THEPAIREDFINSOFANASPIDS:ONEMORE

HYPOTHESISABOUTTHEIRFUNCTION

PHILIPPEJANVIER

UA.12duC.N.R.S.,InstitutdePaleontologie8,

rueBuffon,75005Paris,France

INTRODUCTIONThefirstevidenceofthesepairedfinswas

THEANASPIDSarejawlesscraniateswhicharefoundintheuppermostSiluriangenusPha-

knownfromtheLowerSiluriantotheUpperryngolepisfromRigerike,Norway.InPha-

Devonian.Theyhavebeenshowntopossessryngolepisthepairedfinslooklikeelongated

amedian,dorsalnaso-hypophysialopening,ribbons,extendingfromthepostbranchial

acharacterwhichisregardedasderivedandspinetotheanalregion(seev.l.f.,Figure1.1,

sharedwiththePetromyzontida(lampreys)1.2).Later,Ritchie(1968,1984)foundthe

andtheOsteostraci.Therefore,thesethreesamekindofpairedfinsintheSiluriangenus

groupsareclassicallygatheredintoamono-Jamoytius.Consequently,thistypeofpaired

phyleticunit,theCephalaspidomorphi(Sten-