Oligocene (Pt 17): Dawn of the Kangaroos

Ekaltadeta

Kangaroos are perhaps the single most iconic Australian mammals. As marsupials, we tend to think of them as lost relics of an earlier evolutionary period, and, indeed, they have been around for a long time. Of course, they have been evolving during that time, rather than standing still, but if we had a time machine, we could go back millions of years into Australia's past, and still find animals that were, more or less, kangaroos. But, obviously, there is a limit.

Exactly how far back that limit is partly depends on how kangaroo-like you want your kangaroos to be. But even then, there are some gaps in our knowledge that don't have direct counterparts on other continents. The obvious place to start is with the fossil record, and, here, at least, we can provide a clear answer. The oldest known fossil kangaroos date to around 28 million years ago, towards the end of the Oligocene.

Miocene (Pt 34): The First Kangaroos in Australia

Ekaltadeta

During the Miocene, Australia was further south than it is today. However, it seems that the generally warmer climate of the early part of the epoch more than compensated for this, since we know that there were already coral reefs off the coasts of the main continent and also of New Zealand, which is far too cold for such things today. At the dawn of the epoch, the continent seems to have been largely covered by open woodland but as the world warmed in the Middle Miocene, and Australia edged northward, it became not only hotter, but wetter, until tropical and semi-tropical rainforests became the norm. It was only in the Late Miocene, around 10 million years or so ago, that the climate started drying again, especially in the interior, and the dense jungle began to die away, leading the way for the formation of today's Outback in the following, Pliocene epoch - although, even at the end of the Miocene, the coasts were more heavily forested than most of them are today.

News in Brief #7

Geoffroy's spider monkey

Monkey Sleep, Monkey Poo

Poo is useful stuff to zoologists: a lot of field work involves examining the stuff. It can tell you what an animal has been eating, how it behaves, and maybe something about it's genetics. And, of course, it can also tell you where it's been. Take Geoffroy's spider monkey (Ateles geoffroyi), for example.

Spider monkeys are moderately sized monkeys, noted for their prehensile tails and remarkable agility. I saw some (although not Geoffroy's species) at London Zoo on Monday, and, despite the poor weather, they really were a delight to watch, full of enthusiasm and energy. Seeing them at play, it's hard to escape the impression that they have five arms: their feet are effectively an extra pair of hands, and their tail is so flexible and has such a good grip that it might as well be a fifth one.

They live, unsurprisingly enough, up in the trees - specifically ones in Central America - sleeping in them at night and travelling between them to feed during the day. They have particular favoured trees to sleep in, and deposit a lot of dung at the base over the course of the night. Such 'latrine' use is common among many mammals, and just finding where they are provides a good means of establishing what the monkeys are up to without having to disturb them.

The Lonely Koala

The koala (Phascolarctos cinereus) is, by many standards, a fairly odd animal. Like most medium to large Australian marsupials, it is herbivorous, but it goes further than that by eating nothing but eucalypt leaves, which are not only low in nutrients, but actually poisonous. Presumably, they do this simply because nothing else does, which means that food should always be available, and they deals with the low nutrient content by spending around two thirds of their life snoozing, and with the poison with unusually efficient detoxifying liver enzymes. Like horses, they are hind-gut fermenters, which also helps them to extract what nutrition they can from food that, frankly, isn't very good.

Koalas have no close living relatives. There is only one living species (with no subspecies), and its considered different enough from everything else to be given its own family - one of a number of mammalian "families" that contain just one species. It's now agreed that the closest relatives koalas do have are the wombats, and even a brief glance at the respective animals tells you that they can't be that close.

So the only opportunity we have for really unravelling the history of koalas comes from examining fossils. For, while koalas are the only member of their family alive today, there were, of course, others in the past. But, still, not terribly many. Some other single-species families, such as that of the pronghorn antelope, represent the last surviving member of a group that was one much larger. Once, there were lots of species of North American antelope, many of them pretty weird to modern eyes, but now only the pronghorn remain, a solitary reminder of a once more diverse group.