Delphinids: Common and Bottlenose Dolphins

Common dolphin

When the genus Delphis was first named in 1758 at the dawn of taxonomy, it included three species of small to medium-sized toothed cetacean. By the time the dolphin family, Delphinidae, was named in 1821, one of those species (the porpoise) had been moved elsewhere, but five new ones had been added. Many more followed, but, from the mid-18th century onwards, naturalists began to notice subtle differences between animals that were probably more mysterious to them than land-dwelling mammals, and many species of dolphin began to be separated out into newly created genera.

So much so in fact, that by the time we reach the 21st century, only one species remains in the genus originally created to contain all dolphins and dolphin-like animals. That species is, of course, the one that we believe Linnaeus happened to be thinking of when he named the genus, and therefore is the defining (or 'type') species not only for its genus but for the dolphin family as a whole. This is the aptly named common dolphin (Delphinus delphis).

Call of the Mole Vole

There are over 170 recognised species of vole. The exact number is hard to determine because new species keep being described and not all will necessarily stand the test of time but we can certainly say that there are a lot. Although we might typically think of voles as being all rather similar to one another - small, mouse-like animals with short tails and rounded snouts - within such a large group there is inevitably some variation.

Most obviously different from regular voles are the giant species. Although genetic data shows us that these are voles, in the sense of being offshoots of the vole family tree rather than something distinct, we don't normally refer to them as such in English. Instead, we call them "lemmings" or, in the case of the very largest species, "muskrats". To avoid potential confusion, in more scientific language we would therefore use the taxonomic name when referring to the subfamily as a whole and say that voles, lemmings, and muskrats collectively are "arvicolines". 

Delphinid Dolphins

Of all mammal groups, those that have undergone the most dramatic change from their original form are perhaps the cetaceans. The most thoroughly adapted of all mammals to life in the water, there is little else they could possibly be mistaken for. The cetaceans have been considered a distinct order of mammals since the dawn of taxonomy in 1758, and today are divided into fourteen living families. The largest of these families, in terms of the number of species, is the dolphin family.

Technically known as the Delphinidae, this was named by John Edward Gray in 1821 as part of one of the earliest formal lists of mammal families. Gray's original definition basically included all toothed cetaceans other than narwhals and sperm whales, encompassing four genera, only one of which is still placed in the family today - Delphinus, from which it takes its name. He didn't list how many species he thought that genus contained, but it would certainly have included the two named by Linnaeus in 1758, and probably at least three others that had been described in the interim. Over the following decades, the number expanded considerably, with Gray himself identifying several of them, notably when he catalogued the observations and specimens collected by the Ross Expedition of 1839-43.

Oligocene (Pt 13): The First Porcupines

Prosotherium

The dawn of the Oligocene is marked, in part, by the formation of a deep water channel between South America and Antarctica. To what extent there had been a true land bridge between the two continents in the preceding epoch is debatable, but the separation was certainly more complete than it had been previously, beginning a long period of isolation that allowed unique animals to evolve and flourish. Furthermore, most of the large mammal groups we are familiar with today originated on the northern continents, so much of the fauna of South America was already strange to modern eyes.

 

Much of it, but not all. The exact date of the oldest rodent fossil from South America has been disputed, but recent analysis suggests that it may have lived shortly after the beginning of the Oligocene. How it reached the continent is also unclear. Logically, it must have made a long sea journey, presumably clinging to some storm-tossed piece of debris, either from North America or Africa (the Atlantic being narrower then than it is now). The latter seems the more likely, since South American rodents are more closely related to the African sort than to their equivalent northern counterparts.

The Struggles of a Pollinating Bat

Note the dusting of pollen...

When we think of flowers being pollinated, for most people, the first things that are likely to come to mind are insects, especially bees. But other creatures, including mammals, can also be a part of the pollination process, and this is particularly true of bats. Nor are we talking about some occasional event that merely gives the flower some sort of backup - for some the presence of pollinating bats is crucial to their survival.

Even aside from the obvious importance that this gives bats to the wider ecosystem, this can also have direct economic importance to we humans. For example, sour pitayas are an important cash crop in parts of Mexico. Similar to the much sweeter dragonfruit (although not closely related), they grow on a particular type of cactus that is native to the country but is also commonly cultivated. As it turns out, this cactus relies on bats for pollination. While they are not essential, crop yields drop by over a third when the bats are prevented from reaching them, which would clearly be devastating for a Mexican farmer who may be living on the edge of profitability to start with.

Miniature Mediterranean Mammoths

Insular dwarfism is a phenomenon that has occurred many times throughout evolution. What happens is that a population of some large animal becomes trapped on an island, out of contact with its mainland kin., Because the island has a limited size, it also has a limited amount of food on it, and this is a problem for a large animal that needs plenty to eat,

If the island is particularly small, of course, the animals in question are likely to die out, if not immediately, then dwindling over a few generations until they lack the genetic diversity to sustain themselves. On the other hand, if the island is a large one (such as, say, Britain) then there may not be a problem at all, and nothing happens beyond the usual genetic drift between isolated populations. 

Prehistoric Mammal Discoveries 2024

Zalamdalestes

I have reached the end of another year and that means it's time for what has become a tradition on this blog over the last eight years: a look back at some of the discoveries about fossil mammals made in 2024 that didn't make into the regular posts. As usual, this will be a quick whistle-stop tour of mammalian palaeontology, hopefully focusing on some of the more interesting findings. Like any field of science, it has not been standing still.

Large Herbivores

Woolly mammoths (Mammuthus primigenius) are among the best-known of all prehistorical mammals to the general public and, aided by the fact that some lived recently enough to be preserved in permafrost, they are also amongst the best-studied. But there is still more to learn about the details of their lives and habits. A study published this year looked at the detailed isotopic composition of a fossil mammoth that had died about 12,000 BC in Alaska, showing that she was female, and had migrated over 1000 km (600 miles) during her lifetime, having originally been born in the Yukon. The area in which she died was popular with mammoths, but also with humans - she may have died peacefully, but the presence of people where mammoths congregated may not be a coincidence.