legenda (4)

Stephen A. Czerkas © 2004

BEFORE AND AFTER ARCHAEOPTERYX

Feathers are no longer the key diagnosto charactenstic thal defines what a brd is, because they are also found m plerosaurs and theropods. Havir>g the ability to Iły at least as well as Archaeopteryx. or having lost this ability in becoming secondarily flightless is crucial in determining what a bird is. While Archaeopteryx has only a few physical charactehstics related to its ability to fly, various levels of devek>pmenł towards the modem avian anatomy are readily obvious in the prehistorie brds that came later However, determining what kirrd of ancestral forms led up towards Archaeopteiyx and brds is much morę difticult. The ground dwoił mg theropod dinosaurs appoar to havo an ancestral relationship which may have led towards birds. but the discovery ot Scansorrapteryx reveals that brds did have arboreal ancestors which. perhaps independently of theropods. led towards the deoelopment of avian flight by first being able to climb.

Scansoróptery* nssling

Hypofhelical adult sizc of ScarVOr>Cp<eryx scaleO10 that of Archawęteryx

Archaeoptery*

Golden Eagle

Sinosaaropie/y*. a teathered theropod

AIV)iiniii«CKwiiiiy lmt