10 Extinct Mammals You’ve Probably Never Heard Of

When it comes to long-extinct animals, it tends to be dinosaurs that get all the attention. Nonetheless, some of the extinct mammals that lived millions of years past are no less impressive than the ancestors to modern birds. An oft-overlooked fact is that mammals also coexisted with dinosaurs, for 159-million years in fact, according to The Origin and Evolution of Mammals by T.S. Kemp. Over some 225-million years, entire orders and families of mammals have risen and fallen but, as did the dinosaurs, they’ve left many traces of their existence behind. Many of these many finds have revealed some particularly bizarre creatures, such as the following:

#1. Jugulator

Jugulator Amplissimus

Though more famously an album by Judas Priest, the jugulator was also an early mammal that lived during the middle of the Cretaceous period, making it a contemporary of the spinosaurus, one of the largest carnivorous dinosaurs that ever lived. However, the agile jugulator was most an experienced tree-climber and glider, likely able to escape and outwit such predators. Despite weighing around 750 grams, it was one of the largest mammals of its time, and it lived in what is now north-west America. Superficially, the jugulator vaguely resembled a squirrel, but it belonged to the order of eutriconodonts, which disappeared 70-million years ago.

#2. Platybelodon

Platybelodon grangeri

Having been around for the last 60-million years, elephants and their ancestors have a long and storied history. However, while almost everyone has heard of mammoths and mastodons, the platybelodon was, superficially at least, quite a different beast. This early and distant relative to the elephant had a shovel-like lower lip with two incisors combined with a trunk that vaguely resembled those of modern elephants. The animal was much smaller as well, being no taller than an adult human. Platybelodon lived 10- to 15-million years ago in Asia and the Caucuses, and abundant fossils have been found in the Linxia Basin in China.

#3. Repenomamus

Repenomamus giganticus

Living in the Early Cretaceous between 123- and 125-million years ago, the repenomamus was a contemporary of the dinosaurs. It was also the largest known mammal that existed at any time during the Mesozoic period, throughout which the dinosaurs roamed the Earth. The largest of the species was just over 3 feet (1 metre) in length, and probably weighed around 30 pounds (13 kg). In fact, owing to its large size, and the fact that it was a carnivore, meant that it even fed on small dinosaurs. Superficially, the repenomamus looked a little like a giant prairie dog, though it belonged to the order of gobiconodonts, which vanished 94-million years ago.

#4. Bramatherium



Bramatherium looked like something of a cross between an antelope and a giraffe, but this animal, which lived around five-million years ago, was actually the latter. The small horn-like structures of modern giraffes were far more pronounced in this prehistoric creature, and the long neck wasn’t present either, hence its very different appearance. One of the nearest extant species is the okapi, a similarly short-necked giraffe from Central Africa, minus the bizarre horn-like appendages. The type species was discovered in 1845 and, like modern giraffes, they grazed in savannas and fed on leaves and bushes.

#5. Andrewsarchus

Andrewsarchus Frank Vincentz

Andrewsarchus model

Like giraffes, camels, goats and cows, andrewsarchus was an artiodactyl (even-toed ungulate) but, superficially at least, that’s where any similarities end. In life, some 41- to 48-million years ago, it would probably have looked more like an extremely large and stocky hyena. Standing about as high as a grown man, and sporting a skull 33 inches (83 cm) long, it was one of the biggest terrestrial apex predators of its time. Discovered in 1924 in Mongolia, this ancient beast largely remains shrouded in mystery, since a single enormous skull is the only thing that’s ever been found, but its full body weight has been estimated to be up to two tonnes.

#6. Daeodon

EntelodonHeinrich Harder


The omnivorous entelodonts, popularly known as Hell Pigs, came in eight different varieties. Although they superficially vaguely resembled wild boars, they are not directly related to them, and instead were members of a unique mammalian family that lived between 37- and 16-million years ago. Daeodon, alternatively dinohyus, was the ultimate apex predator of its time. It was also as tall as an adult human at the shoulder, and may have weighed up to 2,000 lb (900 kg), making it one of the biggest carnivorous mammals that ever lived. The skull alone was three feet (1 metre) long, like that of the andrewsarchus, which may have been distantly related.

#7. Eobasileus

EobasileusCharles R. Knight


Eobasileus looked a little like a modern rhinoceros but, this animal, which lived some 45-million years ago during the Eocene epoch, was one of many species that made up the mammalian order of dinocerata. Unrelated to anything alive today, the entire order disappeared some 33-million years ago, perhaps due to competition with the contemporary brontotherids (another, similar extinct order). The herbivorous animal stood about seven feet (2.1 metres) high at the shoulder, and may have weighed up to 4.5 tonnes. It also sported three pairs of blunt horn-like structures, rather like those of a giraffe, and a pair of tusks.

#8. Patriofelis

PatriofelisCharles R. Knight


Patriofelis is Latin for ‘father cat’, which is a bit of a misnomer, since this animal, while looking vaguely like a cat, was not in any way related to them. Instead, is was an oxyaenid, a family of carnivorous mammals that lived between 33- and 60-million years ago. This particular genus lived 45-million years ago and grew up to six feet (1.8 metres) in length, making it about the same size as a mountain lion. Its skull was particularly large, being approximately the size of that of a modern lion. Patriofelis lived in Wyoming, and was first discovered and catalogued in 1870. Judging by its bone structure, it was likely both a proficient runner and climber.

#9. Pakicetus

Pakicetus inachus

It’s hard to believe that whales and dolphins belong to the same order as deer, camels and giraffes, but they all share a common ancestor. The earliest whales walked on the land before they became fully aquatic and their limbs became flippers. One of these so-called ancient whales was pakicetus, an amphibious creature that lived some 50-million years ago. More closely resembling a hoofed animal, it had four fully functional legs and was about the size of a medium dog. Pakicetus had palaeontologists baffled when it was discovered in 1983, but it was eventually classed as a cetacean due to its ear-bone resembling that of whales and dolphins.

#10. Synthetoceras

Synthetoceras tricoronatus skull

Synthetoceras was another member of one of the many families of artiodactyls that have disappeared over the last aeon. Living between 13.6- and 5.3-million years ago, synthetoceras resembled a deer or antelope in many ways, except for one extremely obvious difference; a single long horn with a forked tip mounted on its snout. However, only males featured this bizarre horn, which was probably used in competitions for a mate. Additionally, there were two relatively normal horns above its eyes. With a weight of around 600 pounds (272 kg) and a length of 80 inches (2 metres), synthetoceras was the largest member of the extinct protoceratid family.

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