When Charles Lyell devised the current system of dividing the "Age of Mammals" into epochs in 1833, he originally defined four. A few years later, he revised this to five, but even then, the entirety of what we'd now call the Paleogene was placed into a single epoch, the Eocene. In 1854, however, German palaeontologist Heinrich Beyrich, split off the later part of the Eocene into a new epoch, which he saw as a distinct period of transition in the development of fossil seashells. He called this the Oligocene, and it proved useful beyond his original mollusc-based definition, and so has remained in use to this day. (Beyrich's wife, incidentally, was a children's author, and made the unusual step of favourably commenting on the work of Charles Darwin in a novel for young girls at a time when it was still controversial).
Synapsida
A random wander through the world of mammals
Sunday, 19 March 2023
Age of Mammals: The Oligocene (Pt 1)
Sunday, 12 March 2023
Fruit Bats of Madagascar
On the other hand, it is true that the majority of bat species are not especially threatened, at least on a worldwide scale - although things may be different locally. Bearing in mind that around one in six bat species are so recently identified and so little studied that we simply don't know how common they are, only around another one in six are rare enough to be listed as "threatened" by the International Union for the Conservation of Nature. Still, that's not exactly a small proportion, and since there are somewhere around 1,400 named species of bat, it's not small in absolute terms, either.
Tha bats are a highly diverse group, representing no fewer than 21 taxonomic families, none of which are likely as familiar to the layman as terms such as "cat family" or "deer family". Some of these contain very few species, representing oddities that don't quite fit into any of the main subgroups, but there are still five families with over a hundred species each. Of these, the one that contains the highest proportion of threatened species is the fruit bat or "flying fox" family, the Pteropodidae.
Sunday, 5 March 2023
Friendship and Fission-Fusion
Here, rather than having a long-lasting association, perhaps bonded by ties of family, the animals live in groups but the membership of that group is not constant. New animals are constantly wandering in, while others break off and leave for other groups. On a larger scale, it may be that the individual fission-fusion groups - the actual bands of animals you would see travelling together - are themselves gathered into larger social networks that may have a relatively consistent structure. That is, the new animals joining the group aren't random; they're individuals already known to the group, and rival social networks may exist nearby that do not mix their members.
Sunday, 26 February 2023
The Raccoon Family: The True Raccoons
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Common raccoon |
The common raccoon is found across almost the whole of the contiguous United States, barring only some of the drier parts of the Great Basin, as well as across southern Canada and virtually all of Mexico and Central America. Furthermore, raccoons were introduced to Germany as a hunting animal in 1927 and, with the help of others that escaped from fur farms, since around the 1970s they have been expanding rapidly across Europe. Over the last couple of decades, they have established populations from Spain and France in the west across to Russia and Ukraine in the east. In the 1990s, they were also introduced to Japan and they have also been introduced to Uzbekistan and other parts of Central Asia, probably following escapes from fur farms.
Sunday, 19 February 2023
Tree-Dwelling Almost-Lemurs of the Canadian Arctic
The most northerly island in Canada is Ellesmere Island, whose most northerly point is not far from being the most northerly piece of solid land on the planet, only beaten by parts of Greenland. Midsummer temperatures reach a daily high of about 9°C (49°F) in midsummer, and it often snows in July. Winter temperatures regularly drop below -35°C (-31°F) on January nights. So, yeah, that's uncomfortable.
Sunday, 12 February 2023
Benefits of a Deadly Predator
The reality is more complex than this. Secondary predators also eat herbivores, omnivores are common, really large herbivores aren't likely to be eaten by anything, there may be more than two steps in the chain of carnivores, and we can't forget the detritivores and fungi. And so on. So what we actually have is a "trophic web", a complicated set of interactions where some animals don't fit neatly into a single level on the pyramid. Nonetheless, that doesn't make the basic idea useless and one of the concepts it leads to is the apex predator - the large carnivores that have no predators of their own (at least as adults).
Sunday, 5 February 2023
Haring About
On the other hand, many species are widespread with large populations and seem to be happy in a variety of different habitats. Often, these are animals with a broad diet, able to eat a range of different foods and still remain healthy - the red fox is a good example of this, especially once it started exploiting suburban habitats in the 20th century. Typically, they will not be as good at finding or processing these foods as those that specialise in one particular type but the fact that they can switch food sources easily makes up for this. Indeed, this can be a driver for evolution - an animal becomes really good at exploiting one narrow food source, out-competing the generalists, but the latter remain in the background and, when the world changes and the narrow food source is replaced by something different, become the basic stock from which the next round of specialists will arise.