The main bone (:)) of contention here is wether the dinosaur extinction was very rapid (ca

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The main bone (:-)) of contention here is wether the dinosaur extinction was very rapid (catastrophic) and very numerous (mass extinction) or very slow (gradual) and very few (normal extinction) or something in between. In other words it is a question of *Rate* and *Magnitude*. On the subject of Magnitude, a recent study[1] looked at 111 vertebrate species of undisputed latest Cretaceous age in Montanna and tried to find them in overlying localities of undisputed Early Paleocene (Tertiary) age. Using species-level taxonomy involves complicating factors:- 1) species disappear locally but survive elsewhere - local extirpations, not extinction. 2) rare species (eg a top preditor in an ecosystem) have something like a 5 times higher disappearence rate - artifact caused by rarity. 3) pseudoextinctions - where species evolve into new species (eg mammals, if this process is not considered when looking at the mammals, it appears that the mammals underwent a 95% extinction at the K/T boundary - which is highly unlikely). Allowing for these factors, this study found that the vertebrate extinction rate across the K/T boundary was between 35%-47%, not approx. 75% as has been stated previously. Significant yes, but not quite up the the great mass extinctions of the past. As to the question of rate, a recent study (and the one to which you may have been refering to Mickey) was by Sheehan et al[2]. This study looked at diversity in 8 families of dinosaurs in three sequential sampling levels in the uppermost Cretaceous (Maastrichtian) Hell Creek Formation in eastern Montana. Acccording to the study, all 8 families made it to the K/T boundary. The study concluded that there was no discernable change in the relative abundance of individuals assignable to a family and therefore, "data from the Hell Creek are compatible with abrupt extinction scenarios"([2] p 838). However, there are two main problems with this study. One was that the study was done via surface collecting *only* and in areas which were *thought* not to have been collected for 10 years - one of the criteria for choosing a site was the absence of plaster jacket material from other digs. The second and more important problem was that the study was looking at *ecological* diversity, not taxanomic diversity and as a result the taxanomic level was too crude to deliniate taxanomic diversity and subsequent changes in it. The study was at the Family level and as a result, up to 43% of genera could become extinct without causing one family to disappear. Increases in numbers of surviving genera may make up for the loss of specific genera but nevertheless, *taxamonic* diversity would be decreased. The next question is "Does taxanomic diversity decrease in the Maastrichtian?" and the answer is - Yes. Emphasising a more global approach and at a generic (not familial) level, another recent study[3] has highlighted both a decrease in taxanomic diversity in the Maastrichtian and a bias imparted by North American studies on this interval. This study found that of 73 Maastrichtian dinosaur genera, only 20 are known from the late Maastrichtian and of these 20, 14 are known only from North America. Four hundred specimens of articulated Masstrichtian dinosaurs were identified, of these only 100 are from the late Maas. and of these 95% are from North America. Thus within the Masstrichtian "trends toward reduction in diversity are evident". The record of this interval is biased not only toward North Americal localities, but also toward overrepresentation by North American genera and specimens. North America in the Maastrichtian probably represents the last bastion of dinosaur rule as dinosaur numbers dwindled elsewhere in the world. Thus a meteorite impact theory must explain how an impact could retrogresively affect dinosaur numbers up to 1 million years before it hit - if it is to be considered as the 'prime suspect'. IMHO it may well have toasted a few dinosaurs, but they were already on the slippery slope to the big X. Another problem presents itself. Since the impact ejecta is taken as demarking the K/T boundary, how come (to my knowledge) no dinosaur bones have ever been found in this layer. Since it must have been layed down fairly rapidly, and there must have been a 'great dying' at the time (if it was the main cause) where are the bones surrounded by the ejecta layer - or if it was fairly instantaneous, where are the bones lying above it. Where it is found (I think) there are bones below it, but no bones in it or obviously, above it. [1] Archibald, J. D. & Bryant, L. (1990) Differential Cretaceous/Tertiary extinctions of nonmarine vertebrates; evidence from northeastern Montanna. _Geological Society of America Special Paper_ 247: 549-562. [2] Sheean, P. M. et. al. (1991) Sudden extinction of the dinosaurs: latest Cretaceous, upper Great Plains, U.S.A. _Science_ 254: 835-839. [3] Dodson, P. M. (1991) Maastrichtian dinosaurs. _Geological Society of America, Abstract with Programs_ 23(4): A184-185. See also:- Archibald, J. D. (1992) Dinosaur extinction: how much and how fast? _Journal of Vertebrate Paleontology_ 12 (2): 263-264. > Mickey Rowe (rowe@pender.ee.upenn.edu) Shouldn't that be Mickey Rowe DP ? :-) Chris ================================oOo==================================== Christopher Nedin -- -- Dept. Geology, University of Adelaide, South Australia / \ / cnedin@tellus.geology.adelaide.edu.au / \ / "How can Nedin be trusted" -- -- C Wieland Director, Institute of Creation Research QLD. Australia ================================o0o====================================

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