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Beware of the Gorilla-Horse

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A Hyainailouros sulzeri (300 kg) stalks a herd of Chalicotherium sp. at dusk, but he didn’t count on having to deal with testosterone-filled, ornery bulls (800 kg), France, 13 million years ago.

Chalicotheres were perhaps the most striking beasts of the Miocene epoch (23-5 mya) and a true marvel of evolution as far as placental mammals go. They could accurately be described as Frankensteinian creations, made from bits and pieces of various unrelated animals. Members of the perissodactyl order (the odd-toed ungulates), they are most closely related to rhinos, tapirs, horses and the likewise extinct brontotheres, but didn’t look much like any of them. The earliest chalicotheres, like Eomoropus appeared during the mid Eocene in Asia (45 mya) and by the Late Eocene and Early Oligocene (35-30 mya), the genus Schizotherium, which is known from many albeit fragmentary specimens, was widespread across Eurasia, found from the Atlantic to the Pacific coast.

These were representatives of one of the two subgroups of chalicotheres, the schizotheriines, who looked sort of like jacked-up horses but instead of hooves, they possessed claws, which would have helped them to manipulate branches while feeding. Schizotheriines were very successful and radiated out of Eurasia into Africa and even North America. By the end of the Oligocene, we were seeing massive forms like the long-necked Borissiakia betpakdalensis, known from the Askazansor Formation of Kazahksta (Late Oligocene or Early Miocene) and the similarly-aged Moropus elatus from Agate Springs in Nebraska, who was perhaps the largest of the chalicotheres, at nearly 2 tones.

Schizotheriines were very diverse throughout the Miocene epoch on both sides of the Atlantic, surviving until the Mid Miocene in North America (14-13 mya), with species like Moropus merriami and the bizarre, dome-headed Tylocephalonyx skinneri, but in Eurasia, they continued to thrive well into the Pliocene, most famously with the genus Ancylotherium, which ranged across Africa and Eurasia, with the last of them dying out in Africa at the end of the Blancan (1.8 mya). By the time of the ice ages, their diversity seems to have dwindled severely, with the last record of these animals being Nestoritherium, known from the Early to Mid Pleistocene of India and Myanmar.

You likely heard the term “gorilla-horses” or “knuckle-walkers” in reference to these animals, but that description does not fit the schizotheriines all that well, as they were unique but still mostly conservative ungulates. The group’s reputation as oddities is mainly owed to their other subgroup, the chalicotheriines, who have become more iconic but are far less diverse in the fossil record.

As is obvious, Chalicotherium is the type genus of this group and it was first erected in 1833 by German naturalist Johann Jakob Kaup. He named the species Chalicotherium goldfussia, based on fossils found in Upper Miocene strata in Germany (circa 10-7 mya). The name actually means “pebble beast”, as Kaup thought that its teeth were pebble-like. As more fossils of this animal came to light, workers initially assumed that the massive, clawed forelimbs belonged to some kind of huge anteater-like animal while the rest of the body was properly identified as an odd-toed ungulate, but later it was realized that they had stumbled upon a true evolutionary oddity.

This peculiar creature might have had a head reminiscent of a horse's, but the rest of its body was more akin to a gorilla, with very long forelimbs and rather short hindlimbs, giving it a sloped back and making the head the tallest point on its body, in contrast to schizotheriines, like the sympatric Ancylotherium pentelicum, which had more horizontal backs. Yes, unlike what Walking with Beast showed (which was mainly the result of them cutting corners by reusing models), Chalicotheirum and Ancylotherium were very different beasts www.researchgate.net/figure/Re…


It also sported long, curved claws and walked on its knuckles to protect them, very similar to an anteater and ground sloth. Speaking of ground sloths, chalicotheres were very much the ungulate equivalent of ground sloths and occupied a similar niche in Africa, Eurasia and, for a while, in North America, as the giant xenarthrans did in South America and later, ironically enough, in the chalicotheres' old stomping grounds in North America. And like with ground sloths, chalicotheres likely used their claws for defense against predator as well, and possibly for intraspecies combat, with chalicotheriines in particular having very formidable weaponry.

Along with C. goldfussia, a second species was found in Upper Miocene Europe, named Chalicotherium grande, or alternatively Anisodon grande. While very similar in build, C. goldfussia was a giant, weighing close to a ton and with a head height of over 2 meters, while C. grande was only half that size, at 500 kg. While Chalicotherium is mainly known from Europe, fossils attributed to this genus have also been found in Asia, notably the species Chalicotherium brevirostris from the Upper Miocene Tung Gur Formation in Inner Mongolia, and Chalicotherium salinum from the Sivalik Hills of India, with the youngest known fossils of the latter dating to the Lower Pliocene (5-3.5 mya).

Once more, contrary to what Walking with Beasts would have you believe, Chalicotherium did NOT live in the Oligocene, as there is zero evidence to suggest that. All its species are from the Upper Miocene, with some fossils from the Lower Pliocene, and the oldest evidence of chalicotheriines, which may or may not belong to Chalicotheirum itself, date to the Mid Miocene (16-14 mya) and mainly come from Europe. By the time the knuckle-walking gorilla-horses came onto the scene, both indricotheres and entelodonts were long gone, as was Hyaenodon. The aforementioned Borissiakia did overlap in Asia with Paraentelodon, Paraceratherium and possibly some species of Hyaenodon, and the North American Moropus elatus did coexist with Dinohyus at Agate Springs, with the latter two having strong evidence of a predator-prey dynamic, as some Moropus fossils show clear bitemarks made by the giant entelodont, but both of these animals were schizotheriines.

Early forms of Chalicotherium or at least chalicotheriines of some kinds did, however, coexist for a short while with a large hyaneodont known as Hyainailouros sulzeri, who was a prominent predator in Europe during the Middle Miocene. While mainly known from fragmentary material, we know a lot about its anatomy thanks to one decently-preserved skeleton found near Chevilly, France, which shows that it was a very stocky animal with short legs (making it an ambush predator) and a large head, growing as big as a tiger (up to 300 kg). It was only distantly related to Hyaenodon, as it was a hyainailourid, a derived group of hyeanodonts who duirng the Miocene exchanged the shearing teeth of earlier taxa like Hyeanodon itself for bone-crunching jaws, therefor living up to the “hyena” in their name far more, despite not even being carnivorans.

The lineage that led to Hyainailouros likely originated in Afro-Arabia during the Oligocene-Miocene turnover with Simbakubwa kutokaafrika (300-400 kg), which later gave rise to the massive Megistotherium osteothlastes (20-15 mya), which is one of the largest hypercarnivorus mammals discovered yet, with a body weight of 500-600 kg and a skull 65 cm long.

Fossils attributed to Hyainailouros have been found throughout Africa and Eurasia, from Namibia to Pakistan to Western Europe, dating from various points of the Miocene. Hyainailouros sulzeri itself was one of the last of the hyaenodonts and the last large-bodied species on record, dying out around 14-13 mya. During its day though, it successfully coexisted with carnivorans, most notably the massive bear-dog Amphicyon giganteus, which grew even larger, at nearly half a ton. But while Hyainailouros may have been an early predator of chalicotheriines, their main predators throughout their reign were in fact carnivorans, such as the aforementioned giant bear-dog Amphicyon, saber-toothed cats like Amphimachairodus and the tiger-sized hyena (or close relative) Dinocrocuta.

Yes, despite its bizarre and “prehistoric” appearance, Chalicotherium was in actuality a very recent animal who coexisted with many more familiar creatures, not just carnivorans, but also animals like Deinotheirum in Europe and the basal giraffe Sivatherium in India (likewise known from the Sivalik Hills), and was even a contemporary of early hominids like Orrorin and Ardipithecus, and even early forms of Australopithecus, though it would not have met any of them. Though some chalicothere fossils from the Upper Miocene and Lower Pliocene of Africa have sometimes been referred to Chalicotherium, hence why a plagiarized WWB Chalicotherium showed up in that lackluster French documentary Species Odyssey.

Walking with Beasts also popularized the idea that chalicotheres were gentle giants, passive creatures that you could walk up to and hang around with. While that is possible, there obviously is no way of knowing their temperament from mere bones. It’s also very likely that their level of aggression could have varied greatly depending on species, as modern odd-toed ungulates vary from being shy and docile like tapirs to bad-tempered and standoffish like the black rhino. The reality is that chalicotheres were undoubtably aggressive some of the time, not just when dealing with predators, but also with mothers guarding their calves and testosterone-pumped males during mating season, which is true for all modern ungulates. I always found Chalicotherium itself to be a rather intimidating animal, with its weird proportions, huge arms, long fingers and wicked claws, and it’s easy to imagine what that could do to a predator or to a rival male during agonistic bouts.

 

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Olmagon's avatar

Oddly enough it seems that almost every media depiction of chalicotheres has their whole purpose to be "getting killed by a big predator" the way hadrosaurs have it in media despite them having large claws that could serve defensive purposes, whilst the convergently similar ground sloths seem to get treated more able to fight back.

WDGHK's avatar

Yes, it is a shame, especially since these bizarre animals could make for great focal creatures. As far as extinct, Cenozoic herbivores go, chalicotheres are some of the most fascinating in concept alone, as they are this weird mish-mash of perissodactyl and ground sloth characteristics, so it would make for an interesting story to speculate on just how these animals led their lives. It also doesn’t hurt than many of the biggest and most well-known taxa (Chalicotherium, Moropus, Ancylotherium) come from formations with equally interesting neighbors.

Olmagon's avatar

Well I hear it is possible a paleodocumentary with Nigel Marven narrating is going to be made and have Moropus as one of the focal creatures along with Daeodon so this may finally be their chance to be shown doing more stuff.

WDGHK's avatar

I’ve heard about Forgotten Bloodlines a long time ago. Good models, I like that they also included Menoceras, but I’m not one to get hyped up prematurely. I’m waiting for it to come out and see myself. At the very least, it should cast the spotlight on chalicotheres, as Moropus is touted as one of the two lead animals.

This reminds me a bit of Temple Run ngl

Ender-Skywalker's avatar

Excellent composition!

I always felt that this creature was taken down way too easily by the Hyenadon in Walking with Beasts. With those formidable claws, I feel it should’ve put up more of a fight.

WDGHK's avatar

It did go down rather easily. Though the Hyaenodon in “Land of Giants” was essentially a Megistotherium but double the size of the real deal. In other words, getting pounced by a 900 kg predator with bone crunching jaws would be hard to shake off.

Some large hyainailourids (Simbakubwa comes to mind) lacked crushing dentition and were equipped with similar dental hardware as hyaenodontid hyaenodonts.


And since when did A. giganteus get close to 500kg? I know it was larger than Hyainailouros, but 500kg seems excessive-to my knowledge only A. ingens reached such proportions among amphicyonids.

WDGHK's avatar

I was mostly drawing from memory, as I have heard far greater weight attributed to A. giganteus but I was trying to be more rational and realistic. I also saw this https://www.researchgate.net/publication/342279739_New_fossils_of_Amphicyonidae_Carnivora_from_the_middle_Miocene_MN6_site_of_Carpetana_Madrid_Spain

Inmyarmsinmyarms's avatar

In general sloth-like mammals tend to be depicted as pretty passive, barring the occasional festy ground sloth. Chalicotheres do lack some features more associated with combat other perissodactyls have (like large canines, horns or particularly strong bite forces), but as you say behaviour is hard to predict from fossils so they could have been zebra-like in terms of temperament for all we know.

WDGHK's avatar

No modern ungulate has xenarthran-like claws. I'd say those more than make up for a lack of horns or fangs.

DINOTASIA123's avatar

Sometimes herbivores are just as dangerous as the predators they share they’re ecosystem with.

Dromaeosaurus21's avatar

Honestly, I agree with you that Chalicotheres were undoubtably aggressive some of the time lime modern ungulates.

WDGHK's avatar

That’s hardly a debate, as few animals can survive without the capacity to lash out and combat other animals, unless they evolved in a predator-free island or are far too big to be threatened.

Dromaeosaurus21's avatar

Of course, I totally understand.

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