Friday, June 11, 2010

What does "non-avian dinosaur" mean?

The phrase "non-avian dinosaurs" crops up in many articles. What does it mean? As we see below it means Dinosauria minus Aves. It lumps in the primitive flying and secondarily flightless birds with the real dinosaurs such as Tyrannosaurus - all of them under the same label - "non-avian dinosaur". In other words, it lumps in Paraves with actual dinosaurs.
"Now consider the group consisting of the non-avian dinosaurs (which is what people usually mean by the informal term ``dinosaurs''). This is a paraphyletic group, because it can't be defined simply as ``this animal plus all its descendants'', but must be described as one clade minus another: in this case, Dinosauria minus Aves. The ``non-avian dinosaurs'' make up a singly paraphyletic group because only one clade need be omitted from its base definition."
"it was not until the early 1990s that clearly nonavian dinosaur fossils were discovered with preserved feathers. Today there are more than twenty genera of dinosaurs with fossil feathers, nearly all of which are theropods. "
"By the 1990s, most paleontologists considered birds to be surviving dinosaurs and referred to 'non-avian dinosaurs' (all extinct), to distinguish them from birds (aves)."

AND notice these variations:
"Recent studies by Varricchio et al. reveal that males cared for the eggs of troodontids and oviraptorids, so-called "non-avian theropods" of the Cretaceous".
"The smallest non-avialan theropod known from adult specimens is the troodontid Anchiornis huxleyi, at 110 grams in weight and 34 centimeters (1 ft) in length.[3] "

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