Known mostly for their presence in Antarctica, penguins today live in many islands in the Southern Hemisphere, some even near the equator.
But scientists thought they hadn't reached warm areas until about 10 million years ago.
Now, researchers report in this week's online edition of Proceedings of the National Academy of Sciences that they have found remains of two types of penguin in Peru that date to 40 million years ago.
One of them was a 5-foot giant with a long sharp beak.
Paleontologist Julia Clarke, assistant professor of marine, earth and atmospheric sciences at North Carolina State University, said she was surprised at the new find.
"This is the same age as the earliest penguins from South America. The only other record from the continent of that age is from the southernmost tip of the continent," she said. "The new finds indicate they reached equatorial regions much earlier than anyone previously thought."
The big bird is larger than any penguin known today and the third largest known to have ever lived, she added.
It is particularly unusual for such a large penguin to have been living in a warm climate, she noted. "In most cases, the larger individuals of a species or among related species are correlated with colder climes and higher latitudes."
The beak of the large penguin — Icadyptes salasi — "looks remarkably spearlike," she said. But the researchers don't know its exact feeding style.
The second new species — Perudyptes devriesi — was approximately the same size as a living King Penguin — 2 ½ to 3 feet tall — and represents a very early part of penguin evolutionary history, the researchers said.
The research was funded by the National Science Foundation Office of International Science and Engineering and the National Geographic Society.