Yunnanozoon and the ancestry of chordates

• Autorzy: Dzik J
• Języki publikacji: EN

Abstrakty

EN

The oldest known chordate, Yunnanozoon lividum Hou et al. 1991, from the Chengjiang Lagerstätte of Yunnan shows several features in its anatomy that had not been expected to occur at this stage of evolution. Its metameric dorsal myomeres were separated by straight myosepta. The notochord was located ventrad of the muscular blocks instead of being bordered by them. The pharynx did not contain any filtratory basket but had only seven pairs of branchial arches. These were composed of rows of minute scleritic segments that connected the notochord with a rigid ventral trough. The head region was rather complex in organization and bore a specialized ring-like mouth apparatus. The presence of sensory organs, perhaps large eyes with sclerotic rings, is probable. Only in the remarkable elongation of the notochord and metameric arrangement of oval gonads this early chordate is similar to Branchiostoma. The anterior part of the muscular blocks of Yunnanozoon resembles a little the proboscis and collar of the enteropneusts and may perhaps be homologous with these structures, although in Yunnanozoon they are displaced much behind the mouth. The whole metameric muscular unit is proposed to correspond to the 'quilted pneu structure' of the Ediacaran problematic fossil Dickinsonia. Monotypic Yunnanozoa classis n., Yunnanozoida ordo n., and Yunnanozoidae fam n. are proposed for this early chordate.

PL

Wśród tysięcy skamieniałych zwerząt nie mających mineralnego szkieletu z wczesnokambryjskiego stanowiska Chengjiang w prowincji Yunnan znalazly się też szczątki pierwszych strunowców. Yunnanozoon lividum Hou et al. 1991, opisany jako problematyk przed kilku laty, ukazuje wypełnioną osadem gardziel z łukami skrzelowymi i gonadami po bokach, a nad nią cylindryczną strukturę ubogą w substancje organiczne i z wnętrzem niedostępnym dla mułu - zapewne wypełniony płynem lub zwakuolizowanymi komórkami osiowy szkielet a więc struna grzbietowa. Zaskakującymi cechami Yunnanozoon są prostopadłościenne bloki miomerów, zapewne mające postać umięśnionych, wypełnionych płynem worków oraz rozbudowana głowa z aparatem gębowym o pierścieniowej nierozpoznanej dokładnie strukturze i zapewne z dużymi organami zmysłowymi (oczami?). Dowodzi to, że cechy uważane za osiągnięcia kręgowców charakteryzowały już pierwsze strunowce. Poszukując krewniaków i przodka Yunnanozoon wśród innych kambryjskich i prekambryjskich organizmów (powinni się cechować metamerycznymi workami mięśniowymi ponad jelitem z bocznymi wypustkami otwartymi na zewnątrz) wskazać można na przypuszczalnego konodonta Odontogriphus ze środkowego kambru Burgen i Dickinsonia z prekambru Ediacara i Morza Białego.

Słowa kluczowe

PL

Odontogriphus; kambr; Dickinsonia; Yunnanozoon lividum; skamienialosci; prekambr; paleobiologia; strunowce

• Wydawca: -
• Czasopismo: Acta Palaeontologica Polonica
• Rocznik: 1995
• Tom: 40
• Numer: 4
• Opis fizyczny: s.341-360,rys.,bibliogr.

Twórcy

autor

Dzik J

• Instytut Paleobiologii PAN, Aleja Zwirki i Wigury 93, 02-089 Warszawa

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