Oligocene (Pt 18): Sawfish-Dolphins and Baleen Whales with Teeth

Olympicetus, a simocetid whale

Although the oldest fossils of seal-like animals may date back to the end of the Oligocene, there are very few of these, and the dating may not be wholly reliable. Whales, however, are a different matter and were already well established even at the beginning of the epoch, 33 million years ago. In fact, the Oligocene marks an important phase in their evolution, since it was at this time that the oldest living groups first appeared and that, potentially, the last common ancestor of all living whales roamed the seas.

Even so, especially towards the end of the epoch, it is possible to place some Oligocene cetaceans into groups we are familiar with today. For example, there was Kentriodon, which is better known from the Miocene, but first appeared in the southern oceans at the tail end of the Oligocene. Although it is not placed in any living family, it is the oldest member of a branch that diverged from the common ancestor of dolphins and porpoises around this time. It likely looked rather similar and had a similar fish-and-squid-based diet.

Viverrids: Rise and Fall of a Wastebasket

The carnivorous mammals have been recognised as a taxonomic order since the official dawn of biological classification in 1758. In that first publication, Systema Naturae, Carl Linnaeus listed 36 species. The concept of "families" was a later innovation, but Linnaeus used the rank of "genus" much as we would use families today, and, in the case of what we now call the carnivorans, there were six.

These were the cats, dogs, bears, weasels, seals, and a sixth group that he called (in Latin) "ferrets".

The Family Life of a Spectral Bat

It may not be Halloween just yet, but it is October, so that's as good a time as any to talk about an animal that goes by the name of the spectral bat (Vampyrum spectrum).

You might think from the scientific name that this is a close relative of the vampire bat but, while it does belong in the same family, vampire bats are a side-branch of that family thought to have diverged from the main branch around 50 million years ago. Its closest relative may be the far less fearsomely named "big-eared woolly bat" (Chrotopterus auritus), with which it shares some of its unusual feeding habits. 

Delphinids: Killer Whales

Orca / killer whale

The dolphin family is scientifically defined as including all the species more closely related to the common dolphin than they are to porpoises. The great majority are what we'd normally think of as "dolphins" but four species are so much larger that, instead, we tend to call them "whales". Three, including the two species of pilot whale, are of roughly similar size to each other, but the fourth is noticeably larger still.

It's the biggest "dolphin" of all: the orca or killer whale (Orcinus orca).

That it is a dolphin has never been seriously doubted from a scientific perspective. It is one of just three species of dolphin to be listed as such in the first catalogue of scientific names in 1758 - and one of the other two is a porpoise, and so has since been moved elsewhere. On the other hand, it has been recognised as belonging to a distinct subfamily with the dolphins since 1846, and modern genetic studies confirm that its ancestors diverged from those of most other dolphins unusually early.