摘要:

Asteroids of all geologic ages share a single basic body form, surficial skeletal arrangement, and aspects of water vascular construction. In almost all described Paleozoic species, however, either podial pores to the interior of the arm were lacking, or they are directed laterally, above the adambulacrals. They are internal and above the ambulacrals in known post‐Paleozoic species and the PennsylvanianCalliasterella.Certain features of the ambulacral skeletal arrangement also differ.Calliasterellais the closest known Paleozoic relative of post‐Paleozoic asteroids. Classifications of asteroids that stress only overall form and surticial skeletal arrangement erroneously include Paleozoic and Holocene species in common ordinal or even lower level groupings. Taxonomic revision is premature: however, most known Paleozoic asteroids represent primitive lineages. Transitional forms allow reconstruction of events leading to the modern arrangement. Ampullar and skeletal arrangements of post‐Paleozoic asteroids appear to offer some functional advantages over those of their precursors, but as early as the Ordovician, diverse feeding habits had evolved and ecological roles paralleled those of Holocene sp

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1988.tb02071.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

The well‐known association of platyceratid gastropods with crinoids has traditionally been considered an example of coprophagous commensalism. The Occurrence of several crinoid ‘stands’ (Platycrinitessp.) from closely spaced bedding surfaces in the upper Mississippian Wymps Gap Limestone member of the Mauch Chunk Formation of southwestern Pennsylvania encourages reinterpretation of this relationship. Crinoid calyces were collected from five separate clusters, two of which contained associated platyceratids. ‘Infested’ crinoids either died prematurely or were stunted, compared to crinoids in the ‘uninfested’ clusters. Platyceratid attachment apparently had an adverse effect upon crinoid growth. Serial acetate peels show positioning of the gastropod on the crinoid tegmen over a highly developed anal tube, or chimney. However, the terminus of the anal tube abuts the gastropod's shell and is poorly situated for fecal ingestion by the snail. We suggest that the snail probably pursued another trophic strategy, perhaps taking advantage of aerosol filtration by the crinoid and elevation above

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1988.tb02072.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Czerkas, Sylvia J.&Olson, E. C. (eds.) 1987: Dinosaurs Past and Present.

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1988.tb02073.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

JuvenileTerebratalia transversa(Brachiopoda) metabolize carbohydrates in the anterior‐most marginal mantle at a rate of 0.46 μM glucose/g/hr (in vitroincubation of mantle in C14‐glucose in a carrying medium of 10‐3M non‐radioactive glucose). The rate declines to 0.18μM glucose/g/hr in full‐grown specimens. Carbohydrate metabolism in the marginal (anterior‐most) mantle averages approximately 3.7 times greater than metabolism in (a portion of the ‘posterior’) mantle situated between the coelomic canals and the marginal mantle. This ratio remains constant in specimens of all sizes (i.e. an ontogenetic trend in the ratio is absent atp≤ 0.05). Organic acids are not detectable within the mantle (HPLC techniques) even after simulated anoxia (N2bubbling during mantle incubation). Glucose metabolismin vitrodeclines in both the marginal and ‘posterior’ mantles during anoxia and the metabolic ratio between marginal/‘posterior’ mantles becomes 1/1. We found no difference (atp≤ 0.05) in mean metabolic activity or in sue‐related metabolic trends among populations from depths ranging between mean sea level and 70 m. However, the activity within the ‘posterior’ mantle was more variable in specimens from 70 m than in those from shallower habitats (10 m ‐ mean sea level). The size of the specimens analyzed was most variable in the groups obtained from the shallowest habitats and least variable at 70 m depth. Our results may help define the energetics of fossil as well as living brachiopod shell growth. Brachiopod shell growth is known to be very slow relative to that of bivalves and our results indicate that this is a result of the animals' slow metabolism. The inflation of the valves inT. transversais, in part, a function of the high ratio of intermediary metabolism in the marginalvs‘posterior’ mantle (i.e. parallels the relative growth rates at the shell marginvs‘posterior’ areas). We found that the bivalve,Chlamys hastata, which is commonly associated with T.transversa, has a lower ratio of metabolic activities in the ventral/dorsal mantle areas than the brachiopod has in the anterior/posterior. The difference produces a flatter shell in the bivalve in accord with allometric principles. The higher metabolic rate in the marginalvs‘posterior’ brachiopod mantle and its more pronounced decline with anaerobiosis is reflected in the greater definition of growth increments in the outer shell layer. Our results do not support recent generalizations that correlate shell thickness of a wide variety of invertebrates inversely with metabolic rate. Growth rate as determined from width of shell growth increments is a better index of metabolic rate. Although the genetic basis of glucose metabolism is unknown, the observed metabolic variability is consistent with suggestions that populations of marine organisms living in stable offshore environments are genetically more variable but morphologically more uniform than populations from shallow water. Furthermore, our results support suggestions that bivalved molluscs and brachiopods are very different metabolically, but the data are neutral with respect to theories of competitive excl

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1988.tb02074.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

A venerid bivalvePhacosoma japonicum(Reeve) occurring commonly in the Japanese coastal area preserves periodic growth lines in the shell cross‐section. Long‐term shell growth patterns of this species have been traced for many individuals on the intertidal flat of the Seto Inland Sea, west Japan. Sclerochronological analysis of these individuals and specimens collected monthly shows that several growth cessation marks within their shells are formed during the winter of each year prior to spawning. Hence the marks were used for age and growth rate determinations. As large individuals showed little shell growth for more than two years after the formation of 7 or 8 annual increments, this species probably has a lifespan of more than ten years. Shell growth patterns of this species based on annual increments can be accurately approximated by a von Bertalanffy curve. The number of microgrowth increments formed during a year tends to decrease with age, although it varies markedly among specimens of the same age. Furthermore, even in summer during rapid shell growth, the microgrowth increments do not represent daily and/or sub‐daily tidal rhythms in many specimens. The results of this study and those by several authors strongly suggest that the annual increments are the key for age and growth rate determinations of both living and fossil bivalve sp

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1988.tb02075.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Müller, K. J.&Walossek, D. 1987:Morphology, Ontogeny, and Life Habit ofAgnostus pisiformis from the Upper Cambrian of Sweden

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1988.tb02076.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

In ammonites, the time between two successive septal secretions is assumed to be almost stable during growth within homogeneous sets with regard to phylogeny and morphology. The number of septa (included in the adult phragmocone) is proposed as an alternative standard for age. At each moment of growth, the rate of shell secretion can be directly estimated by the measure of shell length between two septa. Equivalent results are obtained for ribs whose formation is also dependent on an almost stable rhythmical process. Results obtained from septa and size used as age standards are compared in the example of Liparoceratidae‐Amaltheidae evolution. The two standards provide estimations of age which diverge from more than 1 to 2. For example, some small species previously seen as progenetic are now classified as dwarfed. These results emphasize the risk of using size as the only standard of age. Alternative standards not only in ammonites but also in other animal groups should be investigate

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1988.tb02077.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Richly fossiliferous marine sediments exposed along the Sonoran coastline of the Gulf of California near Punta Chueca provide an excellent setting in which to test (a) the strength of the association of skeletal concentrations with sedimentary hiatuses, (b) the utility of taphonomic evidence for reconstructing detailed histories of those non‐depositional episodes, and thus (c) the largely unexploited potential of skeletal concentrations in the identification and interpretation of lithologically obscure unconformities and condensed sequences in shallow marine deposits. Sequence analysis based on discontinuity surfaces is possible in the complex, alluvial fan‐to‐shallow marine transition at Punta Chueca despite rapid facies changes. Progradation of depositional sequences that contain cobbles reworked from older terrace deposits indicates accumulation during a fall in eustatic sea level. The supratidal to subtidal conglomerates and sands contain a variety of predominantly molluscan shell concentrations that, on the basis of postmortem histories of shells, formed during periods of low net sedimentation (i.e. depositional hiatuses); the majority of these shell beds lie along discontinuity surfaces identified by independent physical stratigraphic evidence. Although not all discontinuity surfaces in the terrace are paved by shell material. and not all relative concentrations of shells indicate distinct discontinuities, the strength of the association between skeletal concentrations and stratigraphic hiatuses reveals the high degree of control on fossil occurrence by sedimentation rates, and indicates that skeletal concentrations can provide good clues to stratigraphically significant surfaces. Moreover, the detailed dynamics of non‐depositional episodes are reliably revealed by taphonomic analysis of the associated fossil assemblages, improving interpretations of non‐depositional episodes in local sedimentar

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1988.tb02078.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

The macrofaunal distribution of the mid‐Cretaceous El Abra Limestone reef core is quantified from two measured sections in Taninul Quarry, San Luis Potosi, central Mexico. The faunal structure is transitional between typical Lower Cretaceous reefs dominated by corals with low‐density rudist bivalve packing; and densely‐packed, rudist‐dominated Upper Cretaceous reefs. The macrofauna is predominantly associations of unconnected individuals of caprinid rudists, with a low diversity of other shelly mollusks and corals. An examination of the alternation of paleocommunities defined by the dominant caprinid taxa reveals no pattern of biotic succession within the reef core. Large‐scale sedimentologic features of mud and debris content, coupled with rudist growth type, suggest that paleocommunities may have been physically c

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1988.tb02079.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Discovery ofTremichnus cysticusBrett on a crinoid pluricolumnal from the Willowvale Shale of western New York extends the range of this ichnogenus into the Lower Silurian. Pits attributable toTremichnusapparently represent embedment sites of parasites or commensalistic, filter‐feeding organisms of unknown affinities. Embedment ofT. cysticusmay have been accomplished by localized inhibition of stereom growth within the pits aided by secretion of substances that stimulated accretion of stereom by the host pelmatozoan in areas immediately surrounding the pit

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1988.tb02080.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY