John H. Ostrom, a path-finding paleontologist who established an evolutionary link between dinosaurs and birds and whose dramatic fossil discoveries provided the inspiration for the fictional creations of the film "Jurassic Park," died July 16 at an assisted living facility in Litchfield, Conn. He was 77 and had Alzheimer's disease.
Dr. Ostrom first suggested that birds are descended from dinosaurs in the 1970s, and his idea was met with skepticism or outright derision by other scientists. But with his own research, as well as later discoveries, his ideas have been vindicated and have gained wide acceptance among biologists, geologists and paleontologists.
"He is probably the most influential person in dinosaur paleontology in the last century," said John R. Horner, curator of paleontology at the Museum of the Rockies in Bozeman, Mont., and a leading authority on dinosaurs.
"John is basically responsible for the way we view dinosaurs. We used to see dinosaurs as stupid, coldblooded reptiles. John showed us that they didn't drag their tails and that they gave rise to birds."
Throughout his career, which was spent mostly at Yale University, Dr. Ostrom proposed several provocative notions to show that dinosaurs were more advanced than thought. He believed that many dinosaurs were warmblooded, like modern birds and mammals, instead of sluggish reptiles. He also suggested that birds first developed the power of flight not by gliding through trees, but by running along the ground on their hind legs and eventually taking to the air.
He made his first major discovery on a Montana hillside on the final day of the summer field season in 1964. Noticing a bone protruding from the soil, he uncovered the remains of a two-legged creature with a curving four-inch claw on each forelimb. He dubbed the fossil deinonychus (Greek for "terrible claw") and suggested that, when alive, the animal ran upright at high speeds, extending its long tail behind its body.
In 1970, while visiting a museum in the Netherlands, he made his second notable discovery when he recognized that a fossil skeleton labeled a "pterosaur" was actually a prehistoric bird called an archaeopteryx.
"It took me 15 to 20 seconds to make the identification," he told The Washington Post in 1978.
Even though the archaeopteryx, which lived 145 million to 150 million years ago and was about the size of a chicken, had a primitive form of feathers, Dr. Ostrom noted that it had teeth and other skeletal features that resembled those of small dinosaurs. He saw similarities to his own discovery, deinonychus, and in 1973 proposed the theory that birds evolved from dinosaurs.
The idea was first suggested in 1868 by Thomas Henry Huxley, a friend and defender of Charles Darwin's, but had long been dismissed. Dr. Ostrom maintained that archaeopteryx was the obvious ancestor of modern birds, particularly the flightless ostrich and emu.
Some ornithologists continued to resist Dr. Ostrom's theory for decades, but Horner and other researchers found evidence of dinosaur nests and eggs in Montana to bolster the notion. In 1997, in one of his last scientific forays, Dr. Ostrom joined an expedition in China that unearthed new forms of dinosaurs with feathers, providing further credence to his ideas.
"If there are any people left who don't believe birds came from dinosaurs," Horner said, "I'd put them in the same group as the flat-earth society."
Dr. Ostrom was born in New York on Feb. 18, 1928. He grew up in Schenectady, N.Y., where he graduated from Union College. He originally intended to enter medicine, but while studying at Columbia University, he read "The Meaning of Evolution" by George Gaylord Simpson and immediately decided to devote his life to the study of fossils and evolutionary biology.
He received his doctorate in geology, with a specialty in vertebrate paleontology, from Columbia in 1960, when the study of dinosaurs was all but forgotten.
"John revitalized the field, because he looked at them as whole organisms rather than collections of bones," said Leo J. Hickey, chairman of the department of geology and geophysics at Yale.
Dr. Ostrom taught at Brooklyn College and Beloit College in Wisconsin before joining Yale's faculty in 1961. He wrote more than a dozen books, for both scientific and popular audiences, and retired from Yale in 1992.
For all their professional renown and influence, Mr. Ostrom's ideas probably received their widest recognition as a terror-inducing part of popular culture. In a 1997 interview with the New York Times, Mr. Ostrom said novelist Michael Crichton called him "to find out about the creature that I had discovered in Montana a few years back, [and] that he understood it was a meat eater."
The velociraptor in Crichton's "Jurassic Park" and "The Lost World" and in the subsequent Steven Spielberg movies was based largely on the sharp-clawed deinonychus that Dr. Ostrom had discovered in 1964.
"He did not like limelight," Hickey said of his former Yale colleague, "yet he was one of the great powerhouses producing ideas in paleontology."
Dr. Ostrom's wife of 51 years, Nancy Hartman Ostrom, died in 2003.
Survivors include two daughters and three grandchildren.