摘要:

An assemblage of megascopic, multicellular thallophytes with well‐preserved tissues and microstructures was discovered in phosphate rocks of the Late Proterozoic Doushantuo Formation (approximately 680 Ma old) at the Wengan‐Fuquan Phosphate Mines, Guizhou Province, South China. Two new genera and three new species are erected:Thallophyca ramosan. gen. et n. sp.,Thallophyca simplican. gen. et n. sp. andWengania globosan. gen. et n. sp. The thalli ofThallophycaare embedded in amorphous collophane and consist of differentiated tissues interpreted as cortex and medulla, and distinct structures (conceptacle‐like cavities and special cell‐groups or ‘cell‐islands’). Tissue differentiation and megascopic (millimetric to centrimetric) size of the thalli suggest that the new genusThallophycamay represent a primitive metaphyte. The new genusWenganiais assigned to the Paleozoic algal group Solenoporaceae Pia. This study provides reliable fossil evidence of Late Proterozoic metaphytes and leads to the following conclusions: (1) diverse multicellular thallophytes had evolved during Late Proterozoic Ediacaran time; (2) adaptive radiations possibly took place more or less contemporaneously in both metazoans and metaphytes, and (3) Precambrian phosphate rocks can preserve megafossils with delicate mi

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1989.tb01674.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Among Late Ordovician brachiopods from southeastern Indiana. strophomenids display a ratio of 4:1 parabolic to linear repaired fractures in contrast to the 1:2 ratio found for orthids and rhynchonellids. Additionally, only strophomenids display repaired elliptical fractures. The weakest parts of strophomenid and orthid‐rhynchonellid shells are the regions of the adductor muscle scars and the sulcus, respectively. Fractured biplanate shells of strophomenids are commonly cleaved anteriorly to posteriorly, whereas fractures are localized on the anterior of strongly curved to geniculate conspecific specimens. Rugae on leptaenids, thickened anterior margins of the brachial valve of rafinesquinids, and the dense distribution of pseudopunctate in all strophomenids, functioned to localize anteriorly the (un)repaired linear and parabolic fractures. No sublethal fracture occurs on any biconvex shell where the height is greater than 14 mm, despite the fact that numerous specimens of certain species attained shell heights of 20 mm or more, an observation suggesting the upper limit in the gape of the crushing elements of the predator. Crushing experiments on valve ‘models’ reveal that the inflated equibiconvex, plicate shape of the shells ofPlarysfrophiais the strongest. However, the architecture of the concave strophomenid valves is relatively stronger than the corresponding valves of many orthids and rhynchonellids when normalized for valve thic

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1989.tb01675.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1989.tb01676.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Labrocuspis kobayashii, a Middle Devonian euomphalacean omphalotrochid gastropod from Japan has a wide callus pad on its base similar to that seen in the living trochidUmbonium. L. kobayashiicould support the shell over the cephalopedal mass in a similar fashion to that seen in theUmboniumspecies. This reconstruction indicates that the labral projection in the outer lip was above the head, and the opisthocyrt basal lip and the sinus in the outer lip were loci of inhalant and exhalant currents, respectively. Therefore, the animal is assumed to have had only one ctenidium (the left). The presence of a wide callus pad is indicative of an infaunal life habit for theUmboniumspecies,Labrocuspisand some Paleozoic gastropods; clamping of the shell against the foot is also suggested for some omphalotrochid gastropods. These features indicate an additional adaptive strategy employed by euomphalaceans.

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1989.tb01677.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Carapace morphology was studied biometrically for each instar in a series of populations ofMojczellaOlempska 1988 from the Ordovician strata exposed in Mójcza, Holy Cross Mountains, Poland. Phosphatic coatings of ostracod valves occur there in abundance from the top of the Arenig to the Late Caradoc. The lineage shows smooth acceleration in ontogenetic expression of the junction of crests C1 and C3, which originally were separated throughout the ontogeny, while in the latest populations the separation was preserved only in the earliest moult stage. Moreover, the velar structure, being originally developed as a wide, slightly convex, flange‐like dolon in heteromorphs, became transformed into a convex dol

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1989.tb01678.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

The second specimen ofXenurion auerswaldaePompeckj 1927, found in an erratic boulder of the basal Cambrian Kalmarsund sandstone in Hiddensee island, GDR, appears to represent the part of the body missing in the holotype. This enables reconstruction of the whole animal, which, despite its remarkable size of about 20 cm in length, was of rather simple anatomical organization, lacking any specialized appendages or head organs. It is suggested thatXenusionwas an ancestral walking articulate which had originated from a priapulid‐like crawling ancestor.Xenusionmay be ancestral for Middle CambrianAysheaia, which exhibits distinct tardigradan traits. It is proposed to classify these two lobopod animals in a new class Xenusia, ancestral for both the Onychophora and the Tardigrada. Possible derivations of the arthropods and annelids from the Xenusia are discusse

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1989.tb01679.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Fourier shape analysis ofPleurodictyum americanumandP. dividua, favositid tabulate corals, from the Middle Devonian Hamilton Group of New York State, indicates that colony growth form is variable within species between environments, but that the range of variability in growth form is static through time.Pleurpdictyum dividuadisplays a columnar morphotype; however,P. dividuaandP. americanumcannot be discriminated from one another based on colony shape alone. A major prediction of the punctuated equilibrium model of evolution is morphological stasis throughout the duration of a species. Harmonic means of assemblages ofP. americanumshow no persistent temporal trends. The range of harmonic means present among the oldest assemblages (Centerfield Limestone) are comparable to those among the youngest assemblages (Windom Shale) and to those in the intervening intervals. Character stasis in colony growth form lasted throughout a 2.5‐3.5 my interval. In tabulate corals, where reproductive modes such as fragmentation have not been demonstrated, growth form may be useful in interpreting ancient environments. In addition, the tempo of evolution of growth form can be analyzed when sufficient morphological data are available from a wide distribution of environments. Thus, Fourier shape analysis of growth form provides a powerful tool for paleontologists to interpret the ecology and evolution of colonial marine animal

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1989.tb01680.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1989.tb01681.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Abundant pyritic pseudomorphs of monaxonic siliceous spicules (ophirhabds and ?heloclones) have been found entrapped in the calcareous skeleton of the halysitid tabulateQuepora ?agglomeratiformis(Whitfield) from late Ordovician limestones of Frobisher Bay, Baffin Island, Canada. The finding indicates a poriferan (choristid or sublithistid) affinity of halysitids, early Palaeozoic marine fossils related so far to corals. They probably derived from a monaxonic group of early demosponges that adapted during the Ordovician to Ca2+stress conditions in epicontinental seas by excreting the excessive Ca2+influx to their tissues as variously designed chains of basally secreted calcareous tubes.

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1989.tb01682.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Rates of shell production rarely exceed 500 g CaCO3.m‐2yr‐1in clastic sediments. Loss of shell carbonate by dissolution greatly exceeds loss by bioerosion and abrasion in most habitats. Rates of shell dissolution in modern sediments, estimated from rates of organic carbon degradation or measured directly, usually exceed 1000 g CaCo3.M‐2yr‐1. This taphonomic loss is concentrated at or just below the sediment‐water interface in the taphonomically‐active zone (TAZ). Consequently, except where rates of shell production are very high or rates of organic carbon degradation very low, shells cannot permanently accumulate on the sea floor. Preservation requires rapid burial, usually by physical ‘event’ processes, to slow down taphonomic loss. Only near the base of the TAZ does the long‐term sedimentation rate become an effective mediator of shell preservation as sediment accumulation gradually removes buried shell material from the taphonomi

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1989.tb01683.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY