Image: Glyptodont skeleton
Rudemar Ernesto Blanco
The researchers who studied glyptodont tails appear alongside the fossilized skeleton of a glytodont.
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updated 8/25/2009 7:57:54 PM ET 2009-08-25T23:57:54

Enormous prehistoric armored mammals called glyptodonts swung their spiked tails just as athletes swing tennis rackets and baseball bats, according to a new study.

These massive animals even had a "sweet spot" on their tails right where the biggest, sharpest spike was situated.

The findings about glyptodonts — which looked like a cross between an armadillo and a Volkswagen beetle car — apply to dinosaurs that also had spiked tails, the team of researchers believes.

Both glyptodonts and dinosaurs possessed the lethal tail "sweet spot," technically known as the center of percussion.

"The center of percussion is a point where you can deliver a very powerful blow with a baseball bat, a tennis racket, a sword, an axe or any hand-held implement, but the forces against your hands are almost zero," said lead author Rudemar Ernesto Blanco, a researcher in the Institute of Physics at the Faculty of Sciences in Montevideo, Uruguay.

Glyptodonts lived in both South and North America, first emerging around 2.5 million years ago and going extinct 8,000 years ago, possibly due to hunting by humans.

Blanco and colleagues Washington Jones and Andres Rinderknecht studied tail remains for the giant armored mammals at three museums, including the Argentinean Museum of Natural Sciences.

They determined that in many glyptodont species, such as Doedicurus clavicaudatus, rings of bony scutes, or plates, on the tails were fused, turning the animal's tail into something akin to a baseball bat.

Measurements and calculations found that each tail's sweet spot landed right where scientists had previously speculated the biggest spikes once existed: at the center end of the tail.

8 great extinct speciesLike the horns of living rhinos, these spikes did not preserve well once the animal died.

The study, published in the latest Proceedings of the Royal Society B, "reinforces the idea that in that (sweet spot) was something useful to cause more damage during an impact," Blanco said, adding that glyptodonts might have evolved this defensive technique to help fight off "terror birds," prehistoric South America's dominant predator.

Terror birds stood nearly 10 feet tall and weighed over 650 pounds. Blanco said they "had kicks powerful enough to break bones."

Glyptodonts might have therefore evolved their body armor, not to mention their spiked tails, to withstand this bird's potentially deadly kicks.

Large crocodilians and bear-like marsupials with long, sharp teeth also preyed on glyptodonts.

In addition to defense against predators, Blanco and his colleagues believe glyptodonts used their tails in fights against each other over territory, food, mates and more.

Programs like the Discovery Channel's "Walking with Dinosaurs" show glyptodonts battling each other side to side, looking in opposite directions, but Blanco now believes the animals "probably fought head to head, trying to push down the body of the opponent with the front limbs."

Like limber wrestlers, the glyptodonts "could make a 180 degree turn of the body around the hind limbs, hitting with the tail close to the shoulders or mid-point of the trunk of the rival."

John Hutchinson, a Royal Veterinary College expert on the biomechanics of dinosaurs and other animals, told Discovery News that the new paper "is an interesting study and quite clever."

Hutchinson said he was surprised by "how the positions of spikes and nubbins on the tail clubs in a variety of species seem to line up pretty well with the mechanically most reasonable positions."

He concluded, "That's what evolution should produce, of course, but it's always satisfying finding different kinds of evidence for sufficiently good biological design."

© 2012 Discovery Channel

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