Sunday, 11 April 2021

How Walruses Got Their Tusks

Titanotaria, a tuskless walrus
Few people would argue that the walrus (Odobenus rosmarus) is not a distinctive animal. Indeed, it is so distinctive that, despite there being only one living species, that species has been placed in a "family" all of its own since 1880, distinct from both the seals and sea lions. 

There are a number of features of walruses that make it clear, from a modern perspective, that this was the right decision to make. But the most obvious is surely that they have huge tusks. These are in many ways a remarkable feature, and while other animals, such as elephants, also have large tusks, none that's alive today has anything quite like those of the walrus. 

Walruses have a long evolutionary history, having been distinct from their closest living relatives for many millions of years. Nonetheless, those relatives are, as we might expect, the seals and sea lions and it's apparent that they entered the water long before growing the tusks. Which, in turn, means that the first walruses must have been tuskless. So when and how did this change?

Sunday, 4 April 2021

Armadillos Looking for Love

We can tell a lot about animals by simply observing where they go. While studies on wild animals can cover a wide range of different topics, many of which require close observation of what the creature is actually doing, many of the most basic simply require us to tag the animal with some sort of transmitter and watching it move remotely.

Of course, while I say 'basic', this isn't necessarily all that simple to do in practice. You need to capture the animals, ensuring that they aren't overly stressed by the experience so that they modify their behaviour after the fact, and then you do need to spend a lot of time collating all the date, likely over the course of several months. Still, we do have many such studies for most well-known mammals. Some groups, however, have been comparatively overlooked.

Saturday, 27 March 2021

Before Owls Ate Mice

Palaeoglaux
Most bird species are diurnal. Doubtless, if you're flying about and don't have sonar, as bats do, it helps to be able to see where you're going. Nonetheless, there are many exceptions to this general rule, and none are more obviously so than the owls.

There are well over 200 living species of owl currently recognised, ranging in size from the mighty Eurasian eagle-owl (Bubo bubo) with a wingspan of up to 180 cm (6 feet) down to the tiny elf owl (Micrathene whitneyi) with a wingspan of just 27 cm (10 inches). They are grouped into two closely related families; the great majority of species belong in the Strigidae family, with just 20 assigned to the barn owl family, the Tytonidae. While there are some internal differences between the two, the most visible in the living animal is that barn owls, unlike regular owls, have distinctive heart-shaped faces.

Both families have been around rather longer than most mammal families have, with fossil representatives dating back to at least the Early Oligocene, around 35 million years ago. The two families are, however, rather like pigs and peccaries, each others' closest relatives, together forming the order Strigiformes. Since few people would deny that a barn owl is, in fact, an owl, it's this order that's really the scientific counterpart of our everyday understanding of the word.

Sunday, 21 March 2021

All the World's Deer: Sambar and Rusa

Sambar
Deer are predominantly woodland animals, so it's no surprise that the extensive warm forests of Southeast Asia, with their many isolated islands, are home to a number of different species. Some of these are closely related to the red deer that live in cooler environments further north, so much so that some authors have recommended moving them back into the genus Cervus to join the red deer and their immediate kin. 

Nonetheless, they do seem to form a distinct branch on the deer family tree - although how many species might be in that branch, and even which ones they might be, is debated. For much of the 20th century, just two or three species were recognised, but genetic evidence gathered in the 21st century has made it more obvious that some of the island forms have been isolated from their mainland relatives for long enough to become clearly distinct.

Sunday, 14 March 2021

Miocene (Pt 25): The Large Clawed Cat-Cat and the First Dog in Africa

Lokotunjailurus
Today, the hyena family consists of just four species. All of them live in Africa and, generally speaking, they look somewhat like dogs. Three out of the four are scavengers, with powerful teeth adapted for cracking open bones to consume as much of a carcass as possible. The largest and fiercest of these is the spotted or "laughing" hyena, which is the one most people think of when the word "hyena" is mentioned, although there is more variety in the group than that. But even so, with just four species, it's not what you'd call a large taxonomic family.

During the Late Miocene, however, things were very different. It's hard to know the exact number of species that existed, even among the fossils we have, since some of the subtler differences may not be apparent from bones alone. But there were certainly plenty of genera, spread widely across Europe, Asia, and Africa. They were also more varied than today, and their success at the time may well have been due to the fact that actual dogs were still restricted to North America at the time, leaving the hyenas without direct competitors.

Sunday, 7 March 2021

How Rodents Can See Ultraviolet Light

Primates, including our own species, have unusually good colour vision. This is thought to be due to the need to identify when fruit is ripe and ready to eat. Most other mammals don't see the world in the same way that we do, having colour vision that's at best limited and often, so far as we can tell, absent altogether. 

But at least some animals do have an advantage that we don't: in addition to visual light, they can also see in ultraviolet.

In terms of physics, there's no real difference between visual light and ultraviolet; the latter simply has a higher wavelength. In a sense, as its name suggests, it's just a colour (or range of colours) that are more violet than violet. Our own inability to see it naturally gives us something of a bias here, but, in principle, there's no real reason why an animal shouldn't be able to see UV light if it would be useful to do so.

Sunday, 28 February 2021

All the World's Deer: The Red Deer Species Complex

Red deer
When the first list of scientific animal names was drawn up in 1758, all six known species of deer were placed in the genus Cervus - which is, of course, simply the Latin word for "deer". Over the following decades, as taxonomy became more refined, all but one of those species were moved to other genera, and when the deer family, Cervidae, was named in 1810, it had roughly the same meaning that the genus had had so many years before. As its name implies, though, Cervus was selected as the type genus of the family - the one that defines the archetypal group against which all others are compared. Although newly described species had been added since, the one species that was so obviously deer-like it had never been moved anywhere else thus became, in a sense, the defining species of its family.