I) Geological and stratigraphic environment in Mesozoic: the secondary era, as a whole, was a 180 M.A. long period of relative orogenetic and volcanic calm. Stratigraphy indicates to us that Mesozoic was one vast era of marine transgressions which left immense sedimentary deposits composed of sandstone, marls, sands and especially of thick chalky layers and in particular of chalk (particularly to the Cretaceous as its name indicates it). Thus, a calcareous character environment and sedimentation prevail during most of Mesozoic and almost without sharing during the Cretaceous (except Aptian and Albian clays), until limit K/T. Whereas one admits a calcium average value of the magmatic rocks 3,65 % content, the sedimentary rocks average is much higher (6 %). the connection, in the sedimentary cycle, of carbon and calcium involves a calcium enrichment on the carbonates level and the CO3Ca precipitation is particularly favorable in marine medium (Lapadu-Hargues). Coccolithophoridae, the calcareous nannoplankton, listed since Carnian (higher Trias) (Winter and Siesser 1994), knew a considerable expansion, as well as planktonic Foraminifera, with the middle and final Cretaceous, involving a very wide calcareous sedimentation (Maddocks 1998). With the late Cretaceous, one sees the apparition of an orogenetic activity: the laramian phase which marks, in the mesogean field, the beginning of the large alpine orogenese; the Rocky Mountains (Yale Peabody Museum 1998). Volcanicity becomes intense on the globe scale (a third of India is covered by a thick basaltic layer: Dekkan's Trapps; at U.S.A. NO, occur the vast lava thick flow: Columbia River and Snake River). On all the continents, volcanicity begins again. At the same time, vast underwater eruptions upset the sedimentation conditions and the oceans chemical composition (Auboin, Brousse, Lehman 1985).

II) Animal paleontology in Mesozoic: the principal animal groups which thrive then disappear at the end from the Cretaceous (approximately a hundred families) (Devillers, Chaline 1989) are, among Protists, Coccolithophoridae and Foraminifera; among the Invertebrates, Ammonoids, Rudists and Belemnoids; among Vertebrates, all marine Reptiles and all terrestrial reptilian orders except four (Rhyncocephals, of which only remains Hatteria which seems in extinction process, Chelonia or Tortoises, Squamata, Lizards and Snakes, and Crocodilia). It is remarkable to note that these last reptiles have a metabolism which enables them to survive during months without feeding) (Reichholf 1993).

With the calcic prevalence of the Secondary sedimentary rocks and especially of the Cretaceous, corresponds, as we have just noted it, blooming and an often animal groups explosive diversification whose support apparatus, internal or external, consists of various calcium compounds. The probabilistic favorable factors to the calcium biomineralization are also at work during Mesozoic: orogenetic calm and low volcanicity, hot temperature involving a low CO2 level in the oceans and supporting the CO3Ca precipitation, food marine chain in full activity, from the phytoplankton (Coccolithophoridae) to the zooplankton (Foraminifera). The probabilistic correlation is not ambiguous between the calcium trophic chain intensity, going from the calcic sedimentary environment, the phytoplankton (chalky algae, Coccolithophoridae) and the zooplankton (Foraminifera) of Mesozoic, and particularly of the Cretaceous, as well as the factors favorable to the calcium biomineralization and the living organisms radiation, as well Vertebrates as Invertebrates, whose exoskeleton or endoskeleton, consisted of calcium compounds, is more or less significant. One can say, without exaggeration, that the Cretaceous (and more largely the Secondary) is the calcium food chain era. This probabilistic calcium trophic chain, which goes from the phytoplankton to the microplankton, from the plants to the large predators leads to many animal groups explosive radiations, whatever taxa, where the calcic metabolism plays an essential role (marine and terrestrial Reptiles, Coccolithophoridae, Foraminifera, Rudists, Ammonoids, Belemnoids, Bivalves, Corals, etc...).

III) If one can note an obvious link of probability between animal groups radiations, the biomineralization favorable factors and the environment chemical composition, the mass extinction at the K/T limit must, according to our model, to raise of the same probabilistic factor. One estimates, according to authors, that among the animals, approximately 50 % of the genera disappeared in Maestrichtian (38 % of the marine genera) that is to say 65 to 70 % of the species (90 % of the planktonic species; 100 % of the marine reptiles species; all above mentioned animal groups, Ammonites, Rudists, etc...) (Raup, Sepkoski 1982).

With the finish-Cretaceous, the orogeny resumption (laramian phase) (Auboin, Brousse, Lehman 1985) and of an intense volcanicity on all the globe surface (seas and continents) modifies the geochemical composition considerably. The sedimentary chalky rocks succeeds a dominant siliceous sedimentation. Various paleontological and stratigraphic evidence attests it. We pointed out that the magmatic rocks contain 3,65 % of Ca and the sedimentary rocks 6 %. As for silicates, they have silica contents from 43 to 49 %. (Lapadu-Hargues). Radiolaria and diatoms, if they existed with the Cretaceous, they occupied a modest place. They thrive with the Tertiary and one knows that their association with ash tuffs makes it possible to affirm that they represent marine facies close to underwater eruptions where the siliceous materials abundance supports their proliferation. Silicoflagellates, flagellate Algae, equipped with a opal skeleton, are known from the higher Cretaceous to our days. The higher Cretaceous sees the chalky sponges disappear which thrived with the Secondary (Peronella) whereas the siliceous sponges become very abundant: Lyssacines (Proeuplectella, Cenomanian), Dictyonines (Pleurope, Senonian) (Théobald, Gama 1969). We will see, further on, than at the Cretaceous end the biomineralization disturbing probabilistic factors appear.  

The new geochemical composition breaks the calcium probabilistic chain and disturbs, directly or indirectly, the calcic metabolisms. The animal groups which prosper see the calcium food chain and the biomineralization complex processes seriously disturbed. Thus (on a geological scale) nannoplankton and microplankton brutally disappear, lamellibranch Molluscs and Cephalopods (Ammonoids and Belemnoids, but persistence of Nautiloids), Reptiles, etc...

IV) A fine analysis of the genera percentages, existing with the finish-Cretaceous, which survive at the K/T limit, will enable us to test our correlation model between the calcium trophic chain disturbance and the biomineralization processes and the organisms attack or disappearance to more or less significant calcic metabolism (Emiliani, Kraus, Shoemaker 1981). The groups and percentages of the survivors are data of Emiliani, Kraus and Shoemaker, the endoskeleton or exoskeleton composition of the author:

The total number of the groups is assembled to 30. We will analyze 29 of them, that of the higher plants not seeming to us significant. On these Protists, Vertebrates and Invertebrates 29 groups, 25 have a calcium endoskeleton or exoskeleton composed, 2 of silica (Diatoms and Radiolaria), 1 of cellulose (Dinoflagellates) and 1 of cartilage (Elasmobranchii). If we consider that a group, of which the survival percentage is lower than 25 %, is seriously affected by the calcium trophic chain breakage or the biomineralization abnormal operations at the K/T limit, we note that 19 of them are in this case (including Lacertilia 27 ~ 25).

All these marine or terrestrial groups are characterized by a considerable development of the endoskeleton (Reptiles, with sometimes significant osseous excroissances: Stegosauria, Ankylosaurids, Ceraptosauria - Proceratops, Triceratops -, Pterosauria - Pteranodon) or of the exoskeleton (Ammonoids, Belemnoids, Hippuritidea). Other groups which disappear or are largely touched have an essential calcic metabolism (Coccolithophoridae, planktonic Foraminifera and Orbitoids, Corals, Osteichthya).

A contrario, the groups, where the calcic metabolism does not play a paramount role, are not or relatively less affected: Radiolaria with siliceous skeleton 93 %, Dinoflagellates to cellulose theca 78 %, Diatoms with siliceous skeleton 31 %, Elasmobranchii with cartilageous skeleton 67 %, Mammals, Multituberculs and Pantotheria, First Marsupials and Placental skeleton represented by small organisms 52 %, Amphibia, the Anoura and Urodels osseous skeleton were much more reduced than those of the finish-Cretaceous large reptiles 100 %. Two groups with test or calcareous shell are relatively saved: a) Nautiloids 50 %. One suppose that, contrary to Ammonoids which were to be nourished, as of their existence first days, from the plankton decimated with the final Cretaceous, Nautiloids escaped the extinction while feeding as of their birth, on the bottom, out of deep water, like the adults (Ward 1991); b) Foraminifera (benthic, bathyal, abyssal) 75-85 %. Pelecypoda (43 %) and the Ostracea (32 %) undergo the calcium trophic chain disturbance effects without however disappearing (Inocerams, giant Ostracea, posed on the chalky funds, disappear approximately 1 M.A. before limit K/T (Jaeger 1996).

Out of the 29 considered groups, 4 groups whose calcic metabolism misses or is minor are not or not very affected (Radiolaria, Dinoflagellates, Diatoms, Elasmobranchii). Out of the others 25: 19 whose calcic metabolism is significant disappears or are very affected, 3 are more or less affected (Nautiloids 50 %, Pelecypoda 43 % and Ostracea 32 %), the 3 last are saved. The Amphibia and Mammals have a moderate calcic metabolism. As for Foraminifera, they profit from a completely particular, benthic biotope (bathyal-abyssal), which seems to have protected them from the extinction,

In short, out of 29 groups, 26 (4 + 19 + 3) is 90 % of the groups testify to a correlation (by their persistence, their disappearance or their small percentage of survival) between their endoskeleton or exoskeleton nature and importance and the trophic chain disturbance and the biomineralization calcium processes to the finish-Cretaceous. This level percentage cannot be allotted randomly but is actually due to the calcium probabilistic action. We will see in Paragraph VI the whole disturbing factors of calcium biomineralization which one can count at K/T limit and which caused the mass extinction at that time.

V) The examination of the areas and periods of a terrestrial reptiles group appearance which dominated Mesozoic, the Dinosaurs, brings powerful arguments in probabilistic model favour. One will note, in the analyses which follow, the correlation which exists, in space and time, between the Dinosaurs fossils local appearance and a preliminary transgression, i.e. a marine sedimentation which makes it possible to found the probabilistic calcium trophic chain. The Dinosaurs fossils localization depends on multiple factors: fossilization favorable conditions, mesozoic rocks outcrops, etc... On the other side, the Dinosaurs groups migrations, during Mesozoic, depended largely on the communications existing between the continents: Trias communications between Laurasia and Gondwana, Gondwana division to Jurassic with possible communications between the parts, Laurasia division to the Cretaceous and rupture of the communications with the South continents. We based ourselves, in our research, on various works and more particularly on the Lambert Dinosaurs Guide (1986), the Charig synthetic article (1973) and others (Furon 1959) (Buffetaut 1994).

The Dinosaurs group, which is represented by more than 340 genera, is generally divided into 2 orders, Ornithischia and Saurischia. It concerns small size families, but especially of many big size animals families, compared to the human size (Megalosaurids, Tyrannosaurids, Titanosaurids, Diplodocids, etc...) and with osseous excroissances, Stegosaurids (Dinosaurs with plates), Ankylosaurids (Dinosaurs with armours), Ceraptosaurids (Dinosaurs with horns). On the many families or subfamilies of listed Dinosaurs, in the various continents, with Jurassic and the Cretaceous, more than 80 % are big size animals (Charig 1973). The endoskeletons growth and maintenance and the excroissances require a very active calcic metabolism and the capacity to satisfy there by the existing food chains. It is what was possible throughout Mesozoic and particularly with Jurassic and the Cretaceous where marine calcareous sedimentation dominated (Coccolithophoridae and Foraminifera - Maddocks 1998) and where chalky layers formed the sea-beds (Lambert 1986). If, with Trias, the first Dinosaurs could spread themselves on the near total emerged grounds which formed the Pangea block, it was not thus any more with Jurassic and even less with the Cretaceous where the continents separated and derived with periods from transgression and regression. As we have already pointed out, the communications were thus sometimes established, sometimes broken between Asia and North America, North America and South America, etc... If the risks of fossilization conditions and the outcrops mesozoïc play a significant role in the Dinosaurs fossiliferous sites distribution, the Jurassic and Cretaceous fossiliferous sites analysis in the world shows, nevertheless, a narrow correlation between the localization in the space and the time of these sites and a preliminary transgression, more or less near in time, initiating the calcium food chain and supporting the Dinosaurs families arrival and/or blooming.

We used the census of the Jurassic and Cretaceous principal fossiliferous Dinosaurs sites of Charig (1973), and correlated the corresponding preliminary transgressions. We added a certain number of other fossiliferous sites not quoted by Charig, according to other authors, and corresponding transgressions (Furon 1959).

North America:

1) Alberta - higher Cretaceous (Edmonton Formation, St Mary River Formation, Oldman Formation, higher Milk River Formation) - Trias, Jurassic, Cretaceous transgressions.

2) Saskatchewan - higher Cretaceous (Lance Formation, Frenchman Formation) - Trias, Jurassic, Cretaceous transgressions.

3) Montana - superior Jurassic (Morrison Formation), inferior Cretaceous (Cloverly Formation, Kootenai Formation), superior Cretaceous (Lance Formation, Hell Creek Formation, St Mary River Formation, Judith River Formation, Two Medicine Formation, Eagle sandstone) - Trias, Jurassic, Cretaceous transgressions.

4) Wyoming - superior Jurassic (Morrison Formation), inferior Cretaceous (Cloverly Formation), superior Cretaceous (Lance Formation) - Trias Jurassic, Cretaceous transgressions.

5) South Dakota - superior Jurassic (Morrison Formation), inferior Cretaceous (Lakota Formation), superior Cretaceous (Lance Formation, Hell Creek Formation) - Trias, Jurassic, Cretaceous transgressions.

6) Utah - superior Jurassic (Morrison Formation), superior Cretaceous (North Horn Formation) - Trias, Jurassic, Cretaceous transgressions.

7) Colorado - superior Jurassic (Morrison Formation), superior Cretaceous (Denver Formation, Arapahoe Formation) - Trias, Jurassic, Cretaceous transgressions.

8) Kansas - lower Cretaceous (Dakota Formation), superior Cretaceous (Niobrara Formation) - Trias, Jurassic, Cretaceous transgressions.

9) Missouri - higher Cretaceous (Ripley Formation) - Trias, Jurassic, Cretaceous transgressions.

10) California - higher Cretaceous (Moreno Formation) - Trias, Jurassic, Cretaceous transgressions.

11) Arizona - inferior Jurassic (Navajo Sandstone), inferior Cretaceous (?),superior Cretaceous (?) - Trias,Jurassic transgressions.

12) New Mexico - higher Cretaceous (Sandstone Ojo Alamo, Kirtland Formation, Fruitland Formation) - Trias, Jurassic, Cretaceous transgressions.

13) Texas - lower Cretaceous (Trinity Group), superior Cretaceous (Aguja Formation) - Jurassic, Cretaceous transgressions.

14) Oklahoma - superior Jurassic (Morrison Formation), inferior Cretaceous (Trinity Group) - Jurassic, Cretaceous transgressions.

15) Alabama - higher Cretaceous (Selma Group) - Jurassic, Cretaceous transgressions.

17) Maryland and Washington D.C. - lower Cretaceous (Arundel Formation) - Cretaceous transgressions.

18) New Jersey - higher Cretaceous (Monmouth Group, Navesink Formation, Matawan Formation) - Cretaceous transgressions.

19) Mexico City (Coahuila State) superior Cretaceous (Difunta Formation) - Jurassic, Cretaceous transgressions.

Europe:

20) England - lower Lias, middle Jurassic (Great Oolite, Forest Marble, Stonesfield Slate, Chipping Norton Limestone), superior Jurassic (Kimmeridgian, Corallian, Oxfordian, Callovian), inferior Cretaceous (Lower Greensand, Wealdian, Potton Sands, Middle Purbeck Beds), superior Cretaceous (Lower Chalk, Cambridge Greensand) - Trias, Jurassic,Cretaceous transgressions.

21) Netherlands - lower Cretaceous (Wealdian), superior Cretaceous (Maastrichtian, Santonian) - Trias, Jurassic, Cretaceous transgressions.

22) France - Lias, higher Jurassic (Portlandian, Kimmeridgian, Oxfordian, Callovian), inferior Cretaceous (Gault), superior Cretaceous (Maastrichtian) - Trias, Jurassic, Cretaceous transgressions.

23) Spain - lower Cretaceous (Albian, Wealdian), superior Cretaceous (Maastrichtian) - Trias, Jurassic, Cretaceous transgressions.

24) Portugal - Lias, higher Jurassic (Kimmeridgian), inferior Cretaceous (Aptian, Lower Greensand), superior Cretaceous (Maastrichtian) - Trias, Jurassic,Cretaceous transgressions.

25) Germany - superior Jurassic (Kimmeridgian, Solnhofener, Schiefer), inferior Cretaceous (Wealdian) - Trias, Jurassic, Cretaceous transgressions.

26) Austria - higher Cretaceous (Gosau Formation) - Trias, Jurassic, Cretaceous transgressions.

27) Poland - higher Cretaceous (?) - Trias, Jurassic, Cretaceous transgressions.

28) Transylvania - higher Cretaceous (" Danian " = Maastrichtian) - Trias, Jurassic, Cretaceous transgressions.

29) Spitzberg - lower Cretaceous (?) - Jurassic, Cretaceous transgressions.

Occidental Asia:

30) Kazakhstan - lower Cretaceous (?),superior Cretaceous (?) - Trias, Jurassic, Cretaceous transgressions.

31) Ouzbekistan - higher Cretaceous (?) - Trias, Jurassic, Cretaceous transgressions. 

Eastern Asia:

32) Central and Southerner Siberia - lower Cretaceous (? Udinsk) - Trias, Jurassic transgressions.

33) Sinkiang - superior Jurassic (?),inferior Cretaceous (?)-Trias, Jurassic, Cretaceous transgressions.

35) Eastern Mongolia - lower Cretaceous (Iren Dabasu Formation), superior Cretaceous (?) - Trias, Jurassic transgressions.

36) Inner Mongolia - higher Cretaceous (?) - Trias, Jurassic transgressions.

37) Kansu - superior Jurassic (?),inferior Cretaceous (?), superior Cretaceous (?) - Trias, Jurassic transgressions.

38) Szechuan - superior Jurassic (Kuangyuan Series) - Trias, Jurassic transgressions.

39) Shansi - higher Cretaceous (?) - Trias, Jurassic transgressions.

40) Shantung - superior Jurassic (?),inferior Cretaceous (?),superior Cretaceous (Wangshih Series) - Trias, Jurassic transgressions.

41) Mandchourie (Heilungchiang) - superior Cretaceous (?) - Trias, Jurassic transgressions.

42) Sakhalin - higher Cretaceous (Senonian) - Trias, Jurassic, Cretaceous transgressions.

South Asia:

43) Laos - higher Cretaceous (Senonian) - Trias, Jurassic transgressions.

44) Central India - inferior Jurassic (Kota Formation), superior Cretaceous (Lameta Formation) - Trias, Jurassic, Cretaceous transgressions.

45) South India - higher Cretaceous (higher Aryalur Stage) - Cretaceous transgressions.

South America

46) South Argentina (Patagonie) - middle Jurassic (?),superior Cretaceous (Senonian) - Jurassic, Cretaceous transgressions.

47) North Argentina and Uruguay - higher Cretaceous (?) - Cretaceous transgressions.

48) Brazil (Sao Paulo State) - superior Cretaceous (?) - Cretaceous transgressions.

North Africa:

49) Morocco - middle Jurassic (Bathonian), superior Jurassic (Callovian), inferior Cretaceous (?),superior Cretaceous (?) - Trias, Jurassic, Cretaceous transgressions.

50) Tunisia and Lybie adjacent areas - lower Cretaceous (" intercalate Continental "), superior Cretaceous (?) - Trias, Jurassic, Cretaceous transgressions.

51) Central Algeria - lower Cretaceous (" intercalate Continental ") - Trias, Jurassic, Cretaceous transgressions.

52) Eastern Algeria - superior Jurassic (?), inferior Cretaceous (" intercalate Continental ") - Trias, Jurassic, Cretaceous transgressions.

53) Mali - inferior Cretaceous (" intercalate Continental ") - Cretaceous transgressions.

54) Niger - inferior Cretaceous (" intercalate Continental "), superior Cretaceous (?) - Cretaceous transgressions.

Eastern Africa:

56) Tanzania - superior Jurassic (Tendaguru Formation) - Jurassic, Cretaceous transgressions.

57) Malawi - lower Cretaceous (?) - Jurassic,Cretaceous transgressions.

South Africa:

58) The Cape Province (Bushmanland) - inferior Cretaceous (?) - Cretaceous transgressions.

59) The Cape Province (Southern Coast) - inferior Cretaceous (?) - Cretaceous transgressions.

60) Madagascar - middle Jurassic (?),superior Cretaceous (?) - Trias, Jurassic, Cretaceous transgressions.

Australia:

61) Queensland (North-eastern Coast) - middle Jurassic (?) - Jurassic, Cretaceous transgressions.

62) Queensland (Interior) - inferior Jurassic (Walloon Coal Measures) - Jurassic, Cretaceous transgressions.

63) South News-Wales - lower Cretaceous (? Walgett) - Jurassic, Cretaceous transgressions.

64) Victoria - lower Cretaceous (? Patterson Cape) Transgressions?? (missing Data).

One can add the following fossiliferous sites (Lambert 1986) (Buffetaut 1994):

Yukon and Alaska, higher Cretaceous " polar " layers - Cretaceous transgressions.

Peru - Cretaceous - Trias, Jurassic, Cretaceous transgressions.

Antarctic - higher Cretaceous (Campanian) - Cretaceous transgressions.

Sudan - higher Cretaceous - Jurassic, Cretaceous transgressions.

Kenya - Jurassic - Jurassic, Cretaceous transgressions.

South Scandinavia - Cretaceous - Jurassic, Cretaceous transgressions.

This list, which is not exhaustive, counts nevertheless the Jurassic and Cretaceous Dinosaurs principal fossiliferous sites. It reveals the narrow correlation which exists between the transgressions and the fossiliferous sites posterior localization. It is corroborated, in contrary direction, by the fossiliferous sites absence, everywhere where no transgression mesozoic occurred, thus excluding emergence, in these areas, of the calcium food chain.

Not transgressed areas deprived of fossiliferous sites:

1) North most of North America and Canada (Large Lakes Area, North-West Territories, Ontario, Quebec - except Alaska and Yukon), Groenland (except the eastern coast).

2) South America: the not transgressed North eastern part (Brazil - Amazonia, Mato-Grosso - except Sao-Paulo State and Bahia Région).

3) Africa: all the non covered eastern half by the mesozoic transgressions except the eastern coast (Tanzania, Malawi, Kenya, Sudan) and Madagascar.

4) Australia: the western half of which only the coastal part was transgressed.

5) Europe: Iceland and Scandinavia (except the extreme south transgression).

6) Asia: Angara not transgressed in the Baïkal Lake north.

7) Antarctic: all the Peninsula except the transgressed part at Cretaceous.

It should be noted that, if the fossiliferous sites, by the things nature, are localized in the mesozoic outcrops and, moreover, in beforehand transgressed zones, the reciprocal one is not true. Many mesozoic outcrops, located in not transgressed zones, do not contain fossiliferous sites (Lambert 1986):

1) North America: Extreme-west Alaska cretaceous outcrops.

2) South America: North-East cretaceous outcrops.

3) Australia: Western half continental cretaceous outcrops.

4) Asia: Jurassic and cretaceous outcrops in the Baikal lake North and North-East.

The fossiliferous sites localization in the beforehand transgressed areas and their not transgressed outcrops absence is a powerful argument in favour of the calcium trophic chain probabilistic influence in the Dinosaurs acme and radiation. This observation of the Dinosaurs families emergence, exclusively in the beforehand transgressed zones, excludes, statistically, any randomly distribution of their fossiliferous sites localization. It can support the search for fossiliferous sources by privileging the transgressed areas with the detriment of those which did not know any mesozoic transgression. The Dinosaurs disappearance, at the Cretaceous end, concerns the same factors as the other animal groups i.e. the biomineralization and breakage disturbing probabilistic factors of the calcium probabilistic food chain (in particular the Angiospermae disappearance whose nourished themselves many herbivorous Dinosaurs).

VI) Calcium biomineralization disturbing probabilistic factors at K/T limit:

Factor 2 : Glaciations, fresh or cold temperatures: the oceans temperature cooling of 8°C is a Cretaceous long-term phenomenon which culminated 500.000 years before border K/T. A greenhouse effect heating the atmosphere occurred during 400.000 years. Then, during the last 100.000 years, the climate quickly refreshes 3°C (Gerta Keller 1998). The terrestrial plants sheets, with boreal morphology (lengthened, on irregular board), dominate after K/T then later dominate the sheets with tropical morphology again (round, on smooth board). The tropical and recifales species and the plankton with calcareous skeleton (coccolithophoridae and Foraminifera) were most affected whereas the plankton with siliceous or cellulose skeleton was relatively not very affected (dinoflagellates, diatoms, radiolaria).

Factor 3 : Higher CO2 level: CO2, more soluble in colder waters, supports the CO3Ca dissolution (Maddocks 1998). The Cretaceous end intense volcanicity (Dekkan Trapps - Mc Lean 1997) rejects CO2 in the atmosphere and this one accumulates in the oceans.

Factor 4 : Volcanicity and alpine orogeny, at the Cretaceous end, generate a terrigenous sedimentation and expel CO2 in the atmosphere. An argillaceous layer settles almost everywhere in the world and, in the long run, close to Chixculub where would have occurred a meteoric impact (Gerta Keller 1996).

Factor 5 : The increase in CO2 in marine waters increases the pH acidity (Knoll 1996).

Factor 7 : Food chains ruptures: nannoplankton (coccolithophoridae) and microplankton (Foraminifera) quasi extinction; Angiospermae disappearance (Peak of the ferns - Raup 1993).

We note that on the 7 biomineralization disturbing probabilistic parameters which we listed, 5 appeared at the Cretaceous end. In addition, these 5 parameters are in conformity with the explanatory requirements which we met higher: extinctions pluricausality, gradualism and suddenness, duration, regionalism and globalisation; the fundamental character of the selectivity of the extinctions is largely highlighted.

VII) A certain number of other evidence or solid arguments consolidates the probabilistic model.

a) The mass cause extinction at K/T limit gave rise to many hypotheses. Certains are rather whimsical, the other serious ones, like the marine regressions and climatic deteriorations which resulted from this (Ginsburg 1964). Many (except the volcanic assumption, Courtillot 1987) are nevertheless very speculative: no convincing fact accredits the supernova, star or unknown planet thesis, the earth meeting with galaxy plan clouds, a viral epidemic, the groups senescence, etc... The in vogue impact theory of a meteorite with the earth (Alvarez 1980) received the support of many arguments (iridium traces, shocked quartz spherules and grains, spinels, Chicxulub crater). A certain number of arguments which it proposes can be interpreted, with much relevance, by the volcanic origin concurrent assumption. Other arguments go against this assumption: 1) recent data suggests that the the crater impact, close to Chixculub, would be former to border K/T; 2) consecutive siliceous deposits to a " tsunami " generated by the impact are long-term and noninstantaneous deposits; 3) the impact event, marked by the Iridium anomaly, is above the siliceous deposits; 4) all collected data converge towards a causes plurality (Gerta Keller 1996; MacLeod 1999). In any event, all these arguments can establish only the meteoric impact potential possibility. The causality report with the mass extinction at the K/T limit remains purely hypothetical. Moreover, to allot to a possible local meteoric impact and its catastrophic consequences on the whole planet, the mass extinction at the K/T limit, seems, in the knowledge current state, a very hazardous generalization. Causal plurality, dates and durations problems and, finally the extinctions selectivity, are major difficulties that the impact model does not solve.

A contrario, the probabilistic model proposes a synthetic explanatory model which answers all these impact model difficulties.

Any mass extinctions explanatory model at the K/T limit must be, in addition, able to answer the various arguments which we will expose hereafter.

c) Paleobiogeographic arguments: the fossiliferous sites examination of a terrestrial reptiles group which dominated Mesozoic, the Dinosaurs, brought a probabilistic model unambiguous confirmation. It was noted 1) that the Dinosaurs fossils emergence always occurs after a transgression i.e. a marine sedimentation (Furon 1959) which founds the probabilistic calcium trophic chain 2) a contrario, without preliminary transgression, one does not find Dinosaurs fossils. The direct link between the Dinosaurs appearance and radiation probability and a calcic medium presence thus firmly appears established.

d) The mass extinctions at the K/T limit intervene, generally, following the groups explosive radiation which disappear. Only the evolution probabilistic model interprets these two facts orders by a same factor: a trophic chain introduction and favorable calcium biominéralisation probabilistic factors then their disturbance, whereas the models majority take into account only the mass extinctions to the finish-Cretaceous.

e) The trophic chain and the probabilistic calcium biomineralization factors establish a link between the acme then the "simultaneous" disappearance of very distant animal groups, Vertebrates or Invertebrates, by a common denominator possession: a significant calcic metabolism.

f) Stratigraphy attests sedimentation change at the K/T limit. An argillaceous layer " separates, in the majority of the cuts, the Cretaceous of the Tertiary sector and, in a general way... all the areas where the passage terms between the two systems could be highlighted " (De Bonis 1991). In Gubbio, this layer contains 50 % of clay, whereas the layers majority lower than K/T limit contains approximately 95 % calcium carbonate and 5 % of clay (Alvarez, Asaro 1993). In addition, at the ocean floor, the organic origin calcareous sedimentation coming from micro-organisms skeleton accumulation stops at the Maestrichtian end. The carbonates concentration, at the K/T limit , to the sedimentary sites of El Kef (Tunisia), Caravaca (Spain) and Hole 761 C (off Australia), testifies clearly to the reduction, on this level, of the calcium carbonate concentration: El Kef (from approximately 50 to 5 %), Caravaca (from approximately 70 to 20 %), Hole 761 C (from approximately 90 à.70.%) (Robin, Rocchia 1993).

g) Arguments a contrario: The Foraminifera genera majority disappear with the finish-Cretaceous (Orbitoids, Orbitolinids). They have a significant calcic metabolism; their thick and heavy tests can reach 6 cm in diameter (Orbitolina concava). On the other hand, Silicoflagellates appear with the final Cretaceous. The Diatoms and the Radiolaria ones (93 % of survivors), with the siliceous skeleton, which thrive in the abundant marine siliceous material facies, pullulate with the Cenozoic one, where they constitute sediments considerable masses: diatomites and " muds with radiolaria ". Dinoflagellates, with cellulose theca, also thrive (78 % of survivors) and one often perceives K/T clays limit like a " Dinoflagellates soup " (Smit Ian 1996). Among the Vertebrates ones, Elasmobranchii, fishes with cartilageous internal skeleton, survive 67 %, whereas Osteichthya, with osseous skeleton, disappear almost completely (4 % of survivors).

h) The mass extinction duration is incompatible with a short catastrophe (celestial body impact, star or unknown planet, etc...). It corresponds to the various mass extinctions, like the Dekkan volcanicity estimate duration, about 500.000 years, based mainly on the magnetic field opposite polarity (Courtillot 1987). The trophic chain disturbance and the calcium biomineralization factors is a progressive phenomenon which can occur only for one " geological " length of time and which can engender as well many gradual extinctions (Inoceramids and Rudists) as well as sudden ones (Coccolithophoridae and Globigerina). This extinctions temporal diversity is well in phase with the disturbing probabilistic biomineralization factors multiplicity.

i) Mesozoic, often considered as the Reptiles era, can be considered, more precisely, like the calcium era. The orogenetic activity and volcanicity apparition to finished Cretaceous and the environment chemical and climatic variations which it involves modify the sedimentary composition and break the trophic calcium chain (phosphates, carbonates, etc...). Thus will disappear the Dinosaurs, as well herbivorous as carnivorous. At the same time as the Dinosaurs, Plesiosaurs and Pterosaurs disappear, just as many marine and terrestrial animals, many of big sizes or adapted to a significant calcic metabolism. The biomineralization factors disturbance also will reach the marine organisms majority with calcareous skeleton. This specificity of the attack from organisms with calcium skeleton and metabolism cannot be understood but within the framework of the probabilistic model.