The plot continues to thicken when it comes to bird evolution and the origin of flight. Eosinopteryx brevipenna is the latest feathered, birdlike theropod dinosaur to emerge from rich sites in Liaoning Province in northeastern China. While a diverse group of such creatures have been found in Early Cretaceous deposits, Eosinopteryx is older, dating from the mid- to late Jurassic period, roughly 155 million to 150 million years ago. Along with Anchiornis, another recently described Jurassic specimen of similar body plan, Eosinopteryx shows that, even at an early evolutionary stage, bird-like dinosaurs occupied different niches in the same ecosystem.
Pascal Godefroit of the Royal Belgian Institute of Natural Sciences in Brussels and Gareth Dyke, of the University of Southampton, England, along with four colleagues, described the attributes of the adult—or nearly adult—Eosinopteryx fossil from a complete skeleton finely preserved in slate. The pigeonsize animal is remarkable for its lack of flight feathers, in contrast with Anchiornis, which even on its lower legs bore the stiff, asymmetric feathers that could have enabled it to generate lift and fly or glide. Eosinopteryx’s plumage was anything but aerodynamic. It consisted instead of flexible, downy filaments suitable for insulation, as an aid to incubation, or for sexual display. Eosinopteryx was unable to fly; with its bare legs and short toe claws, it was likely adapted to life as a flightless ground dweller in a then tropical, forested habitat.
Dyke notes that Eosinopteryx, a natural “experiment in different lifestyles,” complicates our picture of the origins of modern birds and flight. The authors’ phylogenetic analysis bolsters theories that the venerable Archaeopteryx might no longer hold a pivotal position as a primitive bird. In fact, it might not be considered a bird at all. Dyke adds that “flight may have evolved multiple times in lineages” of feathered theropods. (Nature Communications)