Delphinids: Dolphins of the Deep Seas

Rough-toothed dolphin

To our human eyes, it's easy to distinguish the major habitat types on land. There are pine forests, tropical jungles, open prairies, deserts, mountains, and so on. When it comes to the sea, however, it's less obvious. Most maps show the sea as a solid mass of blue which is, of course, what most of it looks like from the surface. But there are different environments and habitats within it, even if they aren't necessarily arranged in quite the same way.

While for some dolphin species the only real limitation is pack ice preventing them from surfacing to breathe, most have more specific requirements. Temperature is the most obvious, with some species preferring tropical or subarctic seas, but the depth of the underlying water is also significant. Species such as common and bottlenose dolphins are most comfortable over the continental shelves, where nutrients well up from the sea bed to feed the fish and squid on which they prey. Rather more species prefer shallow waters, close to the coast. Here, the water is shallow enough for light to reach the bottom, allowing seaweed or coral to grow, which benefits a different kind of fish than those further out.

Sea Lions v. The Blob

The waters off the coast of Alaska are supposed to be cold, especially in winter. Yet, in the autumn of 2013, they cooled far less than they normally would. A great mass of warm water, 2,000 km (1,250 miles) across and around 100 metres (330 feet) deep, remained trapped in the North Pacific. Nicknamed 'The Blob', this was caused by the weather patterns over the region remaining stuck in a high-pressure mode, preventing the warm water from dissipating with the winds as it should do. With temperatures stuck at up to 4°C (7°F) warmer than normal, the high pressure did not dissipate for eight months.

When it did, tropical winds pushed the warm water up against the American coast, from southern Alaska to southern Mexico, where it basically sat until El Niño kicked off in 2015... and that kept things unusually warm for another year. Inland, this disrupted weather systems leading, among other things, to frequent thunderstorms that sparked what was (at the time) the worst wildfire season in California's history.

Oligocene (pt 15): Land of the Fire-Beasts

Pyrotherium

Even at the dawn of the Oligocene, South America had already long been isolated from the northern continents, giving it the opportunity to evolve its own distinct mammalian fauna, with many animals quite unlike those seen elsewhere. Most of these strange animals would die out millions of years later when the Isthmus of Panama finally formed. The armadillos are among the exceptions.

Armadillos first evolved on the continent during the previous epoch, if not earlier, but most of the older fossils are incomplete, making it difficult to trace their detailed relationships. The oldest reasonably complete armadillo skulls belong to Kuntinaru, first described in 2011. This lived in Bolivia towards the end of the Oligocene, around 27 million years ago and would already have looked much like modern armadillos, albeit somewhat smaller than the species most familiar to North Americans. 

Delphinids: Small Dolphins of Shallow Southern Seas

Commerson's dolphin

While related, dolphins and porpoises are regarded as distinct types of animals. Each is placed in its own family, with the two separating at least 15 million years ago. However, telling the two apart is not always easy, at least on a superficial look at their external anatomy. Porpoises are, generally speaking, smaller than dolphins and they have a blunt nose rather than a 'beak'. The problem is that we can say exactly the same about some species that really are dolphins.

In 1766, naturalist Philibert Commerson accompanied explorer Louis-Antoine de Bougainville on what would become the first successful French circumnavigation of the globe. While passing through the Straits of Magellan the following year, he spotted an unusual-looking dolphin close to the ship and sent a description of it back to France. (As a side note, later on in the voyage, it was discovered, much to the crew's shock, that Commerson's assistant was secretly a woman; she is now remembered as the first woman to circumnavigate the globe).

Cheating Little Vixens

The majority of mammal species are either polygynous, where one dominant male mates with multiple females, or promiscuous, where both sexes have multiple partners. However, while monogamy may be less common, it isn't exactly rare, either, with it having evolved several times in widely separated mammalian groups. In some cases, this is what we would term "facultative" monogamy, where animals (often large predators) are sufficiently widely spaced that it's simply difficult for a male to find multiple partners, or, if he can, they live sufficiently far apart that he can't plausibly defend more than one of them from his rivals. In others, monogamy is an essential part of the breeding process, typically because the young are too much effort for one parent to raise alone.

Delphinids: White-sided Dolphins

Atlantic white-sided dolphin

The taxonomy of dolphins is far from settled, with exactly how we should classify some species having been an open question for years. There is a good chance that the scientific names I am using for some species in this series will not still be in use in a decade, as old genera are split and the family tree re-arranged. Such is the case, for example, with the dolphins of the genus Lagenorhynchus.

The genus was named by John Edward Gray in 1846 for a specimen of a previously unknown species sent to him for analysis at the British Museum, after having been caught somewhere off the coast of Norfolk. It translates as "bottle-nose", for the shape of the beak... which is, perhaps, unfortunate, given that the animal we refer to in English as the "bottlenose dolphin" is something else entirely. Over the centuries since, five new species have been added to the genus, giving us the six we recognise today.

The Diets of Parallel Pigs

Peccaries from South America

The word "ungulate" refers to a broad category of mammals that are generally large and herbivorous. They form a natural evolutionary group, although only if you include the cetaceans, which are descended from vaguely hippo-like ancestors. The word comes from the Latin word for "hoof", and the great majority of living ungulates have hooves of one kind or another. Even ignoring the cetaceans there are exceptions, but it doesn't take a great stretch of the imagination to see that camels, for instance, are at least the same general kind of animal as deer or cows.

All living ungulates can be placed into one of two mammalian orders: the artiodactyls, which includes the cloven-footed kinds, and the perissodactyls, which includes, among others, the horses. If you start looking at fossils, however, it becomes clear that other ungulate orders once existed. Most were very early, dying out in the first half of the Age of Mammals, representing early branches in the great ungulate family tree that ultimately proved unsuccessful.