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).

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.

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.

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.