Their results agree for the most part with another study that was based on both penguin genes and anatomy, published this June in the journal Cladistics by Dr. Giannini and Sara Bertelli, also at the American Museum of Natural History.

"You see the same major patterns. The picture is well established, I think," Dr. Giannini said.

The Canadian researchers found that the penguin's common ancestor existed 40 million years ago -- more than 30 million years after they think penguins evolved. "There is a big gap there," Dr. Pereira said. He proposed that most of the older fossils of penguins (some more than five feet tall) belonged to extinct branches of the tree.

The study also finds that the living species that belong to the oldest branches of the penguin tree -- the gentoo, chinstrap and king penguins, along with the emperor penguins -- can all be found around Antarctica. "The ancestor of the modern penguins were in Antarctica or very close," Dr. Pereira said.

But the early penguins probably did not have to survive brutal conditions on Antarctica as they do today. "Antarctica was covered in forest, much like we see in New Zealand today," Dr. Pereira said.

The ice came later, about 35 million years ago. Geologists suspect that the change occurred as a result of South America and Australia's drifting away from Antarctica. The ocean currents began to circle the continent, isolating it. This cooling climate may have killed off the older penguins. Some researchers have speculated that they disappeared because they couldn't compete with whales hunting for the same prey.

Not all the penguins became extinct. "Basically, what happened is penguins had to adapt to conditions in Antarctica, or they had to leave," Dr. Pereira said. The ancestors of the emperors and other residents of Antarctica evolved the ability to survive the conditions. Other penguins swam north to milder waters, where they founded new lineages. "Most of the species ended up leaving the continent," Dr. Pereira said.

Penguins may have followed ocean currents carrying cool, nutrient-rich waters northward. They established breeding grounds on new volcanic islands and branched off into new species.