the Scientia Review

EXPLORING
DINOSAURS
Annabel Consilvio
Nikitha Das
Connor Palatucci
Table of Contents
Evidence of Dinosaur Existence..................................................3
Theories of Extinction...................................................................5
Evolution and Dinosaurs...............................................................7
Geological Time Scale....................................................................9
The Triassic Period........................................................................11
The Jurassic Period........................................................................12
The Cretaceous Period.................................................................13
Dinosaur Classification.................................................................14
Dinosaur Intelligence...................................................................15
Dinosur Behavior..........................................................................16
Dinosaur Life-Span.......................................................................17
Dinosaur Diet................................................................................18
Glossary..........................................................................................20
About the Authors........................................................................23
Image Credits.................................................................................24
2
Evidence of
Dinosaur
EXISTENCE
Fossils are currently the only form of studying these ancient
creatures. While most animals simply decompose after death, some animal
skeletons have been
preserved as fossils.
Fossilization occurs
when an animal is
quickly buried under
sand or mud and
covered by sediments.
The skeleton of
the animal becomes
infused with minerals
that harden the bone
into a rock and the
entire skeleton is encased in a hard sediment covering. Even though fossils
may look like bones, they are actually just rocks in the shape of bones!
The excavation of dinosaur fossils has given paleontologists direct
visual evidence of how dinosaurs looked millions of years ago. Most fossils
are excavated from sedimentary layers of rock. Along with skeletal fossils,
footprint fossils of dinosaurs have also been found. Fossil footprints are a
type of trace fossil, physical evidence of the behavior and activities of an
ancient organism. These fossils also support the theory of evolution. A look at the
fossil record shows that there are developmental changes from one species
to another. Simple organisms come first and are followed by more complex
3
Coprolites
Coprolites
are
pieces of fossilized
dung. Paleontologists
can study the contents
of coprolites to see what
exactly the dinosaur
ate. Some coprolites
consist of leaves, bark,
and roots suggesting
that the animal was
an herbivore. Other
coprolites
consist
of bones suggesting
that the animal was a
carnivore. Some of
the largest dinosaur
coprolites
are
40
centimeters (16 inches)
in diameter.
Evidence of
Dinosaur
EXISTENCE
organisms with modified characteristics.
Fossilized organisms with combined
characteristics of two species have also been
found, suggesting their physical transition.
4
Theories of
Extinction
Currently, there are a few different theories regarding dinosaur
extinction; however, it is necessary to first expel some common myths about
their extinction. To begin with, not all of the dinosaurs became extinct at the
same time. Birds and other modern animals are descendants of dinosaurs,
which implies that the organisms had at least enough time to adapt
before complete extinction.
Extinction can be most
easily explained when you
consider the how creatures
adapt to their environments.
In a process similar to
natural selection, where the
strongest outlive their weaker
counterparts,
dinosaurs
simply evolved to adapt to
their current habitat. This
led to the extinction of
the larger dinosaur species
and the formation of their
descendants like birds.
However,
other
theories besides evolution
are currently being used to
explain the mass extinction
as well. The asteroid theory
is often used to explain this
5
Theories of
Extinction
phenomenon. Dinosaurs were becoming extinct around 65.5 million years
ago, and scientists have found extremely high concentrations of iridium, a
rare metal, in samples that date back to the same time period. This suggests
that something was present on Earth while the dinosaurs were dying that
is not typically there. Because iridium is often found in meteorites and
asteroids, scientists believe that a major asteroid may have collided with the
Earth during this time, leading to the extinction of hundreds of species of
dinosaur.
If
such
an
impressive asteroid did
collide with the Earth,
a massive cloud of dust
and solid particles would
have covered the Earth
for years, blocking the
sunlight and stopping
photosynthesis. This
would lead to an extreme
decline in food for
dinosaurs, which would
invariably cause their
extinction. The asteroid
theory is the most
commonly
accepted
theory among scientists, particularly because it explains the heightened
levels of iridium.
6
Evolution and
DInosaurs
Dinosaurs are clear models of the theory of evolution. The first
dinosaurs are believed to have been small bipeds, weighing about 10 kg (22
Lbs) and measuring about 2 meters in length. These carnivorous creatures
evolved into millions of different species of dinosaurs, and even the birds
that we see in the wild today originally evolved from these organisms.
In order for scientists to study the vast amount of species and their
origins, they rely on phylogeny of dinosaurs. Paleontologists explain
this as a family tree of dinosaurs, where a new branch is added every time
a dinosaur evolves into a new species. These trees help researchers see and
study patterns of evolution.
7
Evolution and
DInosaurs
The most dramatic evolutionary change occurred in the body size of
dinosaurs. Dinosaurs progressed into massive animals that weighed over
50 tons and spanned lengths of 40 meters (131 feet) from the first small
bipeds. There are very few instances in which dinosaurs actually decrease
in size after evolving. They appear to follow “Cope’s Rule,” the theory
that animals tend to get larger, rather than smaller, after evolution.
In addition, some dinosaurs evolved to be herbivores. In these
cases, the dinosaurs developed organs, different from those of their their
carnivorous counterparts, that could easily digest plant matter. Some of
these developments helped in the digestion process, while others, like
blunt teeth, aided in chewing and grinding the food down to smaller pieces.
Dinosaurs also developed from bipeds to quadrupeds. They likely evolved
in this way because of their major increase in size.
8
Geological
Time scale
When you hear about something that happened a long time ago, you
probably hear a date that sounds something like “1500 B.C.E.” That means
that it happened 1500 years “Before the Common Era.” For human history,
counting time in thousands of years is reasonable, but the history of life
on earth spans 3.8 billion years before the present. By the most generous
estimates, human history only goes back 20,000 years. That’s approximately
0.00526%. To put this number into perspective, if you wanted to make a 3
hour movie about the history of life on Earth, all of human history, from
hunting and gathering through ancient Egypt and WWI up to your life
today, would be about half of a second. 9
Geological
Time scale
This is where the geological time scale comes in. Scientists divided
the past into several sections in order to cope with the huge spans of time
that predate us.
Geologists set up a hierarchy of divisions of time. The longest
division is a supereon. Below that are eons, then eras (such as the Archaic
or Paleozoic eras), periods (such as the Jurassic period), Epochs, then
Ages (such as the stone age or bronze age). The size of these divisions
was determined by various geological phenomena such as the time it took
to deposit a certain layer of sediment in a geological feature. For example,
The Jurassic period is named after and defined by a layer of rock strata in
the French Jura Mountains.
Dinosaurs lived in the Mesozoic era, a time span of about 186 million
years. This era has three periods: the Triassic, Jurassic, and Cretaceous (from
oldest to newest). These periods were so long and so long ago that the
continents actually shifted through the process of continental drift (for
more information on continental drift and plate tectonics, see Chapter 2 of
Extreme Science in the Scientia Review).
10
The Triassic
Period
The Triassic period began approximately 252.2 million years ago and
ended 201.3 million years ago. The start of the period is characterized by
the Permian-Triassic extinction event. This extinction, the biggest in the
history of life on Earth, also marks the boundary between the Paleozoic and
Mesozoic eras. Due to this event, 96% of marine species and 70% of land
animals became extinct. Life on Earth drastically changed over the next 10
million year recovery and following Triassic period. There are several theories
as to how such a huge
number of species
became extinct, but
most scientist agree
that it was caused by
some sort of massive
volcanic
event.
The land during
the Triassic period
looked like the image to the right. The Triassic period was hot
and dry; geological evidence
shows that even the poles were
temperate with forests rather
than glaciers. The image to the
left is an artist’s depiction of
Triassic life.
11
The Jurassic
Period
The Jurrasic period marked a golden age for massive reptile herbivores
such as the Stegosaurus and the Diplodocus (which could reach lengths of
30 m). It began with the Triassic-Jurrasic extinction event, and ended with
another minor but poorly understood extinction. The Jurassic period saw
the first of many types of animals such as birdlike dinosaurs, sharks, rays,
giant crocodiles, giant quadruped herbivores, and medium sized bipedal
carnivores. By the Jurassic period, the continents had started to drift apart
and probably looked like the model below.
12
The Cretaceous
Period
The Cretaceous period is was the longest period of the Mesozoic era.
Life and diversity flourished in the Cretaceous period for giant carnivores
like the Tyrannosaurus rex, small mammals, and flowering plants. These
animals lived in a
hotbed for life and
evolution
before
their demise at the
end of the period.
When people talk
about the end of
dinosaurs, this is
the extinction event
they’re
probably
referring to. All dinosaur life on land perished, leaving little competition
for the mammals to take their place. Earlier in this book are some theories
on what actually caused this extinction. This period also saw a further
separation of the continents, as shown above.
13
dinosaur
classification
Dinosaurs are reptiles that lived during the Mesozoic era. They
belong to a group called Archosauria, or “ruling reptiles”. Scientists use
some basic rules to classify ancient animals as dinosaurs; the main rule
being that they must have been land inhabitants that lived 250-65 million
years ago. Paleontologists use a classification system based on the anatomy
of dinosaurs as well as behavior and habitat to divide them further into
subgroups.
Dinosaurs in the Archosauria class are divided into two main groups,
reptile-hipped and bird-hipped dinosaurs. The Saurischian order groups
together dinosaurs that have pelvic hips, like lizards, and clawed feet. They
lived from the Middle Triassic to the end of the Cretaceous period and were
both carnivores and herbivores. The Ornithischian order groups together
dinosaurs that have a hip structure like a bird and hoofed toes. They lived
from the Middle Triassic to the end of the Cretaceous period and all of
them were herbivores. Both the Saurischian and Ornithischian groups
are further divided into more specific groups based on their anatomy. An
example of a reptile-hipped dinosaur is the meat-eating Tyrannosaurus
(left). An example of a bird-hipped dinosaur is the Stegosaurus (right).
14
dinosaur
INTELLIGENCE
The intelligence of dinosaurs, among other
animals, can be measured by the Encephalization
Quotient (EQ), which is a ratio of the size of an
animal’s brain compared to its body. In general,
cold-blooded reptiles have lower EQs, meaning that
they are less intelligent than other animals.
For a long time, dinosaurs were considered some
of the least intelligent creatures to have ever existed.
In reality, dinosaurs have a range of intelligence.
The least intelligent dinosaurs belonged to the group
sauropodomorpha. They had an average EQ of
about 0.05. On the other hand, the most intelligent
dinosaurs, those belonging to the troodontids, had
an average EQ of about 5.8. A value of 5.8 on this
scale is high, especially considering humans average
at around an 8.0.
15
The Second
Brain
Theory
Scientists
believed for some time
that larger dinosaurs
actually had two brains.
After finding voids in
the bone structure of
certain dinosaurs, they
figured that a second,
much larger brain was
held in a different part
of the dinosaur. For
example, they thought
that spaces in the tails
and around the hip
area of Stegosaurus
were another system
controlling their hind
legs and lower body
movement. They also
thought that this brain
was far more powerful
than their main cranium.
Eventually, however,
they determined that
these spaces were
actually an enlargement
in the spinal cord and
was most likely formed
from fat and extra nerve
tissue.
dinosaur
behavior
Scientists cannot observe dinosaur behavior directly because they have
been extinct for many years, but they have made inferences and educated
guesses on their feeding, hunting, foraging, and parenting behaviors.
Scientists can deduce the feeding behavior of dinosaurs based on the shape
of their teeth and jaws. Like wolves and lions, many dinosaurs also hunted
in packs, an activity that required collaboration and social intellect. Some
dinosaurs also congregated in herds for to migrate and to protect their
young.
Female dinosaurs produced offspring through sexual reproduction.
They laid eggs in nests that they built and took great care in precisely
arranging their eggs in the nest. Some dinosaurs stood guard by their nest,
while others abandoned their nest as soon as they had laid their eggs. These
eggs ranged from a foot to an inch in size. Some nests were built by just
digging out some earth, while others show complex structures with mud
rims. Some of these nests appear in groups, while others appear alone.
Dinosaurs did communicate with each other, but scientists are not
very sure about what they sounded like. Scientists speculate that some
dinosaurs had aggressive mating displays, but they still do not completely
understand the mating and territorial behaviors of dinosaurs. They observe
animal species that are
present today in hopes
of obtaining a visual idea
of how ancient species
may have functioned.
16
dinosaur
LIFE-SPAN
Scientists have difficulty trying to figure out exactly how long
dinosaurs of specific groups and species lived for, but they have developed
a method to estimate their average life spans. Recently, scientists discovered
that dinosaur bones have growth rings, very similar to the rings that form
on trees as they grow. Each year of growth for the dinosaur leaves a growth
marker, which the scientists can see under a microscope. They then use
the markers to estimate how long the dinosaur lived. Some of the largest
dinosaurs, in the group of sauropods, may have lived for upwards of 100
years, but others, like smaller, bird-like Troodon, lived for only 3-5 years.
Scientists have also used the growth rates of other common reptiles
to make a model for dinosaur lifespan. For example, when using the
maximum growth rate of modern-day reptiles, it would take a Protoceratops
26-38 years to develop into an adult dinosaur. It would take even longer for
Hypselosaurus (shown below) to fully develop. Scientists estimate that it
would take them anywhere from 82-188 years to become full-sized adults.
These extremely large predicated lifespans detract from the credibility of
the model, so instead scientists typically rely on the growth markers to
determine a species lifespan.
17
dinosaur
DIET
The diet of dinosaurs varies greatly from one species to another.
Many dinosaurs were carnivores, but there were even more herbivores.
Plant eaters are identified by their blunt teeth which they used to pull leaves
and vegetation from plants and chew them. An herbivore usually ate much
more than a carnivorous dinosaur in order to obtain the same amount of
energy. Some dinosaurs even ate rocks in order to help with the digestion
of the tough plant fibers.
On the other hand, carnivores are usually identified by their long
legs, which they needed to chase their prey, as well as their sharp teeth and
strong claws. Some carnivores hunted in packs to increase their chances
of obtaining food. Scientists also determined the diet of dinosaurs by
observing their fossilized feces and stomach contents.
18
dinosaur
DIET
The herbivores are also known
as primary consumers because they
fed on plants, or producers. Carnivores
that eat primary consumers are known
as secondary consumers, and tertiary
consumers were the dinosaurs that
fed on the secondary consumers. For
example, a T. rex ate a Triceratops which
ate cycads, a type of plant. This creates a
food chain, where carnivores, herbivores,
and plants create equilibrium.
There is another classification of
animals based on diet. Omnivores are
dinosaurs that ate both plants and meat,
however, there are only a few known
omnivorous dinosaurs.
19
Gastroliths
Gastroliths are rocks
and stones that are found in
the gastrointestinal tract.
The term gastrolith literally
translates
to
“stomach
stone”. These are the stones
that dinosaurs swallowed to
aid in digestion and chewing.
These stones can range in
size from sand to several
centimeters in width. Several
living vertebrates including
crocodiles,
alligators,
herbivorous birds, and seals,
swallow rocks for similar
functions.
Glossary
Adapt - process by which an animal or plant species becomes fitted to its
environment
Age - a particular period of history, as distinguished from others
Anatomy - the bodily structure of an organism
Biped - a two-footed animal
Carnivore - an organism that derives its energy and nutrient requirements
from a diet consisting mainly or exclusively of animal tissue, whether
through predation or scavenging
Continental drift - the movement of the Earth’s continents relative to
each other by appearing to drift across the ocean bed
Cope’s Rule - evolution tends to increase body size over geological time in
a lineage of populations
Decompose (decomposition) - the process by which organic substances
are broken down into simpler forms of matter
Encephalization Quotient - a measure of relative brain size defined as the
ratio between actual brain mass and predicted brain mass for an animal of a
given size, which is hypothesized to be a rough estimate of the intelligence
of the animal
Eon - a measure of time in the geological time scale; multiple eons make
up a supereon
Epoch - a measure of time in the geological time scale; usually tens of
millions of years; multiple Epochs make up a period
Era - a measure of time in the geological time scale; usually several hundred
million of years; multiple eras make up an eon
Equilibrium - a condition in which all acting influences are canceled by
others, resulting in a stable, balanced, or unchanging system
Excavation - the exposure, processing and recording of archaeological
remains
Extinct - is the end of an organism or of a group of organisms; typically
after the death of last individual of a species
20
Glossary
Fossil - the preserved remains or traces of animals, plants, and other
organisms from the remote past
Fossilization - the process of turning remains into fossils
gastrointestinal tract - digestive tract
Herbivore - an organism anatomically and physiologically adapted to plant
material, for example foliage, as the main component of its diet
Hypselosaurus - was a 27-foot (8.2 m) long titanosaurid sauropod that
lived in Europe during the Late Cretaceous Period
Omnivores - species that is a consumer of a variety of material as significant
food sources in their natural diet, including plants, animals, algae, and fungi
Organism - any living thing
Paleontologist - a scientist who studies prehistoric life
Period - measure of geological time; multiple periods make up an era
Photosynthesis - a process used by plants and other autotrophic organisms
to convert light energy, normally from the sun, into chemical energy that
can be used to fuel the organisms’ activities
Primary consumer - an animal that eats grass and other green plants in a
food chain; an herbivore
Protoceratops - a genus of sheep-sized herbivorous ceratopsian dinosaur,
from the Upper Cretaceous Period
Reptiles - a cold-blooded vertebrates of the class Reptilia, that includes
snakes, lizards, crocodiles, turtles, and tortoises.
Rock stratum (plural: “strata”) - a layer of sediment with internally
consistent characteristics different from those of the layer above it, used as
time markers in geological time.
Sauropodomorpha - an extinct clade of long-necked, herbivores,
saurischian dinosaurs
Sauropods - quadrupedal herbivores; some of the largest dinosaurs to
have ever lived
21
Glossary
Secondary consumer - an animal that feeds on smaller plant-eating animals
in a food chain
Sediment - a naturally occurring material that is broken down by processes
of weathering and erosion
Stegosaurus - a genus of armored stegosaurid dinosaur, lived during the
Late Jurassic period
Supereon - measure of geological time; made up of multiple eons
Tertiary consumer - an animal that feeds on secondary consumers in a
food chain
Theory of evolution - the change in the inherited characteristics of
biological populations over successive generations
Trace fossil - are geological records of biological activity
Troodon - a genus of relatively small, bird-like dinosaurs from the Late
Cretaceous period
Troodontids - family of bird-like theropod dinosaurs (an example shown
right)
Tyrannosaurus - a genus of coelurosaurian theropod dinosaur; popularized
as the T. rex
Quadrupeds - a four-footed animal
22
About the Authors
Connor Palatucci is a junior at Mass
Academy. His interests include
longboarding, snowboarding, rock
climbing, slacklining, cooking, auto
mechanics, and ukulele. His spirit animal
is the sloth. He lives in Worcester, MA
and works at Wachusett Mountain as
a snowboard instructor. This summer
he’ll be learning blacksmithing at the
Old Oak Smithy and working on a
patent for his longboard truck designs.
Annabel Consilvio is also a junior at Mass Academy.
She enjoys baking, graphic design, and exploring.
She lives in Auburn, MA and volunteers in a
Drosophila lab at WPI. She’s interested in biology
and biomedical engineering. Her spirit animal is
the bear. She has a strange facination with space
and traveling to new places.
Nikitha Das is a junior at the Massachusetts
Academy of Math and Science. Her spirit animal
is the crow. She will be attending freshman
classes next year at WPI for her senior year of
high school. She lives in South Grafton, MA and
loves to sketch, paint, and bake. She is interested
in studying Biology and loves to play tennis.
23
Image Credits
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http://www.valeriebarrow.com/images/asteroid-dinosaurs.jpg
http://www.enchantedlearning.com/fgifs/Foodchain.GIF
http://en.wikipedia.org/wiki/File:Blakey_220moll.jpg
http://spongebobquh.wikispaces.com/%60+GEOLOGICAL+TIME+SCALE
http://www.astronomers.net/ga4-prehistoric/images/dinosaur_evolution_poster2.jpg
http://upload.wikimedia.org/wikipedia/commons/1/19/Hypselosaurus_BW.jpg
http://upload.wikimedia.org/wikipedia/commons/f/fc/Protoceratops_BW.jpg
http://upload.wikimedia.org/wikipedia/commons/f/f2/AmpelosaurusDB.jpg
http://upload.wikimedia.org/wikipedia/commons/7/70/Stegosaurus_BW.jpg
http://www.telegraph.co.uk/earth/earthpicturegalleries/6251695/Las-Vegas-auctionof-dinosaur-fossils-a-Tyrannosaurus-Rex-woolly-mammoth-and-prehistoric-shark-jaws.
html?image=1
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http://commons.wikimedia.org/wiki/File:Stegosaurus_BW.jpg
http://www.oceansofkansas.com/Coprolites/copro01b.jpg
http://periodictable.com/Samples/077.4/s9s.JPG
http://blogs.egu.eu/palaeoblog/files/2013/04/triassic-dinosaurs_1256_600x450.jpg
http://news.nationalgeographic.com/news/2008/01/photogalleries/dinosaur-pictures/
images/primary/1_DINOSAUR_461.jpgEvidence of Dinosaur Existence
http://www.indiana9fossils.com/dinosaurs/Gastroliths/lg1c.JPG
http://realdinosaurpictures.com/wp-content/uploads/wallpapers/Dinosaurs-TriceratopRiver-HD-Wallpaper-1280x720.jpg
http://imgc.allpostersimages.com/images/P-473-488-90/49/4917/PGL9G00Z/posters/
minmi-dinosaur-eating-grass.jpg/
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