Fossils

Fossils are portions or traces of plants or animals that were embedded and preserved in the earth’s rock formations long ago.  These artifacts often pre-date human history and are generally considered a fossil if they are more than 10,000 years old.  The fossil record gives scientists the chance to study ancient life and the history of the earth, a field of study called paleontology. 

Fossils provide opportunities to learn about many topics of natural history.  Habitats are continually changing.  Where fossils are found provide clues as to what habitats were present and where; the movement of land masses around the globe; and the climate that existed with the plant and animal life at each location.

Many of the plants and animals that lived in the past are quite different from similar species alive today.  Fossils preserve a record of the changes that have taken place over millions of years.  In addition to tracking changes in life forms, as land masses moved across the earth, as well as up and down, fossils may help determine the age of the sediment layers in which they are found.

Fossils come in all sizes, from the microscopic to the largest dinosaurs.  When a plant or animal dies, the body parts begin to decay.  Soft body parts decay rapidly, but harder body parts including bones, teeth, and shells decay more slowly.  Fossils are formed when body parts are buried in sediments of mud or silt, significantly slow down the process of decay.  A specimen that falls to the bottom of a pond or wetland can be quickly buried and preserved.  Preservation may occur in any environment, including land masses with winds depositing sand and silt to cover deceased specimens, although scientists have found this to be a less likely occurrence.

Permineralization, the most common known method of fossil formation, is a process where mineral-laden water seeps through sediment containing porous material such as bones or wood, leaving some of the mineral behind.  As the cavities are filled and dry, most of the original specimen is retained, and a petrified fossil is the result.  An example at the Jurica-Suchy Nature Museum is our Edmontosaurus femur bone, pictured below. 

A second method of fossilization is when a specimen undergoes an extreme amount of compression from the weight of sediment or sea water on top of it.  The museum’s collections include many compression type specimens, a few of which are pictured below.

^{clockwise from top left: Cranefly fossil at JSNM by DonArnold 2026; Crustacean fossil at JSNM by DonArnold 2026; Ordovician fossil, possibly vegetation, at JSNM by DonArnold 2026; Vegetation fossil at JSNM by DonArnold 2026; Plant leaf fossil at JSNM, by DonArnold 2026}

A cast fossil is formed by a two-step process.  A mold is formed in rock when the original specimen completely dissolves over time and leaves a cavity.  Sediments or minerals may fill these cavities at a later time, drying and hardening to form a cast of the original specimen.  A few of the museum’s collection are pictured below, and additional specimens are on display at the museum.  Consider coming by for a visit to learn more about this fascinating topic.

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