Temporal paradox (paleontology)

The temporal paradox, or time problem is a controversial issue in the evolutionary relationships of birds. It was described by paleornithologist Alan Feduccia in 1994. It reflects a conflict between where chronologically fossils are expected to be found based on a proposed phylogeny, and where they are actually found. The temporal paradox can give rise to alternative phylogenies (i.e. the archosaurean hypothesis of bird evolution). Statistical measures have been devised to assess the likelihood of proposed phylogenies based on the size and positioning of gaps in the fossil record.

The concept of a "temporal paradox" is based on the following facts. The consensus view is that birds evolved from dinosaurs, but the most bird-like dinosaurs, including almost all of the feathered dinosaurs and those believed to be most closely related to birds are known mostly from the Cretaceous, by which time birds had already evolved and diversified. If bird-like dinosaurs are the ancestors of birds they should, then, be older than birds, but Archaeopteryx is 155 million years old, while the very bird-like Deinonychus is 35 million years younger. This idea is sometimes summarized as "you can't be your own grandmother". As paleontologist Peter Dodson pointed out:

I hasten to add that none of the known small theropods, including Deinonychus, Dromaeosaurus, Velociraptor, Unenlagia, nor Sinosauropteryx, Protarchaeopteryx, nor Caudipteryx is itself relevant to the origin of birds; these are all Cretaceous fossils ... and as such can at best represent only structural stages through which an avian ancestor may be hypothezised to have passed.

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