Saturday 25 November 2023

The First Whales to Use Sonar?

Other than their obvious physical adaptations, one of the most familiar features of dolphins and whales is their ability to use ultrasound to echolocate. All dolphins, porpoises, and toothed whales (collectively called odontocetes) can echolocate and, while some of the fine details do vary between, say, sperm whales and some of the smaller species, the basic mechanism is much the same. Ultrasound would not have been useful to the large, ground-dwelling ancestors of whales in the same way that it is for bats, so it must have evolved after they entered the water. But how soon after?

We can put some limits on this. At the younger end, since all odontocetes echolocate, it's unlikely to have evolved any later than their last common ancestor, which is estimated to have lived around 34 million years ago. On the other hand, it's notable that the toothless, baleen, whales do not use ultrasound; in fact, they are specialised in the exact opposite direction to produce sounds well below, not above, the range of human hearing. This suggests that they evolved along different lines, and that the origins of ultrasonic echolocation lie somewhere after the two split. 

Sunday 19 November 2023

Learning to Hunt at Sea

One of the distinguishing features of mammals is that they invest a lot of time and effort in caring for their young. Of course, birds do this too, as do some other vertebrates, but the provision of milk is one of the key defining traits that's true of all living mammal species. (Probably most extinct ones, too, although it's hard to tell with the very early species). This means that newborn mammals are entirely dependent on their mothers in a way that the young of, say, most reptiles are not. 

But there comes a point where any mammal has to be weaned and make its way in the wider world. Even then, the maternal investment doesn't necessarily end with the mother continuing to raise and train her offspring for what can be an extended period. Brown bears, for example, are weaned at around six months, but they commonly stay with their mothers for at least another year, and often for two or more. We can see similar patterns in other mammals including, perhaps most obviously, primates.

Sunday 12 November 2023

Defending the Troops

A few weeks ago, I talked about how group-living mammals decide when and where to move, and how their decision-making leadership is structured. But there are other aspects to how animals living in a herd or pack might travel, or, indeed, position themselves when they are not travelling. One of these is the perceived risk of predation. 

It's well-known that predators will tend to pick off weaker individuals if they can, largely to save themselves the effort of capturing something that's more able to escape or fight back. But it's also likely that some positions within a herd are going to be inherently safer than others, and merely being fit may not help much if you're an obvious target. The question then arises as to whether certain sorts of individual are likely to occupy safer or more dangerous positions and as to how the group as a whole arranges itself.

Sunday 5 November 2023

Skunks of the World: Stink Badgers!

Sunda stink badger
As I mentioned at the beginning of this series, for most of the 20th century, skunks were thought to be mustelids, members of the same animal family as weasels, polecats, badgers, and the like. They were given their own family in the 1990s, once it became clear that racoons were more closely related to mustelids than they were. But the genetic analyses that revealed this fact also provided another surprise.

It had been assumed that skunks (as a subfamily of mustelids) lived only in the Americas, much as racoons do. But the genetic studies showed that two species of supposed badger living in Indonesia were not, in fact, badgers at all, but members of the newly erected skunk family. These animals are collectively known as "stink badgers", although the local name of "teludu" and "pantot" are sometimes preferred.

Sunday 29 October 2023

Oligocene (Pt 5): The First Cats

As new herbivores entered Europe at the Grande Coupure, carnivores were bound to follow. As with their prey, these Asian newcomers seem to have rapidly outcompeted the native European forms, leading to a sudden turnover in the types of animals we find on the continent. Although we can say that these newcomers were "carnivorans" - the sort of mammalian carnivores we're mostly familiar with today - where exactly they place relative to the living families is harder to say.

Plesictis is an example here. It looked, so far as we can tell, rather like a polecat and was about the same size, so for much of the 20th century it was thought to be an early example of a mustelid, albeit one no more closely related to actual polecats than, say, badgers or otters are. More modern analyses are more circumspect; it may look like a mustelid in some respects, but it probably lived before those animals diverged from the raccoons and so can't be quite either. Palaeogale, which looked rather similar and was also originally assumed to be a mustelid, in fact turns out to be more related to cats and mongooses, but probably so far down the family tree that it's not yet possible to say much more than that.

Sunday 22 October 2023

Follow the Leader?

By human standards, the majority of mammal species are comparatively antisocial. Some actively avoid others of their kind outside of the mating season, but even those that are more tolerant are often found together in one place purely because that is where the food happens to be. But, of course, there are a great many exceptions to this; animals that habitually live in groups that socialise and travel together.

Animals that live like this have to have some form of decision-making process that all members of the herd, pack, or other grouping choose to abide by. The most obvious example of this would be deciding when and where to move, but it could also include, for example, determining the best way to escape predators. Lacking the sophisticated communication methods of humans, concepts of debate aren't likely to be applicable, but the decision has to be taken somehow, and, over the years, there have been many studies to determine just how egalitarian the process is and exactly which animals within the group are making the decisions if it isn't.

Sunday 15 October 2023

Attack of the Giant Hyenas

I suspect that most non-specialists would assume that hyenas are fairly closely related to dogs. They certainly look more like dogs than they do anything else, so, absent any further information, that seems reasonable enough. But, in reality, hyenas belong to the cat-like, not the dog-like, branch of the carnivoran family tree.

This isn't some new discovery on the basis of molecular evidence, like the splitting off of the skunks from the weasel family; it's been known for a long time. This is because, when you start looking at the structural details of the skull, especially the area around the ear, everything fits with a cat-like ancestry. This much was already obvious when Miklós Kretzoi formally named the two carnivoran branches while he was working at the National Museum of Hungary during World War II. Modern evidence has merely confirmed the view, showing more precisely that the closest living relatives of the hyenas are the mongooses.