In a feat nowhere near as terrifying as the movie Jurassic Park, scientists have reconstructed a light-sensing protein from the ancestors of dinosaurs. It suggests that dinosaurs may have been well-adapted to seeing in the dark. Biologists are excited by the promise of the technique, which predicts the structure of proteins from extinct animals by studying those of living relatives--then brings the protein to life.
Paleontologists learn about extinct animals in two main ways. They study fossils, and they make educated guesses based on existing creatures. Although neither method provides direct information about the molecular inner workings of the animals, inference is rapidly becoming more sophisticated. An intriguing prospect is the comparison of gene sequences to reconstruct molecules. But many scientists suspected this exercise would merely be computer-generated speculation.
Now, molecular biologist Belinda Chang of Rockefeller University in New York City and colleagues have dispelled those doubts. Using the gene sequences that code for the visual protein rhodopsin in 30 living vertebrates, such as alligators, chickens, and more primitive vertebrates such as lampreys, the researchers reconstructed the rhodopsin belonging to the archosaurs. This ancient group gave rise to dinosaurs, as well as extant groups such as crocodiles and birds. Chang's team used a statistical method, known as maximum likelihood, that identifies the series of changes most likely to have generated the observed range of modern proteins and extrapolates the most likely common ancestor--the archosaur protein.
The reality check comes from the team's ability to engineer mammal cells to produce the rebuilt rhodopsin. It turns out to be a fully functioning protein, responding to light in the same way that natural rhodopsins do, they report in the September issue of Molecular Biology and Evolution. Curiously, the protein absorbs light best at a wavelength of 508 nanometers, which is slightly redder than for modern vertebrates. So early dinosaurs may have seen well under dim lighting conditions, which could bolster the controversial hypothesis that archosaurs and other ancestral reptiles were nocturnal.
The study is most important because it confirms the method's potential. "This is the most exciting paper I've seen in many years," says integrative biologist David Hillis of the University of Texas, Austin. "This is the first time someone has reconstructed an entire protein ... and tested its function," he says. "This is like a real Jurassic Park, one protein at a time."