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.