A reconstruction of dinosaurs engaged in sexual display activity: artwork by Lida Xing and Yujiang Han. Credit: University of Colorado Denver Dinosaurs engaged in mating behavior similar to modern birds, leaving the fossil evidence behind in 100 million year old rocks, according to new research by Martin Lockley, professor of geology at the University of Colorado Denver. 
 
 Lockley, a paleontologist, led an international research team that discovered large 'scrapes' in the prehistoric Dakota sandstone of western Colorado. These ancient scrapes are similar to a behavior known as 'nest scrape display' or 'scrape ceremonies' among modern birds, where males show off their ability to provide by excavating pseudo nests for potential mates. 
 
 "These are the first sites with evidence of dinosaur mating display rituals ever discovered, and the first physical evidence of courtship behavior," Lockley said. "These huge scrape displays fill in a missing gap in our understanding of dinosaur behavior." 
 
 The study will be published in the journal Scientific Reports on January 7. 
 
 Lockley, a world-renowned expert on dinosaur footprints, found evidence of more than 50 dinosaur scrapes, some as large as bathtubs, in an area where tracks of carnivorous and herbivorous dinosaurs have also been confirmed. The display arenas, also called 'leks' were found in two National Conservation Areas (Dominguez-Escalante and Gunnison Gorge) on property permitted by the Bureau of Land Management near Delta, Colorado. 
 
 Lockley also discovered evidence of mating areas at Dinosaur Ridge, a National Natural Landmark, just west of Denver. 
 
 University of Colorado Denver researcher Martin Lockley (right) and Ken Cart pose beside large a dinosaur scrape they discovered in Western Colorado. Credit: University of Colorado Denver 
 
 This new fossil evidence supports theories about the nature of dinosaur mating displays and the evolutionary driver known as `sexual selection.' Since prehistoric times, males looking for mates, have driven off weaker rivals. Females, meanwhile, have chosen the most impressive male performers as consorts. 
 
 Similar sexual selection behaviors are common in mammals and birds. But until now scientists could only speculate about dinosaur mating behavior, assuming it might be similar to that of their modern relatives, the birds. 
 
 "The scrape evidence has significant implications," said Lockley. "This is physical evidence of pre-historic foreplay that is very similar to birds today. Modern birds using scrape ceremony courtship usually do so near their final nesting sites. So the fossil scrape evidence offers a tantalizing clue that dinosaurs in 'heat' may have gathered here millions of years ago to breed and then nest nearby." 
 
 Lockley and his team were unable to remove the scrape marks from the gigantic slabs of rock without damaging them. Instead, they created 3-D images of the scrapes using a technique of layering photographs called photogrammetry. They also made rubber molds and fiberglass copies of the scrapes that are being stored at the Denver Museum of Nature & Science. 
 
 Explore further: Pair of star-crossed oviraptors yield new clues about dinosaur mating habits 
 
 More information: Scientific Reports, dx.doi.org/10.1038/srep18952 
 
 

 Did dinosaurs shake a tail feather? Some meat-eating theropods used fancy footwork to attract their mates, leaving behind their fox-trotting tracks in rocks millions of years ago. 
 
 An analysis of the newfound marks suggests they are the first known evidence of a type of mating display behavior known as "scraping," common in modern ground-nesting birds. The dinosaur lads may have performed their paleo-numbers in groups for a (hopefully) swooning female audience, the researchers say. 
 
 Paleontologists found scores of these "scrapes," areas in the rock that were shallowly scarred by multiple scratch marks. These collections of marks, each of which averaged about 6.6 feet (2 meters) in length, were scattered across four different Cretaceous sites in Colorado. The site locations, described by the study's authors as "spectacular," are crisscrossed with numerous dinosaur trackways — consecutive footprints made by the same animal. [Photos: Thousands of Dinosaur Tracks Along Yukon River] 
 
 Surprising scrapes 
 
 Martin Lockley, co-author of the study and emeritus professor of geology at the University of Colorado, Denver, told Live Science that these scrape marks were unlike anything the scientists had seen before. When Lockley and his colleagues first noticed the marks, the prints were partially covered with sand. "We started cleaning them off and taking a closer look at them, and we knew right away that there was something unusual about them," Lockley said. More and more of these scrape traces emerged as their investigation widened, eventually revealing about 60 of them in one of the sites. 
 
 It soon became clear that these unusual scrapes were connected to the dinosaurs whose tracks marched through the area. "We were calling them 'digging dinosaur' traces," Lockley said. "They were obviously made by the feet of dinosaurs, because we could see the claw marks. We could see two sides, a left and a right trough, with a ridge in the middle," he said. 
 
 Some of the scrape traces included the trademark three-toed footprint of a theropod, a group of bipedal and mostly carnivorous dinosaurs, further cementing the strange marks' connection to dinosaur creators. According to Lockley, that's when things really got interesting. "It was like, 'OK, we know what kind of dinosaur made them — what were they doing?'" 
 
 Team leader Dr. Martin Lockley (right) and co-author Ken Cart kneel beside two large Cretaceous-age scrapes from western Colorado that are the first physical evidence that large theropod dinosaurs engaged in courtship behavior. Credit: M. Lockley 
 
 Paleo-detectives 
 
 Like television's Crime Scene Investigation (CSI) detectives, the scientists faced the challenge of recreating a scenario based on the clues left behind. And like detectives, they considered — and ruled out — a number of possibilities. 
 
 Were the dinosaurs digging for water? Not likely, Lockley said. The environment in that part of North America was very wet during the Cretaceous, and water would have been plentiful. Could they have been searching for food? Probably not; carnivorous theropods wouldn't have scratched around in the dirt looking for roots or other vegetation, Lockley explained. And there's no evidence suggesting that floods at the time buried carcasses that the theropods might have dug up and scavenged, he added. 
 
 That's when Lockley and his colleagues realized that they might find an explanation for these extinct dinosaurs' behavior in the behavior of "dinosaurs" alive today — modern birds. 
 
 Perhaps the scrapes were signs of nest building? Existing fossil evidence shows that theropod dinosaurs, like birds, built nests and brooded their eggs. But the study authors were doubtful, because the marks and troughs in the scrapes would likely have been worn smooth by weeks of continued use, as the dinosaurs brooded their eggs and reared their young. And the variable shapes and haphazard placement of the scrapes didn't match up with the more regular nest shapes and spacing in known dinosaur nesting colonies. [Image Gallery: Dinosaur Daycare] 
 
 Dancing like a bird 
 
 But when the scientists reviewed accounts of birds' mating display behavior, they hit pay dirt. Descriptions of activity called "nest scrape display" and "pseudo nest building" seemed to produce similar marks to the ones that they found. 
 
 "During the breeding season, the males start to get excited and show off to their mates by scratching to say, Look, I can build a nest!" Lockley told Live Science. "And they get so excited that they scratch, and move along and scratch again — they make dozens or hundreds of scratches in a short period of time." 
 
 The "nest scrape" explanation, Lockley said, fit well with the Colorado scrape marks. In the study, the researchers point to a "long and diverse" list of birds that perform nest scrape displays, including puffins, a New Zealand parrot, and seven species of shorebirds. And this type of behavior carries across many branches in the bird family tree, according to Paul Sweet, manager of the Ornithology Collections at the American Museum of Natural History. 
 
 Sweet, who was not involved in the study, told Live Science that male sage grouse will gather season after season in a "lek," an open area where they perform high-energy mating displays that can include strutting, fanning their tails and "trying to make themselves look as big as possible," Sweet said. [Animal Sex: How Did Dinosaurs Do It] 
 
 According to the researchers, the four sites where they found the scratch marks could have been leks where groups of theropod males would gather to strut their stuff for an appreciative female audience. The scratches they left behind provide the first physical evidence linking dinosaur mating display behavior to that of living birds, the scientists said. 
 
 Lockley, who has devoted decades to the study of dinosaur trackways, told Live Science that more examples of this fancy footwork are likely to be discovered, now that paleontologists will be looking for them. 
 
 "It seems like every five to 10 years there's a new category of evidence that comes to light, and then it's like, 'Oh, it's everywhere, why didn't we find this before?'" Lockley said. "I wouldn't be surprised if we have dozens of these sites in a few years." 
 
 The findings were published online today (Jan. 7) in the journal Nature Scientific Reports. 
 
 Follow Mindy Weisberger on Twitter and Google+. Follow us @livescience, Facebook & Google+. Original article on Live Science. 

 "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." Photos: Audubon Report Names Birds at Climate Risk 
 
 "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." Tiny Feathered Dinosaur Found 
 
 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." Velociraptor Inspires Fast Running Robot 
 
 "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. World's Earliest Bird Discovered 
 
 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. 
 
 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. New Dinosaur Bolsters Bird-Dino Connection 
 
 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. Nests of Big-Clawed Dinosaurs Found in Mongolia 
 
 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." 
 
 "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. Dinosaurs That Loved the Nightlife 
 
 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." New T-Rex Tracks Add to Pack-Hunting Theory 
 
 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. 
 
 Play Video Dinosaur Sex: How Did That Work? Dinosaurs ruled the planet for 130 million years, so clearly they knew how to perpetuate themselves, but scientists have not had much to go on, in terms of their exact mechanics for doing the deed. DCI 
 
 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. 
 
 “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. 
 
 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.
– It must have been an amazing sight: Paleontologists now say that dinosaurs danced—with gusto. More specifically, they think that some male dinosaurs did so as part of a mating display to woo females, study authors say in a post at Phys.org. The evidence? Telltale scrape marks from claws etched into 100-milliion-year-old sandstone in Colorado, reports Discovery. Some were more than 6 feet long, and researchers at the University of Colorado Denver ran through several possible explanations. Digging for water? Nope, it was plentiful in the area back then. Digging for food? Nope, these were meat-eating theropods not interested in roots. And then the scientists zeroed in on the similarity to a mating ritual of modern birds known as "nest scrape display," reports Live Science. "During the breeding season, the males start to get excited and show off to their mates by scratching to say, Look, I can build a nest!" says co-author Martin Lockley. "And they get so excited that they scratch, and move along and scratch again—they make dozens or hundreds of scratches in a short period of time." Lockley's team realized the scratch marks they were seeing at sites well-traveled by dinosaurs bore these hallmarks. A paleontologist not involved with the study tells the Christian Science Monitor that the theory makes sense. "Considering that modern birds are descended from Mesozoic theropod dinosaurs, it shouldn't be surprising that birds' ancient relatives would have done this, too." (One of the biggest raptors ever was just found in the US.)