Wonderful Fossils?

When is a fossil not a fossil

Crystal Cortez

Fossils have captivated the imaginations of millions for many years. From ancient Chinese finding dinosaur remains and interpreting them as dragons to discovering fossil marine reptiles while walking along the beach in Lyme Regis, England like Mary Anning. The idea of holding and seeing bits of an organism that lived thousands, or millions, or billions of years ago makes our imaginations run wild. This leads many of us to actively seek out connections to ancient worlds but sometimes it doesn't always work out. So when is a "fossil" not a fossil?

Some of the most common questions I get as a paleontologist are related to whether or not a found object is a indeed a fossil. Sometimes objects may look like a fossil but aren't. Sometimes an object may be shaped like a fossil but isn't. And sometimes, an object can be really, really old and still not a fossil. So, what is it?

Here are a few common objects that may seem like fossils but have a completely different origin that can be just as captivating.

Oncoid vs Ammonite

Oncoids

Oncoids are small, round, and textured structures usually formed in the intertidal zone. These sedimentary structures take years to form and could be millions of years old, like the one pictured here that is around 400 million years old. They usually occur in limestone and can be confused with small fossils like ammonites.

Ammonite

The easiest way to determine if you have ammonite is by looking for signs of suturing. Suturing can be as plain as lines or complex like the ones seen in this example. These sutures are related to different chambers the organism would have used to swim while it was alive.

Concretion vs Fossil Eggs

Concretion

Concretions are often mistaken for fossil eggs or turtle shells but are in fact a naturally occurring stone. Usually spherical, concretions occur when sediment accumulates around a nucleus (typically organic). This means, although a concretion itself is not a fossil, there could be a fossil inside.

Fossil Egg

The most visible distinction between concretions and fossilized eggs is fossil eggs usually have cracks on the shell. This is because eggs are often "crushed" during the fossilization process. A concretion will not have these markings.

Fossil vs Rock

Rock

A rock can sometimes be the exact same color or shape as a fossil bone but it is not a fossil. One way to see if you have a rock or bone is by licking it, yes you read that correctly. A rock will be smooth where a fossil will often stick to your tongue.

Fossil Bone

A clear indicator that your object may be a fossil bone is by the presence of tiny rope like holes. These are formed from spongy bone. The next time you get a bone-in steak, try taking a closer look at the bone-in cross section and you will find similar structures to the ones seen in this example.

Fossil Bone vs Bone

Bone

Bone from living animals can often be confused with fossil bone especially if the fossil bone is young. Bones as old as 1.2 million years can have very similar features to bones of today's animals. The easiest way to find if you have a fossil or not is to try the "burn test."

Burn test

The burn test can be a quick and effective method to use when trying to decide if you have a fossil or not. Simply take flame to a small portion of the bone. If you get a smell like burned hair, then it's bone. If there is no smell then it's a fossil.

Dendrite vs Fossil Plant

Dendrite

Dendrites are accumulations of magnesium that are often confused with fossil plants or algae. They appear as black smudges in intricate shapes on stone. These accumulations can look like fossils, and can be very old like fossils but are not fossils.

Plant fossil

Fossil plants can be hard to identify because they mostly occur as impressions. One method to try to identify whether or not you have a fossil plant is by seeing if there is any dimension. When you look at a leaf, it's not just flat, it has dimension. The ribs and veins add to it's structure and these are often preserved in the fossil.

I hope you have found this information helpful. If you have found yourself captivated with the idea of finding fossils please remember to follow local guidelines as there are many laws that protect paleontological resources. For more information about fossil collecting, the myFOSSIL project can be an excellent resource in helping you and fossils, stay safe. - Crystal Cortez, Curator of Earth Sciences