Beavers! Majestic dam makers of Canada. Living on a diet of maple syrup and poutine. Probably. I don’t know.
Much bigger in the past, North America had Castoroides ohioensis, the giant beaver. As big as a bear. With its razor sharp incisors it could have felled trees and predators alike.
Here in Blighty we have a few beavers (Castor fiber) here and there. These prodigal sons have popped up in the Highlands, Argyll, Devon, Tayside. Some are legal beavers, and some are illegal beavers. The beaver population in Argyll, at Knapdale forest, are the product of the first licensed reintroduction of a mammal to Britain. Closely monitored by Scottish Natural Heritage, the Knapdale beavers are recolonisers who have been helped by the Scottish government to return to lands they were only recently removed from. Some of the other beaver populations are of unknown origins, occupying a legal grey area and not offered the same protection. Some of these new beavers have been shot by landowners, who if not actively disgruntled are pretty far from gruntled.
Castor fiber, survived very late in Britain. It only really disappeared in the 16th century, when incessant demand for furs and anal secretions* led to its extirpation.
Anyway, if we go back to the Middle Pleistocene (and why not), there was a big British beaver to be found. Sympatric with Castor fiber, Trogontherium cuvieri had a pretty large distribution from England to China in a fairly narrowly confined band. Its fossils are known from France, the Netherlands, Germany, Russia, although it probably only evolved in the Late Pliocene. It must have had fairly specific climatic tolerances because there are no known fossils from south of the Alps or the Pyrenees. We know it was also a river-dweller as that is where the vast majority of the fossils of this species have been found. While not quite as big as ol’ Castoroides, this was still a sizeable animal. Analysis of skulls show that metrically Trogontherium was nearly 50% bigger than Castor. To put that into some context, the incisors in Trog could be up to seven inches long: that’s as big as the canines of Smilodon fatalis!
There has been a lot of discussion about what Trogontherium was doing with its enormous incisors. General consensus today is that it didn’t use them for cutting down trees, like its modern day cousin. The incisors have a different profile; they are more convex and would have acted more like a gauge than a chisel. We actually have fossil trees from East Anglia, from the Middle Pleistocene when both beaver species were around, and they show tooth marks that match Castor rather than Trogontherium. Fossil trees can in fact be a marvellous repository of information about animals of the past: I remember seeing an early Holocene log on display in the National Museum of Scotland, that clearly shows the gnaw marks of a beaver from long ago. It seems likely that Trog used their oversized teeth for digging at roots or in burrowing into the ground.
One other weird point of discussion has been what the lips of Trogontherium looked like. Based on bony tubercles preserved on the maxilla above the upper incisors, some scientists reconstructed it with hyper-mobile Jagger lips that could act like tiny fingers to slurp up food. It has often been compared to the coypu (Myocastor coypus) which also has prehensile lips. Coypu are also known colloquially as nutria, and they are native to South America. Thanks to humans they have been spread worldwide, to North America, Africa, and Europe. Bred for their fur, escapes and releases have let them into places where they had no right to be. They used to be a common sight in East Anglia, where many Trogontherium fossils have been found. They terrorised Norfolk from about 1929 until an eradication campaign in the 1960s and 1970s. This along with a series of severe winters helped to wipe them out by the late 1980s. I like to think that this bit of accidental rewilding may have given East Anglia something it hadn’t had since the Middle Pleistocene- a Trogontherium analogue!
*yeah. Beaver anal secretions, called castoreum, have long been used as a medicine and perfume. Even back in Roman times. It is still used in the modern era to give perfumes a “leather” note, so you’ve probably smelt it and not realised. But that’s nothing. You’ve also probably eaten it. Castoreum is still used sometimes today as an additive to give food a vanilla flavour. Enjoy your next ice cream!
Written by Ross Barnett (@DeepFriedDNA)
A link to one of the best sight gags ever, from the Naked Gun (source of this article’s title)
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Kurtén, B. Pleistocene Mammals of Europe. London: Weidenfeld and Nicolson, 1968. [Book]
Mayhew, D. F. “Reinterpretation of Extinct Beaver Trogontherium (Mammalia, Rodentia).” [In English]. Philosophical Transactions of the Royal Society of London Series B-Biological Sciences 281, no. 983 (1978): 407-38. [Full Text]
Newton, E. T. “Trogontherium from the Pleistocene of Copford, Essex.” [In English]. Geological Magazine London Dec 6 3 (1916): (322-23). [Full Text]
Owen, R. A History of British Fossil Mammals and Birds. London: John Van Voorst, 1846. [Book]