Thursday, December 2, 2010

Fossil of the Week

12/2/10 – A Slab of Many Fossils

This tiny fossiliferous slab (measuring only 8 x 5 centimeters, or 3 x 2 inches) contains over 60 individual fossils. Included in the piece are holotypes* of two new species of snails, Pleurotomaria floridensis and Murchisonia mohawkensis (indicated by the names and catalog numbers on the labels matching numbers written on the slab), each named by H. F. Cleland in 1900. Notice that the holotype specimens have been outlined on the slab in red ink rather than separated by cutting the slab, maintaining the integrity of the slab and a record of the species found together in the formation. The slab was found at Fort Hunter, New York. Fort Hunter is part of the town of Florida in Montgomery County, northwest of Albany. It lies in the Mohawk River Valley and in the 18th century, was the site of one of the two primary Mohawk Native American settlements. Knowing this, the two species names on these labels now make sense to us – they mean “from Florida” (New York – not the Florida off of Cuba) and “from Mohawk.” A third name (Gasconadia putilla Sardeson, 1896, now classified in Murchisonia) appears on the lower label, apparently indicating another species on the slab.

The weathered slab with its fossils was collected as part of a class in the Cornell Summer School of Geology taught by Professor Gilbert Harris (PRI's founder and first director). The material is from the Early Ordovician Period, about 475 million years old. Herdman Fitzgerald Cleland (1869-1935)** was a professor of geology at Williams College in Williamstown, Massachusetts, and spent summers collecting fossils with Harris. He had many interests, including geology and early human cultures, so the Fort Hunter locality must have been doubly interesting to him. Cleland published the descriptions in Harris’s Bulletins of American Paleontology volume 3, number 13, entitled “The Calciferous of the Mohawk Valley,” 32 years before the founding of PRI, which now publishes the Bulletins. The word “calciferous” in this title might look like an adjective, but is actually the name of a geological outcrop, so think “The Calciferous [Stage] of the Mohawk Valley” for clarity.

Pleurotomaria floridensis is now classified in the genus Straparolina in the extinct family Straparollinidae. Murchisonia mohawkensis is a member of the extinct family Murchisoniidae. Members of both of these families are thought to have been suspension feeders, filtering organic particles from the water, probably through their gill filaments. This is in contrast to scraping the surface of rocks for food, which one might expect of snails today. Both species were rare at the time of their description.

*See Fossil of the Week 8/19/09 - Cerithium gainesensis for a definition of "holotype."

**See Fossil of the Week 11/11/09 - Bellerophon calcifer for more about H. F. Cleland.

Text by Paula Mikkelsen

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