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Sorry Tom, but I can't let this sort of disinformation go by unchallenged.
>
>No one is saying that the comet/meteor itself killed off the dinosaurs and
>~75% of thier contemporaries.
Not true. That is exactly what many people are saying and have been saying
for some time...
Alvarez, L. W., Alvarez, F., Asaro, F. & Michel, H. V. 1980.
Extraterrestrial cause for the Cretaceous-Tertiary extinction. Science,
208, 1095-1108.
Sheehan, P. M., Fastovsky, D. E., Hoffmann, R. G., Berghaus, C. B. &
Gabriel, D. 1991. Sudden extinction of the dinosaurs: Latest Cretaceous,
Upper Great Plains, U.S.A. Science, 254, 835-839.
[see Hulbert, S. H. & Archibald, J. D. 1995. No stastistical support for
sudden (or gradual) extinction of dinosaurs. Geology, 23, 881-884. in
reference to the Sheehan et al. study]
indeed...
Raup, D. M. 1991. Extinction: Bad genes or Bad Luck. W. W. Norton and Co.,
New York.
...has even suggested that all extinctions (mass and background) may be
caused by impacts.
There is a confirmed crater in the Yucatan that
>is nearly 300Km in diameter.
Not certain. There are onging disputes over the so-called crater's size...
Ward, W. C., Keller, G., Stinnesbeck, W. & Adatte, T. 1995. Yucatán
subsurface stratigraphy: Implications and constraints for the Chicxulub
impact. Geology, 23, 873-876.
...have recently argued that the structure may be as small as 100 km and
even those who support the impact model disagree among themselves as to how
large the stucture is.
>But an ecologcal disaster that may have resulted in the
>collapse of the food web seems to have been the trigger for the mass
>extinctions.
This sounds suspiciously like a tautology to me.
When the impact occured 65Ma the area was a warm , shallow
> (<300 m) carbonate platform and tremendous volumes of CO2 were released,
>billions of gallons of sea water vaporized, flash fires ignited thousands of
>miles away form ballistic emplacement of fallout and global ranging tsunamis
>than may have been as high as 2Km all would have had immediate effect on the
>biota! Longer term climatic phenomena may have ranged from a super Greenhouse
>, to a so called "nuclear winter" scenario, acid rains, etc. Massive off-the
>scale earthquakes would probaly continue for centuries (meg-aftershocks).
Most of this is assumption and a-scientific scenario construction.
Paleontology cannot address these issues. However, we can contribute to the
debate by taking these hypotheses (the impact scenario is fine as a
hypothesis), suggesting biotic predictions that uniquely derive from those
hypotheses, and testing those predictions against the data of the fossil
record. This brings us back to Mike Resse's original posting. If all of
these terrible things happened why are there not high levels of extinctions
among "vulnerable" terrestrial invertebrates and vertebrates? There doesn't
even seem to be any change in plant-insect associations in the US west...
Labandiera, C. C. 1992. Diets, diversity, and disparity: Determining the
effect of the terminal Cretaceous extinction on insect evolution. Fifth
North American Paleontological Convention, Abstracts with Programs, Special
Publication of the Paleontological Society, 6, 174.
The fact that you avoid any specific reference to the biotic predictions of
your favored model suggests that you aren't very willing to get into them.
This seems curious to me since claiming that "the impact caused all the
extinctions...except for those that it didn't cause" sounds like a pretty
flimsy "explanation" of a mass extinction event.
>Ecosystems would be hard pressed to withstand this stress and it would be
>inevitable that die offs would ensue. Along with the dinosaurs, I believe it
>was Raup who stated that no land animal over 25Kg survived the event.
How many fossils representing animals over 25kg are present in the strata
within or immediately below the impact debris layer? None. Can you cite a
single section in which a large fossil occurs in this position? If so,
please direct me to that literature. The closest uncontroversial dinosaur
fragment is located 60 cm below the Ir horizon in Montana. Sixty
centimeters represents a lot of time. see...
Williams, M. E. 1994. Catastrophic versus noncatastrophic extinction of the
dinosaurs: Testing, falsifiability, and the burden of proof. Journal of
Paleontology, 68, 183-190.
>Placental mammals were very hard hit
No way to tell really!
Archibald, J. D. & Clemens, W. A. 1984. Mammal evolution near the
Cretaceous-Tertiary boundary. In: Berggren, W. A. & Vancouvering, J. A.
eds., Catastrophes and Earth History: The New Uniformitarianism. Princeton
University Press, Princeton, 229-371.
...show that the (relatively small number of) mammalian extinctions that
are recorded in Bug Creek Montana appear to be related to the facies shift
that occurs at the same time. The facies shift does not appear to be impact
related. See also...
Archibald, J. D. & Bryant, L. J. 1990. Differential Cretaceous-Tertiary
extinction of nonmarine vertebrates; evidence from northeastern Montana.
In: Sharpton, V. L. & Ward, P. D. eds., Global catastrophes in Earth
history: an interdisciplinary conference on impacts, volcanism, and mass
mortality. Geological Society of America Special Paper 247, Boulder,
549-562.
Archibald, J. D. 1993. The importance of phylogenetic analysis for the
assessment of species turnover: a case history of Paleocene mammals in
North America. Paleobiology, 19, 1-27.
>, so were numerous marine ceatures, i.e.
>Ammonites,
Nonsense! Ammonite diversity had been declining for almost 11 million years
prior to the K-T boundary...
House, M. R. 1993. Fluctuations in ammonoid evolution and possible
environmental controls. In: House, M. R. ed., The Ammonoidea: environment,
ecology, and evolutionary change. Systematics Association Special Volume,
13-34.
Kennedy, W. J. 1993. Ammonite faunas of the European Maastrichtian;
diversity and extinction. In: House, M. R. ed., The Ammonoidea:
environment, ecology, and evolutionary change. Systematics Association
Special Volume, 285-326.
The highest ammonite fossil thus far found is still 15 cm below that boundary...
Ward, P. D., Kennedy, W. J., MacLeod, K. G. & Mount, J. F. 1991. Ammonite
and inoceramid bivalve extinction patterns in Cretaceous/Tertiary boundary
sections of the Biscay region (southwestern France, northen Spain).
Geology, 19, 1181-1184.
...in a section that is demonstrably incomplete...
MacLeod, N. & Keller, G. 1991. How complete are Cretaceous/Tertiary
boundary sections? A chronostratigraphic estimate based on graphic
correlation. Geological Society of America Bulletin, 103, 1439-1457.
Ward, P. D. & Kennedy, W. J. 1993. Maastrichtian ammonites from the Biscay
region (France, Spain). Paleontological Society Memoir, 34, 1-58.
rudists clams,
Forget it! No rudistids are present above the middle Maastrichtian...
Kauffman, E. G. 1984. The fabric of Cretaceous extinctions. In: Berggren,
W. A. & Van Couvering, J. A. eds., Catastrophes and Earth History: The New
Uniformitarianism. Princeton University Press, Princeton, 151-246.
Johnson, C. C. & Kauffman, E. G. 1996. Maastrichtian extinction patterns of
Carribean province rudistids. In: MacLeod, N. & Keller, G. eds., The
Cretaceous-Tertiary Mass Extinction: Biotic and Environmental Changes. W.
W. Norton & Co., New York, 231-274.
...this group doesn't even figure in the extinction controversy anymore.
tropical reefs corals,
Rudists were the principle reef-building organisms in the upper Cretaceous.
I'm not completely sure on this point, but I know of no late Maastrichtian
reefs; rudist, coral, or otherwise.
mosasaurs,
Mosasaurs make it into the Maastrichtian, but that's about it. The youngest
Mosasaur comes from the lower Hornerstown Fm. in New Jersey. which is dated
as Maastrichtian, but is widely acknoledged to be incomplete across the K-T
boundary and contains no impact-debris whatsoever. I'm not a specialist on
this group, but I believe that Mosasaurs are declining in taxic richness
from Campanian - Maastrictian. Can anyone out there offer a more precise
summary of the Mosasaur fossil record?
pterosaurs
No way! Pterosaurs originate in the Berriasian and rich their maximum
diversity (10 families) in the mid-Cretaceous. Only two genera make it into
the Maastrichtian and the deposits containing these fossils are not of
uppermost Maastrichtrian age...
Wellnhofer, P. 1991. The illustrated encyclopedia of Pterosaurs. Salamander
Books, London.
> all
>became extinct.
Sure, they all became extinct, but their extinction had nothing to do with
a K-T impact or at least this cannot be proved from the paleontological
evidence.
>Zooplankton was hard hit as well,
Space prevents me from commenting on this one.
>and land plants were
>reduced.
Wrong again! Hickey shows that from a taxic point of view the K-T boundary
didn't substantially effect angiosperms...
Hickey, L. J. 1984. Changes in the agiosperm flora across the
Cretaceous-Tertiary boundary. In: Berggren, W. A. & Vancouvering, J. A.
eds., Catastrophes in Earth History: The New Uniformitarianism. Princeton
University Press, Princeton, 279-313.
...what you're probably referring to is the palynological evidence...
Nichols, D. J. & Fleming, R. F. 1990. Plant microfossil record of the
terminal Cretaceous event in the western United States and Canada. In:
Sharpton, V. L. & Ward, P. D. eds., Global catastrophes in Earth history:
an interdisciplinary conference on impacts, volcanism, and mass mortality.
Geological Society of America Special Paper, Boulder, 445-455.
Johnson, K. R. & Hickey, L. J. 1990. Megafloral change across the
Cretaceous-Tertiary boundary in the northern Great Plains and Rocky
Mountains, U.S.A. In: Sharpton, V. L. & Ward, P. D. eds., Global
catastrophes in Earth History: an interdisciplinary conference on impact,
volcanism, and mass mortality. Geological Society of America Special Paper,
Boulder, 433-444.
...which is taxonomically much-coarser a type of data. Some argue that a
palynological extinction event took place (see above) while others suggest
that the palynological turnover was either localized...
Sweet, A. R. & Braman, D. R. 1992. The K-T boundary and contiguous strata
in western Canada: Interactions between paleoenvironments and palynological
assemblages. Cretaceous Research, 13, 31-79.
Sweet, A. R., Braman, D. R. & Lerbekmo, J. F. 1990. Palynofloral response
to K/T boundary events; A transitory interruption within a dynamic system.
In: Sharpton, V. L. & Ward, P. D. eds., Global Catastrophes in Earth
History. Geological Society of America, Special Paper 247, 457-469.
...or very minor...
Tschudy, R. H. 1984. Palynological evidence for change in continental
floras at the Cretaceous-Tertiary boundary. In: A., B. W. & Vancourvering,
J. A. eds., Catastrophes and Earth History: The New Uniforitarianism.
Princeton University Press, Princeton, 315-337.
...and even those who support the catastrophic interpretation for
low-middle latitudes acknowledge that there was no palynological mass
extinction at high latitudes...
Johnson, K. R. & Greenwood, D. 1993. High-latitude deciduous forests and
the Cretaceous-Tertiary boundary in New Zealand. Geological Society of
America, Abstracts with Programs, 25, A-50.
The way I read these data is that there was probably a localized ecological
disturbance around K-T time in the western US, but that the taxic extent of
this event is unclear. What is clear is that there is no K-T mass
extinction in plants. Many of the plant groups that are (or soon will be)
blooming outside your window would be represented in a Cretaceous
landscape.
>Besides, many of the above taxa such as the dinosaurs and ammonites were
>doing well beforet the catastrophe and then suddenly disappeared.
Nada! There are 22 dinosaur families that make it into the Maastrichtian,
but only 15 that make it to the Upper Maastrichtian. There are many more
dino families in the Campanian, but I don't have that figure handy.
Dinosaurs were certainly declining throughout the upper Cretaceous. The
lack of dino fossils unambiguously associated with impact debris has
already been mentioned above as has the ammonite fossil record.
Finally, it's not like there was nothing else going on the the uppermost
Cretaceous. Eustatic sea level was changing...
Haq, B. 1991. Sequence stratigraphy, sea-level change and significance for
the deep sea. International Association of Sedimentologists, Special
Publication, 12, 3-39.
Haq, B., Hardenbol, J. & Vail, P. R. 1987. Chronology and fluctuating sea
levels since the Triassic. Science, 235, 1156-1166.
Volcanism was increasing...
Courtillot, V. E. 1990. A volcanic eruption. Scientific American, 263, 85-92..
Courtillot, V., Jaeger, J.-J., Yang, Z., Féraud, G. & Hofman, C. in press.
The influence of continental flood basalts on mass extinctions: Where do we
stand? In: Ryder, G., Fastovsky, D., et al. eds., Proceedings of the
Conference on New Developments Regarding the K-T Event and Other
Catastrophes in Earth History. Geological Society of America Special Paper,
Boulder.
Johnson, C. C. & Kauffman, E. G. 1996. Maastrichtian extinction patterns of
Carribean province rudistids. In: MacLeod, N. & Keller, G. eds., The
Cretaceous-Tertiary Mass Extinction: Biotic and Environmental Changes. W.
W. Norton & Co., New York, 231-274.
...and the overall climate was undergoing a series of short-term
warming/cooling episodes from middle Maastrichtian onward...
see E. Barrera's GSA abstracts for 1994 and 1995.
All this was happening before your imapct! In short, I see no evidence for
your assertions and a lot of published, peer-reviewed work by professional
paleontologists to suggest you have your facts wrong. The idea that the K-T
transition "started" with an impact has absolutely no foundation in
paleontological data. If anything the impact occurred within a prolonged
episode of environmental change that had already reduced the diversity of
many clades, thus rendering them more susceptible to extinction by any and
all mechanisms. More to the point, the patterns of extinction and
survivorship we see in the fossil record do not seem to match reasonable
biotic predictions derived from the various impact-related scenarios.
I know you like the impact model and that's just fine. However, certain
facts have been established and interpretations are not facts; especially
when those interpretations are not even widely accepted. In both cases your
posting doesn't do a very good job of summarizing this complex literature.
Norm MacLeod
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Norman MacLeod
Senior Scientific Officer
N.MacLeod@nhm.ac.uk (Internet)
N.MacLeod@uk.ac.nhm (Janet)
Address: Dept. of Palaeontology, The Natural History Museum,
Cromwell Road, London, SW7 5BD
Office Phone: 0171-938-9006
Dept. FAX: 0171-938-9277
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