| Evolutionary Significance of Pylentonemid Radiolarians and Their Late Devonian Species from Southwestern Tianshan, China |
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| 作者姓名： | LIU Yu HAO Shougang |
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| 作者单位： | Department of Geology, Peking University, Beijing 100871 |
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| 摘 要： | A group of radiolarian fossils with a complete morphological gradient of increasing polarization are reported from upper Devonian successions in southwestern Tianshan, China. Specifically, the important transitional mophotypes, Pylentonema transitorum sp. nov., Archocyrtium medium sp. nov. and Quadrapesus transitivus sp. nov, were found. Based on the fact that the new transitional radiolarian fossils resemble more closely to pylentonemids （cyrtoid nassellarians） than to entactinids （spumellarians） in morphology, they are assigned to pylentonemids. Pylentonemids share characters of both the Nassellaria （e.g., horned cephalis, basal opening with pylome） and Spumellaria （e.g., system of trabecular spicules）, and they are thus of evolutionary significance. The evolutionary trend from spumellarians to nassellarians is characterized by （1） internal spicule： from simple trabecular spicules to complicate components （A;Ir,II;D;V;Lr,Li;MB）; （2） polarization of the radiolarian tests due to rearrangment of spine, from radial to an axial symmetry; （3） the gradual formation of a basal opening （aperture, pylome, or podome）; and the transition from a pseudopylome, a primative pylome with a narrow margin on the outer shell, to a true pylome rimmed with a narrow, elevated impermite wall.
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| 关 键 词： | 放射虫 泥盆纪 化石 偏震 |
| 收稿时间： | 2006-06-22 |
| 修稿时间： | 8/8/2006 12:00:00 AM |
Evolutionary Significance of Pylentonemid Radiolarians and Their Late Devonian Species from Southwestern Tianshan, China |
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| Authors: | LIU Yu and HAO Shougang |
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| Institution: | LIU Yu and HAO Shougang Department of Geology,Peking University,Beijing |
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| Abstract: | A group of radiolarian fossils with a complete morphological gradient of increasing polarization are reported from upper Devonian successions in southwestern Tianshan,China.Specifically,the important transitional mophotypes,Pylentonema transitorum sp.nov.,Archocyrtium medium sp.nov.and Quadrapesus transitivus sp.nov.,were found.Based on the fact that the new transitional radiolarian fossils resemble more closely to pylentonemids(cyrtoid nassellarians)than to entactinids(spumellarians)in morphology,they are assigned to pylentonemids.Pylentonemids share characters of both the Nassellaria(e.g.,horned cephalis,basal opening with pylome)and Spumellaria(e.g.,system of trabecular spicules),and they are thus of evolutionary significance.The evolutionary trend from spumellarians to nassellarians is characterized by(1)internal spicule:from simple trabecular spicules to complicate components(A;lr,ll;D;V;Lr,Li;MB);(2)polarization of the radiolarian tests due to rearrangment of spine,from radial to an axial symmetry;(3)the gradual formation of a basal opening(aperture,pylome,or podome);and the transition from a pseudopylome,a primative pylome with a narrow margin on the outer shell,to a true pylome rimmed with a narrow,elevated impermite wall. |
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| Keywords: | radiolarian spumellarian nassellarian entactinids pylentonemids phylogenetic evolution Late Devonian southwestern Tianshan |
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