IV
THE EVIDENCES OF THE PROBABILISTIC
MODEL
As a whole, the
secondary era was a 180 M.Y. relative orogenetic and volcanic long period of
calmness. An environmental and a calcareous sedimentation prevail during most
of Mesozoic and particularly at the Cretaceous (as its name indicates it). With
the late Cretaceous, one witnesses an orogenetic activity and the apparition of
volcanicity (Dekkhan Trapps in the Indies - the Columbia River and the Snake
River in the U.S.A.).
In Mesozoic many
phyla and animal groups thrive, whether Vertebrates or Invertebrates, with an
internal or external significant skeleton (vertebrae, rostres, tests, shells,
etc...) which consisted of various compounds of calcium, calcite, aragonite,
phosphates, carbonates, sulphates, etc...: marine or terrestrial Reptiles,
Rudists, Ammonites, Foraminifera, Coccolithophoridae, Bivalves, Corals, etc...
The mass
extinction in Maestrichtian, at the K/T limit, relates to 50 % of the kinds (38
% of the marine kinds), that is to say 65 to 70.% of the species (90 % of the
planktonic species, 100 % of the marine Reptiles, Ammonites, Rudists species,
etc...). 100 families are extinct.
A fine analysis
of the genus percentages existing at the finish-Cretaceous which survive the
K/T limit (according to Emiliani, Kraus and Shoemaker statistics 1981) makes it
possible to correlate the food chain and the biomineralization processes
disturbance and the organisms with more or less significant calcic metabolism.
disappearance or attack.
Survivors % after limit K/T:
On 29 listed
Groups:
4 whose calcic metabolism
misses or minor are not or relatively not very affected: Radiolaria with
siliceous skeleton - 93; Dinoflagellates with cellulose theca - 78; Elasmobranchii
with cartilage skeleton - 67; Diatoms with siliceous hull - 31.
19 whose calcic metabolism
is significant disappear completely or are very affected: 1) Coccolithophoridae
- 13; 2) Planktonic Foraminifera - 13; 3) Ammonoids - 0; 4) Belemnoids - 0; 5)
Osteichthya - 4; 6) Ichthyosauria - 0; 7) Plesiososauria - 0; 8) Corals - 20;
9) Orbitoids Foraminifera -0; 10) Hippuritids - 0; 11) Cheloniaa - 23; 12)
Sauropterygia - 0; 13) Lacertilia - 27; 14) Snakes - 0; 15) Crocodilia - 12;
16) Saurischia - 0; 17) Ornitischia - 0; 18) Pterosauria - 0; 19) Birds - 0.
3 are more or less
affected: Nautiloids - 50; Pelecypods - 43; Oysters - 32.
3 are saved: Amphibia -
100; Mammals - 52; Benthic Foraminifera - 75/85.
In short, on 29
groups, 26 (4 + 19 + 3) that is 90 % of the groups testify
to a correlation (by their persistence, their disappearance or their small
percentage of survivors) between their endoskeleton or their exoskeleton nature
and importance and the trophic chain disturbance and the calcium biomineralization
processes to the finish-Cretaceous.
The examination
of the surfaces and the periods when the Dinosaurs and the terrestrial Reptiles
appeared , indicates that there is a correlation, in space and in time, between
the apparition of the fossils of Dinosaurs and a preliminary or concomitant
marine transgression which makes it possible to found the calcium probabilist
trophic chain. The 70 Dinosaurs world fossiliferous sites knew a marine
transgression concomitant or former of Trias, Jurassic or Cretaceous. A
contrario, no fossiliferous site of Dinosaurs is listed without any concomitant
or former marine transgression.
One notes the
existence, at the K/T limit, of five factors (out of 7) probabilistic
disturbers of the calcium biomineralization:
1) glaciations
and temperatures fresh or cold
2) a higher CO2
level
3) an orogenetic
and volcanic intense activity
4) an increase
in the pH acidity
5) a food chains
rupture (nannoplancton - coccolithophoridae - and microplancton extinction -
Foraminifera; Angiospermae disappearance).
Other arguments
consolidate the mass extinction probabilistic model at the K/T limit, at the other models expense
(meteorites impact, marine regressions, viral epidemics, etc...): former phyla
acmes and radiations; mass extinction selectivity, distant animal groups acmes
then simultaneous disappearances, stratigraphic arguments, duration of mass
extinction, etc...
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Conclusions
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