Ancient birds may have had modern seed-eating organ: study

WASHINGTON, Sept. 5 (Xinhua) -- Some ancient bird fossils appear to have had a specialized organ characteristic of modern seed-eating birds, according to a study published on Monday in the Proceedings of the National Academy of Sciences.

Zhonghe Zhou, of Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, and colleagues examined hundreds of early-Cretaceous fossils from China and found early evidence for the presence of a crop, a pouch in the bird's esophagus where seeds can be stored and softened by mucus to make them easier to grind in the gizzard.

The ancient crops were identified as a roughly spherical mass of seeds outside the ribcage, in about the same anatomical location as in modern birds. The researchers identified crops in two out of nearly 100 Sapeornis chaoyangensis specimens and in one out of more than two dozen Hongshanornis longicresta specimens, and suggest the crop's apparent rarity may reflect the difficulty of preserving the organ.

The authors also identified a muscular gizzard in Hongshanornis, giving it essentially a modern avian digestive system. Sapeornis and Hongshanornis are two evolutionarily distant lineages, indicating that their crops evolved independently as a specialized seed-eating adaptation, the authors report. Both species also had largely reduced or completely lost teeth, indicating that seed eating may have factored into the reduction of teeth in birds.

The authors concluded that seed-eating was an important factor in early avian evolution.