1. Trilobites 101
The early Arthropods
By Whitney Jetsel
Geology 3A

2. 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.

3. 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

4. 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).

5. 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.

6. 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.

7. Trilobite Photo-
shoot

8. Bibliography
• http://www.trilobites.info/trilobite.htm
• http://www.paleodirect.com/trilobites.htm
• http://palaeo.gly.bris.ac.uk/palaeofiles/fossilgrou
ps/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=FnELT
47kFYmoiAKG45j6Aw&ved=0CFoQsAQ&biw=102
4&bih=555