Zur Evolution basicranialer Gelenke bei Vögeln, insbesondere bei Hühner‐ und Entenvögeln (Galloanseres)

摘要

AbstractOn the evolution of basicranial articulations of birds, especially of fowl and waterfowl (Galloanseres)Basicranial articulations are among the most neglected structures of the avian feeding apparatus. Based on the presented ontogenetic evidence two nonhomologous types of basicranial articulations are distinguished in birds:1. A basipterygoid articulation developing from an early embryonic quadratopolar comissure, which is homologous to the basipterygoid articulation of other amniotes. This diarthrosis is present in all paleognathous as well as in many juvenile and some adult neognathous birds.2. A rostropterygoid articulation developing through apposition of the pterygoid on the parasphenoid. This secondary articulation is known from galliform and ansenform birds (Galloanseres).Based on ontogenetic evidence as well as functional analysis following hypothesis explaining the evolution of rostropterygoid articulations in the Galloanseres is proposed:1. In the groundplan of birds (Aves, sensu Gauthier 1986) a basipterygoid articulation was present continuously during ontogeny. It protected the pterygoid‐quadrate articulation against propalineal distortion by controlling the movement of the caudal end of the flexible, but undivided pterygopalatinal bar. This construction is preserved in recent paleognaths.2. In the groundplan of the Neognathae an intrapterygoid joint subdividing the pterygopalatinal bar was formed in juveniles. Consequently the basipterygoid articulation had lost its function in adults and was therefore developed only in embryonic and juvenile stages. This condition is present in many recent neognaths.3. In the stemline of the Galloanseres the intrapterygoid joint was already formed in embryos. Since an undivided pterygopalatinal bar is absent in any ontogenetic stage of the Galloanseres, no basipterygoid articulation is being formed. The recent Galloanseres retain this developmental pattern.4. In the groundplan of the Galloanseres a newly developed rostropterygoid articulation was present providing a support for the pterygopalatinal bar. This articulation could withstand not only pressure but also increasing tension occurring as a consequence of the development of a gliding jaw joint and a firm grip with beak tips, both consequences of increasing herbivory in the Galloanseres. Since the basipterygoid articulation was reduced, a new secondary joint had to be develope