Late Paleozoic Sponge Faunas of the Texas Region PDF Download

Author: Robert M. Finks
Publisher:
ISBN:
Category : Paleontology
Languages : en
Pages : 160

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Book Description
"The present paper is a taxonomic and faunal study of the siliceous sponges of the later Pennsylvanian and Permian of the mid-continent region, including the standard Permian section of west Texas. It is based primarily on large collections at the United States National Museum and at the American Museum of Natural History, as well as on the type specimens of all previously described species from the same area. A general introductory discussion reviews the composition and historical development of the entire sponge faunas of the area and geologic systems studied, including the calcareous sponges which are not treated taxonomically here. The sponge faunas discussed here are the most diverse known in the geologic record between the Devonian and the Jurassic. The siliceous sponges dealt with in the present paper constitute about half of the total sponge fauna in terms of numbers of species. Forty-three named species are described, plus nine new but unnamed forms. Three new superfamilies, seven new families, 17 new genera, and 32 new species have been established. The anatomy of Heliospongia has been reinterpreted on the basis of excellently preserved material, and it has been placed among the monactinellid demosponges. The evolution of the hexactinellids has been reconsidered, and it is concluded that in the early Paleozoic two main lines diverged from a common stock, one of which gave rise to many later dictyonines. In the descriptions of individual species, particular attention has been paid to individual variation, to ontogenetic development, and to evidences for ecological relationships exhibited by the specimens. The large size of the collections and the generally excellent preservation of the material have made such aspects of the study feasible. Only those species represented by nearly complete specimens have been named, for isolated spicules or small fragments of sponges provide insufficient morphological information. Faunal facies can be recognized, which are related to bathymetry inferred from physical stratigraphic evidence. These are similar in distribution to present communities of sponges. The shoal-water faunas were dominated by calcareous sponges and the deeper-water faunas by siliceous sponges. Evidence is presented that the marginal areas of the stagnant-basin facies of the Texas Permian were not completely anaerobic, despite the high organic content of the sediment, because the sponges and some of the associated faunal elements were autochthonous to the sediments. The late Paleozoic shoal-water sponge fauna in the Texas region shows a continuous and partly endemic development. A significant external faunal element appears at the beginning of the Leonardian. Stratigraphic zonation of the sponges tends to confirm that established on the basis of the other faunal elements. The taxonomic composition of the Permian sponge faunas, in relation to earlier and later faunas, indicates that the Paleozoic-Mesozoic boundary is marked by the extinction of several long-ranging Paleozoic families that flourished until the end of the Permian. The dominant groups of Mesozoic sponges, on the other hand, were already present in the late Paleozoic and seem not to have been affected by the post-Permian withdrawal of epicontinental seas"--P. 7.