Speaker 1: Welcome to Brainstuff, a production of iHeart Radio, Hey brain Stuff,
Speaker 1: Lauren Bobo bomb Here. Mammoths, mastodons, and sabretooth cats weren't
Speaker 1: the only giants roaming ancient America. The Palistocene was a
Speaker 1: global epoch that kicked off two point six million years ago.
Speaker 1: It lasted right up until Earth's most recent ice age,
Speaker 1: ended about eleven thousand, seven hundred years before the present day.
Speaker 1: When you live in a cold environment, being big has
Speaker 1: its advantages. Large animals tend to conserve body heat more
Speaker 1: easily than smaller ones, and this is one of the
Speaker 1: major reasons why colossal mammals were so widespread during the
Speaker 1: frigid Pleistocene. Castroides was very much a product of its time.
Speaker 1: The largest rodent in Pleistocene North America, this very big
Speaker 1: beaver grew to more than seven ft long from tail
Speaker 1: to snout that's over two meters, and could have weighed
Speaker 1: as much as two hundred and twenty pounds or a
Speaker 1: hundred kilos or more, rivaling the American black bear in size.
Speaker 1: Casteroids utterly dwarfed the beavers that live today. Modern Eurasian
Speaker 1: and American beaver species clock in it just around three
Speaker 1: ft long, a bit less than a meter, and weigh
Speaker 1: somewhere between twenty nine and seventy seven pounds that's about
Speaker 1: thirteen to thirty five kilos. Proportionately, Casteroids had a narrower
Speaker 1: tail and shorter legs, albeit with bigger hind feet than
Speaker 1: it's extant relatives. We also know that it didn't eat
Speaker 1: the same foods. Woody plants are a crucial part of
Speaker 1: every living beaver's diet. The critters used chisel like incisors
Speaker 1: that's their front teeth to gnaw through bark and take
Speaker 1: down trees. But even though casteroids incisors grew to be
Speaker 1: a whopping six inches or fifteen centimeters long, the teeth
Speaker 1: had duller edges. By comparison, dental differences would have made
Speaker 1: it a lot harder for casteroids to eat tree bark,
Speaker 1: and indeed, it looks like this was not really on
Speaker 1: their menu. Using isotropic signatures in casteroid's teeth from Ohio
Speaker 1: and the yukon En study found that the giant beaver
Speaker 1: mostly ate softer aquatic plants. The findings say a lot
Speaker 1: about the rodents ecological niche and why it might have
Speaker 1: died out For starters casteroids probably didn't build dams, not
Speaker 1: that there's anything unusual about that. The earliest known beavers
Speaker 1: appeared during the Eocene epoch, which lasted between about fifty
Speaker 1: six and thirty four million years ago. New evidence suggests
Speaker 1: that the wood harvesting specialists came along much later, perhaps
Speaker 1: around twenty million years ago. In all likelihood, these bark
Speaker 1: fanciers used wood as a food source before any of
Speaker 1: them started constructing dams. Since casteroids fed on aquatic plants,
Speaker 1: its survival would have depended on wetland habitats. The animal
Speaker 1: was highly successful for a time. Casteroids fossils representing at
Speaker 1: least two distinct species have been documented in the Great Plains,
Speaker 1: the Great Lakes, the American South Alaska, and numerous Canadian provinces. Unfortunately,
Speaker 1: for the mega sized beaver, North America became warmer and
Speaker 1: drier after the Last Ice Age ended, wetlands grew scarcer
Speaker 1: as a result. Today's beavers used their logging skills to
Speaker 1: reshape the land around them so that it meets their
Speaker 1: own needs. With some well placed wood in the nearest stream,
Speaker 1: a determined beaver can engineer brandon new ponds. Yet, if
Speaker 1: casteroids didn't harvest wood or build dams. It couldn't have
Speaker 1: followed suit. So theoretically, the decline in natural wetlands left
Speaker 1: the giant beaver more susceptible to extinction. The last of
Speaker 1: these creatures perished around ten thousand years ago. Today's episode
Speaker 1: was written by Mark man Scene and produced by Tyler Clang.
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