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Fossil Identification Guide for Invertebrate Fossils of the Calvert Cliffs


Fossil Identification Guide for Invertebrate Fossils of the Calvert Cliffs

Fossil Invertebrate Identification Guide for the Calvert Cliffs of Maryland and the Horsehead Cliffs of Virginia.

Invertebrate fossils are extremely common along the cliffs. Entire shell beds are present. Most invertebrates are bivalves, such as oysters and scallops, and gastropods. The Maryland state fossil is even a gastropod, the Murex shell.


Click on the type of vertebrate fossil or scroll down to browse:
Or go back to the MAIN Calvert Cliffs Page


Fossilized crab claw pieces are failry common along the Calvert Cliffs.

Crab claw fragments are fairly common, but are small and often overlooked for shark teeth. They are usually hollow and have a bluish or tan color.

For additional images of crab claw fragments, go to the Aurora Invertebrate page.

Bivalves (shells)

Bivalves are the most common fossil found along the cliffs. Entire layers of the cliffs are made of them. Below are some of the more common bivalves found.

Chesapecten nefrens

These fossil chesapecten scallop shells were found whole laying in a fresh fall. They tend to break easily.

This shell has a tiny one cemented to it. Kind of neat!

In some places around the Choptank and St. Marys formation, sections of rock contain 100's of casts and molds of the scallop shells.

Glycymeris sp. Bivalve

Identification based on Glaser (1979, p22-23)
These fragile bivalves, often with both halves still attached, are abundant in certain zones along the cliffs.

These fragile bivalves, often with both halves still attached, are abundant in certain zones along the cliffs. They will quickly fall apart if not preserved.

Isognomon maxillata (Deshayes)

The common name for this fossil oyster is the Giant Tree Oyster or the Giant Purse Oyster.

Identification based on Glaser (1979, p22-23).
These large oyster shells are the index fossil for the Eastover Formation. They are also found in the Calvert and Choptank formations. In certain spots along the Choptank, they literally cover the entire ground, and you have to walk on them.
These shells are usually white and flaky. Due to their fragile nature, they are difficult to find with both halves attached.
This oyster genera is characterized by the large grooved ligamental area (place where the two shell halves attach).

Layer of isognomon fossils, tree oysters. This layer is chalk full of them. Calvert cliffs

This layer of isognomon fossils, or tree oysters is found along the Choptank Formation.

This is a view of a front and back of a single shell from a specimen.
This is how they are typically found. Notice the large groves in the ligmental area, the part that attaches to the other.

This is a well preserved specimen with both halves still attached. It was found by Bobby Nuckols in VA. He was nice enough to let me use an image of it for this site.


Ecphora sp.
Extinct Gastropod - Murex Shell

Ecphora Gardnerae is the Maryland State fossil. Their shells are intricately shaped. They are very fragile, and are often found broken.

This ecphora a larger fossil ecphora shell. Usually ones this size are found in fragments. It is approximately 4" wide.

This ecphora fossil has a nice bright orange color.


Sand Dollars

If you collect anywhere along the Choptank, you are bound to encounter fragments like these. They are sand dollar fragments. Occasionally you can still make out the patterns on them.
Complete ones are next to impossible to find.

These are pieces of fossil sand dollars.


Fossil coral fragments are occasionaly found washing in the surf at the Calvert Cliffs. The more common type of coral is Astrhelid.

Barnacles - Balanus sp.

Barnacles are often found at the Cliffs. Sometimes they are attached to fossil shells and bone.

Plants - Lignite

Lignite is a very low grade form of coal that retains it's original wood structure. The type of lignite present at the Calvert Cliffs area is called Xyloid Lignite, or fossil wood. This type of lignite is not yet compacted into the higher grade lignite. It hasn't been buried deep enough or long enough. Xyloid Lignite is usually geologically young, and comes from Tertiery sediments, such as the lignite found in the Miocene Chesapeake Group - Calvert, Choptank, and St. Mary's formations.

At the Calvert Cliffs area, most of the lignite is from Cypress trees that grew in cypress swamps along the ancient shores.
The large amounts of Cypress trees indicate a much warmer climate along the Chesapeake Bay in the past.

If one looks at the cliffs and chunks of cliffs, you will see small dark objects which are mushy to the touch. This is lignite.

This is fossil lignite about 7 feet up in the calvert cliffs. This large chunk is from a cypress tree.

Fossil lignite from the Calvert Cliffs. This is a section of cypress tree eroding out of a cliff chunk that has fallen

Xyloid Lignite Seeds

In one small section of the Chesapeake group, fossil seeds are found throughout a section of cliffs. I'm not sure what these are. They look like little walnuts. I wouldn't rule out cypress seeds, but really have no idea of the plant they came from.

A small section of cliffs has these fossil seeds in them. This is the center of the seed. The outside shells are a little bigger. The lignite is very brittle and quickly flakes apart.

Recommended Books for Shark Tooth Identification

Fossil Shark Teeth of the World
, A Collector's Guide
by Joe Cocke, Copyright 2002

A great book for identifying all those teeth. This book is laid out "as simple as possible." It's ease of use and small size makes it great to carry during collecting trips. This book shows teeth from around the globe, but all the Calvert teeth can be found in it.

Fossil Sharks of the Chesapeake Bay Region
, A Collector's Guide
by Bretton W. Kent, Copyright 1994

This is a classic for identifying all those teeth at the Calvert Cliffs. It's a must for any beginner collector that fossil hunts in the Maryland/Virginia area.
Unfortunately, this book is out of print. There's used ones on amazon for super insane amounts of money, but SOMETIMES there is a used one available for a few bucks.

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