BEIJING, July 6 (Xinhuanet) -- Archaeologists in 1999 uncovered the fossil of a juvenile dinosaur that lived 140 millions ago that now is illuminating how the creatures grew from youngsters to enormous adults.

    The fossil was discovered  in the Lower Morrision Formation of the How Ranch in Bighorn Country, Wyoming. Scientists estimate the dinosaur was about 1 year old when it died toward the end of the Jurassic Period (206 million to 144 million years ago). The research is detailed in the latest issue of the journal Historical Biology.

    "It's the only complete skeleton of a juvenile sauropod we know of," said lead researcher Daniela Schwarz of the Natural History Museum in Basel, Switzerland.

    The 6-foot-long dinosaur sauropod belonged to the family Diplodocidae, which included four-legged vegetarians equipped with long, slender tails. Past research has proposed diplodocids used their tails as whipping weapons. One study found that Apatosaurus louisae could lash its tail at supersonic speeds to produce a ground-shaking boom.

    "We do not know very much about sauropods of this age," Schwarz explained. "So it's not clear how much they change when they grow, and that makes comparisons [with adults] very difficult."
The skeleton is actually missing a tiny portion ¡ª the end of the tail ¡ª so the scientists can't say with accuracy whether the juvenile also possessed the whiplash tail.

    An adult Apatosaurus louisae reached a shoulder height of nearly 10 feet, with a nose-to-tail length of 60 feet, whereas the newfound juvenile dino was only about two feet tall at the shoulder. The juvenile's limb bones show similar proportions as those of adult diplodocids. However, its relatively short neck and lengthy mid-section don't match those of its full-grown relatives.

    "The vertebrae column gets shorter during growth, so the adult specimens have shorter trunks, for example, than the juveniles, at least in this species," Schwarz told LiveScience.
Plant remains found at the site indicate that the dinosaur perished in a watering hole "deathtrap" in an ancient swampland.

    "The locality represents sort of a swampy environment where dinosaurs came and drank," Schwarz said. One possibility is that while drinking, "they were caught in the swamp sediments and they died."

    (Agencies)