Trilobite Dalmanites

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Title: Trilobite Dalmanites limuluurus
Medium: Digital Photography
Photographer: Aaron J. Greenblatt
Camera Type: Panasonic DMC-LZ7 Lumix 7.2 MP
Editing: Edited in PhotoShop 7.0 for color accuracy, size, and to apply copyright and border.

Location: Photograph taken at the 2008 Southeastern Michigan Gem and Mineral Show at the Southgate Civic Center in Southgate, Michigan. Show hosted by the Midwest Mineralogical & Lapidary Society.

Description: Sitting in a white cardboard box out in the open on a fossil dealer's table, was this interestingly-shaped trilobite. It is 2 inches long and named Dalmanites limulurus. It was discovered preserved in Rochester Formation shale. This shale deposit is located in Orleans County, New York State, USA. And this trilobite dates back to the Silurian period - roughly some 444 to 415 million years ago. It was selling for $60.

The trilobite species name "limuluurus" is derived from the perceived similarities in appearance between this trilobite and the modern-day horseshoe crab "Limulus". However, there is no actual relationship between the two.

What Else Was Going On? During the Silurian Period when this trilobite lived, Coral reefs made their first appearance. They were built by extinct tabulate (honeycomb) and rugose (horn) corals. The first bony fish, the Osteichthyes, appeared. Other fish reached considerable diversity and developed movable jaws. A diverse fauna of Eurypterids (sea scorpions) - some of them several meters in length - prowled the shallow Silurian seas of North America. The first leeches appeared. Brachiopods, bryozoa, molluscs, hederelloids and trilobites were abundant and diverse.

The Silurian was also the first period to see the formation of extensive terrestrial biota (plants), in the form of moss forests along lakes and streams. As well, the first vascular plants (land plants with tissues that carry food) appeared in the second half of the Silurian period.

What Was It Like Back Then? During the Silurian Period, the Earth entered a long warm greenhouse phase, and warm shallow seas covered much of the equatorial land masses. Early in the Silurian, glaciers retreated back into the South Pole until they almost disappeared in the middle of the Silurian. The period witnessed a relative stabilization of the Earth's general climate, ending the previous pattern of erratic climatic fluctuations. Layers of broken shells (called coquina) provide strong evidence of a climate dominated by violent storms generated then, as now, by warm sea surfaces.

What Are Trilobites Good For? Trilobite fossils are found worldwide, with many thousands of known species. Because they appeared quickly in geological time, and molted (shed their outer skins) like other arthropods, trilobites serve as excellent index fossils. Thus, they enabling geologists to date the age of the rocks in which they are found. Trilobites were among the first fossils to attract widespread attention from scientists and the general public, and new species are being discovered every year.

Information Sources:
[link] (wiki - silurian)
[link] (wiki - trilobite)
[link] (wiki - osteichthyes)
[link] (wiki - tabulate coral)
[link] (wiki - rugosa coral)


Legal: Copyright © Aaron J. Greenblatt. All rights reserved. Commercial use prohibited. This image and commentary may not be used for any reason without expressed written consent.


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