Trilobites are a diverse group of extinct marine arthropods that thrived from the lower Cambrian to the end of the Permian, existing for nearly 300 million years. Characterized by their hard shells, segmented bodies, and complex eyes, they include over 20,000 species, with sizes ranging from a millimeter to 70 centimeters. Trilobites serve as important fossil indicators in paleontological studies due to their distinct morphology and long geological presence.

1. TRILOBITETRILOBITE

2. • Trilobites are hard-shelled, segmented creatures that
existed over 300 million years ago.
• Trilobites were among the first of arthropods(a phylum
of hard-shelled creatures with multiple body segments
and jointed legs).
• They belong to class Trilobita(9 orders, over 150
families, thousands of genera, over 15,000 described
species.
• The smallest known trilobite is just over a millimeter
long, while the largest include species from 30-70 cm in
length.
• •Life styles of trilobites include planktonic, swimming,
and crawling forms (predators and scavengers). 'Most
trilobites are about an inch long.

4. TRILOBITE MORPHOLOGYTRILOBITE MORPHOLOGY
• Trilobites is divided across the body into a head (or cephalon), thorax, and
tail (or pygidium), and along the body into three lobes - a central axial lobe
covering the main body cavity, and two pleural lobes covering the legs and gills
on either side.
• The head, or cephalon, was generally large relative to the rest of the body,
and is usually divided into a series of sections separated by sutures that
facilitated molting. These sutures form a small number of distinctive patterns
across the cephalon.
• The section of the head outside the facial sutures is known as the free
cheek. The part inside, adjacent to the glabella, is called the fixed cheek. The
eyes of the trilobite could attach to either the free or fixed parts of the
cephalon.
• The eyes of trilobites were typically large and compound, made from multiple
lenses like the eyes of flies. Eyes in arthropods have evolved several times,
and those in trilobites are unique to the group. They had very clear vision,
often using the physical characteristics of calcite to enhance light capture
and focus. The visual range of trilobites was very variable, and appears
strongly related to their mode of life.
• Running down the middle of the head is the glabella, a raised region that
protected the stomach. The size of the glabella correlated to the size of the
stomach, and furrows that partly ran across the glabella may be the external
expression of internal ridges, to which ligaments supporting the stomach were
attached. The mouth is situated underneath the cephalon, near the back of
the head, and is associated with a plate of cuticle called the hypostome. This
could be attached to the front of the cephalon, or could be free lying within
the soft cuticle of the underside ofthe trilobite

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• The Thorax of a typical trilobite was made up of a series of nearly
identical segments, usually between two and 20 in number. Below
each of these was a pair of legs and gills. In Ordovician and later
trilobites these segments were usually jointed in such a way that
the trilobite could roll up for defense
• The Trilobite tail, or pygidium, was usually small and made up of a
series of fused segments that look similar to those on the thorax.
It is likely that the leg/gill pairs occurred under some segments of
the tail in most trilobites, though in some species these segments
may have lacked limbs.
• Glabella: a raised central area of the head under which IS the
stomach compound eye
• Facial suture: a natural break in the exoskeleton to facilitate
molting
• Segments: below each segment is a limb/gill pair
• Hypostome: mouth located at rear. In Calymene the hypostome is
fixed to the front of the cephalon.
• Central groove between legs: food is probably manipulated by the
legs into this groove and then moved to the mouth. The first leg
segments are serrated to provide gripping and tearing functions.
• Leg/gill pairs: one pair for each segment in the thorax, probably
three under the cephalon and several vestigial ones under the
pygidium

9. MORPHOLOGY DIAGRAMMORPHOLOGY DIAGRAM

13. FACTSFACTS

14. •
Trilobites are the most diverse group
of extinct animals preserved in the
fossil record. Ten orders of trilobites
are recognized, into which 20,000+
species are placed.
DISCOVERY OF NEW
TRILOBITE FOSSIL

15. • Trilobites first evolved in the Lower
Cambrian and became extinct by the end
of the Permian.
• They are most common during the
Cambrian, Ordovician and Silurian.
• Therefore they have no modern
equivalents and an understanding of their
soft parts has to be based on modern day
arthropods that show some similarity i.e.
crustaceans.
• They are marine animals

16. • They thrived for almost 300 million years, from the Lower
Cambrian (521 million years ago) to the start of the Mesozoic
(250 million years ago). That means their period was
hundreds of millions of years earlier than the Jurassic, when
dinosaurs ruled the Earth.
• Trilobites are extinct arthropods, and some of the earliest
one at that. They are distant relatives of modern lobsters and
spiders.
• They lived in marine waters, although only some of them
could actually swim. Many burrowed or crawled around on
muddy sea floors.
• They were the first creatures to develop complex eyes.

17. •Trilobites are extinct group in fossil
record
•Time Markers
•Biozone markers
•Paleoclimatic indicators
•Stratigraphic boundarymarkers
•Significance in Phylogenic studies
•Good time markers in Cambrian
Permian as Index fossils
•Short lived but long and significant
markers in Stratigraphic studies.