Researchers recently uncovered a new and remarkable animal in the fossil record in China: Rugosodon eurasiaticus, a chipmunk-like creature that was a member of the multituberculate family. The multitberculates, a sort of proto-rodent family, were eventually out-competed by the first rodents, and went extinct.
But Rugosodon eurasiaticus is remarkable for its longevity. It’s been found in the fossil record with examples dated from both 170 million and 35 million years ago, making it the longest-lived (and, by some definitions, therefore the “most successful“) mammal known to science.
There are lots of animals still around that are remarkably unchanged from millions of years ago. These are popularly called “living fossils,” though that phrase is not usually used by scientists, and often give us insight as to the basal, or primitive forms and evolutionary history of other, more recently evolved animals. They also give us significant insight into the geologic history of the planet; animals survive when they can reproduce at a stable rate, simple as that. But these animals plateaued early, finding a way to breed, often in isolation (on islands, for example), at a stable rate, and remained successful without changing much, physically. We don’t really understand why this happens to some animals and not others, but the facts are pretty clear: they were doing fine, so they pretty much just stayed the way they are.
And you might be surprised at a few of them. Check out the gallery to see seven of the most fascinating.
It would be easy to assume two species of solenodon, found on the Caribbean islands of Hispaniola and Cuba, are just shrews with long noses. They’re small and clumsy and dully colored–but they’re actually one of the rarest and weirdest mammals on the planet. The solenodon is one of the very few mammals to produce its own venom, which flows up through grooves in the incisors in its bottom jaw. The solenodon is found in the fossil record from a whopping 76 million years ago, basically unchanged. That’s about when primitive manatees split from primitive elephants. And it’s so old that the two species, the Cuban and Hispaniolan solenodons, split from each other about 25 million years ago–about the time that early hominids split from Old World monkeys.
The aardvark eats ants, but is not an anteater; it burrows like a pig and has a pig’s flat nose and bristly hair, but is not a pig. In fact it’s the only member of its order, Tubulidentata. The name refers to the animal’s bizarre teeth, which are constructed of many narrow tubes that are filed down and regrow continuously. Its closest relatives are, of all things, elephants. The aardvark is found in the fossil record dating way back to the Eocene–about 55 million years ago, pretty much unchanged from the modern aardvark. And it looks like it’ll be here for a while longer, as well. Though it’s elusive, its numbers do not appear to be significantly shrinking.
Monito del Monte
“Monito del monte” means “little mountain monkey,” but this intriguing creature is no monkey. Nor is it any other kind of primate, nor is it a rodent, which it sort of resembles. It’s actually an ancient marsupial native to Chile and Argentina, unrelated to any other New World marsupial (like the opossum). It’s suspected to be related to the true possums of Australasia, but it would have split from them a whopping 46 million years ago–and scarcely changed since. The tiny monito del monte lives in the highland bamboo forests of mountainous South America, eats mostly insects with some fruit and seeds and nuts, and hibernates, which is unusual for marsupials. It’s listed as Near Threatened by the IUCN.
Laotian Rock Rat
Cursed with a phenomenally un-cute name, the Laotian rock rat is one of the most fascinating animals on the planet–and not actually an ugly animal! It was discovered at a meat market in Laos as, well, meat, back in 1996. Baffled by the peculiarity of the animal’s skull shape, researchers dug deeper into the history of this creature and finally described it properly for the first time in 2005. The original researchers described it as the sole known member of a totally new family, which is highly unusual; new animals are found every year, but they’re usually related to some other animal we know (like the olinguito). But those researchers only compared the Laotian rock rat to other extant mammals, not to the fossil record. The year after, a new crop of researchers published a paper suggesting that the Laotian rock rat is actually a member of a family, Diatomyidae, that’s known in the fossil record. The rock rat isn’t new–it’s actually incredibly old, a so-called “Lazarus taxon.” Lazarus taxon animals are known from the fossil record, but thought to be extinct in modern times, until they’re discovered walking/swimming/flying around. The coelacanth is the classic example. The Laotian rock rat first appeared in the fossil record about 32.5 million years ago, but about 11 million years ago, it disappeared from the fossil record. Nobody knows why, considering the rock rat is still here, and has been living and dying through that entire time. It looks sort of like a cross between a squirrel and a rat, and lives, as its name suggests, on rocky limestone areas of Laos.
The chevrotain, or mouse-deer, is mostly found in southeast Asia, like the Laotian rock rat (though one species is found in Africa). It’s an ungulate, related to deer, but it’s tiny, weighing as little as just a few pounds (about the size of a rabbit). It’s also a bizarrely primitive creature; they have four toes, no scent glands, tiny skinny legs, and pig-like noses. That makes sense, because the chevrotain can be found basically unchanged in the fossil record up to 20 million years ago. They’re not very well understood or known; they are solitary and largely nocturnal, and small enough to hide whenever they don’t want to be found. Despite their looks, they are also excellent swimmers, and some species can hold their breath for 4 minutes.
The Amami rabbit lives on two smallish Japanese islands: Amami and Tokuno. Sometime between 10 and 20 million years ago, it landed on those islands, where there are no other native rabbits, and just kind of…stayed like that. It’s the world’s most primitive rabbit, with short ears and an elongated skull, small eyes, dense woolly fur, and long curved claws. It’s also dangerously endangered, largely because of pit vipers. No, the pit vipers don’t eat the rabbits–the Javan mongooses, released on the islands by the dozens to combat the vipers, do. Turns out weird old bunnies are easier to catch than super venomous snakes.
The internet’s favorite animal, the red panda is a total oddball, evolutionarily speaking. It’s the sole member of its family, Ailuridae, not closely related to, well, any other mammals in the world. It’s distantly related to the giant panda, but that split happened tens of millions of years ago. It’s been classified as a bear, a raccoon, and a weasel in the past. Current consensus is that it’s the sole living representative of what was once a powerful and wide-ranging group of animals. There were red pandas in North America, about 7 million years ago; lots of fossils were found at the Gray Fossil Site in Tennessee. They’ve also been found in Europe and all over east and southeast Asia. And yet today there’s only the one, absurdly adorable creature, bounding around trees in China, India, Nepal, Burma, and Bhutan (this is a smaller region than it sounds).