Yuezhuornis yangyuanensis, described in Nature from a nearly complete fossil in southeastern China, combines an early bird’s skeleton with markedly short forelimbs and a hyperextensible second toe resembling those of deinonychosaurs. The authors’ phylogenetic analysis supports a terrestrial, flightless lifestyle.
The important inference is not “birds once could not fly”—that is hardly news. It is that one of the earliest-diverging avialans had already explored a strongly terrestrial body plan. Early bird evolution looks less like a single march toward better flight and more like several ecological experiments, some of which reduced or abandoned it. Nature, published Oct. 14