The Air Conditioning in Your Nose

The nasal cavities are not mere holes running through the head. Anatomically, at least, that's broadly true at either end - in the vestibule immediately behind the nostrils, and in the nasopharynx above the throat. But in between, in the area above the mouth and separated from it by the palate, the air instead must pass through defined channels. 

These channels are formed by the "conchae", projections from the outer side of each nasal cavity stretching almost to the inner surface, so that most of the air is forced through the narrow slots between them. These conchae are, in turn, formed by the turbinate bones, delicate, paper-thin, sheet-like structures rolled up like a scroll, and covered in the same sort of fleshy lining that we find in, say, the trachea (windpipe). 

Oligocene (Pt 18): Sawfish-Dolphins and Baleen Whales with Teeth

Olympicetus, a simocetid whale

Although the oldest fossils of seal-like animals may date back to the end of the Oligocene, there are very few of these, and the dating may not be wholly reliable. Whales, however, are a different matter and were already well established even at the beginning of the epoch, 33 million years ago. In fact, the Oligocene marks an important phase in their evolution, since it was at this time that the oldest living groups first appeared and that, potentially, the last common ancestor of all living whales roamed the seas.

Even so, especially towards the end of the epoch, it is possible to place some Oligocene cetaceans into groups we are familiar with today. For example, there was Kentriodon, which is better known from the Miocene, but first appeared in the southern oceans at the tail end of the Oligocene. Although it is not placed in any living family, it is the oldest member of a branch that diverged from the common ancestor of dolphins and porpoises around this time. It likely looked rather similar and had a similar fish-and-squid-based diet.

Viverrids: Rise and Fall of a Wastebasket

The carnivorous mammals have been recognised as a taxonomic order since the official dawn of biological classification in 1758. In that first publication, Systema Naturae, Carl Linnaeus listed 36 species. The concept of "families" was a later innovation, but Linnaeus used the rank of "genus" much as we would use families today, and, in the case of what we now call the carnivorans, there were six.

These were the cats, dogs, bears, weasels, seals, and a sixth group that he called (in Latin) "ferrets".

The Family Life of a Spectral Bat

It may not be Halloween just yet, but it is October, so that's as good a time as any to talk about an animal that goes by the name of the spectral bat (Vampyrum spectrum).

You might think from the scientific name that this is a close relative of the vampire bat but, while it does belong in the same family, vampire bats are a side-branch of that family thought to have diverged from the main branch around 50 million years ago. Its closest relative may be the far less fearsomely named "big-eared woolly bat" (Chrotopterus auritus), with which it shares some of its unusual feeding habits. 

Delphinids: Killer Whales

Orca / killer whale

The dolphin family is scientifically defined as including all the species more closely related to the common dolphin than they are to porpoises. The great majority are what we'd normally think of as "dolphins" but four species are so much larger that, instead, we tend to call them "whales". Three, including the two species of pilot whale, are of roughly similar size to each other, but the fourth is noticeably larger still.

It's the biggest "dolphin" of all: the orca or killer whale (Orcinus orca).

That it is a dolphin has never been seriously doubted from a scientific perspective. It is one of just three species of dolphin to be listed as such in the first catalogue of scientific names in 1758 - and one of the other two is a porpoise, and so has since been moved elsewhere. On the other hand, it has been recognised as belonging to a distinct subfamily with the dolphins since 1846, and modern genetic studies confirm that its ancestors diverged from those of most other dolphins unusually early. 

South Africa, 14,000 BC

Paleoecology is the study of how animals and their environments interacted in the distant past. While the basic idea has been around almost since we started the scientific investigation of fossils, it really only became a field in its own right around the 1950s. That's largely because it isn't easy, becoming harder the further back we go.

The basis of the field is to look, not at individual fossils, but at the whole array of fossils at some particular site, correlating them with what we can determine of the climate and environment at the time. Which, among other things, requires a good understanding of exactly what that time was and at least a reasonable confidence that the fossils in question are all around the same age. Often, it relies not just on good and plentiful fossils at a particular site, but on us being able to say what the animals' lifestyles were. Which is a lot harder for those that don't resemble the ones we have today - dinosaurs being an obvious case in point.

Hungry Hippos

The hippopotamus (Hippopotamus amphibius) is an unusually large animal. Among land-dwelling mammals, only the elephants and some species of rhinoceros are larger. It is also, like elephants and rhinos, herbivorous and, since it prefers to eat plants that aren't especially nutritious, this means it needs to eat a lot. 

As in, it eats 35 to 50 kg (77 to 110 lbs) of food each day. 

Which is fine if the hippo happens to be out in the wild, far from human interference. But the reality is that there are fewer and fewer such places around these days. It's not so much the urban sprawl that humans bring, or even the roads and other infrastructure of an expanding African economy, but more the cropland that's required to feed us all. Although hippos are hunted for the ivory in their teeth, the number one threat to their survival is probably the expansion of farmland. Compared with many other animals, this is exacerbated by their reliance on large amounts of fresh water, so even if the farmland isn't near them, they suffer if water is diverted to where it is needed for crops.