Professor John Ostrom

Palaeontologist who showed that birds were descended from dinosaurs
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John Ostrom was a palaeontologist whose careful analyses of dinosaur skeletons revolutionised our understanding of their biology. Gentlemanly and soft-spoken, Ostrom, Professor Emeritus of Geology and Geophysics at Yale University, was revered by younger palaeontologists and taught many of today's leading dinosaur specialists.

Born in 1928 in New York City and raised in Schenectady, New York, Ostrom initially planned to become a physician, and had nearly completed a premedical programme at Union College in Schenectady when he took a required course on evolution. The night before the first class he sat down to read George Gaylord Simpson's 1949 textbook The Meaning of Evolution. He found himself enthralled, stayed up all night reading it, and wrote to Simpson saying that the book had changed his outlook on life. Simpson wrote back urging Ostrom to abandon medicine and come study with him in New York, where he held a professorship in zoology at Columbia University and was Curator of Geology and Paleontology at the American Museum of Natural History. To the dismay of his father, a physician, Ostrom switched his major to geology, and took a series of extra courses so he could graduate in 1951 and study under Simpson.

The American Museum was famed for its displays of dinosaur skeletons and footprints, and had accumulated one of the world's largest collections of dinosaur fossils. But by the 1930s palaeontologists had largely abandoned dinosaur research after concluding that the giants were merely sluggish overgrown reptiles that had died out after becoming an evolutionary dead end. Instead they concentrated on fossil mammals and other animals they considered to be in the main line of evolution. Simpson was typical in his interest; he initially studied fossil mammals, and later turned to evolutionary theory.

Most of Simpson's students followed in his footsteps. But Ostrom took a fancy to dinosaurs, and studied them under Ned Colbert, virtually the only American Museum scientist then working on them. Ostrom earned his doctorate from Columbia for analysing the functions of the skulls of plant-eating duck-billed dinosaurs, and settled at Yale in 1961. Yale also named him Curator of Vertebrate Paleontology at its Peabody Museum, which housed the huge collection of dinosaur fossils collected in the late 19th century by Othniel Charles Marsh. At Yale, he continued his careful analyses of form and function of dinosaur skeletons, and showed the duck-billed dinosaurs, or hadrosaurs, had lived on land rather than in the water as had been thought.

From 1962 to 1967 Ostrom led a team that uncovered dinosaur fossils from a previously poorly known period about 100 million years ago. He became particularly intrigued by a two-legged predator about three metres long which he named Deinonychus. Its skeleton and sharp claws on its hands and feet showed that it must have been an active predator. That led Ostrom to suggest that such an active dinosaur would have been warm-blooded - a break from the traditional view of dinosaurs as cold-blooded and sluggish. Ostrom presented the idea cautiously, but one of his undergraduate field assistants, Bob Bakker, embraced the idea of hot-blooded dinosaurs enthusiastically and went on to write the widely read The Dinosaur Heresies (1986). By 1980, most palaeontologists had come to accept that dinosaurs had active metabolisms and acted like warm-blooded animals. The differences are most vivid in movies: compare the Deinonychus-like raptors of Jurassic Park to the tail-dragging layabouts from the B-movies of the 1930s.

Ostrom also saw that Deinonychus had a very bird-like skeleton, leading him to wonder about the relationship between birds and the family of predatory dinosaurs called theropods that also includes Tyrannosaurus rex and the Jurassic Park raptors. The theory that birds had evolved from dinosaurs was not new. T.H. Huxley proposed it in the 19th century, shortly after the discovery of the earliest-known bird, Archaeopteryx, which had teeth, a long tail and other dinosaur-like features. However, Huxley's proposal had fallen out of favour, and by the 1960s most palaeontologists thought birds had evolved from a small tree-climbing reptile rather than a dinosaur.

In 1970, Ostrom went to Europe to study the skeletons of pterosaurs from the Solhofen fossil beds that also had yielded Archaeopteryx. He found that a fossil in Haarlem, which had been identified as a pterosaur in 1859, was actually the skeleton of another Archaeopteryx. More important for scientists, Ostrom also found that its skeleton was very similar to that of Deinonychus and other small predatory dinosaurs, and concluded that birds had evolved from similar small, swift predatory dinosaurs. That meant that birds would have inherited their active metabolisms from ancestral dinosaurs which might have evolved fluffy feathers for insulation rather than flight.

Ornithologists were particularly disturbed by this conclusion. Further research bolstered Ostrom's case, particularly the systematic analysis of the traits present in fossils. Eventually, most palaeontologists came to believe birds were feathered dinosaurs. However, some questions remained, particularly how two-legged dinosaurs that ran on the ground could have gradually evolved the large wings and flight feathers needed to fly. Sceptics wanted to see a fossil intermediate between the 150-million-year-old Archaeopteryx and its flightless ancestors, but no one had found convincing fossils of the right age. By 1996, Ostrom had come to doubt that he would live to see a fossil between birds and dinosaurs.

Then the Canadian palaeontologist Phil Currie returned from China with photographs of a little feathered dinosaur. The fossil was preserved in an unusual way. The animal had fallen into an ancient lake and its bones had been squashed flat between layers of sediment. But around some of the bones was a frill that looked like primitive feathers. Chinese scientists named it Sinosauropteryx. The photograph stunned and delighted Ostrom when Currie showed it to him in October 1996 at the annual meeting of the Society of Vertebrate Paleontology - held that year at the American Museum in New York.

Sinosauropteryx stunned palaeontologists around the world, and in early 1997 the Academy of Natural Sciences in Philadelphia sent Ostrom and three other specialists to take a closer look. After showing them the original Sinosauropteryx, Chinese palaeontologists surprised the visitors with a series of other feathered fossils. Some were birds, but others were dinosaurs, with arms too short to fly, but feathers much better developed than the fuzzy covering of Sinosauropteryx. When he returned, Ostrom predicted the Chinese fossil beds would keep scientists busy for a century.

Discovery of the Chinese feathered dinosaurs capped Ostrom's career, validating his theories that dinosaurs were active, dynamic animals, and that birds had evolved from small, predatory dinosaurs. Although the Chinese fossils were younger than Archaeopteryx, they showed that small dinosaurs must have evolved feathers long before flight.

Ostrom never became a public figure as did the colourful Bakker. But among dinosaur palaeontologists he was treasured as a father figure and mentor as well as a gifted scientist. He responded graciously to questions from children and journalists. In a posting on the dinosaur mailing list, Taormina Lepore, now a student working on dinosaur footprints Ostrom studied three decades ago, said his replies to her letters when she was nine and 12 had inspired her love of palaeontology.

Tom Holtz, a dinosaur palaeontologist at the University of Maryland who studied under Ostrom, said, "Through his work, and the research he inspired, we now recognise dinosaurs as one of the most successful lineages in the history of the planet, and one which still is present today in the form of birds."

Jeff Hecht