Chapter 05 – Bahia Blanca
So, uh, a three week delay. This was a really dense chapter? That’s true, certainly, but perhaps more relevantly, I completely unexpectedly started an honours degree (I didn’t actually finish the application, and wasn’t exactly planning on doing so this year anyway, but they accepted me anyway). More on that later, but let’s return to the narrative.
… I observed a fact, which seems to me very curious and instructive, as showing how every character, even though it may be in some degree independent of structure, has a tendency to vary by small degrees.
Charles Darwin, The Voyage of the Beagle
After the Beagle sails from Bahia Blanca, Darwin remains on land to ride to Buenos Aires. In this chapter, Darwin discusses paleontology, ecology, the animals he finds in the area, and the war against the Indians. It’s also a rich source for fascinating insights into Darwin’s thinking, and I’ve taken the liberty of bringing out quite a few interesting quotes. Again, we can see how many observations Darwin made that led him to developing his theory.
Nearer the coast there are some plains formed from the wreck of the upper plain, and from mud, gravel, and sand thrown up by the sea during the slow elevation of the land, of which we have evidence in upraised beds of recent shells, and in rounded pebbles of pumice scattered over the country. At Punta Alta we have a section of one of these later-formed little plains, which is highly interesting from the number and extraordinary character of the remains of gigantic land-animals embedded in it.
He describes a number of large fossils of extinct animals he found within area of just 200 square yards:
- a Megatherium the size of an elephant
- another huge sloth – a Megalonyx (a genus discovered by Thomas Jefferson, interestingly)
- a near-perfect skeleton of a Scelidotherium the size of a rhinoceros
- the lower jaw (with teeth) Mylodon darwinii a sloth that’s alone in its genus
- another giant Edentate
- a large animal with a bony fur coat (like an armadillo)
- an extinct kind of horse
- a tooth from a Macrauchenia, a genus in the order Lipopterna
- a Toxodon, a rodent the size of an elephant. Darwin thinks it’s probably aquatic.
Many of these animals have huge hindquarters, and Darwin is impressed by Owen’s theory explaining why. In contrast to one popular view, that past trees were sufficiently large and sturdy that these creatures could climb them – imagine a sloth the size of an elephant climbing a tree, Owen theorises that these animals sat on the ground and pulled the trees down to them, in which case perfect sense would be made of their apparently clumsy skeletal structure.
Now, the only paleontological dig I’ve ever visited was mostly turning up ancient leaves, so the thought of all these fossils, just embedded in a small stretch of beach, seems rather astounding to me. It’s also a poignant reminder of how relatively unexplored natural history was in Darwin’s time – though I guess the same might well be said of the microbial world today. This is a fairly densely packed chapter – all this is just on page one!
How wonderfully the different Orders, at the present time so well separated, blended together in different points of the structure of the Taxodon!
Darwin next considers the ecology that all this megafauna must have existed in, and compares the environment with that of Africa – not a densely jungled environment, but a grassy plain, and disagrees with the general consensus that luxurious vegetation is necessary for large mammals. “… Among the mammalia, there exist no close relationship between the bulk of the species and the quantity of the vegetation in the countries which they inhabit.” I’m curious as to the state of the art here – after all the founding father of ecology hadn’t even been born in time for the first edition. Noting the large size of the animals in Africa, and the large number of large predators hunting them, Darwin writes:
As this able naturalist [Dr Andrew Smith] remarked to me, the carnage each day in Southern Africa must indeed be terrific!
He also describes the rheas – not the first time, certainly. While they mostly eat grass, apparently, some of them seem to go down to the lake and eat small fish. That would make a better food source, but it seems right out of character for a rattite. Some of them also go for a swim – slowly, but they can nonetheless cross a river. He mentions that the Australian explorer Charles Sturt reported seeing some emus swimming. That’s a new one on me, not that I’ve historically been very good at paying much attention to biology (more on that one later, too).
The male incubates the eggs, 20-50 at a time, from several mothers. A female can lay large numbers of eggs over a few days, but incubating them all in one go results in some of them being addled by over-incubation.
This chapter also has Darwin’s famous discovery of the lesser rhea (a.k.a. Darwin’s Rhea) – in his dinner. Fortunately, the head, neck, legs, wings, and many feathers had been preserved.
Later, during a discussion of a snake that Cuvier classifies (somewhat controversially) as in a sub-genus of rattlesnakes, and yet similar to a viper. Seeing this, Darwin comments, “… I observed a fact, which seems to me very curious and instructive, as showing how every character, even though it may be in some degree independent of structure, has a tendency to vary by slow degrees.”
One final note I will make on this chapter, is a cute little reference to the Genesis creation story.
I found only one little toad (Phryniscus nigricans) which was most singular from its colour… If an unnamed species, surely it ought to have been called Diabolicus, for it is a fit toad to preach in the ear of Eve.
March 24, 2009 at 1:10 am