Summary: Evolution and Systematics
Birds are "glorified reptiles" (Huxley 1867)
Birds and modern reptiles have many characters in common:
- simple middle ear with one ear bone (mammals have three)
- lower jaw composed of five or six bones on each side (mammals have one)
- yolked egg; embryo develops by shallow divisions of cytoplasm on
the surface of the egg
- nucleated red blood cells (mammals without nuclei)
- female is heterogametic sex (Z and W sex chromosomes) in birds and
some reptiles (XX in mammals)
Archaeopteryx: the classic not-missing "missing link"
Birds and reptiles are clearly distinguished by a number of characters.
Most importantly, no modern reptile has feathers.
Darwin predicted intermediate evolutionary links between clearly separated
higher taxa in The Origin of Species (1859).
Two years later (1861),
the first complete specimen
of Archaeopteryx lithographica