Sunday, 9 August 2020

Miocene (Pt 21): Mongooses and More

A modern mongoose
When Africa, moving north, collided with Asia around 19 million years ago, a number of hoofed animals, and other large herbivores, headed south to colonise the continent. Naturally, where herbivores go, predators follow, so an influx of carnivorous animals occurred at around the same time.

Until this time, Africa had been an island continent, separated from the larger northern landmasses and lacked many of the kinds of carnivore we are familiar with today. It had, for example, no cats, dogs, or bears, or even such quintessentially "African" animals as hyenas. All of these, and others besides, belong to the group of mammals known as "carnivorans", which essentially includes all large land-dwelling mammalian carnivores today, apart from the Tasmanian devil. They had evolved in the north, and the new land bridge gave them their first chance to reach the more southerly continent.

Sunday, 2 August 2020

Were 'Cave Lions' Really Lions?

A theme that crops up on this blog every now and then is that some animal that many people probably assume is a single species is actually two or more. There are, for example, three species of zebra, three jackals, and seven different kinds of musk deer. The lion (Panthera leo) is not one of these animals; there really is only one species alive today - and it's been around for a long, long time.

I remember a few years ago, at London Zoo, I happened to be passing the lion enclosure when one of the keepers was giving a talk. The lions at the zoo were obtained from the Gir Forest in Gujarat, India, rather than being the African sort. The keeper repeatedly referred to "this species" of lion when, for example, he was indicating how much more endangered the Indian population is than the African one.

Sunday, 26 July 2020

Small Cats: Ocelots and Margays

Of the seven species of cat identified in the 1758 treatise that marks the dawn of biological taxonomy, just three were what could plausibly be described as "small cats": the domestic/wildcat, the lynx, and the ocelot (Leopardus pardalis). Even today, these three (if we include bobcats in with the lynxes) are probably the best-known kinds of small cat, at least to most people in the West. Having already looked at the others, it's about time I turned to the ocelot.

Originally named as Felis pardalis, the ocelot kept this name up until the late 20th century. At that point, the genus Leopardus was resurrected, having first been used for the ocelot by John Edward Gray in 1842. Gray's original description of the genus doesn't fit at all with what we now know (and was almost completely ignored by everyone else at the time, anyway) but, even by the 1960s, it had become clear that there was a striking difference between the Leopardus cats and every other cat species in the world: they have only 36 chromosomes, instead of 38. This presumably reflects an ancient change in their ancestors, although whether it occurred before or after the proto-ocelots entered South America from the North is impossible to know.

Sunday, 19 July 2020

Why Males Are More Muscular

There's a general rule in the animal kingdom that females tend to be larger than males. This is likely because of the extra demands of producing and laying eggs, or of spawning by whatever other method they use. Clearly, it's not a rule that holds among mammals where, while there are some exceptions (especially among bats), it's usually the male that's the larger and more physically imposing sex.

I discussed this a few months ago, in the context of seals, where this size difference is especially noticeable. But it's true in other mammal groups, too, including the primates. In general, the reasons for this are much the same among primates as they are among other mammals; males compete with one another for access to mates, and the most successful ones have more mating opportunities, and hence more children, as a result. Genetic inheritance then carries the trait of "large males" down to future generations, amplifying it until other constraints get in the way.

Sunday, 12 July 2020

He Said, She Said

One of the most distinctive behavioural features of the human species is our ability to communicate. So far as we know, no other animal can convey even remotely as much information as we can by speech alone, never mind the advantages that writing brings. But we didn't come out of nowhere, and other mammals can also communicate vocally, something that may have particular relevance to the development of our own species when we look at other primates.

A number of primate species are highly vocal, such as gibbons or the aptly named howler monkeys. Another example, which may be less obvious. is the common marmoset (Callithrix jacchus). This is a species I've talked about before, a small monkey native to South America with a number of unusual biological and anatomical adaptations related to its reproduction and diet. (Unusual for primates in general that is, not compared with other marmosets). But it is behaviourally interesting as well.

Sunday, 5 July 2020

Small Cats: Lynxes of North America

Canada lynx
For much of the 20th century, it was thought that there were only two species of lynx, one of which lived right across the high latitudes of the Northern Hemisphere, from Portugal to Newfoundland, by way of Siberia and Alaska. That began to be questioned towards the end of the century, and, since about 2005, it's been pretty much universal to consider this widespread animal to actually comprise three different species. Two of those live in Eurasia, with the other one found only in North America.

This, of course, is the Canada lynx (Lynx canadensis); the alternative form of 'Canadian lynx' is also used in some formal sources, but only seems about half as popular. It lives across virtually the whole of Canada south of the tundra but, despite the name, is also found in part of the US. Alaska is the most obvious example here, but Canada lynx can also be found south of the border in the Cascade and Rocky Mountains, around Lake Superior, and in much of Maine. Between 1999 and 2006, a number of Canada lynx were also re-introduced to Colorado, where they had been locally extinct since at least the 1970s; so far, they seem to be doing well enough.

Sunday, 28 June 2020

What's the Closest Living Relative of Whales?

(For the TLDR crowd; just read the last paragraph).

It's been known for a long time that, at the highest level, mammals can be divided into three evolutionary groups based on their method of giving birth: marsupials, the egg-laying monotremes, and the placental mammals. That last group contains around 95% of all living mammal species, including everything from wolves to dolphins and moose to monkeys.

Given that wide variety, it's less obvious how we should divide up the placental mammals into smaller groups that genuinely reflect their evolutionary relationships. It's obvious that, say, cheetahs are members of the cat family and, at a slightly higher level, it's unsurprising that, for example, the dog and bear families are reasonably close relatives of one another. But once you get much higher than that, it becomes less so.