Even though the beginning of the semester (and all the trouble it brings) came too soon this year, I was looking forward to the first day of classes and so far the one class I’ve been to has offered quite a bit of food for thought. I’ll be off to Behavioral Biology later in the evening, but early this morning I had “Soils and Water”, perhaps one of the most-dreaded mandatory classes any 704 (Ecology) student has to take during their time at Cook College. Although I’m sure some parts of it will be more exciting than others, it got me thinking about something we often take for granted when it comes to ecology; soil. Soil often contains the necessary elements and nutrients that allow plants to grow, those plants in turn feeding herbivores and carnivores as we work along the food web.
Thinking about this, something at the back of my brain started kicking, reminding me that I heard that South American soil is lower in calcium content, which is why we don’t see huge animals like elephants in present day South America. This seems to make sense, but it may very well be incorrect (I haven’t been able to find said reference, assuming it exists) and other factors may account for the size of fauna in South America. Indeed, South America used to be home to some very large animals like glyptodonts, giant ground sloths (incidentally related to sloths in the superorder Xenartha), saber-toothed cats (Smilodon populator being larger than others in its genus; most saber-toothed cats weren’t much bigger than extant big cats), and the Phorusrhacidae (“Terror Birds”). Mammoths and Paraceratherium-size creatures do seem to be absent from such ecosystems, but this may be a factor of migration or geographic isolation and does not prove anything about calcium content of the soil.
The environment of South America also must be taken into account, comprising harsh plains, mountains, and dense rainforests. As far as the mountains and jungles go creatures most likely wouldn’t grow too big as size would inhibit movement, and the current lands like that of Patagonia don’t seem like there’s enough flat land or vegetation to support a breeding population of large animals. In thinking about Patagonia, however, I realized that going even further back in time to the Cretaceous period, some of the largest dinosaurs being discovered (such as Giganotosaurus and Argentinosaurus) are coming from Argentina, so obviously there must have been enough bone-building material coming from the soil & into the plants to allow for such giant creatures to be formed. Perhaps the soils were once calcium rich but became depleted, or perhaps the connection is entirely wrong.
This also sparked the thought that it would be more difficult for mammals to attain great size, being that they must keep a constant body temperature and deal with the physical ramifications of heat distribution and loss, as well as the fact that mammal mothers nurse their young on calcium-rich milk. Spotted Hyena (Crocuta crocuta) nurse their young for longer than most other mammals because they ingest so much bone (being such efficient scavengers with bone-crushing jaws), calcium that then cannot be used to make a larger or more robust skeleton. If the males, eating just as much bone, got bigger what would happen with the Hyenas? Contrary to what may be intuitive, the females are more robust and larger than males, even having false penises and being dominant over the males, perhaps keeping them in check. Indeed, the pseudo-penis of the female is used for urination, mating, and giving birth, offering full control over who she mates with and perhaps allowing for smaller, submissive males to be the rule. It seems apparent that scavenging only makes up a small part of a Hyenas diet (despite reputation) and, according to Wikipedia, 75% of kills are made by solitary members, although they often hunt in groups and are more successful during such hunts.
All of this is blind hypothesis and I don’t expect for anyone to really take me seriously; I could be extremely wrong on all the points I’ve made. The distribution of certain bone-building minerals in the soil, however, is an interesting thing I’ll be keeping in mind in order to see if there’s any correlation with the distribution of life across the planet over the ages, perhaps making a wonderful topic for my final presentation at the end of the semester.