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An Occurrence of a Cruziana Population in the Moyer Ridge Member of the Bloomsburg Formation (Late Silurian): Snyder County, Pennsylvania

Thomas L. Garlock and Peter E. Isaacson
Journal of Paleontology
Vol. 51, No. 2 (Mar., 1977), pp. 282-287
Stable URL: http://www.jstor.org/stable/1303607
Page Count: 6
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An Occurrence of a Cruziana Population in the Moyer Ridge Member of the Bloomsburg Formation (Late Silurian): Snyder County, Pennsylvania
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Abstract

Two outcrops of the Moyer Ridge Member of the Bloomsburg Formation (Late Silurian) of central Pennsylvania have yielded the trilobite-produced trace fossils Cruziana and Rusophycus. Trilobite furrows (Cruziana) and resting excavations (Rusophycus) are observed to grade into one another. Therefore, rather than label these fossils according to distinct ichnogenera, this occurrence is more appropriately termed a Cruziana population, showing all gradations of feeding and resting behavior. The size range of the traces varies from 9-12 mm in width. This narrow width range, combined with the width of the Cruziana-type furrow being identical to the Rusophycus-type excavation suggests that only one species and ontogenetic level of trilobite is involved. The traces are characteristically clumped into a high "population density," and may display a subsocial behavioral habit.

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