Toxodon

"I know what these are. I'm pretty sure these are Toxodon. Charles Darwin found their fossils, when he came to South America in the eighteen hundreds."

- Nigel

During his seatch for Smilodon, Nigel Marven encountered a giant herd of Toxodon. He later observed them swiming in a lake and again when a Smilodon preyed on one. Toxodon became extinct at the end of the Pleistocene when North America and South America met and a migration of more competitive herbivores came about, as well as predators, but they were not completely helpless, as they had strong hides and tusks. In addition, many Toxodon fossils have been found accompanied by fossilized arrow heads. This shows that prehistoric humans hunted them, which could have been a leading cause of their demise as well as climate change.

Appearance
Toxodon was what paleontologists call a "notoungulate," a megafauna mammal closely related to the ungulates (hoofed mammals) of the Pliocene and Pleistocene epochs but not quite in the same ballpark. Thanks to the wonders of convergent evolution, this herbivore evolved to look very much like a modern rhinoceros, with stubby legs, a short neck, and teeth well adapted to eating tough grass (it may also have been equipped with a short, elephant-like proboscis at the end of its snout). Many Toxodon remains have been found in close proximity to primitive arrowheads, a sure sign that this slow, lumbering beast was hunted to extinction by early humans.

The vertebrae were equipped with high apophyses, which most likely supported the massive weight and muscles as well as its powerful head.

In his journal, "The Voyage of the Beagle", English national historian Charles Darwin wrote this about Toxodon."Lastly, the Toxodon, perhaps one of the strangest animals ever discovered. In size, it equaled an elephant or megatherium, but the structure of its teeth, as Mr. Owen states, proves indisputably that it was intimately related to the Gnawers, the order which, at the present day, includes most of the smallest quadrupeds. In many details, it is allied to the Pachydermata. Judging from the position of its eyes, ears, and nostrils, it was probably aquatic, like the Dugong and Manatee, to which it is also allied. How wonderfully are the different Orders, at the present time so well separated, blended together in different points of the structure of the Toxodon!"

- Charles Darwin, "The Voyage of the Beagle"

Behaviour
It was initially believed to have been amphibious, but after examining the proportions of the femur and tibia, as well as the position of its head, below the top of the spinal column, palaeontologists realised that it had features similar to terrestrial animals such as elephants or rhinoceroses. The fossils are also usually found in arid and semi-arid areas, typically an indication of a primarily terrestrial life. However, as Nigel discovered, they where indeed like Hippos.

Toxodon had broad jaws which were filled with bow shaped teeth and incisors. These teeth would have allowed the animal to tear through and bite off the plants and leaves.

Where does Toxodon fit into the tree of life? Like its contemporary Macrauchenia, its relationship to living mammals is uncertain. It falls into the larger clade of Notoungulata, literally Southern Ungulates, but the placment of this group within placental mammals is highly uncertain. They maybe have a close relationship with animals in the group Afrotheria but research in mammalian systematics is only beginning to be able to evaluate that, and other hypotheses. So what is Toxodon? We just don’t know. Toxodon would have had a very unusual gait, due to its peculiar proportions. It may have galloped to escape predators, but like a rhino, it probably relied more on its size as protection against predators.

In Prehistoric Park
Nigel goes through the time portal to South America 1 million years ago when the sabre-tooth species known as Smilodon were in their prime (having recently entered South America after the Panama land bridge formed), but the Terror Birds (Phorusrhachids) were dying out; before that South America had been cut off from the other continents for 30 million years. He drives through a moving herd of Toxodon; he follows them to find where they were going, and he sees that they were going to water to swim or wallow in: he sees that they lived like modern hippopotamus, and thus may be dangerous like hippos. A huge male Toxodon chases Nigel's jeep, and he has to drive fast and far before it gives up the chase. It is shown that Nigel owns a copy of Charles Darwins journal in his first scene with the Toxodon.

On site Nigel sees a female Smilodon stalk a Toxodon and then after a short chase, jump on its head and bite its throat to kill it. More Smilodon come, including some 6 to 8 week old cubs. While waiting Nigel has a coffee and the Smilodon eat their fill and go away. When Nigel goes back to the same place, at a later point in time, the Toxodon are all gone, extinct.

Trivia

 * It was indigenous to South America, and was probably the most common large-hoofed mammal in South America at the time of its existence.
 * Toxodon became extinct at the end of the Pleistocene. Many Toxodon fossils have been found accompanied by arrow heads. This shows that prehistoric humans hunted them, which could have been a leading cause of their demise.

Charles Darwin
"Lastly, the Toxodon, perhaps one of the strangest animals ever discovered: in size it equalled an elephant or megatherium, but the structure of its teeth, as Mr. Owen states, proves indisputably that it was intimately related to the Gnawers, the order which, at the present day, includes most of the smallest quadrupeds: in many details it is allied to the Pachydermata: judging from the position of its eyes, ears, and nostrils, it was probably aquatic, like the Dugong and Manatee, to which it is also allied. How wonderfully are the different Orders, at the present time so well separated, blended together in different points of the structure of the Toxodon!"

- Charles Darwin, The Voyage Of The Beagle, 1839

Charles Darwin was one of the first to collect Toxodon fossils, after paying 18 pence for a T. platensis skull from a farmer in Uruguay. In The Voyage of the Beagle Darwin wrote "November 26th - I set out on my return in a direct line for Monte Video. Having heard of some giant's bones at a neighbouring farmhouse on the Sarandis, a small stream entering the Rio Negro, I rode there accompanied by my host, and purchased for the value of eighteen pence the head of the taxodon." Since Darwin discovered that the fossils of similar mammals of South America were different than those in Europe, he invoked many debates about the evolution of species.