The bizarre South American litoptern Macrauchenia is a showcase animal when one thinks of Pleistocene South America, along with Smilodon, and many other weirdos. But, one thing it’s always been depicted with is a trunk. Most famously, the Walking with Beasts Macrauchenia sports one of these long shnozzes. The reasoning behind this trait is a highly reduced set of nasal bones and nares facing upwards. However, this isn’t quite how trunks work. Trunks need reduced nare bones, but not to the point where they are near nonexistent. The levator nasolabialis and levator labii superioris muscles need a base to work off of when lifting and lowering the trunk. On top of that, the animal would need wide cheek or zygomatic bones, for the levator anguli oris and zygomaticus major muscles, the muscles which help you and I smile, and turn our mouths. Macrauchenia lacks these two basic needs for a trunk. Instead, it has a long, thin face, lacking large zygomatic faces and practically has a blowhole. And another important ingredient, is the lack of the dividing wall of bone in the nares that a large number of mammals have. A far more probable alternative would be for the animal to have a giant resonating chamber in its nostrils, similar to hadrosaurs and a few mammals, past and present.
Dr. Matthew Colbert, 2002, "Tapirus terrestris" (On-line), Digital Morphology. Accessed November 22, 2017 at http://digimorph.org/specimens/Tapirus_terrestris/.
Chisholm, Hugh, ed. (1911). "Macrauchenia". . 17 (11th ed.). Cambridge University Press.