Beaver-lution: Meet the Ancestors

Beaver-lution: Meet the Ancestors

Dan Stathers

There’s thumping in the undergrowth, a shiver through the cypress trees. Propelled by muscular hindquarters giving way to delicate webbed feet, an ursine creature flaunting incisors that would not look out of place on a Smilodon enters the glare of the wetland. Despite its bulk, it daintily clears the boggy margins and glides into the teeming waters leaving a tell-tale arrowhead wake. 

This would have been a common sight during the mid-to-late Pleistocene epoch (up to 129,000 years ago), when giant beavers (some weighing more than 200kg!) were believed to have thrived in the middle latitudes of North America, part of a megafauna dynasty which included mastodons, dire wolves and gomphotheres. 

Palaeontologists remain uncertain as to whether the giant beaver, Castoroides, harvested trees and built dams and lodges due to the absence of a chiselled edge to its formidable 15cm-long incisors. This, along with evidence that its brain was proportionally smaller when compared to its modern-day descendants, suggests the giant beaver (which was also a highly adept swimmer) is unlikely to have indulged in complex problem-solving behaviour and was probably more concerned with satisfying its enormous appetite for aquatic plants (macrophytes). 

The giant beaver is just one branch of an extremely diverse family tree. When a strange two-metre-tall corkscrew-shaped fossil was discovered in the White River Badlands of western Nebraska, 20th century researchers were left baffled. Early theories that it was the remains of an extinct freshwater sponge (christened by locals as the “devil’s corkscrew”) or part of an ancient, gargantuan root system were eventually proved wrong. It was, in fact, the silted burrow cast of a prehistoric beaver known as Palaeocastor, the skeleton of which was unearthed in a chamber below. 

These tunnelling beavers have been traced back to the late Oligocene period (33.9 million to 23 million years ago) and were believed to have lived in large colonies, much akin to prairie dog towns. Their spiral burrows were dug vertically downwards to help economise space while also acting as ingenious cooling systems. More recently, palaeontologists from the University of Kansas proved that these burrows were dug with teeth and not claws, spiralling clockwise or anti-clockwise in equal measure. Palaeocastor was one of more than a dozen species of beaver to have flourished on these dusty, clay-rich steppes, in fact, one such group, known as Euhapsis, was so well-adapted to life below ground it was almost certainly completely blind. 

As the earth continued to cool and competition among burrowing rodents intensified, this once vigorous evolutionary path finally reached its point of no return. However, in the race for survival it was the tunnelling beavers’ semi-aquatic cousins which proved a force to be reckoned with. Evolving their woody appetite into industrious tree-cutting behaviour, this resourceful subfamily would spend the next twenty million years establishing itself as one of the planet’s keystone species, spreading from North America into Eurasia by way of the Bering Land Bridge. 

Today, there exists only two species of beaver, the North American beaver, Castor canadensis, and the European beaver, Castor fiber. Equipped with an array of deft attunements, these wetland architects carry with them inimitable know-how as well as a knack for survival. Their ability to help revive our fractured ecosystems has been aeons in the making.*

(*This blog has been written by independent writers outside of our organisation. Beaver Trust welcomes a breadth of opinions, and those expressed within this blog do not necessarily reflect those of the Beaver Trust.)