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The earliest mammals were a very odd bunch of creatures, downright bizarre compared to the modern forms. They generally had sprawling gaits, some of which with odd configurations such as more erect forelimbs. Many were venomous, with venom spurs similar to those of modern platypi being the norm. Nearly all were constrained by epipubic bones: great at stiffening your torso, so much so that you can't undergo long term pregnancy and are forced to give birth to larvaenote , that need to be shielded in a pouch. These odd animals diversified into a variety of groups alongside the dinosaurs. Docodonts were a rare but successful lineage that spawned forms like the aquatic Castorocauda, the arboreal Agiloconodon and the digging, mole-like Docofossor. Eutriconodonts were a lineage of specialized carnivores that spawned into predators capable of giving carnivorous dinosaurs a run for their money and may even have taken to the skies. Multituberculates were a lineage of superficially rodent-like animals with a weird chewing mechanism that quickly rose to dominance across the globe, more common in some areas than even dinosaur fossils. Most of these weirdos disappeared by the mid-Cretaceous, probably due to the spread of flowering plants, which affected ecosystems across the land. Therian mammals, which include today's marsupials and placentals, instead took over, even before dinosaurs became extinct. However, South America was still dominated by a group called meridiolestians, which continued to be the dominant mammals until the mass extinction that also killed off the dinosaurs. Even then they had two last hurrahs: the giant herbivorous Peligrotherium and the much younger mole-like Necrolestes. The exception to these were multituberculates, which did initially diversify alongside therian mammals and did in fact dominate the land mammal faunas even after dinosaurs disappeared, culminating in the panda-sized Taeniolabis. However, they failed to recover their number in Asia, and in the resulting vacuum a lineage of placentals, the rodents, made their debut. Soon, they spread out of Asia and outcompeted multituberculates, which quickly declined until they eventually became extinct.
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, which wiped out almost everything in this folder): there have always been marsupials and monotremes in the Land Down Under. Since modern Australian mammals are already so bizarre-looking, how would the ones we killed off have looked? Not unlike their surviving contemporaries, 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.
- After diprotodonts, the biggest known prehistoric marsupials were kangaroos. These are a very recently-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 body plan was the same of its modern relatives, being well-suited to jump (though probably less-agile). But unlike modern kangaroos, 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. Unlike their modern counterparts, these kangaroos were far too large to hop. Instead, they had large buttocks and their ankle bones suggested that they walked in the same way as human beings. Related with Procoptodon was Sthenurus, which showed a similar size and the same basic traits. Interesting that some smaller prehistoric kangaroos might have been partially carnivorous or even active predators, like Ekaltadeta.
- This distant relative of koalas and wombats is interesting for mainly one feature: the shape of its skull has lead many scientists to believe it had a short, tapir-like proboscis! (There is a possibility of this not being the case, as more recently they have been reconstructing it to look like a more generic giant wombat. Many other reconstructions still keep the trunk, for obvious reasons.) Its grasping claws show that it was most likely a browser, similar to the giant ground sloths and chalicotheres mentioned below. If it did have this "trunk" like scientists theorize, it could have been very helpful in grasping branching to pull leaves off of.
- Modern Australia also was home to an unique animal which has no close modern relatives, with its contemporary the koala, wombat and the Diprotodonts being its closest relative: Thylacoleo, (“pouched lion”) nicknamed the “marsupial lion”, with its species name, carnifex, meaning "executioner". 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, and guillotines instead of molars that it used to slice the neck of the prey to kill it instantly. 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! The combination of Velociraptor-like claws and guillotines proved an awesomely efficient killing arsenal. If not for the fact there were two larger, faster, equally well-armed reptilian predators-Quinkana, a terrestrial crocodile, and Megalania, a giant lizard the size of a bison, it would have been the continent's unrivalled killer. All three predators, modern animals adapted to today's world, met an untimely end at the hands of humans, as they set fires to grow different plant species, which starved their prey to extinction. The same fate occurred to all species of marsupial wolves, the other main mammalian predators of prehistoric Australia other than the lion, whose only species survived in contemporary age (the famous "Tasmanian wolf" Thylacinus cynocephalus, lit. "pouched dog with a dog-head"), has missed the chance to be observed by modern wildlife lovers only for a bunch of decades.
- Though not "marsupials" per se, sparassodonts were a closely related lineage that dominated South America. The largest and most well known of these was Thylacosmilus, the sparassodonts turn at producing a saber-toothed predator. 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. Together with other less-striking sparassodonts such as the bear-like Borhyena and the weasel-like Cladosictis, Thylacosmilus long occupied the top predator niche in competition with terror birds and large crocodilians... before becoming extinct for unclear reasons. It was long thought that true placental saberteeth outcompeted them to extinction, but it appears South America's top predator guilds were gone long before placental carnivores arrived. Nothing Is Scarier...
- More surprising is the presence of sabertoothed predators that lived alongside the dinosaurs. Deltatheroideans were distant relatives of modern day marsupials that specialized into predatory niches, and have even preyed on dinosaurs. One genus, Lotheridium, had long canines, making it a sabertooth long before the more iconic placentals and Thylacosmilus evolved.
- Prehistoric marsupials were not the only oversized mammals in ancient Australia: monotremes, too, were amazing. Modern monotremes are the most archaic extant 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 astounding 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 Knuckles available (not to mention Up to Eleven Komodo dragons and giant running birds)… it's unfortunate that such an episode never materialized.
The elephant's clan
Columbian emperors in the Dzungarian steppes: Columbian Mammoth and Steppe Mammoth
- 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 mammoth species in Real Life, and as a group they lived across most of the Ice Ages. The largest ones did challenge Paraceratherium (see later) as the "biggest land mammal ever" title, but only if you count their weight (Paraceratherium would ever be taller than every mammoth, thanks to its giraffe-like body frame). The most famous is the American Columbian Mammoth; giant mammoths 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. Anther mammoth as large as the latter was the Asian steppe mammoth. The lower popularity of the giant mammoths (despite their size) compared to the woolly one is probably due to their more normal, less-spectacular appearance. 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. Think Mûmak from ''The Lord of the Rings''. Mammoths thrived even after the end of the ice age, as there was more food available. Therefore it was almost certainly humans changing their habitat that drove them to extinction, evidenced by the fact populations on islands lasted much longer than in the more easily accessed mainland areas.
- 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 others lived elsewhere; there were some dwarf mammoths living on the Channel Islands off southern California and on Wrangel Island off eastern Siberia (the latter managed to survive until about 4000 years ago, contemporaneous with Ancient Egypt). 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 Ancient Greece are way too fragmentary due to geological forces (earthquakes and volcanoes) to allow something as fragile as a skull to survive intact. These species were all driven to extinction by humans.
- 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 manatees.
- Though are very rarely mentioned, prehistoric and modern hyraxes are very interesting. Today, hyraxes 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 Embrithopods (see Arsinoitherium below), 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 (including the aardvark) still-living here. Together, all these mammals have recently been grouped in the afrotheres (“African beasts”).
The lion's clan
Saber- scimitar- dirk- whatever- toothed cats: Machairodus, Homotherium, Megantereon, Dinofelis, and Xenosmilus
- 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 (named Machairodontines and not Smilodontines); 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; certainly, 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 speed just to escape these "cheetahs"). All of these species were killed off by humans. note
- 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. 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 canines 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 appearance 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, nimravids are wrongly treated as actual cats.
- True carnivorans (members of the order Carnivora) appeared soon after the start of the Mammal Age, but remained small and unspecialised 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 carnivorans, from bears to lions, wolves to walruses, descend from weasel-shaped critters. However, many small carnivorans 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.
- Pinnipeds (containing seals, sea lions, and walruses) don't have the most extensive fossil record. It was once theorized that they had evolved from two lineages: the true seals (also known as earless seals) from otters, and the eared seals (sea lions and fur seals) and walruses from bears. Currently, they are believed to have evolved from the otter-like Puijila, resulting in the relatively primitive Enalicarctos, before diverging even further. Worth mentioning is that Odobenidae, the family now only containing the walrus, was once a lot more diverse. Probably the most interesting member was Pelagiarctos, which appears to have sharp, shredding teeth like that of a hyena. It is believed to have been one of the top predators of the Miocene seas, feeding on prey ranging from other pinnipeds to the aforementioned Desmostylians.
- In the Early Cenozoic, at the time "true" carnivorans were still weasel-like, creodonts occupied the ecological niche ruled by modern large carnivorans. Very diversified in shape and size, their appearance included that of all modern carnivorans (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 Beasts as a formidable predator, but some hypothesise it was mostly a scavenger. But even bigger creodonts are known to science (for example Megistotherium), 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
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. This mammal is so strange that it is put in its own mammalian order, the embrithopods, fairly close to elephants and manatees (see Titanohyrax above for more on this).
- 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 Megacerops 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). Other more primitive rhinos include the short-limbed hippo-shaped Teleoceras (whose remains are extremely abundant in Middle Cenozoic North America), the forked-horned Menoceras (similarly to the distantly-related brontotheres), and the no-horned Aceratherium. (acera = with no horns). Other prehistoric true rhinos has unusual features such as prominent tusk-like lower incisors, still others were very small for rhino standards, not bigger than a sheep (and they were not insular forms), and potential preys even for small carnivores — contrasting with the almost-invulnerable modern animals. A group of close relatives of rhinos, the amynodontids (among these Metamynodon) were no-horned, hippo-looking and probably similar to hippopotamuses in habits. About indricotheres (or paraceratheres, depending on who you ask), they deserve their own entry below.
- 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. Toxodon was 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 pampas, and were among the last 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 Eocene "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
Rhinozelles and Mooseraffes: Synthetoceras, Sivatherium, Prolibytherium, Cranioceras, and Hoplitomeryx
- Many prehistoric ungulates resembled deer in body-shape and head-shape, but again, not all were members of the deer family like Megaloceros. Many of them had very unfamiliar-looking horns/antlers above their heads. Among pseudo-deer, 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 (2.5m 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 "lengthening 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 buffaloes, sheep, goats and antelopes; 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 appearance. We can mention however the giant bison 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 species of bison still remains in America. We can also mention Pelorovis, an large relative of the African buffalo with even longer horns, living in Africa before the apparition of modern lions; its misleading suffix, however, make thinking it was a prehistoric sheep (ovis = sheep in Latin).
- 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 (once called "Alticamelus", the "lofty camel") was a sort of giraffe-like animal with very elongated neck and limbs. Even taller was Titanotylopus ("titanic camel"), as tall as a giraffe. Other "camels" were more antelope-like and ran 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 resistance 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 and peccaries (which are artiodactyls) and also the tapir (which is a perissodactyl). Among extinct true boars, Metridiochoerus was related with the modern warthog but with straighter tusks. Among prehistoric pseudo-boars most were small (ex. Anoplotherium and the oreodontids), 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 babirusa's, and didn't protrude out of the mouth. Their food habits are still unclear: they might be scavengers that drove away small predators 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 appearance 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 ear bones) 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 (we can mention Hippopotamus gorgops, a close relative of the modern giant hippo but with extremely protruding, periscope-like eyes, as well as Kenyapotamus, which was once considered a "missing link" between hippos and peccaries); 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 dog-like mesonychids (see above), whales are now thought to be artiodactyls (even-toed ungulates), aka the group including camels, pigs, cattle, deer, and hippos (their closest relative). The first whales may have descended from the aforementioned anthracotheres, or possibly Indohyus ("Indian pig"). 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.
- 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, reptile-sounding name ("king lizard"); there was an attempt to rename it Zeuglodon to fix the error, but nomenclature rules prevented that. 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 narwhal 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 juvenile "Megalodon", just because it looks cool.
- A 2008 discovery made in Peru, Livyatan melvillei possesses what may be the largest functional teeth of any animal (that is, not counting tusks). 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 its jaws (think Monstro, but smaller). And these teeth were massive, at their largest growing to a little over a foot in length. It is believed 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. That said, they likely had a wide and varied appetite, as sperm whales do today. A tooth discovered Beaumaris Bay, Australia in 2016 seems to indicate that melvillei—or a closely related species—may have had a wider habitat range than previously indicated, and existed in the area for another two million years after the time period in which the Peruvian population of melvillei is known to have occurred. However, as we only have one tooth to go on, at the time of writing it's mostly speculation. It also happens to be one of those prehistoric animals whose name is a reference, too. "Livyatan" is the Hebrew name for the legendary Biblical sea monster Leviathan (note that the translation of the word "whale" in modern Hebrew is just "livyatan"), and "melvillei" is coined after Herman Melville, the author of Moby-Dick.
From sloths to rabbits
Big Badass Sloths: Megatherium, Eremotherium, Mylodon, Megalonyx, Megalocnus, and Thalassocnus
- One of the largest land mammals that ever lived, Megatherium had the same size of an elephant or a T. rex: reached 5m 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 horse head 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 hind feet (which, curiously, had only one claw each), while the three-clawed forefeet were used to pull down branches. Actually, our "big beast" was neither a horse nor 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 Age: 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 hide 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 herbivores (despite giant sloths might be at least partially scavengers), and when adult, they feared no predators except humans. There is a secret behind giant sloths' and glyptodonts' success: their backbone. It was far, far stronger that every other mammal, permitting them to carry such heavy bodies around without 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 ankylosaur-like of them all. These were among the biggest glyptodonts, 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 scutes 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 ankylosaurs, and their tail was also covered by bone. Like Megatherium, also Glyptodon was known by ancient humans; we now know human hunting wiped out these species, as the species on islands were the last to go, and as there is evidence of human hunting and habitat change in their habitat. 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. Today, rodents are the most successful mammalian group, with about half the species of all living mammals. Even though most ancient rodents were similar-looking to ours (ex the ancient squirrel Paramys, living in the Early Cenozoic), there were also some striking guys in the past: for example, Castoroides (yet another victim of humans) was a land-living beaver-relative as large as a black bear; Palaeocastor was another smaller land-living beaver which built corkscrew-like burrows in the ancient North American plains - a sort of predecessor of the modern prairie dog; Ceratogaulids like Ceratogaulus and Epigaulus had a couple of hornlet on their nose; while several South American capybara-like forms, such as Phoberomys and Telicomys, 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!
- 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 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. note 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 close to the ancestors of live-bearing mammals.
- 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 resembled more a modern Tamandua than a pangolin—indeed, it was long classified as an anteater. The names of both animals are referred to this older classification: Eomanis means “dawn pangolin”, the more obvious Eurotamandua means “European tamandua” (Tamandua is the name of a modern kind of anteater).
From bats to people
Flight of fancy: Palaeochiropteryx, Icaronycteris, and Planetetherium
- 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. Unfortunately, bats are a very poorly-known group in the fossil record because 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 Beasts (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 (see also Yi in "Birdlike Dinosaurs").
- The late Mesozoic and early Cenozoic saw the rise of the primates and their relatives from an ancestor fairly close to rodents. Living at the very start of the Cenozoic, Plesiadapis 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 Mesozoic, 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 above).
- 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 descendants: their look was quite 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 representative 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 extinct apes, see below.
- The largest lemur alive in Madagascar today is the gibbon-sized and endangered indri. However, long ago, there were truly impressive forms. The most well known is the orangutan-sized Megaladapis, also known as the koala lemur, notable for the shape of its skull, which most likely housed a bizarre trunk-like upper lip. There's also Archaeoindris, which came from a long extinct group known as the sloth lemurs. Most sloth lemurs resembled modern tree sloths, but Archaeoindris was more similar to an extinct ground sloth. Larger than a gorilla, this is thought to be one of the largest primates, second only to Gigantopithecus! Sadly, these and other similar creatures went extinct a mere 500 years ago when the first Malagasy settlers arrived in Madagascar.
- 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, at least amongst the religious. 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 harsher savannah environment: The 2 modern chimp species split from each other at roughly the same time our branch split from Lucy (see below).
- The popular idea of the human lineage starting with a quadrupedal ape and gradually turning more erect, as seen in the well-known image of The Ascent of Man, is probably not accurate: Human bipedalism, in contrast to those of birds and other extinct archosaurs, is based on a vertical spine and torso, and so the hands and feet operate at different levels. However, that is also seen in the rest of hominoids: In contrast with monkeys, whose default posture involves a horizontal spine and both hands and feet in the same branch, hominoids have a default posture where the spine is vertical, and the hands grab branches directly overhead. This can be seen in living apes, where the primary tree-dwelling gibbons and orangutans will default to a vertical posture even in the ground, while the more groundbound chimpanzees and gorillas exhibit quadrupedalism, but apparently independently evolved from each other (so their common ancestor, which is also our ancestor, didn't walk on its knuckles). In conclusion, the evolution of our gait, rather that being a transition from 4 legs to 2 so we could see better, was probably more akin to adapting a tree-dwelling position for use on land because we could see better. Gorillas weren't quite as pressured to keep their bipedal posture, and thus evolved an unique sort of quadrupedalism, avoiding species-wide chronic back aches and tendency to fracture hips.
- 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). 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 textbooks for this, but now their relevance is drastically fallen down. However, two apes here are of crucial importance for our purposes: Oreopithecus and Orrorin. Why? Because these two apes show fossils that hint at the very beginning of the human gait, with somewhat human-like pelvises and femurs. Today scientists, thanks to the study of the Molecular Clock, believe that Oreopithecus is just an evolutionary dead end of specialized hominid, while the Orrorin belongs to the clade that would ultimately lead to humans.
- 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 towards 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 they 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. note 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. The following story is a totally different one.
- The beginning of the Homo genus are still a mystery to paleontologists and paleoanthropologists everywhere. Earliest fossil evidence for their origin hints at a date of 2.5 million years ago. The first Homo were actually very much similar to australopithecines (which has indeed lead some scientists to believe these should be classified as a separate species), with the bigger differences being, at first glance, superficial. However, the elements that would make us humans are already well in the making: Homo habilis shows it best, for while sharing many anatomical traits with australopithecines, it's skull was already beginning to show more human-like features. With a slightly larger brain (620 cc in comparison to the 450 cc of earlier australopithecines) and a more specialized hand, this species was enables to achieve the first of many breakthroughs that would define humanity: fabrication of stone tools. These ones were still very crude, though, being mostly just broken rocks with a sharp edge. However, this also marked the beginning of a new behavioral pattern present in latter Homo species: the habit of eating predominantly meat. Meat has far more proteins than just seeds and roots, which in turn, would be a turning point for the millennia to come...
- Homo erectus marks perhaps one of the most important breakthroughts in human evolution. This species can, with relative certainty, be called the very first human. With an anatomical structure very similar to our own (their arms and legs now had human-like proportions and their cranial capacity bordered on 1000 cc), H. erectus was tall, lean and very agile, becoming the very first hominin to hunt big game, with evidence suggesting they often fought against larger predators for food. They had taken the art of stone tool-making to the next level, crafting versatile and compact "handaxes" that had multiple uses, and were often sharp enough to serve as sort of prehistoric knives. Homo erectus is also the first species thought to have learned to use fire, and was also for decades thought to have been the first hominin to migrate from Africa, and while recent evidence from Dmanisi, Georgia may call this into question, it's still by far one of the most successful hominin species in our direct family tree, having evolved nearly 2 million years ago and surviving until as recently as 50 thousand years ago, spreading all across Africa, Europe, Asia and even nearly reaching Oceania.
- Humans these days are a very varied species, with different peoples having different skin color, eye color, height or weight. With such variety, it's not that far a stretch to think that our ancestors had similar varieties. Such evidence is shown by the findings of Meganthropus, a sub-type of Homo erectus that apparently was as tall as 7 to 9 feet, making it a giant amongst hominins, probably resulting from natural selection by competing with the Gigantopithecus. Another example of this would be Homo heidelbergensis, a descendant from Homo erectus and very likely the common ancestor of modern humans and Neanderthals. this species in particular showed variations in height, ranging from an average human heights of 6 feet, to being as tall as 7 or 8 feet. Our last example, being by far the most peculiar, comes to be Homo floresiensis or "the Hobbit" as called colloquially. This species was most likely another descendant from Homo erectus, and distinguishes itself for it's ridiculously small size (barely around a meter tall). This species was found mainly on an Island known as "Las Flores" in eastern Asia. It is currently believed they were a result of Homo erectus that were stranded on the island (How they got there in the first place is still the object of much speculation) and adapted to the micro fauna of the island, eventually becoming this race of dwarves that lasted surprisingly up to the end of the Ice Age itself, nearly 12 thousand years ago.
- Around 500,000 years ago, the descendants of Homo erectus began diversifying all across the Old World. From the branch of Homo heidelbergensis, three species appear to have splintered cross the three continents. The most emblematic of these human species is the famous Neanderthal, which reigned through most of Europe, Northern Africa and Northwestern Asia for almost 200,000 years before the rise of modern humans. Another case, being rather recently discovered, is the Denisova hominin, of which only a tooth had been found. But since Science Marches On, scientist were able to determine it was a new species thanks to the ability to extract strands of DNA from the fossilized tooth and compare it with both Neanderthals and modern human's genome. This newly-discovered species populated mainly north-eastern Europe and the Middle East, and some speculate it may have originated on the Arabian peninsula. Last, but not least, our species began evolving from Homo heidelbergensis at around 300,000 years ago or so, developing what scientists refer to as "Archaic Homo Sapiens", that is, hominins well in the line of modern humans, but don't quite resemble modern humans just yet, with notable examples being the Florisband and Gawis craniums, which show notable transitional elements into Homo sapiens.