Oligocene (Pt 13): The First Porcupines

Prosotherium

The dawn of the Oligocene is marked, in part, by the formation of a deep water channel between South America and Antarctica. To what extent there had been a true land bridge between the two continents in the preceding epoch is debatable, but the separation was certainly more complete than it had been previously, beginning a long period of isolation that allowed unique animals to evolve and flourish. Furthermore, most of the large mammal groups we are familiar with today originated on the northern continents, so much of the fauna of South America was already strange to modern eyes.

 

Much of it, but not all. The exact date of the oldest rodent fossil from South America has been disputed, but recent analysis suggests that it may have lived shortly after the beginning of the Oligocene. How it reached the continent is also unclear. Logically, it must have made a long sea journey, presumably clinging to some storm-tossed piece of debris, either from North America or Africa (the Atlantic being narrower then than it is now). The latter seems the more likely, since South American rodents are more closely related to the African sort than to their equivalent northern counterparts.

Miocene (Pt 28): Miniature Super-horses and the Dawn of the Guinea Pigs

Thoatherium

For most of the Age of Mammals, South America was an island continent, separated from its northern counterpart by a wide sea. Even at the dawn of the Miocene, 23 million years ago, this isolation had already lasted for a long time, and the seas to the north were already a formidable barrier, with just a few islands where Central America is now. In some respects, the variation in climate across the continent was less extreme, especially because the Andes were not so high as they are today and so cast less of a rain shadow. Even so, there was enough variety that many different kinds of animals lived across its great area.

Indeed, the long separation of the continent from the rest of the world meant that it had had plenty of time to develop its own native animals. Whereas, in most of the rest of the world, animals of broad types we would still recognise were already around (early cats, deer, elephants, and so on), most of the larger animals of Early Miocene South America would have been much harder to place, since most of their descendants died out long before the Ice Ages, let alone the present. 

The Life of an Endangered Porcupine

Porcupines are among the most distinctive of all rodents. With their combination of long quills, long tails, and large rodent teeth, they're pretty difficult to mistake for anything else. However, there are actually two families of porcupine, which are not directly related to each other, and which live on opposite sides of the Atlantic Ocean. The porcupines of Africa and Asia and those of the Americas are different in a number of ways; perhaps most notably, the American ones live up trees, while those elsewhere live only on the ground.

Of all the porcupines, though, one of the strangest is the thin-spined porcupine (Chaetomys subspinosa) of eastern Brazil. Although it was first described way back in 1818, for most of the twentieth century, no scientist had even seen one, until a survey in 1986 confirmed their continued existence. Much smaller than other porcupines, and more bristly than spiny, there has been considerable debate as to whether it even is a porcupine. Instead, it's been argued that it might actually be a type of animal called a spiny rat, another fairly odd family of rodents which it does certainly resemble.

The question was settled in 2009 when genetic and chromosomal studies proved, quite conclusively, that it is a porcupine, albeit an unusually small and rat-like one. Indeed, its ancestors seem to have separated from those of all other American porcupines as far back as the early Miocene, around 20 million years ago. In comparison, the next branch we know of within the family is the split between the North American porcupine and its assorted South American cousins around 10 million years ago, with all the other branches being considerably more recent than that.