Report of the Committee on Paleoecology, 1936-1937; Presented at the Annual Meeting of the Division of Geology and Geography, National Research Council, May 1, 1937 (1937) / Chapter Skim
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Brachiopod Ecology and Paleoecology - G. Arthur Cooper
Brachiopod Ecology and Paleoecology - G. Arthur Cooper
Pages 26-53
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From page 26... ...
Although data bearing on the ecology of many groups of animals has been gathered, the ecology of modern brachiopods, as well as their palec -- ecology, has been neglected. The various treatises on modern brachiopods yield little direct information bearing on their habits, their relationships to contemporary organisms, their embryology and life history.
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From page 27... ...
• . J:V •• ' ' This present discussion of brachiopod ecology and paleoecology is admittedly incomplete, because time did not permit an exhauotive search of the voluminous brachiopod literature.
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From page 28... ...
Modern brachiopods occupy all bethymetric zones of the sea. Some species are confined to shallow water!
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From page 29... ...
Lagueus and DaUlna. Sixty percent of brachioijod species thus occupy shallow water but only a little more than half of this percentage is actually confined to shallow water.
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From page 30... ...
The majority of terebratulid species possess a short pedicle by which they are tightly fixed to the substratum. In general the ventral value lies obliquely over the dorsal valve.
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From page 31... ...
'' \ '-'. Modern brachiopods are jiifistly'rare -arid little knpwn animals, but in past geological periods they, were an abundant form of life,' The .Paleozoic Era mightr.be termed, the age.
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From page 32... ...
It is apparent, therefore, that a long evolution of brachiopods preceded the genera named* After these forms the Lower Cambrian stocks persist with little change until the Upper Cambrian, when .a number of new types appear.> A brief survey of the rise and decline of the major stocks of brachiopods will, serve as a background for the ecological discussions to follow.
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From page 33... ...
The punctate dalmanellids outlived the impunctate orthoids and the punctate spiriferids persisted into the Jurassic .after the. impunctate forms had died out in the Triassic, The punctate loopbearers or terebratulids are today the most-.abundant types of brachiopods forming about 70 percent of the known members of the class, thus far outnumbering the rhynchonellids.
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From page 34... ...
In the Upper Devonian of New York the writer has seen large lenses of brachiopod shells consisting almost wholly of the ventral valves of Cyrtospirifer. Most brachiopods are heaviest at the beak end or posterior of the shell, hence many dead brachiopod shells will lie on the bottom with their beaks on the mud but with the anterior portion off the bottom.
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From page 35... ...
a conyexi-concave brachiopod, occurs in a nearly upright position with the convex dorsal valve lying obliquely over the ventral valve. Hesperorthis is found in the reverse position, with the convex ventral valve lying obliquely over the flat dorsal valve.
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From page 36... ...
The entombed brachiopods may not have lived near the shore but may have been cast up by currents and waves from habitats farther offshore. Lingulids are a common form in'sandstones, particularly in the late Cambrian, and from their habits today would be expected to be the commonest forms in the near-shore zone.
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From page 37... ...
in shallow water and probably near the shore, • ' .
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From page 38... ...
. Most Paleozoic deposits crop out on the margins of uplifts which have brought up only the near-shore regions, but even where Paleozoic off-shore zones can be demonstrated, their fossils, current and wave-markings usually indicate shallow water*
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From page 39... ...
Foldin^„ -- All stocks of articulate brachiopods tend sooner or .••' ' later to develop a strong median fold. In the Paleozoic the fold usually • takes the form' of a strong median plica that undulate'si the interior commissure or line of valve junction.
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From page 40... ...
These must have been attached with the dorsal valve below because in most known sulcate (anterior commissure folded ventrally) brachiopods the ventral beak is more or less curved over the dorsal umbo.
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From page 41... ...
The development of a wide hinge is uncommon in modern brachiopods but among the spiriferids this development reached its maximum. It is apparent from the structure of the strophomenids that some were attached by a slender pedicle but others, such as Stropheodgnta which has no functional pedicle opening, lived free on the bottom.
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From page 42... ...
Not only the symmetry of the shell but the strongly incurved beak would make, close attachment to a hard substratum difficult. Because the animal possessed a functional pedicle opening it is believed that Spirifer mucronatus was attached by a pedicle of moderate length anchored in soft mud, with the umbo of the dorsal valve resting on the mud and leaving the extremities free to develop laterally.
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From page 43... ...
may have had setae strong enough to have been useful in restoring the animal to its normal position. Resupinatiqn, -- Everyone familiar with brachiopods has been 1mpressed by the phenomenon of resupination, in which the young shell possesses a convex ventral valve and a flat or concave dorsal valve, but in maturity the condition is reversed, the anterior of the ventral valve becoming more or less deeply concave and the dorsal valve becoming strongly convex.
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From page 44... ...
antero-dorsal direction over the concave dorsal valve. Spines along the anterior border curve postero-dorsally to overhand the dorsal valve.
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From page 45... ...
It seems likely that the productids seen by Muir-Wood and Moore Were supported above the; muddy bottom on which they lived by spines in the manner described above„ If they were not, the animal must surely have perished because it could not have functioned with its entire margin in the mud. In productids with long hinge-spines only it is possible that the animal lay on the bottom on its ventral valve which was by far the heavier• Long hinge-spines extending posteriorly would prevent the creature from 'being tipped over onto its dorsal valve, Marginal frills, such as those of Atrypa.
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From page 46... ...
Howevery:if one considers their enormous numbers in the Paleozoic they must have been a prolific source of food, if not in the adult form, certainly their eggs and larvae must have yielded many a feast. Direct evidence indicates that snails equipped with a radula, actually bored brachiopod shells and devoured the succulent tissues within.
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From page 47... ...
Some linguloids are highly colored by bright or dark green mixed vdth rich brown. Most colored brachiopods are dwellers in shallow water, a feature that is true of other groups of animals as well as the braehiopcds.
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From page 48... ...
National Museum the writer has found that most of the colored species were collected from shallow waters. A feiif colored species are recorded, however, i'rom considerable depth.
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From page 49... ...
Although Penton regarded this association as parasitic it seems rather to have been accidental«, Conclusions Brachiopods are a minority element of modern faunas, but in the Paleozoic and Mesozoic they were very numerous and at times the most abundant form of life. With the exception of the lingulids, modern brachiopods have too wide a bathymetric range to be of use in determining the depth of seas older than the Tertiary.
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From page 50... ...
Too little is known of brachiopod embryology to permit generalizations on distribution of free-swimming larvae.' Colored brachiopods in general indicate shallow, warm waters. Brachiopods are not known to have been truly parasitic but instances of commensalism are well known*
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From page 51... ...
713-729, 1895. Annotated' list of the recent Brachiopoda in 'the 6611ecti6n of the United States National Museum, with descriptions of thirtythree new forms.
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From page 52... ...
Histoire naturelle des brachiopodes vivants de la Mediterranee, Ire Monographic, Histoire naturelle de la Thecidie.
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From page 53... ...
S National Museum, V/ashington, D, C, • i-' : ••- ; ' r «.!
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