Author: Curt Teichert
Permian faunas of Western Australia contain a peculiar crinoid, Calceolispongia, whose crinoid affinities have only recently been recognized. This genus occurs in all areas of Permian rocks in Western Australia and has been found at various horizons throughout a sequence of about 7000 feet of sediments. At present 13 species can be satisfactorily described. Most are short-lived, and seldom more than 2 are found in the same horizon. They make, therefore, excellent index fossils. Their value in this respect is enhanced by a peculiar diagenetic process which takes place under conditions of arid weathering and in which the calcite of the crinoidal plates is replaced metasomatically by limonite and turgite. Large basal plates of Calceolispongia thus become almost indestructible. A detailed morphologic description of the genus is given. Its main characteristics are the greatly enlarged, usually horn- or hook-shaped basal plates. The cup is of simple, poteriocrinitid design and consists of 18 plates. The tegmen is calcareous, the arms are uniserial. Special attention is given to the nervous system which resembles that of the Cretaceous genus Marsupiles. The genus is characterized by the extraordinary variability of most of the cup plates, especially the basals, but also to a lesser extent of the radials and of the first and second brachials. The main evolutionary trends in Calceolispongia are gigantism and spinescence. During the course of its evolution, the basal plates of the genus increased in bulk 40,000 per cent. Spinescence is a trend which occurs repeatedly in the phylogenetic history of the genus, but the last member of the series is nonspinose. The entire evolution of Calceolispongia took place in Artinskian time within a period whose length may be estimated at about 6,000,000 years. During this time a succession of 13 species developed in increasingly rapid succession, whereas the associated faunas in these rocks remain more or less stationary and show no directional changes. It is believed that the evolution of Calceolispongia is not environmentally controlled but that it results from a number of orthogenetic, nonadaptive mutational changes. The applicability of relative growth methods to the study of Calceolispongia is briefly indicated. The relative growth ratio of basal and radial plates of one of its species corresponds to Huxley's relative growth formula y = bxα. Outside Western Australia Calceolispongia is known from Timor and possibly from India. Illustrations of all extra-Australian species are given for comparison with Western Australian forms.
Published: 2/10/1949
Pages: 132
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