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Natural Science Forum / Biology / Paleontology / May 2005Theropodan Dinosaurs
Quick question, Are Theropods saurischian, ornithischian, or something else, and how did modern birds evolve from saurischian ancestors, especially when they are themselves ornithischian? Any information would be appreciated. ~albaradru The mainstream is that most of the dinosaurs can be divide in two groups: 1. saurichians (theropods + sauropodomorphs) and 2. ornitichians (the rest). Alternatively, one can probably group them in 1. Theropoda and 2. Phytodinosauria (sauropodomorphs + ornitichians). It is true that primary dinosaurs were divided on Saurichia ("reptile hip type dinosaurs") and Ornitichia ("avian hip type dinosaurs") mainly for its hip morphology, but then much more diverences were found, the morfology of hip being since only one of characters, but the name of those two clades left unchanged. Later, scientist found out, that there are many different types of hip morphology in dinosaurs, and that avian-like hip morpholgy evolved few times in both groups. Anyway being an saurichian dinosaur doesn't imply having a reptile-like hip. Cheers, Dawid p.s. Sorry for my English. That clears some things up with the morphological part of it, thanks! But I still do not understand the mechanics behind the evolution from let's say, Microraptor, to a chicken. How did an arboreal Dromaeosaurid evolve into a chicken? Thanks, ~albaradru > That clears some things up with the morphological part of it, thanks! > But I still do not understand the mechanics behind the evolution from > let's say, Microraptor, to a chicken. How did an arboreal > Dromaeosaurid evolve into a chicken? Well, Microraptor isn't actually ancestral to chickens, nor is any dromaeosaur. Birds are closely related to dromaeosaurs, but they aren't dromaeosaurs. Still, the common ancestor might have looked something like Microraptor. But what's the problem? What is there about it that you have trouble with? It would seem to me that getting into the air for the first time is the big hurdle, and Microraptor was already there. There are quite a few intermediate fossils on the rough line between something like Microraptor and a chicken. Look at Archaeopteryx, Confuciusornis, Sinornis, and Ichthyornis for a start. >There are quite a few intermediate fossils on the rough line between >something like Microraptor and a chicken. Look at Archaeopteryx, >Confuciusornis, Sinornis, and Ichthyornis for a start. The problem with Archaeopteryx being an intermediate between Microraptor and birds is that it came BEFORE Microraptor, which confuses me to no end. It makes me almost think that Archaeopteryx really wasn't significant in the direct line of birds, and that these arboreal dromaeosarids were, but where exactly is the intermediacy, or have you already told me? (I am not as well read on the last three specimens) Thanks ~albaradru >>There are quite a few intermediate fossils on the rough line between >>something like Microraptor and a chicken. Look at Archaeopteryx, [quoted text clipped - 7 lines] > have you already told me? (I am not as well read on the last three > specimens) Intermediates in morphology (which is what you presumably were asking for) don't have to be intermediate in time. Nobody is claiming any direct line of ancestry and descent for particular fossils. Just evidence of what the ancestors looked like. Archaeopteryx is in fact more closely related to modern birds than Microraptor is. You can think of Microraptor as a "living fossil" during the Cretaceous if it makes you feel any better, a species that preserved some features of the common ancestor of birds and dromaeosaurs. What exactly is your problem with intermediacy? Which features are you having trouble with? >There are quite a few intermediate fossils on the rough line between >something like Microraptor and a chicken. Look at Archaeopteryx, >Confuciusornis, Sinornis, and Ichthyornis for a start. The problem with Archaeopteryx being an intermediate between Microraptor and birds is that it came BEFORE Microraptor, which confuses me to no end. It makes me almost think that Archaeopteryx really wasn't significant in the direct line of birds, and that these arboreal dromaeosarids were, but where exactly is the intermediacy, or have you already told me? (I am not as well read on the last three specimens) Thanks ~albaradru > Quick question, > > Are Theropods saurischian, ornithischian, or something else, and how > did modern birds evolve from saurischian ancestors, especially when > they are themselves ornithischian? Any information would be > appreciated. Didn't you ask this exact question some time ago, and get answers? Theropods are saurischians. Birds are saurischians too. The name "ornithischian" is not significant for phylogeny. Nor is "ornithopod", in case you run into that one too. Basilosaurus is a whale, not a lizard. And so on. |
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