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6 Poriferans and Cnidarians: Sponges, Corals, and Jellyfish

Richard Arnold Davis Indiana University Press ePub

Figure 6.1. A simple sponge, showing a cross-section of the body wall. Inset shows a magnified view of incurrent canals (ostia), collar cells and collar-cell chambers. Drawing by John Agnew.

 

Although sponges are regarded as the least specialized, hence most primitive of multicelled animals, they play an essential role as “sanitary engineers” in aquatic environments, living as active suspension feeders or filter feeders (Plate 3A). By removing minute organic particles from the water, sponges prevent decay products from poisoning the environment. This is a long-running role, as sponges first appear in the fossil record during the late Precambrian, over 540 million years ago.

Sponges

The body of a sponge lacks distinct cell layers, but is composed of different specialized types of cells that perform different life functions. The fundamental sponge cell is the collar cell, equipped with a waving flagellum that draws water into a cone formed of microvilli (Figure 6.1). The simplest sponge is a hollow tube, open at one end. Collar cells line the interior of the tube and create a feeding current that passes through the body wall via openings called ostia and tubular cells called porocytes. The collar cells remove food particles that are digested by amebocytes. The feeding current carries wastewater, depleted of nutrients, out of the sponge cavity through one or more chimney-like openings called oscula. Because sponges are fixed to the substratum and do not move about, they are often regarded as inert or nonliving. In fact they are actively circulating water and processing it for nutrients (Plate 3A).

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2 Science in the Hinterland: The Cincinnati School Of Paleontology

Richard Arnold Davis Indiana University Press ePub

Figure 2.1. Members of the Cincinnati School of Paleontology who were amateur paleontologists: A. U. P. James, publisher and owner of the James Book Store. B. S. A. Miller, attorney. C. Charles Faber, realtor. D. C. B. Dyer, who, after he retired as a maker of soap and candles, devoted himself to fossil collecting. Photograph of Dyer from an old album in the possession of Richard Arnold Davis (© Richard Arnold Davis); all others from the Department of Geology, University of Cincinnati.

 

The rocks beneath and around Cincinnati were deposited in an interval of time universally called the Ordovician Period. This time unit was proposed formally in 1879. In the second half of the nineteenth century, beginning even before the Ordovician Period was named, there was in the region of Cincinnati, Ohio, a group of paleontologists who have been called the “Cincinnati School of Paleontology.” There is no single, definitive list of the members of the Cincinnati School, and different authors have included different people as members, depending on the purposes of their compilations. Nor is there a definitive list of iron-clad criteria as to who should be considered a member and who should not. Nonetheless, the individuals included in the body of this chapter have a number of characteristics in common.

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Epilogue: Diving in the Cincinnatian Sea

Richard Arnold Davis Indiana University Press ePub

 

Many paleontologists, ourselves included, became fascinated with fossils and embarked on scientific careers long before we ever encountered living marine animals. For many of us, the greatest thrill has been our first encounters with living representatives of the animal groups we knew first only as grey, lifeless forms encased in rock. Both of us have been privileged to examine firsthand living relatives of animals of our favorite groups of fossils—crinoids for Meyer and nautiloid cephalopods for Davis. Our experiences have fueled a curiosity that affects practically anyone who contemplates the fossil richness of the Cincinnatian or other comparable fossiliferous strata. Many times, in the field, we stand on a Cincinnatian outcrop where fossils are abundant in almost every rock, and we wonder: what did the Cincinnatian sea actually look like? How did these creatures behave when alive? If we could travel back in time to dive into the Cincinnatian sea, what would we see?

In his book The Crucible of Creation, the paleontologist Simon Conway Morris (1998) takes the reader on a journey through time in an imaginary time machine that lands on the shores of the Cambrian sea in western Canada of 520 million years ago. The time machine then descends into the sea and enables time traveling scientists to view the varied and bizarre animals found as fossils in the famous Burgess Shale. Conway Morris recreated the environment of the Cambrian sea and the life within it from the evidence of the fossils and rocks, but he embellished the scenario with a measure of speculation and fantasy.

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16 Life in the Cincinnatian Sea

Richard Arnold Davis Indiana University Press ePub

Figure 16.1. A. Internal mold of nautiloid, Treptoceras duseri (Hall and Whitfield), with crinoid Xenocrinus baeri (Meek) preserved within body chamber. Richard Arnold Davis collection, Waynesville Formation, Adams Co., Ohio, collected by Thomas T. Johnson. B. Ophiuroid, Taeniaster spinosus (Billings), MUGM 28187, preserved on internal mold of nautiloid, Waynesville Formation, Butler Co., Ohio, scale in mm. C. Trilobites, Acidaspis sp., preserved on internal mold of nautiloid, ?Treptoceras sp., CMC IP 2257, Cincinnatian, vicinity of Cincinnati, Ohio, × 0.9. D. Trilobites, Flexicalymene meeki (Foerste), preserved on internal mold of nautiloid, ?Treptoceras sp., OSU 50329, Cincinnatian, vicinity of Cincinnati, Ohio, × 2.6. C, D from Davis et al. (2001, figures 2, 5), and reprinted by permission of Blackwell Publishing.

 

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14 Type-Cincinnatian Trace Fossils: Tracks, Trails, and Burrows

Richard Arnold Davis Indiana University Press ePub

Figure 14.1. A. Repichnia of the trilobite Isotelus, Asaphoidichnus trifidum Miller, CMC IP 37569, Edenian, Kope Formation, Cincinnati, Ohio, × 1. B. Repichnia of the trilobite Cryptolithus, similar to Cruziana, CMC IP 37622, horizon and locality unknown, × 1. C. Trilobite trail, intermediate between Rusophycus and Cruziana, Maysvillian, Corryville Formation, Clermont Co., Ohio (from Osgood [1970, plate 66, figure 3]), × 0.8. D. Paschichnia, ?Paleodictyon, CMC IP 17431, Edenian, Kope Formation, Cincinnati, Ohio, × 3. E. Fodinichnia or domichnia, the “turkey track,” Trichophycus venosum Miller, CMC IP 37575, Campbell Co., Kentucky, × 0.4. From Osgood (1970, plate 60, figure 7). C, E reprinted by permission of the Paleontological Research Institution.

 

The Cincinnatian is renowned for its abundance of well-preserved shells and skeletons of Ordovician marine invertebrates, and because these fossils represent the remains of long-dead organisms, at first glance one would not expect them to yield much information about the activity and behavior of these animals during life. Of course, we can deduce a great deal about the life habits of Ordovician animals directly from the morphology of shells and skeletons (body fossils) by comparisons to their living relatives, but a vast range of evidence about ancient behavior also comes from a completely different source, namely the trace fossils that are both abundant and diverse in Cincinnatian strata.

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