Species That Don't Get Enough Publicity #6: Moropus

The thing about the featured animal today is you’ve probably seen it before. There’s a lot of museums with it-the Harvard museum, Yale Peabody museum, Field Museum, Denver museum, Smithsonian National Museum, Carnegie museum, and American museum each have a mount of it. There are multiple mounts at the place of its discovery, the Agate Fossil Beds National Monument in Nebraska. I’m sure most of you have seen this one and wandered past it, thinking it a horse or a big bizarre mammal. It is a big, bizarre mammal, but it’s one that’s one of my favorites. This is Moropus, 5 species of a large, successful mammal that roamed the American west.

Moropus was first discovered in 1877, as part of the great paleontologist Othniel Charles Marsh’s endless quest for fossils.  In that season, he found the rodent Allomys, the rhinoceros Diceratherium and Amynodon, specimens of bison, the Cretaceous bird Austinornis, the Jurassic crocodile Diplosaurus, the small ornithopod dinosaur Nanosaurus, the prehistoric stingray Heliobatis, and this new curious mammal. This was in the middle of the famous Bone Wars. At this time, Marsh and his archrival Edward Drinker Cope tried to outdo each other in terms of naming and describing prehistoric animals. While the dinosaurs like Triceratops, Stegosaurus, Camarosaurus, Allosaurus, Apatosaurus and their less famous kin have gotten the main press both now and then, the “Bone Wars” extended to mammals-Uintatherium and Megacerops, among other species, had mountains of synonyms erected by the competition of the rival geniuses. They spent their extensive family fortunes entirely on paleontology, and left the world very poor, bitter, and tired, but enriched both the Yale Peabody Museum (Marsh’s base) and the Academy of Sciences (Cope’s base) with endless fossils.

Things changed for this genus when James Cook, a partner and friend of Chief Red Cloud, found fossils on his ranch in northwest Nebraska in the 1870s. He had also befriended Marsh and Cope in his travels across the west as a cattle wrangler and gave them whatever fossils he could find. This really took off when his son Harold struck up a deal with the eastern museums in the 1920s. For a modest fee, he provided access to paleontologists O.A. Peterson of the Carnegie museum, Erwin H. Barbour of the University of Nebraska, and Henry Fairfield Osborn of the American museum. His career also encompassed the infamous mistake Hesperopithecus, a poorly preserved peccary tooth mistaken for a prehistoric human tooth by the overenthusiastic Osborn. W. K. Gregory managed to prove it as part of the Miocene peccary Prosthennops, a decision accepted by the rest of the scientific community, but Osborn stuck by his ape-man for the rest of his life.

At Cook’s ranch, which he eagerly turned into a national park, New England’s paleontologists unveiled the complete animal, a truly bizarre chimera of ungulate affinities. It was a chalicothere, a family of extinct herbivores distantly related to today’s horses, rhinoceros, and especially tapirs. Chalicotheres had been known for almost a century before these discoveries, but no where near in this state of preservation. Chalicotheres were a very successful family-ranging from North America’s Eoromoropus 40 million years ago in North America to about Ancylotherium 1 million years ago in Ethiopia. 

The skull is dramatically different from its relatives. The tip of the snout, eyes, and the teeth resemble those of a rhinoceros, while the back of the skull resembles a horse’s.  The neck is shorter and thicker than that of a horse, the front limbs long as a horse’s but the bones are proportioned like a tapir. The rest of the animal would resemble a horse (a large, draft horse) but for one thing: claws.

Another interesting trait of the skull is that male chalicotheres have comparatively higher and thicker skull roofs as a sexually dimorphic trait. (Margery Chalifoux Coombs

Systematic Zoology Vol. 24, No. 1 (Mar., 1975), pp. 55-62). Indeed, a later genus, Tylocephalonyx was distinguished for the small dome on top of its head, like a Pachycephalosaurus. It’s very likely that male Moropus head-butted like giraffes or goats for social status and sexual opportunities.

The group of chalicotheres that Moropus is associated with is called Schizotheriinae for their chimerical trait of claws. Instead of a fleshy (tapirs and rhinos) or solid (horse) hoof for fast locomotion, the front and back feet are unfused and tipped with large, curved claws like those of a sloth or a bear.  There has been debate over what they were used for. One model has them being used as billhooks, pulling down branches for browsing in a mode of life similar to that of a bear, gorilla, Therizinosaur, or ground sloth. Another model has them digging for roots and shoots like an armadillo or pangolin. Of course, all of these clawed animals can use them for anti-predator defense, and the claws of chalicotheres could be very powerful weapons if used against the bear dogs and entelodonts that could threaten it.

The long limbs, the large claws, and the wear patterns on their teeth (http://www.wired.com/2010/11/pass-the-twigs-please-toothwear-indicates-the-variety-of-chalicothere-diets/) indicate that they were browsers, again like bears, gorillas, Therizinosaurs, and ground sloths. The difficulty is that bears usually don’t use their claws to browse, and gorillas and pandas eat very different kinds of plants than Moropus. This is a niche that has not existed for 10,000 years, as most living browsers have no need of claws to grasp branches and instead rely on long necks and snouts.  There have been reconstructions of Moropus having a short trunk like its tapir relatives, but the nasal cavity is far too small and positioned forwards for a trunk to be likely.

The fact that browsers were still fairly successful explains a great deal about the paleoenvironment. In the Early Miocene, the earth was still warm despite the gradual cooling since the late Eocene, and grasses became the top plant. North America in the Miocene would have been similar to the savannas of tropical Africa and India. The Miocene was also a peak in animal diversity, with many species from many families coexisting.

There are four well-known species of Moropus, and two obscure ones.  M. matthewi is poorly represented in the fossil record and probably dubious, while the Batesland Formation of about 18 mya has several unassigned specimens of Moropus.

Moropus elatus is the biggest and best known of the species of Moropus, being found in Nebraska and Colorado in the late Arikarrean and early Harrisonian ages, about 20-18 mya. This is the species we see in New York, Chicago, Denver, Washington and Pittsburg.  It shared its environment with the oreodonts (small, piggy artiodactyls) Merychyus, Merycochoerus, Merycoides, and Hypsiops, palaeomerychid (horned, deerlike artiodactyl) Aletomeryx, the peccary Thinohyus, the horses Kalobatippus. Parahippus, and Desmatippus, the small, possibly synonymous rhinos Menoceras and Diceratherium, the bear dogs Cynelos, Daphoenodon, Temnocyon and Ysengrinia, the hyena-like dogs Cynarctoides, Phlaocyon, Cormocyon, Desmocyon, and Osbornodon, the relatives of weasellike Promarte and the giant wolverine Megalictis, musk deer Blastomeryx and Problastomeryx, the giant entelodont (big piglike relatives of hippos) Daeodon, the primitive bear Cephalogale, the llama-like camels Michenia, and Tanymykter, the gazelle camel Stenomylus and the giraffe camel Oxydactylus, the mouse deer Nanotragulus, the gopherlike beaver Palaeocastor, and the horned antelope-like artiodactyl Syndyoceras.

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Moropus hollandi is distinguished from elatus by being smaller and more gracile. However, it lived in the same time period and environment, and may have been the same species. I know of no mounts of the animal, and I strongly suspect it may have been a juvenile or female like the former species Moropus petersoni.

Moropus oregonensis was another small, slender species, found not on the great plains but in Oregon and Florida during the Arikarrean and Harrisonian. It’s possible there were denser forests that restricted body size while supporting thriving populations, or that this new species preceded M. elatus into North America. Stratigraphy suggests this may be the longest lived of the Moropus species-being the first to evolve in America and lasting into the later Miocene, overlapping the time spans of M. elatus and M. merriami. (Coombs, M. C., Hunt, Jr, R. M., Stepleton, E., Albright III, L. B. & Fremd, T. J., 2001: Stratigraphy, chronology, biogeography, and taxonomy of Early Miocene small chalicotheres in North America. – Journal of Vertebrate Paleontology: Vol. 21, #3, pp. 607–620)  Species it coexisted with included the piglike Agriochoerus, the palaeomerychid Barbouromeryx, the camels Gentilicamelus, Poebrotherium, Nothokemas, and Paratylopus, entelodonts Archaeotherium and Daeodon, the mouse deer Hypertragulus, Leptomeryx, and Nanotragulus, the musk deer Pseudoblastomeryx, the oreodonts Eporeodon, Merycochoerus, Merycoides,and Paroreodon, the bear dogs Daphoenus, Daphoenodon, and Amphicyon , the hyena-like dogs Rhizocyon, Cormocyon, Cynarctoides, Phlaocyon, and Desmocyon, the mustelid Oligobunis the paramarsupial Herpetotherium, the insectivore Micropternodus, the rabbit Palaeolagus, the horses Kalobatippus, Miohippus, Archaeohippus, Parahippus, and Anchitherium, the tapir Nexuotapirus, the beavers Meniscomys, Schizodontomys, and Hystricops, the gopher Entoptychus, the pocket mice

Proheteromys, Arikareeomys, Texomys, and Harrymys, the mouse Leidymys, the squirrel Protosciurus, the hedgehogs Parvericius and Centetodon, the rhino Menoceras, and the basal rodent Mylagaulodon

The last species is Moropus merriami from Nebraska and Nevada, surviving as late as 15 million years ago.  Again, there are no known mounts of the animal.  It lived during the Barstovian period, where the forests of North America receded even more as the earth cooled and dried. Part of its problem were that horses and camels were thriving as the grasslands covered the plains, while new species of probiscideans came in from Asia, taking over the browsing role. Moropus has always been found in very warm, wet environments which became more and more rare. It is unlikely they would have survived the Pliocene and Pleistocene, as earth cooled even more and the chalicothere niche in the New World was firmly usurped by ground sloths. Other animals of the area were the pronghorn  Merycodus and Paracosoryx, the camels Miolabis and Paramiolabis, the musk deer Blastomeryx and Parablastomeryx, the oreodonts Brachycrus, Merychyus, Ticholeptus and Brachycrus, the palaeomerychids: Bouromeryx, Dromomeryx,  and Sinclairomeryx, the proceratid Lambdoceras, the peccaries Aptenohyus, Hesperhys, and Thinohyus, the bear dogs Amphicyon, Cynelos, and Pliocyon, the bone-crunching dogs Euoplocyon, Microtomarctus, Osbornodon, Psalidocyon, Tomarctus, Protomarctus Paracynarctus, Aelurodon, Metatomarctus, and Cynarctoides, the dog Leptocyon, the cat Pseudaelurus, the badger Plionictis, the horses Desmatippus, Merychippus, Scaphohippus, Hypohippus, and Acritohippus, rhinos Aphelops, Teleoceras, and Peraceras, the beaver Monosaulax, the basal rodents Umbogaulus, Alphagaulus, and Hesperogaulus, America’s first mastodon Zygolophodon, the early bear Ursavus, the poorly named mouse deer Pseudoparablastomery, today’s modern ringtail Bassariscus and its ancestor Probassariscus, the pocket mouse Apeomyoides, the rabbit Hypolagus, the pika Oreolagus and the mountain beaver Liodontia.

You can tell by the sheer amount of names here that mammal diversity was at its height, and Moropus is symbolic of the weird and wonderful animals that ruled the earth.

Despite its ubiquity in museums and such, it’s never made a named appearance in a documentary or movie, and only two small, old toys have been made. One is a kangaroo-shaped one in a bipedal pose with a bright purple and orange coat by Playvision and can still be found in bins (or its knockoffs). The other is a far rarer quadrupedal sculpt by Starlux. Since Moropus is an archetypical North American prehistoric mammal and is a frequent sight in prehistory books, its rarity is probably due to the age-old neglect of Tertiary animals.  

It’s weird, it’s big, and it’s all American, so I would argue that it needs more respect and awareness.  I'm very glad when I see it in media. Fellow fans of the program My Little Pony will be please to find out fans have made loveable Moropus ponies on Deviantart like these. So Hollywood, give this guy a break. Museums, keep him on display. Toy companies, here’s a new fresh face. Authors, think about the crap you’re writing and how this genus could perk up the place. And remember, shop Moropus where you work or play.