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It’s been a long time since we delved into the animal file and I thought we’d do some ancient history with a couple of stories about every little kid’s favorite ancient animals, the dinosaurs.

Although we’ve sort of realized this all along, a definitive new international study coordinated by researchers at the University of New Mexico says that after the dinosaurs went away 65 million years ago, mammals got bigger ... a LOT bigger, about a thousand times bigger than they had been.

To figure out what happened to mammals after the extinction of the dinosaurs, the researchers collected data on the maximum size for major groups of land mammals on all the continents. Their study included horses, rhinos, elephants and mammoths, armadillos and a number of groups that are now extinct.

They discovered that mammals grew from a maximum weight of about 25 pounds before the dinosaurs went away to a maximum of roughly 17 tons when they had the planet to themselves. I think you’ll agree that’s a big change!

They also discovered what sets the limits for the max body size for land animals. It’s the amount of space available and the climate they live in. The colder the climate, the bigger mammals get – because bigger mammals are better at conserving heat.

So ... definitely the mammals got bigger after the dinosaurs went away, but exactly when DID they go away? There’s been some research about that too. It's widely believed that the dinosaurs all died somewhere between 65.5 and 66 million years ago when debris from a giant meteorite impact blocked out the Sun, causing extreme climate conditions and killing vegetation worldwide. (It’s called the KT extinction.)

Now, researchers from the University of Alberta have dated the femur bone of a hadrosaur found in New Mexico at 64.8 million years.

That date suggests this particular plant eater was alive about 700,000 years after the mass extinction event many scientists believe eliminated all the land dinos. The researchers used a new technique that measures the rate that uranium turns to lead. Living bone contains very low levels of uranium but during fossilization (typically less than 1,000 years after death) bones are enriched with uranium. The uranium atoms in bone spontaneously decay to lead over time; and once fossilization is complete, the uranium-lead clock starts ticking.

The researchers think there could be several reasons why the New Mexico hadrosaur survived the mass extinction 65 million years ago. It's possible the vegetation wasn't all wiped out and a number of hadrosaurs survived. The researchers also say the potential survival of dinosaur eggs during extreme climatic conditions needs to be explored.

The paper’s authors believe their new uranium-lead dating technique will show that more dinosaurs survived the KT extinction, and the end of the dinosaurs will have to be revised.

This doesn’t really surprise me. I’ve always found it a little difficult to believe that EVERY land dinosaur died in the KT extinction. It’s a big planet and apparently there are places even hadrosaurs could hide, at least for a while.

Cruise on over to The Deep website at www.thedeepradioshow.com to learn more about dinosaurs and many other topics. Enjoy!