Fauna

SPECIES                TERMINOLOGY & MORPHOLOGY

The Trenton Group, particularly where exposed at the type location along West Canada Creek in New York , is one of the richest series of strata containing the extinct arthropods known as trilobites. Ostracodes, living representatives of the arthropods within the class Crustacea, are also found throughout these rocks. The great majority of specimens illustrated in the following pages were collected by C. D. Walcott, during the late 1800's, and Thomas E. Whiteley, during the early 1990's, from the Walcott-Rust Quarry near West Canada Creek. The specimens housed in the Museum of Comparative Zoology include 22 species of trilobites and four species of Ostracoda.

The Walcott-Rust Quarry limestone is rich in trilobites, many of which are well studied and researched. The four most abundant species in this fauna are Ceraurus pleurexanthemus Green, Flexicalymene senaria Conrad, Isotelus gigas Dekay, and Meadowtownella trentonensis Hall. Many exceptionally well preserved specimens of Isotelus gigas make up a large portion of the collection, the neotype of the species being one of them. Enrolled specimens of Ceraurus pleurexanthemus Green and Flexicalymene senaria Conrad are also numerous and were of significant importance to C.D. Walcott. It was in thin sections of these trilobites that he discovered preserved appendages inside the carapaces. In a 1999 issue of the Journal of Paleontology completed by Brett et al. a detailed study of the beds and trilobite fauna showed the trilobites were a useful tool in estimating paleo-current direction and the conditions and speed of burial.

Aside from the trilobites, there are many well-preserved specimens of ostracodes in the collection. Those found are mostly leperditids and beyrichids that are exposed on the bedding planes or within the limestone matrix.

SPECIES                TERMINOLOGY & MORPHOLOGY

Brachiopods are very abundant throughout the Trenton Group, but have not been as well studied as other groups, such as the Trenton trilobites and crinoids. They were recognized as components of the Trenton strata very early and are mentioned by John Sherman in his description of Trenton Falls in 1844. James Hall later described many of the common species of brachiopods in some of his publications on the paleontology of New York State (Hall, 1847, 1866a, 1872; Hall and Clarke, 1892). Since Hall's early publications few of the Trenton brachiopods have been studied in detail and redescribed.

Orthids and Strophomenids seem to dominate the fauna with Rafinesquina trentonensis being the most abundant species seen in outcrop within Trenton Gorge and the surrounding areas. The brachiopod fauna of the of the Trenton Group, as represented in the Museum of Comparative Zoology (MCZ) collections, consists of 13 lingulid species, one acrotretid, one siphonotretid, one craniid, four strophomenids, three orthids, one rhychonellid, and two atrypids. The specimens illustrated here were collected by Charles Doolittle Walcott and William P. Rust in the late 1800s.

Bryozoans are very abundant in the Trenton Group limestones at West Canada Creek and it is only logical that bryozoan specimens make up a sizable portion of the MCZ's collections from this area. Even so, these specimens have not been properly identified or updated to modern taxonomy. For publications concerning Trenton Group Bryozoa, see the following list of papers by June P. Ross. 

• Ross, June Phillips. 1964. Champlainian cryptostome Bryozoa from New York State Journal of Paleontology, 38:1-32.
• Ross, June Phillips. 1967a. Evolution of ectoproct genus Prasopora in Trentonian time (Middle Ordovician) in northern and central United States. Journal of Paleontology, 41:403-416.
• Ross, June Phillips. 1967b. Champlainian Ectoprocta (Bryozoa), New York State. Journal of Paleontology, 41:632-648.
• Ross, June Philips. 1968. Trentonian trepostomata, New York State. Special Paper – Geological Society of America, 183 p.
• Ross, June Phillips. 1969. Champlainian (Ordovician) Ectoprocta (Bryozoa), New York State, part II. Journal of Paleontology, 43:257-284.
• Ross, June Phillips. 1970. Distribution, paleoecology and correlation of Champlainian Ectoprocta (Bryozoa), New York State, part III. Journal of Paleontology, 44:346-382.

SPECIES                TERMINOLOGY & MORPHOLOGY

The echinoderm fauna of the Upper Trenton Group is best developed in the crinoid beds in the Spillway Member of the Rust Formation at Walcott-Rust Quarry where the fauna includes 11 described species of crinoids, one paracrinoid, one rhombiferan, two carpoids, two asteroids, one ophiuroid, and one edrioasteroid. The specimens from the Museum of Comparative Zoology that are illustrated here were collected by Charles Doolittle Walcott and William P. Rust in the late 1800s and Thomas E. Whiteley in the 1990s. Some of the echinoderms are also rare to common in similar facies from the Upper Trenton at other localities in the West Canada Creek area. The echinoderm fauna consists of four basic assemblages. The disparid crinoids Cincinnaticrinus varibrachialus and Ectenocrinus simplex dominate the most common one. In addition, largely monospecific associations of the disparid crinoid Iocrinus trentonensis , the camerate crinoid Rhaphanocrinus subnodosus , and the rhombiferan Cheirocystis anatiformis are known. Small numbers of other echinoderm taxa can be found in any of the main assemblages. Diversified trilobites, brachiopods, and bryozoans also occur with the echinoderms.

Preservation of many of the Walcott-Rust Quarry echinoderms is excellent and encourages the reconstruction of paleobiology. Food grooves and covering plates are available for all of the common crinoids and the rhombiferan and these reflect the nature of their tubefeet and the size ranges of the food particles eaten by these suspension-feeding animals. The few complete specimens show the nature of attachment devices and substrates and provide insights about the levels occupied by some of the crinoids and the rhombiferan. The carpoids, starfish, and, the edrioasteroid were restricted to the seafloor. The inferences about living habits are discussed for each species subsequently.

SPECIES                TERMINOLOGY & MORPHOLOGY

The mollusca fauna of the Trenton Group, as represented in the Museum of Comparative Zoology (MCZ) collections, consists of: 23 genera and 3 species of nautiloids; 13 genera and 1 species of bivalves; 15 gastropod species; and 2 species of monoplacophoans. The specimens illustrated here were collected by Charles Doolittle Walcott and William P. Rust in the late 1800s. The Trenton mollusca fanua is mostly dominated by nautiloids and gastropods with bivalves and monoplacophorans being less dominant and in some cases quite rare. Specimens in the MCZ collections were recently identified by Kathleen Histon (nautiloids), John Pojeta (bivalves), and Peter Wagner (gastropods and monoplacophorans).

SPECIES                TERMINOLOGY & MORPHOLOGY

This assemblage of taxa has been grouped together from the rarer and less-understood fossils from the Trenton Group of West Canada Creek. One species of Conchopeltis , three species of conularids, one machaeridian genus, and nine species of graptolites are included in this group. These specimens are not related, although the affinities of Conchopeltis and conularids are still in debate.

Many of these creatures have a history of uncertainty surrounding their placement in the taxonomic hierarchy. One such fossil is Conchopeltis alternata , first described by C. D. Walcott in 1876 and found only in the limestones of Trenton Falls , NY . As discussed by Oliver (1984) Conchopeltis has been linked to gastropods, conularids, and cnidarians (corals, anemones, jellyfish, etc.) at different times over the hundred or so years since its discovery. The unusually large conularid Metaconularia papillata, described by James Hall in 1847, is also a species unique to the Trenton of New York. Conularids are long thought to be related to the cnidaria, yet their classification is still unclear. The machaeridia, another strange and little-known group of organisms, is found in the Trenton as well. It is still uncertain where machaeridians fit into modern classifications. Some paleontologists have attempted to place them with echinoderms, and more recently with tommotiids, a group with early Cambrian origins that have sclerites (hollow calcium carbonate scales or plates).

Graptolites are the most studied and well-known of this section's miscellaneous group of fossils. The graptolithina have been classified as part of the phylum Hemichordata. Examples of graptolites are rarely found in the West Canada Creek strata, which was a shallow marine environment during the Ordovician. They are far more common in rocks nearby like the Utica Shale. At one time, the area was a calmer and deeper ocean deposit, more hospitable for their planktonic lifestyle.