Sunday, 25 September 2016

Flesh-eating Hippos

Hippopotamuses (Hippopotamus amphibius) are amongst the largest of all land-dwelling animals alive today, beaten only by the elephants, and some of the larger species of rhino. They are also distinctive creatures, with their only close relative today being the pygmy hippopotamus, an animal that many people are likely familiar with, if only because they're popular in zoos. While there are, of course, many extinct species, these two are the only living members of the hippo family, the Hippopotamidae.

In the grander scheme of things, hippos belong to the order Artiodactyla, most of the other members of which, such as deer and cattle, are cloven-footed ruminants. Hippos are neither. Like their fellow artiodactyls, the pigs, they are not ruminants, and they have four functional toes. Unlike pigs, however, the toes of hippos are all more or less equal in size and weight-bearing (in pigs, especially warthogs, the two side toes may be used to help steady the animal on slippery or uneven surfaces, but bear little if any of its weight during regular walking).

Sunday, 18 September 2016

Do Gorillas Have Culture?

Animal behaviour is generally instinctual. Their behaviour is, in some way, wired into their genetics, and doesn't vary from one animal to another. Particularly in mammals and birds, individual animals may be shaped by their life experiences, learning new things as they go. But what they can't do, as a rule, is pass that information on to others. Mothers may teach their young how to do certain things, but that teaching process is itself instinctual, so that all animals of a given species learn more or less the same thing as infants.

A large part of the success of our own species is down to our ability to circumvent this, to build on the knowledge of previous generations. This results, among other things, in the development of culture, differences in behaviour based not on the experiences of only one individual, but of their ancestors, in a way that isn't genetic. Britain and Japan are different culturally, not just because of environmental variation (Japan has earthquakes, for example, and has different mineral resources than Britain) but simply because of the vicissitudes of history, the separate evolution of their languages, and so on.

Sunday, 11 September 2016

Bovines: Spiral-Horned Kudu

Greater kudu (male)
Most "bovine antelopes" - those more closely related to cows than, say, sheep - are collectively referred to as "spiral-horned antelopes", because of the shape of their horns. In many species, the horn makes a single 360° turn once it is fully grown, but others have several twists to the spiral. In elands, the twist is tight, marked clearly by a ridge that runs along one edge, but in no species is the spiral perhaps more evident than in the two species of kudu, where the horns are relatively narrow, with a loose, open curve.

The more widespread and common of the two species is the greater kudu (Tragelaphus strepsiceros). These are particularly large antelopes, with the males standing up to 157 cm (5' 2") in height at the shoulder, and weighing up to around 270 kg (600 lbs). Indeed, they are the second tallest species of antelope, after their relatives, the elands. Females are quite a bit smaller, at around two-thirds of the weight, and standing no more than 132 cm (4' 3"). As with most other spiral-horned antelopes, the coat is a brownish colour, with narrow vertical white stripes on the flanks.

The horns, are, however, their most distinctive feature - the second half of their scientific name means "twisted horn". These are typically about 100cm (3' 3") long in fully grown males, and would be even longer were you to measure them along the curve, rather than in a straight line from the base to the tips. Although the occasional horned female has been reported, this seems to be a rare aberration. Even in males, the horns grow slowly enough that it is possible to age younger individuals by how well they've developed; it takes two years to complete the first full turn, and the final adult form, with two to two-and-a-half turns, is reached by around four and a half years.

Sunday, 4 September 2016

Ancient Otters of Idaho

The common river otters of Eurasia and North America are remarkably similar animals. If you placed them side by side you might notice that the Americans ones are (on average) slightly larger, and have a slightly more bland colour to their coat... but, really, it's not easy. I, for one, wouldn't claim to be able to tell which species a particular photograph was of without additional evidence (most obviously, where it was taken).

It was therefore assumed for a long time, not unreasonably, that they had to be very close relatives. As early as 1843, they had been placed in separate genera, as Lutra lutra and Lontra canadensis, respectively. However, it's worth noting that this is 16 years before the publication of On the Origin of Species, so, when he did so, it's isn't obvious that John Edward Gray was necessarily thinking about how "related" they might be. Indeed, for much of the 20th century it was common to ignore Gray and place all of the fairly typical looking clawed otters together into the genus Lutra.

Sunday, 28 August 2016

300th Synapsida

Here, have a marsupial. Or four.
This is, by my count, the 300th post to appear at Synapsida. Which means that, once again, it's time to look back over the last 100 posts to see what has, and has not, been covered, and where I might be going next. Which, considering that I pick the topic for over half my posts on the same day on which I write them, is likely to be a bit vague, but there you go.

The blog has been running for almost six years now, and has settled into a typical audience of between 200-300 hits per day (whatever the heck that means in terms of actual readers). The most frequently used tags over that period have been behaviour and evolution, although this may just reflect how I tag things. Biogeography, for instance, may well have cropped up in all sorts of posts that I didn't specifically note as such.

Looking back over the last 100 posts, carnivorans have probably been the most common animals covered, although there are also plenty of rodents, not to mention cetaceans, bats, primates, and all the rest. As I mentioned last time, my coverage of the main mammal families has been, if not entirely comprehensive, at least pretty broad. Since then, and ignoring posts on fossil beasts, I think I've added four more families to the list of those with a headline mention, all of them either small or obscure (or both): hyenas, degus, cheirogaleid lemurs, and echidnas.

But still no pigs.

Sunday, 21 August 2016

The Sound of Squirrels

It is, of course, well known that bats and cetaceans use ultrasound to help them navigate the world using sonar. However, there is no particular reason why animals should always make sounds that happen to be in the range of human hearing (and, arguably, some good reasons why they might not want to). So, taking the usual definition of ultrasound as anything higher than 20kHz - the approximate upper limit for the hearing of a young, physically fit human - it shouldn't be too surprising that other mammals use ultrasound for purposes like communication. Or, in the case of shrews, for actual echolocation.

There has been significant laboratory research on the use of ultrasound by mice and rats since at least the 1970s, but it has also become clear that they are far from the only rodents to make sounds beyond our hearing range. Last year, I talked about the potential use of ultrasound for sexual seduction among hamsters (and, to be honest, didn't reach much of a conclusion) and we also know that, for example, baby voles call to their mothers ultrasonically if they become separated.

In the case of squirrels, though, we know rather less, and much of what we do know applies to various kinds of ground squirrel. As recently as 2013, however, it was discovered that flying squirrels also use ultrasound, presumably for social communication. Indeed, the sounds were quite complex and varied, not mere repetitive squeaks, implying that they might impart rather more information that one might think at first glance.

Sunday, 7 August 2016

Bovines: The Largest Living Antelopes

Common eland (male)
Over the last few months I have looked at the various species of cow-like bovine, including such creatures as yak, bison, and water buffalo. But we've known, since at least the 1950s, that there are also a number of other animals that are more closely related to cattle than they are to other kinds of bovid. Although the choice of terminology is ultimately arbitrary, these are commonly considered to be members of the subfamily Bovinae, and thus can also be described as "bovines".

They are not, however, physically very cow-like, and so are instead described by the more generic term "antelope" - which really just means "any bovid that's not obviously some kind of cow, sheep, or goat". The great majority of antelopes are therefore not "bovines" in any sense, belonging to their own distinct subfamilies. The majority of those that are are commonly referred to as spiral-horned antelopes. While all bovines are said to have some degree of spiral growth pattern to their horns, it's only in these antelopes that it's really obvious, with multiple turns of the spiral clearly visible to the observer.