During the Silurian, Sweden was located near the equator, and reefs were formed by corals and sponges.

Palaeophonus nuncius

Palaeophonus is one of the very oldest true scorpions that has been found, and this is the only known specimen. Palaeophonus had legs that could bear its weight on land, large claws on the front legs, and a tail with a poisonous stinger. It was probably a predator that hunted the first plant-eating arthropods. But it is not certain that Palaeophonus lived its entire life on land, since this fossil was found in an ocean environment.

Baragwanathia longifolia

Baragwanathia was one of the first clubmosses. It was very large, with stems that could be up to two metres long.

Baragwanathia fossils have been found in the same places as fossils of marine animals, indicating that it lived in river deltas and was occasionally swept out to sea.

Cooksonia bohemica

Only a few centimetres high, Cooksonia was one of the first plants to live on land. It was the first plant which is known to have taken up water and nutrients via the stem.

Meristina

Meristina species were fairly large lampshells with almost spherical shells. Having no stalk, they lay directly on the ocean floor. The shell opening made a sharp turn in the middle. That enabled the animal to suck in water to be filtered and then squirt it out along the sides, without mixing the incoming and outgoing flows of water.

Calymene

These trilobites had hard, jointed shells on their backs and many small legs underneath. Common in the Silurian oceans, Calymene were predators that caught smaller animals. They defended themselves by curling into a ball when larger predators approached.

Calymene

These trilobites had hard, jointed shells on their backs and many small legs underneath. Common in the Silurian oceans, Calymene were predators that caught smaller animals. They defended themselves by curling into a ball when larger predators approached.

Rhipidium

Riphidium species were among the biggest lampshells of their time. They had very heavy shells and lived side by side in large groups in areas with strong currents. The tip of the shell was very thick and heavy, and could thus serve as a sort of anchor. 

Oriostoma

Oriostoma was a snail that fed on algae it scraped from corals and other hard objects in the Gotland reefs.

Its shell was shaped like a discus and had a deep hollow on the underside. Such shells are unusual these days, because they are easily broken apart by predators. But Oriostoma survived well during the Silurian, when there were not many predators that could break open such a shell.

Actinoceras

These cephalopods had long, straight shells with many chambers. The siphuncle — the siphon tube that connected all the chambers with the rest of the body — was wide, making it possible to change the mixture of gas and liquid in the shell in order to efficiently adjust the animal’s buoyancy.

Fossils of Actinoceras are not very common on Gotland, leading scientists to believe that these active predators lived in deeper areas of the ocean.

Octomeroceras unguifer

Octameroceras unguifer belonged to a group of cephalopods, the oncocerids, that have unusual pear-shaped shells. The shell opening grew almost shut in adults. Oddly enough, very few fossils of young animals have been found. Perhaps the adults lived in deeper waters and migrated to coral reefs only to reproduce and then die.

Octomeroceras pugil

Octameroceras pugil belonged to a group of cephalopods, the oncocerids, that have unusual pear-shaped shells.

The shell opening grew almost shut in adults, with only a thin slit remaining. Both the male and female may have died after mating, their dead bodies providing food and shelter for the young. Many adult octopuses do so today.

Pleurotomaria

This snail fed on algae that it scraped up with its rasp-like tongue (radula). It may also have eaten dead animals.

Pleurotomaria belonged to a group of early snails that has survived to the present day, although they are now usually found in deep ocean waters.  

Hormotoma

Hormotoma belonged to a group of snails that may have been ancestors of most present-day snails. They had high, spiral-shaped shells with oval openings.

Like nearly all Silurian snails, Hormotoma species fed on algae which they scraped from corals and other hard objects.

Phragmoceras

Phragmoceras were quite large cephalopods with broad, flat shells. They probably moved slowly across the ocean floor with the shell opening pointing downward. They may have been predators. Just like their Octameroceras relatives, the shell opening grew nearly shut when they became adults.

Strispirifer

Large groups of these and other lampshells covered the sides of the Gotland reefs, in much the same way that mussels can cover rock surfaces along the tidal zones of our shorelines. Large numbers of Strispirifer fossils can therefore be found in some places. Strispirifer lampshells were very common on the Gotland reefs.

Leptaena

Leptaena lampshells were adapted to life on soft ocean bottoms. Their two curved half shells fit together like spoons in a drawer. That made it possible to keep the shell opening above the surface of the sediment, so that none of it could enter and contaminate the interior where the water was filtered. 

Ketophyllum

Ketophyllum were corals that lived as solitary individuals or in small groups amidst stones and shells on the ocean floor around the Gotland reefs. Farthest down on the animals were outgrowths that helped to keep them in place.

The Ketophyllum growth pattern varied: Sometimes the living part became smaller, sometimes larger — possibly due to variations in the available food supply.

Ketophyllum

Ketophyllum were corals that lived as solitary individuals or in small groups amidst stones and shells on the ocean floor around the Gotland reefs. Farthest down on the animals were outgrowths that helped to keep them in place.

The Ketophyllum growth pattern varied: Sometimes the living part became smaller, sometimes larger,  possibly due to variations in the available food supply.

Cystiophyllum

Cystiophyllum corals lived as solitary individuals on the ocean floor. It sometimes happened that an individual was knocked over, for example in a storm, and it can be seen that its growth then changed direction so that the shell opening again pointed upward. The fossil shell is cup-shaped and resembles an elf cap. 

Cystiophyllym

Cystiophyllum corals lived as solitary individuals on the ocean floor. It sometimes happened that an individual was knocked over, for example in a storm, and it can be seen that its growth then changed direction so that the shell opening again pointed upward. The fossil shell is cup-shaped and resembles an elf cap. 

Cystiophyllum

Cystiophyllum corals lived as solitary individuals on the ocean floor. It sometimes happened that an individual was knocked over, for example in a storm, and it can be seen that its growth then changed direction so that the shell opening again pointed upward. The fossil shell is cup-shaped and resembles an elf cap. 

Goniophyllum

Goniophyllum corals had an unusual, square shape. Another distinctive feature was that their polyps had four plates of calcium carbonate which could close the opening in the event of danger. It was an efficient way to protect a coral’s soft parts.

Goniophyllum lived in relatively calm waters. It is unusual to find specimens with the four protective plates preserved. 

Goniophyllum

Goniophyllum corals had an unusual, square shape. Another distinctive feature was that their polyps had four plates of calcium carbonate which could close the opening in the event of danger. It was an efficient way to protect a coral’s soft parts.

Goniophyllum lived in relatively calm waters. It is unusual to find specimens with the four protective plates preserved. 

Stromatoporoidé

Stromatoporoidsponges were among the most important organisms in the Gotland reefs. They held the reefs together so that they were not broken up too quickly, by storms for example.

These sponges built up massive skeletons of calcium carbonate. As they grew, new layers of calcium carbonate were added to the old, forming cushion-shaped or plate-like accumulations that could become very thick.  

Halysites

This type of coral had small polyps and always lived in colonies. The polyps grew a slight distance from each other and were connected by thin walls. The small holes in which the polyps lived formed what looked like chains.

Halysites were among the most important reef-builders during the Silurian, and they could sometimes form continuous surfaces that were tens of metres wide. 

Dartmouthia gemmifera

This is a fossil of a head shield from a jawless fish. They were armoured, somewhat like modern shrimp, but the armour was made of bone tissue. Visible here is the inside of the shield. It could probably not grow, and did not form until the fish reached the adult stage. Can you see the two eye sockets?

Anaspida

These long, dark fossil scales are from a fish that resembled the one in the display in front of you. Unlike other early jawless fish, which had armoured head shields, these species were covered by thick scales just like those of Permian and Jurassic fish. Anaspida means ”without shield”.

Eurypterus

One pair of sea scorpion legs were equipped with claws, just as in all other arachnids. The largest sea scorpions could be up to two metres long, but most were smaller. Eurypterus species were predators that fed on worms and other small animals. They moved over the ocean floor with the help of their front pair of legs. But they could also swim with the use of their flat rear legs, just as many modern crabs do.