Evolution of oral apparatuses in the conodont chordate

• Autorzy: Dzik J.
• Języki publikacji: EN

Abstrakty

EN

The oldest well known conodonts had seven pairs of their phosphatic denticles arranged into a grasping apparatus closely resembling that of the Chaetognatha. During the Early Ordovician apparatuses with three morphologic groups of elements developed, and a single unpaired element that splits the apparatus into two parts, the posterior one being presumably enclosed into the throat. Subsequent evolution resulted in the development of an incisor-like morphology of the anteriormost pair of elements, a filtratory basket in the remaining exposed part of the apparatus, and a heavily molarized, hidden platform complex. Further development resulted in great diversity of forms of the apparatuses, from secondarily simplified, through robust (of the Myxine type), to highly sophisticated apparatuses with all the element pairs being morphologically distinctive. The unusual, ventral location of molarized surfaces in some advanced conodonts suggests some change in muscular armament of the throat. Conodonts reached their greatest diversity in the Middle Ordovician. Co-occurrence of many morphologically similar sympatric species is typical for the Late Paleozoic. A modified classification of the conodonts is proposed.

PL

Pokrój ciała z asymetryczną płetwą grzbietową i V-kształtnymi myomerami tudzież sposób sekrecji fosforanowych elementów aparatu gębowego wskazują na przynależność konodontów do strunowców. Na podstawie wytrawionych z wapieni zespołów zlepionych elementów (clusters) i naturalnych agregatów na powierzchni łupku (natural assemblages) możliwe jest odtworzenie przestrzennego rozmieszczenia elementów aparatu. U najpierwotniejszych konodontów (typu Panderodus) aparat składał się z siedmiu par elementów tworzących aparat chwytny analogiczny do właściwego dzisiejszym szczecioszczękim (Chaetognatha). Dwie pary elementów w przodzie aparatu (ne, hi) wyróżniały się kształtem, a rozmiary elementów zmniejszały się ku tyłowi aparatu. Już wśród konodontów o prostych elementach (typu Protopanderodus) nastąpiło dalsze zróżnicowanie elementów aż do wyodrębnienia trzech serii przejść morfologicznych. Powstał aparat analogiczny funkcjonalnie do żuwaczek skorupiaków, z częścią siekaczową w przodzie, grzebykowatą pośrodku i żującą w głębi. Tuż za skrajnym elementem (ne) z ostrym, masywnym wierzchołkiem następowała seria 4 par (hi, ke, pl, lo) delikatnych elementów połączonych pośrodku symetrycznym nieparzystym elementem (tr); tworzyły one rozwarty ku przodowi kosz filtracyjny. W pewnym oddaleniu od kosza filtracyjnego, zapewne wewnątrz gardzieli, znajdowały się dwie pary masywnych elementów serii platformowej (oz, sp), być może służących do rozgniatania pokarmu. W skrajnych przypadkach każda z par elementów była odmienna morfologicznie a w serii platformowej prawe i lewe elementy różniły się kształtem. Przynajmniej część ordowickich Balognathidae miała trzy pary elementów serii platformowej a u triasowych Gondolellidae powiększona była liczba par elementów kosza filtracyjnego. Do identyfikacji elementów aparatu używa się różnorakich systemów terminologicznych, których omówieniu towarzyszy propozycja ujednolicenia w oparciu o mający pierwszeństwo schemat Jeppsona (z uzupełnieniami von Bittera). Przy opisach elementów winno się respektować fizjologiczną orientację elementów w aparacie zamiast konwencji Pandera, wprowadzonej w wyniku błędnej interpretacji elementów aparatów konodontowych jako rybich ząbków. Artykuł zawiera ilustrowany przegląd poszczególnych typów aparatów i zmodyfikowany system klasyfikacji konodontów, zgodny z nową interpretacją filogenezy.

• Wydawca: -
• Czasopismo: Acta Palaeontologica Polonica
• Rocznik: 1991
• Tom: 36
• Numer: 3
• Opis fizyczny: p.265-323,fig.,ref.

Twórcy

autor

Dzik J.

• Polish Academy of Sciences, Aleja Zwirki i Wigury 93, 02-089 Warsaw, Poland

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