CAMBRIAN POLYMERID TRILOBITES FROM THE NIDANSHAN AND LIUDAOGOU GROUPS,HUALONG,NORTHEASTERN QINGHAI,CHINA
【Abstract in Chinese】 描述青海化隆拉脊山地区寒武纪武陵世至芙蓉世多节类三叶虫34个种,分属于33个属和17个科。其中包含4个新种,即:Paranomocarella dingmaoshanensis sp.nov.,Adelogonus oblongus sp.nov.,Placosema qinghaiense sp.nov.和Meteoraspis qinghaiensis sp.nov.。对有关的属、种及其归类做讨论和修订,研究表明该地区寒武纪武陵世至芙蓉世多节类三叶虫有较高的分异度,为进一步研究祁连山地层区寒武系地层的划分和对比、沉积相分析和生物地理区的划分等,提供重要的古生物依据。
【Abstract】 Thirty-four polymerid trilobite species assigned to thirty-three genera belonging to seventeen families are described from the Cambrian Nidanshan and Liudaogou groups at two localities in the Lajishan Range of the Qilian Mountains,Hualong,northeastern Qinghai Province.Four species are new and sixteen species are in open nomenclature.The new species are identified as Paranomocarella dingmaoshanensis sp.nov.,Adelogonus oblongus sp.nov.,Placosema qinghaiense sp. nov.,and Meteoraspis qinghaiensis sp.nov.,and the species in open nomenclature are referred to Fuchouia,Idamea,Prochuangia,Maotunia, Proasaphiscus,Paradistazeris,Probilacunaspis, Lisaniella,Luyanhaoaspis,Neosolenopleurella, Xintaia,Fatocephalus,Paracoosia,Proceratopyge,and Onychopyge respectively.As reported by Zhou et al.(1996),the polymerid trilobites from the Laijishan Range are in association with agnostoid trilobites belonging to a large number of genera,indicating the Cambrian trilobite fauna from the Lajishan Range is rather highly diverse. The trilobite fauna has affinity with Cambrian trilobite taxa described from the Jiangnan Slope Belt, South China,and the slope areas of the Tarim Block,NW China,including notably Wanshania wanshanensis,Grandioculus truncatus,Iniotoma porosus,Huayuanella zhiqiangi,Jimachongia lata,Luyanhaoaspis,Paracoosia,Proceratopyge, Prochuangia,Fuchouia,Fatocephalus,Placosema and Adelogonus.Revisions and emendations are made to some of early published taxa. Family Anomocarellidae Hupé,1953 Genus Paranomocarella Yang in Zhou et al.,1977 Type species Paranomocarella parallela Yang in Zhou et al.,1977 Paranomocarella dingmaoshanensis sp.nov.(Pl.II,figs.2,3,5,6) Etymology After the Dingmaoshan Hill in Hualong County,Qinghai Province,NW China. Holotype Cranidium(Pl. II,fig. 3. NIGP141293). Paratypes Three cranidia(NIGP141292, 141295,141296). Description Cranidium subtrapezoidal,with length(sag.)as width between palpebral lobes. Glabella convex,subcylindrical,rounded anterior-ly,with 5pairs of lateral glabellar furrows.Posterior pair(S1)long,shallow and narrow,diagonally directed,S2and S3shallower and shorter than S1,oblique rearward,S4and S5short,nearly transverse,more or less obscure.Occipital furrow wide and shallow,slightly curved rearward;occipital ring narrowing abaxially,with posterior margin bowed rearward and a small node lying subcentrally.Axial furrow broad and deep.Preglabellar field about as long(sag.)as anterior border,Preocular field of fixigena broad(tr.,exsag.).Anterior border furrow broad and deep;anterior border moderately convex,narrowing abaxially,bearing a median preglabellar ridge extending onto preglabellar furrow.Palpebral lobe large,about 0.5as long(exsag.)as glabella,lying slightly behind midlength of cranidia.Eye ridge slightly convex,Palpebral area of fixigena moderately convex,width less than half of the glabellar width.Posterolateral projection very narrow(exsag.)and long(tr.); posterior border furrow broad and deep;posterior border of narrow ridge,slightly widening abaxially.Anterior branches of facial suture diverging strongly forward from the anterior ends of palpebral lobes and posterior branches long,extending nearly transverse from the posterior ends of palpebral lobes. Comparison The new species differs from the type species Paranomocarella parallela Yang in Zhou et al.,1977(p.183,pl.54,fig.1,no fig.2) in having a slightly broader cranidium with a longer and narrower glabella that is not expanded at base,longer palpebral lobes,and relatively wider palpebral areas of fixigenae.It is also closely related to Paranomocarella fortis Peng,Lin,and Chen,1995(p.283,294,295,pl.1,fig.12a;pl.3 figs.4—13;pl.4,figs.1—4),but the latter differs in having a relatively narrower and shorter glabella,a notably broader(sag.)preglabellar field and in lacking the lateral convexity on occipital lobe. Occurrence From the lower part of Liudaogou Group of Cambrian at Hualong,northeastern Qinghai.Family Proasaphiscidae Chang,1963 Type species Adelogonus solus pik,1967 Adelogonus oblongus sp.nov.(Pl.II,figs.8—11) Etymology From Latin oblongus,greater length than breadth,referring to the elongated glabellar outline. Holotype Incomplete cranidium(Pl.II,fig. 8,NIGP141298). Paratypes An incomplete cranidium(NIGP141299)and two incomplete pygidia(NIGP141300,141301). Description Cranidium subrectangular, slightly longer than wide.Glabella wide and convex,strongly tapered,obtusely rounded anteriorly or nearly truncate with width at mid-length of glabella occupies about half of cranididal width,and width at glabellar base about 1.6times of anterior end,bearing 3pairs of faintly depressed lateral glabellar furrows.Axial furrow deeply incised. Preglabellar furrow wide and deep.Palpebral lobe large and long,0.36as long as glabella,lying slightly behind the glabellar mid-length.Eye ridge obscure;palpebral area of fixigena moderately convex,0.39as wide as glabella at glabellar midlength;preglabellar field gently convex,narrower than anterior border,bearing apair of curved ridge extending forward and outward from the anterolateral corners of glabella to the anterolateral corners of cranidium.Anterior border furrow wide and deep;anterior border upturned with anterior margin bowed forward.Posterolateral projections triangular;posterior border narrow and convex.Anterior branches of facial suture diverging moderately forward slightly outward at about 30degrees to the sagittal line;posterior branches extending outward and rearward. Pygidium nearly semicircular,0.51as long as the width at anterior margin.Axis strongly convex,tapering rearward almost onto paradoublural line with width slightly narrower than that of pleural field,occupying 0.73of pygidial length and bearing an articulating half-ring,three rings,and a semicircular terminal piece that continues as a postaxial ridge and merges with pleural field before reaching posterior border.Pleural area with inner part gently convex and outer part broadly concave; pleural furrows distinct proximally,becoming shallow or faint distally;border narrow,strongly upturned,defined by shallow or obscure border furrows. Surface covered with fine,densely spaced granules. Comparison The new species differs from the type species Adelogonus solus pik,1967(p.204, pl.8,fig.3,text-fig.70)in that the latter has a broader cranidium,a shorter glabella,relatively shorter palpebral lobes,longer eye ridges,and relatively longer posterolateral limbs(exsag.).It differs from Adelogonus hunanensis Peng,Babcock, and Lin,2004(p.26,27,pl.9,figs.1—7)in having a slightly narrower cranidium that lacks the paired nodes as seen in front of the anterolateral corners of glabella in A.hunanensis,a longer glabella,relatively longer palpebral lobes,apreglabellar field that is narrower(sag.)than anterior border,and a pygidial axis that is less tapered rearward. Occurrence From the lower part of Liudaogou Group of Cambrian at Hualong,northeastern Qinghai. Family Catillicephalidae Raymond,1938 Genus Placosema pik,1967 Type species Placosema caelatum pik,1967 Placosema qinghaiense sp.nov.(Pl.II,figs.17a,b;Pl.III.fig.8) 1996 Placosemasp.Zhou et al.,Pl.III,fig.13. Etymology After Qinghai Province,NW China. Holotype Cranidium(Pl.II,fig.17. NIGP141307). Paratype Cranidium(NIGP141316). Description Cranidium subtrapezoidal, strongly convex,1.41as wide at level of palpebrallobes as long.Glabella subovate defined by wide and deep axial furrow with anterior margin close to anterior border furrow,bearing three pairs of lateral glaballar furrows:the anterior pair(S3), short,almost invisible,and oblique slightly forward;the S2furrows faint,slightly longer and deeper than the S3,oblique slightly rearward;the S1 bifurcate,with long,diagonal,and firmly defined posterior branch and short,transverse anterior branch.Occipital furrow deep,transverse, narrowing abaxially and directing slightly forward; occipital ring crescent with posterior margin bowed rearward,bearing ill-defined medial node.Palpebral lobe small and convex,0.27as long as glabella,lying slightly behind of cranidial mid-length; eye ridge long,gently curved,running forward at 30degrees from the anterior end of the palpebral lobe;palpebral area of fixigena 0.5as wide as glabella,gently convex.Anterior border convex, with wide central portion,becoming slightly narrow laterally with anterior margin bowed forward and posterior margin bowed rearward;anterior border furrow deep and narrow.Preglabellar field very narrow;preocular area rhombus,downsloping forward strongly.Posterior area of fixigena with broad and deep posterior border furrow widening abaxially and gently convex posterior border; posterolateral projection triangular,0.4as long as glabella(excluding occipital ring).Anterior branches of facial suture long,converging forward to meet anterior cranidial margin opposite lateral ends of occipital ring;posterior branches shorter and diverge rearward. Surface of cranidium with coarse,scattered granules. Comparison The new species differs from the type species Placosema caelatum pik,1967(p. 381,382,pl.20,figs.2—4)in that the latter has a glabella that reaches to the posterior margin of anterior border,so that it lacks the preglabellar field.In addition the latter has shorter anterior branches of facial sutures and has a smooth cranidial surface.The new species resembles closely to Placosema bigranulosum Peng,Babcock,and Lin, 2004(p.68,69,pl.26,figs.1—7),but differs in having a more tapered glabella,a relatively wider(sag.)and narrower(tr.)anterior border,and a more posteriorly placed palpebral lobe. Occurrence From the lower part of Liudaogou Group of Cambrian at Hualong,northeastern Qinghai. Family Crepicephalidae Kobayashi,1935 Genus Meteoraspis Resser,1935 Type species Ptychoparia?metra Walcott, 1890 Meteoraspis qinghaiensis sp.nov.(Pl.III,figs.9—13) Etymology After Qinghai Province,NW China. Holotype Nearly complete cranidium(Pl. III,fig.10,NIGP141318). Paratypes Two incomplete cranidia(NIGP141317,141319)and two incomplete pygidia(NIGP141320,141321). Description Cranidium subsquare,slightly longer(sag.)than width(tr.).Glabella convex, subtriangular,twice as long as wide,rounded to acutely rounded anteriorly,with three pairs of obscure lateral glabellar furrows,and defined by narrow and deep axial furrows.Occipital furrow broad and deep,slightly bowed rearward;occipital ring moderately convex(tr.,sag.),narrowing abaxially,with a small,obscure median node lying centrally.Preglabellar field,slightly depressed,a little over as long as the anterior border;anterior border furrow well defined,slightly bowed forward,bearing three small pits;anterior border moderately convex,wide sagittally,narrowing abaxially with anterior margin curved forward notably.Palpebral lobe moderately long,one-third as long as glabella,lying at about cranidial midlength;eye ridge more or less obscure.Palpebral area of fixigena narrow(tr.),gently convex;posterolateral projection nearly triangular,downsloping strongly abaxially;posterior border furrow broad and deep,widening abaxially;posterior border slightly convex,width about 0.5of the basalglabellar width.Anterior branches of facial suture divergent forward slightly,curving gently inward after crossing border furrow;posterior branches diverging strongly rearward to meet posterior border furrow,then extending subparallel to meet the posterior margin of posterior border.Surface of cranidium bears a few of find,scattered granules. Pygidium subtrapezoid,1.5times as wide as long.Axis strongly convex,tapering gently rearward,with posterior end reaching posterior border furrow,bearing 3rings and terminal piece,with one pair of small nodes on each ring.Pleural field moderately convex,with more or less deep pleural furrows and shallow interpleural furrows.Border furrow wide and shallow;border wide and moderately convex with posterior margin bowed rearward,bearing apair of pleural spines that are broad-based,moderately long,and rearward directed.The length of the spine is between two spines occupies about 0.58of pygidial width. Comparison The new species differs from the type species Meteoraspis metra(Walcott,1890)(Walcott,1890,p.273,274,pl.21,fig.7)in having a more tapered glabella being acuter anteriorly and in developing glabellar furrows and eye ridges. The palpebral lobes of M.metra are relatively shorter,lying slightly behind mid-glabellar level. The new species differs from Meteoraspis orientalis Yuan and Yin,1998(p.145.pl.6,fig.6a,b)in having a slightly longer and narrower glabella,a wider(sag.)preglabellar field,relatively shorter palpebral lobes that are more posteriorly placed, relatively wider palpebral areas of fixigenae,and slightly wider(tr.)posterolateral limbs. Occurrence From the lower part of Liudaogou Group of Cambrian at Hualong,northeastern Qinghai.
【Key words】 Trilobita； Cambrian； Qilian Mountains； Hualong； Qinghai；
- 【Source】 古生物学报 ,Acta Palaeontologica Sinica , Editorial E-mail ,2013(04)
- 【CLC code】Q915