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How the Club-Tailed Dinosaurs Got Their Clubs

Scientists might now be one step closer to understanding how one of nature’s most formidable weapons evolved.

The ankylosaurs were herbivorous, armor-plated dinosaurs which first appeared around 156 to 152 million years ago and spread out to every continent but Africa. One advanced subgroup known as the ankylosaurids upped the ante with an extra defense mechanism. At the end of their tails, most species had a gigantic club. Weighing up to 45 pounds or more, these bludgeoning tools could have been swung with incredible—perhaps even bone-shattering—force. 

A new paper, published in Journal of Anatomy, argues that the creatures’ firm tails pre-date these powerful clubs. As co-author Victoria Arbour points out, “In order for an ankylosaur to support the weight of a knob and swing it effectively, the tail needs to be stiff, like an axe handle … otherwise, the momentum generated by the knob’s weight could tear muscle or dislocate vertebrae.”

So, which came first, the inflexible tail or the heavy club? Or did they appear simultaneously? To test all three scenarios, Arbour and fellow paleontologist Phillip J. Currie looked over several million years’ worth of ankylosaur evolution, comparing and contrasting such animals as China’s Gobisaurus and the club-less Lianoningosaurus.

They observed that while stiff-tailed ankylosaurids arrived during the early Cretaceous Period (145 to 100 million years ago), clubbed species didn’t make their debut until much later on. So—to re-use Arbour’s “axe” analogy—it looks like the handle predates the blade. “While it’s possible that some of the species could still have developed … [both] in tandem,” she says, “it seems most likely that the tail stiffened prior to the growth of the … knob, in order to maximize the tail’s effectiveness as a weapon.”

Club-less species had other means of protection. Certain species—like North America’s Sauropelta—came with lethal-looking shoulder spikes. Also, stout Gastonia had shark fin-shaped blades running down its tail.

Virtually all ankylosaurs have been described as “tank-like” in appearance. That’s because bony plates called osteoderms covered much of their skin, rendering it all but impenetrable. With predators like T. rex around, such extreme measures were absolutely necessary. 

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The T. Rex Fossil That Caused a Scientific Controversy
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iStock

In the early 2000s, a team of paleontologists inadvertently set the stage for a years-long scientific saga after they excavated a well-preserved partial Tyrannosaurus rex skeleton from Montana's Hell Creek formation. While transporting the bones, the scientists were forced to break a femur. Pieces from inside the thigh bone fell out, and these fragments were sent to Mary Schweitzer, a paleontologist at North Carolina State University, for dissection and analysis.

Under a microscope, Schweitzer thought she could make out what appeared to be cells and tiny blood vessels inside the pieces, similar to those commonly discovered inside fresh bone. Further analysis revealed what appeared to be animal proteins, which sent Schweitzer reeling. Could she have just discovered soft tissue inside dinosaur leg bone many millions of years old, found in ancient sediments laid down during the Cretaceous period? Or was the soft stuff simply a substance known as biofilm, which would have been formed by microbes after the bone had already fossilized?

Following a seemingly endless series of debates, studies, and papers, Schweitzer's hunch was proven correct. That said, this contentious conclusion wasn't made overnight. To hear the whole saga—and learn what it means for science—watch the recent episode of Stated Clearly below, which was first spotted by website Earth Archives.

[h/t Earth Archives]

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Fossilized Poop Shows Some Herbivorous Dinosaurs Loved a Good Crab Dinner
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Lead author Karen Chin of the University of Colorado Boulder
Courtesy the University of Colorado Boulder

Scientists can learn a lot about the prehistoric world through very, very old poop. Just recently, researchers from the University of Colorado-Boulder and Kent State University studying fossilized dinosaur poop discovered that some herbivores weren't as picky about their diets as we thought. Though they mostly ate plants, large dinosaurs living in Utah 75 million years ago also seem to have eaten prehistoric crustaceans, as Nature News reports.

The new study, published in Scientific Reports, finds that large dinosaurs of the Late Cretaceous period seem to have eaten crabs, along with rotting wood, based on the content of their coprolites (the more scientific term for prehistoric No. 2). The fossilized remains of dinos' bathroom activities were found in the Kaiparowits rock formation in Utah's Grand Staircase-Escalante National Monument, a known hotspot for pristine Late Cretaceous fossils.

"The large size and woody contents" of the poop suggest that they were created by dinosaurs that were well-equipped to process fiber in their diets, as the study puts it, leading the researchers to suggest that the poop came from big herbivores like hadrosaurs, whose remains have been found in the area before.

Close up scientific images of evidence of crustaceans in fossilized poop.
Chin et al., Scientific Reports (2017)

While scientists previously thought that plant-eating dinosaurs like hadrosaurs only ate vegetation, these findings suggest otherwise. "The diet represented by the Kaiparowits coprolites would have provided a woody stew of plant, fungal, and invertebrate tissues," the researchers write, including crabs (Yum). These crustaceans would have provided a big source of calcium for the dinosaurs, and the other invertebrates that no doubt lived in the rotting logs would have provided a good source of protein.

But they probably didn't eat the rotting wood all year, instead munching on dead trees seasonally or during times when other food sources weren’t available. Another hypothesis is that these "ancient fecal producers," as the researchers call them, might have eaten the rotting wood, with its calcium-rich crustaceans and protein-laden invertebrates, during egg production, similar to the feeding patterns of modern birds during breeding season.

Regardless of the reason, these findings could change how we think about what big dinosaurs ate.

[h/t Nature News]

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