What had feathers like a bird, claws like a dinosaur and lived in what is now Madagascar during the Late Cretaceous period? A team of paleontologists, led by Catherine Forster of the State University of New York at Stony Brook, calls it Rahona ostromi, meaning "Ostrom's menace from the clouds." And last week they announced that R. ostromi's remains leave little room to doubt that birds took off from the dinosaur family tree.
For more than 100 years, paleontologists have debated which came first: dinosaur eggs or prehistoric chickens. Based on such primitive birds as Archaeopteryx, most have come to accept that birds evolved from small, terrestrial dinosaurs known as theropods. In February, Luis M. Chiappe of the American Museum of Natural History--one of the researchers reporting now on R. ostromi--made the case, along with Kevin Padian of the University of California at Berkeley, in Scientific American's pages.
But a vocal minority has held out, arguing--among other things--that birds are too old to have therapod ancestry. They note that the most bird-like therapods date to about 115 million years ago, whereas Archaeopteryxspecimens appear in the fossil record no sooner than 150 million years ago.
Compared to Archaeopteryx, though, this new creature is a spring chicken, dating to only 65 to 70 million years ago. And R. ostromi is in many ways even more dino-like. "The skeleton of Rahona exhibits a striking mosaic of therapod and derived avian features," the team wrote in a paper appearing in the journal Science on March 20. In addition to Forster and Chiappe, the authors include David W. Krause of SUNY Stony Brook, who led the group that discovered the bones in 1995, and Scott D. Sampson of the New York College of Osteopathic Medicine.
Perhaps most dramatic new finding is that the raven-sized bird bears a sickle-shaped claw on the second toe of its hind foot--a trait it shares only with fast, predaceous therapods called maniraptorans. This group includes Deinonychus and Velociraptors, made famous in Jurassic Park. In addition, this toe is much thicker on R. ostromi than on other birds, as is also true of meniraptorans. And like Archaeopteryx, R. ostromi has a long, saurian tail.
At the same time, R. ostromi is clearly a bird. Its long bones are light and hollowed, as they are in all birds. And on its forearm bone, R. ostromi has six little bumps, which the researchers believe are quill knobs for feathers. If so, the creature was likely a capable flyer. Researchers continue to debate whether primitive birds used their wings primarily to glide from branch to branch or to the ground, or if they actually flapped them to take off.
R. ostromi is perhaps most bird-like in terms of its hips and legs, and Forster and colleagues presume that it fits in at the base of the bird family tree, alongside Archaeopteryx. The seeming age difference between the two may mean that R. ostromi--having been isolated on Madagascar--represents an evolutionary holdover. Whatever the case, R. ostromi is clearly one of the most primitive birds ever discovered. As for the theory that birds have dinosaur origins, these researchers say, "it clinches it for us."