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Mar 28

Ostrich Mimics of Maryland

Posted on March 28, 2018 at 3:38 PM by Bonnie Man

Not all dinosaurs were big or strange. Some were remarkably similar to modern animals – for example, the ornithomimids that lived in Maryland 115 million years ago looked for all the world like ostriches with long tails. Standing six or seven feet tall, ornithomimids were about the same size as ostriches, and like ostriches they had long necks, small heads, and toothless beaks. Ornithomimid fossils from Alberta, Canada show that these dinosaurs were covered in feathers, including big plumes on their arms (the bald ornithomimid in the image above was painted before this discovery, and is now considered out of date).

Why are ornithomimids so much like modern ostriches? For one thing, these two animals are distant cousins – birds are a specialized type of dinosaur that has survived to the present day. However, ornithomimids are not true birds, nor are they especially close to birds on the dinosaur family tree (the toothy dromaeosaurs, or “raptors”, are much closer). The similarity between ornithomimids and ostriches is in fact a classic example of convergent evolution. Sometimes distantly related animals that live in similar ways and encounter similar problems evolve remarkably similar anatomical solutions. For instance, sharks, dolphins, and extinct marine reptiles called ichthyosaurs all evolved the same fishy shape because they all specialize in hunting fish in the open ocean. In the same way, ornithomimids and ostriches converged on the same set of adaptations to survive in their respective habitats. Long legs and compact feet help them run fast to escape from predators. Big eyes help them see long distances, even at night. And a beak is useful for plucking fruits, leaves, and seeds off of bushes and trees.

Smithsonian scientist Charles Gilmore first identified ornithomimid fossils from Maryland in 1921. We're still finding the remains of these animals today - especially the bones of their legs and feet.

Illustration by Mary Parrish, National Museum of Natural History.