Learning from the Fossil Record
Grade 8 Science
Name:
Date:
Part1 of Performance Assessment Task
In analyzing other features around the fossils in each layer, the scientists were able to identify
some key features that struck them as interesting. They have sent you a description of the
environment that existed at each level, based on the features they found in each layer.
Deepest fossil layer: all
short skull and jaw
Long, skinny tail
Long front legs
Long back legs
No flukes on the tail
Next fossil layer:
some
short skull and jaw
Long, skinny tail
Long front legs
Long back legs
No flukes on the tail
Next fossil layer:
all
Long skull and jaw
Short, fat tail
Front flippers
Short back legs
Flukes on the tail
Next fossil layer:
all
Long skull and jaw
Short, fat tail
Front flippers
No back legs
Flukes on tail
Environmental Evidence:
mostly medium trees
some smaller shrubs
many small creeks
some
Environmental Evidence:
long skull and jaw
taller grasses
short, fat tail
small shrubs
short front legs
swampy
long back legs
no flukes on the tail
Environmental Evidence:
taller grasses
shallow ponds
swampy
Environmental Evidence:
larger, deep lakes
many aquatic plants
By studying present day animals with similar traits, they have inferred that:
1. Long skull and jaw are dominant over short skull and jaw
2. Short thick tail are dominant over long skinny tail
3. Long front legs is dominant over short front legs
4. Long back legs is dominant over short back legs
5. No flukes on tail is dominant over flukes on tail
They do know all of these fossils are related as the area was isolated and no other animals
could come in or go out of the area.
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Learning from the Fossil Record
Grade 8 Science
Name:
Date:
They ask that you add notes to your original report of your findings on the possible genetics and
inheritance of these traits.
Please include, in a new color, the following in your report.
1. Explanations for why the organisms’ features changed from one layer to the next.
Include specifics for each trait that changed.
2. More detailed explanations for those changes that occurred for reasons other than
inheritance.
Each answer will be scored on the following aspects:
a. Does the reasoning behind the answer make sense and is it possible? 0 1 2 3
b. Is the report organized in a logical manner so the reader can understand the explanations
provided? 0 1 2 3
1. Since long skull and jaw are dominant over short skull and jaw, since all the organisms in the
deepest fossil layer have short skulls and jaws, they must be homozygous recessive (tt), for
short skull and jaw. In the next fossil layer, there were some organisms with short skulls and
jaws and some with long skulls and jaws. The ones with short skulls and jaws were offspring
of the organisms in the deepest fossil layer. ( tt x tt = all tt offspring ) The ones with long
skulls resulted from a gene mutation which called for elongated skulls and jaws. In the next
fossil layer, all the organisms had the dominant long skull and jaw trait. This probably came
about because of the mutation being advantageous in the environment—the environment
had changes from short grasses and shrubs to longer grasses and large brushes, so the long
skull-and-jawed animals could reach through the tall grasses and eat prey faster. In the final
fossil layer, all the organisms had the dominant long skull and jaw trait again. This had to
come about due to the Tt x Tt cross resulting ion 75 % having the dominant trait (long skull
and jaw) and 25% recessive trait (short skull and jaw). For some reason the short skull and
jaw organisms could not survive beyond birth (probably because of the fact that the creatures
with the long skulls and jaws get all the food and all the ones with short jaws don’t get any
food) leaving only the dominant organism (TT or Tt) to live to adulthood and continue
breeding. Eventually all organisms would end up with TT only, since the chance of having t
became inferior because they could not survive beyond birth.
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Learning from the Fossil Record
Grade 8 Science
Name:
Date:
2. -In the first fossil layer, all of the organisms had long and skinny tails. This was because all of
the organisms had the ss genotype, homozygous recessive.
-In the next fossil layer, both the long and skinny tails AND the short and thick tails came into
existence. This means that both the ss and Ss/SS genotypes were present. The ss genotype
was present because the creatures mated and had children with ss genotypes, which should
be the only possible combination. For the short tails to exist, a mutation occurred which
changed the tail from long to short in some of the organisms.
-In the next fossil layer, the animals all had short, thick tails. This means that only the SS/Ss
genotypes existed anymore. This was caused by the long-tailed organisms finding some
change in the environment which caused long, dragging tails to be a disadvantage. This was
probably because of the longer grasses and shrubs, which would make it easier for predators
to snatch their tails and kill them. So now only the short-tailed animals were alive because of
their random advantage.
-In the final layer, all of the animals again had short, thick. While this means that, yet again,
the only genotypes were SS/Ss. Now, all physical characteristics of the creature point towards
it being a water-based creature. The short tail probably stuck around now, despite the
possibility of it mutating away (because the animals no longer had to deal with the grasses)
because the longer tail would be much more movement-resisting through water than a short
tail. So if a long-tail mutation came up it must have died right away.
3. In the first fossil layer, all of the organisms have long front legs. Since long front legs are
dominant over short front legs, the genotypes are all either LL or Ll.
-In the next fossil layer, the organisms have both long AND short front legs. As short front legs
is the recessive trait, it is possible if two heterozygous long legged creatures mated and had a
short legged child, having given said child both their recessive genes. So up to this point all
three genotypes (LL, Ll, and ll) are all probably present.
-In the next fossil layer, all of the creatures end up developing flippers in place of front legs.
These flippers developed because of a gene mutation which allowed the creatures use of the
small ponds that were popping up in the environment. The creatures that had NOT gotten
flippers, the ones who still had legs, were dead because they were not able to survive as
effectively with all the water around.
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Learning from the Fossil Record
Grade 8 Science
Name:
Date:
-In the last fossil layer, the creatures all also have front flippers. This is now because the only
gene available is the gene of flippers and because any other creatures that had mutated back
to actual legs in front died right away and were not able to keep the new mutation going.
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