Presence of Bald Ibises (Geronticus Wagler, 1832) (Threskionithidae - Aves) in the Late Pliocene of Bulgaria

Abstract

Fossil data on the history of Threskiornithidae, as well as genus Geronticus are scarce. The only fossil species, G. apelex Olson 1985, was described from the early Pliocene deposits of South Africa. In 1993 a left proximal part of a carpometacarpal bone of an adult specimen was collected in the vicinity of the town of Slivnitsa (NW of Sofia, West Bulgaria). According to the associated fauna of large mammals, the age was determined final of Middle Villafranchian - end of MN 17 zone (over c. l.85 Ma B.P.). Diagnosis of Geronticus balcanicus sp. n.: A Late Pliocene Bald Ibis, dimensionally and morphologically close to Geronticus eremita, but differing by the less concave surface in the proximal end of os metacarpale minus; absence of an enlargement of os metacarpale minus in proximal end; smaller foramen nutritium; inclined, but not upright profile of trochlea carpalis; relatively larger diameter of trochlea metacarpalis; less erected processus pisiformis; less developed (shallower) fossa in the base of facies articularis ulnocarpalis; deeper fossa supratrochlearis and presence of an inception of processus intermetacarpalis. G. balcanicus sp. n. is considered as a probable ancestor of G. eremita, while G. apelex probably lies on the lineage of G. calvus.