The Fossil Field Trip: December 2012
Objectives:
Students will know how to properly collect, classify, and prepare fossils for display. Students will determine if their
collected specimens are index fossils, use qualitative and quantitative data to describe their fossils, and determine in what
time period the organisms that formed their fossils lived, using a field guide.
Building a collection:
The fossils you collect in the field are for the most part, common, and could potentially even be found in your yards. There are
certain fossils you can expect to find, such as fossil oyster shells, brachiopods, echinoids, ammonites, and many mollusks. There
are certain fossils you will not find, either, because the area where you will be excavating Friday was a shallow ocean during the
Cretaceous Period. You would not expect to find any trilobites there, because trilobites were long extinct by then.
It’s important that you write a label for each fossil you find, saying:
where you found it
when you found it
what type of rock you think you found it in
what you think it is
TEKs Addressed:
(7) Earth in space and time. The student knows that scientific dating methods of fossils and rock sequences are
used to construct a chronology of Earth's history expressed in the geologic time scale. The student is expected to:
(a) evaluate relative dating methods using original horizontality, rock superposition, lateral continuity,
cross-cutting relationships, unconformities, index fossils, and biozones based on fossil succession to
determine chronological order;
(8) Earth in space and time. The student knows that fossils provide evidence for geological and biological
evolution. Students are expected to:
(a) analyze and evaluate a variety of fossil types such as transitional fossils, proposed transitional
fossils, fossil lineages, and significant fossil deposits with regard to their appearance, completeness, and
alignment with scientific explanations in light of this fossil data;

Body Fossils (zooliths and phytofossils) and processes:
o
Zooliths, Phytofossils, mummies, Carbonization, Amber entombment, Permineralization,
Petrification, Remineralization (dissolution/replacement)

Indirect Fossils; Ichnofossils
o
Molds and casts, Tracks & burrows, gastroliths, coprolites
(b) explain how sedimentation, fossilization, and speciation affect the degree of completeness of the fossil record

Students will know conditions that favor fossilization, and how to interpret past environmental data based
upon fossil evidence
Pre-Lab Background Information
Quaternary
Tertiary
Cretaceous
Jurassic
Triassic
Permian
Carboniferous
Devonian
Silurian
Ordovician
Cambrian
Precambrian
Geologic Time in Texas
The Precambrian: Precambrian rocks can be seen today in the area commonly referred to as the Llano Uplift of
central Texas and in far western Texas. Fossils are rare to non-existent in these metamorphic and igneous rocks. See
if you can locate it using the legend above as your guide. It is in the central region of Texas, and is orange in color.
The Paleozoic: As you can see in the legend, Paleozoic rocks are well represented in Texas. Paleozoic rocks are
represented by the Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian Periods. The presence of
Cambrian sandstones indicates that sediments were brought into the sea from land areas to the northwest of the state.
The limy sediments (which have a great amount of calcium oxides…CaO) deposited farther out to sea preserved the
remains of trilobites, brachiopods, bivalves, sponges, and other invertebrates.
This deposition of limy sediments continued through the Silurian and Devonian; however, fossils are rare in the Silurian
rocks and most Texas Devonian rocks are subsurface and can only be seen in drill cores, which are columns of material
removed from the Earth’s depths by drilling. Rocks of the Early Carboniferous are not exposed at the surface in Texas,
while rocks of the Late Carboniferous are well exposed in north-central Texas, and fossils are quite common in these
outcrops. Try to locate these late Carboniferous outcrops on the map.
During the Permian, north-central Texas was an area of changing environments, where shallow marine waters gave way
to lowland coastal areas. Extensive Permian salt and gypsum deposits indicate that evaporation rates were high, and the
red beds in this region contain an abundant vertebrate fossil record. An ancient reef system preserved in the Guadalupe
Mountains of far western Texas is evidence that the sea still covered that part of the state. These rocks are rich in
marine invertebrate fossils as well as rare vertebrate fossils, primarily sharks. Try to find these Permian outcrops on
your map, to determine where these rare fossils may be found.
The Mesozoic: Mesozoic rocks are common in several parts of Texas. The Mesozoic Era is represented by three
Periods, the Triassic (earliest), Jurassic (Middle) and Cretaceous (latest). Triassic sands and shales were deposited as
part of a large river system. These rocks contain a well-documented vertebrate fossil record that includes numerous
reptiles and amphibians. These shales, however, are rich in marine fossils, not terrestrial. Rocks of the Jurassic Period
are virtually absent at the surface in Texas, but can be seen in a few small exposures in far western Texas and in
subsurface drill cores. The Cretaceous was a time of fluctuating sea levels in the state. The shoreline shifted back and
forth many times, leaving behind a record of both marine and non-marine environments. These rocks contain a rich fossil
record including dinosaurs, other reptiles, amphibians, birds, fish, and mammals. As you can see from the map, the area
where we live and will be going on our fieldtrip has largely Cretaceous rocks at the surface, and should then contain
Cretaceous fossils.
The Cenozoic: The Cenozoic Era is represented in Texas with the two Periods of the Tertiary (earliest) and Quaternary
(latest…current). During the Tertiary, extensive volcanic activity poured lavas across the landscape in far western
Texas; however, much of the modern High Plains and Texas Coastal Plains are covered by rocks formed from sediment
washed down from the rising Rocky Mountains to the northwest. These sedimentary rocks contain a rich vertebrate
fossil record, including a large assortment of fossil mammals. There is a wide band of Quaternary deposits along the
modern Gulf Coast and in several places in west Texas. Fossils found in these deposits include bones of bison,
mammoths, and mastodons.
At The Outdoor Learning Center in Justin: There are two areas of focus at the OLC in Justin. Area “A” is the wash,
and is located on steep incline area that can be treacherous, so caution is advised. It is an area where seasonal rainfall
has formed a gully which has eroded deeply into the strata of this region. You will be picking through this area, studying
the various strata, and looking for fossils of many types. Some of the more common fossils found in this area include:
(L-R) AMMONITES, ECHINOIDS, and OYSTERS (aka Devil’s Toenails). You
will find many fossils if you know what to look for:
Area “B” is the area down in the Denton Creek bed (which will be dry at this time). While there are
areas of standing water, for the most part, you will have no trouble traversing the dry creek area,
scouring for fossils of all kinds. You will find similar fossils to the ones excavated in the wash. Caution
around the creek-cut edges, as rocks may fall from the sides without warning. You must also watch for
snakes. There are several varieties of venomous and non-venomous snakes at the OLC.
In your journals, create a data table similar to the one below that can contain all your fossil
information that you collect while you’re on this fieldtrip. Please note…this data table should take an
ENTIRE page in your journal, so this example is not to scale. Some of the data will be collected in the
field, and some will be collected in the classroom when we return. The goal is for each student to find
and document at least 4 fossils (two from site A, and two from site B), however, you may only KEEP
two of your favorites to take home to the classroom. If you are extremely adept at locating fossils,
and one of your teammates is not, you may donate fossil finds to them. Be prepared to take plenty of
photographic evidence of the regions, to help you answer your analysis questions. Be mindful of each
of the following, and plan on taking pictures:
 Superposition
 Unconformities
 Cross-cutting relationship
 Inclusions
Fossil A
Description of location
(Qualitative data about fossil
location) Photographic evidence
will earn extra points! Use your
phones, and email me the
photos!
Description of fossil
(Qualitative data about fossil)
Photographic evidence will earn
extra points! Use your phones,
and email me the photos!
Quantitative Data:
Dimensions of Fossil
L x W x H (cm)
Quantitative Data:
Mass of Fossil
Grams
Quantitative Data:
Density of Fossil in g/mL
Detailed Sketch of fossil
Classification of fossil
(Look in fossil guide, or online,
and find best likeness) Done
upon return to classroom
Time Period
(according to fossil guide book
or internet site) Done upon
return to classroom
Type of fossil
(Zoolith; Phytofossil;
ichnofossil…etc) Done upon
return to classroom
Type of fossilization
(How was this fossil likely
formed?) Done upon return to
classroom
Fossil B
Fossil C
Fossil D
Analysis Questions:
1. Compare (similarities) and contrast (differences) this fossil expedition to the expedition we took outside
the school.
2. Judging from the qualitative data collected at the site where each fossil was found, describe the probable
landscape when each of your fossils was forming.
3. While at the Outdoor Learning Center, either at the wash, or in the creek bed, did you see any evidence
of disruption of sedimentary layers that could have been caused by an unconformity?
4. What evidence was there (if present) of a cross-cutting relationship, or inclusions?
5. Using the fossils you found, explain what other organisms may have been abundant in the area.
6. Were the fossilized organisms you found predators, prey, or plants? How do you know?
7. Tell about your favorite part, and least favorite part of the fossil expedition.
8. Could you classify any of your fossils as transitional? Why?
9. If you were to help me plan this expedition next year, what would you suggest to make the experience
even better?
Don’t forget your error analysis and reflection BEFORE you hand in your lab.