g-rh@cca.UUCP (03/16/87)
Bakker, the enfant terrible of paleontology, has finally written a book called "Dinosaur Heresies" which I can heartily recommend. Bakker is the man who argued and publicized the view that the dinosaurs were warm blooded. The book goes over a lot of interesting ideas with a lot of supporting detail and argument. Among the topics are: (a) A lot of detail and discussion on the argument that the dinosaurs were warm blooded. These include the Haversian canal arguments, the predator/prey ratio arguments, and the arguments from physiological structure that dinosaurs must have had high energy metabolisms. He does not discuss the high growth rate of the young argument. (It is now known that Hadrosaurs grew very fast -- 9 feet in the first year. Fast growth rate in the young is characteristic of warm blooded animals and not of cold blooded animals.) He also debunks the theory that dinosaurs were homeothermic, i.e. that they depended on the thermal inertia of large body mass to preserve a high internal temperature. (b) He discusses the arguments for classifying dinosaurs as a class rather than as two subclasses subordinate to reptilia. He also discusses the arguments (which he supports) for classifying birds (Aves) as a subclass of the dinosaurs. (c) He discusses the general superiority of gizzards and the probability that the long necked high grazers (brontosaurus, et al) had gizzards. (The great advantage of the gizzard is that mechanical reduction and enzymatic softening of food can be done concurrently without interfering with the consumption of food.) He argues that the relatively small heads of brontosaurs (a term he uses generically for long necked, four legged plant grazers, rather than just for Apatosaurus) did not bar them from being warm blooded. (d) He convincingly argues that dinosaurs were land animals rather than swamp animals, and that the traditional picture of plant eating dinosaurs living in swamps and eating soft water plants is seriously in error. (e) He is a skeptic about the extraterrestrial hypotheses for the great dying. He is inclined to place the onus on ecological collapse due to the joining of the continents at the end of the Cretaceous. [My opinion is that Bakker is generally right, but that the coup-de-grace for the dinosaurs was indeed extraterrestrial.] (f) He discusses the general argument that the dinosaurs were, on the whole, more successful than the mammals. He argues strongly for their physiological superiority. And, of course, there is the blunt fact that for 150 million years the dinosaurs preempted all large land niches and displaced the therapsids (protomammals) with ease. I can't do justice to the book here; go get a copy and read it. Some obvious questions that occurred to me are: (1) If the birds are modern dinosaurs and the dinosaurs metabolism was superior to that of the mammals, then we should expect that the birds today are metabolicly more effecient than mammals. Is this true? (2) One of the striking things about dinosaurs is that they were large -- there were no very small dinosaurs (and some got very large indeed.) Why? Lack of thermal insulation is the obvious answer. However thermal protection was evolved at least twice (fur for the pterosaurs and feathers for the birds). It is also notworthy that the branches that developed thermal protection did occupy small body niches and took to the air. (3) Why didn't any of the dinosaurs (except birds) survive the great dying. In previous great dyings the dinosaurs came back nicely; moreover the old forms did not go totally extinct. For example, brontosaurus and kindred were typical of the Jurassic and went extinct at the Jurassic-Creataceous die out; however the group did not die out, even though they lost their pre-eminance; Alamosaurus lived in the Cretaceous. -- Richard Harter, SMDS Inc. [Disclaimers not permitted by company policy.]
michaelm@bcsaic.UUCP (Michael Maxwell) (03/19/87)
In article <14011@cca.CCA.COM> g-rh@cca.UUCP (Richard Harter) writes: >[mini-review of Bakker "Dinosaur Heresies"] >... (2) One of the striking >things about dinosaurs is that they were large -- there were no very >small dinosaurs (and some got very large indeed.) Why? I'm curious--how do we know there weren't any tiny dinosaurs, but their bones just haven't survived in sufficient quantities for us to find and identify? I suppose the answer is that bones of tiny animals--mammals (and birds?) have survived, and we have found them. So my question is perhaps better worded, how easy is it to distinguish mammal bones from tiny dinosaur bones? How do we know that we haven't found fossils of tiny dinosaurs, but just incorrectly identified them as mammals (or birds)? If I recall correctly, most of the Mesozoic mammal bones that have been found are jaws and teeth, and I guess the dinosaur teeth pattern is quite different from the mammalian pattern. Is this correct? Has anyone tried to estimate what percentage of the species of dinosaurs that were extant during the Mesozoic have been found? This is related to the question of the preceding paragraph--if we've found fossils of 1% of the dinosaur species that existed, then it would seem quite possible that we might have just missed the small ones. Clearly we cannot know what percent of the unknown number number of species that existed N is (where N is the number of species we've found), but is it possible to estimate what that unknown number is? -- Mike Maxwell Boeing Advanced Technology Center arpa: michaelm@boeing.com uucp: uw-beaver!uw-june!bcsaic!michaelm
chiaraviglio@husc2.UUCP (03/21/87)
These answers are from old memories, so caveat emptor. In article <629@bcsaic.UUCP>, michaelm@bcsaic.UUCP (Michael Maxwell) writes: > In article <14011@cca.CCA.COM> g-rh@cca.UUCP (Richard Harter) writes: > >[mini-review of Bakker "Dinosaur Heresies"] > >... (2) One of the striking > >things about dinosaurs is that they were large -- there were no very > >small dinosaurs (and some got very large indeed.) Why? > > I'm curious--how do we know there weren't any tiny dinosaurs, but their bones > just haven't survived in sufficient quantities for us to find and identify? > I suppose the answer is that bones of tiny animals--mammals (and birds?) have > survived, and we have found them. This sounds right. > So my question is perhaps better worded, > how easy is it to distinguish mammal bones from tiny dinosaur bones? How do > we know that we haven't found fossils of tiny dinosaurs, but just incorrectly > identified them as mammals (or birds)? If I recall correctly, most of the > Mesozoic mammal bones that have been found are jaws and teeth, and I guess > the dinosaur teeth pattern is quite different from the mammalian pattern. > Is this correct? Yes. Also, if I recall correctly, the other bones are different as well (mammal and reptile bones in general are different -- skulls and pelvises come to mind). > Has anyone tried to estimate what percentage of the species of dinosaurs that > were extant during the Mesozoic have been found? This is related to the > question of the preceding paragraph--if we've found fossils of 1% of the > dinosaur species that existed, then it would seem quite possible that we might > have just missed the small ones. Clearly we cannot know what percent of the > unknown number number of species that existed N is (where N is the number of > species we've found), but is it possible to estimate what that unknown number > is? I don't know what the number is, but it is possible to estimate it by looking at the rate of discovery of new fossil types -- the decline (after adjusting for rate of search) gives a hint as to how much is left. Things that could mess this up include undiscovered jackpot formations and poor recording of search missions. Incidentally, are you sure we haven't actually found some small dinosaurs? I seem to remember reading of ones about the size of chickens. -- -- Lucius Chiaraviglio lucius@tardis.harvard.edu seismo!tardis.harvard.edu!lucius Please do not mail replies to me on husc2 (disk quota problems, and mail out of this system is unreliable). Please send only to the address given above.
g-rh@cca.UUCP (03/21/87)
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.]
buyno@voder.UUCP (03/23/87)
Kennneth Hsu in his book, the Great Dying, states that dinosaurs down to chicken size existed. That's fairly small. He also states something to the effect there were none (or none have been found) that were the size of things like mice. Mammals of that size are preserved from the same time, so there is fair confidence that such dinosaurs did not exist. Of course, something like very soft bone in the tiny dinos could always be postulated, but probably never proved.
g-rh@cca.UUCP (03/25/87)
In article <2877@voder.UUCP> buyno@voder.UUCP (Matthew Buynoski) writes: > > Kennneth Hsu in his book, the Great Dying, states that dinosaurs >down to chicken size existed. That's fairly small. He also states something >to the effect there were none (or none have been found) that were the size >of things like mice. Mammals of that size are preserved from the same time, >so there is fair confidence that such dinosaurs did not exist. Of course, >something like very soft bone in the tiny dinos could always be postulated, >but probably never proved. Quite so. Although, to be accurate, small (mouse size) adult dinosaurs have not been found and presumably did not exist. Very small baby dinosaurs have been found. I don't have a reference at hand but I believe the low end size record is held by a baby parrot dinosaur which was small enough to sit on a quarter. What is more, its teeth already showed signs of wear. Does kind of make you wonder about the notion that the dinosaur size limit was dictated by thermal considerations, doesn't it. Incidentally, could you post a review of Hsu's book. I haven't seen it, and it sounds like it is worth reading. -- Richard Harter, SMDS Inc. [Disclaimers not permitted by company policy.]
gagen@bgsuvax.UUCP (03/25/87)
In article <629@bcsaic.UUCP>, michaelm@bcsaic.UUCP (Michael Maxwell) writes: > In article <14011@cca.CCA.COM> g-rh@cca.UUCP (Richard Harter) writes: > >[mini-review of Bakker "Dinosaur Heresies"] > >... (2) One of the striking > >things about dinosaurs is that they were large -- there were no very > >small dinosaurs (and some got very large indeed.) Why? > > how easy is it to distinguish mammal bones from tiny dinosaur bones? How do > we know that we haven't found fossils of tiny dinosaurs, but just incorrectly > identified them as mammals (or birds)? It is currently thought that there were some tiny dinosaurs. One current hypothesis proposes that these dinosaurs are the ancestors of modern birds. Mammallian bones are more dense then either dinosaur bird bones. __________________________________________________________________ Kathi Gagen gagen@bgsuvax Dept of Biological Sciences Bowling Green State Univ. Bowling Green, Ohio