What are Trilobites?

First, they are one of the the Earth's most successful life forms. Trilobites arose during the Cambrian Period. The Cambrian Period existed from about 570 MYA to somewhere between 490 and 505 MYA. (MYA = million years ago, hence 505 MYA is 505,000,000. If you consider a year being 365 days, i.e. rotations of the Earth, this means the Earth has turned 183,820,000,000 times since the end of the Cambrian Period).

Trilobites are believed to have evolved about 543 MYA, during the Lower Cambrian Period. The last Trilobites died out about 248 MYA in the upper Permian Period. Therefore Trilobites lived for a period of about 295,000,000 years on the Earth.

Let's compare that with the existence of human kind (not just modern humans, what are called Cro-Magnon). The period of time which some form of human kind has been on the Earth keeps getting pushed back but it is currently believed to be something like 4 to 6 million years. Modern humans have been around for a much shorter time, arguably between 35,000 to 50,000 years.

The Trilobites became extinct in the Great Permian Extinction when 90%+ of all species became extinct. However some scientists hold out for the possible future location of some form of Trilobites in the poorly explored deep sea environments. Strange things like this have happened before, such as when the Crossopterigian fish was found off the coast of Madagascar in December, 1938. Until 1938 all Coelacanths (also called ) were considered to be extinct. It was believed that the last Coelacanths lived approximately 70 million years ago. In December of 1938, however, fishermen off the eastern coast of South Africa caught a living coelacanths (because it was so similar to the fossil coelacanths, it was called a living fossil). Since then a number of other coelacanths have been found.

Now to answer the original question, What is a Trilobites. Trilobites are are ancient Arthropods. They belong to the same Phylum as lobsters, crabs, shrimp, crawfish, insects and other living things which have hard exoskeltons and multiple body segments and jointed legs. It was seldom that the legs, antennae and other of the more delicate structures of Trilobites were preserved.

Trilobites constitute an extinct Class of Arthropods. This class is called Trilobita which consisted of nine Orders, over 150 families, about 5,000 genera and that's before we get to species, which is believed to have numbered about 15,000 species which have been described. Each year amateur Paleontologists and professional Paleontologists unearth and describe new species of Trilobites.

Therefore Trilobites hold the distinction of being the single most diverse group of organisms which are now extinct. Perhaps this is why next to dinosaurs, perhaps Trilobites are one of the most popular fossils around.

Trilobites have such a variety of body plans, within the generalized body plan of Trilobites, that they range in size from the smallest which is just under a millimeter long while the largest which includes some species in the range of 30 to 70 centimeters long. To use American measurements, 1 cm is 10 mm and 1 inch = about 25 mm or 2.5 cm. That makes the biggest Trilobites better than 24 inches long.

It is presumed that Trilobites, like most life forms over a period of time in various ecological conditions, filled many roles in their evolution of body forms, feeding niches and patterns. It is assumed that many were detrivores (eaten the fallen decaying plant life); predators (eating other live things, including other Trilobites); and scavengers (eating dead things).

One appeal of Trilobites, unlike a T-rex, Triceratop, or other dinosaur, most are from a fraction of an inch to at most a couple of inches. Therefore you can actually hold one in your hand and examine it, turn it over and threaten your sister with it.

All Trilobites, regardless of size have a similar body plan which help define them as Trilobites. These are:

  1. cephalon, which is the head.
  2. thorax, which is the segmented middle body part (compare this with the human chest area).
  3. pygidium, which is the tail piece.

One interesting thing about some Trilobites is that some had eyes on stalks and many had delicate and elaborate spines. As you might imagine, getting a Trilobite out of solid rock with these delicate appendages is not easy.

The way that Trilobites are often found is by cracking open pieces of rock in quarries where fossil Trilobites are known to exist. When the excavator cracks open a rock and finds a Trilobite split into two, the excavator glues the rock back together and takes it to be prepped. This consists of using an air abrasive gun to tear off the softer matrix, i.e. the rock in which the Trilobite is located. As the prep person is doing this, they must be very careful to keep from destroying the delicate parts of the Trilobite. It is not unusual for spines and eye stalks to be broken off. They can be reglued back on, under a microscope or such, so that the finished Trilobite is perfect or close to it, with all the delicate spines and eye stalks in their proper place and no sign of the regluing of those which came loose.

There is a ton of more information on these fascinating creatures which most everyone loves to see and read about. But you would probably like to view some of those which the Proctor Museum of Natural Science has on display.

Cordania falcata
Coal County, Oklahoma
Trilobite 01
Huntonia linguifer
Coal County, Oklahoma
Trilobite 03
Kettneraspis williamsi
Coal County, Oklahoma
Trilobite 04
Paciphacops cambelli
Coal County, Oklahoma
Trilobite 05
Reedops deckeri (large)
Coal County, Oklahoma
Trilobite 06
Reedops deckeri (small)
Coal County, Oklahoma
Trilobite 07
Reedops deckeri (enrolled)
Coal County, Oklahoma
Trilobite 08
Reedops deckeri (enrolled)
Coal County, Oklahoma
Trilobite 09
Homotelus bromodensis
Carter County, Oklahoma
Trilobite 10