I was looking up dinosaurs with my 4 year old son and came across this...prehistoric giant beavers...it quickly reminded me of "Rodents of Unusual Size (R.O.U.S.'s)!" Apparently they were real!

http://www.nature.ca/notebooks/english/giantbev.htm

"The giant beaver was the largest rodent in North America during the last ice age. It was about 2.5 m (8 ft.) long and is estimated to have weighed 60 to 100 kg (132 to 220 lb.)."