Halysites Chain Coral Uncovered

Golden Beach grass dune
Oval Beach Saugatuck, Michigan  (Winter 2012)

I was super excited to discover several fossils on Oval Beach in Saugatuck, Michigan, USA that are highly unusual to find in winter. The fossil below was lying under deep layers of sand, but luckily, the mild weather with minimal snowfall allowed winter winds to push sand off the under layers. Also contributing to fossil hunting were the low water levels from a long dry spell during summer 2012, which produced more beach to explore.

Halysite Coral
Halysites Chain Coral Fossil Found on Lake Michigan Beach

These fossil samples are extinct tabulate corals, reef building colony-type corals, Halysites, commonly called, Chain Corals. They are fairly easy to distinguish due to the chain-link raised marks for which they’re named.

Halysites Chain Coral Fossil Found on Lake Michigan Beach

In life, the extinct Halysites corals possessed small tubes where the jelly-like polyps resided. The coral polyps contained stinging cells for protection and also for siphoning plankton and organic matter passing by in the ocean currents. As the Chain Corals grew, they built up walls of tube-like chambers called theca which steadily multiplied while adding more links to the chain. In their heyday, they built large limestone reef structures on the seabed. They thrived especially during the Silurian period as far back as 425 million-years-ago!

Halysites Chain Coral Classification

Kingdom: Animal

Phylum: Cnidaria (means stinging animal)

Class: Anthozoa (means flower animal)

Order:  Tabulata (possess inner horizontal dividing walls from growth patterns)

Family: Halisitidae (means chain coral)

Genus: Halysites  Species: unknown

Halysites Chain Coral Rendering Showing Polyps Extended

Explore more Lake Michigan fossils in another photo-essay I provided, otherwise, keep scrolling!

All rights reserved © Fossillady 2011


Mysterious Sponges

Lake Michigan Sponge Fossil, Side View

This is one of the more unusual fossil finds from our shores of Lake Michigan in Southwestern Michigan USA! I’m 99.9 % sure it’s a fossilized sponge and not a coral due to the lack of septa, vertical growth walls. From the side view, you can see how the tubes, or pores, permeate down into the structure.

Lake Michigan Sponge Fossil, Top View

INTERESTING SPONGE FACTS:   The most fascinating fact about sponges is their long extended history on Earth beginning 580 million years ago. The type of sponges we’re most familiar with are the ones we use for our households. Those are actually referred to as, demosponges, having entirely soft fibrous skeletons with no hard elements of which there are only a few species. After thousands of years, humans had almost harvested them to extinction by the 1950’s.  Many are now being researched for a possible source of medicines.

Popular Tourist Spot Selling Natural Sponges, Source: en.wikipedia.org

HOW SPONGES LIVE: Sponges have delicate skeletons and rely on a constant water flow through their bodies to capture food and obtain oxygen. They don’t have a digestive or circulatory system like we do. They can actually change the shape of their bodies for maximum water flow.  Most species have the ability to contract and squeeze the water out of their pores in order to flush out sediments clogging them. They can even  escape from predators by squeezing out the water and shrinking themselves. For further defense, many shed spiky spicules to create a dense hazardous carpet around them which keeps away predators such as star fish.


Kingdom:  Animalia       Phylum:  Porifera (means to possess pores)

Four Classes

Demosponges Largest class; Inner structure reinforced with collagen fibers and spine-like spicules made of silica minerals; Usually barrel shaped; Can live in a wide variety of habitats

Hexactinellida – Glass Sponges; Spiny spicules made of silica minerals forming inner scaffolding structure with gelatin substance weaved in between framework; likes Polar Regions

Calcareous – Outer exoskeleton and inner spicules made of calcium carbonate. Restricted to shallow marine waters where production of calcium carbonate is easiest to obtain.

Scleropongiae (Coralline or Tropical Reef Sponges) soft body that covers a hard, often massive skeleton made of calcium carbonate, either aragonite or calcite.  The layered skeletons look similar to reef corals, therefore are also called coralline sponges.


Cephalopod Nautiloids Have a Long History

Cephalopod nautiloids date back to the Early Ordovician Period almost 500 mya and survived to the Late Triassic about 230 mya. Some believe they even survived through the Cretaceous Period about 150 mya.  Wow!  Their fossilized shells have been discovered all around the world in large assemblages and commonly occur in marine rock, especially lime stone .

Orthoceras Nautiloid Fossil

The straight shelled nautiloids were closely related to the ammonites which evolved spiraled shells. But due to their long linear shells and a weak muscle, they probably weren’t as agile. They moved about the same way, though, with the use of a siphuncle tube that runs the entire length of the shell through each of its inner chambers. Once filled with water, the cephalopod nautiloid could force the water out, propelling itself backward with a kind of jet propulsion. By releasing the water and leaving air space, the tube could serve as a buoyancy device allowing the animal to rise and lower itself to different depths.

Orthoceras Nautiloid Fossil

Their fossils have been quarried by Europeans for many years and adorn floors, stairs, jewelry, gravestones and more with their durable and desirable beauty.

The Orthoceras nautidoids display extreme diversity in size from a few inches to 14 feet in length. One of the largest cephalopod nautiloid giants from the earliest years, Cameroceras, reached 30 feet in length.



Kingdom:  Animalia

Phylum:    Mollusk  (large diverse group of invertebrates with soft bodies  encased in a shell i.e. clams, snails, oysters )

Class:      Cephalopoda  (means prominent head and tentacles i. e. squid, octopus, nautilus, cuttlefish)

Subclass: Nautiloidea   (series of chambers of increasing size connected by a central tube)

Order:     Orthocerida  (extinct group of  cephalopods possessing long straight shells)

Family:     Orthoceridae

Genus:    Orthoceras (means straight horn)

Cephalopod Nautiloid Drawing Rendition

Brachiopods and Their Fossils Are Significant

No other organisms typify the Age of Invertebrates more than brachiopods. They are the most abundant Paleozoic fossils, except for maybe trilobites. Paleontologists use them to date rocks and other fossils along the same rock strata.  Countless billions accumulated on the ocean floor with over 30,000 forms. Today, there are far fewer species, only about 300 species which live mostly in cold, deep ocean environments.

Brachiopod Fossilized Mold Cast found along Lake Michigan Shoreline

The brachiopod fossil specimens shown above and below are casts of the animal’s former shells which had filled with sediment after the creature died and later the sediment turned to stone leaving an impression of the shell. The original shells very possibly broke up into pieces and washed away settling onto the seafloor along with multitudes of other brachiopod and clam shells.

fossils 005
Fossilized Brachiopod Mold Cast

Thick shelled forms of brachiopods are ribbed and live in shallow water. Thin shelled forms are smooth and live in deep water. Some brachiopods grow to 9 inches across, but most are about an inch in diameter. They 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, a crown of tentacles.

Sample of stone found on Lake Michigan beach embedded with broken shell pieces

Brachiopods were the first of their kind to lose mobility and develop a hard covering. They look like clams but are very different inside. To tell them apart, clams (pelecypods) have uneven shaped left and right shell valves, but the tops and bottoms are identical. Brachiopods have evenly shaped (symmetrical) left and right valves, but the bottom valve is smaller.


Common Name: Brachiopod or Lamp Shell (named for resemblance to ancient Roman oil lamps)

Kingdom: Animalia

Phylum:   Brachiopoda (means arm and foot)

Class:      Articulated (shells clamp together by a hinge)

Inarticulated (shells clamp together by a muscle)

Genus: Brown Sample possibly Pseudoatrypa sp   Grey Sample possibly Atrypa, reticularis

Brachiopods in the Ocean Mist
Brachiopods in the Ocean Mist