Bird fossil reveals history of flight.

Bird fossil reveals history of flight

Spanish and Argentine paleontologists have discovered a fossil bird that represents an important link between the oldest known bird and all modern birds. The bones of this creature, which would have been no bigger than a robin, are filling in evolutionary details about the early avian journey from ground to sky.

Found in the Las Hoyas limestone outcrop in Cuenca, Spain, the fossil dates back to the early Cretaceous period, approximately 120 million to 130 million years ago. The oldest bird known from the fossil record is Archaeopteryx, which has been found in 150-million-year-old formations.

"The new fossil, reported here, represents a previously unknown level in the organization of birds, intermediate between Archaeopteryx and later birds," according to the discoverers of the Las Hoyas bird, J.L. Sanz of the Autonomous University in Madrid, J.F. Bonaparte of the Argentine Museum of Natural Science in Buenos Aires and A. Lacasa of the Institut d'Estudis Ilerdencs in Lleida. The researchers report their find in the Feb. 4 NATURE.

Although the fossil lacks a skull, the rest of the specimen is relatively complete. The bird had primitive pelvic bones and hind limbs, but displays some more modern adaptations that are particularly important in flight. Most notable of these characteristics is a bird-like coracoid- a bone in the shoulder that helps translate muscular force into the power stroke of a wing. And at the end of the vertebrate column, the fossil has a bone called a pygostyle, which is the skeletal basis of an avian tail.

Because it combines primitive and modern characteristics, say the researchers, "the new fossil suggests that the early evolution of birds was firmly and rapidly influenced by the requirements of flight."

According to vertebrate paleontologist Joel Cracraft, who comments in the same issue of NATURE, the find "clarifies our knowledge of character evolution and provides important new interpretations regarding the early diversification of birds."

Cracraft, from the University of Illinois in Chicago, told SCIENCE NEWS that the Las Hoyas limestone formation is the type that often yields many fossils. "There's a good possibility of finding more of these," he says.

Photo: In Las Hoyas fossil (left), coracoid (c) is bird-like shoulder bone. Pygostyle (py), part of the tail, is at end of vertebrate column. Feather fossil (below) may have belong to the Las Hoyas bird.