Kathi writes about fossils and other earthly subjects, plus the natural fauna of Michigan, features in her community, poetry, and more.
I Found a Fossil on the Beach and Wondered
While enjoying a walk on the beach, something catches your eye in the sand. It's not driftwood or beach glass or even a pretty rock. You suspect you have found something that was once a living creature and you can't let it go.
Has that ever happened to you? A deep sense of wonder and childlike imagination may drive you to find out what you may have picked up on the beach of our freshwater or saltwater shores.
Well, I have found out a lot of stuff wanting to know what the creatures may have looked like when alive and how they lived. I also wanted to know how they showed up so prevalent along our fresh water beaches. Taking things a step further, I have drawn illustrations of their living beings and started a more in-depth fossil blog of all my discoveries.
Below, you will find fascinating information about some of my favorite sand-smoothed fossil finds with photos and colorful illustrations in the following order:
- Petoskey Stones
- Favosites Honeycomb Corals
- Horn Corals
- Chain Coral Halysites
Some of the most common fossils found along Lake Michigan beaches are crinoids. They're often referred to as, Indian Beads, because Native Americans are known to have created necklaces with their broken pieces shaped like cheerios, perfect for stringing. They've also been referred to as, Lucky Stones! Spotting one takes a keen eye as most of the pieces are quite small.
As living creatures, each circular section was stacked one on top of another constructing the animal's entire framework. The hole in the center of each section contained soft tissue supplying nutrients throughout the animal.
Crinoids possessed a long single stem topped with a sort of cup structure where branching arms grew out from. They were sessile creatures—in other words, they remained attached to the sea floor. Some varieties are known to have towered several meters high. Their loose structure resulted in the living organism's beautifully colored and flowerlike appearance which granted them the common name, Sea Lilies.
Sea lily crinoids captured tiny food particles passing by in ocean currents with their feathery network of fingers that functioned like traps. Crinoids fit into the phylum of Echinoderm, meaning spiny skin, and are cousins to starfish, sea urchins, and feather stars.
Sea lily, crinoids lengthy history dates far back to the Ordovician Period around 500 million years ago, although the fossil record reveals their heyday occurred during the Mississippian Period around 345 mya. Today, there are far few species, but they lack the long meandering stems common in Paleozoic varieties.
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How Are Saltwater Crinoid Fossils Found as Far North as Michigan?
The answer is easy enough to explain. During their Paleozoic lifetimes, much more of the world's continents were covered under warm, shallow, saltwater seas, including the Great Lakes regions. When thousands of Paleozoic species died, including crinoids, they became buried in sediment and under certain conditions, fossilized.
Millions of years later, around ten thousand years ago, the giant glaciers sculpted deep basins forming the Great Lakes. In the process, they also dug into the deep layers of sediment where crinoid remains, and their counterparts, lay buried and were released. Since then, the perpetual wave action of the big lakes continue to deposit them on our beaches where we have the privilege of finding them!
We also find Paleozoic Era bryozoan fossils on the beach. They earned the common name, lace corals, due to their delicately threaded appearance, but they were not true corals. Instead, they were moss-like animals belonging to the family of Fenestellida known for their fan-shaped, mesh-like constructs. They lived in tight colonies sculpted by hard, limy, branching structures. The colony consisted of thousands of individual animals called zooids. Each individual zooid lived inside its own limy tube called a zooecium. The zooecium were the size of sewing needles. A single zooid began the colony.
A modern day bryozoan colony has been observed growing from a single zooid to 38,000 in just five months. Each additional zooid is a clone of the very first.
It's interesting how bryozoans feed. Each zooid has an opening through which the animal can extend its ring of tentacles called, lophophores, to capture microscopic plankton passing by in the oceanic currents. If one zooid receives food, it nourishes the neighboring zooids joined by strands of protoplasm. If only we humans could be more like them, ensuring everyone on the planet is fed!
Their incredible fossil record dates back 500 mya, with 15,000 known species. Today there are about 3,500 living species.
No other organisms typify the Age of Invertebrates more than brachiopods. They are the most abundant Paleozic fossils, except for maybe trilobites. Because of this, paleontologists use them to date rocks and other fossils. Countless billions accumulated on the ocean floor in over 30,000 forms. Today there are far fewer species, only about 300, which live mostly in cold, deep ocean environments.
Brachiopods look like clams but are very different inside. Clams (Pelecypods) have uneven-shaped shells, but both top and bottom halves are identical. Brachiopods are symmetrical at a glance, but the bottom shell is smaller. Brachiopods are commonly called "lampshells" due to their similarity in shape of a Roman oil lamp.
Brachiopods live in communities attached to objects by a muscular foot called a pedicle. They strain water in and out of their shells, filtering microorganisms with their lophophores or crown of tentacles.
I found these clam fossils on the shore of Oval Beach in Southwestern Michigan. The shell of the dark grey sample has been completely replaced by minerals and is petrified to stone. It's a mold cast of the animal's shell, where sediment and minerals permeated inside the crevice's after the animal died. Its smooth surface is a telltale demonstration of the big lake's sand and water action. The lighter-colored sample below clearly reveals hardened muddy sediment that has completely encrusted the clam shell.
"Clam" can be a term that covers all bivalves. Some clams bury themselves in sand and breathe by extending a tube to the water’s surface. Bivalve oysters and mussels attach themselves to hard objects, and scallops can free swim by flapping their valves together. All types lack a head and usually have no eyes, although scallops are a notable exception. With the use of two adductor muscles, they can open and close their shells tightly. Very fittingly, the word “clam” gives rise to the metaphor “to clam up,” meaning to stop speaking or listening.
Bivalves have occupied Earth as early as the Cambrian Period 510 million years ago, but they were particularly abundant during the Devonian Period around 400 million years ago. Their fossils are discovered in all marine ecosystems and most commonly in near shore environments. In 2007, off the coast of Iceland, a clam was discovered that was estimated to be about 507 years old. It was declared the world’s oldest living creature by researchers at Bangor University in North Wales.
I have written more in-depth information about extinct clam species here.
Petoskey Stone Coral Fossils
About Petoskey Stone Coral
I found the above Petoskey Stone on Oval Beach in Southwestern Michigan. It's a good example demonstrating Lake Michigan's natural polishing process caused by perpetual winds, waves, and sand movement. It's a fairly large sample at least the size of a man's fist.
The side view of it shown below reveals the stem where the coral attached to the ancient seafloor. It's kind of rare to see that because so many of these coral fossils are sanded down and polished for their intricate beauty and sold as gifts. This sample is rough and raw, nothing has been manipulated.
Interesting Facts About Petoskey Stones
During the Devonian time slot, over 350 million years ago, Michigan was covered by a shallow, saltwater sea. That's where mass coral colonies called, Hexagonaria, percarinata, commonly known as Petoskey Stones, flourished. The ancient seascape must have been lit up with a quilt work of colors by their vast colonies. Sadly, they became extinct at the end of the Permian Period's mass extinction.
The name “Petoskey” originated from an Ottawa fur trader chief named, Petosegay. A northern Michigan city was named after him, later, the name was modified to Petoskey. Because the coral fossils are so abundant along Michigan shorelines, especially in the northern regions near the city of Petoskey, Governor George Romney signed a bill in 1965 making the Petoskey Stone the official state stone.
Each individual coral hexagon structure called, corrallite, is visible in most Petoskey Stone fossils. Corallites held a single animal (polyp) which opened a mouth to expose tentacles. The tentacles took in food and were also used to sting other organism or even neighboring coral tentacles that came too close. Calcite, silica, and other minerals replaced the original corallite exoskeleton.
Collecting Petoskey Stones is a popular past time for many Michiganders and attracts fossil hunters from all over the U.S. Tourists enjoy purchasing their uniquely carved and polished creations in giftshops. The Petoskey Stone paperweight shown above is one of the more simple gift items, but quite lovely revealing the intricate corallite patterns .
Favosites Honeycomb Coral Fossils
About Honeycomb Favosites Coral
If you live in Northern Michigan, particularly near Charlevoix, you can find these fossils fairly often, but they are more rare to find in Southwestern Michigan where I found my samples. Favosites is an extinct order of coral called tabulate corals which also formed colorful reefs and lived in warm, shallow waters during the same period as the Petoskey Stone corals. The favosites can easily be identified by the honeycomb patterns enfolding their exterior fossil remains. Consequently, they are often referred to as, Honeycomb Corals, but one particular species is called, Charlevoix Stones, because of their dominant appearance in that region of Michigan.
The tabulae (horizontal internal layers) of favosites were built outward as the organism grew. These layers can clearly be seen in the photo above. The walls between each corallite (cup housing of the individual animal polyps) are pierced by pores known as mural pores which allowed a transfer of nutrients between polyps.
Horn Coral Fossils
About Horn Coral
It's fun to find these curious coral fossils when beachcombing. Horn corals belonged to the extinct order of rugose corals which appeared as early as 450 million years ago until about 250 mya. That's an astounding 200 million years living on Earth. Their name derives from their unique horn-shaped chamber with its wrinkled (or rugose) wall. When viewed from its widest opening, it looks like a pinwheel where the coral polyps once poked out from to sift microorganisms passing by in the ocean currents. Some species grew two meters high from the seafloor. They were mostly solitary animals, with a few exceptions that grew in mass colonies.
Chain Coral Fossils
About Chain Coral
The trail of chains in these beach-smoothed limestones is another occasional fun find on the lakeshore. The chains are a dead give away for what's called "Chain Coral" from the Halysite family of the order Tabulate corals. This is another coral type that began its reign during the Silurian Period approximately 450 years ago. As with most coral polyps, they possessed stinging cells which also grasped plankton floating by in the currents. As their coral polyps continued to multiply, they added more links to the chain, sometimes building large limestone reefs.
You're combing the beach in search of something interesting to examine. You pick up a common smooth stone, admiring its sleek texture. Little did you know, it's actually a fossil.
When wet, the stone reveals its layers of striations. It's a stromatolite fossil, the oldest of all fossils, dating as far back as 3.5 billion years. Their heyday was long before the Cambrian creatures evolved (stromatolites actually paved the way for their existence). Stromatolites were simple cyanobacteria capable of photosynthesis. Their structures grew solid, layered, and varied, some of which looked like giant mushrooms reaching eight feet tall. Through photosynthesis, they changed Earth's atmosphere from carbon-dioxide-rich to oxygen-rich. Scientists believed they were extinct before 1956, when living stromatolites were discovered in Shark Bay of Australia. Since then, there have been many more stromatolite discoveries around the globe.