Sunday, December 27, 2015

North American camels: not the run-of-the-mill Christmas camels

In North America and Europe, camels generally keep a low profile except for December, when they show up as part of Christmas iconography: the Three Wise Men, Nativity scenes, etc. The general scarcity of camels in these landmasses makes them exotic. Camels and llamas today evoke specific areas: camels bring to mind deserts from north Africa into central Asia, and llamas are shorthand for the Andes. However, camelids (including camels, llamas, alpacas, and so forth) are actually a North American innovation, circa middle Eocene. Through no particular fault of their own, there are now no longer any native camel species in North America, although as recently as the late Pleistocene, about 126,000 to 11,700 years ago, camels were common. The two flagship models at this time were Camelops hesternus, which translates to the evocative "yesterday's camel", and Hemiauchenia macrocephalus, also known as the "North American llama". The exact taxonomy, of course, is somewhat more bushy when you get into it, but this isn't bad for broad strokes. The camel family filled a number of niches in North America over the Cenozoic, from what we would recognize as roles similar to modern camels and llamas, to giraffe analogues like Aeypcamelus, to plus-sized forms like Megacamelus and Titanotylopus, to analogues of deer and gazelle, such as Poebrotherium (also of note as the first fossil organism named from the White River Badlands; Prout's "Palaeotherium" doesn't count because he didn't actually name it). Here are a couple of examples from the now-vanished North American empire of camels:

Stenomylus hitchcocki is a well-known extinct camel, represented by dozens of skeletons from the Early Miocene-age "Stenomylus Quarry" of what is now Agate Fossil Beds National Monument in western Nebraska. At least 32 institutions have fossils of this small camel from the quarry (Knudson and Miller 2004), including remains of 18 or so individuals that went to Amherst (Loomis 1910) and another 30 to 40 that went to the Carnegie Museum of Natural History (Peterson 1911). The quarry itself includes two main fossiliferous layers, separated by about 4 ft/1 m. The upper layer is the one that produced the excellent articulated skeletons of Stenomylus (Loomis 1910). While not exactly a "pocket camel," Stenomylus was not quite what a modern observer would expect from a camel, being a slender animal more along the lines of a gazelle or pronghorn, but smaller (think on the order of 2 ft/60 cm at the shoulder). It was part of an ecosystem also populated by "beardogs", pig-like entelodonts, chalicotheres (kind of like a horse given oversized sloth arms), and an abundance of rhinos. The conditions that created the quarry have long been a matter of debate, although some form of death under drought conditions tends to be popular.

Stenomylus from Agate Fossil Beds under glass, American Museum of Natural History

Turning from the Miocene of Nebraska to the Pleistocene of California, we have a relatively recently described genus and species dubbed Capricamelus gettyi, a camel about the size of a modern guanaco. The name Capricamelus means "goat camel", for a good reason: Capricamelus is essentially a camel rigged like a mountain goat. Mountains not being nearly as good at preserving fossils as basins, we can only guess that there were more types of similar "mountain camels" which remain unknown. In this case, we know of Capricamelus due to some fortuitous circumstances (fortuitous for us, of course; not so great for the camels). It is represented by a group of at least fifteen individuals found together southeast of Death Valley in the basin of Lake Tecopa, one of the many now-desiccated lakes that once dotted the Basin and Range. The skeletons were found at a site called "Standing Camel Basin", because feet and lower legs are found articulated and standing up. Apparently the camels were traversing the lake shore and became mired in mud, perhaps breaking through a seemingly safe "cap". Capricamelus differed from modern camels in a few other ways besides its goat-like limb proportions, notably the relatively short neck and relatively elongate skull. The teeth are interpreted as adapted for very coarse vegetation. This unusual camel was described by Whistler and Webb in 2005, and some of the evolutionary implications are covered at The Theatrical Tanystropheus. (A brief note on the age: the quarry is about 10 ft/3 m below a 2.1-million-year-old ash bed. When the description was published, this was in the late Pliocene, but the Pliocene–Pleistocene boundary has since been pushed back to about 2.58 million years ago, to fully account for the "ice ages", so the quarry would now be considered early Pleistocene. In case you're curious, true mountain goats, represented by extinct Oreamnos harringtoni, don't show up in the fossil record until near the end of the Pleistocene, although again their fossil record is limited by the same environmental issues that would affect mountain camels. We know of O. harringtoni mostly from cave records.)


Knudson, R., and S. J. Miller. 2004. Stenomylus research and management needs at Agate Fossil Beds National Monument. Abstracts with Programs - Geological Society of America 36(5):53–54.

Loomis, F. B. 1910. Osteology and affinities of the genus Stenomylus. American Journal of Science 29:297–323.

Peterson, O. A. 1911. A mounted skeleton of Stenomylus hitchcocki, the Stenomylus quarry, and remarks upon the affinities of the genus. Annals of the Carnegie Museum 7:267–273.

Whistler, D. P., and S. D. Webb. 2005. New goatlike camelid from the late Pliocene of Tecopa Lake basin, California. Contributions in Science 503.

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