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Giant Beaver - Castoroides ohioensis
#1
Giant Beaver - Castoroides ohioensis

[Image: gibeaver.gif]

Scientific classification 
Kingdom: Animalia 
Phylum: Chordata 
Class: Mammalia 
Order: Rodentia 
Family: Castoridae 
Subfamily: †Castoroidinae 
Tribe: †Castoroidini 
Genus: †Castoroides
Species: Castoroides ohioensis

The giant beaver (Castoroides ohioensis) was the largest rodent in North America during the ice age (Quaternary - the last 2 million years). How did it look? How large was it? How is it related to living beavers (Castor sp.)? These are just a few of the questions people ask when they first hear about the giant beaver. 

Unlike the woolly mammoth (Mammuthus primigenius), cave bear (Ursus spelaeus) and steppe bison (Bison priscus) whose images are so vividly recorded on the walls of European caves by Stone Age (Paleolithic) hunters, there is no record of the giant beaver's actual appearance. However, the great similarity between giant beaver and modern beaver skeletons leaves no doubt that the two animals were much alike in appearance and were adapted to similar surroundings. There was one remarkable difference - size! A skeleton displayed in Chicago's Field Museum is nearly 2.5 m long the size of a black bear (Ursus americanus). An animal of this size may have weighed as much as 200 kg compared to a 1 m-long modern beaver weighing about 30 kg. Modern beavers are, to put it simply, "distant cousins" of Castoroides. 

[Image: GiantBeaver2.jpg]

Other differences were in the teeth and tail of the giant beaver. Unlike modern beavers with their short smooth-surfaced cutting teeth (incisors), giant beavers had cutting teeth up to 15 cm long with prominently-ridged outer surfaces. Perhaps these strong enamel ridges would have acted as girders to support such long teeth. Although experts on ancient life (paleontologists) do not agree on the function of the cutting teeth, it seems that they could have acted as both wood cutters and gougers. Giant beaver cheek teeth also differ from those of modern beavers in their larger size and simpler enamel configuration. Molar teeth of Castoroides, like its relatives Dipoides and Procastoroides, typically have grinding surfaces with an s-shaped enamel pattern. 
[Image: bc-071a-lg.jpg]
By studying the length and width of giant beaver tail vertebrae in relation to those of modern beaver and its actual tail dimensions, I estimate that Castoroides had a scaly tail that was about 65 cm long, 12 cm across the base and 14 cm across the widest part. Definitely a beaver-like tail, but relatively narrower. Although well adapted for swimming, the hind legs of giant beavers are relatively short. Considering the great weight of the animals, their ability to disperse overland as some living beavers do, would have been reduced. 

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The first recorded remains of this animal were found in a peat swamp near Nashport, Ohio, and were described, but not named, by S.R. Hildreth in 1837. The geologist J.W. Foster called the specimen Castoroides ohioensis in a publication a year later. 

What about their ancestry? A primitive beaver called Dipoides that occupied Eurasia and North America during the late Tertiary (some 5 million years ago) evidently gave rise to Procastoroides, a large beaver about two-thirds the size of the giant beaver. It is worth noting that slight enamel ridges were first seen on the cutting teeth of the Idaho beaver (Procastoroides idahoensis), although the closely related Sweet's beaver (Procastoroides sweeti) lacked them. So probably the Idaho beaver, or a very closely related form, gave rise to the giant beaver about 3 million years ago. A study of the development of the cheek-tooth pattern in giant beavers also supports the Dipoides - Procastoroides - Castoroides lineage. 

Another "giant beaver" (Trogontherium - not much bigger than a modern beaver) lived in Europe and Asia during the early part of the ice age. Despite some basic similarities in shape, Trogontherium and Castoroides are at extreme ends of two different lineages. However, perhaps both had developed similar ways of living in relation to modern beavers, with which they coexisted. 

Castoroides ranged from Florida to the Yukon, and from New York State to Nebraska, but it has not been found outside of North America. Giant beavers seem to have flourished in the region south of the Great Lakes toward the close of the last glaciation. In fact, three nearly complete specimens are known from Fairmont and Winchester, Indiana, and from Minneapolis, Minnesota. 

The most northerly records are from the Old Crow region of the Yukon Territory (1), which lies 150 km north of the Arctic Circle. Here, many fossils (consisting largely of jaws, teeth, leg bones and vertebrae) have been found in deposits varying in age from the last (Sangamonian) interglacial (about 130,000 years ago) to the early part of the last (Wisconsinan) glaciation (about 60,000 years ago)(2). Fossils show that both giant beavers and modern North American beavers (Castor canadensis) coexisted near Old Crow during the last part of the ice age. The only giant beaver fossil found elsewhere in Canada is a cutting tooth from last interglacial deposits in the Don Valley, Toronto. 


How did giant beavers get so far north? And when? Perhaps they spread rather rapidly northward into the Yukon through chains of lakes which tend to form along the southern margin of the Canadian Shield (for example, during the present interglacial - the relatively warm period covering the last 10,000 years some are: Lake Superior, Lake Manitoba, Lake Athabasca, Great Slave Lake and Great Bear Lake). A likely time for this northward shift would have been near the beginning of a warm period such as the last interglacial, when ice sheets of the second last (Illinoian) glaciation were melting back. 

Where did giant beavers live? A possible giant beaver lodge was discovered near New Knoxville, Ohio about 1912. Part of a Castoroides skull and the lodge were located in a peaty layer surrounded by loam. The lodge was said to have been roughly 1.2 m high and 2.4 m in diameter, and formed from saplings about 7.5 cm in diameter. 

Giant beavers seem to have preferred lakes and ponds bordered by swamps as their habitat, because their remains have been found in ancient swamp deposits so often. Perhaps a rather sudden reduction of these surroundings due to changing climate linked with the giant beaver's apparent inability to build dams like those of Castor canadensis and its inability to disperse readily overland to new drainage systems when drought occurred may have resulted in its extinction and the survival of the smaller, more adaptable modern beaver. Likewise, the Eurasian "giant" beaver, Trogontherium, gave way to the living Eurasian beaver (Castor fiber), but earlier. 

Giant beavers evidently died out near the close of the last glaciation about 10,000 years ago. Because they coexisted with early humans in North America, it seems unusual that there is no evidence that people hunted them. Surely a Castoroides pelt would have made an excellent coat or sleeping robe! 




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[Image: wildcat10-CougarHuntingDeer.jpg]
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  • Claudiu Constantin Nicolaescu
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#2
Giant beavers didn’t eat wood and that’s likely why they didn’t survive the last Ice Age

MAY 9, 2019


[Image: Giant-Beaver-Final-Colours-700x391.jpg]
Illustrated by Luke Dickey

The Giant Beaver (Castoroides), a truly mega-sized prehistoric rodent, weighed as much as 100 kilograms (220 lbs.) -- roughly the same size as a small black bear.

North American beavers, which weigh between 25 to 75 pounds as adults, are the largest rodents living in Canada. That’s today. Go back 10,000 years to the last Ice Age and giant beavers – roughly three times larger than the modern North American beaver – walked the Earth with woolly mammoths and mastodons until they too became extinct.

A new study from Western University has uncovered a possible reason why the giant beaver, like so many other species of large terrestrial fauna, went extinct at the end of the last Ice Age.
More importantly, for the first-time ever, Western earth scientists have discovered that giant beavers did not eat wood – a distinct (and perhaps deadly) divergence from its dentally-endowed descendant.
[Image: giant-beaver-skeleton_Canadian-Museum-of...00x344.jpg]
Tessa Plint/Western UniversityGiant Beaver Skeleton (Canadian Museum of Nature)

Tessa Plint, a former Western graduate student currently continuing her studies at Heriot-Watt University (UK), and Fred Longstaffe, Western’s Canada Research Chair in Stable Isotope Science, found that giant beavers (Castoroides) ate submerged aquatic plants. This diet made the giant beaver, which weighed approximately 220 pounds, highly dependent on wetland habitat not only for shelter from predators but also for food.

“We did not find any evidence that the giant beaver cut down trees or ate trees for food,” says Plint. “Giant beavers were not ‘ecosystem-engineers’ the way that the North American beaver is.”

Beavers and giant beavers actually co-existed for tens of thousands of years in North America during the Pleistocene epoch before the latter went extinct. After the last Ice Age (known scientifically as the Last Glacial Maximum), the ice sheets retreated and the climate became much drier. This climate change was bad news for giant beavers.

“The ability to build dams and lodges may have actually given beavers a competitive advantage over giant beavers because it could alter the landscape to create suitable wetland habitat where required. Giant beavers couldn’t do this,” explains Longstaffe. “When you look at the fossil record from the last million years, you repeatedly see regional giant beaver populations disappear with the onset of more arid climatic conditions.”

Plint and Longstaffe used stable isotopes (chemical tracers) of fossil bones and teeth to determine the diet of giant beavers. They collaborated with Grant Zazula from the Yukon Palaeontology Program for the study, which was published by Scientific Reports – Nature.

Terrain map of North America indicating sample collection sites can be found here.
MEDIA CONTACT: Jeff Renaud, Senior Media Relations Officer, 519-661-2111, ext. 85165, 519-520-7281 (mobile), jrenaud9@uwo.ca, @jeffrenaud99

https://mediarelations.uwo.ca/2019/05/09...B2jvJwXmcU
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  • Claudiu Constantin Nicolaescu, Taipan
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