Modern ocean-dwelling animal groups

Eolates gracilis

Eolates gracilis was a predator and a representative of a modern fish group that evolved after the Cretaceous mass extinction. Eolates is among the perch-related fish which comprise the largest order of vertebrates; the order includes over 10,000 species today.

The perch-related fish provide a good example of the evolution of many different vertebrate animals during the Palaeogene and Neogene periods. That evolution has resulted in the biological diversity of today.

The two small fish of the Myripristis genus belong to a small group of fish with 157 present-day species, all of which evolved during the Palaeogene and Neogene periods.

Coral

This spherical, colony-forming coral is closely related to some corals of today. A polyp lived in every opening of the coral, and large colonies were formed with many individual polyps.

Corals live partly by capturing plankton with their tentacles; but the polyps also host microscopic algae which provide the animal with nutrients. Spherical corals usually live in quiet ocean waters.

Heliastraea

Heliastrea was a colony-forming coral and is closely related to some modern coral species. A polyp lived in every opening of the coral, and large colonies were formed with many individual polyps.

Corals live partly by capturing plankton with their tentacles; but the polyps also host microscopic algae which provide the animal with nutrients. Massive branching corals like Heliastrea often lived in habitats with flowing water.

Plocophyllia

This spherical, colony-forming coral is closely related to some corals of today. A polyp lived in every opening of the coral, and large colonies were formed with many individual polyps.

Corals live partly by capturing plankton with their tentacles; but the polyps also host microscopic algae which provide the animal with nutrients. Plocophyllia corals had large polyps which divided over and over again to grow into tree-shaped colonies.

Crassatella

Many mussels of today live buried in sandy bottoms near the shore, just as this mussel once did. It filtered its food from ocean water with a siphon — a sort of breathing tube that the mussel could extend upward through the sand.

Nummulites

These shells are fossils of single-celled amoebae called foraminifera. Even though they only have one cell, they are very large — in fact, the largest single-celled organisms on Earth. The shell protects the amoeba’s only cell, which can extend its hair-like outgrowths through the numerous microscopic holes in the shell. Those outgrowths, called pseudopodia, are used to move about and capture food.

In some places, Nummulites foraminifera were so abundant that their shells accumulated into thick layers of limestone. The Egyptian pyramids are built of such limestone. 

Carcharocles megalodon

This huge tooth is from a 16 metre long Carcharocles megalodon, an extinct species of shark. It is the largest shark ever known to exist. Carcharocles co-evolved with its prey — large marine birds such as giant penguins, and marine mammals such as early whale and sea cow species.

Carcharocles is related to a group of sharks that consists of 17 present-day species, including the white shark.

Coeloma

This little crab used its powerful claws to crush the shells of snails and mussels in order to get at their soft flesh. This crab was preserved when calcium precipitated from the water and a limestone ball formed around the dead animal’s shell. The crab was found when a palaeontologist cut the limestone ball in half. The other half is a relief impression of the animal.

Charonia

The trumpet snail Charonia had a strong shell with nodes and a reinforced shell opening for defence against crabs and other predators.

Species of Charonia still exist today. They are large snails whose food includes starfish which they creep up on and then attack with their ”tongue”, the radula. On the surface of the radula are many small teeth.

Spondylus

Spondylus cemented its shell to the ocean floor, just as oysters do today. But Spondylus was descended from scallops that lived unattached on the ocean floor. By attaching itself to the right place, the mussel could effectively compete for food and living space.

Clavilithes

Most modern relatives of Clavilithes are predators that hunt mussels and other snails. They locate their prey by smell and pry open the shells by using their own as levers; then they suck out the soft parts.

Volutospina

The snail Volutospina was a predator that lived on small snails and other invertebrates. Its ”tongue”, the radula, had tiny teeth with which they scraped through the shells of their prey. Volutospina lived in shallow tropical oceans.

Lobster 

Lobsters like this were predators that lived on the ocean floor. This specimen was found in gravel at Langeland, Denmark. Both the gravel and the fossil were probably carried there by a glacier, but from where is not known. It is therefore not possible to determine exactly when this lobster lived.

Eocernina

Eocernina was a snail whose smooth shell was adapted for burrowing through the ocean floor. Most modern relatives of Eocernina are predators that hunt mussels. Eocernina burrowed to its prey, made holes in their shells with dissolving acid, and then sucked out the soft parts.

Clypeaster

When this sea urchin lived, it was covered with many small spines. They were used partly to capture small food particles, partly to move across and burrow into the ocean floor. They lived partly buried in sandy ocean bottoms. During the course of evolution, this type of sea urchin developed increasingly flatter shapes so that they could more easily bury themselves.

Gigantopecten

This large mussel is related to scallops and lived on ocean floors. It was unattached and, if threatened, could move by quickly closing its open shell. The water between the shelf halves was thus forced out, thrusting the mussel backward from the recoil.

Mene rhombea

At Monte Bolca in the Italian Alps are many well-preserved fossils of fish. The specimens found there consist partly of fish genera which survived the Cretaceous mass extinction, and partly of newer genera which evolved after the mass extinction. An example of the latter is this fossil of an extinct coral fish species that is closely related to perch living today in the Pacific Ocean.