Trilobites of the Rochester Shale, New York
Locality: Caleb's Quarry, Middleport, New York (this outcrop is just one good representation of this formation)
Stratigraphy: Lewiston Member, Rochester Shale Formation, Clinton Group
Age: Lower Silurian (Wenlockian), 425 million years ago
The Silurian Period (443-416 million years ago) was a relatively shorter time interval compared to the Ordovician or Devonian Periods, commencing with the recovery from the major late Ordovician extinction and ending with a minor extinction before the Devonian. Despite this fact, Silurian deposits in New York State show great variation, indicative of a wide range of environments. The Silurian was characterized by a return to the greenhouse conditions following the late Ordovician glaciation and overall, worldwide climates were comparable.
Abundant numbers of the 119 invertebrate species collected at Caleb's Quarry (opened in 1988) have resulted in greater knowledge on the ecology and range in size of these animals. Trilobites displaying healed injuries imply that predators were active, while larger trilobites with epibionts (e.g. brachiopods) suggest that these bigger individuals did not molt frequently, allowing time for other creatures to grow on their exoskeletons. The most commonly found Lewiston Member trilobites are listed below, with those found at Caleb's Quarry marked with an asterisk, along with the maximum size found for each species.