Twilight beasts come in all shapes and sizes, with some being more familiar, like the sabretooth cat, Smilodon, and others less so, like the strange mini-sheep, Myotragus. Although we have some fossils, there are still a lot of awesome things to learn about many extinct animals. After almost 200 years from the discovery of the first member of a very bizarre group of creatures, little is still known about them even today. This beast isn’t an iconic mammal, but it should be; it was one of the last of its kind, and also witnessed the origins of our own species.
Tracing its beginnings back to the Eocene, around 40 million years ago, Chalicotheres were a successful group of animals that only relatively recently vanished from the world. Ranging across North America, Asia, Africa and Europe, they were a widespread group flourishing across the northern hemisphere. (They didn’t reach southern continents such as South America and Australia because these were cut off by oceans). They may have been long-lived and a promising group of mammals, but they were also pretty weird.
Chalicotheres are grouped together with horses, rhinos and tapirs (in the order Perissodactyla, meaning ‘odd toed’). Like rhinos, they had three toes on each foot. Unlike rhinos, or any other Perissodactyla, they had claws on their feet instead of hooves. Some suggest these often oversized claws were used to pull down branches for easier browsing. It is equally as likely that they were used in defence.
A defining feature of the group is their oversized arms compared to their legs and for a creature that walks on all fours, this is quite unusual. Their shorter, squat back legs took a lot of weight as the big animal walked. Some fossils even show evidence of callosities in the hip bone, indicating that that some species may have sat down whilst feeding, similar to gorillas today. Oddly, some species had another similarity to gorillas as result of the Chalicothere’s elongated arms; some walked on their knuckles, with enormous claws on the front hands curved backwards when they walked.
These big claws were not used to catch prey. Their odd teeth give away their less ferocious table manners. We all can find a skull, or even a single tooth, and automatically ‘know’ if the creature was a carnivore or a herbivore. Chalicotheres were herbivores with their large, flat ridged molars. The top jaw (the maxilla) didn’t have any incisors, and all the molars are quite unworn, suggesting that generally this group browsed on fairly soft vegetation which didn’t wear down the teeth.
North American Chalicotheres were successful for around 10 million years with the last Genus, Moropus becoming extinct around 13.6 million years ago. Across the Atlantic, although fossils are not common, the group was still strong, with specimens found in Greece, Turkey, Asia and Africa.
Ancylotherium was the last surviving Genus of this successful group. Taller than a horse, its massive head would have scoured the land for luscious trees as it moved around on the African savannah. Typical of Chalicotheres, this magnificent beast had longer forelimbs than it did back limbs, but the fossil hand and feet bones show that it didn’t walk on its knuckles. Remains of this big beast have been discovered at several sites in Africa along with hominin fossils (including Laetoli, Olduvai and Omo).
Even though the group of Chalicotheres were around for over 40 million years, with fossils turning up all over the northern hemisphere, not much is known about these amazing creatures. Their unusual body form, dentition and mode of locomotion have caused debate since the very first fossils were discovered in 1833. Our Twilight Beast, Ancylotherium hennigi, was the last of a once great group of magnificent creatures. A change in climate, and perhaps increased competition could have given the final blow to this species, vanishing an entire group forever. Often the most specialist creatures are more vulnerable to extinction; if the climate changes and the food they rely on vanishes, they will vanish too. And vanish these strange beasts did.
Chewing soft luscious leaves in the shade on the savannah, this wonderful animal may have absent mindedly watched a funny group of apes walking on two legs hurrying through the grass whilst constantly looking around them: another Twilight Beast, that of our ancestors.
Written by Jan Freedman (@JanFreedman)
Art by Tabitha Paterson (@TabithaPaterson)
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