Download An Introduction to Trilobites

M. Cunniffe
Stanford IISME Fellow, 2013
The Trilobite: An extinct
Arthopod
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Chelicerates
Trilobites
Hexapods
Crustaceans
Myriapods
What is a Trilobite?

 Trilobites were marine organisms that lived on Earth for
over 270 million years and are considered known to be
one of the most successful early animal groups
 Trilobites are a member of the Arthropods. Of the five
types of Arthropods, only the trilobites are extinct. The
four extant Arthropod groups include:
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Chelicerates (spiders, scorpions)
Crustaceans (lobsters, crabs, barnacles, shrimp)
Myriapods (millipedes, centipedes)
Hexapods (insects)
 Trilobites are a highly diverse and geographically
dispersed species with new species of fossil specimens
discovered every year
Trilobite Fossil
Distribution

Evolutionary History of
Trilobites

 Trilobites first appeared in the Early Cambrian.
 The height of their diversity occurred in the early
Paleozoic.
 Adaptive radiations occurred in the Ordovician,
Silurian, and Devonian periods.
 After the Devonian mass extinction, only two
families in one single order of trilobites remained.
 At the Permassian-Triassic mass extinction event, no
trilobites were left.
Patterns of Marine Animal Diversification
Raup & Sepkoski, Science 1982

Trilobite Diversity
Treatise of Invertebrate Paleontology (1997) figure p. 269 modified, S. Gonn website www. trilobites.info
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Ecospace Coding

 Ecospace coding for trilobites and other groups is
based upon three ecological areas of interest:
 Tiering: where in the ocean did they live?
 Motility: did they move and if so, how freely were
they able to move?
 Feeding Mechanism: how did they get their nutrition?
Tiering

 1. Pelagic (out in the water column)
 2. Erect (benthic, extending into water mass)
 3. surficial (benthic, not extending upward)
 4. Semi-infaunal (partly infaunal, partly exposed)
 5. Living in the top ~5 cm of sediment
 6. Living more than ~5 cm deep in sediment
Tiering
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Motility
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 1. Freely, fast moving (regularly moving, unencumbered)
 2. Freely, slow (as above but with strong bond to substrate)
 3. Facultative, unattached (moving only when necessary,
free-lying)
 4. Facultative, attached (moving only when necessary,
attached)
 5. Non-motile, unattached (not capable of movement, freelying)
 6. Non-motile, attached (not capable of movement, attached)
Feeding Mechanism

 1. Suspension (capturing food particles from the water)
 2. Surface deposit (capturing loose particles from a
substrate)
 3. Mining (recovering buried food)
 4. Grazing (scraping or nibbling food from a substrate)
 5. Predatory (capturing prey capable of resistance)
 6. Other (photo- or chemo- symbiosis, parasites)
Ecospace Coding

 Sea Star (echinoderm)
 Tiering: 4
 Movement: 2
 Nutrition: 5
Ecospace CubeTemplate

Ecospace Cubes

Ecospace vs. Niche
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Niche
Ecospace
 The range of conditions and
resources within which
individuals of a species can
persist
 Is specific to each
individual species
 Competition and predation
restrict the distribution of a
species across its
fundamental niche
resulting in a species’
realized niche
 A more general way of
looking at species
specialization and
interaction within a
community
 Unlike niches, more than
one type of organism can
inhabit the same
ecospace
More on Niches

 For higher diversity in a community, there must be less
competition between species
 How?
 Greater resources available
 Reduced resource demand (general predation)
 Intensified predation of a species subset (camoflauge in
moth population)
 Greater inter- and/or intraspecial ecological specialization
of organisms
 Morphology (species diversity) can be used as an
indicator of niche diversity (Structure Function)
Trilobite Fossils

 Trilobite easily fossilized
due to their easily
preserved exoskeletons
 Soft parts such as eyes
can also be found due to
the nature of the materials
that surround the fossils
 Trace fossils can be either
resting or sediment
furrows:
 Hard fossils indicate
protection, hunting,
resting
 Furrows in sediment
suggest movement
 Trilobite fossils can be
used as index (aka
guide, zone, or
indicator) fossils to
determine the age of
surrounding rocks
 Geologists and oil
companies in particular
use this process known
as biostratigraphy
The Paleozoic Era

 The Paleozoic Era consists of 6 time periods:
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Cambrian ~541-485 mya
Ordovician ~485-443 mya
Silurian
Devonian
Carboniferous
Permian ~298-252 mya
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The Geologic Clock

Geologic
time
periods
Anatomy of a Trilobite

 Trilobites are
arthropods and have
 segmented bodies,
 An exoskeleton
 Jointed appendages
 In addition, trilobites
have complex and
diverse eyes and a
variety of mouthparts
known as hypostomes
Trilobite Feeding

 Trilobites used their
hypostomes to prepare
food for digestion.
 Conterminant
hypostomes are firmly
attached to the body
and allowed for the
digestion of a different
type of prey than
natant hypostomes,
which did not have
extra reinforcement for
crushing moving prey
Extension: Body Size Data

 All trilobite body size
 Body size in organisms is
a biologically important
data set
 The study of allometry
relates body size to other
biological significant
factors such as:

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Body shape
Anatomy
Physiology
Metabolism
Behavior
data is included on the
original spreadsheet (see
Attachment #7).
 By sharing the
spreadsheet with students
electronically, students
can reorganize data to
create graphs for a variety
of data groupings:
 body size vs. ecospace
designation
 ecospace designation
throughout various
geologic time periods