N.Wells
Posts: 1836
Joined: Oct. 2005
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| Quote (cryptoguru @ Feb. 17 2015,09:39) | I'm back through popular demand ... can't be bothered to read through all the replies since I last visited. But happy to debate on one topic at a time.
Yeah I never answered all the questions, because some I didn't read as there were so many, and some I didn't have time to answer as the conversation kept changing direction or different angles were being approached by different people at the same time, plus the entropy of contributors who think discussion is simply calling your opponent stupid and rejecting everything they say without basis. So let's take this at a more reasonable pace ... because I do have a life.
So McOgre (Kevin),
When you say I lost the debate about dinos->birds ... is that the one where you said that dinos evolved into birds and I showed that hundreds of birds in their modern form appear in the fossil record alongside dinos in the Cretaceous layer without transitional form? And you got upset because I said that therefore Velociraptor and T-Rex couldn't have been bird ancestors as they have been widely depicted in the media and literature and museums. And you just wanted to talk about Archaeopteryx? (which looks remarkably like a Hoatzin) And they've found another "earlier" Jurassic feathered bird fossil in China (Xiaotingia). Anyway the birds from dinos thing is quite funny, but even assuming evolution is true there's no proof for dino-bird evo at all, it's simply assumed. Arguing from similar morphology is stupid, as we could simply assert that sharks (fish) and dolphins (mammals) are closely related. |
Cretaceous birds are often "modern" (used very loosely) in some aspects while not in others. Xiaotingia is one of a growing number of fossils somewhere in the base of archaeopterygids, dromaeosaurs, and troodontids, and how it gets classified depends on how the groups are defined. However, it isn't a bird in most senses of the word. The most detailed analysis (Senter et al., 2012) found Archaeopteryx to be a avialian, Anchiornis to be a troodontid, and Xiaotingia to be a basal deinonychosaurian, but this is likely to change as new fossils are found of other critters and as definitions shift to accomodate the new information. This complexity happens because all these guys are extremely similar in a great many details. Modern classification of fossils without DNA depends on statistical analysis of similarity using many dozens of characters, because similarity overall matches relatedness in living forms. Classification no longer rests on single characters picked by an expert (the "it has feathers, so it's a bird" school of classification), and absolutely never relied on gross similarities unsupported by similarities in fine details (your "Archaeopteryx looks like a hoatzin" idea). Archaeopteryx does not look very like a hoatzin at all when one looks at its fine details. However, it does match Velociraptor in quite a lot of details.
Descent of birds from theropods is not an "assumption", but a comclusion, based on cladistic analysis of data from comparative anatomy. No dinosaur experts claim that Tyrannosaurus and Velociraptor were direct ancestors of birds: they are close relatives (Tyrannosaurus a bit less so), but T & V are Cretaceous, whereas birds apparently date back to the Jurassic.
Bear in mind that the Cretaceous lasted about 80 million years (longer than the time since the non-avian dinosaurs went extinct), so the presence of primitive members of comparatively modern Neornithine bird groups by the end of the Cretaceous should not be confused with the abundance of Enantiornithine birds without any neornithines earlier in the Cretaceous.
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