Evolution of Anuran Assemblages in the Tertiary and Quaternary Of

Evolution of anuran assemblages in theT ertiary and Quaternary of Europe, in thecontext of palaeoclimateand palaeogeography

Jean-ClaudeRage 1, Zbynek† Rocek† 2

1 Laboratoirede Palé ontologie, UMR 8569 CNRS, Musé um National d’ HistoireNaturelle, 8 rueBuffon, F-75005Paris, France 2 Dept.Palaeontology, Geological Institute, Academy ofSciences, Rozvojová135, CZ-165 00 Prague,and Dept. Zoology,Charles University,CZ-128 44 Prague, Czech Republic

Abstract. Thehistory of the faunas of anurans during the Tertiary and Quaternary in Europe is presented. Twofamilies (Discoglossidaeand Palaeobatrachidae) were recordedfrom the Cretaceous ofEurope and both survivedthe Cretaceous/ Tertiarycrisis. Theearliest knownTertiary anurans, represented by theDiscoglossidae andperhaps Palaeobatrachidae, come fromHainin, Belgium (middle Paleocene). Only the Bufonidae appear tojoin them beforethe end of thePaleocene, however, they subsequently disappeared only to re-appear at the beginningof the Miocene. The paucity of Paleocene data is dueto a lack offossiliferousstrata, rather thana post-Cretaceousdiscontinuity of the anuran fauna. Europe and North America were separated bythe Atlantic Ocean inthe early Eocene(50 Ma) andclimate at thattime was tropical.Ranidae, Pelobatidae, Pelodytidae, Leptodactylidaeappeared in the Eocene; the last familywas representedby thegenus Thaumastosaurus which is aGondwananelement. Others were eitherimmigrants, probably from Asia, ororiginatedin Europe (Pelodytidae) orinNorthAmerica (Pelobatidae).Supposed temporary presence oftheMicrohylidae and Rhacophoridae in the EuropeanEocene requires further con rmation. A dropof temperature at theend of theEocene (one of thecauses ofacrisis called the‘ GrandeCoupure’ ) is associated withthe de nitive disappearance oftheLeptodactylidae in Europeand of palaeobatrachids from the region of the British Isles, as well as thetemporary disappearance ofthepelodytids (until they re-appear intheMiocene). During the Oligocene, the European anuran fauna was comparativelystable, only forms belongingto the group of greenfrogs (Ranidae) appeared in the early Oligocene. Inthe early Miocene,the Hylidae appeared, whereas thePelodytidae and Bufonidae re-appeared. Themost diversied anuran fauna in the history of Europe was inearly Miocene(approx. 20 Ma) whensome extantgenera andeven species rst appeared.Since then, the diversity of the European anuran assemblages decreased, mainly as aresultof climatic deterioration.During the early Pleistocene,the discoglossid genus Latonia andthe entire familyPalaeobatrachidae became extinct,undoubtedly because ofcontinentalglaciation.

Introduction

Morethan 85 extinctspecies of anuranswere describedfrom theT ertiaryand Quaternary ofEurope(about 70 inthe Tertiary, about 16 inthe Quaternary). Of them,only 26 appearto bevalid(25 in theTertiary and only Pliobatrachuslanghae intheQuaternary). Others are eithersynonyms of recentspecies, nominadubia , nomina vana, or nomina nuda (mainly basedon Sanchiz, 1998a). Supposedly, a numberof extinct species have not yet been discoveredin the European T ertiary.Nevertheless, all these data collected since the rst halfof 19th century (i.e., in nearly 200 years) from morethan 300 localities (Sanchiz, 1998a),represent a basisfrom whichthe principal features of evolution of the entire amphibianassemblages in Europe may be inferred. Here we presentresults concerning theanurans. Amphibiansare ectothermic vertebrates and as suchtheir distribution re ects climatic conditionsin whichthey live. This is whythey may be used as a toolfor palaeoclimatic reconstructions.In addition, they are limited in their movements, so their fossil distribution reects palaeogeography.

Thefollowing review ofevolutionof anuran assemblages is inferredfrom the geochronologically arranged list ofEuropeanTertiary and Quaternary anuran-bearing fossil sites andtheir faunal composition. That part of the tablecovering Tertiary may bedownloaded from http:/ /rocek.gli.cas.cz/tertianura.pdf,or is available on request fromthe authors.

Geochronology (table 1)

Catastrophicevents that took place 65 millionyears ago marked the end of theMesozoic andtherefore the beginning of theCenozoic. No signi cant event occurred at theTertiary- Quaternarytransition; the ageof thisboundary is xedat 1.64 Ma (‘Ma’is theabbreviation for ‘millionyears’ ). TheTertiary is subdivided into epochs (or series) andstages. International reference stagesare de ned in themarine realm, but recently stages based on mammals,restricted tothe continental realm of Europe, have also been de ned. Unfortunately, correlations betweenmarine and continental stages remain poorly resolved. In addition, stratigraphic unitsof short duration were dened in the Tertiary: Standard levels (‘ MPunits’) inthe Paleogene(Schmidt-Kittler, 1987) and MN zonesin the Neogene (Bruijn et al., 1992). Theyare used in this paper .Itis worthmentioning that the duration of eachunit, MP or MN,isunknown;durations are not equal. TheQuaternary comprises the Pleistocene and Holocene. Here, we usethe classical subdivisioninto early (lower), middle,and late (upper) Pleistocene. The boundarybetween theearly and middle Pleistocene was assignedan ageof 0.7Ma whereasthe middle-late Pleistocenelimit is xedto about 0.13 Ma. The Holocene (also called ‘ Recent’) represents thelast 10,000 years.