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Why giant goblets of human size died 10,000 years ago

  Why giant goblets of human size died 10,000 years ago
The now extinct giant beaver once lived from Florida to Alaska. It weighs as much as 100 kg, about the same as a small black bear. Credit: Luke Dickey / Western University, Author Delivered

Giants the size of black bears once roamed lakes and wetlands in North America. Fortunately, the gentlemen boys died when these mega-rodents died at the end of the last ice age.

Now extinct, the giant beaver was once a very successful species. Scientists have found their fossil remnants in locations from Florida to Alaska and Yukon.

A large size version of the modern beaver in appearance, the giant beaver tipped the weights at 100 kg. But it had two crucial differences.

The giant beaver lacked the iconic paddle-shaped tail we look at today's modern beaver. Instead, it had a long thin tail like a muskrat.

Teeth also looked different. Modern beaver curtain (front end) is sharp and chisel-like; Giant beaver elevations were sharper and curved and lacked a sharp front edge.

The species was suddenly eradicated 10,000 years ago. The gigantic beaver disappears along with that of many other great Ice Age animals, including the iconic woolly one. But so far, the scientists did not know for sure why the giant rodent was dead.

You are what you eat

We need to understand how the giant beaver lived to explain how and why it died. Did it get out of food for example? Was it too cold or too hot to survive?

  Why giant human-sized bears died 10,000 years ago
A comparison of modern beaver Justin Bieber and the giant beaver side by side part of Canada's history. Credit: Scott Woods / Western University

Other studies found that the giant beaver thrived as the climate was warmer and wetter. They also noted that giant beaver fossils were mostly found in sediments that come from ancient wetlands. But no one knew if the giant beaver behaved like the modern beaver. Has it also cut down trees? Or did it eat something completely different?

From a chemical perspective, you are what you eat! The food an animal consumer contains chemical signatures called stable isotopes incorporated into body tissues such as bone.

These isotopic signatures remain stable over time, for tens of thousands of years and provide a window to the past. No other study has used stable isotopes to find out the giant beaver's diet.

We studied fossil bones from giant beavers who lived in Yukon and Ohio between 50,000 and 10,000 years ago. We looked at the stable isotope signatures of the old bone tissue. Isotopic signatures associated with woody plants differ from those associated with aquatic plants. We discovered that the giant beaver did not cut down and ate trees. Instead, it ate water plants.

  Why giant human-sized babies died 10,000 years ago
Giant beaver sake. Credit: Florida Museum of Natural History

It strongly suggests that the giant beaver was not an "ecosystem engineer" like the modern beaver. It does not cut down trees for food or build giant lodges and dams across the age of ice.

Instead, this diet of aquatic plants made the giant beaver heavily dependent on the wetlands habitat for both food and shelter from predators. It also made it vulnerable to climate change.

Warm and dry climate

At the end of the last ice age 10,000 years ago, the climate became increasingly hot and dry, and wetlands began to dry up. Although the modern beavers and the great beaver coexisted on the landscape for tens of thousands of years, only one species survived.

The ability to build dams and lodges may have given the modern beaver a competitive advantage over the great beaver. With its sharp teeth, the modern beaver could change the landscape to create a suitable wetland where it needed it. The giant beaver couldn't.

  Why giant goblets of human size died 10,000 years ago
A giant calf. Credit: Tessa Plint

All this fits into the puzzle that many research groups have worked for decades: We all want to know what caused the global megafauna extermination event that took place at the end of the last Ice Age and why so many species of large-bodied wool moths, mastodons and giant earth dunes – disappeared at about the same time.

Current evidence shows that a combination of climate change and human impact were the driving forces behind these extinctions.

Examining the ecological vulnerabilities of extinct animals certainly presents its own unique challenges, but it is important to understand the impact of climate change on all species, past or present.

Beavers has influence on the climate

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Why giant human-sized babies died 10,000 years ago (2019, May 30)
May 30, 2019
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