Echinoderm Fossils

Echinoderm Fossils

Fossil Echinoderms
Echinoderms are a huge group of marine animals. Some of them are familar like starfish, sand dollars, and sea urchins. Some not so much like the sea cucumbers, crinoids, and blastoids.

As a group echinoderms are well represented in the fossil record. Most of them have hard parts that easily fossilize, and they have been an abundant group of animals since the Cambrian Period. Sea urchins and sand dollars make shells called tests that are found all over the world. Crinoids and blastoids created huge reefs at times leaving fossil beds many feet thick in places. Starfish are less plentiful as fossils because the tissue that holds the hard parts together falls apart quickly after they die. They are preserved only in a few places where they have been buried soon after death.


So what is an echinoderm?

Echinoderm is the commonly used name for the phylum of animals Echinodermata. At first glance these animals don’t seem to belong together. Taking a closer look they have many shared characteristics. They all have radial symmetry as adults, a watery circulatory system, and bumpy or spiny skin.

The name comes from the ancient Greek word Echinos, meaning hedgehog. So we get skin like a hedgehog or spiny skin.

The phylum has over 7000 living species and 13,000 extinct species. There are no known terrestrial or freshwater members.


Prehistoric Echinoderm Families
The oldest of the echinoderm fossils is called Arkarua, which was initially found in Precambrian Australia. It appeared as disk-like with spiral ridges and had a depression with radial lines. The echinoderm fossils have an extensive record and the first to be globally accepted was discovered in the lower Cambrian Period and included crinoids groups. A simple motile, symmetrical, and bilateral animal with a gut, mouth, and anus is linked with the origin of echinoderms. This motile ancestor had an attached mode of existence, and it got nutrients through suspension feeding. These original echinoderms later gave rise to groups which had free movement.

By the Ordovician Period all of the major groups of echinoderms became firmly established and except for the blastoids, which went extinct at the end of the Paleozoic Era, all of the echinoderm groups are still present in todays oceans.

Echinoderm Life Cycle

Echinoderms development begins with a symmetrical bilateral embryo. The larva undergoes several development stages which have their names derived from the adult taxonomic names. When the larva undergoes full development, a radial symmetry is developed, losing the bilateral system. Echinoderms have simple body systems which include a simple radial nervous system, coelomic circulatory system and simple gaseous exchange system.

Environmental Habitat of Prehistoric Echinoderms and the Places They Exist in the World

Echinoderms are distributed in all latitudes, environments, and depths worldwide. They are highly distributed in reef environments but are also widespread on shallow shores in the pole regions. Some also dwell in deep sea where borrowing and bottom- dwelling sea cucumbers are the majority. Some members of this phylum live on the sea beds while others float and moved by ocean currents over long distances, leading to global distribution of this phylum.

Feeding of Echinoderms

Different echinoderms taxa have varying feeding modes. Nearly all starfish are carnivores. Sea urchins are herbivores, and they mostly feed on algae. Some also feed on dead fish and other animal matter. Suspension feeders include crinoids. blastoids, and basket stars. Some secure food particles with their mucus suspension strands, while others are scavengers.