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But if there weren't dinos, extinct mammals as a whole would be much, much more popular than they are today: a lot of them were in Real Life as large and powerful as many stock dinosaurs. Not to mention the fact a consistent part of them were the ancestors of modern hairy, milk-producing vertebrates. In short, they would be very interesting guys to show in fiction. And yet most of them still remain docu-related animals - if they're lucky enough.
Programs from the 2000s like Walking With Beasts and the Ice Age film series tried to partially avert the trope, but even these shows didn't escape the Everything's Better with Dinosaurs fate: not only the well-known case of "Dawn of Dinosaurs". Though it's little-known, Walking With was initially intended to show prehistoric mammals, but producers received money "only for a show about dinosaurs" - only after the dinosaurs' success they could start with Beasts, changed to a simple sequel at that point.
Here is a very partial list of extinct mammals. If you want to see more about the stock ones (Mammoths and sabertooth Cats) see Stock Dinosaurs.
The elephant's clan
- It is often heard the mammoth was bigger than a modern elephant. This is not true if we consider the stock guy, the hairy, curly-tusked tundra-dweller called Woolly mammoth all people know: but this is true talking about other mammoth species. There were indeed many species of mammothes in Real Life, and as a group they lived across most of the Ice-Ages world. The largest ones did challenge the "indricothere" (see later) as the "Biggest land mammal ever" title, but only if you count their weight (the indricothere would ever be taller than every mammoth, thanks to its giraffe-like body frame). The most famous are two American species, the Imperial mammoth and the southerner Columbian Mammoth; giant mammothes have been discovered in the famous US tar-pits like La Brea along with sabertoothed Smilodon fatalis and many other mammals (prehistoric camels, mastodons, giant ground sloths, giant wolves, pronghorns, American lions ans so on), some of them still-living today and other extinct after the Ice Ages. Other mammothes as large as the latter were the Asian Steppe Mammoth, and the less-known but possibly the largest of them all, Mammuthus sungari. The lower popularity of the giant mammothes (despite their size) compared to the woolly one is probably due to their more normal, less-spectacular appearence. They were more similar-looking to modern elephants than to the popular image of "the mammoth" because they were mostly hairless and with classic-shaped tusks (though longer than modern bush elephants); this because they inhabited relatively warmer climates, and their greater size was enough to preserve heat without the woolly covering.
- There were A LOT of other extinct elephant relatives in prehistory: not so in Prehistoria. Don't expect to see any proboscideans in TV outside docus unless it's a woolly mammoth or an American mastodon, even though many of them were far cooler-looking than the latter two. If you don't believe us, take a look at the following examples. Platybelodon resembled a cross between an elephant and a hippo, with its shovel-like lower jaws. Smaller than modern elephants, it was once classified within the "mastodonts", but the latter has revealed to be an artificial assemblage of archaic proboscideans, only united by one thing: they had a pair of tusks both in their upper jaw and in the lower one. In Platybelodon, the upper ones were small and normal-looking; the lower tusks were placed on the tip of the jaw, were flat and very untusk-like, maybe used to "gather" ground-level vegetation like a literal shovel. The platybelodont is often shown with a bizarre flat trunk, but this is actually unproven--trunks have not bones within, so they didn't fossilize. Other "mastodonts" were more similar to elephants, but even they would appear cool-looking by our standards: see Anancus the "European mastodon", with its straight, spear-like upper-tusks (while the lower ones were almost missing). A more primitive proboscidean lineage includes the huge Deinotherium ("terrible beast"). Unlike the former, it had only two tusks like modern pachyderms.... only, they grew out of the lower jaw. Curved downwards, the function of these tuskes is still uncertain (maybe to leave the bark out from trees). Some deinotheres were as big as the aforementioned giant mammothes, but others were not bigger than a modern Asian elephant. Deinotheres lived in most Cenozoic era, and some managed to survive enough to meet our first human ancestors in Africa.
Lilliputian cyclopes: Dwarf Elephants
- Among extinct members of the elephant clan, don't forget some island-dwellers which lived in the Ice Ages and almost managed to survive until human history: the oxymoronic dwarf elephants. Yes, they were real, and some sheep-sized. Most of them lived in the Mediterranean islands, but other lived elsewhere; all achieved their dwarfism probaby due to lacking of abundant vegetation and/or because they lose the necessity to defend against big mainland predators. Just for curiosity: many of the larger elephant and elephant relative bones (and the smaller ones, too) which were found in the Mediterranean were identified by the ancient Greeks as the remaining bones of monsters, heroes and animals from the Age of Heroes. Some of these bones were identified as cyclopes, due to the alleged misunderstanding of the elephant's nasal opening, put in the place where cyclopes'd have their one eye. But... this is a myth on its own. No elephant skulls were found as often said. The fossils of Anceint Greece are way too fragmentary due to geological forces (earthquakes and volcanoes) to allow something as fragile as a skull to survive intact.
All began with a tapir: Moeritherium
- How did elephants looked at the start of their evolution? Not really like pachyderms. The most classic ur-elephant is Moeritherium, found in Egypt in the Eocene period. Classicaly mentioned as "the first elephant" (but some proboscideans were even more ancestral), Moeritherium didn't resemble an elephant at all. Not bigger than a large pig, with its short tusks, hippo-limbs and (arguably) pig.like trunk, it was also more tapir-looking rather than elephant-looking. Living in a mixed aquatic-terrestrial habitat, the moerithere is often though an amphibious animal living a bit like modern hippopotamuses, but its actual lifestyle is still unknown.
- Elephants had some still-living relatives which don't resemble elephants much, but share a similar inner anatomy and a similar dentition. Sirenians (manatees and dugongs) descended from hippo-like ancestors, but then achieved a fish-like shape very convergently with cetaceans (see further). Another group of sea mammals related with proboscideans is now totally extinct: the little-known Desmostylians. They were a sort of "herbivorous seals" which protruding teeth a bit like walruses, but ate weeds like their relatives the manatees.
Elephant's kin? Titanohyrax
- Though are very rarely mentioned, prehistoric and modern hyraxes are very interesting. Today, hyracoideans are small, guineapig-like mammals living in african savannahs and forests. Once, however, they were very diversified, and some were even cow-sized, like the meaningfully-named Titanohyrax. Hyraxes were once the dominant group of large herbivorous mammals in Africa along with elephants, but then were replaced by the still-ruling odd-toed and even-toed ungulates. Hyraxes, along with Desmostylians, Sirenians and Proboscideans, make together the so-called “Paenungulates” (“almost hoofed”). Once thought related with true hoofed mammals (the “ungulates”), they are now believed a more ancient mammalian branch, arisen in Africa and related with some modern shrew-like animals still-living here. Together, all these mammals have recently been grouped in the Afrotheres (“African beasts”).
The lion's clan
- There were dozens kinds of sabertoothed cats in Real Life other than the stock American Smilodon from the Ice Ages. Some of them are nicknamed according to the form of their fangs: Homotherium was the "Scimitar-tooth", Megantereon the "dirktooth". While Machairodus was the Euro-Afro-Asian sabertoothed equivalent of Smilodon, not to mention the actual prototype of the group; many European paleoartists have considered Machairodus as the real stock sabretooth instead of Smilodon. But there were also more familiar-looking cats in the past: these ones are mentioned later in another section. However, Dinofelis, despite resembling more a leopard, was actually a short-fanged saber-toothed cat. The habits of all these whatever-toothed cats is still a mystery; certsinly, they were not identical among each other, and it's arguable they had different hunting styles according to the shape of their fangs; maybe some were solitary while others were pack-hunters, just like the difference between modern tigers/leopards/whatnot and lions. A curious thing is, some prehistoric meat-eating mammals which were not cats at all, developed a bewildering "sabre-toothed" look before true cats appeared: two main examples are the pseudo-cat Eusmilus (mentioned later) and the marsupial Thylacosmilus, in particular the latter, being closer to kangaroos than to cats. Imagine a sabretooth with a kangaroo pouch and you'll have the idea.
- There were not only sabre/scimitar/dirk/whatevertooths in Prehistory. There were also more normal-looking cats, which together make the subfamily Felinae - while sabretooths make the Machairodontinae. The former are known as "biting cats" the latter "stabbing cats", guess why. The most well-known "biting" cats were the American Lion and its European cousin, the Cave Lion, both simply larger, Ice Ages-related subspecies of the modern lion, well adapted to live in colder climates along with the mammoths. Some think they were the main predators of ancient humans, but this is not certain. Anyway, it seems males haven't any mane, at least according to some prehistoric paintings. Another interesting biting cat was the American Cheetah (Miracinonyx), actually more related with cougar than to cheetah, possibly a specialized hunter of modern pronghorns (which developed their fastness just to escape these "cheetahs"). Not all prehistoric cats were large, though: most were as small as many modern felines, and one of them was the ancestor of our domestic friend.
- Bears are a very recent group. They have roamed our planet for only 5 to 10 million years. Many prehistoric bears were rather different than our grizzlies: for example, the North American Short-faced Bear (Arctodus) had long limbs and a bulldog-like snout and was probably an agile runner and specialized hunter. The most famous extinct bear is, however, the Cave Bear (Ursus spelaeus), whose remains are extremely abundant in European caves. Quite similar to a modern kodiak in shape and size, but with a bigger hump on its shoulder and a more prominent skull, Cave Bear is often portrayed as the archenemy of Neanderthals, because both lived in the same places (Pleistocene Europe) and were forced to share the same caves to repair themselves from the rigid Ice Age winters. But it's more probable that Neanderthals were actually the worst enemies of cave bears, and some think they could even have contributed to cave bears' extinction.
- Prehistoric wolves and hyenas were not so different-looking than ours, but sometimes were larger. The Dire Wolf (Canis dirus) was a sort of wolf bigger than ours, possibly a hunter of giant bisons in competition with lions. It has been often found in the same tarpits in which Smilodon remains have been discovered, along with several other American mammals (elephant relatives, ground sloths, but modern-living mammals as well); the most famous is Rancho la Brea, in Los Angeles. Of course, not all extinct dogs were large, don't forget there were fox-ancestors as well. Among extinct hyenas (which by the way, are more closely related to cats than dogs) we can mention the Cave Hyena, similar to modern spotted hyenas but living in northern territories during the Ice Ages. Other hyena species were very different: some were as large as bears, others resembled more cheetah or even weasels! On the other hand, some extinct canid were deceptively hyena-like: Borophagus from the Middle Cenozoic is one example, while the archaic Hesperocyon was more weasel-like. As a side-note: all modern domestic dogs from Chihuahuas to Great Danes descend from the grey wolf, no matter how big they are or how they look; an amazingly rapid evolution, really, lasted only few thousands years.
- Before cats, bears, dogs and hyenas appeared on Earth, there were their pseudo-looking relatives, whose appearence was similar to their successors or a mix of these animals. Bear-dogs are more correctly called Amphicyonids: some were very fox- or wolf-like, while others were more similar to bears. Amphicyon is the prototype of the group. A very dog-like "bear-dog" appears in Walking With Beasts. Nimravids (the pseudo-cats) were also very diversified: the aforementioned Eusmilus was indeed a sabretoothed member of the pseudo-cat family, while the namesake Nimravus was more similar to modern big cats. The latter has left a perforated skull which revealed an astonishing story; it was stabbed in its head... by another sabretooth. The skull wound was also partially healed, meaning the Nimravus survived. Sadly, in some sources, Nimravid are wrongly treated as actual cats.
I'm not a weasel: Miacis
- True carnivores (members of the order Carnivora) appeared soon after the start of the Mammal Age, but remained small and unspecialized for a long amount of time. In the Eocene most of them were still weasel- or genet-like like Miacis , but they already showed the separation in the two main branches still-living today: the dog branch (dogs, bears, raccoons, weasels and seals) and the cat branch (cats, genets, mongooses and hyenas). All modern large-sized carnivores, from bears to lions, wolves to walruses, descend from weasel-shaped critters. However, many small carnivores retain still today their ancient shape/size: because of their small size, they are much rarer in the fossil record and their evolution is less understood. Also poorly-understood is the evolution of Pinnipeds (seals, sea-lions and walruses), as their fossils are rare. We are sure however, they were a more recent group than Cetaceans and Sirenians, and descended from otter-like or bear-like ancestors.
I'm not a hyena: Hyaenodon and the Creodonts
- In the Early Cenozoic, at the time "true" carnivores were still weasel-like, creodonts occupied the ecological niche ruled by modern large carnivores. Very diversified in shape and size, their appearence included that of all modern carnivores (hyena-like, dog-like, bear-like, weasel-like, tiger-like, or a mix of all these). However, creodonts were more primitive and arguably slower-moving than our meat-eating mammals: this has been often cited as the cause of their extinction, but scientists aren't sure of that. Hyaenodon is regarded as the stock creodont. There were several species, from dog-sized to cow-sized: the largest hyaenodont species appears in Walking With as a formidable predator, but some hypothize it was mostly a scavenger. But even bigger creodonts are known to science, some of them could have even been the biggest land meat-eating mammals ever, rivalling the alleged "Biggest carnivore" Andrewsarchus (see later).
From horses to rhinos
A run toward the future: Horse Ancestors
- Horses. The eternal symbol of Evolution. Almost the same level the Dodo is the icon of extinction. And yet, horse ancestors weren't so cool-looking compared to most other extinct hoofed mammals, really. The most famous of these is, obviously, the less horse-like of them all: Eohippus --> Hyracotherium --> Eohippus --> Protorohippus. An almost-unbelievable Science Marches On affair has encircled horse's evolution, despite its iconic role in popular science. Anyway, all this doesn't involve us so much. Expect to see this (whatever name is to be used) small, basal ungulate called horse anyway, despite it, actually, having nothing more in common with horses than with tapirs or rhinoceri: the "Hyracotheohippus stew" includes several different early ungulates, some of theme were horse-ancestors and some weren't. Systematics of primitive ungulates (called "Condylarths") is a total mess. Among sure horse ancestors, they make a sort of pun if read together: Mesohippus, Merychippus, Pliohippus and dozens other hippus... all North American. Also worth of note is Hipparion which, sadly, breaks the pun having hippus as prefix: it also breaks the geographic rule, being an Old World critter, an offshot of the horse tree which didn't leave any descendents. Remember that all modern equines did descend from North American ancestors. And oh: the latter were not only horse's ancestors: also donkey's and zebra's, never forget this. Modern equids are so closely related each others, they could well be considered variations of a single kind of animal; indeed, they are all put in a single genus, Equus.
Saber-toothed rhino: Uintatherium
- As we'll say later, not all rhinoceros-looking fossil mammals were real rhinos; but they'll probably get identified as such in popular media. The most well-known are Uintatherium and Brontotherium, both found in huge numbers in several fossil deposits of Western Usa. The poor uintathere is perhaps the most mistreated extinct mammal of them all: expect somebody describing its appearence as "monstrous/scary". Right, it had six giraffe-like horns and two upper protruding tusks: but, honestly, if Uintatherium was alive today, it would appear not more scary than an elephant, rhino, hippo or giraffe... Also expect a crack about its "tiny" brain (just what happens to its Woobiesaurian equivalent, Stegosaurus), and just like the stegosaur, expect the writer saying its dumbness being the real reason of its extinction! In Real Life, uintatheres were among the very first mammals to reach large size (up to a modern-day rhino), and their body-plan was very successful at the time, to the point they roamed northern continents in huge numbers for million years in Early Cenozoic, before being substituted by the even larger brontotheres (see below).
- Brontotherium is the prototype and the most well-known member of its group of mammals, the brontotheres. While Uintatherium was not related with any modern hoofed mammals, brontotheres were distant relatives of horses, tapirs and rhinos. The biggest brontotheres were almost Triceratops-sized or Elephant-sized, and their cool-name indeed means "thunder beasts". They had a more rhino-like look than uintathere, having one single "horn" on their nose: Brontotherium 's prominence was forked and slingshot-like, while that of Embolotherium (the brontothere portrayed in Walking With Beasts) was shovel-like and not forked. Like uintathere, brontotheres too roamed plains of the northern continents in huge numbers in Early Cenozoic: then they eventually gone extinct, perhaps because they weren't capable to adapt to the diffusion of the very first grasslands which replaced their former food (made of scrub and non-grass herbs).
The Pharaoh's megahorn: Arsinoitherium
- This one was the most peculiar-looking among "pseudo-rhinos": Arsinoitherium, sometimes misspelled "Arsinotherium". This is only due to its huge, yet light-weighed, hollow "quadruple-horn" (sometimes even asymmetrical). The same size as modern rhinos, this animal is often described as a "cross between a rhino and a hippo" because of its short legs and amphibious habits: it lived along the coasts bordering the shallow seas which covered modern-day Egypt, together with the ur-elephant Moeritherium. It's worth noting that, unlike Moeritherium, Arsinoitherium was not an elephant predecessor as said in Sea Monsters, and maybe didn't have that tapir-like nose seen in the program: this mammal is so strange that it is put in its own mammalian order, the Embrithopods, only distantly related to elephants.
- Modern rhinos are often referred as "prehistoric-looking" in media (and the genus now housing the White Rhino (Ceratotherium) dates back 7 million years). Many classic prehistoric mammals were indeed rhino-looking though with different horn-shapes (the aforementioned six-horned Uintatherium and the fork-horned Brontotherium are the most well-known examples), but only some of the extinct "rhinoceroses" were really such. Among them, the most spectacular were the Woolly Rhino, the Unicorn Rhino, and above all, the Indricothere (ironically, this one wasn't so rhino-looking). The Unicorn (Elasmotherium sibiricum) is often confused with the Woolly (Coelodonta antiquitatis) because of their similar appearence: however, the latter was not larger than modern white-rhinos and had two horns as well; the former was much larger (5 tons, like a modern bush elephant) and with one single horn... perhaps as long as a grown man, and put on the front rather than upon the nose: hence unicorn rhinoceros. Both lived in the Ice Age in cold climates, alongside mammothes in northern Asia, but the elasmothere was southerner than the coelodont; the latter lived alongside the other, more popular woolly, (guess what). Interesting that both woollies have left soft part of their bodies other than bones, hair included. While the "unicorn rhinoceros" is often said to have been the inspiration of that other unicorn when still alive, but this is probably a legend. About Indricotheres (or Paraceratheres, depend on who you ask), they deserve their own entry below.
Brontomammal has many names: Paracera-Indrico-Baluchi-therium
- Here is Our Majesty, the biggest land mammal ever lived - though some recent research seems to indicate that some mammoths were heavier, but certainly not as tall. Despite its really gigantic size - it was as tall as an apatosaur up to the shoulders, and weighed as three elephants or, better, as three T. rexes - it still had a quite slender, elegant frame: a sort of muscular giraffe with long neck, small hornless head, and long, slender limbs. Its behavior itself was probably more giraffe-like than rhinoceros-like, browsing the tree tops. In short, it was the new mammalian brachiosaur. Lived at the middle of the Cenozoic (the Age of Mammals), and was only the biggest member of a whole group of extinct "rhinoceri" (better, rhino-relatives): the Hyracodontids, most of them were horse-sized and more similar to horses than to rhinoceros. Our record-holder is also a prime example of I Have Many Names among prehistoric critters: now called Paraceratherium, its traditional names are Indricotherium and Baluchitherium.
- Chalicotheres are the best example of Mix and Match Critter among prehistoric mammals. They had the head of an horse, the body-shape of a gorilla, and sloth-like forelimbs with hooked claws for pulling down branches or excavating the soil in search of roots: some nickname them sloth-horses. A very successful group of hoofed mammals, distantly related to horses and rhinos (like the aforementioned brontotheres); chalicotheres roamed for a long time in most continents, and some think the famous "Nandi Bear" that could live in modern African rainforests is just a surviving chalicothere. The two most well-known family-members are the north-american Moropus and the Asian namesake Chalicotherium - the latter was even stranger since literally knuckle-walked like a gorilla. The latter was portrayed in Walking With Beasts, along with another species, african Ancylotherium - maybe the last chalicothere, unless the Nandi Bear....
- South America was isolated from other continents for most of the Mammal Age, and thus its fauna developed in its own direction. There were not only elephant-size sloths and tank-like glyptodonts: there were also less-armoured but still odd-looking "ungulates", not related with any modern animal today, but similar in shape/size to camels, horses, hippos, buffalos, elephants, rhinos, hyraxes, and even chalicotheres (a great example of Convergent Evolution). The two most represented are Macrauchenia and Toxodon. Macrauchenia was a bit camel-like; often depicted with a floppy, elephantine nose because of the shape of its skull, but we don't know if it really had this thing. Toxodon was more like a stock-built, no-horned buffalo, but it has also been compared with a rhino or a hippo. These two guys lived during the Ice Ages in South American grasslands ("pampas"), and were among the latest members of their groups; but other relatives lived much earlier, always in South America.
- Once, "ungulates" (hoofed mammals) were believed a natural group of mammals; now we know that several mammalian lineages reached the ungulate body-plan independently, and they do not make a real ensemble. Those which lived at the beginning of the Cenozoic were rather undifferentiated each other, and did not resemble most modern hoofed mammals. The two most famous are the small "ur-horse" Eohippus/Hyracotherium/Protorohippus and the large Uintatherium, both from the Eocene epoch: among the other eocenic "ungulates", Coryphodon and Phenacodus are frequently portrayed in books. Coryphodon was perhaps the first land mammal to exceed 1 ton in weight, and was rather similar to an hippo in shape. Phenacodus was not larger than a dog: with its several small hoofed digits, it was similar to Eohippus with a very long tail, and it is often mentioned as the prototypical "basal ungulate". Just like Eo/Hyraco/Protorohippus, Phenacodus could have been a possible prey of the famous giant bird Gastornis; while the massive Coryphodon and Uintatherium were too powerful to be threatened by any predator when adults, like modern rhinos and elephants.
From deer to whales
Up to eleven trophy: Megaloceros aka the "Irish Elk"
- Now we enter the world of the most successful ungulates today, Artiodactyls (even-toed ungulates), and how could make this without starting with the most spectacular extinct deer (and one of the most astonishing mammals ever)? But wait: even though it is commonly referred as the "Irish elk", Megaloceros (more precisely Megaloceros giganteus, also called "Megaceros" in older sources) was more related with European fallow-deer. Maybe it was not the largest deer ever (being moose-sized), but its antlers were another stuff: they could make the modern mooses' ones appear insignificant in comparison. Each one was as long as the entire animal's body, and each one weighed more than 100 kg. Obviously, only males had such a thing above, as most modern deer. Some scientists said that just this headgear was the cause of its extinction, having grown too much, and making the animal too clumsy... but this is unlikely; if they actually were too big, evolution would have made it smaller at one point, simply. Megaloceros lived in Europe in the Ice Ages alongside woolly mammoths and other large mammals, and was possibly prey for ancient human-ancestors; its nickname "irish elk" is due to its remains are very common in Oireland.
- Many prehistoric ungulates resembled deers in body-shape and head-shape, but again, not all were members of the Cervids (the deer family) like Megaloceros. Many of them had very unfamiliar-looking horns/antlers above their heads. Among pseudo-deers, the most portrayed are Synthetoceras and Sivatherium. The former was a distant camel-relative, but was antelope-shaped and also with a bit of rhino inside: it had three horns, two of them were antelope-looking, but the third one was on its nose and was forked just like that of Brontotherium, though longer and more slender. Sivatherium was moose-like and very large (2.5 m tall at the shoulder), and had deceptively moose-like pseudo-antlers: it actually was a giraffe relative, a sort of short-necked giraffe. Just about this detail: remember the classic Lamarckian "lenghtening of the giraffe's neck" we have learned at school? Indeed, no other extinct mammal has has such a long neck other than our giraffe: modern animals often are not so overshadowed by their prehistoric relatives, really.
- Bovids (the group containing buffalo, sheeps, goats and antelope; that is, all ruminants with true horns) are the most successful ungulate group today, and are very diversified: their prehistoric relatives were not much different in their appearence. We can mention however the Giant Bisons which lived in Ice Age North America. There were many species of them, some were larger than their present-day relatives and often with more developed horns as well; these traits were perhaps to defend themselves against prehistoric lions (see further). Only one specie of bison still remains in today-America.
- In prehistory, extinct relatives of camels and llamas were very diversified: the great majority of them were North American, where they started their evolution. Some were even taller than our modern dromedaries: Aepycamelus was a sort of giraffe-like animal with very elongated neck and limbs. Other "camels" were more antelope-like and runned the ancient North American plains. The well-known specializations for desert-life has appeared very recently in camel story, and regard only modern Old World species: their ancient North American relatives lived mainly in grasslands, thus is unlikely they would have fat-storing humps and resistence against thirst.
- Many hoofed mammals of the distant past were pig-like in shape: indeed, the pig-frame was the most primitive among "ungulates", still retained by some modern hoofed mammals, the best example being boars, peccaries and also the tapir (which is a perissodactyl). Most prehistoric pseudo-boars were small, but some were not: Entelodonts are the most striking ones. They were bison-sized at the most, and had several bony knobs on their head and jaws, resembling giant warthogs, but their tusks were much smaller than a warthog's or a babyrousa's, and didn't protrude out of the mouth. Their food habits are still unclear: they might be scavengers that drove away small predator from their kill, but also ate vegetation and might even be active hunters sometimes. North American Daeodon (also called Dinohyus) is the largest and one of the most depicted entelodont. Walking With Beasts has shown an unnamed Asian relative, and affected its appearence to make it scarier, exaggerating the opening of its mouth.
- Andrewsarchus is one of the most enigmatic mammals, from the first part of the Cenozoic (the Eocene period). Only a skull is known, about 3 ft long and vaguely wolf-like. Some argue it was the largest carnivorous land mammal ever, but we haven't any proof about that; it might be omnivorous instead. It is often depicted as a scavenger of large herbivores' carcasses, but has also been shown as an active hunter. Andrewsarchus was traditionally considered to be closely related to the much smaller Mesonychids. However, later phylogenetic studies indicate that it might have actually been a close relative of the aforementioned entelodonts (though obviously any phylogenetic placement is only tentative at this point).
- The mesonychids were the first meat-eating mammals which obtained a size larger than a house cat. Rather dog-like or hyena-like in shape, they had hooves in their feet similar to modern pigs. Once, mesonychians were considered the ancestors of whales, because their skull (specifically their teeth and earbones) resembles that of the most primitive cetacean known, Pakicetus. We know now that the hippopotamus is the closest relative of whales and dolphins. The fossil record of prehistoric hippos is poorly known; on the other hand, the similar-looking Anthracotheres have a rich number of species described. They were probably the closest hippopotamus relatives, or even their ancestors. The main difference with hippos is their much smaller mouth; they probably didn't "yawn" like hippos do today.
- All mammals were small and rodent-shaped in their evolutionary beginnings. Some became larger and more derived after the extinction of the dinosaurs, but none to the same level as whales. The first whale ancestors appeared only 10 million years or so after the non-avian dinosaurs' extinction. Once thought to have descended from doglike mesonychids (see above), whales are now thought to be artiodactyls (even-toed ungulates), such as camels, pigs, cattle, deer and particularly hippopotami. The first whales may have descended from the aforementioned anthracotheres, or possibly Indohyus ("Indian pig"), which was only discovered in 2007. They probably spent much of their time on land, feeding on dead fish and drowned animals. Ambulocetus (the "walking whale") is a good example of this: still four-limbed, it was already a good swimmer, but still resembled anything but a whale. Walking With Beasts showed it as an ambush-hunter of small land-mammals, like a modern Nile Crocodile; actually its lifestyle is unknown. Maybe Ambulocetus was a specialist fish-hunter like modern otters.
A dinosaur of whale: Basilosaurus
- Among the first fish-shaped cetaceans, Basilosaurus reached the length of a modern baleen whale, but was much more slender, sometimes mentioned "eel-like" (by the way, it was still a whale!). When first discovered, its elongated shape was misidentified for a mosasaur-like marine reptile: hence its strange, dinosaurian-sounding name ("king lizard"). At that time, all whales still were active hunters, like modern orcas and sperm whales, but still with differentiated teeth: pointed the anterior ones, serrated the posterior, an old legacy which betrays their origins from land mammals. The first filter-feeders appeared much more recently, when our planet turned colder and immense shoals of krill began to float in polar waters. Other cetaceans, however, remained small and active predators, originating our dolphins. See also here to learn more about this fascinating story.
- Among those ancient dolphin-like cetaceans, some reached very unusual traits compared with the modern ones (even though our Narwal is not far away): Squalodon ("shark-toothed") had serrated teeth similar to a shark; Eurhinodelphis ("good-nosed dolphin") had a prominent upper jaw similar to a swordfish as well as the unrelated ichthyosaur Eurhinosaurus. But the most astonishing is Odobenocetops the "walrus whale", with its two long tusks protruding backwards, and asymmetrical just like the modern single-tooth of the narwhal (in both case, the overgrown tooth is the left). The function of both the teeth of the odobenocetops and the tooth of the narwhal is still uncertain (maybe courtship device). Of course the Odobenocetops was the chosen cetacean in Sea Monsters as a prey of the giant shark "Megalodon", just because it looks cool.
My, what big teeth you have: Leviathan
- A recent discovery (2008) made in Peru, Livyatan melvillei possesses what may be the largest functional teeth of any animal. Full stop. The size of the partially preserved skull indicates that Livyatan reached a length between 44-57 feet, possessing a head three meters long. It was quite similar to the modern sperm whale, only it had teeth in both of it's jaws. And these teeth were massive, at their largest growing to a little over a foot in length. It is theorized to be one of the area's apex predators, along with the giant shark C. megalodon, who lived in the same area at the same time. It's also theorized that they may have had a similar taste in preferred prey too; baleen whales. It's also one of those prehistoric animals who's name is a reference, too. "Livyatan" is the Hebrew name for the legendary biblical sea monster Leviathan and "melvillei" is named after Herman Melville, the author of Moby Dick.
From sloths to bats
- One of the largest land mammals that ever lived, Megatherium had the same size of an elephant or a T. rex: reached 5 m when fully erect, and its name means...well... big beast. Lived just few thousands years ago in South America, and ancient humans knew it, to the point that they actually might have used it and other relatives as a... living pantry! Megathere's remains have been discovered in ancient caves, and it is said that some human hunters enclosed some of these animals in those caves. In old portraits, Megatherium was classically shown with a horse-like head and sometimes a giraffe-like tongue to reach foliage on the tree-tops; the horsehead and giraffe-tongue are probably mere fantasies, but the high-browsing habits aren't; indeed, the robustness of its body allowed it to stay only on its hindfeet (which, curiously, had only one claw each), while the three-clawed forefeet were used to pull down branches. Actually, our "big-beast" was not a horse o a giraffe relative... was a sloth. More precisely, the stock animal within the group called “Giant Ground Sloths”, related with anteaters and armadillos, not to ungulates. Megatherium represent the Up to Eleven example, but many other "giant sloths" weren't so giant-things (even though still large by human standards). Very strongly-built and weaponed with enormous claws, they were actually capable to walk around with their body upright, a bit like giant bears. Being members of the Xenarthran group, they were prevalently South American (some of them migrated to the North however) and had primitive teeth: nonetheless, they were so well-adapted to their environments that they flourished for almost the entire length of the Mammal-Ages: they got mysteriously extinct only few thousand years ago. It's also worth noting that modern sloths are just members of the same group, but specialized to the familiar tree-living style. Their slowness is arguably an evolved trait to mimetize them within the canopy; giant ground sloths were arguably faster-moving, like a modern giant anteater.
- After Ankylosaurs went extinct, evolution decided to create their mammalian equivalents: the glyptodonts. They were Xenarthrans as well, but related to armadillos rather than to sloths. Lived in South America for dozen million years, before going extinct only few thousands years ago: in short, they had the same identical history of their cousins, the giant sloths. Both groups were veggie-eaters (despite giant sloth might be at least partially scavengers), and when adult, they feared no predators except humans. There is a secret behind giant sloth's and glyptodonts' success: their backbone. It was far, far stronger that every other mammal, thus permitting them carrying such heavy bodies around withouth suffering back pain. Glyptodon is the most well-known glyptodont, but it's also worth of mention Doedicurus: with its mace-like tail, it was the most Ankylosaurus-like of them all. These were among the biggest glyptos, and thus the most depicted. Talking about glyptodonts' armor, it was the most powerful among every land-vertebrate (tortoises excluded). It was made by a single piece made by several ossicles fused together, smooth and usually round-shaped, unlike ankylosaurs whose armor was more flexible and spiky. With their compact frame and rigid armor, Glyptodonts were probably slower-moving than ankylosaurs, but still faster than a Galapagos' tortoise. Despite these differences, the glyptodont's armor was astonishingly similar to an ankylosaur's; only the upper parts of the body were covered, the underbelly was unarmored like ankylosaurs and hairy like modern armadillos; the head had a "shield" again like ankylos, and their tail was also covered by bone. Like Megatherium, also Glyptodon was known by ancient humans; but we are not sure what was the real thing that made these amazing animals extinct: climatic changes? Human hunting? Or what? Now, only far smaller xenarthrans survive; armadillos, tree-sloths and true anteaters (sadly, the natural history of anteaters is poorly-understood).
- The rodents' fossil record is very scant: no surprise, since they are so small, and small animals usually hardly fossilize unlike the large ones. Even though most ancient rodents were similar-looking to ours, there were also some striking guys in the past: for example, Castoroides was a land-living beaver-relative as large as a black bear; Ceratogaulids had a couple of hornlet on their nose; while several South American capybara-like forms, such as Phoberomys, were cow-sized and the largest rodents ever. It's not a casual connection, that modern-day capybara (South-American as well) is the biggest modern rodent: as already said, South American mammals were, and still are, very unfamiliar to a North American or European observer. On the other hand, Lagomorphs (rabbits, hares and pikas) had always had the same small-size and look they still preserve today. They are a sibling group of rodents, with a similar dentition but more specialized to eat grass. It’s hard to believe, but the affinity lagomorphs / true rodents was definitively proven only few years ago. Before, rabbits and so on were once thought not related at all with rats and squirrels!
After dinosaurs... squirrel-monkeys: Plesiadapis
- Another group of prehistoric mammals which have recently been found to be related with rodents is a much more surprisingly one: Primates. Given the subjective relevance of this group by our standards, they are described in a section on their own. However, one close relative of primates can be mentioned here: Plesiadapis. Living at the very start of the Mammal Era, it was a sort of middle way between a squirrel and a monkey, with a lemur-body but gnawing teeth like a rodent. Living in trees, it resembled a lot some ancient mammals which lived in the former Dinosaur Era, particularly Purgatorius (see The Origin Of Mammals. Today, there’s still an animal which strongly resembles Plesiadapis, though devoid of gnawing teeth: the Tupay. Improperly called “tree-shrew”, the latter was once classified as an “insectivore” (see below).
- Traditionally we have put in the “Insectivores” group all those mammals whose anatomy is comparable to that of most Mesozoic mammals: small size, generic mouse-like look and non-specialized teeth. Actually modern insectivores (bug-eaters) are very different among each other; while the most commonly known (hedgehogs, moles, shrews) are closely related, many other less-familiar “insectivores” (tupays, tenrecs, sengis) are not. Their resemblance is just due to the fact they still preserve a body-plan similar to the most common one in the Mesozoic, while non-insectivoran mammals modified it becoming more recognizable. Several "insectivores" are known from the Cenozoic's fossil record, but they, being usually small, are rather uncommon like rodents. Maybe the most famous and specialized is Leptictidium, a hopping animal similar to a 3 ft long kangaroo with shrew-like teeth and (maybe) a shrew-like mobile nose. Not related with any modern mammal, Leptictidium appears the main character in the first Walking With Beasts episode, and was also the inspiration for Scrat in the Ice Age films.  More shrew-like, Zalambdalestes lived before the non-avian dinosaurs’ extinction—Late Cretaceous, along with guys like Velociraptor, Oviraptor, and Protoceratops. Traditionally believed an “insectivore”, recent research seem suggest it was a proto-marsupial.
- During mammal evolution, some groups reached the ability to glide. The most known extinct glider is perhaps Planetetherium, belonging to the same group of the so-called “flying lemur” of our days. But no other mammalian group managed to fly actively like bats. Just like birds, bats are a very poorly-known group in fossil record, both for the same reason: their skeleton is way too fragile to fossilize well. Despite this, awesomely well-preserved bat remains have been discovered in the most famous fossil deposit from Early Cenozoic: Messel Pit, in Germany. This deposit has also many, many other early mammals: among them, the aforementioned hopping bug-eater Leptictidium and the basal ungulate Propalaeotherium have been recently made famous by Walking With (even though the propalaeothere wasn't an early "horse" as said in the program). These and other mammals from this deposit are so well preserved that even their fur and stomach contents are known. In short, we know'em almost like they were still-living animals. The very first bats have been discovered here, and show us all the traits associated with their modern relatives: fingered wings, large ears, and even structure for echolocating are known from these finds. This has lead scientists to make an intriguing hypothesis: perhaps some sort of gliding proto-bats were already living on Earth before pterosaurs and non-avian dinosaurs disappeared? This would also mean bat-winged critters did exist at the Age of Dinosaurs, thus making the "Mesozoic bat-winged fliers" trope partially Truth in Television.
- Among the numerous mammals found in the aforementioned Messel Pits, also worth of note are two animals belonging to a very ancient group: Eomanis and Eurotamandua are the first known pangolins. As expected from Messel animals, their remains include soft parts of their body. Their shape was already that of their modern relatives, with long muzzles and a long sticky tongue to catch ants and termites. However, their external look was very different from each other: Eomanis had the familiar tile-like scales covering most of its body, and was virtually identical to modern pangolins; Eurotamandua was hairy and resembed more a modern Tamandua than a pangolin—indeed, it was long classified as a Xenarthran anteater. The names of both animals are referred to this older classification: Eomanis means “dawn pangolin”, the more obvious Eurotamandua means “European tamandua”.
From kangaroos to echidnas
Giant rhinowombat: Diprotodon
- Australian mammalofauna hasn't changed much since the non-avian dinosaur extinction (not counting human influence of course): there have always been marsupials and monotremes in the Land Down Under. Since modern Australian mammals are already so bizarre-looking, how would their predecessors have looked? Not unlike their descendants, really; but some were a bit larger. The Up to Eleven examples were the herbivorous Diprotodonts, called after their most well-known member: Diprotodon. Related with modern wombats, they were a lot bigger: the largest species reached the size of a rhinoceros. With their robust limbs and massive body, they literally resembled hornless rhinos, and resembled also several extinct “Ungulates” (like the South American Toxodon or the early Coryphodon). Indeed, Australian marsupials have made an extraordinary case of Convergent Evolution with “placental” mammals. Among differences between diprotodonts and ungulates, other than (of course) their reproductive system, is that the former had the same rodent-like incisors seen in modern wombats.
Giant koalaroo: Procoptodon
- After diprotodonts, the biggest known prehistoric marsupials were kangaroos. These are a very recent-evolved and specialized subgroup of Australian marsupials related with koalas, wombats and diprotodonts. Together, these animals (plus others) make the most diversified marsupial subgroup, incidentally called “Diprotodonts” as well. One of the biggest extinct kangaroos was Procoptodon. 10 ft tall (twice a modern red-kangaroo), it had a short stocky tail and a flat, round snout; the latter has given to it the nickname “Koala-faced kangaroo”. Despite these difference, its bodyplan was the same of its modern relatives, being well-suited to jump (though probably less-agile). But unlike modern roos, Procoptodon was probably a browser of high tree-foliage no other animal could reach. As a whole, kangaroos are considered the Australian equivalents of the hoofed mammals from every other landmass. Indeed, the “koalaroo” made this even more than the others: its feet had only one toe each, ending with a true horse-like hoof.
- Ancient Australia seen also an unique animal which has no modern relatives: Thylacoleo, (“pouched lion”) nicknamed the “marsupial lion”. It was so-called because its body shape, sharp claws, and short head remember modern big-cats; but unlike the latter, it had rodent-like incisors instead of the classic fangs. Scientists once thought it was indeed vegetarian like a rodent; they now know it was predatory. Not only that, it could have been the most efficient mammalian predator ever. Despite being not bigger than a jaguar, some think it was able to kill even Diprotodonts and giant kangaroos! There was another marsupial which convergently resembled a cat even more than the former: the similar-named Thylacosmilus (“pouched smilodont”), nicknamed the “marsupial sabertooth”. The same size of the “marsupial lion”, Thylacosmilus had two ever-growing upper fangs virtually identical to actual sabre-toothed cats, and possibly used in the same way. To protect these fangs, the lower jaw has a couple of bony “sheaths” covered with skins, which could have given it a curious “drooping lips” appearance. The most curious thing, however, is Thylacosmilus was not Australian at all: it was South-American, and lived before true sabertoothed cats (Smilodon populator) outcompeted it in South American plains. Today, possums and possum-like animals are the only marsupials left here. Their Aussie relatives were more lucky: before the Ice Ages, placental mammals didn’t manage to reach the Land Down Under (rats-bats excluded). That’s why kangaroos, wombats and so on are still-living today. Sadly, their enlarged relatived missed the opportunity, perhaps due to a new kind of colonizers arrived only some thousands years ago: humans.
Sonic the giant echidna: Prehistoric long-beaked Echidnas
- Prehistoric marsupials were not the only oversized mammals in ancient Australia: monotremes, too, were amazing. Modern monotremes are the most archaic still-living mammals, and are well-known because they have preserved the original habit to produce eggs instead of alive newborns. Their extinct relatives are poorly-known in fossil record, and were not different than the modern ones (platypus and echidna). However, one member of the echidna group reached the size of a sheep: Zaglossus hartmanni, closely related with modern long-beaked echidnas. It’s weird that the astouning fauna which lived once in Australia was totally missed by the Walking With producers. With giant koalaroos, giant rhinowombats, rat-toothed uberlions, and giant ancestor of Sonic available (not to mention Up to Eleven komodo-dragons and running “terrorbirds”)… they have missed another perfectly good opportunity.
The origin of Mankind
Are we really descended from Apes? Ancestral Primates
- Man-Is-Descended-From-Apes. Man-Is-Descended-From-Apes. Man-Is-Descended-From-Apes. NO!!! Man didn't descend from other modern apes (that is, chimps, gorillas, orangutans, gibbons): we humans and chimps/gorillas/orangutans/gibbons all descend from a common ancestor, often called "ape" in popular media but no more closely related to chimps as it was to ourselves. Primate evolution is of particular interest for obvious reasons, but it'd be a too long argumentation here, and would go much beyond the aim of this trope: talking about the most interesting extinct critters. Indeed, most ancient non-hominid primates weren't particularly interesting compared to their modern descendents: their look was a lot monotonous, some resembled more a lemur, other a tarsier, other a monkey, and other modern apes. Most of them were small as well, although oversized baboons and overgrown lemurs are known in fossil record. We can mention one representant for each lineage, from the furthest to the nearest to humans. Adapis was an ancient relative of lemurs; Omomys was a sort of proto-tarsier; Aegyptopithecus was one of the first true monkeys. For exctint apes, see below.
An overview about Hominids: Prehistoric Hominoids
- Until he extends the circle of compassion to all living things, man will not himself find peace. That's why the closest human ancestors are at the bottom of this page dedicated to Mammals. Technically a subset of Primates, hominids is a group of animals somewhat controversial to talk about, for obvious ethical reasons: so we'll talk only about those which were not clearly human, and let's end our Time Travel with australopithecines. The hominid group itself fluctuates in definition, going from all beings closer to us that to chimps, to all things closer to us that to baboons; the most widely accepted use includes the great apes; that's is, all beings closer to us that to gibbons, and that's the one to be used here. Anyway, this family split off from gibbons about 15 million years ago, and not long after, it split off in two main branches: The Asian branch, nowadays made up of the 2 species of orangutan; and the African branch, which includes gorillas, chimps and us. Focusing in that latter branch, the branch gorillas belong to splits off from the main branch 7 million years ago, and the chimp branch splits from the branch that would lead to us shortly after. That latter branch was subject to selective pressure due to having to adapt to the harshed savannah environment: The 2 modern chimp species split from each other at roughly the same time our branch split from Lucy (see below).
Between a Bigfoot and a Silverback: Gigantopithecus
- Due to jungles not being good places for fossilization, not many species of extinct apes are known. The most notable one is Gigantopithecus, a relative of the orangutan (that also exhibited gorilla-like characters). Its name means "giant ape", and with reason. It measured up to 10 feet when standing upright, two times bigger than a modern silverback gorilla: a sort of middle-way between a Real-life gorilla and King Kong. Not only that, it was discovered near the Himalayas: could it be the mythical Yeti? If so, this would mean it could be still alive (don't be too excited: experts say it's highly improbable that such a large animal has remained unobserved for such a long amount of time...). Sadly, the only certain thing we know about it is just a lower fossil jaw; the shape of the teeth show us it was a plant-eater, possibly specialized to a bamboo-based diet, to the point that some experts think competition with the giant panda actually drove it to extinction. Other extinct apes were once considered true human ancestors, or at least the common ancestors of apes and humans, but now are believed only distant relatives which shared some apparently human-like traits. Proconsul, Dryopithecus, "Ramapithecus" (now Sivapithecus), and still others, are often mentioned in old textbook for this, but now their relevance is drastically fallen down.
Nearly humans: Australopithecines
- The beings included in the Australopithecines evolutionary grade are generally ape-like, being to the rest of apes what baboons are to other old-world monkeys: savannah-adapted relatives of a mostly forest-living group. As we get torwards modern times, the species of australopithecines become steadily more bipedal, adapt their feet to ground locomotion, and generally become more human-like. In the past, all the closest relatives of the genus Homo were classified in the genus Australopithecus (“southern apes”, because were found in Africa). As Science Marches On, recent taxonomical revisions have split off 2 other significant genera from Australopithecus: the earlier Ardipithecus, and the specialized Paranthropus (“near-human”). The latter included some robust, man-sized species (P. boisei, P. robustus) adapted to a strict diet made of bamboos or other fibrous plants; the other australopithecines were much smaller and more gracile, and were more generalist-feeders.  Significant species of Australopithecus are A. afarensis, best known for the specimen found in 1971 and known as Lucy; and A. africanus (the first discovered australopithecine, in 1925), likely an ancestor of the genus Homo. But the following story is a totally different one.