Toxodon platensis

Toxodon platensis was a large, heavy-bodied herbivorous mammal, roughly the size of a rhinoceros, with a massive head, short legs, and a robust barrel-shaped body. It had chisel-like incisors and large nostrils positioned high on the skull, and its anatomy combined features seen in multiple unrelated mammal groups, which initially confused early paleontologists.

Toxodon belonged to Notoungulata, an entirely extinct order of hoofed mammals that evolved in isolation in South America when the continent was an island continent for tens of millions of years. This long isolation produced a unique fauna of marsupials and placental mammals found nowhere else, and the notoungulates were among the most diverse and successful groups before most went extinct.

Yes, Charles Darwin collected Toxodon fossils during his voyage on the HMS Beagle in the 1830s while traveling through Argentina and Uruguay in South America. He shipped the specimens back to England, where Richard Owen formally described and named Toxodon based partly on Darwin's material, which Darwin discussed in his geological and zoological writings.

Toxodon platensis survived until near the end of the Pleistocene epoch, roughly 11,000 to 10,000 years ago, when much of South America's megafauna disappeared. This extinction event coincided with both dramatic climate changes at the end of the last ice age and the expansion of human populations across the continent, and the relative contributions of each remain debated.