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. 

The Importance of Blue Bullshit

Monkeys and apes in general, and humans in particular, have a relatively poor sense of smell but the same is far from true of most other mammal species. For such animals, scent can be an important method of communication and this is often done through scent-marking, leaving long-term messages that can be understood by other passing members of your species.

A common way to do this is by rubbing specially adapted scent glands onto objects - these glands are often on the feet or the sides of face, which is why many animals will rub their heads against things to mark their territory. An alternative is to either urinate or defecate in a particular location, the natural aroma of the excreta often being aided by anal scent glands. We are all familiar with a dog's need to mark its territory in this way and it's hardly alone in this respect.

This can provide all sorts of useful information to other animals from the same species, such as territorial ownership, social dominance, willingness to mate, and so forth. When the method used to deposit this information is defecation rather than urinating, the result is termed a latrine or midden - which, in the biological sense, are basically alternative words for "dungheap". Animals that use this method of scent-marking include rhinoceroses, lemurs, and antelopes. (And we can but wonder what human cities would be like had we evolved from a species that communicated in this way).

Plague and the Prairie Dogs

Populations of animals are not always stable from year to year, even ignoring the effects of direct human activity or climate change. If there is a prolonged drought, plants may die off, reducing the population of herbivores, which, in turn, reduces the number of predators that feed on them. This much is part of the natural cycle of life and death.

Perhaps the most famous example, sufficiently so to turn up in some school textbooks, is the case of the Canada lynx. This eats almost nothing but showshoe hares, so when the supply of the hares runs low, the lynx are more likely to be malnourished, so that mothers give birth to smaller litters. This means that there are fewer lynx around, which leads to the snowshoe hare booming, which means more food for the lynx, so they have larger litters, their population increases, they eat the hares so that the hare population goes down... and so on. Because the effect works through the litter size of the lynx, which take time to reach maturity, the lynx population rises and falls about a year behind that of the hares, and the entire cycle takes a decade or so to come full circle. We have records of this going back to the early 19th century from the fur-trappers of the Hudson Bay Company, and it doubtless goes back well into prehistory.

Leaf-Eating Monkeys: Monkeys on the Mountainsides

Golden snub-nosed monkey

Much of eastern China is dominated by two great river basins: the Yellow River in the north and the Yangtze in the south. In the western parts of the country, the upper reaches of the two basins are separated by the Qinling Mountains, running eastward from the vast Tibetan Plateau. And here, in addition to many other unique animals and plants, we find a rather strange species of monkey.

This is the golden snub-nosed monkey (Rhinopithecus roxellana) and its oddity merely begins with its unusual appearance. As the name implies, its fur is mostly golden, ranging from a brownish-red hue to a much brighter golden-yellow. Contrasting stripes of black fur run down the outer edges of the limbs and there are white patches on the back of the thighs. All of these colour patterns are brighter in the males, which are also noticeably larger than the females, indicating that these are likely used in sexual signalling - something supported by the fact that the genitalia also have a contrasting dark colour.