摘要
前言 云南晋宁梅树村剖面位于北纬24°44’,东经102°34’(插图1),是国际前寒武系-寒武系界线候选层型剖面之一。1984年8月,侯先光在此剖面工作时,在下寒武统筇竹寺组Eoredlichia-Wutingaspis带一层灰绿、灰黄色泥岩内(野外号AEF-k10)发现了少量水母、蠕虫、大型双瓣壳节肢动物等化石。
The Meishucun section in Jinning County Yunnan(Text-fig.1),one of the candidates for the global stratotype section of the PrecambrianCambrian boundary,represents the oldest Cambrian chronostratigraphic unit in China,with a fauna characterized by diverse small shelly fossils,such as Anabarites,Paragloborilus and Sinosachi tes.The Meishucun Stage is followed by the Chiungchussu Stage which is characterized by the appearance and flourish of trilobites and bradoriids and can be divided into two trilobite zones,including the Parabadiclla Zone below and the Eoredlichia-Wutingaspis Zone above.During the field work in 1984,the former writer first found a few soft-bodied fossils and others from the Eoredlichia-Wutingaspis Zone of the Early Cambrian Chiungchussu Stage at the Meishucun section,Jinning.In 1986 the writers returned to this section and found many excellent specimens from the same horizon.The new material illustrated here from the Meishucun section in Jinning includes the priapulid worms Cricocosmia jinningensis gen.et sp.nov.and Cricocosmia sp.,the probable annelid worm Palaeoscolex sinensis sp.nov.and the archropod Odaraia?eurypetala sp.nov.,associated With the trilobite Eoredlichia,the bradoriids KunMingella and Kunyangella,the large bivalved arthropod Isoxys auritus(Jiang),the hyolithid Ambrolinevitus ventricosus Qian,the medusa Heliomedusa orienta Sun et Hou,etc.The Chengjiang Fauna was first discovered in 1984 by the former writer from the EoredlichiaWulingaspis Zone of the Early Cambrian Chiungchussu Stage in Chengjiang County,Yunnan,with some its members having been preliminarily studied(Zhang Wen-tang and Hou Xian-guang,1985;Hou Xian-guang,1987;Sun Wei-guo and Hou Xian-guang,1987).The remarkably well-preserved fossils from Jinning are yielded in the same position as those from Chengjiang,both fossil localities being about 40 km away from each other in the same sedimentary environment.The sedimentary sequence of the Chiungchussu Stage is characterized by black to greyish black shales and mudstone in the lower part and weathered grayish yellow,greyish green mudstone in the middle and upper parts,intercalated with thin-to mediumbedded sandstones,representing the deposits in an old bay of the western littoral part of the marine area on the Yangtze platform.New findings from the Meishucun section further illustrate the diversity of the Chengjiang Fauna and extend the stratigraphic range of the Palaeoscolcx and probable the Odaraia downwards to the much lower Cambrian.The fossils consist of parts and counterparts.Definition of the part is normally based on the relative prominence of the fossil as compared to the counterpart,but the distinction between part and counterpart may be arbitrary when the fossils are preserved as flattened films.Fossil Descriptions Phylum Priapulida Class,Order and Family uncertain Genus Cricocosmia gen.nov.Etymology:Genus name derived from cricoand cosmia,Greek,circle and ornamentation,with reference to the small circular structures on the annulations.Type species:Cricocosmia jinningensis gen.et sp.nov.Diagnosis:Body cylindrical and bilaterally symmetrical,divided into anterior proboscis and annulated trunk.Proximal zone of fully everted proboscis armed with spines.Surface of annulations with small distinct circular structures.Gut straight and simple.Cricocosmia]inningensis gen.et sp.nov.(Pl.I,figs.1-7)Material:Specimens of three incomplete individuals flattened in greyish yellow mudstone.Bodies of the holotype,Cat.No.IGP 103803 and a paratype,Cat.No.IGP 103804,extended and almost straight.Body of the other paratype,Cat.No.IGP 103805,also extended but curved with one end folded and compressed upon the annulated trunk.Description:Body cylindrical,2-2.5 mm in width.Proximal zone(i.e.,Zone I,Conway Morris,1977,p.66)of everted proboscis armed with spines as clearly shown in the holotype(P1.I,figs.1-3;Text-fig.2).Trunk clearly annulated,with no ornamentations on annulations in the anteriormost region where annulations count about 40 per cm(Pl.l,figs.1-3;Text-fig.2).Each annulation on the flattened surface bearing a pair of small circular structures in the main region of the trunk(except the anteriormost region),where annulations count about 20 to 24 per cm.Small circles symmetrically arranged in two longitudinal rows on the flattened surface.A dark median bank represen ting a gut,which is straight and simple.Discussion:In the main region of the trunk each annulation is marked with a pair of small circles on the flattened surface.Since the flattened surface represents approximately one-half of the body’s original circumference,each complete annulation might bear two pairs of small circles.Cricocosmia Jinningensis gen.et sp.nov.is characterized by the clear annulations and the occurrence of paired small circles on the annulations,thus differing from other priapulids.It differs from Sabellidies yunnanensis and S.badaowanensis both from Jinning(Luo Hui-lin and Zhang Shi-shan,1986)in the presence of small circles on the annulations and the possession of a proboscis.?Phylum Annelida Class Palaeoscolecida Conway Morris et Robison,1986 Order uncertain Family Palaeoscolecidae Whittard,1953 Genus Palaeoscolex Whittard,1953 Palaeoscolex sinensis sp.nov.(P1.III,figs.1-4)Material:A complete individual,holotype Cat.No.IGP 103808,with O-shaped coils.Description:A coiled worm flattened in greyish yellow mudstone,measuring approximately 62 mm in fully extended length and 2 mm in flattened maximum width.Morphological details at either end obscure.Straightly extended portion being regarded here as the possible anterior end.Annulations and papillate bands not appearing to extend onto this anteriormost region,on which although there are irregularly scattered papillae.No jaw apparatus apparent(see Whittard,1953).Segments numbering about 48 per cm averagely with the body thus composed of 250 to 300 segments.Entire external surface almost occupied by transverse rows of papillae alternating with transverse rows of minute pits.Each segment marked with double transverse rows of papillae and demarcated by the ridge bearing double tran sverse rows of minute pits(Pl.III,figs.3,4;Textfig.5).Each transverse row containing 20-25 papillae and 30-40 minute pits;thus original ring of the body probably bearing 40-50 papillae and 60-80 minute pits.Papillae roughly hemispherical in outline and 30-45 um in diameter.Gut flattened,looking like a dark band.Discussion:Palaeoscolex sinensis sp.nov.differs from P.piscatorum Whittard in the double transverse rows of minute pits between papillate bands,and from P.ratcliffei Robison and P.cf.P.ratclijffei Conway Morris et Robison in the presence of minute pits between papillate bands.Measurements listed in Table 1 indicate some other differences among these four species.In ornamentation Palaeoscolex antiquus is rather different from other species,and thus it is doubtful to place the species in the genus Palaeo scolex(Conway Morris and Robison,1986).Moreover,new material further indicates that P.antiquus does not seem belonging to this genus.Phylum Arthropoda Class and Order uncertain Family Odaraidae Simonetta et Delle Cave,1975 Genus Odaraia Walcott,1912 Odaraia?eurypetala sp.nov.(Pl.II,figs.4-6)Etymology:Species name derivcd from euryand Petala,Greek,broad and leaf,with reference to the broad telson fluke.Material:An incomplete specimen,holotype,Cat.No.IGP 103807,with posterior trunk and telson well preserved in parallel aspect.Description:An only specimen preserved in parallel aspect,showing 13 trunk somites with a gradual increase in width and with no obvious change in sagittal length from posterior to ante rior.Intersomite boundaries straight,while trunk somites overlapping,each inserting into the adjacent anterior one:thus intersomite boundaries ap pearing double,being made up of the posterior margin of one somite and the anterior margin of the next(Pl.II,fig.4;Text-fig.6).Posterior margin of each somite not appearing to be fringed with spines.Telson elongate,ap?earing to increase in width posteriorly,with two large and bilaterally symmetrical lateral flukes.Lateral telson flukes broad,fan-shaped in outline in parallel aspect.Existence of a distinct conjunctional groove between lateral fluke and telson probably indicating the flukes articulating with the telson.Extero-lateral area of each lateral telson fluke bearing three grooves,with the aneriormost one extending forward and intersecting the groove between fluke and telson at antero-middle area.A feature which bears the marginal filaments and occurs in the interolateral area of the right lateral fluke(Pl.II,figs.5.6:Text-fig.6),probably representing the median telson fluke.Discussion:Odaraia?enryyctala sp.nov.is incompletely preserved,probably representing the trunk somites and telson extending bevond the carapace.It appears relatively similar to Odaraia alata Walcott,1912(Briggs,1981),but differs from the latter in the elongate telson,the broad telson flukes,especially in having an evident boundary(groove)between the telson and telson fluke and the three grooves on each lateral fluke.Based on these characteristics the new species is here temporarily designated to Odaraia.
作者
侯先光
孙卫国
Hou Xian-guang;Sun Wei-guo(Nanjing Institute of Geology and Palaeontology,Academia Sinica)
出处
《古生物学报》
1988年第1期1-12,139-142,共16页
Acta Palaeontologica Sinica
