Report of the Committee on Paleoecology, 1935-1936: Presented at the Annual Meeting of the Division of Geology and Geography, National Research Council, May 2, 1936 (1936) / Chapter Skim
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Habits of Trilobites - William E. Scheville
Habits of Trilobites - William E. Scheville
Pages 29-43
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From page 29... ...
96) the appendages of Triarthrus ware doubtless displaced backwards witn the collapse of the ventral membrane against the.dorsal shell, -- why not, therefore, the metastoma as \7ell?
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From page 30... ...
impressions are observable on animals with otherwise smooth tests and that as the surface of the glabella becomes roughened, the special impressions are lost. This might be construed to mean that he considered the general granulose sculpture of the shell to serve as attachment for a diffuse muscle web, whereas the distinctly localized impressions indicated a more localized musculature, though he does not expressly say so.
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From page 31... ...
by pointing out'the similar dorsal and ventral silhouettes of the refle:ced alimentary canal. That is, from the ventral mouth the slender oesophagus widens forward Into the stomach, whereas dorsally the wide stomach narrows behind into .the intestine, this constriction being controlled, as he puts it,.by the mandibular muscles, as well as by the dorsal furrows, which may also have supported radial gastric muscles.
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From page 32... ...
Richter believes, moreover, that pronounced frontal muscle scars indicate a double stomach (apparently connecting the vigorous activity of the "gastric mill" with the exceptional development of the muscle insertions) , and that this further confirms the conception that the Phacopidae, along with their cousins the Cheiruridae, were the most powerful and active.of trilobites.
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From page 33... ...
and von Staff aid Reck (35) , themselves overenthusiastic followers of Dollo, some rather glittering generalities on trilobite locomotion have found their way into the literature.
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From page 34... ...
cit.) and others have pointed out, it is probable that many trilobites habitually covered themselves thinly with loose sediment by way of concealment, as do shrimps and many other Recent crustaceans; but how an animal so buried as were the Vogdesias at Elgin, Iowa (13, and 23, p.
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From page 35... ...
The trilobite exopodites approach the various forms of Recent crustacean pleopods most nearly, - much more so than any known form of trilobite endopodite. For this reason nearly all authors, except Raymond (23)
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From page 36... ...
Some, as, for example, Palaemonetes, have a marked kink in the abdomen, but the double imbrication referred to by Richter is a special, but not too uncommon, feature of the pleura and does not occur in the tergum of the segment in question. There is an apparent reverse imbrication in the rachis at the joint between the carapace and the first abdominal segment, but this is merely a deceptive appearance.
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From page 37... ...
Von Staff and Reck mentioned esnong their criteria for a retrogressively swimming trilobite eyes stalked or otherwise adapted for rearward vision. Other explanations may, however, be offered.
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From page 38... ...
103) , who names Isotelus and Dalmanites, whereas Richter selects his "Pha.cops-type." Almost the only point of coincidence of the conceptions of criteria for swimming trilobites of Raymond and Richter is the agreement that large subequal shields indicate such habits.
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From page 39... ...
in search of facetted pleura and information on enrollment. The majority wore enrolled, and very finaly, so that attempts to unroll them or to enroll extended individuals were abandoned for fear of injuring them (they were alcoholic specimens)
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From page 40... ...
The general assumption has been that such passive defense as enro! 3ment and spines afforded was about all ttiat trilobites were capable of; similarly they have been considered chiefly as scavengers, and portrayals of predaceous habits in trilobites have been repudiated (e.g., 23, p.
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From page 41... ...
Tril. I: Das Kopfschild von Chasmops Odini.
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From page 42... ...
Chimneys of burrowing crayfish,' Observer, vol.
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From page 43... ...
- 43 36. Stelninger, J
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