Ammonites are fossils of an extinct class of cephalopods. They are related to squid, octopus, and the chambered nautilus. Typically they have a flat spiral shell. As the ammonite grew it added on to its shell, moved forward, and sealed off the old part of the shell with a divider called a septa. The shell is divided into many such sections.Ammonites first appear in the fossil record of the Devonian period, about 390 million years ago. This period was named after the Devon area of Great Britain. Ammonites were so plentiful and there were so many different kinds that paleontologists use them to date rock strata. They were predators. They became extinct about 65 million years ago at the end of the Cretaceous Period. This was one of the great extinctions and many species of animals disappeared from the ranks of the living at this time.
Crinoids are echinoderms. They are related to sea urchins and starfish. Common names for crinoids are sea lilies if they have a stalk and feather stars if they are without stalks. Crinoids are considered a living fossil. They have been around since the Ordovician Period, and there are still a few species of crinoids living in the oceans today, though they are not as plentiful as they were during the Paleozoic Era. They are a kind of sea animal that look like a flower. Some varieties grow on thick stems permanently attached to the ocean floor. Others have no stems and can move about on tiny appendages called cirri. Crinoids are filter feeders meaning they get their food from the water that flows past them. The feathery arms of the crinoid catch the food particles. Crinoid food is made up of algae, small crustaceans, invertebrate larva, and other organic matter.
Brachiopods are another living fossil as they first appeared during the Cambrian and there are many species alive today. They have two valves or shells connected by a hinge or by muscles. Unlike clams or oysters, the two shells of a brachiopod are not exactly the same. They are not related to clams or oysters and are not even mollusks. They are Lophophores, and are related to bryozoans. They are filter feeders and gather their food by passing sea water through a specialized tube called a lophophore which acts as a strainer to collect small bits of organic matter. The brachiopod does not move. It is either attached to the ocean floor by a thin stalk called a pedicle or lies on the ocean floor. Some live buried beneath the sand.
Belemnites were squid like cephalopods. They had a shell but it was internal rather than external. It is the internal shell that is commonly found as fossils. The soft body parts rarely become fossilized. Belemnites are related to the ammonites. They first appeared during the Carboniferous Period about 200 million years ago. As a group they were very successful with many species. The belemnites became extinct at the close of the Cretaceous Period along with the dinosaurs.
Ichthyosaurus were reptiles adapted to marine living. They had streamlined bodies and were strong swimmers. They had to surface to breathe because they had lungs and were air breathers. Ichthyosaurus grew to be 30 feet (9 meters) in length and were fearsome predators. They first show in the fossil record in the Triassic Period. They were most abundant in the Jurassic period and became extinct during the Cretaceous Period.
This article has been written by guest writer Doug Mann, an expert on fossils. To learn more about fossil collecting please visit his website Fossils Facts and Finds.