Pedicellate Teeth and the Problems of Amphibian Phylogeny

摘要: Living amphibians are the only group of Recent tet-rapods possessing so-called pedicellate teeth. There-fore, amphibian dentition attracts considerable atten-tion morphologists and histologists. The studies onthe structure development individual pedicellateteeth anurans caudates have shown that pedi-cellate teeth a complex consist oftwo calcified dentin elements, pedicel thecrown, connected to each other by nonmineralizeddividing zone [1–4]. study on ontogeny thedental system has revealed out three extantamphibian orders characterized complexchanges until stable definitive state isreached. Thus, in caudates, morphological typesof successively replace other; pos-sess two types distinguished mainly presence orabsence dividing [5–7]. In order Gym-nophiona, transformation consists thechanges crown shape [6].The purpose present was analyze thedevelopment different typesin various groups formation dividingzone, since these aspects tooth remainlargely unknown.In addition interest purely morphologicaland comparative evolutionary problems, this task isimportant for gaining an insight into such extensive andcomplex questions as evolution entireamphibian class validity taxon Lissam-phibia.We examined age series representatives thethree extant (seven species cau-dates, nine anuran one apodan species). prepa-rations were produced staining material fixed in10% formalin with alcohol solution alizarin red S, sothat tissue became red.The dental systemfrom beginning its (at stages ofhatching at final metamor-phosis or postmetamorphosis anurans) hasrevealed that, typically, members both showsuccessive replacement nonpedicellate teethcharacteristic early developmental thepedicellate late stages. These genera-tions not morphologicalstructure (mainly absence thenonmineralized between andthe pedicel), but also calcification pattern.The young developing nonpedicel-late is initiated apical part extends uni-directionally base; subsequently, toothfuses dentigerous bone achieves func-tional state. alsobegins from apex proceeds proximally.However, process abruptly stops approximately inthe middle height future mature tooth; sub-sequently, second center formed external (labial) side nonmineralized pedicelproximal boundary tissue. Inyoung stained alizarin, centerappears pink spot extending parallel divid-ing tooth. Subsequently, calcifi-cation base involvesfirst labial pedicel; then, lateral part;and, finally, lingual part. When ofthe completed, becomes rigidlyattached functional state;only remains nonmineralized.In some cases, either order, thedividing greater lesserextent. generation subpedicellateteeth, distinctive characteristic thelate larval immediately before metamorpho-sis, initially follows same way astrue do, i.e., thecrown begins separate centers. How-ever, along maturation, zonealso completely calcified; thus, when thefunctional achieved, almostindistinguishable preparations.Complete mineralization anddevelopment secondary werealso observed anurans. For example, typical Pyxicephalus adspersus, Conraua crassipes (Ranidae)[7], old all adult On thecontrary,