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The basal bird Archaeopteryx, from the Jurassic, is well known as one of the first "missing links" to be found in support of evolution in the late 19th century. Though it is not considered a direct ancestor of modern birds, it gives a fair representation of how flight evolved and how the very first bird might have looked.
A turning point came in the early twentieth century with the writings of Gerhard Heilmann of Denmark.An artist by trade, Heilmann had a scholarly interest in birds and from 1913 to 1916, expanding on earlier work by Othenio Abel, [12] published the results of his research in several parts, dealing with the anatomy, embryology, behavior, paleontology, and evolution of birds. [13]
The WAIR hypothesis, a version of the "cursorial model" of the evolution of avian flight, in which birds' wings originated from forelimb modifications that provided downforce, enabling the proto-birds to run up extremely steep slopes such as the trunks of trees, was prompted by observation of young chukar chicks, and proposes that wings ...
The shared history of birds and dinosaurs is well-established, but exactly how true birds evolved during the Mesozoic is a bit of a mystery. Adding to this conundrum are fossilized footprints of ...
The fact that the two earliest-known birds display quite different anatomies and inhabited different parts of the world - separated by about 5,500 miles (8,800 km) - suggests that millions of ...
Evolution of the creodonts, an important group of meat-eating (carnivorous) mammals. 62 Ma Evolution of the first penguins. 60 Ma Diversification of large, flightless birds. Earliest true primates, [who?] along with the first semelid bivalves, edentate, carnivoran and lipotyphlan mammals, and owls.
Archaeopteryx continues to play an important part in scientific debates about the origin and evolution of birds. Some scientists see it as a semi-arboreal climbing animal, following the idea that birds evolved from tree-dwelling gliders (the "trees down" hypothesis for the evolution of flight proposed by O. C. Marsh).
The evolution of the modern avian traits such as the compact body, clawless wing and the alula are now known to appear over successive stages. Today the Archaeornithes are classified into a series of nested monophyletic groups, and the name is rarely used in modern literature.