I « UNIVERSITY OF | ILLINOIS LIBRARY AT URBANACHAMPAIGN GEOLOGY The person charging this material is re- sponsible for its return to the library from which it was withdrawn on or before the Latest Date stamped below. Theft, mutilation, and «nder.lnln9 of book, are reasons for disciplinary action and may result In dismissal from the University. To renew call Telephone Center, 333-840O UN.VERSITY OF IUINOIS UBRARY AT URBANA-CHAMPAIGN APR 2 *mJt JUL & '991 mn '997 L161— O-1096 <— f<^c~(^t>> ^r FIELDIANA Geology Published by Field Museum of Natural History Volume 20, No. 5 December 9, 1970 Redescription of Ischadites elrodi (S. A. Miller, 1892) a Lower Devonian Receptaculitid Matthew H. Nitecki Associate Curator, Fossil Invertebrates Field Museum of Natural History Abstract Ischadites elrodi (S. A. Miller, 1892) a Lower Middle Devonian receptaculitid from Indiana is redescribed as a dasycladacean alga closely related to Silurian Ischadites koenigii Murchison, 1839. Introduction S. A. Miller (1892a) described and illustrated a new species of Receptaculites elrodi from the Lower Middle Devonian of Indiana. He assigned it to the family Receptaculitidae, class Porifera, sub- kingdom Protozoa. He considered that it may belong to Ischadites, but because of the concave shape of the top of the fossil he preferred to assign it to Receptaculites. Miller based his description upon one specimen only (fig. 1). This fossil is now housed with the University of Chicago collection (Walker Museum) in Field Museum of Nat- ural History. The species has not been systematically studied since Miller's (1892a) first description. Miller (1894) republished his original de- scription and figures, and the fossil has been listed in catalogues (Miller, 1892a; Head, 1895; Nitecki, 1965). Nitecki (1969) tenta- tively suggested that /. elrodi belongs with I. koenigii Murchison, 1839. However, the detailed study of the holotype indicates that elrodi, although closely related to koenigii, constitutes a distinct species. Therefore, Ischadites elrodi (Miller, 1892) is now redescribed as dasycladaceous alga. Library of Congress Catalog Card Number: 73-11*1885 Publication 1115 77 (IIEOLOGY LIBRARY MAY 1 5 1972 University of Illinois at Urbans-Champajgn 78 fieldiana: geology, volume 20 Systematic Description Class Chlorophyceae Klitzing, 1845 Order Dasycladales Pascher, 1931 Family Receptaculitaceae Eichwald, 1860 Tribe Receptaculiteae Nitecki, 1969 Genus Ischadites Murchison, 1839 Ischadites elrodi (S. A. Miller, 1892). Figures 1-3. Receptaculites elrodi S. A. Miller, 1892, Palaeontology. In advance 18th Rept. Geol. Surv. Ind., pp. 3-4, pi. 1, figs. 1-3; S. A. Miller, 1892, First appendix, p. 668; S. A. Miller, 1894, 18th Rept. Geol. Surv. Ind., pp. 257-258, pi. 1, figs. 1-3; Head, 1895, Cat. Paleo. sponges, p. 4; Nitecki, 1965, Fieldiana: Geol., 13, p. 503. Ischadites koenigii (in part) Nitecki, 1969, Geol. Soc. Amer. Abstr., part 6, pp. 33-34. Definition. — Thallus pyriform; stalk probably elongated; main axis basally thin, apically possibly inflated; thin, weakly calcified laterals distributed throughout main axis; lateral heads present; cal- cified stellate structures of three, four or possibly more ribs; growth in helix; Lower Middle Devonian. Description. — Thallus: The shape of the thallus is well pre- served. The lower broken end is suggestive of an elongation of the body in the form of a stem (fig. 2) . The area at the very top of the thallus is slightly collapsed and somewhat damaged in a manner com- mon to many other receptaculitids. There is a slight flexure to the otherwise erect plant, and the thallus appears somewhat bent. Main axis: The main axis is not calcified and hence is not pre- served. Its anatomy is deduced from the length and distribution of laterals. In the lower part of the thallus the proximal ends of laterals are almost in contact with each other (fig. 3). This indicates that the main axis is very thin in the older lower parts of thallus. Upper part of the plant is expanded and the body shape suggests that the main axis is apically inflated. Laterals: The laterals are thin but distally are expanding rapidly and form heads. There are about 32 laterals at the base of the thallus (fig. 3). The number of laterals at the equatorial region of the plant appears much larger but their exact number cannot be determined. There are about 20 spiral lines and approximately 40 apparent whorls (fig. 1). NITECKI: ISCHADITES ELRODI 79 3 cm Fig. 1. Ischadites elrodi (S. A. Miller, 1892). Dolomite; near Hartsville, Indiana. Holotype UC 6052; Geneva Laterals are arranged in a helix and new laterals are added apical- ly. The laterals are seemingly packed in whorls. This is common to many ischaditids and is caused by the compression of the helix. Laterals are distributed throughout the main axis. Stellate structures: Stellate structures are preserved on many laterals. They appear to consist of three, four, or perhaps even more ribs; however, four ribs seem the commonest arrangement. The stellate structures are often misplaced and are thus found at differ- ent levels of laterals below or even above the lateral heads. This misplacement is possible because these structures are relatively 80 FIELDIANA: GEOLOGY, VOLUME 20 Fig. 2. Reconstruction of i". elrodi. The stalk may have been shorter. strong and not easily damaged. Stellate structures are not observed in the lower part of the thallus. Calcification: Calcification is weak along the proximal parts of the lateral branches and heavy on the distal parts. Lateral heads are thin and their impressions are very conspicuous; therefore, the exterior of the heads was heavily calcified. The stellate structures are very common and well calcified. NITECKI: ISCHADITES ELRODI 81 Fig. 3. Diagrammatic representation across the lower broken-off part of thallus of J. elrodi. The number of laterals (32) is reconstructed; second row of laterals is suggested; stellate structures are omitted. Discussion. — Relationship: This fossil is similar to specimens of I. koenigii Murchison in the following ways: the shape of thallus, the distribution and general shape of laterals, the growth pattern, and the presence of three or four ribs of stellate structures. The species differs from koenigii in the possible presence of more than four ribs of stellate structures, in its stratigraphic distribution, larger facets, and apparently smaller number of branches. The laterals are distributed on all parts of the main axis, and not only around the api- cal part of the central vesicle, as is the case in I. koenigii. Nitecki (1969) assigned /. elrodi to /. koenigii; however, until more specimens are located the species elrodi is retained here. Ecology: The alga is preserved in an erect growth position, how- ever, there appears a slight curvature to the thallus, an indication of a gentle water movement or current. The plant has not been moved about the bottom. 82 FIELDIANA: GEOLOGY, VOLUME 20 Preservation : The exterior of the thallus consists of crystalline quartz with well-developed pyramidal and prism faces. The interior of the fossil is of quartzite-like silica with imbedded fine-grained quartz. The black material within the grooves is graphite or india ink that washes away with a brush. It appears to have been used in preparation for Miller's original figures. The fossil is a cast and the small holes on the surfaces represent cross-sections of laterals. One part of the surface of the thallus is cut, and another portion is somewhat abraded. The area on top of the fossil appears to have "many apertures" (Miller, 1892a). These apertures may possibly be morphological structures; however, they are highly suggestive of poor preservation aided by mechanical abrasion. Stratigraphic position and locality. — Miller (1892a and subse- quent) lists the locality as Upper Helderberg Group, near Harts- ville, Indiana. He suggests that the fossil came from a limestone matrix and indicates that the locality is known to him. The mu- seum catalogs and labels do not provide any additional information. The Hartsville area was visited in the fall of 1968, but no additional specimens were found, nor was the exact stratigraphic location deter- mined. The fossil is assigned (with reservations) to the Geneva Dolomite of the Lower Middle Devonian. Growth. — The growth is in a distinct helix. However, the direction of the helix cannot be determined. Material. — Holotype UC 6052, Gurley Collection, University of Chicago, now housed in Field Museum of Natural History. Measurements. — Height of thallus 5.37 cm., maximum diameter of thallus 4.61 cm. Acknowledgments Dr. Carl B. Rexrod, Indiana Geological Survey, commented on the stratigraphic position of Ischadites elrodi (S. A. Miller) and Dr. Alan Horowitz, Department of Geology, Indiana University, guided the author in the field. Mr. Richard Roesener prepared the drawings. References Head, William R. 1895. Palaeozoic sponges of North America. Published by the author, Chi- cago, Illinois. 11 pp. NITECKI: ISCHADITES ELRODI 83 Miller, S. A. 1892a. Palaeontology. Advance sheets from the 18th Rept. Geol. Survey Indiana. 79 pp., 12 pis. 1892b. First Appendix, 1892 [to North American Geology and Palaeontology). Pp. 665-718, text-figs. 1,195-1,265. 1894. Palaeontology. Indiana Dept. Geol. Natural Resources, 18th Ann. Rept., pp. 257-356, 12 pis. Nitecki, Matthew H. 1965. Catalogue of type specimens in Chicago Natural History Museum. Porifera. Fieldiana: Geol., 13, no. 6, pp. 477-509. 1969. Nature and variations of Ischadites koenigii Murchison. Geol. Soc. Amer. Abstr. Programs for 1969, part 6, pp. 33-34.