How birdlike was Archaeopteryx?
Beak - Yes
Feathers - Yes
Wishbone - Yes
Growth pattern of blood vessels - Not quite there yet
By comparing the structure of the bone of Archaeopteryx with modern birds and fossil dinosaurs, researchers found out the growth pattern of blood vessels in Archaeopteryx was more like dinosaurs than modern birds. Archaeopteryx individuals seem to have taken a longer time to mature than modern birds do.
Archaeopteryx lived about 150 million years ago and is the earliest bird-like creature to have been found yet. A younger bird-like fossil -Ichthyornis dispar - dated about 94 million years ago shows several characteristics of quick growth, giving us an idea of the timing of the various changes in morphology and physiology that were taking place within the Maniraptor dinosaurian clade as they evolved characteristics that are recognized as bird-like.
By the way this is not some earth shattering find. The basic relationship that small carnivorous dinosaurs evolved into birds still holds. But the study highlights how difficult categorizing a creature which is a composite of ancestral and derived traits can be.
It doesn't matter in the larger view if Archaeopteryx is classified as a dinosaur or a bird. The value is in demonstrating that evolution of a complex suite of characters takes place in fits and starts, some features evolve earlier than others preserving the historical trajectories that major transitions in evolution have taken.
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