Ornithomimids, or "ostrich mimics," were bird-like dinosaurs. These fast runners had long, slender legs, a long neck, a stiff, tapered tail, short arms, a small head, large eyes, and a toothless, beaked mouth. Ornithomimids lived during the late Jurassic period until the late Cretaceous period. These omnivores probably ate small animals (like insects and small reptiles) and plants. Ornithomimus, pictured above, was an ornithomimid dinosaur.

Dr. John M. Rensberger, a vertebrate paleontologist (specializing in mammals) from the University of Washington, USA, and Dr. Mahito Watabe, a paleontologist from the Hayashibata Museum of Natural Science, Japan, carefully examined the bones and teeth of many modern-day and extinct animals, studying how they varied as a function of the animals' habitat and food sources (published in Nature, August 10, 2000).

Microscopic structures like canaliculi (tiny passages in bone which connect blood vessels to cells) and collagen fibers (which strengthen bone) were painstakingly observed in thin sections of bones. It was found that birds and ornithomimid dinosaurs share similar arrangement of canaliculi, but those in mammals and plant-eating dinosaurs (like Triceratops and duck-billed dinosaurs) were quite different (the canaliculi were jumbled in birds and dinosaurs, but were radially arranged in mammals). A similar result was found for collagen; mammals and plant-eating dinosaurs had collagen fibers that were more systematically arranged than those of birds and ornithomimid dinosaurs.

Rensberger is planning on further, related investigations, including adding crocodiles to the study.

RELATED LINKS:
A page on birds and dinosaurs

A page on duck-billed dinosaurs, plant-eaters also called hadrosaurs.

A page on Triceratops, a three-horned plant-eating dinosaur.

All about birds.

A page on Archaeopteryx, the earliest-known bird

All about mammals