Embryonic dinosaurs kicked and wiggled in the egg, a new discovery of a baby-dino-bone bed suggests. 
 
 The bones, all from not-yet-hatched embryonic dinosaurs, are among the oldest dinosaur-embryo fossils ever found. What's more, the embryo fossils came from separate nests and the dino embryos were at different stages of development when they died — two discoveries that will enable researchers to study how dinosaurs developed before hatching. 
 
 "It tells us quite a bit about early embryonic stages and changes that occur in the embryonic life of these animals — something we haven't really seen before," said study researcher Robert Reisz, a paleontologist at the University of Toronto. 
 
 In addition to discovering evidence of in-egg kicking, the researchers found that the embryos, which probably belonged to the long-necked Lufengosaurus, grew faster than the embryos of any birds or mammals alive today. [See Images of the Tiny Dino Embryos] 
 
 Tiny-bone find 
 
 Timothy Huang, a chemist at National Chung Hsing University in Taiwan and an amateur archaeologist, discovered the embryonic bones about three years ago in Yunnan Province, China. The bone bed has an area of about 3 square feet (1 square meter) and a thickness of about 4 to 8 inches (10 to 20 centimeters). In this small patch, the researchers eventually uncovered more than 200 itsy-bitsy bones. 
 
 A cross-section of an embryonic dinosaur femur found in Yunnan, China. The honeycomb-like area is bone tissue with large spaces for blood vessels, indicating rapid growth of the bone. Credit: A. LeBlanc 
 
 A geological analysis of the spot revealed that slow flooding probably smothered the eggs, which seem to have been laid in a colonial nesting site. After the flood, the embryos and eggs rotted and fell apart, leaving a mound of disarticulated bones. The bones date to the Lower Jurassic period, or between 199.6 million and 175.6 million years ago. That makes them just as ancient as the oldest known embryos ever found, which were discovered at a nesting site of long-necked Massospondylus dinosaurs in South Africa. 
 
 It was a boon for science that the dino embryos had fallen apart, instead of fossilizing inside their eggs, Reisz told LiveScience. 
 
 "People are extremely possessive and fond of their embryos inside their eggs — imagine us asking them to take pieces out and do the sections on them and cut them, and essentially do damage to them," he said. "These bones are completely disarticulated, and we have a lot of them — so it's not unreasonable to be able to take a few and cut them, and see what their internal anatomy is like." 
 
 How baby dinos grew 
 
 The bone bed contained spinal bones, limb bones, shoulder blades and even a few fragments of skull, but Reisz and his team focused their analysis on the most prevalent and best-preserved bones: femurs, or thigh bones. These little leg bones ranged from 0.5 to 0.9 inches (12 to 22 millimeters) in length, shorter than matchsticks. 
 
 The bones were porous, filled with cavities that would have once allowed blood to flow to the growing tissue. The size of the cavities is determined by how fast the animal grows — which made researchers realize these embryos got big quickly. 
 
 "They grow very fast — faster than we expected, and faster than most other dinosaurs that have been studied this way," Reisz said. 
 
 The fast growth rate makes sense, given that Lufengosaurus grew to 20 feet (6 meters) in length. 
 
 Lufengosaurus grew to be about 20 feet (6 meters) in length. Credit: Phil Gilston 
 
 The researchers also found an asymmetrical thickening in the femurs associated with muscle action on the bone. The finding suggests the little dinos were kicking and twitching inside their eggs. 
 
 The team also discovered evidence of organic material — probably collagen, part of the connective tissue that forms ligaments and tendons. If the material isn't too deteriorated, it could be compared to collagen in living animals, thus providing a new way to look at relationships between modern creatures and the extinct dinosaurs, Reisz said. 
 
 "We're setting a new benchmark as to what can be done in dinosaur embryology," Reisz said. He and his colleagues report their findings Thursday (April 11) in the journal Nature. An upcoming goal, Reisz said, is to give the embryos their first dental exam. 
 
 "One of the things we may try in the near future is to look at the embryonic teeth themselves," he said. "They're very cool." 
 
 Follow Stephanie Pappas on Twitter and Google+. Follow us @livescience, Facebook & Google+. Original article on LiveScience.com. 

 A rare cache of fossil dinosaur embryos unearthed in China reveals that these extinct behemoths grew faster in the egg than any bird or animal known, an international research team reported in Nature. Robert Lee Hotz has details. Photo: A. LeBlanc. 
 
 A rare cache of fossil dinosaur embryos discovered in China reveals that these extinct behemoths grew faster in the egg than any animal known, an international research team reported in Nature on Wednesday. 
 
 The researchers believe the 195-million-year-old remains belong to a long-necked, plant-eating dinosaur called Lufengosaurus, which grew to as long as 30 feet. This dinosaur family, once common in China, eventually evolved into the largest creatures to ever walk the Earth. 
 
 "These things were growing faster than anything we've ever seen—faster than any living mammal or bird today or any known dinosaur," said paleontologist Robert Reisz at the University of Toronto at Mississauga in Ontario, who led the team of experts in China, Taiwan, Australia and Germany that analyzed the specimens. 
 
 The fossils are the oldest collection of dinosaur embryos ever found, the researchers said. 
 
 "They give us an unprecedented look into the very early embryology of these developing dinosaurs," said paleontologist Mark Norell at the American Museum of Natural History in New York, who wasn't involved in the find. 
 
 By bombarding the fossils with an infrared synchrotron beam—a noninvasive way of analyzing a material's internal chemistry—the scientists said they detected molecular traces of an organic protein inside the mineralized bones. They suspect it may be the residue from the decay of once-living tissue cells, not just bone—a finding stirring skepticism among other paleontologists. 
 
 The tiny bones, each about the thickness of pencil lead, were first spotted three years ago by a local caretaker in the outwash from a steep hillside near a well-known fossil site outside Kunming, China. A visiting amateur fossil hunter from Taiwan recognized them as embryonic remains. Working on their hands and knees, scientists soon traced the pieces back up the hilltop to a slab of red siltstone, where they so far have found 200 bones mingled with crushed eggshells. 
 
 View Slideshow Robert Reisz Paleontologists and volunteers worked at an embryonic dinosaur bone bed site in Dawa, Yunnan Province, China. The work of collecting tiny dinosaur fossils—about the thickness of pencil lead—is painstaking, requiring diggers to get down on their hands and knees. 
 
 Unlike previous finds, the newly discovered embryo remains weren't enclosed within eggs or found within a nest or the fossilized body of a mother. Bones from many partial skeletons, each in a slightly different stage of development, were found pulled apart and sorted by size, perhaps by an ancient flood or the ripples of a primordial pond. 
 
 "It is really nice that is an accumulation of different stages," said paleontologist James Clark at George Washington University, who wasn't involved in the project. "It gives you an ability to look at changes it goes through as an embryo." 
 
 Write to Robert Lee Hotz at sciencejournal@wsj.com 
 
 Corrections & Amplifications 
 
 The surname of Robert Reisz was incorrectly spelled Reiz in an earlier version of this article. 
 
 A version of this article appeared April 11, 2013, on page A5 in the U.S. edition of The Wall Street Journal, with the headline: Fossils Suggest Dinosaur Embryos Grew at Rapid Rate.
– A trove of 195 million-year-old fossilized dinosaur embryos—among the oldest ever found—has given scientists an "unprecedented" look at how those ancient creatures grew. The Wall Street Journal reports on the Chinese discovery, which first came to light three years ago and is believed to be the remains of what would have grown into the 30-feet-long Lufengosaurus, a common plant-eater in the early Jurassic period. "These things were growing faster [in the egg] than anything we've ever seen—faster than any living mammal or bird today or any known dinosaur," says the paleontologist who led the expedition. Dinosaur eggs are usually found mostly intact, so people are reluctant to cut them open and examine the embryos. But these bones, found in Dawa, Yunnan Province, China, weren't encased in eggs, or even near the remains of a nest or mother; scientists have thus far unearthed 200 tiny bones among crushed eggshells, and note that they comprise embryos in different stages of development. Researchers think the eggs were probably swamped and crushed by a flood. Another neat revelation from the find: Dinosaurs probably kicked and twitched in their eggs, reports LiveScience.