Troodon
Name: Troodon(Wounding
tooth).
Phonetic: Tru-oh-don.
Named By: Joseph Leidy - 1856.
Synonyms: Pectinodon bakkeri,
Polyodontosaurus grandis, Stenonychosaurus inequalis.
Classification: Chordata, Reptilia, Dinosauria,
Saurischia, Theropoda, Troodontidae, Troodontinae.
Species: T. formosus (type).
Type: Usually depicted as a Carnivore, some have
suggested a possibly omnivorous diet.
Size: 2.4 meters long.
Known locations: North America.
Time period: Campanian to Maastrichtian of the
Cretaceous.
Fossil representation: Many individuals recovered.
Discovery
Remarkably
when Troodon was first 'discovered' it was only
known from a
tooth, and it was the description of this tooth that gave rise to the
genus. Although naming a creature after only discovering its teeth is
hard to imagine today, it was a common place practice in the
nineteenth century, and at least in the case of Troodon
the teeth
were different to most others.
Two
problems arose from describing Troodon from only
teeth. One, while
these teeth were curved like in a carnivore, they had curved
serrations similar to some herbivores. Two, because no one knew of
any skeletal remains, no one knew what kind of dinosaur it actually
was, or even if it really was a dinosaur for that matter.
When
named by Joseph Leidy in 1856, Troodon was
classed as a lizard.
When classed as a dinosaur in 1901, Troodon
was assigned to the
megalosauridae, a wastebasket group at the time that was used as a
dumping ground
for any carnivorous dinosaur whose kind and position among others was
not known. In 1924 Troodon 'became' a
pachycephalosaur, a
herbivorous kind of dinosaur known for having dome headed skulls,
with the grouping made on the basis of similarities between their
teeth, notably the serrations. It should also be mentioned that as
Troodon was grouped with them, all
pachycephalosaurs
known at the
time were classed under troodontidae, until 1945 when Troodon
was
removed from the group on the basis that its teeth were for a
carnivorous purpose. Because the group could not be called after a
dinosaur that was no longer a part of it, they were re-named the
pachycephalosuars after Pachycephalosaurus.
It
turns out that while some of above was unfolding, skeletal material
for Troodon did actually exist, although it was
classified under the
name of Stenonychosaurus. The material for Stenonychosaurus
was
discovered in 1932 but was fragmentary, and when compared to the
zero skeletal remains of Troodon, no one knew any
better than to
create a separate genus. The discovery of more fossil material
throughout the twentieth century would slowly bring Stenonychosaurus
and Troodon together, but it would not be until
1987 when Dr
Philip Currie studied material attributed to both that the connection
was made. Currie found that the only differences between
Stenonychosaurus and Troodon
were the products of the age of the
individuals and they were one and the same. Not only did
Stenonychosaurus become a junior synonym, but Polydontosaurus
and
Pectinodon also became junior synonyms of Troodon.
Not
long after this reclassification occurred many, including Currie
himself, questioned if it was actually correct to name just one
species of Troodon. This is based upon the facts
that Troodon
specimens are separated by large geographic distances as well as
several million years in the fossil record. With this in mind there
have been calls to re-examine all Troodon fossils,
to see how many
species there actually are. The problem here returns to the fact that
the holotype specimen that all subsequent fossil finds are compared to
is a only a tooth. The only possible way to sort things out with
Troodon remaining a valid name and not a Nomen
dubium would be
establish a neotype specimen. This is where more complete material is
set as the 'standard' for a species so that future material can be
compared against it for the purposes of identification. The
establishment of a neotype is not unknown and had to be done with
another well-known dinosaur, Coelophysis.
Biology
Although
small for a dinosaur, Troodon is still the
largest member of the
troodontidae group. Troodon also had large eyes
that faced forwards
allowing Troodon to make use of stereoscopic
vision. Aside from
having a good degree of depth perception, the eyes may well have also
allowed for exceptional night vision due to their large size.
The
characteristic teeth of Troodon do not make its
diet easy to
establish. Although overall they are recurved like those of a
predator, they have serrations that suggest herbivore. What can be
gathered is this; as a Theropod, Troodon had
carnivorous
ancestors, and this is confirmed in the recurved shape of the teeth.
Recurved teeth curve towards the tip so that they point to the back of
the mouth. This design is a common trait in predators and exists so
that seized prey cannot escape.
The
teeth serrations however are more like those of a herbivore that
specialises in soft vegetation, and similar serrations can be seen in
the teeth of herbivorous dinosaurs such as Pachycephalosaurus
and even
Stegosaurus.
Either the serrations are an 'evolutionary
experiment', or Troodon possibly included some
plant material into
its diet. One thing that is certain about the teeth, they would
have been almost useless against hard material like bone, or even
tough branches and Troodon would have had to focus
on only softer food
items.
The
snout on Troodon has a 'U' shape to it when
viewed from above.
This has been suggested as an herbivorous trait as it is often seen in
herbivorous lizards. It should be remembered though that one of the
most famous carnivorous dinosaurs of all time, Tyrannosaurus,
also
had a 'U' shaped snout, an adaptation that allowed it to take
bigger bites.
When
considering the other predatory traits such as forward facing eyes,
long legs, and light weight build and the presence of a sickle claw
on each foot, it is almost certain that Troodon
was a predator.
Even with this reasoning however, it is still possible that Troodon
may have been an occasional omnivore, should Troodon
have found the
right food item.
Another
feature that makes Troodon stand out from other
dinosaurs is the
presence of an opposable finger. Although not constructed like a
human hand, the best way to describe it is if you try grasping
something between your thumb and just two of your fingers. It is
unknown how much use Troodon would have given this
adaptation, but
the fact that it developed in the first place would suggest that there
was at least one good reason for it occurring. It may have been to
better manipulate ground objects or moving undergrowth branches when
searching for prey.
While
old depictions of Troodon (then known as Stenonychosaurus)
show a
lizard like dinosaur with bare skin, most modern reconstructions
place a covering of primitive feathers over its body. This is quite a
reasonable supposition as not only did other smaller members of the
troodontidae have feathers, Troodon is known from
as far north as
modern day Alaska. Such a northern latitude even at the end of the
Cretaceous period would have been much cooler than areas just a few
hundred miles south, quite easily necessitating the presence of
insulating feathers.
Reproduction and nesting.
The
discovery of fossilised nest sites in the Two Medicine Formation has
revealed very interesting insights into how Troodon
laid
and brooded
over their eggs. Troodon nests were dish shaped
with a one meter
diameter. The nests seem to have been built from just sediment with
no other material in the construction. The nests examined show
evidence of between sixteen and twenty-four eggs per nest with some
seen to have hatched.
The
eggs themselves are like elongated teardrops. When laid, the
pointed end is stuck into the sediment, and is presumably shaped for
this purpose. The eggs are also laid at an angle pointing towards the
centre of the nest. Because eggs are grouped into pairs, it is
thought that in life, Troodon would have had two
oviducts,
something which is seen in modern crocodiles.
Different
nest sites reveal different stages in the incubation, but all point
to the same conclusion. Nests are not found where only a few of the
eggs have hatched, either they all are, or none at all. Also
analysis of fossilised embryos in unhatched eggs of the same nest show
that they are all at the same developmental stage. It would probably
be impossible for a Troodon to lay up to two dozen
eggs in one go, so
it is thought that the eggs were laid two at a time. The main
brooding did not begin until all of the eggs had been laid so that all
of the young could develop and more importantly hatch at the same time
as one another.
One
nest site was also found with the remains of an adult Troodon.
Analysis showed that this individual was a male, based upon the fact
that is did not have the same bone resorption patterns as would be
expected in a female during ovulation. This has raised the notion
that male Troodon had an active role in the
brooding of the nest as can
be seen in many of today’s birds.
Intelligence
Because
of its large brain size relative to its overall body mass. Troodon
is
considered to quite possibly be the smartest dinosaur known to exist.
This is based upon the brain to body mass ratio, and sometimes the
encephalization quotient. The encephalization quotient is considered
the more accurate of the two as it takes the relative size of the
animal into account. Both systems work by comparing the size of the
brain to the size of the animal.
Although
both of the systems seem quite complex to understand, they actually
run on a pretty basic principal. Neural cells that make up the brain
are the same size regardless of the size of the creature. This means
that a larger brain is made up of more cells, and more cells is taken
to mean more brain power. An animal with a larger body may need more
of this power for motor skills (moving of muscles), and with this
taken into account, the general intelligence of the animal is
estimated.
The
problem with both systems is that neither takes into account the type
of neural tissue. Brains are made up of different areas, sight,
smell, memory, etc. If two different animals still had the same
size brain as one another, one still may be more intelligent than the
other if one had more neural tissue associated with things like memory
and problem solving than sight and smell. Although that animal would
not be as physically able as the other, it would have greater
intelligence.
Back
to the subject of intelligence in Troodon,
interpretation and
re-creation of the brain have been key areas of study. On the EQ
scale, mankind places about 7.4-7.8. Some studies have placed
Troodon as high as 5.8, quite an achievement
when you consider that
most dinosaurs chart under 2 on the scale, with most herbivorous
dinosaurs under 1. Modern animals like a Chimpanzee chart around
2.2-2.5, and Bottlenose Dolphins just over 4.
As
stated above it is the kind of tissue that matters. Troodon
had large
eyes, and coupled with its presence in Northern latitudes, may have
needed more brain power just to process visual information. However
this does not disprove Troodon intelligence.
Brains in higher forms,
including people are 'folded'. This is the wrinkled look of
brains when they are seen outside of the body, and occurs in order to
get more neural tissue working in a smaller area. The brains of more
primitive animals are usually just amorphous clumps of neural cells.
Reconstruction of Troodon brains has revealed
early indications of the
brain beginning to fold on itself, something that is considered to be
radically different to other reconstructed dinosaur brains.
Again
this does not mean that Troodon was more
intelligent, but it does
indicate that it had more potential brain power that was developing
along even more special lines. It is also worth remembering that by
having hands that could grasp things, Troodon
would have had even
greater opportunity to learn from its environment.
The Dinosauroid.
The
idea of dinosaurs with increasing intelligence and dexterous hands has
led many too wonder how dinosaurs like Troodon
would have evolved had
the KT extinction not occurred sixty-five million years ago. Well in
1982 a man named Dale Russell put form to the thought. Based upon
Troodon ( then still known as Stenonychosaurus),
Russell
presented a humanoid dinosaur, which means that it was depicted as
walking in a similar stance and posture as a human being. The body
proportions were also close to that of a human. The eyes were still
large, and the Dinosauroid was envisioned as giving birth to live
young and feeding them upon regurgitated food.
Although
some have criticised the reconstruction on the grounds that it is
'too human', and descendants would have probably retained a more
'classic' theropod body, it is somewhat missing the point as the
Dinosauroid reconstruction is more of a 'what if' than an
absolute. It is still worth thinking about though that mankind is
thought to have evolved from apes over the course of hundreds of
thousands of years. Imagine what a dinosaur already smarter than a
Chimpanzee could do over sixty-five million.
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