Sunday 30 June 2019

Small British Mammals: Bank Voles

I had intended to wrap up voles a couple of weeks ago, but it turned out that there was so much to say about water voles in particular that it made more sense to add in an extra post to cover everything else. So, here we are with the fourth and final species of vole found in Britain: the bank vole (Myodes glareolus).

Although water voles are more closely related to common voles and their kin than the bank voles, it is the latter that have the closest physical resemblance. While most voles are broadly similar in shape, bank voles are also roughly the same size as the common and field voles, and can be distinguished (without close examination of the skeleton) by the fact that the fur on their backs typically has a distinct reddish tinge. A few instances of individuals with other colours have been noted - including a pure white one that had somehow survived to adulthood without being eaten - but these are rare.

Sunday 23 June 2019

The Last of the Chinese Zebra-Donkeys

Asian wild asses
With the exception of our own species, few mammals have been the subject of quite so much interest in their evolutionary history as the horse. The number of named species of fossil horse far outweighs the number of species that are alive today. A great many of these are, of course, the older three-toed horses, with all living horses being placed in the single genus Equus.

Today that genus consists of just seven widely recognised living species. But, even among just this genus, and ignoring all the older, extinct ones, there were once many more species than there are today. But just how many is that? That's a matter of considerable confusion and debate.

In a way, that's hardly surprising, especially when you consider the focus of attention that there has been on horse evolution. Even just looking at the living species, not everyone agrees that 'seven' is the appropriate number, with some authorities arguing that particular subspecies are distinct enough that they should really be species in their own right.

Sunday 16 June 2019

Small British Mammals: Ratty and the Water Voles

Four different species of vole live wild in Britain, with, perhaps, the field vole being the one that is most typical of the wider group. However, it's perhaps a different species that has the most claim to fame, appearing as one of the central characters (confusingly named "Ratty") in the popular children's book The Wind in the Willows.

Ratty is a water vole (Arvicola amphibius), an animal with a number of differences from common and field voles, despite being fairly closely related to them. Before discussing the species in more detail, we should acknowledge that, over the years, there has been considerable confusion as to what the scientific name of this animal actually is - and, for once there's quite a good reason for it.

Sunday 9 June 2019

Miocene (Pt 14): Sabre-toothed Sea Otters

When bears first entered North America is really more a matter of definition than of our understanding of the fossil evidence. Going by what is probably the most common current definition, bears first appeared in Europe about 20 million years ago, in the form of Ursavus elmensis. Noticeably smaller than modern bears, this developed into a number of species across Europe and Asia, and to the closely related Ballusia in China.

Almost immediately, however, Ursavus also crossed into North America, probably arriving around 19 million years ago. It seems to have been far less common there than it was in Europe, with the local species, Ursavus pawniensis (there were probably others, but that's the only one we know of for sure) living in relatively small populations across the west, from Nebraska to Oregon and Saskatchewan. It doesn't appear to have left any descendants, being eventually replaced by more modern species of bear from Asia rather than evolving into anything uniquely American.

Sunday 2 June 2019

The Porcupine Sleeps Tonight

The book All Yesterdays presents, among other things, unusual, but scientifically plausible, depictions of dinosaurs and other prehistoric animals. One picture, for example, shows a T. rex asleep - something that they must logically have spent quite a lot of time doing despite the fact that typical dinosaur books never show it.

Well, it's not as exciting as fighting a Triceratops.

In general, though, even when it comes to living animals, it's probably fair to say that behavioural scientists don't spend a lot of time thinking about how they sleep. All animals advanced to have a brain sleep in some fashion, so far as we know, and obviously, that includes mammals. To be sure, this isn't terribly obvious in the case of dolphins and the like, since they can be both asleep and awake at the same time, but everything that lives on land has to take a nap from time to time.