Paleoecology of the Whitewater Formation (Cincinnatian, Upper Ordovician) of Southeastern Indiana

College of Wooster Invertebrate Paleontology Class Investigation, Fall 2000

The Whitewater Formation exposed at Stop #1 of the September 2000 Invertebrate Paleontology field trip. This photograph was taken earlier in the summer when the sun was shining! Note the resistant nature of this outcrop, showing the high ratio of limestone to claystone. See the project pages for the underlying Waynesville and overlying Liberty Formations.

The Whitewater Formation Student Team

Katherine Nicholson is a sophomore geology major from West Columbia, South Carolina. Her project responsibilities include the Whitewater bryozoans.

Abby Bowers is a sophomore geology major from Napoleon, Ohio. She is working on the Whitewater gastropods and bivalves.

Nick Welty is a sophomore from Three Rivers, Michigan. His duties include the Whitewater corals and any other cnidarians.

Jared Rhode is a sophomore geology major from Port Clinton, Ohio. He is responsible for assessing the Whitewater brachiopods.

 

The Whitewater Mollusks
(by Abby Bowers)

Figure 1: This unclassified conispiral gastropod is encrusted and preserved by a heliolitid coral.

Gastropods, i. e. "snails," possess a stomach which rests on a muscular foot. Some have shells to protect these soft body masses against nature and predators; on the other hand, a few have lost their shells all together in exchange for other forms of defense. Figure 1, collected form the Whitewater Formation of southestern Indiana, is a preserved shell of a marine gastropod. Amazingly, gastropods can be found in marine, freshwater, and terrestrial habitats, making them one of the most abundant and diverse classes of the Phylum Mollusca. Gastropods are predominantly benthic vagrant epifaunal herbivours, crawling across the surface and scraping up algae or feeding on plants. There are a few gastropods that are scavengers, detritus feeders, and even predators! Some gastropods have a well developed foot that can be used to burrow into soft substrates, leading to an infaunal life mode. The geologic record of gastropods is well represented thorugh various modes of preservation, like internal molds and external molds, or the original hard parts may still be present. A majority of gastropod fossils are preserved as internal molds, called steinkerns, because the original aragonitic shells dissolved away over time. These internal molds do not preserve the external ornamentation, which makes it difficult to classify the gastropod fossil at the species level. Homeomorphy and environmental plasticity also makes it difficult to classify gastropods.

The Whitewater Formation of the Upper Ordovician Cincinnatian series is known to contain Holopea and Loxoplocus.

Bivalves are the second most abundant and numerous class of the Phylum Mollusca. The most common sea shells found on a beach are these bivalve shells. Bivalves have two valves and are symmetrical between the valves. Common bivalves are clams, oysters, scallops, and mussels to name a few. Unlike gastropods, to survive, they need a fresh food and oxygen rich water to cover their gills. Because of this, bivalves do not live on land or occupy anoxic environments.

Bivalves fall into one of the following five life modes: Labial palp detritus feeders, epifaunal filter feeders, infaunal siphonate filter feeders, infaunal nonsiphonate filter feeders, or infaunal mucus tube feeders. The bivalves of the Whitewater Formation of the Upper Ordovician Cincinnatian Series were predominantly epifaunal filter feeders. Living on top of hard substrate, these had no siphons. Fillibranch gills, a more complex set of gills, were used by these bivalves for feeding and respiration in the high energy environments. The geologic record for bivalves is extensive and well preserved. Fossils appear as external molds, internal molds, bryozoan encrustings, or the original hard parts may still remain. Because most bivalves are made of aragonite, internal molds are the most common mode of preservation. When the original hard parts are available, they are useful in recording seasonal changes in their growth lines and climactic changes in their shell chemistry. Unfortunately, bivalves are not very useful in biostratigraphy because they have long stratigraphic ranges.

The Ordovician bivalve, Ambonychia robusta, pictured above is an external mold. The mold is uniquely preserved by an encrusting bryozoan.

Figure 3: Growth lines of this bivalve, Caritodens demissa, are visible above running parallel to the external valve margin. A small encrusting bryozoan may be seen in the lower left hand corner of the shell.
 The Whitewater Formation of the Upper Ordovician Cincinnatian series is known to contain Ambonychia sp., Ischyrodonta sp., Caritodens demissa, Cyrtodontula umbonata, and Anomalodonta gigantia.

 

The Whitewater Bryozoans
(by Katherine Nicholson)

Homotrypa flabellaris, a unilaminate bryozoan.

Bryozoans are colonial, filter-feeding organisms that are almost entirely marine. They are nicknamed "moss animals" because their colonies, made up of thousands of individuals, often resemble feathery coatings of moss on shells or other hard surfaces. Bryozoans bear a striking resemblance to coral, but they are more closely related to brachiopods. Both bryozoans and brachiopods are lophophorates--that is, they possess a fan-like cluster of tentacles called a lophophore that is used for filter-feeding. Bryozoans, like brachiopods, also have a "U"-shaped digestive tract but no heart or vascular system. Individuals, known as zooids, are able to collect oxygen and expel wastes by diffusion. Each zooid measures about 1 mm in length and is joined to others by common tissue. Not all zooids serve the same purpose; several specialized types exist. Autozooids are limited to feeding activities; gonozooids carry out the reproductive process; kenozooids add surface area to the colony; avicularia use their hard "beaks" to guard the colony against encroaching animals; and vibracula rotate single hairs to sweep debris from the colonial surface. Maculae, or bumps, on the colony's surface are concentrations of a single type of zooid. The specialization of zooids allows a colony to use its energy efficiently.

A bryozoan's colonial skeleton, or zooarium, is usually composed of calcite. Because this mineral is not easily broken down, fossil bryozoans are most often found with their hard skeletons unaltered. Their soft parts are never preserved, however. Acetate peels from longitudinal, transverse, and tangential cuts of fossil bryozoans, when observed under a microscope, provide the best means of studying the structure and function of the individuals in a colony. This is also the primary means of identification for bryozoan fossils.

Bryozoans were the second or third most common fossil group, behind brachiopods and crinoids, in the Ordovician, the period represented by the Whitewater Formation. This is evidenced by the relatively large number of bryozoan specimens collected from this site. Two primary types of bryozoan specimens are found in the Whitewater Formation: ramose, or branching, bryozoans and massive bryozoans. The most abundant species of massive bryozoan, based on our field collections, is Batostoma varians. This bryozoan has obvious maculae and extensive skeletal material. Homotrypa wortheni, is the most abundant branching species. The maculae of this bryozoan come to sharp points, and its zooaria often form thin, delicate branches. Homotrypa dawsoni, another branching species, is also present but is less common. It closely resembles H. wortheni but has less-pointed maculae. Homotrypa flabellaris, a sheet-like bryozoan, is also present. It is common but less so than the massive and branching forms. Its surface has an even appearance, and it forms uni- and bilaminate colonies.

Homotrypa wortheni, a branching bryozoan with prominent, pointed maculae.

Batostoma varians, a massive bryozoan with visible maculae.
 The taxa represented at this site, like most bryozoans, are associated with shallow, tropical seas. Most of the species present would have benefited from, but not required, a hard substrate. Their massive or branching forms could have prevented them from being carried off by the current. Because their delicate feeding mechanisms are easily clogged, they would have preferred clear water with little wave activity.

 

The Whitewater Brachiopods
(by Jared Rhode)

Shown here is the articulate brachiopod, Hiscobeccus capax. One can notice major plications and a zig-zag commisure when looking at this specimen. Pictured here is the exterior, dorsal valve. Also, growth lines that cross the plicae are evident in this photo.
 The brachiopods of the Phylum Brachiopoda are by far the most diverse and abundant of all the skeletonized invertebrates of the Paleozoic. There are approximately 300 species that exist today and over 30,000 are evident in the fossil record. Brachiopod can be translated to mean "arm-foot". Brachiopods had many different body forms and occupied many different niches throughout the seafloor. Brachiopods are entirely marine. Brachiopods were once again very common in the Paleozoic, but became extinct in the Permian.

Characteristic of the brachiopods are two valves with one usually being slightly larger than the other. Brachiopods bear adductor and diductor muscles that help them open and close their shells. The top valve on the brachiopod is considered the dorsal valve and the ventral valve would be the bottom valve, which sticks out slightly toward the posterior. Brachiopods were solitary, sessile, and benthic. They were also filter feeders and the lophophore was a very important part of the brachiopd's filter feeding habits. The lophophore enables the brachiopod to filter feed, because of it's feather-like circular structure with tentacles. Brachiopods could live on hard or soft substrates. Some were able to spread out on soft sediments. They are considered to be stenohaline. The articulate brachiopods are stenooxic and the inarticulates are euryoxic. Today, brachiopods are found in cooler waters. Brachiopods are also found in shallow, turbid waters. With no siphons, brachiopods were not able to burrow. All brachiopods were therefore, epifaunal. The pedicle of the brachiopod attached it to the sediment.

This is an exterior view of Hebertella occidentalis. This is an articulate brachiopod and one can see the characteristics of the dorsal valve in this photo.

Shown here is Rhynchotrema dentatum. It is an articulate brachiopod with large plicae. Pictured here is its exterior, dorsal valve. This specimen has a very pointed beak. It is also very small in size.
 Brachiopods are fossilized showing their exterior shells. Almost no evidence of original soft parts exist. Therefore, most brachiopods are preserved as molds. When looking at these molds of brachiopods one can determine many features. Evident are the plicae or costae, fold, sulcus, growth lines, and commisure. They can also be described as strophic or astrophic. A strophic brachiopod has a long hinge line and an astrophic brachiopod has a short hinge line. In the formation that we studied, the Whitewater Formation, brachiopods were vey prevelent. The most common brachiopods included Hebertella occidentalis, Hiscobus capax, and Rynchotrema dentatum. These can also be seen in the photographs. Other brachiopods that were found at the Whitewater Formation are Holtedahlina sulcata, Rafesquina ponderosa, Platystrophia clarksvillensis, and Platystrophia acutilirata. Of course, other brachiopods could be found at the Whitewater Formation, but these were all that were located.

 

The Whitewater Corals
(by Nick Welty)

An example of Protaraea richmondensis. Each individual depression is a corallite.
 The corals found in the Whitewater formation are members of the group Cnidaria, sometimes referred to as "Coelenterata." Cnidarians are characterized by the presence of stinging cells called nematocysts. Besides the corals, the Phylum Cnidaria also includes the Class Scyphozoa (jellyfish), which includes the much-debated conulariid order. Morphologically, the cnidarians are relatively simple. Although they have true tissues, they have no discrete organs. While they lack specific excretory, respiratory, and circulatory systems, they do have a nervous system, muscular system, and reproductice system. A cnidarian body is made up of specialized cells in two layers, the ectoderm and the endoder, with a layer of mesoglea in between. The ectoderm is the outer layer and encloses the body and mouth. Also, the ectoderm secretes a skeleton in corals. The endoderm, the inner layer, digestes food trapped by the tentacles. Another characteristic of cnidarians is that they can alternate between mobile and sessile lifestyles by alternating their generation reproduction.

During a cnidarian's life, it will live both as a sessile polyp attached to substrate, and as a mobile medusa. Corals spend the majority of their life as a polyp, and jellyfish as a medusa. Additionally, the corals found in the Whitewater formation are entirely marine. Today, corals are found on reefs, where they are utilized as excellent indicators of climate and latitude.

This is another example of Protaraea richmondensis. Protaraea is a compound coral that grows as a crust on other objects. This specimen displays that well. The coral has actually encrusted a gastropod, and retained the gastropod's shape during preservation.

Finally, this is a specimen of Grewingkia canadensis. A side view would display the septa on the interior. Also, faint growth-lines are present on the exterior. In the center of the picture, a bryozoan can be seen encrusting Grewingkia.
 Only two species of cnidarians are found in the Whitewater formation, Grewingkia canadensis, and Protaraea richomdensis. Grewingkia was the most common specimen found, while Protaraea was very rare. Both Grewingkia and Protaraea belong to the Class Anthozoa, and both are found on this page.

 

The Whitewater Formation Paleoecology
(by the Whitewater Team)

The Whitewater Formation is representative of a shallow marine shelf environment in the Upper Ordovician. The most prominent organisms are strophomenid and rhynchonellid brachiopods, cnidarians, and bryozoans. A moderate number of bivalves are present. Gastropods are relatively uncommon, and no cephalopods or trilobites are represented. Based on this distribution of organisms, the water energy was interpreted to be moderate to high with little to moderate turbidity. This was inferred from the presence of bivalves, cnidarians, bryozoans, and brachiopods, all of which are stenoturbidic and require clean, nutrient rich water. All of the organisms present are commonly found in the photic zone because they need abundant oxygen, and many may have had photosynthetic zooxanthellae. The hermatypic corals present are indicative of a stenohaline and stenothermal environment. The brachiopods present likely thrived in tropical waters. Most of the organisms present prefer a hard substrate, especially bryozoans and corals, although the sediment should have been soft enough to allow bivalves to wedge themselves into it.

The dominant organisms of the Whitewater Formation are brachiopods, specifically Hebertella occidentalis, Platystrophia acutilirata, Platystrophia clarksvillensis, Hiscobeccus capax, Rhynchotrema dentatum; bryozoans, specifically Batostoma varians and Homotrypa wortheni; cnidarians, specifically Protarea richmondensis and Grewingkia canadensis; gastropods, and bivalves. Compared to the Whitewater Formation, the Liberty Formation has a much greater number and diversity of brachiopods; many cephalopods, fewer bivalves, cnidarians, gastropods, and bryozoans; and many trilobites. The Waynesville Formation has abundant brachiopods, especially strophomenids, but fewer than the Liberty Formation; fewer bryozoans than the Whitewater Formation; no cnidarians; abundant gastropods; few bivalves; and a moderate number of trilobites. The above organism distributions show that the Liberty Formation has a greater presence of carnivores and deposit feeders than the other formations. It is a more diverse community than the Whitewater Formation because it contains abundant vagrant benthic and nektonic organisms. The Waynesville Formation, like the Liberty, has abundant deposit feeders and carnivores. Because of this, it has fewer filter feeders. Though gastropods, vagrant benthic epifaunal herbivores, are present, most of the Whitewater Formationís organisms are sessile benthic epifaunal filter feeders.

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