a receptaculitid–echinoderm pioneer community in a middle ordovician reef

A receptaculitid-echinoderm pioneer community in a Middle Ordovician reef LEONARD P. ALBERSTADT AND KENNETH R. WALKER

Alberstadt. L. P. & Walker. K. R. 197607 IS: A receptaculitid-echinoderm pioneer community in a Middle Ordovician reef. Lethaia, Vol. 9, pp. 261-272. Oslo. ISSN 0024-1164.

The Elk River Reef of Tennessee has an assemblage of incrusting bryozoans. ‘incrusting’ echinoderms, and receptaculitids (calathids) concentrated near its base. This assemblage is thought to have initially inhabited small local sites in a substrate of pclmatozoan sand containing various amounts of carbonate mud. The gregarious style of growth of these organisms and their close interrelationships stabilized the substrate and produced a biological hardground, later occupied by colonial corals and stromatoporoids to form the main reef body. The anastomosing root structurcs of the echinoderms helped stabilize the substrate and hindered sediment movement. In an effort to support themselves, these echinoderms achieved additional baffling effects of their incrusting and engulfing growth abilities. They particularly attached themselves to calathids. Calathids are the most noticeable taxon in the community. They differ from other calathids presently known in that they have a ‘porous’ convoluted outer wall very much like a sponge in appearance. The Elk River Reef and its contained receptaculitids fall within 10-1So of the presently accepted position of the Ordovician equator.

Leonard P. Alberstadt. Geology Department, Vanderbilt University, Nashville, Tennessee 37235, U.S.A .; K . R . Walker, Deparlment of Geological Sciences, University of Tennessee, Knoxville, Tennessee 37916, U.S.A.; 14th July. 1975.

Fossil reefs are important features in the geo- logic record and have been the objects of numerous studies describing their many characteristics. One especially intriguing aspect of reefs is the vertical changes that many go through during their development. The reasons for this developmental history are not completely known and disagreements in interpretations are numerous. Alberstadt & Walker (1973) and Alberstadt et af. (1974) recently discussed the vertical development of an Ordo- vician patch reef in the Carters Limestone of south-central Tennessee (Fig. 1) and in Ordo- vician reefs in general. In ascending order the stages of this vertical development were designated (1) the stabilization stage in which biological or inorganic processes change an unstable or soft substrate into a more stable or cohesive substrate, (2) the colonization stage in which a distinctive biotic assemblage occu- pies the stabilized site, (3) the diversification stage in which the colonizing community be- comes more complex, primarily through an increase in the number of species, and (4) the domination stage in which one or two taxa

occur in greater abundance than any other and, therefore, tend to dominate the community. Wa!ker & Alberstadt (1975) presented an analysis of the succession model and its possible significance in interpreting the fossil record. In that study it is concluded that the later diversification stage in most reefs repre- sents the climax community in terms of ecological succession.

The Elk River Reef is well exposed in the bluffs of the Elk River just a few miles north of the Tennessee-Alabama state line (Fig. 1). This reef has a well-developed stabilization community composed of three types of taxa: (1) incrusting bryozoans, (2) calathids (sponges or algae), and (3) an echinoderm or echinoderms that had an incrusting and ‘engulfing’ mode of attachment. Other taxa such as algae, gastropods, and trilobites were also members of the community, but were clearly secondary in importance as far as their role in the stabilization process is concerned. We believe that this assemblage of organisms stabilized the substrate, and created a condition conducive to supplemental reef development.

262 L. P . AIbers!adt and K . R . Walker LETHAIA 9 (1976)

Techniques and data

1 N O R T H

E L K T O N

Fig . I . Location map of Elk River Reef (stippled area).

Although the reef is well exposed, outcrop studies alone are insufficient for understanding the intricate growth relationships among the organisms and between the organisms and the substrate. In fact, the assemblage was not even recognized until after we had completed thin section studies across the bedded-nonbedded transition near the base of the reef (Fig. 2). Once we had determined the general attributes of the assemblage from thin section studies, outcrop recognition was much easier and eval- uation more meaningful. However, in re- examining the outcrop several times we found many calathid specimens weathering into relief, but no articulated echinoderms. The rock does not weather in such a way as to yield free complete specimens and the calathids are more easily recognized because of their characteristic cross-sectional profiles and are more readily preserved because of their skeletal construction. The articulated construction of the echinoderms and the high energy of the environment probably accounts for the absence of complete specimens.

In describing this community and evaluating its functional significance we do not feel that it is necessary to specifically identify all of the taxa involved. Such formal descriptions and identifications should be left to appropriate specialists. All of our calathid material has been made available to Matthew Nitecki for inclusion in the revision of the tribe Calathieae which he is presently undertaking. Because most of our information is based on thin section studies and only a few three-dimensional specimens, it is doubtful that specific identifica-

Fig. 2. Sketch of Elk River Reef above bedded grainstone. Black bar indicates the stratigraphic position of the pioneer community.

LETHAIA 9 (1976) Pioneer community 263

tions are possible for anything other than bryozoans. Fig. 6D shows the only three-dimensional pelmatozoan found. Several three-dimensional calathid specimens were recovered from insoluble residues of selected limestone blocks dissolved in dilute hydrochloric acid (Fig. 3). However, the Middle Ordovician rocks in the vicinity of Birmingham, Alabama, have ‘reefoid’ assemblages containing calathids similar to thosc in thc Elk Rivcr Reef. We examined several of these Alabama assemblages and collected some well-preserved three-dimensional specimens for comparison with the Elk River specimens. One of these is shown in Fig. 7B.

The substrate The stabilization community occurs near thc base of the reef in rocks that vary from wacke- stones to packstones to boundstones (Fig. 2). The rocks upon which the reef rests are grainstones. Many fossil recfs have a foundation of carbonate sand composed primarily of pelmato- zcan material, but little is known about why or how certain areas of such a substi-ate become conducivc for reef development. Thc fundamental point in this regard is how a soft or mobile marine substrate can be altered to a hard or immobile bottom. In essence, either a lithologic or biologic hardground has to be produced before a reef can fully develop. In the Elk River Reef the pioneer community prcduccd a biologic hardground which allowed further rcef development upward.

Incrusting bryozoans Several bryozoan genera occur in the stabilization community of the Elk River Reef, but as mentioned above it is not necessary to identify them all. Only the incrusting growth habit is of functional importance in helping to stabilize the substrate and form a biological hardground. Nicholsonella and Barosroma are by far the I’ ix . 3. Silicified spccimens of calathids from the Elk

River Reef. 0 A. Transverse view showing hollow abundant genera with such a habit, ccntral area but a fairly thick outer wall. Note the although other incrusting genera are present. extremely thick cstension of material around one Bryozoans incrust calathids (Fig. 6A) much branch of the specimen. X2. OB. Lateral view of external wall. X?.

than they incrust echinoderms. cases it is difficult to decide whether a bryozoan colony is incrusting part of an echino-

264 L. P . Albcrsfadt and K . R . Walker LETHAIA 9 (1976)

above the level of the pioneer community. No specimens of Echinosphaerifes were found in the pioneer community. The only partially intact pelmatozoan was a stem with two radicular cirri (Fig. 6D). From this specimen, thought to be in growth position, and from thin section examinations it is possible to determine the growth habits of these organisms. They grew incrusted and attached to other organisms and had the ability to completely ‘engulf’ individual fragments (Fig. 5A-D). Al- most all have canals or irregularly shaped internal cavities permeating all or parts of the skeletal framework. Many individuals appear to have had a stem with an axial canal running throughout. The secondary branches from the central stem have a relatively large canal (Fig. 6D).

The stems, radicular cirri, and the various appendages of the root system grew affixed to large skeletal fragments (Figs. 5D and 6C). In thin section many of the specimens appear as an irregular arrangement of plates or a gregarious mass (Fig. 6E). Many of these appear to be root systems but many are clustered in such a way and have such contorted shapes that they do not appear as ‘normal’ root systems embedded in the substrate. Some of these masses adhere to other fragments and to one another (Fig. 5D). Many adhere to calathids, sometimes in close association with bryozoans (Fig. 6A and E).

In one sample the incrusting part of the echinoderm can be traced completely around a calathid branch (Fig. 6E). In this, one of the best examples available, the incrusting segment has a hollow interior filled with carbonate mud. This attachment mechanism is similar to the one described by Sardeson (1908) from the Ordovician of Minnesota.

The most curious aspect of these echinoderms was their ability to completely engulf other particles (Fig. 5A-B), and even invade the living chambers of dead organisms. Fig. 5A shows echinoderm material completely engulfing a bryozoan fragment and partially invading the interior of an unidentified bivalved organism. This engulfing material appears to be a single plate in that it undergoes unit extinction under crossed nicols (Fig. 5B).

Fig. 5C shows the thin section appearance of an extension partially wrapped around an echinoderm ossicle. This is similar in appearance to the three-dimensional specimen in

Fig . 4. Bryozoan (Trixonodictya?) showing characteristic extensions in direction of mesotheca and normal to it. XIS.

derm or whether the echinoderm is incrusting the bryozoan. I t is probably more realistic to view these two taxa as mutually incrusting if they occur in some close entangled association. The important point is that such an entangle- ment creates substrate stability and by its very presence helps to form a biological hardground.

In addition to the common sheet-like incrusting bryozoans such as Nicholsonella and Batosfoma, the bifoliate bryozoan Trigono- dictya shows a unique growth habit (Fig. 4). This genus was able to wrap around adjacent fragments by forming elongate extensions of the mesotheca. These extended areas have no zooecia, or very poorly developed zooecia, and form a part of the colony that incrusted or wrapped around neighboring grains. Regardless of the origins and adaptive significance of such a growth habit it fits in well with the other stabilizing taxa of the community.

Incrusting echinoderms Incrusting echinoderms are an important com- ponent of the pioneer assemblage. The only complete theca found was that of the cystoid Echinosphaerites from near the middle of the Elk River Reef (Alberstadt et af . 1974), well

LETHAlA 9 (1976) Pioneer community 265

Fig. 6D in which a radicular cirrus is partially wrapped around a calathid specimen (note the canal in both echinoderm specimens).

Much of this material has peculiar aspects not normally attributed to echinoderms. How- ever, several attributes of these organisms indicate that they belong to some group of echinoderms. In thin section the echinoderm masses are composed of articulated plates, each plate having unit extinction indicating that it is a single crystal (Fig. 5A-B). The plates contain the characteristic reticulated meshwork (stereom) so prominent in many echinoderms (Fig. 6C).

Calathids Calathids are the dominant and most visible elements in the pioneer community. These double-walled organisms are easily seen on the outcrop because they weather into relief, and have a characteristic transverse section (Fig. 6D). Calathids are now believed to be dasycladacean algae (Nitecki 1967), but the receptaculitids (sensu stricto) are considered to be sponges by some (Foster 1973). As will be shown later the calathids in the Elk River Reef have characteristics that appear sponge-like. However, it is not the purpose of this paper to evaluate the taxonomic affinities of the organisms, but to broadly describe their general structures and evaluate their role in the community, particularly in regard to substrate stabilization. A complete review of the tribe Calathieae is underway at present (Nitecki 1972). However, Nitecki (1972) presented an excellent description and illustrations of Culu- thiurn egerodae from the Racine Dolomite (Silurian) of Illinois and Wisconsin. Unfor- tunately all of the specimens he examined are dolomitic molds and no thin sections were studied. The primary differences between the Silurian specimens studied by Nitecki and those from the Elk River Reef are (1) the shape of the thallus, (2) the degree and nature of the calcification of the outer layer, and (3) branching of the thallus. The Elk River specimens do not have the characteristic twisted thallus or the inverted cone-like growth form shown by C. egerodue. The Elk River specimens differ from the Silurian forms in the style of calcification of the outer layer. Finally, some of the Elk River specimens branch, a characteristic

not attributed to C. egerodue, but possibly present in some other genera (Nitecki 1972). Few taxa of the Family Receptaculitaceae have branched thalli.

A few three-dimensional specimens were collected from the Elk River Reef by etching scveral selected limestone blocks (Fig. 3). These are not as well preserved as those from the ‘reefoid’ assemblages of Alabama (Fig. 7B). The detailed structures of the Elk River specimens are best displayed in thin section, but the unsilicified three-dimensional specimens from Alabama provide useful information regarding structure. Whether the Alabama and Elk River specimens are conspecific is not clear as yet, but they appear to be very similar.

In thin section most of the calathid specimens appear as porous plates (Fig. 6E). This appearance is a result of carbonate mud (micrite) filling the void space in the center of the main axis and between the wall of the main axis and the wall of the outer layer. Sec- tions through these parts of specimens cut across the mud surrounding the lateral rods which extend from inner to outer wall. The ‘pores’ are actually cross sections of laterals.

The Elk River calathids have a main central axis separated from an outer calcified layer or wall. Numerous unbranched lateral rods (laterals) extend from the central axis outward (Fig. 7A, B, D, E, and G). At their distal extremities the laterals form calcified enlarge- ments (heads) which join together to form the outer layer. In many calathid specimens the main axis and outer layer are completely recrystallized. Nevertheless, thin sections of transverse views clearly show the extension of the proximal end of the laterals into the main axis. Laterals are well preserved in the region between the main axis and outer layer. The unsilicified specimens from Alabama show the laterals exceptionally well (Fig. 7B). The outer terminal ends of the laterals have four pointed stellate structures (Nitecki 1972) just behind the expanded head which forms the outer layer. When viewed in both transverse (Fig. 7G) and longitudinal section (Fig. 7D) these appear as right-angled extensions of the lateral. The stellate extremities (rays) of adjacent laterals overlap to form a double layer in the same manner as described by Nitecki (1969) for Zschudites iowensis (Owen). Such overlap is indicated by the presence of circular and elliptical shaped patches of coarse calcite lying

266 L. P . Albcrsradt and K. R . Walker LETHAIA 9 (1976)

Fig. 5. 0 A. Photomicrograph showing incrusling echinoderm completcly surrounding a bifoliate bryozoan fragment and partially inside a small articulated brachiopod(?). X20. gB. View of part of photomicrograph in A showing echinoderm complclcly surrounding bifoliate bryozoan. This photomicrograph is with nicols crossed to show unit extinction of echinoderm. X20. OC. Photomicrograph of an echinoderm segment (radicular cirrus?) showing ‘wrap around’ attachment characteristics. X 5.5. 0 D. Photomicrograph of a typical echinoderm-calathid assemblage. Echinoderm characterized by cxtcnsions with canals. Most have irrcgular shapes, some slightly recrystallized. Note particularly the close incrustations on calathid in lower right (1) and thc entangled echinoderm-bryozoan mass incrusting calathid (2). X4.

LCTHAIA 9 (1976) Pioneer community 267

Fig . 6 . 0 A. Photomicrograph of a transverse view of calathid specimcn from Elk River Reef showing thin section appearance of hollow central main axis; inclined radiating laterals and thin outer layer of expanded heads. Specimen incrusted by bryozoan (upper left) and echinoderm (lower right). XS. 0 B. Irregular distribution of porous thick outer layer and the connective relationship of this layer and calathid stalks. X3.4. 0 C. Photomicrograph showing the reticulated meshwork along the right sidc of an echinoderm segment incrusting the outer wall of a calathid specirncn. XSO. 0 D. Outcrop view of calathids from Elk River Reef in growth position. Note echinoderm stem with attached radicular cirri, one of which is wrapped partially around a calathid (I) . X 1.7. 0 E. Photomicrograph of calathid (longitudinal view) incrusted by sac-like echinoderm which in turn is incrusted by sheet-likc bryozoan on thc left and top of specimen. X3.2.

268 L. P . Alberstadt and K . R . Walker LETHAIA 9 (1976)

Fig. 7. Idealized cut away drawing showing calathid structure. Surrounding photomicrographs show the actual appearance of the various parts indicated. 0 A. Lateral with stellate structure embedded in thick outer layer. X68. 0 B. Transverse view of a three-dimensional calathid specimen from Alabama showing the heavily calcified central main axis with hollow interior, surrounding region with numerous radiating laterals. and heavily calcified outer layer showing a sponge-like porous? appearance. X4.1. UC. Photo- micrograph of the convoluted outer wall of a calathid showing some of the internal openings now filled with carbonate mud and others filled with pore-filling calcite. Note the difference between the calcite that fills the openings and the skeletal calcite of the wall. X38. 0 D. Longitudinal view of stellate structure showing circular cross sections of overlapping rays of adjacent stellate structures. X58. 0 E. Longitudinal view of area of laterals showing carbonate material filling voids between laterals. X58. OF. Photomicrograph of a tangential cut through outer layer showing characteristic rhomboidal outlines of lateral heads. X58. 0 G. Transverse view of a stellate structure showing the amorphous enlargement of the lateral head to form the outer wall. X58.


along a line just behind the expanded terminal heads. Thin sections tangential to the external layer commonly show the rhomboidal outline of the facets (Fig. 7F). Such facets were not seen on any of the threedimensional specimens. On the contrary, many Elk River specimens and all from Alabama have a most interesting and peculiar outer calcified wall. In these specimens the outer layer is much more heavily calcified than in most calathids described from elsewhere. This calcification is so thick that the rays of the stellate structures are ‘embedded’ deep within the outer layer (Fig. 7A) rather than being just behind it as is the case with most receptaculitids.

The details regarding the specific origins for such a calcified layer are not clear from the specimens we have examined. The outer layer has all the appearances of the convoluted wall of a sponge (Fig. 7B-C). The specimens from Alabama show this feature better than .those from the Elk River Reef. Thin section studies suggest that this outer layer is probably formed by the amorphous enlargement and possible fusion of the lateral heads. Nitecki (1969) also noted that the lateral heads of calathids ‘are often modified as to be amorphous without the definite and regular pattern so characteristic of the other receptaculitids’. There are two reasons for this interpretation. First the appearance of the coarse calcite in these convoluted outer walls is identical to that of the lateral heads, laterals, and main central axis (Fig. 7A and G). Second, there is no demarcation between the lateral heads and the region of the convoluted outer wall proper. Therefore, such a thick porous outer wall can form if the heads do not become too large and fuse in all directions so as to form a solid calcified structure.

One aspect of this oyter wall is difficult to explain. All specimens do not have such a thick wall, and of those that do, few have it formed equally around the entire thallus (Fig. 6B). The wall is developed to different degrees, and in some it extends as a prominent protru- sion.

Paleoecology of the pioneer community The calathids, incrusting echinoderms, and incrusting bryozoans form a unique assemblage

which occurs in local patches in the lower parts of the Elk River Reef. The mode of growth of all three taxa and the closeness of their associations indicates that, as an assemblage, they probably played a significant role in stabilizing the substrate. The rocks just below the Elk River Reef are grainstones, but the assemblage occurs more commonly in packstones and boundstones. Thus, although there is appreciable carbonate mud there is also much detrital carbonate debris of larger size. It is our belief that the high mud content is a reflection of binding and trapping abilities of the organisms involved, and not an indication of low energy conditions. On the contrary, we believe the environment was one of high energy as indicated by cross-stratification in adjacent, contemporaneous grainstones. After the pioneer community sufficiently altered the substrate, the overall conditions were such that colonial corals and stromatoporoids could grow in abundance and form the main body of the reef (Alberstadt et al. 1974).

The role of incrusting bryozoans is straight- forward and has long been recognized. The echinoderms present several questions. It is not clear whether all were stalked, or whether some were sac-like and ‘stalkless’, living some- what like edrioasteroids on the substrate or possibly attached to calathid branches. Similar growth habits have been reconstructed for the echinoderms of a Devonian hardground community of Iowa by Kock & Strimple (1968). There is no conclusive evidence in the Elk River samples to indicate that these incrusting segments were attached directly to a stem. Nevertheless, because of Sardeson’s (1908) descriptions and interpretations of Ordovician echinoderm attachments and because we were unable to positively identify edrioasteroid-like organism, we chose to reconstruct the echinoderms as ‘staked’ forms. Therefore, all of the incrusting segments are considered to have been support mechanisms attached in some way to a stem. In our reconstruction (Fig. 8) some of the incrusting holdfasts are without stems. This we believe might have occurred due to the death of the individual, or possibly at a certain ontogenetic stage the stem became detached, later to reattach itself in the substrate.

The calathids were the most prominent and possibly the most abundant group of the three and grew as rigid upright stalks, some branch-

270 L. P . Alberstadt and K . R. Walker LETHAIA 9 (1976)

Fig. 8. Idealized reconstruction of pioneer community showing upright branching calathids. incrusting bryozoans. and echinoderms.

ed. They were probably not incrusters as such, but grew in such numbers that they functioned as stabilizers. Fig. 8 is an idealized reconstruction of what we envision to have been the main elements of the pioneer community and their mode of life.

Several workers have commented on certain aspects of the paleoecological significance of calathids and receptaculitids in general (Bymes 1968; Nitecki 1973; and Church 1974). Recep taculitaceans occur most commonly in reefs; particularly in the Silurian and Devonian more so than in the Ordovician, but they are also found in level bottom muddy sediments as well. Most reports of calathids are from reef com-

munities (Toomey & Ingels 1964; Church 1974; Alberstadt ef al. 1974). Nitecki (1972) and Church (1974) reported that the calathids in the Silurian reefs of Illinois and in the Fillmore Formation (Lower Ordovician) of Utah occur most abundantly on the tops of the reefs. In fact, in the reefs in the Fillmore Formation the domination stage is recognized as the Cala- thium community, so designated because of the superabundance of this taxon. In the Elk River Reef no calathids are found anywhere near the top of the structure.

Accepting the interpretation that all receptaculitids are ancient dasycladacean algae, they have been used to evaluate some recent paleo-


geographic interpretations, particularly those related to the position of the Ordovician equator. The Ordovician equator is thought to have had a slightly northeasterly trend through the middle of the North American continent (Irvin 1964; Whittington & Hughes 1972; Ross 1975). Ross’s Ordovician equator is slightly farther northwest than that of Irving (1964) and Whittington & Hughes (1972). Based on these average positions the position of the Elk River Reef was close to 10”s latitude. The Lower Ordovician ‘mounds’ described by Toomey (1970) and reported to contain calathids would have been situated about 2-3”s latitude. Such information suggests that the taxon Recepta- culitaceae was restricted to a rather narrow equatorial belt (Bymes 1968). However, Nitecki (1972) questioned such a restriction and reported receptaculitids from northwest Africa in rocks that appear to have formed near Ordovician polar regions. If receptaculitids are algae, the climates and water temperatures would have had to have been warmer and more uniformly distributed than at present for this to be true (Nitecki 1972). However, would any of these distributional enigmas be lessened if receptaculitids were sponges rather than algae? We think not, because most receptaculitids occur along with the remains of Girvanella, Hedstroemia, Garwoodia, and other organisms of unquestionable algal affinities. Therefore, assuming that ancient algae were affected by the same overall environmental stimuli that affect modern algae, we agree with Nitecki that presently accepted Ordovician paleogeographic reconstructions are not wholly satis- fying.

Summary A unique assemblage of incrusting bryozoans, incrusting echinoderms, and upright branching calathids (algae?) occur in the lower parts of the Elk River Reef in southcentral Tennessee. Because of their numbers and incrusting and gregarious growth characteristics these taxa stabilized the substrate by limiting the movement of carbonate mud and skeletal debris. The incrusting bryozoans and echinoderms grew over and around each other and each incrusted calathids, eventually forming a bit+ logic hardground. The echinoderms had the

peculiar ability to ‘invade’ the living chambers of dead organisms and completely ‘engulf‘ entire fragments. The calathids described herein have a thick, commonly amorphous outer layer formed by the expansion of the heads of laterals which extend outward in all directions from the central axis. The fusion of these irregularly shaped heads forms a ‘porous’ sponge-like layer; a feature which has not been previously described in calathids.

The local sites stabilized by this assemblage were later occupied by stromatoporoids and colonial corals forming the main body of the reef (for a discussion of the upper parts of these reefs see Alberstadt et al. 1974).

REFERENCES Alberstadt, L. P. & Walker, K. R. 1973: Stages of

ecological succession in Lower Paleozoic reefs of North America. Geol. SOC. Am. (Abstracts with Programs; discussion paper) 5, 530-532.

Alberstadt, L. P., Walker, K. R. & Zurawski, R. 1974: Patch reefs in the Middle Ordovician (Carters Lime- stone) in Tennessee and vertical zonation in Ordovi- cian reefs. Geol. SOC. Am. Bull. 85. 1171-1182.

Byrnes, J. G. 1968: Notes on the nature and environmental significance of the Receptaculitaceae. Lethaia

Church, S. B. 1974: Lower Ordovician patch reefs in western Utah. Brigham Young University Geology Studies 241, 41-62.

Foster, M. 1973: Ordovician receptaculitids from California and their significance. Leihaia 6. 35-65.

Irving, E. 1964: Paleomagnetism and its Applicafion to Geological and Geophysical Problems. John Wiley and Sons, New York.

Kesling, R. V. 1963: Morphology and relationships of Cyclocystoides. Michigan Univ. Contrib. Mus. Pale- ontol. 18, 157-176.

Kock. D. L. & Strimple, H. L. 1968: A new Upper Ordovician cystoid attached to a discontinuity surface. Iowa Ceol. Surv.. Rep. Inv. 5 . 49 pp.

Nitecki, M. H. 1967: Systematic position of receptaculitids. Geol. SOC. Am. Spec. Pap. 115, 165-166.

Nitecki, M. H. 1969: Surficial pattern of receptaculitids. Fieldiana (Geology) 16, 36 1-376.

Nitecki, M. H. 1972: The paleogeographic significance of receptaculitids. 24th Inr. Geol. Congr. Sect. 7 ,

Nitecki, M. H. 1973: North American Silurian receptaculitid algae. Fieldiana (Geology) 28.

Ross, R. J. Jr. 1975: Early Paleozoic trilobites, sedi- mentary facies, lithospheric plates, and Ocean cur- rents. Fossils and Strata 4, 307-329. Universitets- forlaget, Oslo.

Sardeson, F. W. 1908: Discoid crinoidal roots and Camarocrinus. I . Geol. 16, 239-254.

Toomey, D. F. 1970 An unhurried look at a lower Ordovician mound horizon, southern Franklin Moun- tains. West Texas. I . Sediment. Petrol. 40. 1318-1334.

Twmey, D. F. & Ingels, J. J. C. 1964: Reported Silurian occurrence of Calathium from the Thornton

I , 368-381.

303-309.

111 - Lethaia 3/76

272 L. P . Alberstadt and K . R . Walker LETHAIA 9 (1976)

Reef, Illinois: A correction. I . Paleontol. 38, 1102- 1104.

succession as a function of structurc in fossil com- 235-278. munities. Paleobiology I, 238-257.

Whittington, H. B. & Hughes, C. P. 1972: Ordovician geography and faunal provinces deduced from trilo-

Walker, K. R. & Alberstadt, L. P. 1975: Ecological bite distribution. Roy. SOC. Lond., Phil. Trans. B:263.

LETHAIA NEWSLETTER PRESENTATIONS LETHAIA 9 (1976) 272

The Ostracodologist - newsletter for ostracode workers EPHRAIM GERRY

The feasibility of a newsletter to serve ostracode workers, both palaeontologists and zoologists, was first brought up at the symposium on Ostracodes as Eco- logical and Palaeoecological Indicarors, held at Naples, 10th-19th June, 1963. The need was felt for having a bulletin, primarily informative in nature, to keep the interdisciplinary groups of ostracode workers in- formed of each other’s activities. changes in field of research and address. as well as group activities such as symposia and congresses.

It was decided to produce such a newsletter, and E. Gerry was requested to act as editor. The first issue, in 1964, mimeographed on a few pages, was sent to 180 persons. The last number (22/23) was issued in 550 copies, and approximately 100 libraries and institutions were sent copies. The newsletter is sent free of charge by surface mail to anyone re- questing it.

Problems in editing such a newsletter may be divided into three groups:

(1) Financing. - Costs have to be kept to a minimum. The newsletter, if at all possible, should be circulated free of charge. Even a nominal sum makes it difficult, and in many countries impossible, to subscribe, and the book-keeping, handling of cheques and money orders for small amounts in various currencies is often more trouble than it’s worth. In the case of The Ostracodologist. fortunately no such difficulties have been encountered. During the first year the local oil companies, and since 1965 the Israel Institute of Petroleum and Energy, covered the costs of printing and postage.

(2) Number oj issues. - As we have no problems of financing, this problem is closely connected with the thlrd group: the contents. One cannot publish a newsletter without ‘news’. Rising postage costs (besides the fact in our particular case that it is strictly a

one-man operation) also tend to push us towards publishing larger, less frequent issues. This on the other hand makes some of the items, especially pre- liminary information on group activities, out of date.

Lately the average has been one issue per year.

(3) Contents. - Originally news reports were received from colleagues in several countries, but unfortunately this source has gradually ‘dried up’. The two regular items in our newsletter are: field of interest and address of ostracode workers who notify us or publish, and address changes; a bibliography of works received or read by the editor. In the bibliography preference is given to material not in the large international journals. Information on meetings, type collections and type localities is also published. It is on contributions of the latter type where we occasionally come to the dangerous question: what is a publication? As a matter of principle, I do not refuse to publish material of general interest and informative nature. The list of a long forgotten type collection or the non-existence of a-genotype might not find its way into the major palaeontological or zoological journals, but it is of primary interest to ostracode workers.

While The Ostracodologist (and I think most of the other small professional newsletters) does not have an editorial board, nor sends material to referees, some material which would otherwise remain un- published is used, quoted and included in current bibliographies. I do not think newsletters should in- clude descriptive works. Authors should be advised in the case of important informative material to publish or republish in professional journals of a wider range.

Contributions and requests should be addressed to: The Ostracodologist? Ephraim Gerry. P.O.B. 5283, Jerusalem, Israel.

a receptaculitid–echinoderm pioneer community in a middle ordovician reef

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