800th Synapsida

Some primates, to make up for a scarcity of posts...

This will be the 800th post to be posted in this blog. That means it is once again time for me to take a break from doing anything original and take a look back at the last couple of years or so. There have been some changes in how I've been doing things since the last of these updates, but they're relatively minor, and posting has generally been pretty regular.

The most common topic in the last 100 posts has been animal behaviour, which has overtaken the usual frontrunner of evolution. It's a broad topic, of course, and the exact ranking will come down to the variability of how I happen to label posts, but it shows that it's not all taxonomy and anatomical adaptations here. In particular, there have been several posts about sociability of late, partly due to the discussions of how different dolphin species associate into pods. There have also, as usual, been several posts on diet and habitat, both topics that inevitably come up a lot when I discuss particular living animals, or even the way that they have changed over millions of years. 

Eocene (Pt 6): Gophers, Camels, and Lady Gaga

Leptomeryx

World climate fluctuated during the Eocene epoch, but it was consistently warmer than it is today, including the lengthy Climatic Optimum, the hottest the world has been since the extinction of the non-avian dinosaurs. This naturally affected not just the weather, but where different types of vegetation were found. Much of North America was covered with subtropical forests, with at least some palm trees reaching as far north as Alaska, and temperate woodlands on the northern Canadian islands.

The animals you would have encountered in these woods would also have been unfamiliar, with most of the mammals not fitting within any family we would recognise today. Nonetheless, there were some exceptions.

All the World's Antelopes: Waterbuck and marsh-dwellers

Kob

One of the features of the reduncinine subfamily of antelopes, as opposed to most of the other groupings, is that they require ready access to standing water. Many of them, such as the reedbucks, are grassland animals, avoiding the driest areas, but otherwise living in plains and mountains, only retreating to riverbanks and marshes during the dry season. Others may, if anything, be even more tied to the water.

The kob (Kobus kob) lives across the savannah belt south of the Sahara, from Senegal to Uganda. It is said to never be seen more than 10 km (6 miles) from standing water, and usually much less. The unusually blunt scientific name comes from two different authors, with Charles Hamilton Smith having added the first half in 1840, after the animal had been originally described (as Antilope kob) by Erxleben much earlier, in 1777.

Dishonest Bears

Mammals use a variety of means to communicate with one another: vocal, scent, and visual. Even those that are mostly solitary need to do this from time to time, whether to mark out their territories as a warning to others or to attract mates. 

Often these signals need to convey more than the basic message, but also provide some information about the animal that left them. This often includes physical fitness, whether to intimidate potential intruders or to advertise oneself as a sexual partner. At close range, this can be achieved through such things as growing huge antlers, proving that you have the physical capacity to waste resources on something that's otherwise pointless. But, at longer range, a simple indicator of size may be all that's required.

All the World's Antelopes: Reedbuck and Rhebok

Bohor reedbuck

Quite where, within the larger bovid family, the reedbucks belong was long a matter of contention. They are medium-sized antelopes, tending to prefer habitats with plenty of water, distinguished by the fact that not only their visible horns, but also the bony cores on the inside, have transverse ridges running round them. The detailed structure of their teeth has some resemblance to that of the true bovines (that is, cows, bison, and the like) but it's hard to see that as anything other than parallel evolution. 

The most widely followed scheme in the late 20th century placed them with the grazing antelopes, such as sables and their kin, but even then there was a suspicion that this was only because nobody knew what else to do with them. Once we were able to do detailed genetic analysis, it turned out that they are pretty much in a group of their own, not especially close to anything, having diverged from the ancestors of the true grazing antelopes before that group diverged from the goats. Our best guess is that this happened between 16 and 14 million years ago; there are antelopes with longer lineages, but not many.

Hippos in the Tiber

The hippopotamus (Hippopotamus amphibius) is an iconic African animal. While their distribution is very patchy, in part due to their reliance on large waterways, they are found across essentially the whole of Africa south of the Sahara and north of the Kalahari and the South African veldt. A second, endangered, species belonging to the same family, the pygmy hippo (Choeropsis liberiensis), lives only on the southern coast of West Africa, between Sierra Leone and Côte d'Ivoire. 

But hippos were once common in Europe and southern Asia. In the case of Europe, for example, we have fossils from Portugal to Greece, and as far north as the UK. Nevertheless, hippos have never been especially diverse, at least in comparison to groups such as deer or pigs, and they are grouped into no more than around six widely accepted genera. This includes the two that are still with us, and we don't have a large amount of information on three of the others.

All the World's Antelopes: Sables and Other Horse-Antelopes

Sable antelope (male)

The hippotragines are one of several small subfamilies of antelope. Small that is, in terms of number of species, because physically they are quite large. The name literally translates as "horse-goat", but that second part is often used taxonomically as a term for antelopes, so "horse-antelope" might be closer to the intent. It was coined in 1845, partly on account of the physical build of the animals, with their long legs and muscular, horse-like necks.

The subfamily includes the oryxes and gemsbok, but arguably the most horse-like members of the group are the sable antelope (Hippotragus niger) and its closest relatives. Sable antelopes stand around 140 cm (4'7") at the withers, which is almost exactly the official height that separates full-size horses from ponies. They weigh between 160 kg and 230 kg (350 and 510 lbs), which is well within the range for domesticated ponies, indicating a slighter build than animals bred, in part, to bear the weight of humans. Their shape, however, is quite horse-like, an effect accentuated by the presence of a clear mane down the back of the neck.