Sunday 16 June 2024

Antelopine Antelopes: Blackbuck and Springbok

The gazelle-like body form has evolved at least three times within the "antilopine" subfamily, and arguably a few more times among antelopes more generally. A fast-running animal, able to outpace many of its predators, is clearly a useful thing to be if you're a herbivore. Only one of these three evolutionary events led to what zoologists would describe as the "true gazelles", although at least one of the others resulted in an animal so strikingly similar to gazelles that it's surprising that molecular evidence tells us it doesn't have an immediate common ancestor.

The blackbuck (Antilope cervicapra), however, does not look much like a gazelle. It is one of the five currently recognised species of antelope whose scientific name dates back to the origins of modern taxonomy in 1758. In 1766, Peter Simon Pallas first distinguished antelopes from goats, creating the genus Antilope to incorporate no fewer than seventeen species - including the Dorcas gazelle, which would later go on to become the defining species of the Gazella genus when that was created in 1816. While every other living species was eventually split off elsewhere, the blackbuck remained, and its genus gives its name to the entire subfamily. (The second part of the name, incidentally, translates as "deer-goat" and remains the name of the animal in French).

Sunday 9 June 2024

Oligocene (Pt 9): Rise of the Dogs

Many of the carnivorous mammals present in North America during the Oligocene were of types also found in Eurasia. However, this far back in time, they did not necessarily belong to any family of animals we would recognise. Cats, for example, first appeared in Europe at the end of the epoch and did not reach the Americas until much later. Other groups, such as raccoons, simply didn't exist yet. 

But we do, for example, have Palaeogale, an animal also known from Europe that looked somewhat like a polecat, but was actually more closely related to cats and mongooses without, so far as we can tell, being either. Corumictis looked similar, but analysis of the skull has shown that it much closer to true mustelids. About the size of a modern weasel, it lived in Oregon at least 29 million years ago, towards the middle of the epoch. It may make it the first mustelid to reach North America from Eurasia, home to the very similar, and slightly older, Plesictis. It's far enough back that it might, however, belong to an early musteloid group rather than to the modern family (that is to say, it may be equally related to mustelids and raccoons, and thus, strictly speaking, neither). Oaxacagale is almost as old, and lived in what is now Mexico; it's probably another close relative but, it too, has so many primitive features that it's hard to place precisely.

Saturday 1 June 2024

Wombats Moving Home

There comes a time in the life of many young mammals when they have to leave home. There are at least two major reasons for this. Firstly, any given place only has so many resources, so unless your parents die as soon as they've finished raising you (unusual among mammals, although not unheard of), at some point, you have to move elsewhere or there won't be enough food for both of you. Secondly, if the whole family stays together in one place, you'll never meet new sexual partners, forcing you to mate with your siblings - and we all know where that leads.

Understanding how and when animals disperse from their place of birth can be important for conservation as well as, on a broader scale, how new species and subspecies evolve and adapt. Nor is it necessarily something that only applies to young approaching maturity, since older animals may also choose to move from one place to another and often for similar reasons - competition or a lack of suitable mates. Whether a given animal chooses to move home, and how far they travel to do so, can be influenced by several different factors. 

Sunday 26 May 2024

The Vocabulary of Sperm Whales

It's well known that whales and dolphins can communicate using sound, sometimes over long distances. In some cases, this can involve sophisticated "whalesong" that animals can use, for example, to identify each other, and that may impart other information, too. But there are a great many species of cetacean, and what is true for one won't necessarily be true for all of the others, just as what's true of chimps won't always be true for baboons or marmosets.

We'd expect the most complex messages to come from those species with the most complex social lives. In these cases, it would be useful for the animal to identify not only its gender, fitness, sexual status, and so on, but also which other whales it might associate with, and where it stands in the local hierarchy. Most (but not all) cetaceans live in pods although, for many, we haven't gotten very far in identifying how those are structured. They all, however, have relatively large brains and it can be worth asking, for any given species, just how complex their communication really is.

Sunday 19 May 2024

Antelopine Antelopes: The Largest Gazelles

Grant's gazelle
The word "gazelle", as used in everyday English is a little vague, referring to a general concept of slim, agile, antelopes but not to anything with a precise scientific definition. Strictly speaking, however, it refers to a specific group of closely related animals, and some species that are commonly called "gazelles" strictly speaking aren't. During the 20th century, all true gazelles were placed in a single genus, Gazella, and it's this that defines the more rigid definition of what does and doesn't count. 

In more recent decades, Gazella has been split in three, with the resurrection of two 19th-century names as "new" genera. The original Gazella is widespread, including animals from both Asia and North Africa, but the other two are exclusively African. Eudorcas (literally "true antelope" in Ancient Greek) includes Thomson's gazelle of the Serengeti and its various relatives, while the remaining genus is Nanger, whose name apparently comes from a local Senegalese word for one of the species.

Sunday 12 May 2024

Before Cats Could Purr

Although the differences are obvious when we can see the spots or stripes on their fur, the various species of cat are often very similar in form, and it can be hard to tell them apart based on the skeleton alone. For this reason, through much of the 20th century, all of the "purring cats" except the cheetah were placed in the single genus Felis. That's not the case today, when we distinguish genera not only for the larger purring cats, such as pumas and lynxes, but others that modern genetic evidence tells us are distinct, such as the group that includes the ocelot.

Given this, it's hardly surprising that the same should go for fossil species, too. It may well be that if we had genetic evidence on those, or could even just see their coat colour, we would be more willing to distinguish them but, when all you have is an often fragmentary skeleton, there isn't much to go on.

Sunday 5 May 2024

Squirrels, Advance!

The rapid growth of human population over the last century or so has led to a decline in many species. As I talked about last month, however, some animals can live alongside us even in urban environments, and there are many more than can tolerate us in rural - yet not truly wild - habitats, such as cropland or pasture. Any species that can do this clearly has an advantage, in many cases being able to move into new parts of the world previously inhabited by some similar, but less human-tolerant species. Thus, we can see some native species replaced by foreign invaders, as has happened, for example, with mink in continental Europe and jackrabbits in the American southwest.

In Britain, the most familiar example of this is probably the replacement of our native red squirrels (Sciurus vulgaris) by invasive eastern grey squirrels (Sciurus carolinensis). Red squirrels were once common across the British Isles, but have now vanished from most of England and Wales, surviving in the far north of England and a few pockets elsewhere, but otherwise replaced by the greys. In large part this is due to the greys carrying a virus to which they are immune but the reds are not, but simple competition is another factor.