Publication Date:
1989-09-01
Description:
Two alternative hypotheses for proximal column growth are tested in Taxocrinus cf. T. whitfieldi, a late Mississippian flexible crinoid. The first hypothesis states that new columnals are added at the base of the proximal column (immediately above the generating columnal), whereas the second hypothesis has columnals of the proximal column inserted beneath the aboral cup. In both hypotheses, middle column columnals are inserted beneath the generating columnal and are independent from the proximal column.External features used to determine points of columnal insertion include wedge-shaped columnals and sharp changes in columnar morphology. Sagittal sections reveal the presence of small columnals, some of which can be interpreted as the last columnals inserted prior to death. Data collected on Taxocrinus cf. T. whitfieldi confirm the first hypothesis. This hypothesis may be applicable to other crinoids with xenomorphic columns.
Print ISSN:
0022-3360
Electronic ISSN:
1937-2337
Topics:
Geosciences
Permalink
