This undated handout image provided by Michael Skrepnick, Dinosaurs in Art, Nature Publishing Group, shows a Deinocheirus. Nearly 50 years ago, scientists found two large powerful arm bones of a new dinosaur species in Mongolia and figured it was a fearsome critter with killer claws. Now scientists have found the rest of the dinosaur and have new descriptions for the dinosaur: 'goofy' and 'weird.' The dinosaur probably lumbered along like a cross between TV dinosaur Barney and Jar Jar Binks of Star Wars fame: 16-feet tall, 36-foot long, 7-tons with a duckbill on its head and a hump-like sail on its back. Throw in those killer claws, tufts of feathers here and there, and no teeth _ and try not to snicker. And if that's not enough, it ate like a giant vacuum cleaner. (AP Photo/Michael Skrepnick, Dinosaurs in Art, Nature Publishing Group)
This undated artist rendering provided by the journal Science shows the dinosaur lineage which evolved into birds shrank in body size continuously for 50 million years. From left are, the ancestral neotheropod, the ancestral tetanuran, the ancestral coelurosaur, the ancestral paravian and Archaeopteryx. Scientists have mapped how one group of dinosaurs evolved from the likes of the fearsome Tyrannosaurus rex and primitive Herrerasaurus to the welcome robin and cute hummingbird. The surprisingly steady shrinking and elegant evolution of some Triassic dinosaurs is detailed in the journal Science on Thursday. Comparing fossils of 120 different species and 1,500 skeletal features, especially leg bones, researchers constructed a detailed family tree of theropod dinosaurs. That suborder of dinos survives to this day as birds, however unrecognizable and improbable it sounds. (AP Photo/Davide Bonnadonna, Science)
This artist rendering provided by Jeffrey Martz shows a Daemonosaurus chauliodus and its size relative to an modern American quarter. The species name chauliodus is derived from the Greek word for âbuck-toothedâ and refers to the speciesâ big slanted front teeth. The surprising discovery of a fossil of a sharp-toothed beast that lurked in what is now the western U.S. more than 200 million years ago is filling a gap in dinosaur evolution. (AP Photo/Jeffrey Martz)
A worker moves a shipping case at the Museum of Natural Science after installing Sue, claimed to be the largest, most complete, and best preserved Tyrannosaurus rex, in Halifax on Wednesday, Jan. 12, 2011. Sue is named for paleontologist Sue Hendrickson, who discovered the dinosaur remains during a fossil-hunting trip in the summer of 1990. (AP Photo/The Canadian Press, Andrew Vaughan)
This image provided by the Carnegie Museum of Natural History shows the skull of Daemonosaurus chauliodus, narrow and relatively deep, measuring 5.5 inches long from the tip of its snout to the back of the skull and has proportionately large eye sockets. The upper jaw has large, forward-slanted front teeth. The surprising discovery of a fossil of a sharp-toothed beast that lurked in what is now the western U.S. more than 200 million years ago is filling a gap in dinosaur evolution. (AP Photo/Carnegie Museum of Natural History)
In this January 2014 photo released on Saturday, May 17, 2014 by the Museo PaletontolÃ³gico Egidio Feruglio, Spanish paleontologist Jose Ignacio Canudo lies alongside a sauropod dinosaur femur, believed to be the largest in the world, in Trelew, Argentina. Paleontologists from the Museo PaletontolÃ³gico Egidio Feruglio, announced Friday, May 16, 201, the discovery of the fossil remains of the sauropod dinosaur near Trelew. (AP Photo/Museo PaletontolÃ³gico Egidio Feruglio)
FILE - In this May 24, 2007 file photo, Ken Ham, founder of the nonprofit ministry Answers in Genesis, poses with one of his favorite animatronic dinosaurs during a tour of the Creation Museum in Petersburg, Ky. Ham, who recently debated evolution with TV's "Science Guy" Bill Nye, says fundraising after the widely watched event helped to revive stalled plans to build a 510-foot replica of Noah's Ark. (AP Photo/Ed Reinke, File)
Fossil of a short-tailed pterosaur, a flying reptile, Pterodactylus kochi, Upper Jurassic Solnhofen limestone, Eichstaett, Germany, Photographed under controlled conditions (Specimen courtesy of Raimund Albersdoerfer, Germany), (Photo by Wild Horizons/UIG via Getty Images)
Fossil of a short-tailed pterosaur, a flying reptile, Pterodactylus kochi, Upper Jurassic Solnhofen limestone, Solnhofen, Bavaria, Germany, Photographed under controlled conditions (Specimen courtesy of Raimund Albersdoerfer, Germany), (Photo by Wild Horizons/UIG via Getty Images)
CANADA - OCTOBER 30: The spiked skull of a Styracosaurus, Toronto, Canada (Photo by Ira Block/National Geographic/Getty Images)
UNITED STATES - SEPTEMBER 09: A Hyolith from the Cambrian has an armored shell body, Museum of Natural History, Washington, District of Columbia (Photo by O. Louis Mazzatenta/National Geographic/Getty Images)
CANADA - MAY 30: The skull and crest of a Parasaurolophus, Toronto, Canada (Photo by Ira Block/National Geographic/Getty Images)
UNSPECIFIED - MARCH 23: Struthiomimus dinosaur hunting a dragonfly (Struthiomimus altus) (Photo by De Agostini Picture Library/De Agostini/Getty Images)
UNSPECIFIED - MARCH 23: Side profile of an aellosaurus walking (Photo by De Agostini Picture Library/De Agostini/Getty Images)
06/09/98 - Location- Smithsonian Natural History Museum caption- Nathan Myhrvold has some interesting theories on the evolution, disappearance of dinosaurs. His models have been created on computer. His day job is Chief Technical Officer of Microsoft. Rear is the Diplodocus that has the long tail with the fused sections in all the tails, leading Myhrvold to the belief that the dinosaur cracked its tail like a whip, the end section moving near the speed of sound. - Photo By Craig Herndon TWP (Photo by Craig Herndon/The Washington Post/Getty Images)
The skull and jawbone of a Tyrannosaurus bataar skeleton is displayed during a ceremony of its repatriation to Mongolia, in New York, Monday, May 6, 2013. The 70-million-year-old fossil was looted from the Gobi Desert and illegally smuggled into the U.S. (AP Photo/Richard Drew)
A preview of a Tyrannosaurus rex growth exhibit features three specimens of varying ages, at the Natural History Museum of Los Angeles County Wednesday, Jan. 19, 2011. Featured are fossils of a 30-foot-long young adult, about 18 years old, top right; a 20-foot-long juvenile, about 14, left; and an 11-foot-long baby, about 2, said to be the youngest known specimen, right. The T. rex trio will be the centerpiece of a new, expanded Dinosaur Hall, with some 300 fossils, 20 full-body specimens, interactive and video exhibits, in two large galleries that will more than double the previous space. The hall is scheduled to open to the public in July, 2011. (AP Photo/Reed Saxon)
An image from documents released from the U.S. Attorney's office, Monday, June 18, 2012 shows the fossil of a Tyrannosaurus bataar dinosaur at the center of a lawsuit demanding its return to Mongolia. A lawsuit brought by the U.S. government demanded Monday June 18, 2012, the fossil be turned over to the United States by an auction house so that it can be returned to its home in Mongolia. (AP Photo/U.S Attorney Office for the Southern District of New York, Handout)
People look at a model of Uberabatitan Ribeiroi, a Late Cretaceous period dinosaur, is seen at the Federal University, in Rio de Janeiro, Wednesday, Sept. 24, 2008. Three specimens were found in different fossil sites of Uberaba County, in the Brazilian state of Minas Gerais. The Uberabatitan Ribeiroi, which lived in what is currently Brazil some 65 million years ago, had a length of more than 20 meters and weighed some 16 tons. (AP Photo/Silvia Izquierdo)
Panthera leo from the cuaternari Russia (Kike Calvo via AP Images)
In this image released by the Institute of Vertebrate Paleontology & Paleoanthropology in Beijing Wednesday June 13, 2007, a sketch of a newly discovered Gigantoraptor dinosaur is seen compared to a human. Fossilized bones uncovered in the Erlian Basin of northern China's Inner Mongolia region show that the Gigantoraptor erlianensis was about 8 meters (26 feet) in length and weighed 1,400 kilograms (3,000 pounds), said Xu Xing, a paleontologist at the Institute of Vertebrate Paleontology & Paleoanthropology in Beijing. The discovery of the giant, birdlike dinosaur indicates a more complicated evolutionary process for birds than originally thought, scientists said Wednesday. (AP Photo/Institute of Vertebrate Paleontology & Paleoanthropology, Beijing, HO)
In this image released by the Institute of Vertebrate Paleontology & Paleoanthropology in Beijing Wednesday June 13, 2007, an artists impression of a newly discovered Gigantoraptor dinosaur, top, with other smaller dinosaurs is seen. Fossilized bones uncovered in the Erlian Basin of northern China's Inner Mongolia region show that the Gigantoraptor erlianensis was about 8 meters (26 feet) in length and weighed 1,400 kilograms (3,000 pounds), said Xu Xing, a paleontologist at the Institute of Vertebrate Paleontology & Paleoanthropology in Beijing. The discovery of the giant, birdlike dinosaur indicates a more complicated evolutionary process for birds than originally thought, scientists said Wednesday. (AP Photo/Institute of Vertebrate Paleontology & Paleoanthropology, Beijing, HO)
Dr Adam Yates, from the Bernard Price Institute for Paleontological Research, looks at the 'Aardonyx Celestae', a newly discovered fossil skeleton in Johannesburg on November 11, 2009. South African palaeontologists announced the discovery of a new species of 'transition' dinosaur that straddles the divide between the four-legged giant plant-eating sauropods and their bipedal carnivorous predecessors. The dinosaur roamed the area between 183 million and 200 million years ago, measured between 7 and 9 metres long. The specimen was a juvenile, which was aged between 7 and 10 years. The Aardonyx Celestae, as the new dinosaur has been named, was discovered on a farm in central Free State province in the Karoo Basin, an area rich in fossils. AFP PHOTO / ALEXANDER JOE (Photo credit should read ALEXANDER JOE/AFP/Getty Images)
UNDATED - In this handout provided by the Carnegie Museum of Natural History, an artist's redering depicts a previously unknown bird-like dinosaur that was formally introduced to the scientific community by scientists with the Smithsonians National Museum of Natural History, the Carnegie Museum of Natural History and the University of Utah March 19, 2014. Dubbed Anzu wyliei, referring both to a mythological feathered demon and the name of a Carnegie museum trustee's grandson, the seven-foot-tall creature weighed about 500 pounds when it roamed western North America 66 to 68 million years ago. (Illustration by Mark Klingler/Carnegie Museum of Natural History via Getty Images)
UNSPECIFIED - CIRCA 2003: Reconstruction of the flora and fauna of a marshy environment from the Jurassic Period, drawing. (Photo by DeAgostini/Getty Images)
A general view of atmosphere seen at Twentieth Century Fox 'Walking with Dinosaurs', on Thursday, Dec, 12, 2013 in Los Angeles. (Photo by Eric Charbonneau/Invision for Twentieth Century Fox/AP Images)
An Apatosaurus display is seen at Field Station Dinosaurs in Secaucus, N.J., Friday, May 25, 2012. There will be 31 types of life-sized dinosasurs displayed at the Jurassic expedition that opens Saturday, May 26. (AP Photo/MelÂ Evans)
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By SETH BORENSTEIN
WASHINGTON (AP) - Scientists have mapped how a group of fearsome, massive dinosaurs evolved and shrank to the likes of robins and hummingbirds.
Comparing fossils of 120 different species and 1,500 skeletal features, especially thigh bones, researchers constructed a detailed family tree for the class of two-legged meat-eaters called theropods. That suborder of dinos survives to this day as birds, however unrecognizable and improbable it sounds.
The steady downsizing and elegant evolution of the theropods is detailed in the journal Science on Thursday.
"They just kept on shrinking and shrinking and shrinking for about 50 million years," said study author Michael S. Y. Lee of the University of Adelaide in Australia. He called them "shape-shifters."
Lee and colleagues created a dinosaur version of the iconic ape-to-man drawing of human evolution. In this version, the lumbering large dinos shrink, getting more feathery and big-chested, until they are the earliest version of birds.
For a couple decades scientists have linked birds to this family of dinosaurs because they shared hollow bones, wishbones, feathers and other characteristics. But the Lee study gives the best picture of how steady and unusual theropod evolution was. The skeletons of theropods changed four times faster than other types of dinosaurs, the study said.
A few members of that dino family did not shrink, including T. rex, which is more of a distant cousin to birds than a direct ancestor, Lee said.
He said he and colleagues were surprised by just how consistently the theropods shrank over evolutionary time, while other types of dinosaurs showed ups and downs in body size.
The first theropods were large, weighing around 600 pounds. They roamed about 220 million to 230 million years ago. Then about 200 million years ago, when some of the creatures weighed about 360 pounds, the shrinking became faster and more prolonged, the study said. In just 25 million years, the beasts were slimmed down to barely 100 pounds. By 167 million years ago, 6-pound paravians, more direct ancestor of birds, were around.
And 163 million years ago the first birds, weighing less than two pounds, probably came on the scene, the study said
Paul Sereno, a dinosaur researcher at the University of Chicago who wasn't part of this study, praised Lee's work as innovative.
The steady size reduction shows "something very strange going on," Sereno said. "This is key to what went on at the origin of birds."
People may think bigger is better, but sometimes when it comes to evolution smaller can be better because bigger creatures are more likely to go extinct, Sereno said.
And when the theropods started shrinking there weren't many other small species that would compete with them, Lee said.
"The dinosaur ancestors of birds found a new niche and a new way of life," Lee said.
Sereno added, "When you are small, it's a totally different ball game. You can fly and glide and I think that's what drove it."