I took these from this site after doing google search on Hollow legged birds!
Explore the ancient southwest!http://www.rain.org/campinternet/southwest/dinosaurs/triassac-gallery.html
Dinosaurs - Triassic Gallery
In the Triassic period, only the lizard-hipped dinosaurs lived in the Ancient Southwest. There were two legged meat eaters called Theropods, and there were four legged plant eaters called Sauropods.
In New Mexico, the oldest type of dinosaur in North America has been found, and they were found in family groups. These early dinosaurs are called Coelurosaurs and were small Theropods that stood on two slender hind legs, had long necks, small heads, short front arms, and long tails. Their name means they were hollow-boned dinosaurs, which made them light and probably fast runners.
The Coelurosaurs are one of the few Dinosaurs with relatives living in all three periods of the Mesozoic Era. These hollow-boned creatures are the ancestors of today's birds, and make a link that proves dinosaurs are not really extinct - they evolved into birds!
An example of a Coelurosaurs is a Coelophysis, Paleontologist and Ichnologists think they lived in herds, cared for their young, and ate meat and insects.
Another very different types of dinosaur lived in the southwest during the last half of the Triassic. These were Prosauropods, meaning ancestors of the Sauropods. Sauropods are the huge four legged plant eaters - like Brontosaurs - many of us easily recognize as a major dinosaur type. The Prosauropods were smaller than their descendents and had the ability to run on their hind legs or stand on four legs to eat or drink.
The Anchisaurus was a Prosauropod measuring eight feet in length, his long neck and long heavy tail together were twice as long as his body. He could stand and walk on all fours, but probably raised up on his stronger hind legs to run, using his four toes for balance. The Anchisaurus was a plant eater with a long flexible neck helpful in gathering leaves from tall tress, and to drink with out getting down on its belly.
A small rabbit-sized dinosaur that lived in the Ancient southwest was the Segisaurus, named after the canyon where it was found in Arizona. This small creature was apparently a fast runner, ate small reptiles, and it bones were solid, not hollow. The Segisaurus lived during the late Triassic and Early Jurassic.
The Dilophosaurus was a crest headed dinosaur that ran on two strong heavy back legs weighed about 1,000 pounds, and measured 20' nose to tail. He lived in Arizona during the late Triassic and early Jurassic when it was a desert. He had sharp dagger-like teeth for eating prey and the claws on his front and hind hands and feet helped him catch his meals. His unusual head crest was made o two side be side crests on the top of his head. When found in Arizona, there was a group of three discovered together, implying it may have run in a small herd.