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.