Archaeopteryx and the Origin of Flight

Abstract

Reexamination of the specimens of Archaeopteryx, which constitute the only direct evidence pertaining to the habits and mode of life of the earliest stages of avian evolution, indicates that neither the highly favored arboreal theory nor the much critized cursorial theory offers adequate explanation for the origin of avian flight. The osteology of Archaeopteryx, in virtually every detail, is indistinguishable from that of contempraneous and succeeding coelurosaurian dinosaurs-especially in the details of the manus, forelimbs, and pectoral arch. It is proposed that these conditions reflect a highly predaceous mode of life for Archaeopteryx, rather than being arboreal adaptations. Plumage, in the form of contour feathers, is believed to have arisen in response to the need for controlling heat loss (and gain) and was secondarily modified on the fore limbs to enhance the prey-catching function of the hands. Enlargement of the primordial "primaries" and "secondaries" transformed the forelimbs of "proto-Archaeopteryx" into large, continous, trapping surfaces-natural insect nets-activated by powerful ventral adductor muscles (the pectoralis group). These adaptations were admirably preadaptive for active, flapping flight. The primordial insulative function of contour feathers and the predatory hypothesis for the enlargement of the remiges seem to account for the otherwise paradoxical presence in Archaeopteryx on essentially modern "flight" feathers in the absence of virtually all of the skeletal specializations that are associated with (or required for ?) modern bird flight, whereas those skeletal specializations that are present in Archaeopteryx are the same, or nearly the same, as those that are preserved in various (presumed) predaceous coelurosaurian dinosaurs.