palmer@cit-vax.Caltech.Edu (David Palmer) (04/19/86)
Organization : California Institute of Technology Keywords: dinosaurs, bipedalism, hunting, escape One advantage that humans have, which is primarily due to their bipedalism, is the ability to walk and run at a wide variety of gaits. A hunting human can eventually catch up with just about any animal, (assuming that it doesn't hide or burrow) just by walking at a pace that the prey cannot use efficiently. Of course, this doesn't help if you are being chased by a cheetah, but if you are chasing an impala, you can eventually tire it out and catch up with it David Palmer
friesen@psivax.UUCP (Stanley Friesen) (04/21/86)
In article <32@sphinx.UChicago.UUCP> Beth Christy writes: >[] > > Humans have no natural enemies and hence do not need >the speed advantage for survival. I'm under the impression (although I >could, of course, be wrong) that there were no species which preyed on >the bipedal dinosaurs either (or if there were, escape was not the >dinosaurs' defense). > Much of this is simply not true. Many herbivorous dinosaurs of the group known as Ornithopods are bipedal and lack any defense except running. Examples include such famous forms as Camptosaurus and Hypselophodon. And while modern Humans have no natural enemies, the earliest Hominids *did*, and they were already bipedal. Our current lack of predators is due to our success, not the other way around. -- Sarima (Stanley Friesen) UUCP: {ttidca|ihnp4|sdcrdcf|quad1|nrcvax|bellcore|logico}!psivax!friesen ARPA: ttidca!psivax!friesen@rand-unix.arpa
friesen@psivax.UUCP (Stanley Friesen) (04/21/86)
In article <204@spar.UUCP> ellis@spar.UUCP (Michael Ellis) writes: >>>Evolution is undirected: ie. it has no long-term goals. > > Survival? Existence? > Those are not really "goals" they are more like mechanisms. > > Few, if any, animals are as DANGEROUS as humans skilled in the use a > club or projectile -- witness the accuracy and power of a typical baseball > batter or pitcher. Or as utterly vindictive as a tribe of Humans one of whose members has been killed. > Chimpanzees, in fact, sometimes use sticks in self-defense. The > effectiveness of such tactics seems to be quite limited for knuckle > walkers. Some argue that our bipedalism evolved simultaneously as our > increasing reliance on balance transformed what began as an occasional > defense mode into a devastating form of attack. > An additional point. By this argument Human bipedalism becomes a very effective adaption to *carnivory*! In fact it seems to have appeared about the time our ancestors shifted from minimal utilization of meat as a dietary supplement(as in Chimpanzees) to deliberate hunting for meat as a major portion of the diet(Australopithecus). -- Sarima (Stanley Friesen) UUCP: {ttidca|ihnp4|sdcrdcf|quad1|nrcvax|bellcore|logico}!psivax!friesen ARPA: ttidca!psivax!friesen@rand-unix.arpa
friesen@psivax.UUCP (Stanley Friesen) (04/21/86)
In article <2529@jhunix.UUCP> (Thomas Richard Holtz) writes: > >Basically, the best palaeontological explaination for why dinosaurs were >bipedal and most mammals aren't boils down to: > > Why were most dinosaurs bipedal? > Because they evolved from bipeds (the thecodonts). > > Why are so few mammals bipeds? > Because they evolved from quadropeds (the therapsids). > >I know it's not a very exciting answer, but don't complain to me. >Complain to Mother Nature; she made the rules. :-) > Yes, quite correct, at least as far as we can tell with current data. However this only moves the question back one step. Why were thecodonts bepedal and therapsids quadrupeds? Actually I think this may have a more "satisfying" answer. That is my studies suggest that there were adpative reasons for the shift to bipedalism among thecodonts. But I will refrain from saying what I think until other people have had a chance to speak. -- Sarima (Stanley Friesen) UUCP: {ttidca|ihnp4|sdcrdcf|quad1|nrcvax|bellcore|logico}!psivax!friesen ARPA: ttidca!psivax!friesen@rand-unix.arpa
beth@sphinx.UChicago.UUCP (JB) (04/22/86)
[If God had wanted us to go around naked, we'd have been BORN that way.] In article <1109@psivax.UUCP> friesen@psivax.UUCP (Stanley Friesen) writes: >In article <32@sphinx.UChicago.UUCP> Beth Christy writes: >>[] >> >> Humans have no natural enemies and hence do not need >>the speed advantage for survival. I'm under the impression (although I >>could, of course, be wrong) that there were no species which preyed on >>the bipedal dinosaurs either (or if there were, escape was not the >>dinosaurs' defense). >> > Much of this is simply not true. Many herbivorous dinosaurs >of the group known as Ornithopods are bipedal and lack any defense >except running. Examples include such famous forms as Camptosaurus and >Hypselophodon. And while modern Humans have no natural enemies, the >earliest Hominids *did*, and they were already bipedal. Our current >lack of predators is due to our success, not the other way around. My mistake - sorry for the misinformation. Just out of curiosity, what creatures preyed on early Hominids, and how do we know? Same question(s) for Ornithopods. (Sorry for my ignorance here - I'm just a casual reader.) -- --JB ((Just) Beth Christy, U. of Chicago, ..!ihnp4!gargoyle!sphinx!beth) All we learn from history is that we don't learn anything from history.
friesen@psivax.UUCP (Stanley Friesen) (04/23/86)
In article <71@sphinx.UChicago.UUCP> beth@sphinx.UUCP (JB) writes: > >My mistake - sorry for the misinformation. Just out of curiosity, >what creatures preyed on early Hominids, and how do we know? Lions, Hyenas, and Sabre-toothed cats. We know because we have found a number of early hominid bones with tooth-marks on them which match these species. One rather remarkable Autralopithecus skull has four holes in it space just right for the canines of some known carnivore(a Sabre-tooth I think). Apparently the cat had dragged the Ape-man by it head to its lair to eat it! > Same >question(s) for Ornithopods. (Sorry for my ignorance here - I'm >just a casual reader.) > With the Ornithopods it depends on *which* ones and when. Among the predators on these forms were such animals as Tyrannosaurus, and Deinonychus. It is also possible that Allosaurus preyed on some members of the group. How do we know? Well, tooth-marked bones are known for dinosaurs too. Also, at least some Ornithopods showed flock nesting behavior(some mass nest sites have been preserved, there was a Scientific American article on this last year). This kind of nesting behavior in living animals is usually a form of defense against predators. Then of course there is the evidence of the speed adaptions, such as long legs, weight supported on the toes, and light build, in certain small ornithopods(Dryosaurus, Hypselophodon &c), again usually associated with escape from predation in living *herbivires*. It is also possible that the heavy, spiked thumb of Iguanodon was a defense mechanism against predation. -- Sarima (Stanley Friesen) UUCP: {ttidca|ihnp4|sdcrdcf|quad1|nrcvax|bellcore|logico}!psivax!friesen ARPA: ttidca!psivax!friesen@rand-unix.arpa
ins_atrh@jhunix.UUCP (Thomas Richard Holtz) (04/28/86)
In article <71@sphinx.UChicago.UUCP> beth@sphinx.UUCP (JB) writes: >My mistake - sorry for the misinformation. Just out of curiosity, >what creatures preyed on early Hominids, and how do we know? Same >question(s) for Ornithopods. (Sorry for my ignorance here - I'm >just a casual reader.) >-- >--JB ((Just) Beth Christy, U. of Chicago, ..!ihnp4!gargoyle!sphinx!beth) > > All we learn from history is that we don't learn anything from history. As with almost all of paleontology, we don't *KNOW* (as in 100% certain) anything. However, we can make pretty good guesses: in the Holocene (that's "now" for those of you who aren't into geological time) the big cats, wolves, and similar types prey upon primates (including the occasional humans). In the fossil record of the Pliocene and Pleistocene we find the remains of big cats, wolves, other hunters, and hominids. By comparative ecology (and using the tooth marks found on a few hominids) we can make a very good hypothesis that these creatures ate our ances... er (better make this safe for the Net, Tom :-)) that is, the hominids. The ornithopods were most certainly hunted by the carnosaurs, the family of carnivorous dinosaurs that included the tyrannosaurs, megalosaurs, and similar hunters. We have found many tooth- and claw-marks on ornithopod bones, and there are even tracks of ornithopods being chased by theropods (trivial point: the classic record of a chase scene, from Texas, I believe, does not have an ornithopod starring as the prey, but rather a sauropod [one of the long necked, heavy dinosaurs like "_Brontosaurus_"). Thomas R. Holtz, Jr. JHU Department of Earth and Planetary Sciences "If history repeats itself, why is there so much of it?"
michaelm@bcsaic.UUCP (michael maxwell) (04/28/86)
In article <397@cit-vax.Caltech.Edu> palmer@cit-vax.UUCP (David Palmer) writes: >A hunting human can eventually catch up with just about any animal, >(assuming that it doesn't hide or burrow) just by walking at a pace >that the prey cannot use efficiently. Of course, this doesn't help >if you are being chased by a cheetah, but if you are chasing an impala, >you can eventually tire it out and catch up with it I'd heard this before (in Analog, a science fiction/ science fact magazine), but I had/ have trouble believing it. Has it ever *really* been "proven"? What's the original source? -- Mike Maxwell Boeing Artificial Intelligence Center ...uw-beaver!uw-june!bcsaic!michaelm
g-rh@cca.UUCP (Richard Harter) (05/03/86)
In article <> michaelm@bcsaic.UUCP (michael maxwell) writes: >In article <397@cit-vax.Caltech.Edu> palmer@cit-vax.UUCP (David Palmer) writes: >>A hunting human can eventually catch up with just about any animal, >>(assuming that it doesn't hide or burrow) just by walking at a pace >>that the prey cannot use efficiently. Of course, this doesn't help >>if you are being chased by a cheetah, but if you are chasing an impala, >>you can eventually tire it out and catch up with it > >I'd heard this before (in Analog, a science fiction/ science fact magazine), >but I had/ have trouble believing it. Has it ever *really* been "proven"? >What's the original source? I don't have sources at hand, but it's probably true. Apaches used to catch horses by walking them down. It was an all day proposition, but the Apache could go all day at an average pace that a grass grazing horse cannot maintain. The high speed predators (cheetah, impala, et. al.) can run at impressive speeds, but they can't maintain them for very long. My recollection is that the cheetah can hit 70 mph but can only maintain that speed for a few hundred feet. Richard Harter, SMDS Inc.
friesen@psivax.UUCP (05/15/86)
In article <7648@cca.UUCP> g-rh@cca.UUCP (Richard Harter) writes: > > The high speed predators (cheetah, impala, et. al.) >can run at impressive speeds, but they can't maintain them for very long. >My recollection is that the cheetah can hit 70 mph but can only maintain >that speed for a few hundred feet. > Quite correct. In fact, if the Cheetah fails to catch its prey it is down and out for many hours "catching its breath" before it can try again!(reference - last month's Scientific American). -- Sarima (Stanley Friesen) UUCP: {ttidca|ihnp4|sdcrdcf|quad1|nrcvax|bellcore|logico}!psivax!friesen ARPA: ??