Birds and Dinosaurs

"Gigantoraptor erlianensis stood more than 16 feet (five meters) tall and weighed a ton and a half, or roughly 1,400 kilograms. Featuring a toothless beak on its head and a short tail for balance, the enormous birdlike dinosaur measured more than 26 feet (eight meters) in length. Living more than 65 million years ago at the end of the Cretaceous period, this big bird precursor has complicated the seemingly shrinking descent from Archaeopteryx to the modern sparrow."

"The finding complicates the evolutionary descent of birds from dinosaurs. 'Progressively from within advanced theropods you get smaller and smaller towards birds,' Norell says. But 'after some species originate and spring off the bird line, you get secondary gigantism.'

No one can say why for sure. 'Big size has some advantages such as having fewer predators and having more food resources that are unavailable for small animals,' Xu notes. But he adds that early oviraptorosaurs, this animal's ancestors, 'are among the smallest dinosaurs.'"

"So what did this prehistoric 'Big Bird' eat? Another mystery, as the animal bore no teeth in its jaw, had a small head and long neck (common in herbivores) but also sharp claws (common in carnivores). '[It] could be omnivorous,' Xu says. Norell adds: "Lots of things that have no teeth like hawks and eagles are pretty efficient carnivores.' It seems the world of dinosaurs—and bird ancestors—was as diverse as that of their latter-day descendants."

Portions of this are from Scientific American.

Gigantoraptor


Remains of a petite dinosaur named Mahakala Omnogovae reveal that some of the ancestors of birds had already shrunk in size before flight evolved.

The dinosaur, a mere 2 feet long (70 centimeters) and weighing the equivalent of two cans of soda, roamed the Earth 80 million years ago during the Cretaceous period (between 146 and 65 million years ago).

"This specimen shows that dinosaurs evolved small size earlier than we previously thought," said study team member Julia Clarke, a paleontologist at North Carolina State University and the North Carolina Museum of Natural Sciences.

A prerequisite for flight is the ability to lift one's body off the ground. So for dinosaurs to take to the skies, they first had to "lose some weight." But did already-small dinosaurs shrink further in size after they took to the air and became birds? Or did they first shrink in size before they could fly?

Paleontologists had previously assumed it was the first scenario that occurred, but the new finding, detailed in the Sept. 7 issue of the journal Science, suggests otherwise.

"Paleontologists have long thought that miniaturization occurred in the earliest birds, which then facilitated the origin of flight," said lead author Alan Turner, a graduate student at the American Museum of Natural History and Columbia University in New York. "Now, the evidence shows that this decrease in body size occurred well before the origin of birds and that the dinosaurian ancestors of birds were, in a sense, pre-adapted for flight."

From LiveScience