The oldest known tracks of web-footed birds from the lower Cretaceous of South Korea.

We describe the oldest tracks of web-footed birds from the Early Cretaceous in South Korea. The tracks are characterized by a wide divarication angle and a long reversed hallux. The web is semipalmate and restricted to the proximal portion of the three forward digits. The tracks from the Early Cretaceous in South Korea are smaller than those of the Late Cretaceous, therefore confirming the trend of size increasing in the early evolution of birds as shown by skeletal fossils. The discovery of web-footed tracks with abundant non-web-footed tracks indicates that there was a considerable diversification of shore birds as early as the Early Cretaceous.