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Re: Doesn't George have a point?



The time problem with regard to Archaeopteryx and its close nonavian 
maniraptoran (gack!) relatives is of course not a deal-breaker with respect 
to the relationship between dinosaurs and birds. Here's the situation. In the 
Jurassic, we do find so-called "small" theropods (say, a meter or three 
long), and literally none of them is a theropod as birdlike as the 
ornithomimosaurs, oviraptorosaurs, deinonychosaurs, or troodontids (OODT 
theropods), which overwhelmingly populate this theropod size range (and 
larger!) throughout the Cretaceous. If OODT theropods >in this size range< 
occurred during the Jurassic, where are they? They >should< be as findable as 
their Cretaceous counterparts, if they existed. For many years, however, I've 
been suggesting that Jurassic OODT theropods were very small 
(Archaeopteryx-size), probably volant, probably arboreal, almost certainly 
feathered, lightweight dinobirds that are the lousiest possible candidates 
for preservation in the fossil record. That's why we don't find OODT 
theropods in the Jurassic (though instead we sometimes find these teeny teeth 
and bones that look vaguely like OODT material). The significantly larger 
Cretaceous OODT theropods are simply the large, flightless, cursorial 
descendants of the very small Jurassic OODT theropods, just as today's ratite 
birds are simply the large, flightless, cursorial descendants of early 
Cenozoic volant ratites.

An interesting question is, What happened at the Jurassic-Cretaceous boundary 
that eliminated the less birdlike theropods and permitted the OODT theropods 
to take over those niches?