Richmond is a time, too!

Richmond is our town, but did you know that it’s given its name to a section of geological time? The Richmondian age lasted from about 449 to about 445 million years ago, during the Ordovician Period.

 

Our town looked very different 449 million years ago! It was so close to the equator that it was warm and humid. It was at the bottom of a shallow sea that covered most of what is now the midwestern United States. There were large mountains to the east, with volcanoes like those now found in Japan.  These types of volcanoes are formed as an ocean plate subducts, or moves underneath, a continental plate.  When the ocean plate moves down into the Earth’s mantle and melts, the magma rises through the continental plate to form volcanoes.

 

The Richmondian ocean was full of life, but we would not recognize most of the creatures living there, such as shelled animals called brachiopods (Greek for “arm-foot”).  Even though brachiopods are related to mollusks like clams or scallops, their bodies are quite different: clams’ shells are symmetrical and they have a left and right shell that are shaped the same, but brachiopods have a top and bottom shell that are shaped differently.  The rocks around modern Richmond have fossils from many different brachiopod species, including  Hebertella, Hiscobecus, and Rafenesquina.

 

767px-Hebertella_occidentalis_pedunculate_valve

Hebertella fossil. Source: Wikimedia contributor dwergenpaarje.

 

Corals, bryozoans, and crinoids were also common in the Richmondian ocean.  Corals first became common in this area during the Richmondian.  Most of the coral reefs in today’s oceans are formed by many individual corals (a relative of jellyfish!) living in colonies together.  The Richmondian horn corals were solitary, with “horn” the home of a single animal.  The Richmond Fossil Park contains many fossils of the horn coral Grewingkia.

 

RugosaOrdovician

Grewingkia fossil. Source: Wikimedia contributor Wilson44691.

 

One animal that looked very similar to today’s colonial corals, and their fossils have many small openings where the individual animals lived were the bryozoans (“moss-animals”). Bryozoans may look a lot like corals, but they are actually more closely related to brachiopods.

Bryozoa_8679

Bryozoan fossil. Source: Wikimedia contributor Regiomontanus.

The strangest looking of the Richmondian’s ocean creatures – they looked like an upside-down starfish on a stem – are the Crinoids (“lily-forms”). The stem kept their arms off the bottom so that they could catch food from the water.  Crinoid stems are very common in the rocks of modern Richmond.

Agaricocrinus_americanus_Carboniferous_Indiana

Crinoid fossil. Source: Wikimedia contributor Vassil.

The top predators of the Richmondian ocean were nautiloids, distant relatives of today’s squids.  They had shells that looked like torpedo cases and could be anywhere from a few inches to eight feet long.  A hungry nautiloid could eat anything it wanted!

Orthoceras_BW

A artist idea of what a nautiloid looked like. Source: Wikimedia contributor Nobu Tamura. 

The astonishing animals that lived here so long ago are called the Richmondian Fauna, and their fossils are very common in the rocks around modern Richmond.. To learn more about nearby fossil-hunting sites, visit the Joseph Moore Museum and get your fossil passport!

 

Sources:

https://www.tonmo.com/pages/nautiloids/

http://www.indiana.edu/~paleoind/Lectures/Lecture%209%20-%20Ordovician%20and%20Richmondian%20Invasion.pdf

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