Goo Goo G'joob

"Pinnipeds" is the technical term for flipper-footed aquatic mammals that are able (although often with difficulty) to move about on land. Although there had previously been some speculation on the point, we now know that they are a natural group of animals, all descending from a single distant ancestor. They are carnivorans, more closely related to dogs than to cats and probably represent the third major branching within the living dog-like carnivores, after the dogs and bears, but before (for example) the raccoons, skunks, and weasels.

The living species of pinniped are placed within three families, although one or two extinct ones are also recognised. Most pinnipeds belong to the Phocidae, or "seal family". While the term "seal" is often used in modern English to refer to pinnipeds in general, the seal family proper consists of animals especially well-adapted to living in the water. They lack visible ears, and their hind limbs are arranged so to be efficient for propulsion underwater, but almost useless on land, forcing them to haul themselves about using their front flippers only.

Miocene (Pt 36): Dawn of the Seals

Allodesmus

In this series so far, I have covered the mammalian wildlife of the Miocene continent by continent, showing how the diversity of animals then was just as great as it is now. But there is a group of mammals that a time traveller to the period would have been able to observe along the coasts of those continents - especially during their breeding season - that I have not yet mentioned.

Today, the seals are divided into two subfamilies (I have reviewed all living species of seal here): the phocine or "northern" seals, which live in the Northern Hemisphere, and the monachine or "southern" seals, which are primarily found in the Southern Hemisphere, but do include three living species in the north. 

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?

Prehistoric Mammal Discoveries of 2020

The largest known Oligocene whale was
moved into the new genus Ankylorhiza
this year

Well, that year was... different. Fortunately, it didn't stop me posting and, indeed, a cancelled summer break meant that you got one more post than anticipated you lucky people, you. But as 2020 finally passes into the history books where it can bloody well stay, it's time for the end-of-year roundup of paleontological discoveries that didn't make the regular blog. As always, no theme, just a random assortment of journal papers that may, for all I know, be thoroughly contradicted by this time next year. But this is a collection of things that some scientist, somewhere, thinks that they demonstrated in 2020:

The Beaches of Bakersfield

Modern walrus skull

Seals have a moderately long fossil history, with some of the oldest examples dating from Europe, around 15 million years ago. Although they are now found worldwide, back in those early times, they seem only to have lived in the North Atlantic, reaching the Pacific only around 11 million years ago (probably by the simple expedient of swimming through the seas that then covered what is now Central America).

However, one of the world's best fossil sites for recovering fossil aquatic mammals is at Sharktooth Hill, just outside of Bakersfield, California. Part of the larger Temblor Formation, the deposits here consist of silts and sands, laid down just over 15 million years ago, when California was sweltering in the Middle Miocene Climatic Optimum, a time of unusually high worldwide temperatures - and correspondingly high sea levels. This was before seals had reached so far west, but that does not mean that a number of similar animals did not already live there at the time.

Tuskless Walruses of Japan

There are a number of mammal "families" that contain just one living species. Of course, what constitutes a "family" of animals is an arbitrary distinction, rather like the one that says Pluto isn't a planet. So, really, all we're saying is that there are some mammal species that, in our subjective and pro-mammalian opinion, are do distinct and unusual that we feel they ought to be placed in a group all of their own. If they were insects, or snails, or something like that, we'd probably feel differently. But they're mammals, like us, so we don't.

One such family is the walrus family, containing - you've guessed it - the walrus (Odobenus rosmarus). Walruses are pinnipeds, which is to say, they are related to seals and sea lions. Just by looking at them, we can tell that walruses can walk on all fours like sea lions and fur seals, but unlike "true" seals, yet lack the external ears that sea lions and fur seals have and true seals don't. When you get to the interior structure of the skeleton, and so on, there are a number of technical differences that tell us that, no, this isn't just our imagination, they really are a bit different from all the others. And, there's, you know... the tusks.

News in Brief #8

Attack of the Killer Walrus (Or Not)

The two principal families of fully aquatic carnivoran are the seals and the sea lions. To the casual observer, they can most easily be distinguished by the shape of their hind limbs. Sea lions can walk on all fours (albeit with a comical waddle), while true seals have to drag themselves about on land, their hind flippers being of little use out of the water. It's this that tells us that fur seals, for example, are members of the sea lion family, and not 'true' seals. But seals and sea lions are not the only aquatic carnivorans: there are two others. Firstly, there's the sea otter, a member of the weasel family. And then there is the walrus.

Walruses are kind of weird, when you think about it. Although they're probably more closely related to sea lions than they are to true seals, they're actually neither, and the walrus family is one of those odd mammal "families" that has only one species in it. But, as is so often the case with such "monotypic " families, that's only true if you count the living species. Because there used to be more.

Part of the reason that the walrus is so obviously peculiar is that it's adapted to doing only one thing (eating shellfish) and, moreover, doing it in a fairly specific habitat. But not all prehistoric walruses were the same. Some, for example, used to live in subtropical waters, and by no means all of them fed on shellfish.