Trilobites 101

The early ArthropodsBy Whitney Jetsel

Geology 3A

What are Trilobites?

• Dictionary definition: Any marine arthropod of the extinct class Trilobita, from the Paleozoic Era, having a flattened, oval body varying in length from 1 inch or less to 2 feet.

• Trilobites are segmented, hard-shelled marine creatures that were in existence over 520 million years ago.

• These creatures are considered one of Earth’s earliest complex life forms and are a main feature of the Paleozoic Era.

History• Trilobites constitute an extinct class of arthropods, the

Trilobita, made up of ten orders, over 150 families, about 5,000 genera, and over 15,000 known species.

• The earliest appearing trilobites belong to the suborder Olenelloidea , a little later, the secondarily blind Agnostida. Later in the Early Cambrian the Corynexochida and Ptychopariida appeared. The Late Cambrian was largely dominated by Ptychopariina.

• They ultimately died out near the end of the Permian period, during the “great extinction” that wiped out 95 percent of all species in the Earth’s oceans. Trilobites were evolutionary experts and survived for millions of years. Had it not been for the Permian extinction event they might be living still.

Anatomy of a Trilobite• Trilobites come in many

shapes and sizes but they all have the same basic body layout.

• The trilobites body is made up of 3 main parts: a head (cephalon), a body (thorax) and tail (pygidium).

• Trilobites bodies can also be divided vertically in three ways, into two outer pleural lobes and a central axial lobe, and it is on this division that the name trilobite is based (known as the a three-lobed creature).

Lifestyle• Most trilobites lived in fairly shallow water.

They walked along the bottom of the ocean floor, and fed on nonliving organic material.

• As one walked, a trilobite would stir up food with its legs and pass it forward to its mouth. Because the mouth had no large mandibles, it is inferred that trilobites were not predatory and were restricted to soft food, With a few exceptions.

• Most pelagic trilobites were rather poorly streamlined, and it is unlikely that they swam very fast.

Fossils• When trilobites first appeared in the fossil

record they were already highly diverse and spread around the world, on every continent. Because trilobites had wide diversity and an easily fossilized exoskeleton an extensive record was left behind, with about 15,000 known species spanning Paleozoic time.

• The most common fossil of trilobites is the mineralized dorsal exoskeleton of the creature. This is found in partial form from molting or in complete form when the animal was buried and died instantly.

• It has been reported that 4 to 5 new species are discovered every year in Morocco alone.

Trilobite Photo-shoot

Bibliography

• http://www.trilobites.info/trilobite.htm• http://www.paleodirect.com/trilobites.htm• http://palaeo.gly.bris.ac.uk/palaeofiles/fossilgroups/trilobites/page2.htm

• http://en.wikipedia.org/wiki/Trilobite• http://www.google.com/search?q=trilobites&hl=en&rlz=1T4ADRA_enUS456US456&prmd=imvnsb&tbm=isch&tbo=u&source=univ&sa=X&ei=FnELT47kFYmoiAKG45j6Aw&ved=0CFoQsAQ&biw=1024&bih=555