[Flashpoint]

It never existed. God put it's bones there to confuse us. Just like the dinosaurs.

Isn't intelligent design a lovely intellectually lazy answer!

Large body types are better suited to cold weather (less heat loss due to Haldane's principle - as an animal gets bigger, its surface area increases more slowly than its volume. At a certain point, the amount of body heat lost is less than that which is generated).

That's why the last ice age produced so many "giant" versions of species still seen today (I seem to recall Elk, Sloth, and even a beaver). Camel seems a little unusual given their current proclivity for warmer climates, but I am uncertain that's significant as far as habitat goes. It seems likely that at the conclusion of the last ice age when temperatures began to increase again, many of these larger animals died out.