Saturday, 28 November 2020

Miocene (Pt 23): Giraffes Become Tall, Hippos Stay Dry, and Antelopes... Get Eaten

Palaeotragus, a short-necked giraffe
About half-way through the Late Miocene, around 8 million years ago, worldwide temperatures began to drop significantly, and even tropical Africa did not escape the effects. In its case, this didn't lead to cold and barren steppelands, and, indeed, the world may still have been slightly warmer than it is today, but there is evidence of the expansion of grasses across many parts of the continent. Perhaps enhanced by the closure of the Mediterranean Sea during the Messinian Salinity Crisis and disruption of the monsoons, North Africa also became much drier than before, although whether the Sahara as we know it today dates back quite that far remains controversial; there is some evidence of sand dunes that far back, but also of numerous rivers crossing the region.

These changes in climate also affected the animal life on the continent, to the benefit of some and the detriment of others. Pigs are omnivorous animals, and one might expect them to have survived such changes relatively unscathed. In a sense, this is true, since they remained common on the continent, but the nature of particular species living there did change.

Sunday, 22 November 2020

The Best Place to Den

Winter is a difficult time for many animals at high latitudes. Food is scarce, and the cold climate itself is a problem. Although many mammals do manage to keep going through the winter, others migrate to warmer climes, while many of those that don't hibernate instead. While this is by no means easy, for animals that can manage it, it allows them to preserve their energy, surviving off body fat without the need to search for food.

There has, historically, been some dispute as to whether bears truly hibernate or not. This is because the sort of undoubted hibernation practised by, say, bats, involves an almost total shutting down of normal metabolic functions with the animal effectively becoming cold-blooded for the duration. Bears do not do this; while they are asleep through the winter, their body temperature drops from a normal level of 37°C (99°F) to a low of 33°C (91°F). Now, this is not insignificant, since a human with a body temperature that low would be suffering from clinical hypothermia and in fairly urgent need of medical treatment. But still, you're not going to be so cold that dew literally starts forming on you, as happens with bats.

Sunday, 15 November 2020

Small Cats: Rare Cats of Southeast Asia

Asian golden cat
Wild cats are generally quite elusive species, once we ignore the "big cats" such as tigers and leopards. Some of the small to medium species are nonetheless fairly well-known in the west, including such animals as lynxes and ocelots. But many of them are rather more obscure, tending to be stealthy, nocturnal hunters whose success at feeding themselves often relies on them not being seen. If we combine small size with heavy undergrowth - and, perhaps, not being found in Europe or North America - we are likely to find a few species that are rarely seen at all. 

The forests of Southeast Asia are particularly good place for such creatures to be found, and, in fact, I've already described a number of small cat species that inhabit the region. Those all belong to the "leopard cat" and "domestic cat" evolutionary lineages, but there are a further three species that occupy yet another branch on the cat family tree. Given what I've said above, it shouldn't be surprising that we don't know very much about them.

Sunday, 8 November 2020

Last Gasp of the Australian Seals

Today, true seals only live much further south
In common English parlance, the word "seal" refers to a range of animals that, scientifically speaking, constitute two different, but related, mammal families. (A third related family, which today includes only the walrus, is distinctive enough that most people probably don't think of them as "seals" in the regular sense). I've previously written a post that goes into detail about what the difference between these two families is, but the technical names are phocids (for "true" or "earless" seals) and otariids (for the sea lions and fur seals, both of which have visible ears).

For simplicity, I'm going to refer to these two groups as "true seals" and "sea lions" in this post, although you should be aware that the so-called fur seals fall into the latter group. We've long known that "fur seals" aren't really a specific type of animal, but are at least two different kinds of sea lion that coincidentally look a little different from their relatives.

Sunday, 1 November 2020

Porpoisely Quiet?

Way back in the early 19th century, the naturalist Karl Ernst von Baer, better known for his work on embryology, made an interesting discovery that seems fairly obvious to us in hindsight: the blowhole of a porpoise is, in fact, its nostril. Other anatomists followed up on this, leading to the further discovery that a number of air sacs appear to be connected to the nasal cavity. They can hold a fair amount of air when fully inflated, but nothing like as much as the lungs, so exactly what they were for wasn't clear.

Fast forward to 1956, and scientific research confirmed another interesting fact about such animals: they can echolocate by sending out sonar pings. In 1968, the two facts were put together when it was demonstrated how the unusual structure of the porpoise's head allows it to transmit the necessary sound pulses, which are initially generated somewhere in the nasal passages.

Sunday, 25 October 2020

The Social Lives of Ground Squirrels

There are almost 300 recognised living species of squirrel. As one might expect given that large number, there is a fair degree of variety among them. To people living in Britain, for example, the word "squirrel" typically conjures up a small, tree-dwelling animal with a bushy tail. We only have two local species (one of them invasive) and they're very closely related. Take a look further out in the squirrel family tree, however, and we see some significant variations on the general theme of "squirrel-ness".

Perhaps the most obvious of these are the ground squirrels. Most ground-dwelling squirrels belong to a single evolutionary group, which includes something like a quarter of all known squirrel species. Many of these - the animals most commonly known simply as "ground squirrels" - look much like their tree-dwelling kin, but the group also includes such animals as prairie dogs and marmots as well as the semi-arboreal chipmunks.

Sunday, 18 October 2020

Small Cats: Servals in the Savannah, Cats in the Congo

Serval
The best-known wild cats living in Africa are, of course, the large ones: lions, leopards, and cheetahs. South of the Sahara, they are joined by two species of small cat: the African wildcat (from which the domestic animal is descended) and the black-footed cat, both of which I have already described in this series. To these, we can add the caracal, a medium-sized cat that closely resembles the lynxes of Eurasia and North America. But, although this was most likely the animal that the word 'lynx' was originally coined to describe, the caracal is not closely related to what we would now regard as the 'true' lynxes. Instead, it is part of a distinctively African lineage of similarly medium-sized cats, containing just two other living species.

The more familiar of the two is surely the serval (Leptailurus serval), an animal that is not only widespread across Africa, but that happens to be relatively easy to breed in zoos. The name apparently derives from an alternative (and now obsolete) Portuguese name for the lynx that has now replaced variants of the older English name of "tiger cat" in most non-African languages. (It's still tierboskat - literally "tiger-forest-cat" - in Afrikaans, and, unsurprisingly, languages such as Swahili had perfectly good words for it already).