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Article Dans Une Revue Quaternaire Année : 2007

Faunes de reptiles et changements climatiques en Europe Occidentale autour de la limite Plio-Pléistocène.

Résumé

ABRIDGED ENGLISH VERSION REPTILES FAUNA AND CLIMATIC CHANGES AROUND THE PLIO-PLEISTOCENE BOUNDARY IN WESTERN EUROPE All squamate reptiles are ectothermic animals whose body temperature is connected to external one. They lack internal mechanism able to produce heat and their vital functions more or less depend on the environment temperature too. Morever, they are fundamentally oviparous animals. The success of embryonic development depends to climatic conditions (mainly temperature). Their dependence on climatic factors for the preservation of vital functions and for reproductive success gives to this group significance as climatic marker. In this way, the study of squamate faunas present in Western Europe from the Middle Pliocene to the Early Pleistocene, represents a good example of contribution to the knowledge of past climates. The archaeo-palaeontological sites studed in this work, are well as their ages, are indicated in the French version (fig. 1 and 2). Squamate faunas: During the first half of the Middle Pliocene (Late Ruscinian, Biozone MN15 and MN15/MN16 boundary), at least 13 squamate families are present (tab. 1). The fauna is similar to that from the Miocene, although becoming slightly impoverished but still retaining a tropical character, as shown by the presence of Varanidae, Aniliidae s.l. and Elapidae. Today, these families inhabit tropical areas and their northern boundary is essentially situated between the 20oC and 25oC mean annual temperature isotherms (fig. 3). The great majority of modern representatives of these families basically live in arid or semi-desert regions. Nevertheless, such an arid character is somewhat mitigate in the South-East of France by the presence of some amphibian species confined to humid and aquatic environments. During the second half of the Middle Pliocene (Early Vyllanian, Biozone MN16), the squamate fauna becomes more impoverished (only 9 families, fig. 4)) and more thermophilous families disappear (tab. 2). Only families that are still currently present in the Mediterranean area and whose northern boundary is situated between the 15oC and 20oC mean annual temperature isotherms persist (fig. 3). The arid character of the climatic seems to be increasing. During the Late Pliocene (Late Vyllanian,MN17, tab. 3, fig. 4), scolecophidian snakes, some Gekkonidae different from the current species, the Scincid Mabuya, and oriental vipers no longer live in the region, whereas other thermophilous groups (Agamidae, Blanidae and some Colubridae) are affected by a southward withdrawal. At the same time, some species coming from Central Europe arrive in France (fig. 4). Apparently, the establishment of the present fauna take place during the Early Pleistocene (tab. 4 and fig. 4). At that time, exotic family (Agamidae) is no longer present and the last Ophisaurus (Anguidae) has found refuge, before final local disappearance, in the South of the Iberian Peninsula (Barranco León 5 and Fuente Nueva 3). Climatic data (fig. 6): During the first half of the Middle Pliocene, some families with unquestionable tropical tendencies are well represented. The climate may still have hold some tropical character (mean annual temperature > 20oC with a poor contrasting seasonality) and aridity. During the second half of theMiddle Pliocene, the families with basically tropical affinities are no longer represented. This faunal scarcity seems to point out a significant climatic degradation, with a decrease of the temperature (mean annual temperature < 20oC) and the establishment of a climate with contrasted seasons (probably ofMediterranean type). At the same time, the aridity seems to increase. During the Late Pliocene, the drop in temperature becomes more pronounced and some Centro-European species arrive in France. The mean annual temperature do as not seem to exceed 15oC atMontoussé 5, 16oC at Vallirana and 18oC at Casablanca-Almenara 3. The Early Pleistocene seems to begin with cooler climatic conditions. The disappearance of the last Agamidae corresponds to a fall of the mean annual temperature below 15°C.
Les reptiles constituent un groupe de vertébrés non homéothermes et essentiellement ovipares dont le maintien des activités vitales et le succès reproducteur sont directement liés aux conditions climatique. Cette sensibilité leur confère un rôle important dans la reconnaissance des climats du passé. L'étude des reptiles squamates présents en Europe occidentale du Pliocène moyen au Pléistocène inférieur permet d'nférer des hypothèses sur l'évolution climatique de la région au cours de cette période. – Limite MN15/MN16 (Ruscinien/Villanien) : disparition des familles à caractère tropical (Varanidae, Aniliidae s.1. et Elapidae) liée à une péjoration climatique importante température moyenne annuelle < 20° C) et mise en place d'une saisonnalité contrastée. – Au Villanien inférieur (MN16) d'autres groupes de reptiles disparaissent [une partie des Gekkonidae, les Lygosominae (Scindae) et les serpents du type Scolecophidia, Eryx (Boidae) et le groupe des vipères orientales] ou subissent un retrait vers la péninsule Ibérique [Blanidae et Ophisaurus (Anguidae)]. Le refroidissement climatique semble s'accentuer (température moyenne annuelle d'environ 15°). – Le Pliocène supérieur (MN17, Villanien supérieur) voit l'arrivée en France de taxons provenant de l'Europe centrale ; un gradient de températures est bien reconnaissable dans la région et la faune de squamates de l'Europe occidentale semble montrer des affinités biogéographiques avec la faune actuelle. – Le Pléistocène inférieur débute dans des conditions climatiques plus froides (température moyenne annuelle <15°C) respobnsables de la disparition de la dernière famille exotique (Agamidae) et du retrait méridional des taxons méditerranéens.
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hal-00483388 , version 1 (14-05-2010)

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  • HAL Id : hal-00483388 , version 1

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Salvador Bailon, Hugues-Alexandre Blain. Faunes de reptiles et changements climatiques en Europe Occidentale autour de la limite Plio-Pléistocène.. Quaternaire, 2007, 18 (1), pp. 55-63. ⟨hal-00483388⟩

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