Posted by: Rob Viens | October 21, 2013

Toxodon Dentistry

Between October 16th and the 20th, Darwin continued his leisurely trip down the Rió Parana, and by the end of the weekend he was back in the Rió de la Plata and ready to return to Buenos Aires.  Most of the trip was quiet and uneventful.

“Some leagues above Rozario we came to cliffs, which are absolutely perpendicular. — these form the West bank to below St Nicholas; & the whole coast more resembles that of a sea than a fresh-water river. — It is a great draw back to the scenery of the Parana, that from the soft nature of the banks, all the water is very muddy.— The Uruguay is much clearer, & I am told where the two waters flow in one channel, they may clearly be distinguished by their black & red colours. In the evening, the wind not being quite fair, the master was much too indolent to think of proceeding. — Moored 5 leagues above St Nicholas.” (Oct 16)

This is the region where three weeks ago, on October 1st, Darwin explored some old bones. On that day he noted:

“I found a curious & large cutting tooth.” (Oct 1)

I had assumed that he was talking about a mammoth tooth that day, since he also found some mammoth bones (see Of Mastodons and Missionaries). However, it turns out that this curious tooth came from another prehistoric giant – the toxodon. (This was sort of the opposite end of the spectrum from the Tiny Tuco-Tuco Teeth Darwin pulled out of the sediment last year.)

Toxodon skeleton (from Wikipedia Commons)

toxodon skeleton

The toxodon was a large hoofed mammal (an ungulate) that lived on the pampas until about 10,000 years ago, at which time they went extinct with the other large mammal fauna of the region. In this case, the presence of arrowheads with fossil remains support the idea that hunting may have played a role in their demise.

Toxodon reconstruction by Robert Bruce Horsfall (1913). Early interpretations, as is shown here, suggested toxodons were aquatic, like hippos. However, more recent information suggests they probably roamed the grasslands – more like rhinos.  (from Wikipedia Commons)

toxodon by Horsfall

Adult toxodons where about 9 feet (~3 m) long, 5 feet (~1.5 m) tall and weighed well over 3 tons (~1500 kg). This makes them similar to, but just a bit smaller than, a modern-day rhinoceros (also an ungulate). Like rhinos, toxodons were grazers that likely thrived on the Pleistocene pampas.

Darwin found pieces of toxodon (including a skull next month) in several locations around Uruguay and Argentina.  In fact, here is one of the sketches of his tooth samples from Zoology on the Voyage of the Beagle.  In that publication, Richard Owen was officially the first person to describe and name the species Toxodon platensis (named for their unusual teeth).

Toxodon teeth collected by Darwin:

toxodon teeth

The remainder of the trip passed uneventfully, and Darwin’s entries where short and mostly about the weather:

“Gale. — remained stationary. (Oct 17)

“Sailed quietly on with gentle winds, & anchored in the middle of the night near the mouth of the Parana, called Las Palmas.” (Oct 18/19)

“I was very anxious to reach B. Ayres, so that I determined to leave the vessel at Las Conchas & ride into town a distance about 20 miles. — After changing my vessel three times in order to pass the bar, I obtained a canoe, & we paddled quickly along to the Punta de St Fernando. — The channel is narrow & several miles long. — On each side the islands were covered with peaches & Oranges. These have been planted by nature, & flourish so well, that the market of B. Ayres in the fruit season is supplied by them. — On one of the islands I saw a bevy of fine gallinaceous birds of a black colour & nearly the size of a Turkey. — Upon leaving the canoe, I found to my utter astonishment I was a sort of prisoner. ” (Oct 20)

What was that – Darwin a prisoner?  A cliff-hanger ending today….You’ll have to wait till the next post to see what happened… (RJV)

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Responses

  1. […] more on toxodons see Toxodon Dentistry posted last month. Below are images from Zoology of the Voyage of the Beagle showing a side view of […]

  2. […] to be are closely related to the toxodons (see Toxodon Dentistry), and both orders may have evolved from the same primitive ungulate (the condylarth) that led to […]


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