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# Dinosaurs/Talk

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Therepoda are a subgroup of Saurischia, so that change is not correct --Arco Scheepen

That seems to be the current best guess, but there is not a huge amount of evidence and it is possible opinions might change. In any case Therepoda are sufficiently different to the other Saurischia that i thought they needed a mention on the front dinosaur page. I am happy with the arrangement there now.

245M years ago is *way* too early.

Permian ended 230M years ago, and there were certainly no dinosaurs at that time. And they didn't appear until middle Triassic.

So correct number is most probably somewhere between 220M and 210M years ago.

What about reptiles relationship to dinosaurs? --rmhermen

Interesting question. Does it belong here or in reptiles? Of the surviving reptiles they should be closest to crocodiles, but of course they are even closer to birds. The statement about thecodonts on the page is interesting. My understanding is that thecodonts are supposed to be the common ancestor of dinosaurs birds and crocodiles. Some experts now regard thecodonts as a very dubious grouping, with some of the supposed thecodonts now believed to be not closely related to the others, and much disagreement about what actually are and are not thecodonts. What is the current concensus about this?

Current concensus is that the thecodonts are simply the basal Archosaurs, and so form a group paraphyletic to the dinosaurs-and-birds, pterosaurs, and crocodylians, in the same way that the reptiles are simply the basal amniotes and form a group paraphyletic to birds and mammals. Whether or not you accept either as a valid grouping depends on whether you restrict groups to monophyly. There is an increasing tendency to do this, but I don't think it's near universal yet.

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Last edited August 12, 2001 9:57 am (diff)
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