Lesson Description

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La Brea Tar Pits
Your name: Abigail Curtis
Grade Level: 9-12
Subject(s): Biology, AP Biology
Summary:
Students explored several topics relating to the Rancho La Brea Tar Pits. The Rancho La Brea
Tar Pits are a unique fossil site because they are situated in the middle of Los Angeles, whereas
most fossil locations are in remote locations. The Rancho La Brea Tar Pits provide a glimpse of
Ice Age Los Angeles from 10,000-40,000 years ago. They are also unique for the overabundance
of large, predatory animals including sabertooth cats and dire wolves found there. Students
examined the taphonomy (how this fossil assemblage accumulated) of the Tar Pits by examining
real bones to determine the age distributions of animals found in the asphalt, frequency of
pathologies, and how fossils accumulated at the tar pits. They also explored how paleontologists
are able to determine behavior or extinct species by examining data collected from specimens at
the Tar Pits.
Time Required: 1, 50 minute class period
Group Size: 6 groups of 6 students (36 Students total)
Cost to implement: No Cost
Learning Goals:
After this lessons students should be able to:
1. Recognize how the Rancho La Brea Tar Pits are a unique fossil assemblage, and that they
contain a record of the Los Angeles environment and species that lived in Los Angeles
10,000-40,000 years ago.
2. Distinguish bones of adult versus juvenile animals, and understand what the relative
frequency of different age groups tells scientists about how fossil assemblages
accumulate (i.e. if we observe a lot of old and very young individuals, the fossil
assemblage might represent a location that attracted inexperienced or elderly individuals
that were less successful at hunting versus if we observed mostly individuals of prime
age).
3. Identify pathologies on bones and understand what the relative frequency of injured/sick
individuals to healthy individuals indicates about how the species ended up at this site.
Students will also understand how presence of healed or long-term pathologies indicates
social behavior (i.e. healed injuries often indicate that an animal was a part of a social
group that allowed it to gain access to food while it healed)
4. Interpret patterns shown in graphs of data taken from Tar Pits Specimens and form
hypotheses to explain these patterns.
5. Discuss and evaluate which hypotheses are more likely given the data and how to further
investigate them.
Level of Inquiry:
Students were engaged in guided inquiry throughout this lesson. They made their own
observations from fossils and interpreted what they found. Students also examined graphs of data
collected from the Tar Pits. They interpreted these data and came up with hypotheses to explain
the data they were shown within their groups. Each group shared their hypotheses and as a class,
we discussed which hypotheses were the best supported and how they could be further
investigated.
Introduction / Motivation:
I polled the students to see how many have been to the tar pits and asked them what they knew
about it. I then gave a brief introduction to the Tar Pits and the major species found there.
Lesson Background Concepts for Teachers:
Scientists gain a lot of important knowledge about what ancient ecosystems and
organisms were like over the history of our planet by examining fossil assemblages. It is also
important to understand how a fossil assemblage formed so that one is making correct
interpretations of species interactions and behaviors. The Rancho La Brea Tar Pits are unique for
their overabundance of mammalian carnivores, which are usually rare in ecosystems (think about
the relative numbers of elk to wolves in Yellowstone National Park). Why are there so many
carnivores in the Tar Pits? Was the ecosystem drastically different 10,000-40,000 years ago in
Los Angeles than they are today? The best supported hypothesis for how the Tar Pits fossils
accumulated is that a large herbivore would become mired in the asphalt, would call for help
from its herd, which was essentially a dinner bell for the large social carnivores in the area who
also became mired in the asphalt. This explains the overabundance of carnivores relative to
herbivores, and is supported by experiments in modern ecosystems (Carbone, et al. 2009).
One of the most exciting aspects of paleontology is trying to reconstruct how extinct
animals behaved in their environments. Evidence, such as healed or chronic injuries or diseases
can indicate that an organism lived in a group that allowed it to gain access to food while it was
too weak to feed independently. Also, by examining what species are most commonly found at
the Tar Pits and comparing them with modern analogues, it is possible to predict which species
were animals were social versus solitary. This is what allowed scientists to conclude that
sabertooth cats were social animals (Carbone, et al. 2009), even though there is only one living
species of cat that is considered social (lions).
Procedure:
1. Students will be introduced to basic information about the Tar Pits and share what they
know about them.
2. Students will then examine bones from the Tar Pits to try to identify the age (juvenile vs.
adult) of specimens, and discuss implications of understanding age structure in a fossil
assembly.
3. Students will discuss modern ecosystems and the proportions of predators and prey and
apply this knowledge to the fossil record. They will try to explain the unusually high
proportion of predator specimens found at the RLB Tar Pits.
4. Students will examine specimens for pathologies and discuss what different types of
pathologies signify (i.e. social behavior)
5. Students will look at the numbers of individual carnivore species at the RLB Tarpits and
compare them with data from the African Savannah to test whether sabertooth cats were
solitary or social.
6. Students will look at RLB fossils for post-mortem features, such as weathering, water
damage, rodent gnaw marks, fragmentation, etc. This has implications for how long
bones sat on the surface before they were buried in the asphalt.
7. Wrap-up to review what students learned and open time to look at fossils they didn’t get a
chance to see fossils that aren’t at their table and some extra fragile specimens I am
bringing in.
Materials List
Each pair of students will need:
 One fossil or image of a fossil
 One laptop to access google docs form, or printed form to fill out by hand
Safety Issues:
 If students are working with real fossils, they need to be instructed on how to
properly handle them.
Lesson Closure:
As a class, we reviewed what students discovered in class and took time for them to ask
questions and observe specimens they didn’t get to see.
Assessment:
Throughout the lesson, I used a “Think, Pair, Share” model, where I posed questions to the
students; they discussed it with a partner/group, and then shared their ideas with the class. We
then discussed the students’ ideas together as a class. Students also entered their observations
from real bones into a google docs form, which could be reviewed after the lesson.
References:
RLB Tar Pits: tarpits.org
RLB and African Carnivore Data: Carbone, C. et al. 2009. Parallels between playbacks and
Pleistocene tar seeps suggest sociality in an extinct sabertooth cat, Smilodon. Biology Letters. 5,
81-85.
Attachments:
Lesson Powerpoint: Winter Lesson.pptx
Google Docs Form: Tar Pit Lesson Form.docx
List CA Science Standards addressed:
8. Evolution is the result of genetic changes that occur in constantly changing environ- ments. As
a basis for understanding this concept:
a. Students know how to analyze fossil evidence with regard to biological diversity, episodic
speciation, and mass extinction
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