A New Specimen of the Tiny Middle Eocene Bird Gracilitarsus Mirabilis (New Family: Gracilitarsidae)

A new, second specimen of the tiny Middle Eocene bird Gracilitarsus mirabilisMayr 1998 shows several previously unknown osteological features. The species represents a bauplan unknown among recent birds in that it combines swallow-like length proportions of the major wing bones with a long and slender tarsometatarsus. The feet of Gracilitarsus mirabilis are highly unusual in that the three anterior toes are very short and of nearly equal length, and in that the claws are of great dorso-ventral depth. Gracilitarsus mirabilis is classified within a new family in this study. The species shares some derived characters of the tarsometatarsus with the Paleocene South American species Eutreptodactylus itaboraiensisBaird and Vickers-Rich 1997.