Animals

Dinosaurs Danced in Bird-Like Mating Rituals

The dinos danced with such enthusiasm that they left behind fossilized footprints as evidence of their moves.

Dinosaurs not only danced, but they also did so with such enthusiasm that they left behind fossilized footprints as evidence of their moves, a new paper by an international team of paleontologists reports.

The discovery confirms prior speculation, based on dinosaur head crests and colorful feathers, that some dinosaurs engaged in mating displays that were similar to those of modern birds. The dancing dinos, according to the paper published in the journal Scientific Reports, were likely large theropods, meaning two-legged carnivorous dinosaurs.

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"They were evidently very active and perhaps driven into frenzies by the excitement of the breeding season," project leader Martin Lockley of the University of Colorado Denver, told Discovery News.

"This is typical of some bird species," he continued. "The extensive scrape evidence suggests much high-energy activity. If small birds get excited when breeding, imagine what big theropods might have done!"

Lockley and his team found the fossilized dinosaur scrape marks in 100-million-year-old Dakota sandstone in western Colorado. Since the footprints could not be removed from the rocks without causing damage, the scientists recreated them in virtual 3-D, using a technique of layering photographs known as photogrammetry. Rubber molds and fiberglass copies of the footprints were also made and are now stored at the Denver Museum of Nature & Science.

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Various interpretations of the fossilized footprints were considered, such as whether or not dinosaurs made them while digging for food or marking territory. These were all discounted for multiple reasons, with only mating dance behavior providing the best explanation for the ancient prints. In fact, the marks closely match those created by dancing birds today, such as Atlantic puffins and ostriches.

The time and location of the prints indicate that they were made by Acrocanthosaurus, a dinosaur that grew close to 38 feet in length and weighed up to 6.8 short tons. Its rhythmic stomps and scratches, comprising what the researchers call a "scrape ceremony," must have reverberated for quite a distance. The dinosaur probably vocalized as it performed the ritualistic scraping and bobbing movements, as today's birds do.

The scientists also suspect that males of this and certain other carnivorous dinosaur species were the primary dancers.

"Males are the main show offs, at least in birds today," Lockley explained. "This seems to be a hormone- and instinct-driven behavior of the breeding season to attract and pair with a mate."

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Males probably then competed during the spring breeding season while females looked on. The dancing displays likely occurred in assembly areas known as leks.

The behavior might date to long before the Cretaceous, but that remains unclear for now. Carnivorous dinosaurs were among the most active of all dinos, helping to explain why they were the dancers. It is doubtful that large, lumbering herbivores, such as sauropods, moved much for mating rituals, much less for other activities.

It is probable that some carnivorous dinosaurs gave rise to bird descendants that retained the display abilities, but Lockley said that "there is no reason to suppose that all theropods developed this behavior, or that all descendants should have inherited it."

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Mark Riegner is an ornithologist and a professor of environmental studies at Prescott College. He told Discovery News that the new paper presents compelling evidence that dinosaurs did engage in mating displays.

"While these findings are, in one sense, certainly surprising, in another sense they are predictable, as many birds -- from hermit hummingbirds to the ostrich -- perform courtship displays in leks," Riegner said. "So perhaps it was only a matter of time, and a keen eye for recognition, until such Cretaceous arenas were discovered."

Both Riegner and Lockley believe that dinosaur tracks and trackways are more significant than many people tend to think, because they can offer a window into the life, movements and behaviors of creatures that lived millions of years ago.

Shown is a reconstruction of dinosaurs engaged in a mating display dance.

Paleontologists have just assembled the most comprehensive family tree of meat-eating dinosaurs. Published in the journal Current Biology, the family tree reveals how diverse carnivorous dinosaurs were and how birds eventually evolved from them. Tyrannosaurs, including

Tyrannosaurus rex

, are one key group on the meat-loving dino family tree. Lead author Steve Brusatte of the University of Edinburgh's School of GeoSciences told Discovery News, "The most iconic dinosaurs of all, tyrannosaurs were more than just the 13-meter-long (nearly 43 feet long), 5-ton monster predator

T. rex

." "Tyrannosaurs were an ancient group that originated more than 100 million years before

T. rex

, and for almost all of their evolutionary history they were small carnivores not much bigger than a human in size."

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"Some of the rarest theropods (two-legged carnivorous dinos) of all, compsognathids are represented by about half a dozen species," Brusatte said. "They were small, sleek meat-eaters which ate small prey like lizards." One of the more recent finds, Juravenator from Germany, is known from a nearly complete fossil.

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Ornithomimosaurs were theropods called "ostrich mimic" dinosaurs -- for a reason. "Like living ostriches, they could run fast on their long legs and used their sharp, toothless beaks to eat a varied diet of small prey, plants, and perhaps even small shrimps in the water just like living flamingos," Brusatte explained. "A recent find in Canada showed that not only were ornithomimosaurs feathered, but they also had complex feathers on their arms that would have formed something of a wing, although they couldn't fly."

Brusatte describes therizinosaurs as "perhaps the weirdest theropods of all." "These were big, bulky, cumbersome dinosaurs that ate plants. They had fat barrel-shaped chests, stocky legs, and big claws on their arms," Brusatte said. For many years paleontologists argued about which group this dinosaur belonged to, only recently settling on theropods. This means they were fairly closely related to birds, despite their weird anatomy.

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Alvarezsaurs were among the smallest dinosaurs of all, measuring just a few feet long and weighing less than 5 kilograms (10 pounds). "Some of them had only a single functional finger on their hand, which they probably used to prod deep into the nests of bugs, which were one of their main food sources," Brusatte said.

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Oviraptorosaurs, were a group of small omnivores that were lightweight, lacked teeth and had tall, hollow crests on their skulls. The recently discovered Anzu -- the so-called "

chicken from hell

" -- came by its nickname honestly. It towered more than five feet tall, weighed more than 400 pounds, and was covered in a coat of feathers.

"Troodontids were probably the smartest dinosaurs of all, as they had the largest brains relative to their body size of any dinosaur group," Brusatte said. "Most troodontids were small, fast-running dinosaurs that probably ate both meat and plants." Among the most recently discovered of this group are the small, feathered Anchiornis and Xiaotingia, which lived in China about 160 million years ago. "They look eerily similar to birds, so much so that some researchers think they could be primitive birds rather than troodontids with wings and feathers," Brusatte said.

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Dromaeosaurids were "raptor dinosaurs" that include Velociraptor from "Jurassic Park" fame. These dinosaurs were pack hunters who wielded a sharp, hyper-extendable "killer claw" on their second toe. "One of the most recently discovered dromaeosaurids is Balaur, a poodle-sized terror from Romania which had not one, but two 'killer claws' on each foot."

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"The oldest birds, like Archaeopteryx that lived 150 million years ago in Germany, are very hard to distinguish from their closest dinosaurian relatives," Brusatte said. "Unlike living birds, they had teeth, sharp claws on their wings, and long tails." "Over the past two decades," he continued, "over 50 new species of Mesozoic birds have been discovered in northeastern China, in the same rock units as the famous 'feathered dinosaurs.' So many birds are preserved here because entire ecosystems were buried by volcanic eruptions, turning animals to stone like a dinosaur version of Pompeii."

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"The 10,000 species of birds that live today -- from hummingbirds to ostriches -- are modern dinosaurs," Brusatte said. "They are dinosaurs in the same way that humans are mammals. The classic body plan of living birds -- feathers, wings, wishbones, air sacs extending into hollow bones -- did not evolve suddenly but was gradually assembled over tens of millions of years of evolution. But, when this body plan finally came together completely, it unlocked great evolutionary potential that allowed birds to evolve at a super-charged rate." "They underwent a burst of evolution early in their history, which eventually led to the 10,000 species alive today -- more than twice the number of mammals."

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