Sunday, 9 May 2021

Miocene (Pt 26): Planet of the Monkeys

The primates are one of the major mammalian orders alive today, with a great many species spread across three continents: Africa, Eurasia, and South America. They have an ancient history, and, even by the dawn of the Miocene, were already divided into the two main groups we have today: the prosimians and the anthropoid primates (most of which are monkeys, or 'simians').

It's probably fair to say that most scientific attention has been paid to the latter of those groups, but we do have a number of fossil prosimians from the Miocene. Madagascar, where most prosimian species are found today, was already an island, and had been since the time of the dinosaurs, but there are few known fossils of the relevant age there to tell us much about the early history of lemurs and their kin. Nonetheless, during the Miocene, prosimians were more widely spread than they are today. 

Sunday, 2 May 2021

Mammals That Sense Magnetism

Traditionally, there are said to be five senses: vision, hearing, taste, smell, and touch. From a modern scientific viewpoint, however, this is clearly a significant underestimate, since things are rather more complicated than that.

How many senses even a human can be said to have is a matter of definition, although it's generally agreed to be more than five. An extreme way of counting would be to consider every specific type of sensory cell as representing one 'sense'. This, however, results in the conclusion that vision is four separate senses: one for black-and-white (the rod cells) and one each for the primary colours (the cone cells). This, it's probably fair to say, is not something that's widely considered helpful - although it may well be useful to neurobiologists.

If we don't go that far, then, we can still consider vision, hearing, taste, and smell to be singular senses. It is, however, not uncommon to consider the ability to sense temperature as distinct from the ability to sense that you are physically touching something. Pain can also be considered a distinct sense, since you can obviously 'feel' when you have, say, a headache, but it's hard to argue that that should count as 'touch'.

Sunday, 25 April 2021

Naked Aggression

Evolutionarily speaking, it is in the interests of animals to have as many offspring as they can, so long as those offspring will themselves reach reproductive age. However the means for a male to do this may be different from those best employed by females. This is especially true in mammals, because the female has to put considerable resource into pregnancy, lactation, and general care of the young until they are old enough to fend for themselves. The male, however, doesn't have to do any of this, and, in many species, his role in matters may be completed as soon as he's finished mating.

This leads to the concept of sexual selection, where the evolutionary demands on the male may be different than those on the female, leading to different behaviours and appearances. There are often said to be two main driving forces behind such sexual selection. The first is the need for males to compete with one another for access to females, resulting in larger, more heavily built males, often with natural weapons of some kind, such as horns or tusks. The second is driven by the females, when they choose a mate based on some particular feature, leading the males to emphasise that feature in response. (This is, perhaps, most obvious in birds).

Sunday, 18 April 2021

All the World's Deer: Deer With Spots

Fallow deer
The fawns of most (but not all) deer species are born with spotted coats, which likely help to camouflage them among the dappled light of a forest. In some species, the spots disappear shortly after birth, while others retain them for a while longer. In five species, however, they keep them all the way into adulthood. I've covered two of these species already: the sika deer of Japan and the um... spotted deer of the Philippines. 

To Europeans, however, the best-known is surely the fallow deer (Dama dama). This is Europe's medium-sized deer, and one of the six original species of deer identified as such in the first list of scientific names in 1758. It lives in woodland areas across most of western and central Europe, preferring broadleaf forests but happy enough with conifers or Mediterranean scrubland. They don't like deep snow, and so aren't found in the Alps or all but the most southerly parts of Scandinavia, but otherwise, they seem pretty adaptable and widespread. Yet, despite being such a familiar animal, they're arguably not really native to the continent.

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

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.