October 26, 2012
Researchers Announce First Feathered Dinosaur Specimens Found In The Western Hemisphere
[ Watch the Video: Fossils of First Feathered Dinosaurs from North America Found ]
April Flowers for redOrbit.com - Your Universe Online
Remember the scene in the original Jurassic Park movie when the giant ostrich-like dinosaurs run from an enraged Tyrannosaurus rex? The scaly, fleet-footed animals moved like a flock of birds, gracefully wheeling across the landscape. A new study, recently published in the journal Science, reveals that this depiction of the bird-mimic dinosaurs is not entirely accurate. The ornithomimids should have had feathers and wings.
Othniel Charles Marsh in Colorado first discovered Ornithomimus — the bird mimic dinosaur — in 1890. Marsh had only a foot and part of a hand to start with, but the entire skeleton was later discovered, confirming Marsh's theory that the animal was bird-like. Ornithomimus ran on two legs and had a beaked, toothless mouth. It vaguely resembled an ostrich, despite its long tail and grasping arms.
The results of this study, led by paleontologists Darla Zelenitsky from the University of Calgary and FranÃ§ois Therrien from the Royal Tyrrell Museum of Paleontology, describes fossils recovered from 75 million-year-old rocks in the badlands of Alberta, Canada. These fossils are the first ornithomimid specimens preserved with feathers. Two of the specimens are new, having been found in 2008 and 2009 by Frank Hadfield; a third was an almost complete skeleton found in 1995. All three are housed at the Royal Tyrrell Museum.
"This is a really exciting discovery as it represents the first feathered dinosaur specimens found in the Western Hemisphere," says Zelenitsky, assistant professor at the University of Calgary and lead author of the study. "Furthermore, despite the many ornithomimid skeletons known, these specimens are also the first to reveal that ornithomimids were covered in feathers, like several other groups of theropod dinosaurs."
A juvenile and two adult skeletons of Ornithomimus, a dinosaur belonging to the ornithomimids group, were found with evidence of feathers. The team suggests that this is evidence that all ornithomimid dinosaurs would have feathers. They say the specimens reveal an interesting pattern change in feathery plumage during the life of Ornithomimus.
According to Thomas H. Maugh II of the Los Angeles Times, modern-day birds have feathers that develop at a very young age, shortly after hatching. The juvenile Ornithomimus edmontonicus, however, was covered only with down-like feathers like those found on the bodies of the adults.
"This dinosaur was covered in down-like feathers throughout life, but only older individuals developed larger feathers on the arms, forming wing-like structures," Zelenitsky said in a prepared statement. "This pattern differs from that seen in birds, where the wings generally develop very young, soon after hatching."
The study suggests that the initial use of these early wing structures in dinosaurs too big to fly was not for flight. Long feathers with stiff shafts down the middle, much like modern feathers, were found on the short, wing-like forelimbs of one adult. These flightless wings are called pennibrachia, and the long stiff feathers are known as proto-feathers, or "dino-fuzz." The research team hypothesizes that these feathers were for attracting a mate, suggesting that this animal was male, and that the long feathers didn't develop until sexual maturity
"The fact that wing-like forelimbs developed in more mature individuals suggests they were used only later in life, perhaps associated with reproductive behaviors like display or egg brooding," says Therrien, curator at the Royal Tyrrell Museum.
Feathered dinosaur skeletons have been recovered from fine-grained rocks in China and Germany almost exclusively until now.
"It was previously thought that feathered dinosaurs could only fossilize in muddy sediment deposited in quiet waters, such as the bottom of lakes and lagoons," says Therrien. "But the discovery of these ornithomimids in sandstone shows that feathered dinosaurs can also be preserved in rocks deposited by ancient flowing rivers."
Dinosaur skeletons are most commonly preserved in sandstone, making the Canadian discoveries important for the potential they represent for the recovery of feathered dinosaurs worldwide.
According to a Discover Magazine article, another reason this discovery is so exciting is that simple fuzzy feather-like filaments have been found on dinosaurs pretty much across the board but pennibrachia and wing with complex feathers have only been found so far on maniraptorans — small predators that are most closely related to birds.
Ornithomimus belongs to a group that appeared much earlier than manirapotorans. If Ornithomimus had pennibrachia, the structures must have developed much earlier than previously thought.
“They fill a significant gap in the record of fossil feathers,” Zelenitsky told Discover Magazine. “This is the earliest and most primitive occurrence of wings in that group of dinosaurs that led to birds.”
Since 1996, more than 30 feathered species have been identified, including giant tyrants, glossy four-winged gliders and a squirrel mimic.