This weekend the Beagle was on the “road” back to Montevideo. First, however, they made one last stop in Bahia Blanca for Darwin to pick up a few more fossils. They stopped at the site where several crewman (including Darwin) had recently been stranded (see Stranded, Cold and Hungry and Survivor: Darwin), hence the name he gives the “point”:
“The Captain landed for half an hour at Monte Hermoso, (or Starvation point as we call it) to take observations.— I went with him & had the good luck to obtain some well preserved fossil bones of two or three sorts of Gnawing animals.— One of them must have much resembled the Agouti but it is smaller.— We are now at night pressing on for the Rio Plata.” (Oct 19)
This time, unlike the giant ground sloths fossils that Darwin had uncovered a few weeks earlier (see Darwin’s Sloth), it was some little critters whose bones he dug out of the cliff face. Zoology of the Voyage of the Beagle lists them as belonging to the (genus) Ctenomys – a small rodent whose living descendants go by the name tuco-tucos.
Brazilian tuco-tuco – Ctenomys brasiliensis (from Alcide Dessalines d’Orbigny, 1847)
The tuco-tucos, like all rodents, have teeth that continuously grow – an adaptation to a way of life that involves gnawing. Their body shape lends itself well to their burrowing lifestyle. Some species live in colonies and are very social, while others go it alone. (Several sites compare them to North American pocket gophers.)
Flamarion’s tuco-tuco – Ctenomys flamarioni (from Wikipedia Commons)
Here is what Darwin had to say about the tuco-tuco (including the origin of their name):
“The Tucutuco (Ctenomys Brasiliensis) is a curious small animal, which may be briefly described as a Gnawer, with the habits of a mole. It is extremely numerous in some parts of the country, but is difficult to be procured, and never, I believe, comes out of the ground. It throws up at the mouth of its burrows hillocks of earth like those of the mole, but smaller. Considerable tracts of country are so completely undermined by these animals, that horses in passing over, sink above their fetlocks. The tucutucos appear, to a certain degree, to be gregarious: the man who procured the specimens for me had caught six together, and he said this was a common occurrence. They are nocturnal in their habits; and their principal food is the roots of plants, which are the object of their extensive and superficial burrows. This animal is universally known by a very peculiar noise which it makes when beneath the ground. A person, the first time he hears it, is much surprised; for it is not easy to tell whence it comes, nor is it possible to guess what kind of creature utters it. The noise consists in a short, but not rough, nasal grunt, which is monotonously repeated about four times in quick succession:* the name Tucutuco is given in imitation of the sound. Where this animal is abundant, it may be heard at all times of the day, and sometimes directly beneath one’s feet. When kept in a room, the tucutucos move both slowly and clumsily, which appears owing to the outward action of their hind legs; and they are quite incapable, from the socket of the thigh-bone not having a certain ligament, of jumping even the smallest vertical height. They are very stupid in making any attempt to escape; when angry or frightened they uttered the tucu-tuco. Of those I kept alive several, even the first day, became quite tame, not attempting to bite or to run away; others were a little wilder.” (Voyage of the Beagle)
Today there are up to 60 species of Ctenomys (depending on your source), all living in the southern half of South America. Interestingly, it has been suggested that the genus underwent rapid speciation over the last couple of million years – most likely as a result of populations becoming isolated. So Darwin’s fossils probably help shed some light on their story.
Sketches of Ctenomys fossils from Zoology of the Voyage of the Beagle (R. Owen):
On the 20th the crew was working their way back up the outer coast, and Darwin’s entry is brief:
“The wind is very light.” (Oct 20)
On Sunday he was silent – possibly working away in his cabin cataloging his new rodent samples. (RJV)