The curious chalicotheres

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Moropus, a chalicothere. From The Annual Report of the American Museum of Natural History.


Suppose for a moment that you are walking across a dry, wind-swept landscape known to be rich in fossils. During your perambulations you notice a large fossilized claw sitting on the surface; what sort of animal could it be from? There is a lot you would have to know about the area, like how old the rock in that spot was, but it would seem reasonable that the claw belonged to a large predator.

Nature, of course, is not so straightforward. Panda bears have teeth and claws that reveal their carnivoran ancestry and yet they primarily eat plants. Giant sloths and the even more ancient therizinosaurs also had extraordinarily large claws on their hands but were herbivores. We focus on the claws of predators because we know the damage they can do, but a claw by itself tells us little about the animal it once belonged to.

There are few creatures that exemplify this anatomical lesson better than the extinct chalicotheres, relatives of horses and rhinoceros. Indeed, the chalicotheres were incongruous creatures that looked like a cross between a horse and a giant ground sloth, with long necks, a downward sloping back, and feet with tipped with claws instead of hooves. This set them apart from their other perissodactyl relatives, and their bizarre nature made it initially very difficult to determine just what sort of creatures they were.

The genus Chalicotherium was named in 1833, but it was not based on much. The 1851 edition of the Iconographic encyclopaedia of science, literature, and art, for instance, reveals that little more than the teeth of Chalicotherium had been found;

The genus Chalicotherium is known only by its dentition, which indicates an affinity with Anoplotherium. Two species have been found in the meiocene deposits of Germany, whose bulk, it is supposed, reached that of the rhinoceros.

Anoplotherium was an artiodactyl famously described by Cuvier from the gypsum quarries of Paris and it seemed that Chalicotherium was a similar, if larger, herbivore. Fossils of this genus remained frustratingly elusive, or so scholars thought. Elements of its limbs had already been found and attributed to a different animals called "Macrotherium" and "Ancylotherium" which paleontologists thought resembled giant anteaters or sloths. There was no reason to think a creature with teeth like an ungulate would have long arms like a giant sloth, but this is precisely what Charles Forsyth-Major proposed.

As a autobiography of Forsyth-Major's colleague W.B. Scott reveals other paleontologists were incredulous;

When ... Forsyth Major declared his belief that these two apparently unrelated animals [Chalicotherium and Ancylotherium] were one and the same, Weithofer and I scandalized and energetically dissented from such a heresy. However, we were anxious to learn Forsyth Major's reasons for his belief and asked him to explain. He replied substantially as follows: "No one had ever found the feet of Chalicotherium, or the skull, or teeth of Ancylotherium, yet they always occur together in the same beds; where you get one, you get the other." I admitted the force of this, but remained unconvinced.

Some weeks after this conversation, I was in Paris, where the eminent French palaeontologist, M. Filhol, invited me to come to the museum and see the new fossil mammals which he had been excavating at Sansan in the south of France. Among these was a complete skeleton, with the bones in their natural connections, which completely confirmed Forsyth Major's interpretation; the skull and teeth were those of Chalicotherium, while the feet were those called Ancylotherium! In a paper which I wrote shortly after my return home, I was happy to bear witness to Forsyth Major's independent discovery of this more interesting relation, thereby causing him to write me a very grateful letter.

Forsyth Major had been vindicated and Scott considered the story to be especially instructive of one of the hazards of paleontological work. During a lecture on paleontology at Wood's Hole in 1895 Scott said;

Extraordinary blunders have sometimes been committed in this work [of properly associating fragmentary fossil remains]. In the remarkable genus Chalicotherium the skull was at first referred to one mammalian order and the feet to another, and Forsyth-Major's suggestion that they all belonged together was received with incredulity.

Despite the discovery of a more complete skeleton, however, some naturalists were still unsure of just what sort of creature Chalicotherium was. It had some relationship to other hoofed mammals but how could an animal with claws be ranked among those with hooves? The 1904 Annual Report of the Geological Survey of Canada, for instance, had this to say about Chalioctherium;

Chalicotherium represents a distinct order and had a curious assemblage of characters amongst which were notably the possession of clawed feet, and teeth suggestive of the Perissodactyls.

Ernest Ingersoll, in the 1907 edition of the Life of Animals followed Henry Woodward's classification presented in a 1904 address to the Royal Microscopial Society and kept the chalicotheres within the group Ancylopoda. This was an anomalous group that Ingersoll placed in association with a few other groups that had defied stable classification. This largely had to do with the fact that they were unlike any living creatures and this apparently led Ingersoll to cast them as "losers";

None of the foregoing seem to have been successes, so to speak; that is, they were unable to change with the gradually altering conditions of climate and vegetation as time advanced, and were crowded out by the more adaptable progenitors of modern hoofed mammals.

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Moropus, from The American Museum Journal.


The 1906 textbook Outlines of Zoology likewise remained vague on the systematic position of the group and simply stated that Chalicotherium and its allies were "remarkable type[s]" of perssodactyl. W.B. Scott's A History of Land Mammals in the Western Hemisphere published in 1913 would finally bring the chalicotheres closer to our present understanding. Despite the apparent existence of a complete skeleton in Paris since the late 19th century a large part of the systematic dilemma was that chalicothere remains were often fragmentary. America, in particular, contained little more than bits and pieces and it was difficult to tell whether the North American genera closely resembled those from Europe and Asia.

(I also have to wonder if, for whatever reason, the complete Chalioctherium from Paris was not as widely-reported or well-studied as it might have been. This would explain why so many naturalists seemed tentative or confused about what sort of creature it was.)

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The feet of Moropus, from The American Naturalist.


Strangely, however, it would be an American chaliocthere that would give naturalists a better look at this group. In 1877 O.C. Marsh described the chalicothere genus Moropus. It, too, was known from petrified bits and pieces, but by 1907 complete enough remains of it were found for O.A. Peterson to confirm that not only was Moropus a chalicothere, but that the chalicotheres represented a kind of "aberrant" type of perissodactyl.

Ten years later a complete Moropus skeleton was found and mounted in the American Museum of Natural History. It was featured in an article of Natural History by W.D. Matthew, and now that the general form of these creatures was known greater attention could be paid to the question of how they were using their claws. Matthew stated;

The only plausible suggestion that has been made is that the great claws were designed to aid the Moropus in scraping away sand in dry riverbeds or other suitable places to make a water hole where lie might drink. There is good reason to believe that the western country where lie lived was even then more or less arid, with a scanty water supply in the summer or seasons of drought. In Central Africa today the animals congregate in great numbers around the scattered water holes, and some of them may dig out the holes more or less with their paws. Our Moropus could do that sort of thing to great advantage, and the powerful claws often might enable him to dig down in a sandy riverbed to water that otherwise would be beyond his reach.

Unfortunately the paleobiology of Moropus and its relatives remains mysterious. They are certainly not the media darlings that dinosaurs are, and like many groups of fossil mammals they are probably only studied by a handful of paleontologists. There are still many unanswered questions about chalicotheres and how they lived, but this provides plenty of opportunity for any intrepid students of paleontology who are looking for a neglected group of organisms to study.

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I have read that European scientists, when examining Chalicotheres, refused to believe that the claws belonged to the rest of the skeleton, because a large herbivorous mammal with claws was unprecedented, and it took more discoveries to confirm that yes, this was a plant-eating, clawed relative of horses and tapirs. The claims of some that chalicotheres ate roots and bulbs doesn't match their low-crowned dentition, so a lifestyle like the groundsloth, pulling down leaves on which to browse, seems to make the most sense (though scraping in the ground to obtain water in the dry season, as Matthews suggested, certainly isn't out of the question,and we know there were killing droughts in places like Agate Springs, Nebraska, where Moropus was fairly abundant.) I'm personally fascinated by these creatures because they have no modern analog-they're bizarre, outlandish, "prehistoric" if you will.

By Raymond Minton (not verified) on 23 Feb 2009 #permalink

Thing looks like an animal tank. The rib cage is solid, and it appears the ribs are thickest perpendicular to the 'surface' of the ribcage, the joints have massive bone spurs, and I wouldn't be surprised if some of the apparent bowing to the bones was from some serious musculature..

Not that it's my field or anything but it certainly looks like an herbivore that could defend itself pretty darn well.

Or, in the last picture, like a pet dog that just realized it's master was angry at it for pooping on the floor, slinking away ;-)

A question, though: is part of the skull missing, or did the chin really project as far in front of the teeth as it seems to?

Something I hadn't noticed before about Moropus: on the hind foot, the middle tow is the largest, as you'd expect from a Perissodactyl, but on the front it is the innermost (the index finger, I suppose, assuming that Perissodactyls lost their thumbs before the ancestors of Moropus went off on their autapomorphic trajectory! Further evidence, I'd guess, that at least the front feet were being used for something other than walking on.

By Allen Hazen (not verified) on 23 Feb 2009 #permalink

Dreikin; Click the link to the Peterson paper and scroll down. You'll see another reconstructed skull of Moropus that's a little more defined. It seems the lower jaw did jut out a little but not very much. The front of the snout may have been like a rhinos fleshy, prehensile lips, though, so it might be harder to tell whether the jay jutted out in front in life.

> it certainly looks like an herbivore that could defend
> itself pretty darn well.

Chalicotheres have been among my favourite prehistoric (? - very similar animals are depicted in Scythian art) mammals since my childhood, the "firepower" aspect, impressive to schoolboys of all ages, certainly was one of the reasons. Of course, the ability for self defence was probably needed in the presence of entelodonts, especially in an animal that was neither peculiary fast nor r-selected.

> The front of the snout may have been like a rhinos
> fleshy, prehensile lips, though, so it might be harder to
> tell whether the jay jutted out in front in life.

The shape of the skull actually makes one onder why all the reconstructions of Chalicotheres - including my Bullyland replica - show a horse-shaped snout, rather than a tapir-like short trunk.

Looking again, it seems that frontmost part of the upper jaw of the Moropus skull above was missing. It stuck out as far as the lower jaw. Even so, the "horse model" can be called into question. I have my doubts about a tapir-like trunk, but something more akin to a black rhino with a big fleshy lip might be a better fit than the squared-off horse snout.

Sci; Try here. As said in other comments, though, the shape of the snout has traditionally been interpreted as horse-like even though this might not have been so.

Indeed, the chalicotheres were incongruous creatures that looked like a cross between a horse and a giant ground sloth, with long necks, a downward sloping back

Moropus is a member of the chalicothere subfamily Schizotheriinae which lacks the gorilla-like posture and looks more horse-like. Members of Chalicotheriinae were the bizarre ones - Mauricio Anton has an excellent drawing of members from both subfamilies here.

Very interesting! I didn't know before how people started to realize that the claws and the teeth belonged to the same animal.
I've read somewhere that Cuvier described chalicothere claws as that of a giant pangolin, and I've seen a paper from the 1830s by Kaup that argued that they actually belonged to Dinotherium. I've also read (in a book by Simpson, I think) that in the case of the clawed artiodactyl Agriochoerus, the skull, forelimbs and hindlimbs were originally assigned to three different animals.

By Lars Dietz (not verified) on 24 Feb 2009 #permalink

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Roxanne: It is NOT a dinosaur, but a mammal.

I've always thought that the scene in Walking With Beasts where the Hyaenodon leaps onto a chalicothere and takes it down was a very one-sided affair. They should have at least shown the chalicothere's strength, perhaps by having one of them fend off an attack by shoving the creodont aside.

Look what I have found:

http://www.cryptomundo.com/wp-content/gazeka.jpg

Somebody had the trunk-lip idea before - although those four digits (not what you would expect on a perissodactyl, especially one from the Neogene) and the carnivorous looking dentition are not very convincing. And those Tcho-Tchos really have a bad hair day ;-)!

The picture by Mauricio Anton that Cameron McCormick linked to (five responses up) is one of the many beautiful pictures in "Mammoths, Sabertooths, and Hominids: 65 million years of mammalian evolution in Europe" by Jordi Agusti and Mauricio Anton (Columbia University Press, 2002-- title pretty much describes content, though the European mammal story involves a lot of "immigrated from Asia at this time" in addition to a bit of "evolved in situ" ... fun book, roughly at the level of Kurten's "Age of Mammals" on the popular to technical spectrum, or maybe just a bit more wonkish than Kurten's book): this image is on page 144.

Like many of the "parade of suspects" illustrations in the book, the animals are shown passing a wall of squares: in some these are one-meter squares, in others 50-centimeter: alas, the caption of this one doesn't specify the dimension! ... I'd ***guess*** that they are 50 cm, which would make the big Schizotheriine (Ancylotherium) about the size of a large horse and the Chalicotherium in the foreground more the size of a large gorilla: if they are meter squares these would be seriously BIG animals, in the Elephas and Megatherium size range. But I'm not sure of this.

By Allen Hazen (not verified) on 25 Feb 2009 #permalink