Animals of Devonian Michigan facts for kids

Fossils of many water-dwelling animals from the Devonian period are found in rock layers in Michigan, USA. This was a time when Michigan was covered by a warm, shallow sea!

Some of the most common fossils you can find include bryozoans (moss animals), corals, crinoids (sea lilies), and brachiopods. Less common finds are armored fish called placoderms, snails, early sharks, stromatolites, trilobites, and blastoids.

Bryozoans: Tiny Moss Animals

Bryozoans are small marine fossils often found in Michigan. They are very common in many places. You might find them with corals, crinoids, and brachiopods.

Bryozoans can be tiny, just a few millimeters, or grow to several feet tall. When they were alive, they were filter feeders. This means they ate tiny bits of food from the water. They competed with corals and crinoids for food.

There were three main types of bryozoans in Michigan:

• Branching bryozoans: These were the most common. They looked like slender branches and grew in small, forest-like groups.
• Encrusting bryozoans: These lived on the shells and skeletons of dead sea animals. They formed a mat-like colony.
• Fan-like bryozoans: These were the least common. They had a broad, fan shape and grew in ancient reefs.

Crinoids: The Sea Lilies

Crinoids are amazing fossils found in Michigan's Devonian rocks. They are echinoderms that filter-fed, just like starfish and sea urchins. Crinoids were very common during the Devonian Period.

They could be just a few inches tall or grow several feet high. This helped them reach water that other animals weren't filtering. Crinoids had several parts, each with a special job.

Crinoid Stems and Disks

The stem of a crinoid was made of many small disks. These disks were stacked like poker chips. They supported the top part of the crinoid. Each disk was round with lines pointing inward to a small hole. This hole carried food and waste.

Crinoid disks are the most common part found as fossils. You can find hundreds of them in some rock layers. They were made of hard calcite, which formed much of today's limestone. Sometimes, you can even find groups of disks called columns, or even whole stems!

Crinoid Anchors

Crinoid "anchors" were parts of the stem that attached the crinoid to a hard surface. This helped them stay in place and get food. Anchors were also made of disks. They are not rare, but they are not as commonly found as the stem disks.

Crinoid Arms

Crinoid "arms" were long, feathery parts that came out of the top of the crinoid. They filtered food particles from the water. These arms are the rarest part to find as fossils. They looked like feathery arms, which is why crinoids are often called "sea lilies." Their arms were very delicate, so they rarely turned into fossils.

Crinoid Balls

The crinoid "ball" was a large, cup-shaped part at the top of the stem. It held all of the crinoid's organs. Some crinoid balls even had spikes! The arms grew out of the crinoid ball.

It's rare to find a complete crinoid ball with its arm attachments. But in some places, many can be found together. The inside of a fossil crinoid usually has calcite crystals. This is because their skeletons were made of calcite.

Crinoid Spikes

Some crinoids had spikes growing from their "ball" part. These spikes are very rare to find because they were fragile. Scientists think these spikes might have helped protect the crinoids from predators.

Corals: Reef Builders

Corals were very common animals in Devonian Michigan. There were three types of coral found: branching, colony, and solitary corals. You can find their fossils in almost every fossil site in Michigan.

The Devonian period was a time of huge reefs. These reefs covered most of the world's oceans. Corals were super important for building these reefs.

Solitary Corals

Rugose corals are a type of solitary coral. They grew as single individuals and were very common in Devonian reefs. They made a horn-shaped skeleton from calcite. They added a new layer each year, like tree rings. This helps scientists figure out how old the coral was.

These corals had fleshy tentacles to catch small creatures, much like sea anemones. They could be less than an inch to about a foot long. Finding large ones is hard because they took decades to grow. Rugose corals became extinct at the end of the Permian period.

Colony Corals

Colony or Tabulate corals are made of hundreds of individual corals packed together. They were generally filter feeders and grew very large. A famous example is Hexagonaria, also known as the Petoskey stone. This is Michigan's state stone! Its name comes from the hexagonal (six-sided) shape of each coral part. These corals are very easy to spot.

There are also many kinds of Favosites corals. One type is called Honeycomb Coral. This is because its small hexagonal parts look like a honeycomb. These corals are quite common in Michigan.

Branching Corals

Branching corals are the least common type found in Devonian Michigan. Some Favosites corals grew in branching forms. These can sometimes be confused with bryozoans, but they are different.

Other branching corals were usually small. They often grew on brachiopods. They got their name because they grew on stalks with branches. It's rare to find a branching coral fossil still in its original growth position.

Snails: Ancient Gastropods

Gastropods, or snails, are not very common in Michigan's Devonian rocks. Usually, only pieces of their shells are found. But sometimes, you can find complete snail fossils. Most fossil snails in Michigan are small. However, some grew as big as a human head!

You might even find the snail Platyceras attached to a crinoid or brachiopod. This suggests they might have eaten the waste of these animals. Many of these ancient snails ate algae. They are often found near corals, crinoids, and bryozoans.

Fish: The Age of Fishes

The Devonian period is often called the "Age of Fishes." Large armored fish called Placoderms ruled the seas. Early sharks also appeared for the first time. Today, we mostly find their armor plates as fossils. Sometimes, a full body fossil is found.

Fossils of placoderms are rare in Michigan. But some pieces of armor have been found. They usually look like flat blue flakes. It can be hard to tell them apart from brachiopod pieces. Under a microscope, fish armor might show different patterns than brachiopod shells.

Acanthodians are another type of ancient fish. They are sometimes called "spiny sharks." They had spines on all their fins, which helped them defend themselves. They were among the first fish to have jaws. Their fossils are extremely rare and not well understood.

Sharks: Early Ocean Hunters

Sharks first appeared in the middle of the Devonian period. Their fossils are very rare to find anywhere. You can see different types of shark teeth from this time in collections. Some teeth were long and sharp, while others were flat.

Fossil spines from their fins have also been found. These spines were likely used for defense. These early sharks probably hunted fish, snails, brachiopods, and ammonoids.

Stromatolites: Ancient Oxygen Makers

Stromatolites are some of the oldest known living things on Earth. They can be found in Devonian rocks in Michigan. They started forming billions of years ago!

Stromatolites are created in shallow water. Tiny microorganisms, especially cyanobacteria (blue-green algae), trap and bind together sedimentary grains. These ancient life forms started releasing oxygen into the atmosphere. This changed Earth's air and made it possible for other life to evolve.

Fossil stromatolites usually look like large mounds or bumpy layers on rocks. The bumps are the outer layer, and the layers inside show how they grew. Most fossil stromatolites in Michigan are found in the northern Lower Peninsula. You can still find living stromatolites today in places like Shark Bay, Australia.

Brachiopods: Shelled Sea Creatures

Brachiopods are shelled creatures that were very common in the Devonian Period. In fact, they were the most common shelled animals during the entire Paleozoic Era. Today, there are only about 500 species left, but there were once tens of thousands!

Brachiopods had two halves to their shell, joined by a hinge. They were attached to the seafloor by a fleshy stalk. While common, complete brachiopod fossils can be quite beautiful.

Brachiopods were filter feeders. They used a special organ called a Lophophore to create a current. This current helped them trap tiny food particles from the water. Many types of brachiopods can be found in Michigan. Some common ones include Mucrospirifer (which had "wings"), Atrypa, and Strophodonta.

Sharks, placoderms, and snails probably ate brachiopods. Scientists can see marks on some fossil shells that show signs of being attacked.

Straight-Shelled Cephalopods: Cone-Shaped Hunters

These are some of the more ancient types of shelled cephalopods. Cephalopods are a group that includes modern squids and octopuses. During the Ordovician period, some of these animals grew to huge sizes, like telephone poles! By the Devonian, they were smaller but still fierce predators.

You can find some of these animals in Michigan, but they are quite rare. They hunted smaller shelled invertebrates. They used their strong tentacles and a hard beak to crush their prey's shells. They are named for their shells, which look like long ice cream cones. Most Michigan fossils are a few inches to a foot long.

Ammonoids are another type of cephalopod. They first evolved in the Devonian period and became very successful. They also hunted small shelled creatures. Ammonoid fossils are extremely rare, and finding a complete one is even rarer.

Trilobites: Ancient Arthropods

Trilobites are an extinct group of ancient marine Arthropods. They lived from the early Cambrian period (about 541 million years ago) until the great Permian extinction (252 million years ago).

The name "trilobite" means "three lobes." Their body had three main parts:

• The axial lobe ran down the center of the animal.
• The pleural lobes were on either side of the axial lobe.

Their body was also divided into three sections:

• The Cephalon (head)
• The Thorax (body)
• The Pygidium (tail)

Trilobites are special because their eyes often fossilized. This is because the lenses in their eyes were covered with calcite. Some scientists believe trilobites had the first true eyes!

Trilobites were very successful. They lived in many different ways, like scavengers or filter feeders. Their closest living relative might be the horseshoe crab. They also look a bit like a modern woodlouse.

Like many modern arthropods, trilobites shed their exoskeleton (outer shell) as they grew. This means one trilobite could leave several fossils! Finding complete trilobite fossils takes a lot of patience. Usually, you find just a tail or a body segment.

Trilobites were most successful during the Cambrian period, which is called the "Age of Trilobites." After that, their numbers slowly went down. During the Ordovician period, new predators appeared, like sea scorpions. To protect themselves, trilobites started rolling up into a ball. They also grew sharp spines.

Their numbers dropped even more during the Devonian period. They faced many new, well-evolved predators. Rolling up no longer protected them as well. Many trilobite families became extinct quickly. They did not survive the great extinction at the end of the Permian period.

Blastoids: Crinoid Cousins

Blastoids are small marine echinoderms. They are related to crinoids. They first appeared in the Ordovician period and became extinct at the end of the Permian. They were never as diverse as their crinoid cousins.

Blastoids were very similar to crinoids in how they were built. They had a stem that attached to the seafloor. A "head" held their internal organs. Their head is what makes them easy to tell apart from crinoids. It had a five-pointed "star" shape on its outer shell. At the top of the head were five small holes for eating and getting rid of waste.

Blastoids were common in the early Carboniferous period. However, they are extremely rare in Michigan. They have occasionally been found in certain fossil sites.

Images for kids

• Crinoid fossil on rock.jpg

  A fossil crinoid, often called a sea lily.

• Hexagonaria fossil.jpg

  A fossil of Hexagonaria, also known as the Petoskey stone.

• Platyceras fossil.jpg

  A fossil of Platyceras, a type of snail.

• Stromatolite fossil.jpg

  A fossil stromatolite, showing its layered structure.

• Mucrospirifer fossil.jpg

  A fossil of Mucrospirifer, a common brachiopod.

• Phacops fossil.jpg

  A fossil of Phacops, a common trilobite.