Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!utgpu!water!watnot!watmath!clyde!rutgers!mit-eddie!genrad!decvax!cca!g-rh From: g-rh@cca.UUCP Newsgroups: talk.origins,sci.bio Subject: Re: Dinosaur Heresies Message-ID: <14186@cca.CCA.COM> Date: Sat, 21-Mar-87 09:45:21 EST Article-I.D.: cca.14186 Posted: Sat Mar 21 09:45:21 1987 Date-Received: Sun, 22-Mar-87 21:33:48 EST References: <14011@cca.CCA.COM> <629@bcsaic.UUCP> <1223@husc2.UUCP> Reply-To: g-rh@CCA.UUCP (Richard Harter) Organization: Computer Corp. of America, Cambridge, MA Lines: 36 Xref: utgpu talk.origins:441 sci.bio:160 Summary: Small is relative In article <1223@husc2.UUCP> chiaraviglio@husc2.UUCP (lucius) writes: > > Incidentally, are you sure we haven't actually found some small >dinosaurs? I seem to remember reading of ones about the size of chickens. > You are correct. However that is the minimum size for dinosaurs (not counting baby dinosaurs). As animals go, chickens are fairly large. (We tend to be anthropomorphic in our opinions about large and small.) There are mammals and birds which are much smaller than chickens, e.g. mice and hummingbirds. Reptiles also span the scale size from small to large. The point is that the minimum size for dinosaurs was much larger than the minimum size for other vertebrates. At first sight this makes sense if we grant (a) dinosaurs were warm-blooded, and (b) they did not have thermal protection, e.g. hair or feathers. Small warm blooded animals lose heat faster than large ones which implies a lower limit on size. Reptiles, which can be small and are not thermally protected, get by because they let their body tempature drop. One might argue that in a tropical climate with an even temperature thermal protection is not needed. I am not prepared to evaluate this argument, but it seems dubious. Even tropical climates have major temperature variations (cool nights, rainy seasons). The size question is relevant for Bakker's arguments. Bakker argues that dinosaurs were warm blooded. In my opinion, the case for this is very good at this point (at least for the carnivores and for the hadrosaurs). He also argues that the dinosaurs were one group rather than two (the conventional view) and that both pterosaurs and birds were offshoots of the dinosaurs. Birds are indubitably thermally protected, and there is strong evidence that pterosaurs had fur (i.e. were also thermally protected.) So, on Bakkers view, dinosaurs can and did evolve thermal protection. So, again, why weren't there any small dinosaurs? -- Richard Harter, SMDS Inc. [Disclaimers not permitted by company policy.]