Macrauchenia (Owen), a genus of fossil herbivorous animals, forming one of the connecting links between the palaeotherium and other extinct pachyderms of the Paris basin and the camel family, especially its American representatives. This genus was established in 1838 by Prof. Owen on some vertebrae and bones of extremities obtained by Mr. Darwin in Patagonia, from an irregular bed of pale reddish earth and sand, evidently of subaqueous origin, overlying the porphyrinic gravel at St. Julian, in lat. 49° 14' S.; the gravel bed itself was over the pumiceous strata and argillaceous beds of the upper tertiary formation. The bones were found in a deep furrow in the upper tertiary filled with the earthy deposit, evidently but recently elevated above the sea; indicating that this animal lived after the gravel was spread over this plain, and long after the existence of recent shells, which, according to Dar-win, are among the most common now living on the coast. The M. Patachonica (Owen) was as large as the present hippopotamus and rhinoceros.

The cervical vertebras were very much like those of the llama, forming a long and slender neck, bearing probably a comparatively small head without a proboscis; as in the llama, these have no canal for the vertebral artery in their transverse processes, this vessel passing for a considerable part of its course in the spinal canal itself; their form is also elongated, with a slight anterior convexity and posterior concavity on their articulating surfaces, indicating a less freedom of motion in the neck. The lumbar vertebras, though seven in number as in the llama, in their form and the structure of their articulating surfaces resemble those of pachyderms, and indicate a slight concavity in the region of the loins. The union of the radius to the ulna, and of the fibula to the tibia, approximates it to the ruminants; but the feet resemble those of pachyderms (like the tapir) in having separated metacarpals, and three almost equal fingers terminating each in a small rounded hoof. According to Pictet, the molar teeth resemble those of the palaeotherium, the last lower one having no third lobe, and the premolars being more simple.

For details see Owen's description of the fossil mammals in the "Zoology of the Voyage of the Beagle" (1840).