C*4 CO ^» « UNlVtRSlTY OF ILLINOIS LIBRARY AT UP3A.4A-CHAMPAICN GFOLOGY FIELDIANA: GEOLOGY A Continuation of the GEOLOGICAL SERIES of FIELD MUSEUM OF NATURAL HISTORY VOLUME 30 FIELD MUSEUM OF NATURAL HISTORY CHICAGO, U.S.A. TABLE OF CONTENTS 1. A New Hydrozoan from the Pennsylvanian of Illinois. By Matthew H. Nitecki and Eugene S. Richardson, Jr 1 2. The Mazon Creek Caridoid Crustacea. By Frederick R. Schram 9 3. A Trematopsid Skull from the Lower Permian, and Analysis of Some Characters of the Dissorophoid (Amphibia: Labyrinthodontia ) Otic Notch. By John R. Bolt 67 4. Caryocrinitidae (Echinodermata: Rhombifera) of the Laurel Limestone of Southeastern Indiana. By T. J. Frest 81 ^ V SEP H 1972 FIELDIANA the library or the Geology Published by Field Museum of Natural History UNIVDflOITV Or ILLINOIS Volume 30, No. 1 AT URBA^^A^AIGN A New Hydrozoan From the Pennsylvanian of Illinois Matthew H. Nitecki Associate Curator, Fossil Invertebrates AND Eugene S. Richardson, Jr. Curator, Fossil Invertebrates ABSTRACT Drevotella proteana, a new genus and species of colonial hydrozoan, is described from the Middle Pennsylvanian Francis Creek Shale of the Mazon Creek area of northeastern Illinois. It is represented by numerous specimens preserved in iron- stone concretions in which the large, irregularly branched colonies appear as flattened impressions visible by virtue of color contrast. INTRODUCTION In the last decade, the Mazon Creek area in Will and Kankakee counties, northeastern Illinois, has yielded many unusual soft-bodied fossils. These organisms, enclosed in siderite concretions in the Middle Pennsylvanian Francis Creek Shale, are dominantly marine invertebrates constituting the Essex Fauna (Johnson and Richard- son, 1966). The only coelenterates previously reported are two spe- cies of medusae represented by fairly abundant specimens (Johnson and Richardson, 1968). Many specimens of a soft-bodied ramose organism have recently come to our attention in private collections. Some of these have been deposited in Field Museum of Natural History. If they are plants, there is nothing in the known Paleozoic flora to which they may be compared. On the other hand, they closely resemble colonial hydroids of the modern fauna. Many of them appear to represent complete colonies, or appreciable portions of colonies, and as a whole they exhibit a general uniformity of habitus, though with great Library of Congress Catalog Card Number: 70-189359 Publication 1149 1 GEOtotf ^^ FIELDIANA: GEOLOGY, VOLUME 30 individual variability. Little but the gross form is preserved. We describe this organism as a colonial hydroid. The hydroid specimens are preserved as color markings rather than impressions. As described by Richardson and Johnson (1971, pp. 1,226-1,227), the color difference is due to a preferential com- bination of oxygen with the organic residues in the fossil rather than with the iron in the matrix during early stages of weathering. SYSTEMATIC DESCRIPTION Phylum Cnidaria Hatschek, 1888 Class Hydrozoa Owen, 1843 Order Hydroida Johnston, 1836 Suborder and Family unknown Genus Drevotella, n. g. The definition of the genus is that of the only species. Type: Drevotella proteana, n. sp. Drevotella proteana, n. sp. Diagnosis. — Arborescent sessile colonies a few centimeters in height; shape and size of colony variable; one or more erect or prostrate, irregularly divided stems of variable length and thickness; branching racemose; hydranths broad and rounded, terminal on branches. Description. — Almost all colonies are arborescent, with dichoto- mous or irregular branching. Irregularities of branching may be exaggerated by post-mortem deformation. Both prostrate stolons and erect stems (hydrocauli) are probably present. The stems are thick, and bear rather widely-spaced hydranths and hydranth-bear- ing branches. Growth is apparently "monopodial," and perhaps "hydrorhizal" as well (Hyman, 1940, p. 403). Bases are poorly preserved. In some specimens there is an ill-defined area (fig. lb) that may represent a basal expansion deriving from a mat or tangle of stolons. This may be similar to the attachment structure of the modern fresh-water to brackish-water thecate hydroid Cordylophora (Kinne, 1956). Branches arising from the stems are simple or profusely divided. A medial structure observable in some branches (fig. la) may repre- sent a colonial gastrovascular cavity, and while it is possible that Figure la shows a hydrocaulus encased in stolons (Hyman, 1940, NITECKI & RICHARDSON: NEW HYDROZOAN Fig. 1. Drevotella proteana, n. sp. Specimens from the collection of Mr. and Mrs. Ted Piecko. a. HTP 20039, a specimen with several major stems, b. HTP 5080, a specimen with slender stems apparently arising from a basal expansion. fig. 116B) the appearance makes this seem unlikely. Rather, from the relative thickness of the inner core and the thinness of the external layer, this could represent a thin perisarc or periderm sur- rounding the coenosarc (body tissues) inside. No surface detail is observable; if there was a chitinous periderm, it was only lightly sclerotized. The swellings at the ends of the finest branches probably represent hydranths, the expanded terminal portions of polyps. Some of the hydranths may be adnate on the major stems (fig. 2b). Tentacles have not been observed. Discussion. — Structural diversity of the hydroids may be ex- pressed by means of two suborders, the non-thecate gymnoblast hydroids and the thecate calyptoblast hydroids (Hyman, 1940, p. 370), or by means of three (Hill and Wells, 1956), if the solitary non- thecate eleutheroblast hydroids are considered separately. Drevo- tella is clearly colonial; unfortunately, however, it is not possible to ascertain whether the terminal swellings are naked hydranths (gymnoblasts) or hydranths situated within sclerotized hydrothecae (calyptoblasts) . The branching habit of Drevotella has analogues in both colonial suborders. For the present, we do not assign the genus to a suborder. Fig. 2. Drevotella proteana, n. sp. a. Holotype, FMNH, PE 18105. b. and c. Specimens from the collection of Mr. Corliss Ingels. NITECKI & RICHARDSON: NEW HYDROZOAN 1 cm Fig. 3. Drevotella proteana, n. sp. a. FMNH, PE 18109, a specimen that may fall outside the range of variation of the species, b. Piecko collection, HTP 13067, a specimen with two major stems. Few Paleozoic hydroids have been described (Hill and Wells, 1956) . The only North American forms, thecate hydroids from the Devonian of Michigan (Decker, 1952) are different from our speci- mens. Certain Cambrian forms from Australia (Chapman and Thomas, 1936) are closer to Drevotella. The Australian fossils are better preserved, and details of the hydranths and periderm are said to be discernible. Variability of colonial form is typical of modern hydroids and of Drevotella as well. Such uniformity of habit as is displayed by our specimens is no doubt largely due to the colonies having in- habitated a restricted and fairly uniform habitat. A specimen is illustrated (fig. 3a) with a rather different form: both branches and polyps are smaller and more crowded than in typical Drevotella. We suggest that this specimen is outside of the permissable range of variation of Drevotella proteana and thus represents a different species and probably a different genus. ECOLOGY Drevotella is the only sessile benthonic form yet reported from the Mazon Creek fauna. There are also a few specimens of Lingula, FIELDIANA: GEOLOGY, VOLUME 30 but preserved parallel to the bedding and with no evident pedicle. Errant benthonic forms (chitons, polychaetes, etc.) are common, indicating adequate oxygenation of the bottom. The substrate was a mud, soft enough to show trails and to provide grazing for abundant holothurians but firm enough to support the rich bottom-dwelling fauna. Such substrate is today occupied by a spectrum of sys- tematically diverse hydroids (Hand and Jones, 1957). Hydroid colonies may be anchored to floating plants, or may attach them- selves to soft bottoms (Hyman, 1940, pp. 445-446). There is no evidence that Drevotella was fastened to anything but the bottom itself. A rather ill-defined area of organic substance associated with some specimens (fig. lb) may represent a mass of stolons (Hyman, 1940, p. 403) or a "coenenchyme body" from which arise the prin- cipal stems of the colony. Specimens lacking that structure may have been separated from it before burial, or may have arisen from simple stolons. ACKNOWLEDGEMENTS We are grateful to Prof. Donald P. Abbott of Stanford University for his critical reading of the manuscript, and to Messrs. Corliss Ingels and James Turnbull and Mrs. Ted Piecko, who allowed exam- ination of their specimens. REFERENCES Chapman, F. and D. E. Thomas 1936. The Cambrian Hydroida of the Heathcote and Monegeeta Districts. Proc. Roy. Soc. Victoria, 48, n. ser., pt. 2, pp. 193-212, pis. 14-17, 2 text-figs. Decker, Charles E. 1952. A new hydrozoan from the Devonian of Michigan, Jour. Paleontol., 26, no. 4, pp. 656-658, 2 text-figs. Hand, Cadet and Meredith L. Jones 1957. An example of reversal of polarity during asexual reproduction of a hydroid. Biol. Bull., 112, no. 3, pp. 349-357, 5 text-figs. Hill, Dorothy and J. W. Wells 1956. Hydroida and Spongiomorphida, pp. 81-89, text-figs. 65-74. In Moore, R. C, ed., Treat. Invert. Paleontol., Part F, Coelenterata. Geol. Soc. Amer. and Univ. Kansas Press. Hyman, Libbie Henrietta 1940. The invertebrates: Protozoa through Ctenophora. xii + 726 pp., 221 text-figs. NITECKI & RICHARDSON: NEW HYDROZOAN 7 Johnson, Ralph G. and Eugene S. Richardson, Jr. 1966. A remarkable Pennsylvanian fauna from the Mazon Creek area, Illinois. Jour. Geol., 74, pp. 626-631. 1968. The Essex fauna and Medusae. Fieldiana: Geol., 12, pp. 109-115, 6 figs. Kinne, Otto 1956. Uber den Einfluss des Salzgehaltes und der Temperatur auf Wachstum, Form and Vermehrung bei dem Hydroid-polypen Cordylophora caspia (Pallas), Thecata, Clavidae. Zool. Jahrb., Abt. Zool. Physiol., 66, no. 4, pp. 565-638, 39 text-figs., 22 tables. Richardson, Eugene S., Jr. and Ralph G. Johnson 1971. The Mazon Creek faunas. North Amer. Paleontol. Convention, Chicago, 1969, Proc, 1, pp. 1,222-1,235.