摘要:

Trophic analysis of communities consists of three methods: (1) measuring energy flow, (2) reconstructing food chains. and (3) describing feeding habit ‐ substrate niche patterns. The latter two methods are useful in interpreting evolutionary patterns and depositional environments of paleocommunities. Because the preserved trophic structure may differ significantly from the actual structure. each study must test the hypothesis that preserved trophic structure is related to the environment. Analysis of several modem marine communities shows that their ‘preserved’ structure would not differ greatly from the actual structure. A comparison of some Holocene communities with Tertiary and Cretaceous communities shows that some communities from comparable environments have distinct feeding habit‐substrate niche patterns. Differences can be explained by the evolutionary stage of the biosphere. Trophic structure seems to be partly related to over‐all environmental stability, to food resources, and to subst

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1978.tb01210.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1978.tb01211.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

A principal point of disagreement in conodont ecology between the pelagic depth stratification model and the benthic model of lateral segregation is the mode of life of the conodont animal. A study of the literature on certain Recent benthic and planktic organisms that may serve as ecologic analogues (chaetognaths, isopods, foraminifers) indicates that distributional patterns alone are not definitive of a pelagic versus a benthic habit. Therefore, we doubt that it is possible to determine the major ecologic mode of conodonts solely from distributional data. Because there is not consistent congruence between lithofacies and conodont biofacies, it is unlikely that conodonts were infaunal or sessile epifaunal benthos. The probable alternatives are nektobenthic or neritic pelagic animals and these may have been subject to such similar controlling hydrographic factors that it is now extremely difficult to distinguish between them, especially in an extinct group of uncertain zoologic affinity. Apparently, the only significant line of evidence for pelagic mode is the Occurrence of some conodonts in black shales that are devoid of unquestioned benthic fossils and presumably formed under anoxic bottom conditions.

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1978.tb01212.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1978.tb01213.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Five examples of symbiosis between gastropods and trepostome bryozoans are described from the Ashgill (late Ordovician) of Cumbria (England). The gastropods are invariably found associated with the bryozoans. whereas the bryozoans may be free‐living. Encrustation is considered to have taken place, in most cases, on mature, living gastropod shells, resulting in the trepostome utilizing the shell as a surrogate basal disc. Three specimens show encrustation on an empty gastropod shell, causing the trepostome to develop a basal disc similar to non‐encrusting forms. The bryozoan colony probably benefited from the symbiotic relationship by increased water flow over the colony, caused by gastropod locomotion, whereas the gastropod was afforded protection from predators. The new speciesSpiroecus nidhoeggi. Diplotrypa hvergelmiandMonotrypa fontinalisare descri

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1978.tb01214.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

The Ludlow Series of the Welsh Borderland represents a gradient from quiet. deep shelf muds to shallow, storm‐deposited silts. A fauna of 44 bivalve species shows a pattern of overlapping environmental ranges which span the full extent of the shelf gradient. Bivalve abundance is highest at the extremes of this gradient, where endobyssate forms are common in storm‐deposited silts, and nuculoids locally dominate the fauna of the deep shelf muds. Species diversity of bivalves, however, is highest in low‐stress. mid‐shelf environments, where bivalves of small population sizes comprise a minimal proportion of the benthic fauna. Niche sizes, species diversity. and total environmental range of the bivalves is comparable to that of Ludlow brachiopods, even though the latter group is far more abundant as indi

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1978.tb01215.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1978.tb01216.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

The irregular echinoidsPlesiechinus ornatus(Buckman) (Pygasteroida) andGaleropygus agariciformis(Forbes) (Cassiduloida) occur together in beds of themurchisonoeZone, Bajocian, outcropping in the Cheltenham region of Gloucestershire. These species were largely restricted to different lithofacies within the carbonate shelf environment. Both adopted a hidden mode of life but achieved this by different techniques.Plesiechinushad fairly short spines and strongly muscular podia over the whole corona and was able to cover itself with coarse substrate particles. The oral tubercles are bilaterally symmetrical and are radially arranged. The oral spines are thought to have pulled sediment out from beneath the test, excavating a small depression for it.Galeropygusbore a dense covering of very small spines and its tube feet were differentiated into aboral respiratory podia and oral suckered podia. It had a preferred anterior direction of locomotion and is thought to have buried itself completely by excavating and ploughing into the substrate as it moved forward.Plesiechinusfed using only its lantern and postulated peristomial tube feet, whereasGaleropyguswas a continugus sediment swallower and used its phyllode tube feet and peristomal lip spines in transferring particles towards the mouth.

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1978.tb01217.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1978.tb01218.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Previous work by the author has shown thatLaqueus californianus. Terebratulina unguicula, and. to a lesser extent,Hemithyris psittaceawill actively reorient to water currents in the laboratory;Terebratalia transversawill not. This active reorientation is effected primarily by the dorsal adjustor muscles; the ventral adjustors function to depress and tilt the shell. The torque around the pedicle generated by drag on the shell is low at moderate current speeds. The dorsal adjustor muscles are competent to resist these torques up to current speeds of 35 cm/s forL. californianusandH. psittaceaand 56 cm/s forT. unguicula. Shell shape, gross pedicle form, and form of the pedicle foramen are unreliable indicators of a brachiopod's ability to actively reorient. Shape of the pedicle bulb and position and size of the pedicle connectives are better indicators but. on functional grounds, the dorsal adjustor muscle morphology is the best indicator of active reorientation. An angle α (the maximum possible rotation of the shell that can be produced by contraction of one of the dorsal adjustor muscles) correlates well with both the maximum observed rotations and the exhibition of active reorientation to currents. For fossil material, the existence of dorsal adjustor muscle scars that touch medially should also be a good indicator of active reorientation ability

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1978.tb01219.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY