsis carolinensis)

The Carolina Parakeet (Conuropsis carolinensis) was a bright green parakeet that previous to the 20th century was found throughout most of what’s now the continental US — to be more particular, found all throughout the South, the Northeast, the Midwest, and the Plains States.

The species was the only native ‘parrot’ and was responsible for long-range seed dispersal for a number of trees and plants in the regions that they lived — some which have lost the ability to disperse their seeds across wide distances since the extinction of the species.

While the Carolina Parakeet didn’t go extinct until the early 1900s, its population numbers fell off a cliff during the the centuries beforehand as a result of the extreme deforestation of the US during this time, and also other anthropogenic activity. Practically none of the old-growth forests of these earlier times, filled with truly massive trees in some areas, survives to this day. (For an idea of what I’m talking about, see: Soil Erosion Rates Rose More Than 100-Fold In The US Following Colonization Via Deforestation & Industrial Agriculture).

In addition to the habitat loss through deforestation — hunting, for their colorful feathers (women’s hats), and also to reduce crop theft/damage, also definitely played a part in the animal’s extinction. Their predilection for flocking, even around dead birds, seems to have made mass slaughter a relatively simple affair much of the time. Pet trade also likely played a minor role, as they were commonly kept as pets during some fad periods. (Poultry disease from introduced livestock may have played a part as well.)

Notably, though, despite the damage that they sometimes did to crops, they were also an important check on the growth of “invasive” cockleburs (Xanthium strumarium), considered by farmers of the time to be a problem — which not many animals can eat, owing to the toxic glucoside present in them.

Interestingly, this seems to have made the Carolina Parakeet itself poisonous, as noted by the naturalist John J Audubon — who observed that cats often died after eating them.

Favored habitat for the species was in the old-growth forests that used to edge the rivers and swamps of much of the eastern, southern, and midwestern US. The Mississippi-Missouri drainage basin, in particular, was favored environ. Nesting sites were varied, but old, hollow trees seemed to have been very commonly used — with cypress and sycamore, being common choices.

Population estimates vary substantially, but at the least there are thought to have been no fewer than several million of the birds in the US until recent times. Flock numbers were themselves quite large, with several hundred birds often flocking together at any one time.

As noted above, the diet consisted mostly of the seeds and fruits of the trees and shrubs of the regions where it lived — this included sycamore, cypress, oak, elm, beech, hackberry, maple, pine, apple, and fig. They were considered to be a pest in orchards. Other foods included sandspurs, thistles, grapes, berries, and, of course, cockleburs.

The Carolina Parakeet is thought to have first entered North America, from South America, around 5.5 million years ago — previously to the Panama land bridge forming. Going further back, the parrots of the Americas are the descendants of parrots that entered South America from Antarctica — sometime after the breakup of the Gondwana supercontinent.

Jaguar (Variants That Lived Throughout The US Until Recently)

While the jaguar is itself not extinct, the various subspecies that populated most of what’s now the US until recently certainly are. While there is a very limited population of jaguars, which may or may not be viable, in Arizona and New Mexico, jaguars previously lived throughout the South, Midwest, Mountain States, and West Coast.

Strong evidence shows that they lived as far north as Ohio, Pennsylvania, and Michigan, until just the last few hundred years. Following European colonization the species seems to have been wiped out in the US fairly rapidly — likely mostly as a result of mass deforestation and habitat loss.

Notably, a similar situation seems to have occurred in South America, where jaguars lost the southern-most extent of their range. Jaguars are still present to some degree or other in the parts of South America where forests remain, but range and numbers have definitely been diminished.

Also notable, is that fossil evidence shows that ice-age jaguars in North America were much larger than modern ones — with individuals growing to be at least 425 lbs.

As far as the jaguars still around go, the species is the largest cat of the Americas, and the largest carnivorous mammal still extant in South and Central America (following the extinction of various bear species there, amongst others). Weights vary quite a lot — from as high as 350 lbs to 100 lbs, depending on sex, region, and food availability. They are built much more stoutly than the other big cats, with particularly short, powerful limbs as compared to the other big cats.

As a result of their build, they are excellent climbers and swimmers. Indeed, they are often found in highest population densities around river systems. They also have very powerful bites, and can crush turtle shells as a result. Also a result, rather than the blood/constriction chokes used by many big cats, they are able to simple crush the skulls of many of their prey — a simpler, faster, and likely less dangerous killing method.

Prey species are widely varied — with jaguars eating everything from tapir, to deer, to caimans (crocodiles), to dogs, to cattle, to capybaras, to anacondas, to mice, to birds, to fish, to turtles, to monkeys, to sloths, to armadillos, to bears, to frogs, etc.

Interestingly, jaguars are much less prone to attacking humans than the other big cats are. Though, this has apparently been changing in recent times as mass deforestation and human ‘development’ continues encroaching on the remaining jaguar habitats of the regions in question.

The jaguar has featured in the stories and beliefs of the vast majority of the peoples who have had regular contact with it — including the Olmecs, the Mississippian Culture, the Aztecs, the Maya, etc.

Elephant Bird (Aepyornithidae)

Elephant birds are (were) what they sound like, enormous birds. Enormous ratite birds that is (as their relative the southern cassowary is). How big are we talking about? Up to 10 feet tall (3 meters) and 1,100 lbs (500 kilograms).

The elephant birds were classified within the extinct family Aepyornithidae, and the genera Mullerornis and Aepyornis, and were, as you’ve probably guessed, flightless. They lived solely on the island of Madagascar, apparently, and are thought to have gone extinct in the 1600s or 1700s.

The cause of extinction is almost definitely related to human activity. In particular to hunting, deforestation, egg theft, and habitat loss. The eggs in question were massive, around 22 lbs to be exact, so I’m sure that you can guess the motive for stealing them. These are apparently the largest type of bird eggs every found — in some cases having a circumference of more than 3.3 feet (1 meter).

As people brought chickens and guineafowl with them to Madagascar it may also be that introduced diseases played a part in the extinction of the elephant birds as well.

Interestingly, despite having lived relatively close to the ostriches of the Arabian peninsula and South Africa, DNA evidence has shown that’s its closest relative is the kiwi (New Zealand). What this means is that the ratites (elephants birds, ostriches, moa, kiwis, rhea, emus, cassowaries, etc) very likely didn’t diversity from one another following the breakup of the supercontinent Gondwana as a result of drift. But rather all (or some) diverged from a common ancestor that dispersed (by flying) across the world sometime after the supercontinent breakup.

Haast’s Eagle (Harpagornis moorei)

The Haast’s Eagle (Harpagornis moorei) is the largest eagle to have ever existed, and by a large margin. It went extinct only fairly recently, sometime around 1400-1500 — a few hundred years after the Maori arrived in its territory (South Island, New Zealand).

The females, which were larger than the males, grew to be somewhere between 22 and 33 lbs (10 and 15 kilograms) — quite heavy for a bird of prey. Some sources estimate that weights could have reached as high as 36 lbs. Wingspans varied somewhat, from an average of 8.5 feet (2.6 meters) to extremes of over 9.8 feet (3 meters). Compared to the body size those are actually relatively short wings for an eagle — probably an adaption to hunting in areas of forest or heavy scrubland. (The Philippine Eagle and the Harpy Eagle, which both hunt in forests, have similar adaptions.) Standing height is estimated to have been around 3 feet.

Why so big? Because their primary prey were giant 500 lbs (~230 kilogram) flightless birds, the moa. The moa are of course now extinct as well — the two extinctions no doubt being closely related. The moa are thought to have been rapidly hunted to extinction by the Maori (this includes egg theft, the moa laid really big eggs).

Interestingly, it’s massive size was gained over a period of only 700,000 to 1.8 million years — following its divergence from the little eagle or the booted eagle, both relatively small eagles. That means that the species grew 10 to 15 times larger in just that period of time — no doubt related to the complete absence of competitors on the South Island until people, rats, and dogs arrived. And to the enormously lucrative business of moa hunting. (Notably, the 500 lb kills would have been easy for the Haast’s Eagle to dominate for however long it took to consume the whole bird.)

During attack its estimated that the Haast’s Eagle would have reached speed of up to 50 miles per hour (80 kilometers per hour) — thereby delivering the force equivalent of a cinder block falling from an 8-story building. The particularly large beak would have been useful for opening prey up quickly, and bleeding the victim out.

European Lion

The European Lion was a species or subspecies (Panthera leo europaea) of lion that lived in Europe until fairly recently — going extinct sometime around 100 BC and 0 AD, presumably. Previous to extinction the European Lion had lived throughout Southern Europe (including France), the Balkans, the Near East, the Middle East, and West Asia.

While they were of similar size to modern African lions, averaging around 4 feet (1.2 meters) tall at the shoulders and 400 to 450 lbs (180 to 200 kilograms), they are thought to have been generally more similar to Asiatic lions. There appear to have been differences though, with the lack of abdominal and lateral manes being a notable one. (Indian lions, and also the lions shown in very old Persian art, tend to grow abdominal manes when living in cool climates.)

Notably, the Cave Lions that once occupied much of Eurasia, and the American Lions as well, were both much larger than any modern lions, and, were always depicted in cave art as being mane-less. So, going by descriptions and depictions of the relatively modern European Lion it seems likely that either the cave lions died off and the European lions moved into Europe, or there was a species displacement, rather than that European Lions are notably descended from the Cave Lions.

Going by the writings of Herodotus, European Lions were rather common in Greece circa 480 BC, became rare by 300 BC, and were more or less gone by 100 BC. In addition to habitat loss, hunting for pelts is likely to have played a part as well, going on contemporary reports.

Notably, lions of one type or another persisted in the Transcaucasia until the 900s AD.

Irish Elk (Megaloceros giganteus)

The Irish Elk (Megaloceros giganteus) is one of the biggest species of deer to have ever existed — around 7 feet (2.1 meters) tall at the shoulders, and weighing up to 1,500 lbs (~700 kilograms). This puts them on a similar size scale to the Alaskan Moose subspecies (Alces alces gigas).

The antlers, though, were the largest of any known cervid — growing to a known maximum of 12 feet (3.65 meters) long, and a weight of up to 88 lbs (40 kilograms).

Despite the name, the Irish Elk wasn’t actually an ‘elk’ — the two elks are the moose (Alces alces) and the wapiti (Cervus canadensis) — but rather a very large deer. The species’ closest relative is likely to either be the red deer (Cervus elaphus) or the fallow deer (Dama dama).

Species range is thought to have been all across Eurasia in the Pleistocene — from Ireland on one side to Siberia and China on the other. The species seems to have lived in Northern Africa as well, at various times. The name ‘Irish Elk’ is owing to the fact that many specimens have been found in Irish bogs, and because people at first thought that the bones were of an American Moose relative, not a deer.

The most recent remains yet found have been dated to around 7,700 years before present. They were found in Siberia.

The Irish Elk diverged from its relatives over the past few million years, likely owing to the recurring ice-age and interglacial cycles. The species is thought to have descended from M. antecedens. While the majority of Irish Elk remains date from between 11,750 Before Present and 400,000 or so years ago, there are few outliers. These include some remains found on the Isle of Man and Ballaugh dating to around ~1400 years after the presumed extinction. Notably these individuals were smaller than those of earlier times. This sort of relict island population phenomenon is fairly common — a type of American Mammoth for instance survived on an island near Alaska until only a few thousand years ago.

Investigating the cause of extinction of the Irish Elk is a muddy affair. There are quite a variety of opinions on the matter, including habitat loss, over-hunting, a runaway sexual selection process for nutrition-intensive giant antlers (that have to be grown every year), etc.

The likely truth is that a wide variety of phenomena converged to cause the extinction, as is often the case. And there no doubt was a lot of regional variety as far as causes go. Anything more solid than that we’re unlikely to get. (Notably the most recent remains found in Siberia show no sign of nutritional stress.)

Some of the speculation on the matter though is interesting, including the idea that adaptions allowing for improved mineral metabolism (to grow the ridiculous antlers) may have proved maladaptive when major vegetation changes came to many of the regions where the species lived at the dawn of the Holocene. (Notably, there were periods of time near the end of the Pleistocene when the growing seasons were drastically shortened for years at a year, for a variety of reasons.)

“According to an article written by researchers Silvia Gonzalez, Andrew Kitcheneri, and Adrian Lister, in 2000, a reduction in forest density into the Late Pleistocene decreased nutritional selection and is believed to have led to a conflict between sexual selection and ultimately a decrease in antler and body size, which can explain what may have caused their demise. High amounts of calcium and phosphate compounds are required to form antlers, and therefore large quantities of these minerals are required for the massive structures of the Irish elk. The males (and male deer in general) met this requirement partly from their bones, replenishing them from food plants after the antlers were grown or reclaiming the nutrients from discarded antlers (as has been observed in extant deer). Thus, in the antler growth phase, giant deer suffered from a condition similar to osteoporosis. When the climate changed at the end of the last glacial period, the vegetation in the animal’s habitat also changed towards species that presumably could not deliver sufficient amounts of the required minerals, at least in the western part of its range.”

No doubt this is only part of the story though, going by evidence it seems fairly likely that people played a part in at least some local extinctions.

Cave Hyena (Crocuta crocuta spelaea)

The Cave Hyena (Crocuta crocuta spelaea) was a much larger cousin of modern African Hyenas, that is known to have actively preyed on humans. It’s known range spread all across Eurasia, from far-eastern Siberia all the way to the Atlantic coast of Europe. Going by how incredibly common remains and fossils of the Cave Hyena are, the species seems to have been a very common one.

The species is itself responsible for huge bone pits in caves, sinkholes, and muddy depressions along rivers — filled with a variety of animal remains, including those of the ancestors of domesticated horses, woolly rhinoceros, steppe wisent, reindeer, Irish Elk, red deer, ibex, European ass/donkey, chamois, etc. Cave hyena seem to have favored horses, probably much as modern hyenas favor zebra as prey. They seem to have occasionally preyed upon wolves as well, likely when in competition with them for caves.

Notably, some cave sites show rapidly alternating occupation of caves by cave hyena, cave lions, Neanderthals and/or Denisovans, and cave bear. The species in question seem to have at least occasionally competed for caves.

It should probably be noted here that while Neanderthals and other hominids certainly did utilize caves for shelter (understandably, caves are excellent shelter when properly utilized), other means of shelter approximating long-houses and yurts (and sweat-lodges for that matter) go far, far back into prehistory. As do temporary, but extremely energy efficient shelters such as wigwams. These peoples weren’t using caves because they were the only option, they were using them because they are prime real-estate in very cold environments (especially when utilized intelligently).

As far as broader interactions between Neanderthals and Cave Hyena, fossil evidence shows that Neanderthals apparently at least occasionally butchered cave hyenas. What they did with them isn’t something that can be known for sure. Considering that Neanderthals living at least as long as 176,000 years ago were traveling deep, deep underground to perform what appears to have been very complex rituals, who knows (see: Neanderthals & Denisovans — Who Were They? Comparison Of Evidence Against Pop-Culture Projection).

Causes of extinction aren’t quite clear, but in Western Europe at least, the decline seems to have coincided with the growth of woodland, and a corresponding decline in grasslands. Judging by their African relatives, Cave Hyena likely relied on the open nature of grasslands for their hunting strategies. In woodlands, Cave Hyena may possibly have had trouble remaining competitive (with regard to hunting) with wolves, humans, bears, and others.

They seem to have disappeared completely from Western Europe by around 11,000 years ago, and lasted somewhat longer in eastern Asia. Decline seems to have begun, in at least some regions, as early as 20,000 years ago.

As far as Cave Hyenas themselves go, as mentioned above they were much bigger than their living relatives — with average weights of around 225 lbs (102 kilograms), and some individuals apparently having grown much larger. Their frame was a bit different than that of African hyenas though, with the back-leg bones being longer, and the the front leg bones being thicker and shorter. Some cave art of prehistory shows that the Cave Hyena possessed a spotted-pelt, presumably fairly similar to that of modern hyenas.

In keeping with the hyena family tree, female Cave Hyenas seem to have been notably larger than males (and presumably produced more testosterone than the males, as modern female hyenas do).

As one would expect given the climate, and the species name, Cave Hyenas relied upon dens, whether cave or otherwise, as a means of getting out of the cold.

American Cheetah (Miracinonyx trumani & Miracinonyx inexpectatus)

The American Cheetah (Miracinonyx) was a genus, composed of at least two species of big cat, that lived in North America from around 2.6 million to ~12,000 years ago. While morphologically very similar to the modern cheetah (Acinonyx jubatus), the two are not closely related at all, but appear to be a case of convergent or parallel evolution. (Evolving to fit similar ecological niches despite very different starting points.)

The closest living relative of the two American Cheetah species (Miracinonyx trumani and Miracinonyx inexpectatus), is actually the ecologically very different Puma, or cougar. (DNA evidence supports this.)

The American Cheetahs and the American Cougars appear to have diverged from one another sometime around 3 million years ago, though exacts are hard to know because fossils of the animals are sparse.

As far as a description of the animals — they were very similar to the modern cheetah, with short faces; large, expanded nasal cavities (more oxygen); and legs and body proportions well suited to high-speed running.

Notably, though, they were a good deal larger than modern cheetahs, and more similar in size to modern northern cougars — with average weights of probably around 150 lbs (70 kilograms), and large individuals weighing possibly more than 210 lbs (~95 kilograms). Body length would have averaged around 67 inches (170 cm), and tails would have been around 36 inches long (92 cm). Shoulder height wouldn’t have been that different than northern cougars — around 33 inches or so (85 cm).

With regard to differences between the two known species — M. trumani was the most similar to modern cheetahs, and lived apparently primarily on the prairies and plains of western North America. Presumably prey would have been similar to that of modern cheetahs — likely pronghorns, and others. Evidence actually suggests that pronghorns and American cheetahs likely got locked in an “evolutionary arms race” and that the great speed of both was due to the other. After all, pronghorns run far faster (up to 60 mph) than any modern predators in the areas they are native to (wolves, coyote, cougars, jaguars, etc).

As far as M. inexpectatus, this species was a bit more similar to cougars than M. trumani was — with a build that was more cougar-like, and fully retractable claws. The species was probably a fair bit faster than modern cougars though, and thanks to the retractable claws and thicker build, better suited to climbing than M. trumani — so the species probably lived in some sort of intermediate environ.

Glyptodonts, Glyptotherium Texanum, & Glyptodon (Giant Armadillos)

The glyptodonts were an armadillo-like group of animals native to the Americas that grew to be the size of cars (some species), and to reach weights of at least 2,000 kilograms. While superficially similar to armadillos (ignoring scale), there are actually quite a lot of differences between the different groups of animals — including large, bony mace-like tails; distinctly deep jaws; and heavier body-armor (composed of bony deposits in the skin referred to as osteoderms.

The animal group seems to have first emerged in South America during the Miocene. One of the earliest and oldest of the type yet found was discovered in Chile. Following the formation of the Isthmus of Panama around 3 million years ago numerous glyptodont species moved into North America (along with a great many other animals, including armadillos). This spread included Glyptotherium texanum.

Notably, different species of glyptodonts had different osteoderm patterns and shell morphology. (Different primary predators?) The mace-like spiked tail, and the general appearance, makes for another interesting example of convergent or parallel evolution as with the American Cheetah discussed above — the dinosaurian ankylosaurs, and the extinct giant meiolaniid turtles (Australia), both utilized somewhat similar morphology and defense tactics despite being spread across time and space.

Very notably, the glyptodonts resembled the ankylosaurs more than the giant meiolaniid turtles — this is interesting because they likely dealt with similar carnivores. The glyptodonts dealt with a variety of giant flightless predatory birds that lived in South America at the time of their emergence, including phorusrhacids. The ankylosaurs of course dealt with animals that would have been rather similar to the giant carnivorous flightless birds present in South America during the Miocene.

As far as diet, the glyptodonts were themselves grazing herbivores — ones that possessed no canine or incisor teeth though, and instead relied on their “cheek teeth.”

The exacts of extinction aren’t known for sure, but the glyptodonts died out right around the same time as many of the other megafauna animals of the region, right at the end of the last ice age. Multiple stressors, including climatic changes and changing environments, are very likely to have played a part in the extinctions. Megafauna animals are generally much more affected by changes to their environments, because of their nutritional and range requirements, than their smaller relatives — hence the survival to this day of armadillos.

Giant Short-Faced Bear (Arctodus spp.)

The Giant Short-Faced Bear is a beautiful animal, in its way. Was one, that is. It was also (one of the species) one of the very biggest terrestrial mammalian carnivores to have ever existed. As you’ve probably noticed from the reproduction above, the animals had a longer build than modern grizzly/brown bears do, and likely occupied a somewhat different ecological niche.

Recent estimates state that the Giant Short-Faced Bears (Arctodus pristinus and Arctodus simus) stood at least 8 to 10 feet tall (2.4 to 3 meters), and could get at least as tall as 12 feet (3.66 meters). The animals’ vertical arm-reach would have been around 14 feet (4.3 meters). Even when walking on all fours, and not reared up in the back legs, the bears would have been tall enough to look people in the eye — with shoulder-height when on all fours being around 5 to 6 feet (1.5 to 1.8 meters).

Notably, there’s a series of claw marks made by a giant short-faced bear at Riverbluff Cave, Missouri, that are up to 15 feet high.

As far as weights, a somewhat recent study examined the mass of 6 fossil specimens — the largest was 2,110 lbs (957 kilograms), and a full one-third of the specimens would have weighed around 2,000 lbs (900 kilograms).

The short-faced bears are known to have lived in North American from around 1.8 million years ago until around 11,000 years ago. It was very common by 800,000 Before Present — with a population concentration around California apparently, but a range from the Mississippi Valley to New Jersey, to Alaska. Interestingly, Arctodus pristinus was particularly prevalent in what’s now Florida (at various points much larger than it is now).

(The West Coast population would have shared its living space with the giant teratorn birds, the size of small planes, and the massive 10-foot-long saber-tooth salmon, amongst others).

It’s extinction coincides with that of the teratorns, and others as well, and also with the start of the Younger Dryas cooling period, circa 10,900 BC — which may well have been caused by a large meteor or comet impact in North America. (There’s a lot of debate on the last matter.)

As far as the name goes, it’s due to the face/head being seemingly shorter than that of many other bears, the spectacled bear (a close relative) excluded. This is something of an optical illusion though.

It’s not completely clear if the giant short-faced bears were omnivores as most bears are, or if meat made up a more substantial part of their diet. Some bone analyses (for nitrogen-15 concentrations), suggest that this was the case at least part of the time, or in some regions. If they were highly carnivorous, and engaged in lots of activity, than a a large male would have required around 35 lbs (16 kilograms) or meat a day.

As far as ecological niche, there’s a lot of debate there as well. The long limbs would have allowed for some very fast sprinting speeds (up to 40 miles per hour by some estimates), but they don’t seem to have been built for rapid turning — so it’s unclear that they would have been successful chasing agile prey. Given that they were a very successful group of animals though, that lasted quite a long time, they clearly weren’t having too much trouble getting their food. So what were they doing then? Were the long limbs for climbing? Rocky terrain? Striking (as bears certainly do)? Long distance endurance travel?

According to research from the University of Alaska Fairbanks, there’s likely something to that last guess, as they would have supposedly utilized an energy efficient pacing motion when traveling. Owing to this quality some researchers have argued that they located kills made by other carnivores and then took over the kill site. The idea being that their great bulk would have allowed them to scare off groups of dire wolves, American lions, or saber-toothed cats.

Something that I haven’t heard discussed much, is that the oceans were very productive during cold periods (big plankton and krill blooms) and filled much of the time that the bears were around with animals such as the truly massive saber-toothed salmon. Considering that population densities were highest along the west coast, it may well have been the case that the long legs were useful for long distance travel between feeding sites that were used at different times of the year — congregating for salmon runs along the coast, heading elsewhere when that’s done, etc. Regular long distance travel is a lot simpler when you have long legs.

As someone who has spent a lot of time in bear country, I’ll note that I’d be very surprised if the giant short-faced bears didn’t binge on berries and nuts when possible. Or that they didn’t rely on sedges, etc, when not much else was available.

Dimetrodon

Despite easy categorization in the pop consciousness as a “dinosaur,” Dimetrodon was actually a genus of animals that lived, and died, well before dinosaurs were even around. Dying out some 40 million years before the first dinosaurs are known to have appeared. Roughly, from around 295 to 272 million years ago, during the Early Permian.

As noted above, the dimetrodons (family Sphenacodontidae) were synapsids — to be more specific they were non-mammalian synapsids, or mammal-like reptiles, depending on who you ask. The clade Synapsida encompasses mammals, along with non-mammalian synapsids. Dinosaurs, birds, reptiles, are classified in a completely different clade, Sauropsida. It’s probably important to note here that dimetrodons aren’t direct ancestors of mammals.

You’ve probably seen recreations of dimetrodons before, as they are quite recognizable — sort of like a giant lizard with a big sail on its back. They weren’t actually lizards, or even reptiles, though, but rather had some psychological qualities in common with mammals. It’s not known whether the dimetrodons were warm-blooded or not.

Most fossils of dimetrodons discovered to date have been in Texas and Oklahoma, in the Red Beds geological deposits. Recently though a dimetrodon fossil was discovered in Germany, extending known range (the two fossil locations weren’t anything like as far apart at the time as they are now).

The larger dimetrodon species were very likely some of the top predators of their time, and possessed a varied diet consisting of tetrapods, fish, amphibians, and reptiles, apparently.

As far as the distinctive sails of the dimetrodons, there’s, you guessed it, a lot of debate on the matter. Temperature regulation? Spine stabilization? Sexual politics? All of the above?

A couple of points to make on that — the sail was formed apparently through the elongation of neural spines coming out of the vertebrae; some fossil specimens show deformed areas where fractures were healed over, the bone that grew over these fractures was highly vascularized (soft tissue of some kind seems likely then); and, some specimens show bending in the distal portions of the sail (meaning that maybe the soft tissue didn’t extend all the way up).

Related to that, no fossil evidence has yet been found of what dimetrodon skin was like — a somewhat closely related animal, though, Estemmenosuchus, had very smooth skin, that was apparently heavily glanded (so maybe not too dry?). Bony protection may have been present on the belly and the underside of the tail as in many other synapsids.

More generally, most dimetrodon species were fairly large — growing to be more than 15 feet long (~4.5 meters) in some cases. Weights in some species may have exceeded 550 lbs (~250 kilograms).

Some species were notably smaller though, with D. teutonisimg being around 2 feet long (60 cm). The largest known species was D. angelensis.

Interestingly, dimetrodons had skulls that were much more heavily built than that of dinosaurs. They also possessed a nearly unique shape to some of their teeth — teardrop.

So why did dimetrodon species get so big? Research indicates that many species were involved in ‘evolutionary arms races’ with some of their primary prey. As their prey items continued to get larger and more heavily armored, so did they. The potential expense of such an approach, though, is that if there is an ecological collapse (rapid climate change, meteor or comet impacts, endemic plant disease, a species invasion from land bridge formation, etc) then there is an attendant lack of flexibility. Larger animals (and systems) simply have too many requirements and needs to rapidly adjust to rapidly changing circumstances.

It’s often an advantage in the short term to grow as much as possible and to get as big as possible, but over the long-term it’s essentially a path to non-existence. Being tied to a niche and environ that may well soon get tossed to the bottom of the ocean of the universe (Tartarus, to use the Ancient Greek terminology).