Les rhinocérotidés du Miocène de Lisbonne - systématique, écologie, paléobiogéographie, valeur stratigraphique (texte)

Abstract

This paper concems the study of miocene rlûnoceros from the region of Lisbon in Tagus basin. The main results are as follows: l) Only two forms have been recognized in division 1 (local stratigraphic scale), lower Burdigalian in age: Protaceratherium tagicus (ROMAN) and Diaceratherium cf. aurelianensis (NOVEL). The first one in the result of a local evolution from a stock of the earUest Protaceratherium. D. cf. aurelianensis is easily linked to an earlier representative weil known in the French Aquitanian, D. aginense, which is derived from the stampian D. lemanense. 2) In laterBurdigalian beds, IVb division, three forms have been identified, ail of which are common in the french middle and upper Orleanian: Prosantorhinus cf. germanicus (WANG), Diaceratherium aurelianensis (derived from the earlier D. cf. aurelianensis) and Aceratherium platyodon MERMIER. 3) In the upper Burdigalian Va, P. cf. germanicus still exists without any evolutionary changes; Aceratherium lumiarense nov. sp. is c1early advanced when compared with its logical ancestor A. platyodon from IVb. 4} In Va a new taxon is also present: Gaindatherium (Iberotherium) rexmanueli nov. sgen. nov. sp. This is new for Europe at genus level. These animais are 50 far unknown in contemporary localities in France, Gennany, etc. and seem to be immigrants that might have reached Iberia through the Alpine arch (then a more or less continuous archipel from Zagros until Betic massif). Strong beasts, probably able to swim like their close extant relatives Rhinoceros unicornis and Eurhinoceros sondaicus, they certainly could swim across sorne narrow sea channels. Il is noteworthy to stress that in Lisbon region G. (I.) rexmanueli substitutes Diaceratherium aurelianensis. This last species is substituted elsewhere in Europe, i. e. in France (sables de l'Orléanais and Garonne basin), by Brachypotherium brachypus. It seems c1ear enough that both migrations are almost contemporaneous, but that these two immigrants (somewhat different in ecology and in origin) did not follow the same pathway. As Gaindatherium is more hypsodont and so probably bener adapted to cirier environriJents it may he assumed that it followed the southemmost one. 5) In the lower Langhian Yb, the number of rlûnocerotid taxa is double of that of Va division: ail three from the previous level were still in existance, but there were three new ones, including Dicerorhinus sansaniensis (LARTEn, common in the Astaracian from France and Gennany and probably arrived from the european platform. However the other ones, Chilotherium ibericus ANfUNES and Hispanotherium matritensis (LARTET in PRADO), are totally unknown in Europe except in iberian peninsula. Both should have passed through a mesogean pathway, an island arch across the Mediterranean. Chilotherium and Hispanotherium, which show (like Gaindatherium) a c1ear tendency towards hypsodonty, ail used the same way for migration since they came from the same dispersal center in Asia and had rather close ecological characters. Hispanotherium is now known in eastem parts of the Alpine arch: Anatolia and Caucasus, while Chilotherium has been found in Italy. Begertherium, Coemenrodon and Beliajevina are considered as junior synonyms for Hispanotherium. During the quite short time span corresponding to Yb division six rhinocerotid species, belonging to six genera, coexisted. This ecological anomalymay he easily explained by the geographical situation of lower Tagus basin, which represented the end and confluence of two migration pathways, one from the Northeast and another from the Southeast. Such coexistence of six different rhinocerotidS could not last long; indeed in the following levels, Serravallian in age, ail three migrants that came through the Betic massif vanished. Changes in c1imate towaros an increase in humidity, related to the serravallian transgression might have been unfavourable to such forms somewhat lost in this tenninal part of the continent and bener adapted to less humid envïronments. During Serravallian times only sorne forms (also common in the basin of Aquitany) survived in Iberia: Aceratherium cf. tetradactylum. Dicerorhinus (Lartetotherium) sansaniensis and Aceratherium (Alicornops) simorrensis. 6) In conclusion, the study of the miocene Rhinocerotidae of Lisbon allowed us to recognize the middle mesogean as a new and hitherto unexpected migration way for land mammals. Taking this in accouRt it would be interesting to reexamine the place and origin of other iberian miocene mammals like the Cervid Palaeoplatyceros hispanicus or the Giirids Praearmantomys (P. ginsburgi and P. crusafonti) and Armantomys (A. aragonensis).