Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!seismo!cmcl2!yale!husc6!mit-eddie!genrad!decvax!mcnc!duke!evs From: evs@duke.UUCP (Ed Simpson) Newsgroups: sci.bio Subject: Re: evolution, parthogenesis, ad nauseum. Message-ID: <9014@duke.duke.UUCP> Date: Tue, 30-Dec-86 22:10:43 EST Article-I.D.: duke.9014 Posted: Tue Dec 30 22:10:43 1986 Date-Received: Wed, 31-Dec-86 04:01:17 EST References: <7436@utzoo.UUCP> <531@cdx39.UUCP> Reply-To: evs@duke.UUCP (Ed Simpson) Organization: Duke University Medical Center, Durham, NC Lines: 61 In article <531@cdx39.UUCP> jc@cdx39.UUCP (John Chambers) writes: >Hmmm...I thought that birds had been classified as a suborder of >the dinosaurs, not a class. Anyone out there know what the official >taxonomy really is these days? Like, draw me a cladogram, perhaps, >and label the 'class' and 'order' levels. In the most commonly accepted classificatory schemes Dinosuars belong to the class Reptilia and birds comprise their own class, Aves. The phylogeny is as follows: Phylum Chordata -> Subphylum Vertebrata -> Class Aves. Birds arose from the group of dinosuars called saurischians (meaning "lizard- hipped", which is kind of strange since the other major group of dinosaurs were ornithiscians, meaning "bird-hipped"). Birds are so different from living reptiles that it warrants placing them in a class separate from reptiles. I think the dispute is whether dinosaurs should be placed in the class Reptilia. Both birds and mammals have a four chambered heart and are endothermic (traits arrived at independently) and there is some evidence that dinosaurs were also endothermic. Does anybody know anything about the structure of the dinosaur heart? Dinosaurs may have been sufficiently different from living reptiles to justify placing them in their own class, perhaps including birds in this separate dinosaur class. However their are some people who think birds should be placed in the class Reptilia as surviving dinosaurs. A common phylogenetic tree for reptiles and their descendents is as follows: Turtles Tuatara Lizards Snakes Crocs Birds Mammals | | | | | | | | | |__________| | | | | | | ______________| | | | | | | | | | | | | | | Plesiosaurs | | | | Pterosaurs | | | | | | | | | | | | | | | | | | | | | | | | Ornithiscian Saurischian | | | | | \ | Dinosaurs Dinosaurs | | | | \ \ | | / | | | -------\ \ \ | / | | | \ \ \ | / Ichthyosaurs | | | \ \ \ | / / | | |______________ \ \ \____ | / / | | \ \ \ | | | / | | \ \ ------Thecodonts / | |______________________ \ \ / / | \ \ \ / / Therapsids \ \ \ ____/ / / \ \ | | / / \ | | | __________/ / | | | | | / Stem Reptiles-------------------------/ ------------------------------------------------------------------------------- {decvax, seismo}!mcnc!duke!evs Ed Simpson, P.O.Box 3140, Duke Univ. Medical Center, Durham, NC 27710 -- {decvax, seismo}!mcnc!duke!evs Ed Simpson, P.O.Box 3140, Duke Univ. Medical Center, Durham, NC 27710