ornithuromorphs from the early Cretaceous period. It is known from two fossil specimens of a single species, Archaeornithura meemannae. The specimens have been dated to the Hauterivian age, 130.7 million years ago, making A. meemannae the oldest known ornithuromorph, the lineage that gave rise to modern birds, and contains all living birds as well as many of their extinct relatives.[1]
Discovery and naming
Both specimens of A. meemannae, the
Zhou Zhonge of the Institute of Vertebrate Paleontology and Paleoanthropology, Beijing. Archaeornithura is the first ornithuromorph found in the Huajiying Formation, which represents the earliest diversification period of the Jehol Biota, "the most important and diverse fossil avifauna known to science".[1] Previously, the only birds known from the Huajiying Formation were Enantiornithes
.
The genus name means "ancient ornithuromorph"; the
Stephen Brusatte, who was not affiliated with the study, called the discovery of A. meemannae "one of the most important [bird fossils] found over the last decade".[2]
Description
Archaeornithura had a moderately advanced plumage, fan-shaped tail feathers, a U-shaped
derived and has many advanced features of modern birds," said discoverer Wang Min.[3] Before its discovery, the oldest known ornithuromorphs had been species living about 125 million years ago.[2]
It also suggests that key evolutionary advantages of birds – skilled flight and rapid growth in development – arose rapidly, and that
plovers, suggesting that it was a shore bird that waded into shallow water to feed. The species appears to have been adept at flying.[2] Both known specimens of A. meemannae are excellently preserved, including substantial feathers.[3] Some Archaeornithura feathers feature a central groove, a trait thought to arise from derived flight feathers. This feature was not previously known in the Ornithuromorpha, suggesting that modern feather morphology, in which it is lacking, evolved separately from the Archaeopteryx lineage in a later subset of the ornithuromorphs.[1]
Archaeornithura is distinguished from its closest relatives by a combination of the following traits, each in itself not a unique
metacarpal. The second phalanx of the second finger is longer than the first phalanx. The thighbone is short relative to the tarsometatarsus.[1]
Classification
Archaeornithura was placed in the
metatarsals II–IV and the expanded shape of the outermost trabecula of the sternum in common. The specialized wading features of Archaeornithura suggest that the hongshanornithids originated in a semi-aquatic environment.[1]
The position of Archaeornithura in the
evolutionary tree is shown by the following cladogram
