For instructor use only:
Species
Order
Acidiphorus
Proetida
Agonstus
Agnostida
Arctinurus
Lichida
Aulacopleura
Proetida
Balcoracania
Redlichida
Bathyurus
Proetida
Condylopyge
Agnostida
Cornuproetus
Proetida
Cyphaspis
Proetida
Cyphoproetus
Proetida
Damesella
Lichida
Dicranopeltis
Lichida
Fallotaspis
Redlichida
Kettneraspis
Lichida
Olenelloides
Redlichida
Olenellus
Redlichida
Paedeumias
Redlichida
Pagetia
Agnostida
Paradoxides
Redlichida
Phaetonellus
Proetida
Phillipsia
Proetida
Platyantyx
Redlichia
Selenopeltis
Tsunyidiscus
Unidentified trilobite
found in drawer
Yunnanocephalus
Unidentified trilobite
found in drawer
Proetida
Redlichida
Lichida
Agnostida
Time
Middle Ordovician
Middle Ordovician
Middle Ordovician
Upper Silurian
Middle Cambrian
Lower Ordovician
Upper Ordovician
Devonian
Lower Silurian
Permian
Lower Silurian
Upper Cambrian
Lower Cambrian
Upper Silurian
Middle Cambrian
Middle Cambrian
Middle Cambrian
Upper Cambrian
Middle Cambrian
Upper Ordovician
Upper
Carboniferous
Lower Silurian
Lower Cambrian
Upper Silurian
Lower Ordovician
Ptychopariida
Upper Cambrian
Other Information
Pennsylvanian
Ptychopariida
ancestral to
Proetida???
Developed by BJ Shaw and TC Lindsay from the following websites:
1.
This lab exercise is modeled after one developed by The Biology Corner
Retrieved from the internet 2 October 2005: http://www.biologycorner.com/worksheets/fossilrecord.html
2. Amazing site on Trilobites by Dr. Sam Gon III
Retrieved from the internet 7 April 2006:
http://www.trilobites.info/index.html
3. Drawings of the relative and absolute dating borrowed from University of California Berkeley
Retrieved from the internet 10 April 2006
http://evolution.berkeley.edu/evosite/lines/IIIdistribution.shtml
4. Plate tectonic maps (Cambrian, Silurian, and Permian modified for printing clarity) by C. R. Scotese,
PALEOMAP Project, (www.scotese.com)
Retrieved from the internet 24 April 2006
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For instructor use only:
For
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Examining the Trilobite Fossil Record
Objectives:
Students will
 produce a to-scale time converted to distance model of the
Paleozoic
 analyze characteristics of fossil Trilobites
 compare placement of fossils and determine relative ages
 develop a model evolutionary tree based on the morphology and
age of fossils
Background:
Fossils
Fossils are the remains or traces of organisms that lived in the past. When scientists find fossils,
they carefully note where the fossils are located, both on Earth (i.e. Burgess Shale, British
Columbia, Canada) and stata or layer of earth, for analysis of the age of the fossil.
A geologic concept called superposition states that the layers of earth at the surface are younger
than layers of earth below. For example, in the Grand Canyon, the rock that is the oldest is down
by the river, and the youngest, most recent rock is located at the top of the canyon.
Ages and Dating
Absolute age is determined
though radiometric dating
and determining the layer of
rock in which the fossil was
found, and can have a rather
small margin of error for the
exact age. An example would
be the K-T boundary, which
ended the dinosaur reign 63.9
to 65.4 million years ago
(MYA). That is a 1.5 million
year or 2.3% margin of error.
younger
Dating of
volcanic ash
older
Relative Dating
Relative age cannot determine exactly how old a fossil is, but
instead can give a range in which this fossil lived. For
example, we find a fossil between two layers that have been
radiometric dated 13.6 and 33.8 MYA. We can state with
assurance that this fossil’s age is between 13.6 and 33.8
million years old.
The age and morphologies (shapes and forms) of fossils can
be used to place fossils in sequences that often show patterns of changes that have occurred over
time. This relationship can be depicted in either a cladogram or an evolutionary tree (also known
as a phylogenetic tree).
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Gradualism and Punctuated Equilibrium
There are two major hypotheses on how evolution takes place (and both hypotheses are accepted
to explain the two different observations made in the fossil record – in other words, they are not
mutually exclusive): gradualism and punctuated equilibrium. Gradualism suggests that
organisms evolve through a process of slow and constant change. For instance, an organism that
shows a fossil record of gradually increased size in small steps, or an organism that shows a
gradual loss of a structure. Punctuated equilibrium suggests that species evolve very rapidly and
then stay the same for a large period of time. This rapid change is attributed to a mutation in a
few essential genes. The sudden appearance of new structures could be explained by punctuated
equilibrium.
Gradualism: organism’s body segments shorten and fuse.
Punctuated equilibrium: organism head shape changes, then loss of body segment.
Speciation
The fossil record cannot accurately determine when one species becomes another species.
However, two hypotheses regarding speciation also exist. Phyletic speciation suggests that
abrupt mutations in a few regulatory genes occur after a species has existed for a long period of
time. This mutation results in the entire species shifting to a new species. Phyletic speciation
would also relate to the Punctuated Equilibrium hypothesis regarding evolution. Divergent
speciation suggests that a gradual accumulation of small genetic changes results in subpopulation
of a species that eventually accumulate so many changes that the subpopulations become
different species. This hypothesis would coincide with the gradualism model of evolution. Most
evolutionary biologists accept that a combination of the two models has affected the evolution of
species over time.
Phyletic Speciation:
Species A
Species B
Species C
Species A
Divergent Speciation:
Species A
Species A
Trilobites:
Introduction
Trilobites are Class Trilobita in the Phylum Arthropoda, together with insects, spiders,
centipedes, millipedes, crustaceans, and some lesser known animals. Trilobites are first found in
542 million year old rocks of the lower Cambrian. They are well preserved because they had
calcified exoskeletons. They increased in numbers of species through the Ordovician (488-444
MYA) to 46 Families. The number of Families suddenly dropped at the end of the Ordovician,
and in the Sulurian, only 13 Families remained. By the Permian (299-251 MYA) only 2
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Families remained when they entirely went extinct at the Permo-Triassic Boundary. These
remarkable animals diversified into 5000 genera, and over 15,000 described species. Trilobites
survived for about 300 million years. Not bad, especially compared to humanoid’s appearance a
paltry 6-7 million years, and Homo sapiens appearance less than 1 million years ago.
Evolutionary Trends in Trilobites
Reduced Segment
Thoracocare
Elongate Form
Crotalocephalina
Plesiomorphic Form
Redlichia
Increased Segments
Balcoracania
Transverse Form
Harpillaenus
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Morphology in Trilobites
The name "trilobite"
(meaning "three-lobed")
is not based on the body
sections cephalon, thorax
and pygidium, but rather
on the three longitudinal
lobes: a central axial lobe,
and two symmetrical
pleural lobes that flank
the axis.
The trilobite body is divided into
three major sections, a cephalon
with eyes, mouthparts and sensory
organs such as antennae, a thorax
of multiple similar segments (that
allowed some species to roll into a
defensive ball), and a pygidium,
or tail section.
Rostral
plate
Anterior branch of
the facial suture
Rostral
suture
Connective
suture
Cephalic
doublure
Hypostome
Postenor
branch of the
facial suture
Pleural
doublure
Pygidial
doublure
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Pagetiidae
ORDER AGNOSTIDA
Pagetia
Introduction: Small
trilobites (usually only a
few mm long) with
cephalon and pygidium
strongly similar in outline
and size.
Cephalon: cephalic shield
with deeply parabolic
outline, maximum width
usually anterior of genal
angle, border convex;
glabella fusiform, widest
at base, glabellar
segmentation highly
variable, sometimes
complex, but in some species entirely effaced; most species eyeless; sometimes specialized with
ribbon-like wings; rostral plate lacking.
Thorax: segments 2 (Agnostina) or 3 (some Eodiscina), axis typically broad.
Pygidium: strongly matching cephalic margin.
Occurrence: Lower Cambrian to Upper Ordovician.
ORDER LICHIDA
Introduction: typically spiny
with densely granulate or
tuberculate exoskeletons.
Cephalon: glabella broad, large,
extending to anterior border,
lobation simple
(Odontopleuroidea) to complex,
with fused lateral and glabellar
lobes (Lichoidea); eyes typically
present.
Thorax: variable, 8-13 segments,
usually spine-tipped, sometimes
with distinctive spines (e.g.,
Odontopleuroidea).
Pygidium: typically isopygous to
macropygous, but sometimes
short (e.g., Odontopleuroidea),
often longer than wide, often with 3 pairs of furrowed pleurae, typically ending in spinose tips.
Occurrence: Middle Cambrian to Upper Devonian
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ORDER PROETIDA
Introduction: typically small
trilobites, exoskeleton sometimes
with pits or small tubercles. The last of
the trilobites was of this order
(Phillipsiidae).
Cephalon: opisthoparian sutures;
glabella large, vaulted, well-defined,
typically narrowing forwards, typically
4 pairs of glabellar furrows with
posterior-most pair longest and deepest,
those anterior shorter and fainter;
eyes, usually present, holochroal,
often large, convex; rostral plate
narrow and backward tapering; long
hypostome; typically with genal spines.
Thorax: 8 – 22 (typically 10) segments, tips
variable, blunt to long-spined.
Pygidium: micropygous to subisopygous, often spineless, and usually with 4 – 10+ distinct
pleural furrows.
Occurrence: Lower Ordovician to Upper Permian
ORDER REDLICHIIDA
Introduction: Primitive trilobites with
numerous thoracic segments with spinose tips.
Cephalon: large and semicircular; glabella
typically long, well-segmented, tapering or
expanding forwards; genal spines typically
present, strong, usually continued from a
narrow, tubular cephalic border; eyes typically
large, crescentic, with large, inflated palpebral
lobe ridges running toward front of glabella
(anterior of S3); eye ridge may be subdivided;
hypostome typically conterminant, usually very
wide rostral plate present.
Thorax: with numerous segments (up to 60+),
pleurae usually with spinose tips; may be
subdivided into prothorax and opisthothorax.
Pygidium: typically tiny (micropygous), one or very few segments.
Occurrence: Cambrian
Materials (per team of 2-4 students):
Butcher paper cut into 1.5 m segments
Color pencils
Black marker
Meter stick
Tape or glue stick
Copy of lab
Scissors
Masking tape
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Procedure:
We are going to examine the phylogenetic relationships of selected species from 4 (out of 9
total) orders of trilobites. As a class, discuss trilobites, when they are found, how they are
found, their relationship to extant (living) species, etc. All trilobites are extinct, but during their
existence, they were extremely successful.
1. The diagram you are creating requires a large space. To create your workspace, cut butcher
paper into 1.63 meters (5.5 ft) lengths, one per team. (Note, Upper and Early are
interchangeable terms, as are Lower and Late. One refers to strata and the other time.)
Time Period
Trilobites
(20 cm wide)
(remaining width of paper and 5 cm deep)
Permian
This space is 20.5 cm deep
286 — 245 MYA
Carboniferous Upper
(Pennsylvanian)
320 — 286 MYA
Carboniferous Lower
(Mississippian)
360 — 320 MYA
Devonian Upper
374 — 360 MYA
Devonian Middle
387 — 374 MYA
Devonian Lower
408 — 387 MYA
Silurian Upper
421 — 408 MYA
Silurian Lower
438 — 421 MYA
Ordovician Upper
458 — 438 MYA
Ordovician Middle
478 — 458 MYA
Ordovician Lower
505 — 478 MYA
Cambrian Upper
523 — 505 MYA
Cambrian Middle
540 — 523 MYA
Cambrian Lower
570 — 540 MYA
This space is 17 cm deep
This space is 20 cm deep
This space is 7 cm deep
This space is 6.5 cm deep
This space is 10.5 cm deep
This space is 6.5cm deep
This space is 8.5 cm deep
This space is 10 cm deep
This space is 10 cm deep
This space is 13.5 cm deep
This space is 9 cm deep
This space is 8.5 cm deep
This space is 15 cm deep
2. Use the meter stick to draw the chart on your workspace as depicted above. Each of the time
periods will be a different size depending on the length of time. Each 5mm (½cm) equals 1
million years.
3. The "fossils" you will work with are paper representations of real trilobites. Each trilobite on
your sheet is marked with a time period. Cut out on the border so that the picture trilobite
together with the time period and subdivision.
4. Color the 3 body sections (cephalon, thorax, and pygidium) with different colors and count
the number of segments.
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5. Place the trilobites in the correct time period. Examine and group the trilobites with similar
characteristics (refer to order characteristics on pages 5 – 6. Once all the trilobites have been
placed correctly according to time and morphology, tape or glue the fossils in place.
6. Assume the oldest trilobite is the ancestral form to all other trilobites. Connect the trilobites
with phylogenetic lines of how they may have speciated. This is a model of speciation.
Analysis:
1. Give a brief description of the evolutionary changes that occurred in the organism.
2. During which time period did the fossils differentiate into two or more branches?
3. Explain how the chart illustrates both punctuated equilibrium and gradualism. Use specific
fossils from the chart to support your answer.
4. Making the assumption that each fossil represents a separate species. Explain how the chart
illustrates divergent and phyletic speciation. Use specific fossils from the chart to support
your answer.
5. Define the following terms:
a. morphology
b. fossil
c. phylogenetic tree
6. While working in a museum, you find these two unidentified trilobites. Develop a list of
their characteristics. Where would you place them on your chart and why?
Species 1
Species 2
"Fossils" are on the following page.
Extensions:
 Math – Students complete a to-scale time converted to distance model of geologic time.
What is the percentage of geologic time that was the Hadean, Archean, Proterozoic, and
Phanerozoic (the Eons), and within the Phanerozoic, divide into Paleozoic, Mesozoic,
and Cenozoic (the Eras). The Eras can be further divided into the Periods (for example,
Cambrian, Ordovician, etc.) Periods are further divided into Epochs.
 Math and Science – Students transform 1 million and 1 billion years into other models
(i.e. use a world map and transform 1 million years to 1 mile, or calculate how old
students will be when they are 1 million and 1 billion seconds old)
 Writing – Assign a report about a Phyla or Class from the Paleozoic.
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Acidiphorus
Mid Ordovician
Balcoracania
Mid Cambrian
Cyphaspis
Lower Silurian
Agnostus
Mid-Ordovician
Bathyurus
Lower Ordovician
Cyphoproetus
Permian
Arctinurus
Mid Ordovician
Condylopyge
Lower Ordovician
Damesella
Lower Silurian
Aulacopleura
Upper Silurian
Cornuproetus
Mid Devonian
Dicranopeltis
Upper Cambrian
9
Back Page of Trilobite Pictures
10
Fallotaspis
Lower Cambrian
Paedeumias
Mid Cambrian
Phillipsia
Pennsylvanian
Kettneraspis
Upper Silurian
Pagetia
Upper Cambrian
Platyantyx
Lower Silurian
Olenelloides
Mid Cambrian
Paradoxides
Mid Cambrian
Redlichia
Lower Cambrian
Olenellus
Mid Cambrian
Phaetonellus
Upper Ordovician
Selenopeltis
Upper Silurian
(Upper Carboniferous)
11
Back Page of Trilobite Pictures
12