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*To*: <Philidor11@aol.com>*Subject*: Re: EARLY EVOLUTION OF 'BIRDS'*From*: "John V Jackson" <jjackson@interalpha.co.uk>*Date*: Fri, 6 Nov 1998 17:07:17 -0000*Cc*: <dinosaur@usc.edu>*Reply-to*: jjackson@interalpha.co.uk*Sender*: owner-dinosaur@usc.edu

--Original Message-- From: Philidor11@aol.com Date: 06 November 1998 05:01 >>'Say the ratio of maniraptorans living in the K to those living in the J was >A:B; >Say the ratio of the chances of an indiv living in the K ever being found to >that of one in the J is C:D; >The ratio of the chances of a maniraptoran we have found coming from the K >to from the J is (A/B)*(C/D). >The probability of any maniraptoran we have found coming from the K is 1/(1 >+ 1/ ((A/B) * (C/D)) ). > >The chance of N maniraptoran fossils all appearing after Archaeopteryx is >this expression raised to the power of N.' >> >It'll take me a while to untangle the parentheses and confirm what I think >you're saying. >However, remember that small proportions of small samples have huge ranges and >that any detail of the group you're looking at has approximately no validity >at all. Small samples are less statistically significant, but according to that well known statistical principle, "Many a mickle macks a muckle". You can add up small samples to make any degree of confidence required, so long as you have enough small samples. The "Law of Averages" refers to this kind of situation. (The phrase has passed into idiomatic folklore, but it's still proper stats.). Of course, the fact that *any* large and statistically significant sample could be notionally fractured into smaller segments each of no useful significance, shows that having small stat. insignificant segments on its own says nothing about the significance of the whole. >Awhile ago I was analyzing the results of a 1,000 response telephone sample >which found a less than 1% rate of probable pathological gamblers. Guess how >valid the demographics of that subsample are. To approach useful numbers >you'd need 6 or 7 times as many samples (at about $70 apiece) and >stratification (does not mean under rocks). That's because the original 1000 was not core data you were interested in, only a population containing it. However, fossils identified as members of the maniraptora have a likelihood considerably greater than 1% of being genuine. >Aside from this issue, remember that fossils are found not only where they can >be preserved but also where they can be looked for comparatively easily. >If you wanted to be sure of getting a valid sample of a world population you'd >have to look in a lot of randomly selected places. You might end up in my >backyard. My term C:D is defined to include not just the relative likelihood of fossils existing, but also of being found. >In re birds, are you satisfied that the gap between archaeopteryx and the next >'bird' is short enough to disprove the assertion that archaeopteryx was an >anticipation of birds, but not necessarily even a close relative of the bird >ancestor? But your position requires that a gap many times that size *before* Archae was no problem. A gap of five million years tops with no small fossil of a particular type found? Look at the Gasosaurus gap: until ten years ago a gap existed of 25mys with no theropod of any kind, even large ones. As for proofs, no-one is ever going to positively prove any family tree in vertebrate palaeontology. It is all a question of a feel for likelihood, of 'the general feeling by the community'. (Positive evidence *is* useful for this - positive evidence is used in legal cases (in practice, even in criminal cases), and by animals, because absolute certainty is not required - which in real life is generally the situation.) >Seems like this type analysis has rules for validating hypotheses I'm not sure >I understand. Well, of course I'm up against the operating limit myself in this as far as statistics goes; however, if you could find six proper statisticians, who were equally au fait with these dinos, how many opinions would they have amongst them?! My position is "We ask not for proof, only for recognition. Though the 'All from Archae' idea seems to us (well me, anyway) to be preferable, it surely requires at least equal acceptance as a hypothesis until a lot more consideration has been given to the issue". Taking rough but conservative data from TMKeeseys excellent website: http://www.gl.umbc.edu/~tkeese1/dinosaur/genera.htm , totals of individual specimens found so far for all the subgroups can be estimated as: Tyrannosauroidea: 70 Troodonts: 28 Ornithomimos: 24 Oviraptors: 20 (assuming 5 _O_ sp.) Protarchaeopt+Caudipt.: 4+ Deinonychs: 25 Total: 171 So, 171 (at the very least) Arctometatarsalia + Maniraptora have been found after _Archaeopteryx_ and none before (if we discount the Segno J Jaw). This is a lot more than I thought, and is going to give some strong opposition to any hypothesis claiming any (Arctos/Mani's) occured before Archae. The 170th root of 0.001 is just over 0.96 . This means that if you toss a coin 170 times and it comes up heads every time, even if the null hypothesis is that the coin is weighted to land heads 96% of the time, the result is *still* so unlikely that you have to discard that idea in favour of the notion that it has heads on both sides, ie that it doesn't have a tails... which in our terms means that even if there are 24 times as many Arctos/Mani's to be found in the Cretaceous as in the Jurassic, there is only a 1000:1 chance of this evidence appearing. You may say "Well, there *were* 24 x as many - even 100 x - even 10,000 times. It was just at the start of the group's evolution". The trouble is, the further along that line the argument is taken, the more my point is made. That looks like 'it', chaps. Anyone mentioning the idea that any Arctos/Mani's preceded Archae without also mentioning the possibility that Archae was the first is really being a long way short of 'scientifically' . . . 'fair'. So much for "none pre-Archae". But Archae was one. If we are looking for something that *gave rise* to such an illustrious line, wouldn't we be looking for something rather unusual? Might not Archae be a good candidate? Perhaps as an idea that deserves better coverage than a total blackout? JJ

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