During Cambrian animals evolved which could dig into the sediments on the ocean floor.

Cambropallas

This large trilobite was probably a predator which fed on worms and other soft animals on the ocean floor or in its sediment. The left side of this fossil is partly reconstructed.

Trilobites had hard shells on their backs, and limbs with flexible joints that enabled them to move efficiently. They had compound eyes, along with two antennae that protruded from under the head and two more on the rear section of the body.

Paradoxides gracilis

This specimen was discovered in what is now the Czech Republic; similar species also lived in Sweden. This particular animal discarded its large cheek spines when it shed its shell. Paradoxides was probably a predator, and common during the Cambrian Period.

Since trilobites were joint-limbed animals, they had to shed their shells in order to grow. Their heads had special sutures along which the shell split open. Then the cheek spines fell off and the animal could crawl out of its old shell through the head section.

Fuxianhuia

Both eyes and the short antennae are visible on this specimen. Fuxianhuia was an early arthropod (invertebrate animal with jointed limbs), and may have been closely related to ancestors of modern spiders and crustaceans.

Impressions of numerous short limbs under the body, and of the animal’s heart and brain have been found on other specimens.

Anabarochilina

Anabarochilina was one of the first crustaceans. The shiny black area of the fossil is the outer shell that enclosed most of the animal.

Many of these crustaceans floated freely in the water as zooplankton and were an important source of food for other types of animal.

Gogia

This animal rose above the ocean floor on its short stem to catch plankton and tiny animals in the water with its many arms.

It was probably an ancestor of the sea lilies that were a very common marine animal for hundreds of million years.

Mickwitzia

Mickwitzia had a two-piece shell that was covered with thin bristles. It lay unattached on the ocean floor, where it filtered plankton and other tiny food particles from the water.

This lampshell is among the first shell-bearing animals that are known to have existed.

Mickwitzia

Mickwitzia had a two-piece shell that was covered with thin bristles. It lay unattached on the ocean floor, where it filtered plankton and other tiny food particles from the water.

This lampshell is among the first shell-bearing animals that are known to have existed.

Ellipsocephalus

Ellipsocephalus had no eyes, unlike most trilobites which had well developed eyes. They probably lived in deep water, beyond the reach of sunlight. Down in the darkness, they most likely fed on sludge and small animals in the bottom sediment.

Skolithos

This sandstone is full of narrow tunnels. They were excavated by an unidentified worm-like animal that lived in great abundance in sandy areas of the Cambrian ocean floor in what is now southern Sweden.

The vertical tunnels were used as dwelling spaces. The reddish colour is from the iron oxide that formed when oxygen entered the excavated tunnels.

Paleophycus

This fossil is named Paleophycus and contains traces left by worms that dug horizontally through the mud of the ocean floor. The tunnels they excavated were then filled with sand,during a storm, for example and that is why it has been possible to discover them in the present day.

Based on the sizes of the tunnels, it can be seen that they were dug by two different worm-like animals.

Rusophycus and Paleophycus  

This fossil contains traces of several different animals. The tunnel-shaped traces were left by worms as they dug through sediments. The larger, cone-shaped traces were left by trilobites and other arthropods (joint-limbed invertebrates), possibly when they were hunting the worms.

The arthropods dug with their legs, which is why their traces are full of scratches.