TThe Fossil Field Trip: December 2011
Objectives:
Students will know how to properly collect, and classify fossils. 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.
TEKs Addressed:
(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.
The Paleozoic: Paleozoic
rocks are well represented in Texas. Within the legend,
Paleozoic rocks would be 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. You will find shales at the outcrop below the Lake Worth Dam where we will be on Tuesday.
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 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 Lake Worth Dam: From the parking lot all the way down to the dam, gullies, paths, and washes, all are littered
or stuffed with Cretaceous fossils. The large AMMONITES are the big draw. Going down further, heart urchins,
Hemiaster whitei (see below), are abundant in the white chalk... There are easy pickings all the way down (the formation
is 114 feet thick at this point) and once you reach the dam the oysters (Devils Toes are in layers 3 feet thick) are
abundant. You will find many fossils if you know what to look for:
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. Also, 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 at least 4 fossils, however, if you collect more, you may have to either expand your table, or
select your favorite four, donating others you find to students who were perhaps not as lucky.
Fossil A
Fossil B
Fossil C
Fossil D
Description of location
(Qualitative data about fossil
location)
Description of fossil
(Qualitative data about fossil)
Quantitative Data:
Dimensions of Fossil
L x W x H (cm)
Quantitative Data:
Mass of Fossil
Grams
Detailed Sketch of fossil
Classification of fossil
(Look in fossil guide, and find
best likeness)
Time Period
(according to fossil guide book)
Type of fossil
(Zoolith; Phytofossil;
ichnofossil…etc)
Type of fossilization
(How was this fossil likely
formed?)
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.
a.
b.
c.
d.
3. Describe the process used to extract the fossils from the rock matrix they were embedded within.
4. Using the fossils you found, explain what other organisms may have been abundant in the area.
5. Were the fossilized organisms you found predators, prey, or plants? How do you know?
6. Tell about your favorite part, and least favorite part of the fossil expedition.
7. Could you classify any of your fossils as transitional? Why?
7. 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.