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The most popular kinds of extinct mammals described in Stock Dinosaurs (Non-Dinosaurs) do not match the huge variety of them in Real Life. Compared with dinosaurs and the other Mesozoic reptiles, prehistoric mammals have traditionally-been less-common in Fictionland (Everything's Better with Dinosaurs, useless to say it).

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. The primary exception seems to be mammoths and giant other ice age mammals, which are often used in pop-culture as a shorthand for the Pleistocene just as dinosaurs are for the Mesozoic.


Programs from the 2000s like Walking with Beasts and the Ice Age film series partially averted the trope, but even these shows didn't escape the Everything's Better with Dinosaurs fate: not only the well-known case of Ice Age 3: Dawn of the 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, some of them are compared in size with other extinct creatures here. If you want to see more about the truly-stock or the little-stock ones, see Stock Dinosaurs (Non-Dinosaurs).

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    The Earliest Kinds 

  • 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 undeveloped youngnote . 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 even flying squirrel-like gliders.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 still harbored a group called meridiolestians, which continued to be a prominent group of mammals until the mass extinction that also killed off the dinosaurs. Even after, 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 

Marsupial Tapir?: Palorchestes

  • 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.note . 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. Other examples of diprotodontids include the panda-like Hulitherium, the small Neohelos, and the "horned" Zygomaturus. An example of prehistoric true wombat is Phascolonus. Palorchestes was a relative of the diprotodontids, and is interesting for mainly one feature: the shape of its skull has lead many scientists to believe it had a short, tapir-like proboscis note  Its grasping claws show that it was most likely a browser, similar to the giant ground sloths and chalicotheres. If it did have this "trunk" like scientists theorize, it could have been very helpful in grasping branching to pull leaves off of.

Hopping or Walking?: Sthenurus

  • After the diprotodonts, the biggest known prehistoric plant-eating marsupials were kangaroos. These are a very recently-evolved and specialized subgroup of Australian marsupials related with koalas, wombats, australian possums, and diprotodonts (while american opossums and carnivorous marsupials were only distantly related). Together, kangaroos, koalas, wombats, australian possums, diprotodonts and still others make the most diversified marsupial subgroup, incidentally called “Diprotodonts” as well, and mostly herbivorous. The biggest known extinct kangaroo was Procoptodon, more precisely Procoptodon goliath, nicknamed the "short-faced kangaroo". 9 ft tall when erect (one and half more than a modern red kangaroo), and weighing three times more than it (being also more massively-built), Procoptodon had a short stocky tail, powerful front-limbs, and a flat, round snout; the latter has given to it the nicknames "short-faced kangaroo" and also “koala-faced kangaroo”. Despite these difference, its body plan was the same of its modern relatives, being apparently well-suited to jump (though probably less-agile), and with the typical upward-opened pouch in the females to carry the youngsters around. But unlike modern kangaroos, Procoptodon was probably a browser of high tree-foliage no other animal of the time could reach (not even Diprotodon). 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. Some have recently proposed that unlike their modern counterparts, these kangaroos were far too large to hop; they had large buttocks, and their ankle bones suggested that they walked in the same way as human beings. Related with Procoptodon was Sthenurus ("strong tail"), which was a bit smaller but showed the same basic traits of the procoptodont. Both kangaroos were members of a distinct subfamily in respect to modern kinds, within the Macropodids (the kangaroo family). Interesting that some smaller prehistoric kangaroos might have been partially carnivorous or even active predators, like Ekaltadeta.

Early Sabertooths: Deltatheroida

  • It could be surprising the presence of sabertoothed mammals 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. The prototype of the group is Deltatheridium, similar to the former but without the "sabers".

Knuckles 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 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). Steropodon and Obdurodon were ancient platypuses with a smaller beak. 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 (Thylacoleo), and giant ancestor of Knuckles available (not to mention Up to Eleven Komodo dragons and giant running birds, the "mihirungs")… it's unfortunate that such an episode never materialized.

    The Elephant's Clan 

Seaweed-eating Walruses: Protosiren & Rytiodus

  • Elephants and their extinct relatives are all mentioned in the Stock Dinosaurs (Non-Dinosaurs) page. But they have 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 (Prorastomus and Pezosiren), but at the same epoch of the cetaceans achieved a fish-like shape very convergently with them. Examples of prehistoric sirenians are the early Protosiren (lit. "first mermaid"), contemporaneous with Basilosaurus, and the more recent tusked Rytiodus, bigger than the four living species of sirenians and closer to dugongs than to manatees like most extinct members of the group. Interesting that the familiar modern North American manatee has nails surprisingly similar to an elephant's in its flippers! Among extinct sirenians, we can't forget the Steller's Sea Cow: a relative of the modern dugong 9m long and weighing 10 tons, much bigger than extant sirenians (and also more than most prehistoric relatives) which are 5m long at most and weighing no more than 1.5 tons. This animal lived in northern Pacific until 1768, when it got extinct merely 27 years after its discovery because of overwhaling. This is the only modern large sea-mammal that didn't manage to escape the fate many true whales still risk to do: perhaps because the Steller's sea-cow was a very specialized animal devoid of teeth (unlike manatees & dugongs) that, eating only seaweed, was too dependent to limitate environments and thus expecially vulnerable to hunting.

Seal or Hippo?: Desmostylus

  • Another lineage of sea mammals related with proboscideans is now totally extinct: the Desmostylians. They were a bit similar to small hippopotamuses but with shorter hindlimbs than forelimbs, thus having been compared with "herbivorous seals". Desmostylus ("bundle-pillar") is the prototype and the most known of the group; another is Paleoparadoxia ("ancient paradox"). Desmostylus was first-found by Marsh in the USA during the Bone Wars; the group as a whole lasted relatively few, living 20 million years in the middle-Caenozoic seas around the world and got extinct before the appearence of the first hominids. They had four protruding tusk-like incisors (a couple for each jaw) similar to those of early proboscideans like Moeritherium, making them looking a bit like walruses; but their tusks were shorter, and unlike the shellfish-eating walrus the desmostylians ate weeds like the closely-related dugongs and manatees. Desmostylians made a mammalian order on its own, the Desmostylia, because their molars were very complex and totally different of every other mammal.

Elephant's Kin? Titanohyrax an the other extinct Hyracoideans

  • 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 (Arsinoitherium and relatives), Desmostylians, Sirenians and Proboscideans, make together the so-called “Paenungulates” (“almost hoofed”); modern hyraxes too still preserve nails very similar to those of an elephant. 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 (the elephant-shrew, the golden mole, the tenrec, the otter-shrew, but also the much larger 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: Megantereon, Homotherium, and Dinofelis

  • 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 ("sword-tooth") 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: some of them are mentioned in the section below. However, Dinofelis ("terrible cat"), despite resembling more a leopard or a jaguar, was actually a short-fanged saber-toothed cat. In Walking with Beasts it acts as a literal leopard, carrying human-ancestors with its mouth by grasping them from the head note  and transporting them up to the trees. But in reality 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 early carnivoran Eusmilus and the marsupial Thylacosmilus, in particular the latter, being closer to kangaroos than to cats. Imagine a sabretooth with a possible kangaroo pouch and you'll have the idea.

False and true Cheetahs: the American Cheetahs and the Eurasian Giant Cheetah

  • Among the closest relatives of modern felines, other then the more-known American Lion and Cave Lion there were also the so-called American Cheetahs (two species of the genus Miracinonyx, meaning "wonderful cheetah" in Latin/Greek). Despite the name they were actually more related with modern cougar (Puma concolor) than to modern cheetah (Acinonyx jubatus), but shared with the latter a very slender running body shape with expecially long legs. The Miracinonyxes lived in North American Ice-Age pleistocenic prairies, and were possibly specialized hunters of modern pronghorns (which developed their speed just to escape these "cheetahs"). A real prehistoric cheetah was the Eurasian Giant Cheetah, Acinonyx pardinensis ("panther-like cheetah"). It was very similar and closely-related with the modern african cheetah and was also a slender long-legged runner, but is unknown if it was speedier or not than the living one. It was surely bigger, the size of a modern lion, and arguably more powerful than the famously weak modern-day cheetah. Both american "cheetahs" and the eurasian true cheetah, however, were still less-mighty hunters than their contemporaneous relatives, the American and Cave Lions respectively, which were bigger than modern lions; Acinonyx pardinensis was perhaps less-powerful than the Cave Hyenas as well (see below). All of these species were killed off by humans. 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.

Big Badass Wolfhyenas: the Giant Hyena and Borophagus

  • 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 Crocuta crocuta spelaea aka the "cave hyena", a subspecies of the modern spotted hyenas (Crocuta crocuta) living in northern territories during the Ice Ages. Other hyena species were very different: some were as large as bears like the Giant Hyena (Pachycrocuta), others resembled more cheetah (Chasmaporthetes) or even weasels (Ictitherium)! On the other hand, some extinct canines were deceptively hyena-like: Borophagus (once called "Osteoborus") from the Middle Cenozoic is one example, while the archaic Hesperocyon and Cynodesmus were 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.

Pseudo-cats and Half-dogs: Nimravus and Cynodictis

  • 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 (ex Cynodictis, "dog-weasel"), while others were more similar to long-tailed bears, like Amphicyon ("half dog"), the prototype of the group. A very dog-like "bear-dog" appears in Walking with Beasts. Among true bears and related forms, other than the Cave Bear and Short-Faced Bear, we can mention the archaic bear Agriotherium (which lived also in Africa, where no bears roam today), the panda-relative Indarctos, and South American Chapalmalania (actually related with the raccoon, and once nicknamed the "south-american giant panda" in a time pandas were believed giant raccoon cousins as well). Nimravids (the pseudo-cats) were also very diversified: Eusmilus ("good knife") was indeed a large sabretoothed member of the pseudo-cat family, while the namesake Nimravus (also large) was more similar to modern big cats. Eusmilus resembled a lot Smilodon except for its shorter legs, and is sometimes nicknamed "the false sabretooth tiger". Nimravus has left a perforated skull which revealed an astonishing story; it was stabbed in its head... by a sabretooth, possibly Eusmilus itself!. The skull wound was also partially healed, meaning the Nimravus survived. But in some sources (even recent ones), nimravids are wrongly treated as actual cats. Other nimravids include the small Dinictis ("terrible weasel"), not to be confused with "Dinichthys" (the older name of the giant fish Dunkleosteus), and Hoplophoneus ("armed killer").

My ancestor is a Weasel: Miacis and Viverravus

  • 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, 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). Miacis was once believed a forerunner of the "dog branch", while Viverravus was thought of the "cat branch"; today both are considered too primitive and just outside the Carnivora group. 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. We can mention Chamitataxus, an ancient mustelid related with modern badger.

From an Otter to killer Walruses: Puijila, Enaliarctos, and Pelagiarctos

  • 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 Enaliarctos, Desmatophoca, and Allodesmus (still with proper legs instead of true "flippers"), 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 ("sea bear"), 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.

Not true Carnivores: Megistotherium, Machaeroides, and the other Creodonts

  • In the Early Cenozoic, at the time "true" carnivorans were still weasel-like, creodonts ("meat tooth") 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 ("hyena tooth") is regarded as the stock creodont, notable for its extremely powerful jaws to crush bones (hence the comparison with hyenas). There were several species of it, from dog-sized to cow-sized: the largest hyaenodont species appears in Walking with Beasts, described as rhino-sized and a formidable predator, but some hypothesise it was mostly a scavenger. But even bigger creodonts are known to science (for example Megistotherium, "huge beast"), some of them could have even been the biggest land meat-eating mammals ever, rivalling the alleged "biggest carnivore" Andrewsarchus. Other smaller creodonts included the "sabertoothed" Machaeroides (whose name recalls the true sabertooth Machairodus), the fast-running Tritemnodon and Sinopa, the hyaenodon relative Pterodon, and so on.

Carnivorans or Pangolins?: Oxyaena, Patriofelis, and Sarkastodon

  • Oxyaenids were primitive carnivorous mammals, traditionally classified as creodonts. North American oxyaenids were the first carnivorous mammals to appear during the late Paleocene, while smaller radiations of oxyaenids in Europe and Asia occurred during the Eocene. They were superficially cat-like or weasel-like beasts that walked on flat feet, in contrast to modern cats, which walk or run on their toes. Anatomically, characteristic features include a short, broad skull, deep jaws, and teeth designed for crushing rather than shearing, as in the hyaenodonts or modern cats. The species that named the famly is Oxyaena ("sharp" or "drawn-out hyena"), a cat or wolverine-like creature with a body length of 1 meter and short limbs, presumed to be a leopard-like predator that could climb trees in search of prey. The cat-like Patriofelis (Latin for "father cat") was bigger- between 1.2 and 1.8 meters long, making it around the same size as a modern cougar. It had long legs with broad feet, suggesting that it may have been a poor runner, but a quite good swimmer. However, the biggest and baddest member of the family was Sarkastodon ("flesh tearing tooth‭"), which lived during the Eocene in Mongolia. Having a body length of 3 meters, the Sarkastodon was probably an apex carnivore that preyed on large mammals in its range such as brontotheres, chalicotheres, and rhinoceroses. While the oxyaenids have been originally considered basal carnivorans recent scientific studies and discoveries have revealed that they are actually closer related to pangolins, which are an entirely separate and unique order of mammals despite resembling anteaters.

    From Rhinos to Horses 

True Rhinos: Teleoceras, Menoceras, and Aceratherium

  • Modern rhinos are often referred as "prehistoric-looking" in media: there's a bit of truth in this, because the genuses now housing the White Rhino and Sumatran Rhino, Ceratotherium ("horned beast") and Dicerorhinus ("two-horned nose") respectively, date back 5-10 million years. But the trope originated for another reason: many classic prehistoric mammals were deceptively rhino-looking (though with different horn-shapes): the six-horned Uintatherium, the fork-horned Megacerops, and the bizarre Arsinoitherium are the most well-known examples. But only some of the extinct "rhinoceroses" were really such, being classified in the Rhinocerotidae. Among them, the most spectacular were the Woolly Rhino and the Unicorn Rhino. Other more primitive true rhinos include the short-limbed hippo-shaped Teleoceras (whose remains are extremely abundant in Middle Cenozoic North America), the small, forked-horned Menoceras (similarly to the distantly-related brontotheres), and the no-horned Aceratherium (acera = with no horns). Other prehistoric true rhinos has features such as prominent tusk-like lower incisors (modern indian rhinos also have them but not visible externally); 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.

Rhino-Horses and Rhino-Hippos: Hyracodon and Metamynodon

  • Two groups of close relatives of rhinos were the Hyracodontids and the Amynodontids. The hyracodonts, other than "the biggest land mammal ever" Paraceratherium, included smaller animals like Juxia and the namesake Hyracodon, both more horse-looking than rhino-looking just like the "indricothere". The hyracodontids' real rhino-affinities could be betrayed by their feet that were three-toed (not one-toed like modern horses), and often bigger heads than those of horse-ancestors. The Amynodonts (among them Metamynodon) were no-horned, hippo-looking and probably similar to hippopotamuses in habits; they convergently resembled some other extinct unrelated animals like the toxodonts, the coryphodonts, or the even-toed anthracotheres (see further).

True and false Tapirs: Palaeotherium and extinct Tapirids

  • Among ancient perissodactyls, it's also worth of note Palaeotherium ("ancient beast"): a tapir-like horse relative that lived in eocenic Europe, it is the prototype of the equids' sister-family: the Palaeotherids indeed, which perhaps includes also the alleged "horse" Hyracotherium. Modern true tapirs are the only living odd-toed ungulates which still retain the original body plan of the archaic forms (except for the trunk that is a very specialized trait): for example, they have four digits in their forefeet, like the most primitive members of the horse family like Eohippus, and unlike horses & rhinoceroses have remained forest critters still today. Miotapirus from Miocene was virtually identical to modern tapirids; Hyrachyus ("hyrax-pig"), Helaletes, and Heptodon were earlier tapir-like perissodactyls without the trunk. Returning to Paleotherium, it detains the honor to be one of the four only mammal kinds portrayed in the famed Crystal Palace Park in London, together with Megaloceros, Megatherium, and Anoplotherium (see below), in a time in which many other extinct mammals were already known by science.note 

South American Imitators: Astrapotherium, Pyrotherium, Thoatherium, and Homalodotherium

  • 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.note  These two guys lived during the Ice Ages in South American pampas, and were among the last members of their groups (Litopterns and Notoungulates respectively); but other relatives lived much earlier, always in South America. Pyrotherium ("fire beast") was rather like a gomphothere, Astrapotherium ("star-footed beast") looked like the ur-elephant Moeritherium above; while Thoatherium (a litoptern) was a perfect imitator of the horse-ancestors. Theosodon was also related with Macrauchenia, but without the large "nose" of the latter. On the other hand, Homalodotherium was related with Toxodon, but with sharp front-claws like a sloth. Thomashuxleya, another notoungulate, was named in early 1900 by the most important Argentinian palaeontologist, Florentino Ameghino, from famous English biologist Thomas Huxley.note  Rhynchippus, despite its equine name, was a small Toxodon relative. Typotherium was also a notoungulate like the 1-ton toxodont, and yet was resembled a rodent in shape and size!

The first large Herbivores: Barylambda, Pantolambda, and the other Pantodonts

  • 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 (even though the two main groups of modern ungulates, perissodactyls and artiodactyls, are still related to each other according to genetics). Those which lived at the beginning of the Cenozoic were rather undifferentiated each other, and did not resemble most modern hoofed mammals. Among the most famous there are the small "ur-horses" Eohippus/Hyracotherium and the large Uintatherium, both from the Eocene epoch: among the other Eocene "ungulates", Coryphodon and Phenacodus are frequently portrayed in books. Coryphodon ("crested tooth") was one of the first land mammal to exceed 1 ton in weight, and was rather similar to an hippo in shape, with a short tail and small tusks like the latter. The coryphodont was one of the biggest members of the mammalian order called the Pantodonts ("all teeth"), which also included Titanoides ("similar to a titan") and the Paleocenic Barylambda and Pantolambda among the others. The latest two were smaller and more basal than Coryphodon, with still the archaic long tails of most early mammals. Barylambda was bigger/more massive and arguably more specialized for herbivory, while Pantolambda was more weasel-like and probably more omnivorous.

The first Hooves: Meniscotherium, Didolodus, and Protoungulatum

  • Phenacodus was once put in the obsolete order of basal mammals called the "Condylarthrans", which included also the similar Meniscotherium and south-american Didolodus, and less-ungulatian animals such as Ectoconus, Hyopsodus, the carnivorous Mesonychians, and even huge Andrewsarchus; today the phenacodonts are mostly considered very basal odd-toed ungulates. Phenacodus ("imposter tooth") was not larger than a dog: with its several small hoofed digits, it was similar to Eohippus but with the long tail of the most basal hoofed mammals, and thus it is often mentioned as one of the prototypical "basal ungulates". Just like Eohippus/Hyracotherium, Phenacodus was often depicted as a possible prey of the famous giant bird Gastornis; while the massive Coryphodon and Uintatherium were probably too powerful to be threatened by any predator when adults, like modern hippos, rhinos, and elephants today.

Rodents or Ungulates?: Stylinodon and Trogosus

  • Also worthy of notes among the earliest placentals are two little-portrayed groups of early ungulate-like mammals, the Taeniodonts and the Tillodonts. Both from Eocene or so, they were possibly related with Coryphodon an the other Pantodonts, but had specialized strong frontal teeth for gnawing (anticipating the more evolved rodents and rabbits) and robust bodies apt for digging burrows. Stylinodon and Trogosus were examples respectively of the taeniodonts and the tillodonts: like the pantodonts, these early lineages of herbivores got extinct without leaving descendants today. Protoungulatum (lit. "the first ungulate") was even more archaic than the above: many think it was already-existing in the Late Cretaceous, along non-bird dinosaurs! Some, however, think it was not even a true placental but only a close placental-relative.


    From Deer to Whales 

Rhinoceros-Deer: Protoceras and Syndyoceras

  • Many prehistoric ungulates resembled deer in body-shape and head-shape, but again, not all were members of the deer family (the Cervids) like Megaloceros. Many of them had very unfamiliar-looking horns/antlers above their heads. Among pseudo-deer, the most portrayed in popular books have been Synthetoceras and Sivatherium, even though neither made its way in Walking with Beasts unlike the "Giant Irish Elk". Synthetoceras tricornatum ("three-horned fused horn") was a distant camel-relative, but unlike the latter was antelope-shaped, with typical antelopine hooves, running legs, and an elongated head not unlike a modern hartebeest antelope. But the synthetoceras had three horns, placed in a way that astonishingly resembles a Triceratops! (and the african modern-day Jackson's chameleon as well). Indeed, the two frontal horns were short, recurved, and antelope-looking, but the third one was on its nose and was forked just like that of "Brontotherium", though longer and more slender. It should be noted that this combination of horns is not so unusual as one might think: the male of the modern four-horned antelope has a couple of small hornlets in front of the typical ones, and even our modern giraffe has also a bump in front of the two familiar "horns" (better, "ossicones") above its head, which in some individuals can grow up to become a true "horn"! Other relatives of Synthetoceras were simpler-horned: Syndyoceras was similar to the latter even in its name ("fused double horn"), but had a shorter nasal forked horn; the basal Protoceras ("first horn") had a combination of horns more similar to a uintathere, and also small tusk-like "canines" like the latter. This is the official prototype of the family of even-toed ungulates Synthetoceras belonged to: the Protoceratids.

Moose-Giraffes: Climacoceras and Prolibytherium

  • Sivatherium giganteum ("giant Shiva's beast") is the most known prehistoric member of the Giraffids, the giraffe family of the even-toed ungulates. It was much less tall than a modern giraffe (Giraffa camelopardalis), being "only" 2.5m tall at the shoulder, but was more massively-built and perhaps heavier than a giraffe itself. But the sivathere didn't look like a giraffe at all: it had deceptively moose-like pseudo-antlers, and had a short neck not unlike the other only modern giraffid: the Okapi, which looks like the ancestors of the family. Thus, this mammal could be qualified as sort of "moose-giraffe". The "Shiva's beast" was found in several places, among them Africa and India (hence the Indian-sounding name), and lived as recently that it could have met prehistoric humans. Related with Sivatherium but not proper giraffids (belonging to a closely-related family) were the smaller, more ancient but equally pseudo-antlered Climacoceras and Prolibytherium from Northern Africa or Europe. Returning to the giraffe family... 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.

Ancient Pronghorns and Musk-Deer: Cranioceras and Hoplitomeryx

  • The three-horned pronghorn-like Cranioceras ("horned skull") and the five-horned muskdeer-like Hoplitomeryx ("armed fawn") belonged to extinct families of ruminants with no modern close relatives; their heads mixed up deer and antelope traits, like those of the modern Pronghorn and the Muntjak deer. Our pronghorn "antelope" (Antilocapra americana) is not a true antelope (antelopes are bovids, see below); it's the only-surviving species of its own family of ruminants, Antilocaprids, which once included many more species (Ilingoceras, Hexameryx, etc.) in North America, with very variously-shaped horns. Modern musk-deer, too, are not deer at all but belong to their own family of ruminants, the Moschids. The fossil record of their ancestors is poorly-known, as well as that of the tiny Tragulids (the modern "mouse-deer" or chevrotains).

Tatanka's Relatives: Bison latifrons and Pelorovis

  • Bovids (the family containing buffaloes, sheep, goats and antelopes; that is, all ruminants with true horns) are the most successful ungulate group today, and are very diversified, with more than 100 described existing species. As a group they have appeared more recently than most other ruminants, and their prehistoric relatives were not much different in their appearance. 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 above). Bisons reached North America from Eurasia very recently in terms of geological times, and have since then replaced most other ungulate groups (like horses and camels) in the Great Plains — with the exception of the aforementioned pronghorn. Only one species of bison still remains in America: the other living species of bison is European and extremely rare today. Among extinct bovines it's also worthy of 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). Another ancient bovine living in Europe, almost managed to survive until today: the Aurochs.

Giant Camel: Titanotylopus

  • In prehistory, extinct relatives of camels and llamas were very diversified: the great majority of them were North American, where they started their evolution — only recently did they colonize other landmasses. Thus, camelid evolution has often been compared with that of equids (which also started in North America and then spread elsewhere). Some extinct camelids were even taller than our modern dromedaries: Aepycamelus (once called "Alticamelus", both names meaning "lofty camel"), the most famous of them, was a sort of giraffe-like animal with very elongated neck and limbs. Even bigger was Titanotylopus ("titanic camel"). Other "camels" were more antelope-like (ex. Stenomylus): they still had true hooves and not the (unusual for artiodactyls) cameltoes yet, and ran the ancient North American plains. The recently-extinct Camelops ("camel look") was instead very similar to a modern camel both in shape and in size, and has also been found in the famed tarpits like La Brea, together with pronghorns. Note at this point that 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 (except maybe Camelops) and resistance against thirst.

Ancient Boars and Peccaries: Metridiochoerus, Kubanochoerus, and Platygonus

  • Many hoofed mammals of the distant past were pig-like in shape: indeed, the pig frame is considered a primitive one 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 (the Suids, aka "the pig family"), Metridiochoerus was related with the modern warthog but with straighter tusks. Kubanochoerus was stranger: it had a long prominence above its head for uncertain purpose. While Platygonus was an ancient peccary relative. Almost-surely these animals were omnivores like their modern counterparts and shared the same tubular nose of modern swines, even though its shape doesn't fossilize (just like the trunks of the elephants and the tapirs). Some prehistoric suids (aka the boars) and tajassuids (aka the peccaries) were bigger than ours, but never at the same level of the biggest Entelodonts, traditionally considered pig-relatives but maybe closer to hippos (see below) according to recent research.

Early Even-Toes: Merycoidodon and Anoplotherium

  • There was another group of smallish to large pig-like even-toed ungulates that were abundant in ancient north american prairies, the Oreodonts, such as Merycoidodon. Once considered true pigs, recent research suggest they were not closely related with pigs but with camels instead. Indeed, modern genetics has shown camels are arguably the most basal living artiodactyls, not the suids & hippos as traditionally thought: since modern pigs & hippos don't ruminate, the camelids' rumination was obtained by parallel evolution with the more evolved true ruminants (bisons, giraffes, deer etc.). Anoplotherium ("unarmed beast") was one of the most primitive artiodactyls, with generic head and long tail — resembling more basal "ungulates" like Phenacodus. As said above, this is one of the four extinct mammals portrayed in the London Crystal Palace Park.

Hoofed Stanleys and small-mouthed Pats: The Mesonychians and the Anthracotheres

  • Pat & Stanley in Prehistory! The two popular hippo & dog characters of the Internet could be linked with two early groups of even-toed ungulates: the dog-like Mesonychians and the hippo-like Anthracotheres. Mesonychians (or mesonychids) were the first meat-eating mammals which obtained a size larger than a house cat, at the beginning of the Mammal Age. Their prototype has traditionally been the wolf-sized Mesonyx ("split nail"). Rather dog-like or hyena-like in shape but with comparatively larger heads and longer tails, they had hooves in their feet a bit similar to modern pigs. Mesonychids are today thought the closest relatives of artiodactyls, but were once placed in the artificial "condylarth" grouping together with other critters mentioned in other folders: interestingly, the alleged giant hunter Andrewsarchus was once often considered a gigantic overgrown member of the mesonychians. Once, mesonychids have also usually been considered the ancestors of whales, because their skull (specifically their teeth and ear bones) resembles that of the most primitive cetacean known, Pakicetus. Thanks to modern genetics, we know now that hippopotamuses are the closest relative of whales and dolphins. Sadly, the fossil record of prehistoric hippos is poorly known (unlike that of prehistoric rhinos): we can mention Hippopotamus gorgops, a close relative of the modern giant hippo but even bigger and with extremely protruding, periscope-like eyes; another is Kenyapotamus, which was once considered a "missing link" between hippos and peccaries. On the other hand, the similar-looking Anthracotheres ("coal beasts") have a rich number of species described, among them the namesake Anthracotherium. 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 to scare enemies or rivals.

Early Cetaceans: Protocetus, Remingtonocetus, and Dorudon

  • 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 (not even the unrelated manatees, which still have a partially land-mammal-looking head). 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 (the latest ones were 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. Pakicetus and Ambulocetus are well-known examples of this, but both were found only at the end of the XX century. Protocetus atavus (lit. "ancestral first whale") was named so because it was one of the very first early cetaceans discovered by science, at the start of the 1900. Dorudon, also found in early 1900, was more evolved: similar to an undersized Basilosaurus but with not such an elongated body, it's portrayed in Walking with Beasts as a prey of the latter. Only recently-found, Remingtonocetus was an example of an early freshwater-dwelling "whale". These kinds (and several others, like Indocetus, Rodhocetus, Zygorhiza, etc.) lived only few million years after Ambulocetus and Pakicetus, but had already reached a more fishy-shape and were mainly or fully aquatic. Despite this, they still maintained hind-flippers as a memory of their terrestrial origins just like their larger cousin, Basilosaurus.

The first modern-looking Whales: Cetotherium, Mammalodon, and Kentriodon

  • The first totally-swimming cetaceans note , the most famous being the huge yet slim Basilosaurus, progressively developed more powerful tails with a fluke, eliminated the visible neck, lost their hair substituting it with fat blubber under their skins, and placed their nostrils above their head until they became blowholes (sadly, soft tissue is unknown among early cetaceans). They were all active hunters like modern orcas and sperm whales, but still had differentiated teeth note : pointed the anterior ones, serrated the posterior, an old legacy which betrays their origins from land mammals. Then, some cetaceans lost altogether their teeth substituting them with baleen (the "Mysticeti"). Mammalodon ("mammal tooth") was a very early mysticete that still preserved small teeth; the first true filter feeders, among them Cetotherium ("whale-beast", similar to a modern grey whale or a pygmy whale, and smaller than an orca) appeared much more recently than the archeocetan whales, when our planet turned colder and immense shoals of krill began to float in polar waters. The other main group of advanced cetaceans (the "Odontoceti"), however, has preserved the teeth, but these teeth became all similar to each other (in other words, they became "homodont"). Some of them (ex. Kentriodon) were related to our dolphins and porpoises, while others (see below) were more similar to sperm-whales or narwhals. All odontocetans, curiously, lost their right nostril altogether, so their blowhole is made only of the left one. They also developed a fatty prominence above their heads for complex echolocation, maybe compensating the almost-unexisting olfact of cetaceans and their relatively poor underwater vision. Modern whales & dolphins have smaller eyes than many fish and squids (the indian river dolphin is totally blind) and they cannot "smell" at all: olfact is useless when you keep your nostrils eternally closed underwater — if water enters in their lungs they'll be suffocated. Obviously, we don't know exactly when whales lost the ability to detect scents. See also here to learn more about the fascinating story of the evolution of cetaceans.

Sharks/Swordfishes/Walruses of Whales: Squalodon, Eurhinodelphis, and Odobenocetops

  • Among the ancient dolphin-like odontocetans, some reached very unusual traits compared with the modern ones — even though our narwhal and some beaked whales are 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": found in 1993 in Peru, it had two long tusks protruding backwards, and often asymmetrical just like the modern single-tooth of the narwhal (in both cases only males had this feature, and in both cases the overgrown tooth is the left). The function of both the teeth of the odobenocetops and the spiral tooth of the narwhal is still uncertain, maybe courtship devices. Of course the Odobenocetops was the chosen cetacean in Sea Monsters as a prey of juvenile "Megalodon", just because it looks cool. A very recent discovery (2014) is Semirostrum ("half beak"), a porpoise-relative with lower jaw twice longer than the upper one.

My, what big Teeth you have!: Livyatan

  • A 2008 discovery made in Peru, Livyatan melvillei could make appearing the so-much celebrated "prehistoric killer whale" Basilosaurus quite insignificant in comparison: indeed, it possesses what may be the largest functional teeth of any animal (that is, not counting "tusks" like the elephant, mammoth, walrus, and narwhal ones). The size of the partially preserved skull indicates that Livyatan reached a length between 44-57 feet (like the modern sperm-whale, Physeter macrocephalus), possessing a head three meters long (twice shorter than a large sperm-whale's head). Livyatan was indeed quite similar to the modern giant 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 is, they likely hunted even more powerful preys than the modern giant and colossal squids eaten by sperm whales 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. Other similar contemporaneous sperm-whale relatives with smaller (but still huge) teeth have been found in different places of the world about the same time of the discover of Livyatan (or a bit earlier): they were Acrophyseter from Peru, Brygmophyseter from Japan (portrayed in Jurassic Fight Club as the rival of Megalodon), and Zygophyseter from Italy.

    From Sloths to Rabbits 

A variety of Extinct Sloths: Mylodon Eremotherium, Megalocnus, and Thalassocnus

  • Megatherium is the stock animal within the group called giant ground sloths, related with anteaters and armadillos. But the megathere represent only the Up to Eleven example: many other "giant sloths" weren't so giant-things (even though still large by human standards). More robustly-built than modern tree-sloths, with long, strong tails unlike the latter (but equally weaponed with the typical large claws), giant gruond sloths belonged to different families within the xenarthran subgroup named the Folivores ("leaf-eaters"). One of these families, the Megalonychids, has survived until today: the modern two-toed sloth (Choloepus) belongs to it. note  Thanks to their powerful backbone, many (but probably not all) ground sloths were actually capable to walk around with their body upright, a bit like giant bears. Being members of the archaic mammalian group called xenarthrans, they were prevalently South American (some of them migrated to the North however). In spite of having primitive teeth and small brains, 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 a bit faster-moving, looking like a modern giant anteater. The south-american Mylodon (family Mylodontids) is one of the best-known: smaller than Megatherium but still large, it has left remains of fossil hair like the latter, and perhaps it too was kept in caves by ancient people as a source of food. Eremotherium was of the same family of Megatherium (the Megatherids): it was one of its closest relatives, and nearly as large as it, but unlike the latter managed to reach North America. The exclusively North American Megalonyx ("big nail") and Nothrotheriops ("sloth beast") were smaller: the first one is the prototype of the aforementioned still-living Megalonychids; the second was closer to Megatherium and nicknamed the "Shasta's ground sloth". Megalonyx has had a curious scientific story briefly mentioned in Stock Dinosaurs (Non-Dinosaurs), in the megathere chapter of course. The similarly-named relative Megalocnus was a Caribbean kind of ground sloth with short limbs. Hapalops was a small primitive South-American sloth (one of the first-appeared of the group) that was perhaps able of climbing. Last example, the small megatherid Thalassocnus which was one of the most bizarre sloths ever, being semi-aquatic, and ultimately becoming a marine sloth! (in greek "thalasso" = sea). Its lifestyle was probably similar to a modern sea-otter but remaining plant-eating (not fish or shellfish-hunting) convergently with the elephant-relatives Desmostylians, and its limbs remained like those of a land sloth (it didn't develope the paddle-like limbs of a seal).

Ancient Armored Mammals: Glyptotherium, Hoplophorus, Stegotherium, and Utaetus

  • Giant glyptodonts were not the only ancient relatives of armadillos: there were also smaller Cingulates (aka armored xenarthrans) as well. All were South- or North-american like modern armadillos. One of them, Stegotherium, has a name that recalls a famous armored dinosaur. Another, Utaetus, was one of the first true cingulates, from Eocene. Glyptotherium and Hoplophorus ("armor-bearer"), on the other hand, were true glyptodonts but smaller than the two stock guys Glyptodon and Doedicurus. A little-known critter, South American Macroeuphractus, was a 100kg armadillo with bone-crushing jaws and sharp teeth, showing adaptations towards carnivory. Modern armadillos are insectivorous at the most, with their small undifferentiated teeth. It's worth noting that cingulates were almost the only mammals that developed true bony armors on their bodies, even in prehistoric times: the pangolins's armor is indeed made of horny scale-like structures without any bone (see below). Metacheiromys from early Caenozoic North America was once thought an ancestor of xenarthrans, but was actually a pangolin relative: it had the generic long-tailed look of early mammals (pangolins included), and some specializations for insect-eating.

The Rodents' Success: Epigaulus, Palaeocastor, and Josephoartigasia

  • The rodents' fossil record is very scant: no surprise, since they are usually so small, and small animals usually hardly fossilize unlike the large ones. However, today rodents are the most successful mammalian group, with about half the species of all living mammals. This success is probably due to their very specialized maxillary grinding mechanism other than the robustness of their ever-growing pairs of incisors, which make them capable of eating almost-everything. They also have agile manipulative hands, keen senses, intelligence, good social skills, and the ability to build complex structures (think about the famous "dams" of the beavers and the "underground cities" of the Prairie "dogs" and the South American viscachas). All these traits are shared with another group of mammals, the monkeys & apes: indeed, rodents and primates have recently discovered to be related to each other thanks to genetics. Even though most ancient rodents were similar-looking to ours, ex the ancient squirrel Paramys ("nearly mouse") living in the Early Cenozoic, there were also some striking guys in the past: for example, Castoroides ("false beaver", yet another victim of humans) was a land-living beaver-relative as large as a black bear, weighing 150 kg; Palaeocastor ("ancient beaver") was another smaller and earlier land-living beaver which built corkscrew-like burrows in the ancient North American plains - a sort of predecessor of the modern prairie dog. Both "beavers" lacked the adaptations for swimming of modern beavers (like palmated feet and paddle-like tail), and obviously didn't build "dams" in the rivers and lakes. The most unusual-looking paleo-rodents were, however, the Ceratogaulids (nicknamed "horned gophers") like Epigaulus and Ceratogaulus, which had a couple of hornlets on their nose a bit like a miniature brontothere. Note that, despite their wild diversity (climbers, gliders, runners, hoppers, swimmers, diggers) no living rodent has any horny prominence on its head. These horned rodents were small-sized and lived in burrows, like many modern relatives. And then, there were several South American ungulate-like forms with long limbs and hoof-like feet (similarly to their modern relative, the capybara), convergently with ungulates. Two known examples are Phoberomys ("fearsome mouse") and Telicomys, which were cow-sized and long believed the largest rodents ever (capybara do not exceed the size of a large dog), until the recent (2008) discover of the bison-sized Josephoartigasia, another south american critter named from real people continuing the tradition started in the 1900 by Ameghino (see above). The closest modern relatives of these giant rodents is a little-known animal, the rare Pacarana (Dinomys), still one of the largest living rodents, the size of a modern water beaver. It's not a casual connection, that modern-day capybara (South-American as well) is the biggest modern rodent: South American mammals were, and still are, very unfamiliar to a North American or European observer, beated only by the Australian ones.

The Origin of Rabbits: Extinct lagomorphs

  • On the other hand, Lagomorphs (rabbits, hares and pikas, once believed true rodents as well) 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. Unlike true rodents, lagomorphs had two pairs of ever-growing incisors in their upper jaws (the smaller ones are behind the familiar larger ones), while their lower jaws had only one pair of incisors. Curiously, rabbits & hares have the little-known habit to eat their own feces: they are rich of undigested nutritious food, and they definitively expel them only the second time after having digested better their first feces. This is their method of "ruminating". It’s hard to believe, but the affinity lagomorphs / true rodents was definitively proven only few years ago, again thanks to genetics. Before, rabbits and so on were once thought not related at all with rats and squirrels. According to different scientists, lagomorphs were believed related with ungulates, with primates, or even with carnivores! An interesting recently-extinct lagomorph is Prolagus sardus, known as the Sardinian Pika: similar to a short-eared rabbit but more related with pikas indeed, it lived in the Mediterranean islands of Corsica and Sardinia in historical times, but the real reason of its extinction is not fully known.

Early Insect-Eaters: Leptictis, Pholidocercus, and Deinogalerix

  • 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 (making the Eulipotyphles aka "true insectivores" together with the caribbean venomous Solenodonts and the historically-extinct Nesophonts), many other less familiar “insectivores” — that is, the Asian tupays or tree "shrews", the tenrecs of Madagascar, the golden "moles", otter-"shrews", and sengis or elephant "shrews", all from mainland Africa — 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 just like the rodents and the lagomorphs. Maybe the most famous and specialized is Leptictidium ("slender weasel"), a long-legged 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, it was once put in the "protoeutherian" ("first eutherians") artificial group of basal placental mammals. Its uncertain if Leptictidium and its relative Leptictis were runners like a ground bird or a small dinosaur, or more traditional hoppers: none of the kangaroo-shaped mammals today (the marsupial true kangaroos and the rodents jerboas, kangaroo-rats, springhares etc.) do run, but being the Leptictids not related with any of them, this is still possible. The leptictidium appears as the main character in the first Walking with Beasts episode, which portrays a whole family living in the ancient Eocene forests. This singular animal was even believed by some the inspiration for Scrat in the Ice Age films; as it is, however, Scrat actually bears a close resemblance to the Mesozoic mammal Cronopio, although this was pure coincidence. More shrew-like than Leptictidium and Leptictis was Zalambdalestes, that lived before the non-avian dinosaurs’ extinction—Late Cretaceous in Asia, 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. Deinogalerix ("terrible gymnure") was a hedgehog relative, thus a "true" insectivore, but with a longer tail more like the modern Gymnure or Moonrat (the biggest modern insectivore) than the hedgehog; it was probably covered in fur or at least bristles, but not spines. Pholidocercus ("scaly tail") was the exact opposite: similar but not closely related with a hedgehog, it was found in the famous eocenic Messel Tar Pits (see below), and did preserve signs of spines. Dimylus was once believed an ancient relative of moles and desmans (in the Talpid family), but today it's classified in a distinct group.

Scales, or not-Scales? Eomanis and Eurotamandua

  • Among the numerous mammals found in the German 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, short legs with robust claws, long tails, 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 south-american anteater than a pangolin — indeed, it was long classified as a proper anteater. The names of both animals are referred to this older classification: Eomanis means “dawn pangolin”, Eurotamandua means “European tamandua” (Tamandua is the name of a modern kind of middle-sized anteater of Central and Southern America).

    From Bats to People 

The Mammals' First Flight: Palaeochiropteryx, Icaronycteris, and Planetetherium

  • During mammal evolution, some groups reached the ability to glide: some rodents, some marsupials, and the dermopterans. The most known extinct glider is Planetetherium ("gliding beast"), belonging to the same group of the so-called “flying lemur” (the Dermopteran) of our days. But only bats developed powered flight. Unfortunately, Chiropterans (the scientific name of bats, meaning "winged hand") 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, the early pangolins Eurotamandua & Eomanis, and even a basal ungulate, Propalaeotherium. 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. One of the very first bats, Palaeochiropteryx ("ancient chiropteran") has 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. Even earlier but also fully-chiropteran was Icaronycteris ("Icarus bat") from North America, believed the most ancient known bat to science. The younger Archaeopteropus from Italy was one of the first ancestors of megabats or "flying foxes". According to experts, bats achieved their nocturnal habits to not compete with the mainly-diurnal birds in the search of food. The earliness of the "first bats" 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 "Prehistoric Life - Birdlike Theropods").

After dinosaurs… Squirrel-Monkeys: the Plesiadapiformes

  • 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 ("almost Adapis", see below) is often mentioned in books as the "first primate", but it was probably only a close relative, like the Dermopterans above.note  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 Mesozoic, particularly Purgatorius (see The Origin Of Mammals). Today, there’s still an animal which strongly resembles Plesiadapis and Purgatorius, though devoid of gnawing teeth unlike the former: the tupay. Improperly called “tree shrew”, the latter was once classified as an “insectivore” (see above). Interesting that one modern true primate, the lemur Aye-Aye (Daubentonia madagascariensis), has independently developed gnawing teeth as well.

Early true Primates: Adapis, Omomys, Aegyptopithecus, and other 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 these notes: 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 (see just below) 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 ("Egyptian monkey") was one of the first true monkeys. Walking with Beasts chose to portray other two animals, the Adapis relative Godinotia (wrongly shown with a monkey head) and the early true monkey Apidium in the two first episodes respectively. For extinct apes, see further.

Giant Baboons and Malagasy Pseudo-Apes: Dinopithecus, Megaladapis, and Archaeoindris

  • The largest true monkeys living today are baboons and their relatives like the mandril, widespread in African grasslands and forests. However, at the time of the earliest human ancestors there were some "giant baboons" in african savannas, among them Dinopithecus ("terrible ape"). Maybe bigger than a gorilla, it was probably a competitor with our human ancestors when there was a prey or a carcass to be contended. Unlike most african megafauna of the time (Pliocene-Pleistocene) giant baboons didn't manage to reach our days, maybe depleted by us humans. About the much more primitive lemurs: the largest lemur alive in Madagascar today is the gibbon-sized and endangered indri (Indri indri). However, long ago, there were truly gigantic forms. The most well known is the orangutan-sized Megaladapis ("large Adapis"), also known as the koala lemur, notable for the shape of its skull, which most likely housed a trunk-like upper lip. There's also Archaeoindris ("ancient Indri"), 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 the famous Gigantopithecus. Sadly, these and other similar creatures went extinct a mere 500 years ago when the first Malagasy settlers arrived in Madagascar (See also the Elephant bird).

Bipedal or Quadrupedal Ancestry?: Prehistoric Hominoids

  • Until he extends the circle of compassion to all living things, man will not himself find peace. The closest human ancestors are at the bottom of this page dedicated to Mammals because of this. Technically a subset of primates, hominids is a group of animals somewhat controversial to talk about, for obvious ethical reasons. 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.

Real and alleged Human Ancestors: Proconsul, Oreopithecus, Dryopithecus, Pliopithecus, Sivapithecus (former "Ramapithecus"), and Orrorin

  • Due to jungles not being good places for fossilization, not many species of extinct apes are known. The most popular one is surely Gigantopithecus, a relative of the orangutan (that also convergently exhibited gorilla-like characters), because of its size. Other extinct apes were much smaller, not bigger than our chimpanzees (Pan) or orangutans (Pongo). Many of them 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 ("before Consul": Consul was a chimpanzee), Dryopithecus ("oak ape"), "Ramapithecus" ("Rama's ape", now Sivapithecus "Shiva's ape"), Pliopithecus ("Pliocenic ape"), 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 ("mountain ape") and Orrorin ("original man" in African native language). 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 First Apemen: 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 towards modern times, the species of australopiths 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 all found in Africa). As Science Marches On, recent taxonomical revisions have split off 2 other significant genera from Australopithecus: the earlier Ardipithecus ("ground ape", found in 1994 and originally put in one single species, A. ramidus), 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 — again, convergently with gorillas (Gorilla); the other australopithecines were much smaller and more gracile, and were more generalist feeders. note  Significant species of the modernly-intended genus Australopithecus are A. afarensis ("Afar People's southern ape"), best known for the specimen found in 1971 and known as Lucy; and A. africanus ("African southern ape", the first discovered australopithecine, in 1925), likely an ancestor of the genus Homo. The australopiths of the namesake Australopithecus genus were portrayed in 2001 as the main characters of the forth episode of Walking with Beasts: here a group of them is shown acting rather like a middle-way between chimpanzees and humans.

Handy Hominins: Early Homo.

  • The beginning of the Homo genus is still a mystery to paleontologists and paleoanthropologists everywhere; as is known, fossil remains of hominids have traditionally been much, much scantier compared to other big-sized fossil mammals. Earliest fossil evidence for their origin hints at a date of 2.5 million years ago. The first Homos were actually very much similar to australopithecines (which has indeed lead some scientists to believe these should be classified as a separate genus), 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, the most classical early Homo (described in year 1964), shows it best: while sharing many anatomical traits with australopithecines (small overall size, ape-like skull but with human-like dentition etc.), it's skull was already beginning to show some human-like feature, in particular a slightly larger brain (620 cc in comparison to the 450 cc of earlier australopitheces). It had also more specialized hands ("Homo habilis" literally translates into "handy man" in Latin), and this species was enables to achieve the first of many breakthroughs that would define humanity: fabrication of stone tools. note  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. For comparison, australopithecines, even of the omnivorous Australopithecus genus, mainly ate fruits, seeds, and roots, and only occasionally took animal food (insects and carrion of large mammals).note 

The Upright Man travelled Far Away: Homo erectus

  • Homo erectus (trad. "Erect man" or "Upright man") marks perhaps one of the most important breakthroughts in human evolution. This species can, with relative certainty, be called the very first true 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. 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.

  • It's worth of note that Science Marches On has been a big affair about the "upright man": its first fossil (the "man of Java", found in Indonesia in 1893, in the isle of Java indeed) was originally called Anthropopithecus erectus ("upright man-ape") and immediately after renamed Pithecanthropus erectus (literally meaning "upright ape-man"). Another found later near Beijing, China (in the Zhokouthien site to be precise) was labeled Sinanthropus pekinensis ("Beijing's chinese man") and nicknamed the "Beijing man". Both names are very common in old textbooks, but now are universally regarded as specimens of Homo erectus. Another recently-made name for the African erectus has been Homo ergaster, lit. "the working man" — and still there are those that prefer this name for the african fossils.

Between Giants and Dwarves: Meganthropus, Homo heidelbergensis, Homo floresiensis

  • Humans these days are a very varied species, with different peoples having different skin color, eye color, height or weight, oddily in contrast with our extreme genetic uniformity compared with other mammal species. With such external variety, it's not that far a stretch to think that our ancestors had similar varieties. Such evidence is shown by the very recent (2005) findings of Meganthropus (lit. "big man"), 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 ("man from Heidelberg", a town of Germany), 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, by far the most peculiar, was also found in the 2000s: Homo floresiensis (lit. "Man of Flores") or "the Hobbit" as called colloquially. This species was most likely another descendant from Homo erectus, and distinguishes itself for its incredibly small size (barely around a meter tall). This species was found mainly on an Island known as "Las Flores" in eastern Asia (Indonesia), not far away from Java. 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 up to the end of the Ice Age itself, nearly 12 thousand years ago.

The End of the Line: Neanderthals, Denisovans and Archaic Homo sapiens

  • 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 (Homo neanderthalensis), which reigned through most of Europe, Northern Africa and Northwestern Asia for almost 200,000 years before the rise of the first modern humans (traditionally named Cro-Magnons). Another case, being identified at the start of The New '10s as distinct, 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-identified 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.


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