Marine Fossils Guide (Types + Tips & Advice)

Common marine fossils guide

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On a planet that is billions of years old, there are so many ancient treasures to be found. Fossils are nature’s way of preserving things from millions of years ago and they tell us a lot about the past.

If you have been exploring the coastlines, then you may have come across marine fossils. Or perhaps you’re keen to start finding some of these beautiful, natural treats and want to find out more.

This guide will tell you everything you need to know.

How are Fossils Formed?

How are fossils formed?

The formation of a fossil begins as soon as an animal or plant dies. But this is just the start of a lengthy process. Normally, the soft parts of an animal are eaten by scavengers, or they rot away. But things like teeth and bones may turn into a fossil, although this is actually quite a rare phenomenon.

The process begins when the body is covered in a layer of sediment very quickly after death. Over time, the sediment builds up more and more before eventually turning into rock. This process is known as lithification.

As this happens, any moisture in the sediment seeps into the hard parts of the animal which also turn to stone.

What is the Importance of Fossils?

What is the importance of fossils?

People seem to get really excited by fossils – but they’re just old rocks, right? That is anything but true, as fossils play an important role in helping us understand the past.

Fossils come in many forms and they help scientists to understand things like evolution, how animals may have lived in the past, and even tell us about geological changes in the earth over the course of time.

There are even times that fossils can give us an insight into how the animal died as well as its behavior during life. Depending on where the fossil is found, we can also determine the age of the country.

This might all seem highly scientific but what’s great is that anyone can learn information from fossils and there’s nothing more important than understanding the history of the very planet we inhabit.

What Types of Rocks are Fossils Commonly Found In?

You’ll only find fossils in sedimentary rocks

In order for fossils to form, there needs to be perfect conditions. While there are several different types of rocks, not all of these rocks provide what is needed to create a fossil. That’s why you’ll only find fossils in sedimentary rocks.

You might find fossils in sedimentary rock such as shale or sandstone and there are some types of sedimentary rock that preserve fossils better than others.

The reason that it’s almost always sedimentary rock that helps in the creation of fossils is because sediment has to build up over the dead animal or plant over time. That’s also why you almost always find fossils in and around water since the sediment is better able to build up here.

Types of Fossil Preservation

If it was living at some stage or another then there’s a good chance you can find it in a fossil. But what’s interesting is that there isn’t just one type of fossil preservation. In fact, the way that this organic matter is preserved could happen in one of four ways.


Fossil preservation petrification
Petrified Wood

Petrification, sometimes known as permineralization, happens when the deceased life form becomes buried.

When the lifeform was living, there would have been spaces within it that were filled with gas or liquid. But now, these spaces are filled with groundwater that’s high in minerals. Where this water sits can be in the smallest of spaces such as between cell walls.

The minerals within the water act as a preservative and, over time, will turn the lifeform to stone; which is known as petrification.

Molds & Casts

What are mold and cast fossils?
Ammonite Mold and Cast Fossil

It is possible for an organism to create an impression in the rock after it has decomposed. This is known as a mold. Over time, sediment may refill this mold and the resulting shape is called a cast. While this isn’t the actual fossilized remains of the organism, it does give a detailed picture of what it would have looked like.

How are mold and cast fossils formed

Compression & Carbonization

Fossil preservation - compression & carbonization
Carbonized Fern Leaves Fossil

When looking at fossilized plants, one of the most common forms of preservation is compression. This happens when the remains of the organism are compressed between layers of sediment and this creates an imprint. The sheer weight of the overlying rock as well as things like water is what is responsible for the imprints. Amazingly, these imprints can take as long as 300 million years to form!

Preserved Remains

Fossil preservation preserved remains
Preserved Insect Remains in Amber

While preserved remains are the least common type of fossil, there are still plenty out there. Think about the mosquito in amber on the end of the walking stick in the movie Jurassic Park, and that’s exactly what we’re talking about here.

This happens when the soft tissue of the animal is preserved in some other substance. Amber is a common material, but there have been entire mammoth remains found in glaciers and even neanderthal human remains. What an amazing opportunity to look at life from millions of years ago!

Main Fossil Groups

Fossils can be categorized into one of several different groups depending on what type of animal they were, how old they are, and many other factors.


Ammonites are fossils that come from both the Jurassic and Cretaceous periods and this covers around a 140 million-year period

Ammonites are fossils that come from both the Jurassic and Cretaceous periods and this covers around a 140 million-year period. However, at the end of the Cretaceous period, these creatures became extinct so you won’t find their fossils any later than this.

Ammonites are very similar to the nautilus and have a curled shell. What’s fascinating is that the size of these creatures varies greatly with some being no more than a couple of centimeters while others spanned more than two and a half meters!

How did an ammonite look like?
Illustration Depicting how an Ammonite May Have Looked Like

Looking at fossilized remains, scientists have discovered that ammonites would likely have eaten plankton and plants on the ocean floor.


Belemnites come from the Jurassic and Cretaceous periods and are more closely related to something like the modern squid

Just like ammonites, belemnites come from the Jurassic and Cretaceous periods. But these were not at all similar in appearance as a belemnite is much more closely related to something like the modern squid. The main difference was that they had a solid internal skeleton.

However, there were a lot of soft parts to the belemnite and these rarely become fossils. So, what we usually find are partial remains that have a cigar-like shape. These are typically the guard and the phragmocone.

Belemnites were a Type of Cephalopod and Would have looked Similar to a Squid

Belemnite fossils can range in size but the largest was around 18-inches (46 cm). When you compare this to the size of the animal it came from, you’re looking at a creature that could have been up to five meters in length!


Bivalve fossils refers to several different creatures including mussels, oysters, clams, and other types of shellfish with a two-part shell

The term bivalve refers to several different creatures including mussels, oysters, clams, and other types of shellfish with a two-part shell. It is believed that these creatures have been on earth for around 500 million years; that’s almost 300 million years before dinosaurs walked on this planet!

Bivalves are among some of the most commonly discovered fossils. However, it’s uncommon to find one with the two parts of the shell together since the soft tissue that holds the parts together is rarely fossilized.

From what fossils tell us, prehistoric bivalves filter feed, just like their modern equivalents. However, it’s thought that they were able to bury themselves much deeper in the seabed as a form of protection.


Brachiopods are perhaps the most common type of fossilized shellfish

From the paleozoic era, brachiopods are perhaps the most common type of fossilized shellfish that are being discovered today. Out of all of the types of fossils, they’re also considered to be the oldest with most being around 550 million years old!

Brachiopods make up the phylum Brachiopoda, and while there are a few modern examples, these are not extremely common. Ancient creatures from this family ranged in size dramatically with the largest being around 11.8-inches (30 cm) while the smaller specimens may have only been a couple of millimeters across.


Coral fossils largely come from the Cambrian period which occurred around 500 million years ago

Corals largely come from the Cambrian period which occurred around 500 million years ago. These living organisms were made from a polyp which was the living soft-tissue part surrounded by a calcareous skeleton. There were tentacles surrounding the animal that delivered a toxic sting and the way that these animals fed was quite unique since food was taken in through the mouth but any waste was also discharged from there.

If you were to compare these animals to something that lived today, the closest relatives would be the sea anemone or the jellyfish. Although, there is a range of modern corals that are still found in oceans today.


Echinoid is a term that simply refers to a sea urchin

Echinoid is a term that simply refers to a sea urchin. These fossils have a rather unique appearance but the animals can still be found in oceans today. They have a spiny appearance, which is where they get their name (echin is Greek for spiny), and a rounded shape.

However, it’s highly unlikely that when you find an echinoid, the spines will still be intact as these typically fall off when the animal dies. So these commonly found fossils have a more ball-like shape. It’s quite common to find echinoid casts, especially around the southern coasts of the United Kingdom.

Echinoids date back to the Cambrian period, around 550 million years ago although there are examples found from periods coming after this including the Mesozoic and Jurassic eras. What’s great about their fossilized remains is that they can tell us a lot about how these creatures lived.

There are regular and irregular echinoids and this refers to how the animals moved, rather than their shape. While this might not seem important at first, it does tell us how the animals dealt with predators and how they fed.


Coiled shells are among some of the most commonly found fossils in the world

You’ll probably be more familiar with the terms slugs and snails, which is just another term for gastropods. These animals have been found as fossils dating back to the Cambrian period although, since the Paleogene, these have been considered to be the most common type of mollusk.

Gastropods have a foot, a shell, and tentacles but one of their most distinctive features is their feeding organ which is called the radula. The coiled shells are among some of the most commonly found fossils in the world.


Graptolites just like corals, were colonial animals, but instead of attaching to the seafloor, they would typically float around in their groups
James St. John / Flickr / CC BY 2.0

Graptolites frequented waters during the Paleozoic era and were small creatures that lived as many as 540 million years ago. However, the youngest examples of graptolites are thought to be as little as 318 million years old.

These small, shiny-looking fossils are found on rocks. In fact, the name literally translates to writing on the rock and they’re one of the most common types of fossils out there.

How did graptolites look like?
Graptolites were Tiny Filter-Feeding Organisms

Graptolites, just like corals, were colonial animals, but instead of attaching to the seafloor, they would typically float around in their groups.


Sponge fossils ren’t super common because they will often break up once they die

If you’re keen to discover a super old fossil, then it might be worth keeping your eye out for sponges. According to National Geographic, one sponge fossil was discovered in Canada that is believed to be around 890 million years old! Although, there is something of a debate between scientists about this timeframe.

Nonetheless, sponges are ancient fossils that can tell us a lot about how these animals lived. The problem is that they aren’t super common because they will often break up once they die. But if you are going to find one, looking in chalky locations is a good bet.


Trilobites are a prehistoric creature that isn’t all that dissimilar to the modern woodlouse

Trilobite fossils usually come in the form of imprints within the rock, and unlike some other types of fossil, there are a handful of examples that have been found in hard rock. Although, they are mostly found in sedimentary rock.

Trilobites are a prehistoric creature that isn’t all that dissimilar to the modern woodlouse. While the fossils are relatively common, they’re pretty difficult to handle as the animal’s shells would typically break up when they died.

How did trilobites look like?
Trilobites were Marine Arthropods that Lived about 250 million Years Ago

These fossils usually date back to the Cambrian period but by the time the Permian period came in, they were largely extinct so the youngest examples would be no less than 250 million years old.

How Are Fossils Dated?

How Are fossils dated?

To the untrained eye, any two fossils might look largely the same, and being able to tell how old they are isn’t easy. But scientists have developed several ways to date a fossil and the results are astonishingly accurate.

For starters, they will look at how deep the fossil was buried. Since fossils are formed when layers of sediment form over the top of the animal, it goes without saying that, the deeper the fossil is buried, the longer it has been there.

While this technique doesn’t give you an exact age, there are things that scientists can do to get a more accurate age. One of the ways in which they do this is by determining the presence of potassium or radiocarbon as this allows them to figure out when the rock was formed.

As an amateur fossil enthusiast, you may not have the equipment to test rocks for the presence of radioactive materials but you can get a geological map of the area you are hunting in. This will give you some idea of what fossils and rocks are in the area and their ages.

Useful Fossil Hunting Gear to Take with You

Useful fossil hunting gear to take with you

Going fossil hunting is certainly exciting. But if you want to get the most out of it, you need to come prepared. Here is a list of some of the most important fossil hunting gear you’ll need to take on your trip.

  • Safety glasses – Protect your eyes from pieces of flying rock debris when hammering with a pair of safety glasses or goggles.
  • Hand lens – Sometimes fossils can be small or obscured by dirt and debris. Taking a hand lens will allow you to get a closer look at your findings.
  • Geological hammer – To break up rocks and remove fossils, you will need a geological hammer. However, while this tool is designed for the job, it’s important to be gentle to avoid damaging the fossils.
  • Work gloves – Protect your hands from the rocks and your tools with a durable pair of work gloves.
  • Chisels – Sometimes, your hammer just won’t cut it and when you need to get in between layers of rock, a chisel will become your new best friend.
  • Bag – When you’ve found your fossils, you’ll need somewhere to store them, along with all of your other equipment until you return home.
  • Hat & sunscreen – If you’re fossil hunting in hot or sunny weather, you need to protect yourself from the harmful rays.
  • Water bottle – You’ll likely be out in the heat for a good amount of time, so it’s essential to stay hydrated.
  • Hiking boots – Fossils are normally found on terrain that isn’t overly friendly underfoot. That’s why taking a good pair of hiking boots is important; you’ll have a better grip on the ground and your feet will remain comfortable.
  • Notebook & pen – Keep track of what you are finding and where. You can include sketches, notes, and anything else that helps you or others to relocate the spot should you need to.
  • Soft paper – Something like an old newspaper or tissue paper will allow you to protect any fossils that you discover.
  • First aid kit – In the event that you or a member of your team sustains an injury, having a First Aid kit on hand is essential.
  • Brush – Sometimes a fossil will be covered in soft, loose material that needs to be brushed away. Once you have done this, you’ll better be able to see how to extract the fossil without damaging it.
  • Padded box – If you discover very small or delicate fossils, you’ll need a padded box to make sure that they aren’t damaged when you transport them.
  • Cell phone – Make sure to stay in contact with someone so that they can send help should there be an emergency.
  • Hard hat – When working around cliffs, there is a risk of falling rocks, but a hard hat will afford you the protection you need.

Hunting for Coastal Fossils Tips & Advice

Hunting for coastal fossils tips & advice

It’s super exciting to head out to the coast in search of fossils, but we must ensure careful planning. This could be a dangerous activity if you aren’t prepared, so be sure to adhere to the following tips and advice.

1. Dress Appropriately

You’re going to be exposed to the weather when you’re fossil hunting, so make sure to wear the right gear.

When it’s sunny, wear a sun hat and make sure to regularly apply sunscreen as this will prevent burns. Also, remember to take lots of water, especially on hot days to stay hydrated.

In colder weather, you’ll need to make sure you wrap up; wearing layers is the most effective way to keep warm.

Regardless of the weather, it’s essential to wear non-slip footwear to avoid slipping on rocks, algae, and other surfaces.

2. Wear Protective Eye-Wear

Looking for fossils might mean extracting them from rocks and this means that there is a risk of rock chips flying into your eyes. For this reason, it’s essential to wear proper eye protection such as safety goggles or glasses; it is not worth risking your sight!

Only ever use tools that are designed to be used with rocks such as a geologist’s hammer as this will be far safer.

3. Search for the Right Types of Rock

Fossils almost always form in sedimentary rock. This includes rocks such as shale, limestone, and sandstone so these are what you need to keep an eye out for. If you’re searching on the beach then you’re likely to see sandstone but take a look at the characteristics of the rock in order to identify it.

These sedimentary rocks will be made up of layers so this is your first clue. Rocks that easily flake or can be chipped away at easily are also likely to be sedimentary.

4. Check Exposed Rock

You don’t only find fossils buried deep within layers of rock, although this is very common. If you’re lucky, you may be able to find fossils in other areas such as at the base of cliffs and within the shingle on a rocky beach.

Coastal bluffs, which are steep slopes along the shoreline, are made up of sedimentary rock and are a prime location for finding fossils.

When the tide goes out and the foreshore is exposed, take the time to look for fossils here as the tide often reveals them right before your very eyes. Here, there will also be rock pools that could house fossils. However, you should be careful taking fossils from the foreshore as this is often illegal. To ensure you are fossil hunting on the right side of the law, be sure to check out any restrictions before your hunt.

The furthest part of the beach, near the cliffs, is known as the backshore and while this is often above sea level, it’s not uncommon to find fossils here. Do keep in mind that, due to falling rocks, this is one of the more dangerous areas to search so be sure to wear appropriate safety gear.

5. Be Aware of the Weather Conditions & Local Tide Times before Heading out

Before you hear out, take the time to check the weather and conditions. If there is any chance of dangerous conditions, wait until another day.

You’ll want to check what time the tide changes and make sure that you aren’t going somewhere that you may get caught out.

6. Be Cautious of Crumbling Cliffs

Many coastlines have a lot of cliffs and while these are beautiful, they can also be incredibly dangerous. Things like landslides are more than possible and even if it’s not a full-on landslide, individual falling rocks are always possible.

If you notice a particularly crumbly cliff then it’s probably wise to steer clear and take your search elsewhere. To be safe, it’s a good idea to wear head protection such as a hard hat.

7. Let Others Know Of Your Exact Location & When You Plan to Return

While we would like to think that our careful planning would be enough to keep us safe, accidents can always happen. For this reason, it’s super important to let someone else know where you are going and what time to expect you back.

You may get caught out by a tide, be injured by a falling rock, or fall and injure yourself, leaving you unable to return home. If someone else knows where you are then sending help can be much easier.

That said, it’s still always a good idea to take your cell phone so you can call for assistance in an emergency. Leave your location on so that you’re even easier to find.

Frequently Asked Questions

Types of marine fossils

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