Abstract. Troodon is a relatively small, bird-like dinosaur known from the Campanian age

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1 Lydia Clark Dr. Parker Dino Paper 16 November 2015 Abstract Troodon is a relatively small, bird-like dinosaur known from the Campanian age of the Cretaceous period. It has at least one species, Troodon formosus, however it is possible there are several species in this genus. This dinosaur was among the first found in North America. From the discovery of the first tooth, to the final determination of the anatomy of the Troodontid the process was complex and long. Troodon is the most well known for the fact that it is thought to be the smartest dinosaur to roam the earth. Troodon was originally feathered but overtime lost its feathers and began to resemble a more reptilian dinosaur. The speed, superb eyesight, night vision, and opposable thumbs are worth noting and also allow these creatures to be a threatening predator. Also the teeth of the Troodon are serrated and perfect for wounding animals however there are aspects of them that make them appear herbivorous as well. Introduction Known to have roamed the earth during the Campanian to Maastrichtian ages of the Cretaceous time period, Troodon was a relatively small, extremely smart dinosaur. The classification of the Troodontids is Chordata, Reptilia, Dinosauria, Saurischia, Theropoda, Troodontidae, Troodontinae. It is usually depicted as a carnivore, however there is a possibility that it had an omnivorous diet. Remains of the Troodon were found in North America, close to what today is known as the state of Alaska. Although the

2 original research of the species began off the discovery of a single tooth, overtime many individual specimens have been recovered, including many nests, and juvenile and adult remains. Discussion Discovery of Troodon Although the tooth of the Troodon was originally founded in 1856, since then paleontologists have been examining the specimens trying to determine the genus of the Troodon. Acording to the article, How was the Troodon Discovered? written by Bob Strauss, Troodon was discovered in the mid-19 th century. The first part of a Troodon that was found was a single tooth by American paleontologist Joseph Leidy in Montana s Judith River Formation. Leidy defined the new genus Troodon (wounded tooth), but it was first classified as a lizard, not a dinosaur. Troodon remained a lizard for about 50 years until there was a reevaluation of the tooth in 1901, when paleontologist, Nopsca, determined this genus was closely related to Megalosaurus. Although this was established it didn t advance the study of the Troodon, seeing that the Megalosaurus was and still is one of he least understood carnivorous dinosaurs. (Currie) Twenty years later Charles Gilmore examined the tooth and came to a different conclusion, that Troodon was instead a pachycephalosaur, which are known as boneheaded dinosaurs, closely related to Stegoceras. Gilmore was convinced that this was the correct classification for a couple of decades, and the Troodons became referred to as the

3 troodonts until 1945 when Charles M. Sternberg proved that the Troodon was a theropod, a carnivorous, bipedal saurischian dinosaurs. Back in 1932, Sternberg had found bone fragments from the Canadian province of Alberta and defined the new Genus Stenonychosaurus, narrow clawed lizard, which he later discovered (1951) had teeth strikingly similar to the unusal tooth structure of the Troodon. The question was then raised, was it possible this was the same dinosaur? Twenty years later, in 1969, the paleontologist Dale Russell took a close look at the Stenonychosaurus and rather than associating the dinosaur with the Coelurosaur, he believed they were related to the feather dinosaur, Saurornithoides. It was then up to paleontologist Phil Currie, in 1987, to examine the fossil evidence for Stenonychosaurus and two other theropod genera and conclude that they were all possible synonyms of Troodon. (Just when it was thought that the issue of the Troodon had been settled, paleontologists began to wonder if the umbrella of the Troodon had become too wide and that in actuality some of the specimens referred to it needed their own genus (Horner). The specimens that were originally used to diagnose the Stenonychosaurus, in some areas now referred to as Troodon inequalis, and the Pectinodon fossils are assigned to Troodon bakkeri. These would then reflect with the Troodon species determined by Leidy 100 years before, Troodon formosus and Troodon asiamericanus. Finally, in 2011 a paper was released by a group of paleontologists who had reviewed all of the evidence associated with Troodon, and also the species and genera linked to it. These paleontologists concluded that is it possible that the Pectinodon was a valid genus,

4 however they determined that Joseph Leidy s discovery of the tooth was an insufficient basis to create the genus Troodon to begin with. (Strauss) Environment Skeletal remains show that the Troodon dinosaurs lived on the Alaskan North Slope during the late Campanian-early Maestrichtian time, about 66 to 76 millions years ago, in an environment dominated by herbaceous vegetation. The high ground terrestrial plant community was a mild- to cold-temperate forest made up mostly of coniferous and broad leaf trees. The high paleolatitude, ranging from 70 to 85 degrees North, makes scientists assume there was extreme seasonal variation in solar insulation, temperature, and the herbivore food supply. The vast distances of migration to evergreen floras and the discovery of both adult and juvenile Troodons suggests that they remained in the same environment year round and did not migrate seasonally. This would challenge the idea that short-term periods of darkness and temperature decrease eventually lead to dinosaurian extinction. (Clemens, 1992) Fossil Information Many specimens of the Troodon have been found in parts of Montana and Wyoming. A specific location that fossil nests of the Troodon have been found is the famous Egg Mountain. Egg Mountain is in Montana and at that site elongated eggs were found and originally attributed to a different dinosaur but were later identified belonging to the Troodon.

5 As a result of this small dinosaur had long, slender limbs that would allude to the fact that is was a fast runner. It is likely that its diet consisted of small animals, specifically mammals and a large consumption of plants. It is not known that the Troodon was feathered but it descended from the Sinornithoides, which were feathered. Anatomy Although the Troodon is a small dinosaur it is the largest member of the troodonitdae group. Troodon measured approximately two to three and a half meters long, one meter tall, and weighed about one hundred pounds. Figure 1 shows what an average sized Troodon looked like in comparison to the size of an average size man. Based on images of the Troodon, specifically Figure 2, the Troodon was thought to of resembles a reptile in the idea of its color scheme, being dark greensm yellows, and browns. The eyes of Troodon were forward facing, allowing it to use the stereoscopic vision and has a good degree of depth perception. (Fiorollo, 2008)

6 Figure 1: This image shows the comparison of a full-grown Troodon to the size of a fullgrown man in order to give the viewers a better idea of the size of the Troodon. (Fiorillo, 2008) Figure 2: Image showing the assumed color of the Troodon. (Allred, 2010)

7 The teeth of the Troodon did not make it easy for researchers to establish the diet of the dinosaur, most of the teeth seem to be curved like a predator, but they have serrations that suggest they were herbivores. Because the Troodon is a Theropod its ancestors were carnivorous, this being verified in the recurved shape of the teeth towards the tip, meaning that they point towards the back of the mouth allowing them to capture prey and keeping it from escaping. However the serrations on the teeth resembled a more herbivorous animal that would eat a softer vegetation, the same type of serrations are seen in dinosaurs such as he Stegosaurus. These serrations are either an evolutionary experiment or the Troodon diet included some plants. Also the U shape of the Troodon snout alludes to the idea of it being an herbivore, resembling herbivorous lizards such as iguanas. However, to contrast that idea, the Tyrannosaurus Rex developed a U shaped snout allowing it to take bigger bites. Based on observations of the teeth it can be concluded that the Troodon teeth were not capable of eating hard objects such as large bone, but rather softer material. When all the characteristics of a Troodon are taken into account, the forward facing, large eyes, long legs, light build, sickle claw on each foot and widened jaw, it is very convincing that the Troodon would be a predator. Even with all of this evidence there are still a few facts that make it possible that the dinosaur was an omnivore at times when it could find the appropriate food item. The opposable finger is another trait of the Troodon that causes it to stand out. Although it is not as useful as a human hand with a thumb, it is similar to how it would be for a human to grasp something with two fingers and a thumb. It is still in question

8 why a Troodon would need a claw or hand like this, but the fact that the adaptation occurred in the first place suggests that there was a need for it. Scientists think it might have been to allow for better grasping of objects that are on the ground or moving branches and undergrowth when looking for prey. Most pictures of the Troodon depict a lizard-like dinosaur with bare skin, however in more recent depictions the dinosaur has had a covering of primitive feathers on its body. In 2009, a theropod with feathers was found in China named Anchionoris. Based on the anatomy of the specimen found ot was placed in the same line as the Troodon, a theropod not thought to of originally have feathers. (Daniels, 2013) Figure 3: Image showing the possibility of a Troodon possessing feathers. (Daniels, 2013)

9 Reproduction and Nesting The findings of fossilized nests in the Two Medicine Formation in Montana has revealed information on how the Troodon nested its eggs and then brooded over them. The nests were typically in a dish shape and had about a 1meter diameter. The nests were constructed of sediment and no other materials and contained anywhere from sixteen to twenty-four eggs. The eggs were in the shape of a teardrop with the pointed end sticking into the sediment of the nest and the eggs were pointed towards the center of the nest. The eggs were grouped into pairs,which makes scientists believe that the Troodon has two oviducts, something that is also seen today in crocodiles. The incubation appeared different at all the nests yet they all revealed the same pattern. No nests were found with only some of the eggs hatched; they had either all hatched or none had. After studying the embryos of the non-hatched eggs the observation was made that all of the embryos were in the exact same stage of development. It would be impossible for a Troodon to lay eggs in one single session so the thought is that the eggs were laid in twos. In order for all of the eggs to develop and hatch at the same time the main brooding did not begin until all of the eggs had been laid. As shown in Figure 4 the remains of an adult Troodon were determined to be a male. Based on the fact that it did not have the same bone reabsorption patterns as is typically seen in females during ovulation. This made scientists begin to wonder about the role of the male in the brooding of the nest.

10 Figure 4: Adult Troodon Brooding on a Nest (Bryner, 2008) Intelligence The brain size of the Troodon in comparison to its overall body mass makes scientists believe that it was the smartest dinosaur ever known to exist. This theory was formed based on the brain to body mass ratio and the encephalization quotient (EQ); which is the ratio between the actual brain mass and the predicted brain mass of a specimen of a given size and is the rough estimate of the intelligence of the specimen. The EQ is considered the more accurate of the two different methods because it takes the relative size of the dinosaur into account. However both the brain to body mass ratio method and the EQ are sufficient to measuring brain size to body mass because they both compare the brain size to the actual size of the animal. Both systems of measuring seem complex however they are both based on the same principal, neural cells. The neural cells of the brain are the same size no matter what

11 the size of the creature, meaning that the larger the brain the more cells and the more cells there are the more brain power. An animal of a larger body size would need to use more of this power for motor skills, however the Troodon is a relatively small dinosaur as mentioned earlier, and based on this idea the general intelligence can be determined. The main problem with these systems is how different brain regions aren t taken into account. Brains are made up of different areas of our sensory perceptions. Two different dinosaurs could have the same size brain but one could still be more intelligent than the other because more of the neural tissue is associated with things like memory and problem solving rather than sensory perceptions like sight and smell. The interpretation and recreation of Troodon have been key areas of study when it comes to the intelligence of dinosaurs. Troodon had large eyes and with its presence in in Northern latitudes, its possible it needed more brain power simply to interpret and process visual images. However this doesn t disprove the extremely high intelligence. The brain surfaces in higher humans, animals, and even dinosaurs are folded allowing for more neural tissue to work in a smaller space. Reconstruction of Troodon brain reveals indications of the brain beginning to fold on itself, which is not typical in the case of dinosaur brains, which are usually just a clump of neural cells. All of this information and data does not necessarily mean that Troodon was more intelligent than other dinosaurs but it does show that it had more potential brainpower and a greater opportunity to learn. Dinosauroid According to Dale Russell, the man who discovered the Troodon, dinosaurs had the capability of becoming intellectual beings. Referring to them as dinosauroids, he

12 thought they would ve had a strikingly similar look to that of humans today. Troodon has features, which assisted Russell in alluding to this idea, such as their opposable thumbs and binocular vision. Also, because the Troodon was a social species it is thought that they were beginning to develop into intelligent life forms. Russell took note of the brain size in comparison to the body size of the Troodon and the brain size of dinosaurs in general. After more research he came up with the fact that the dinosauroids today would have about the same brain volume as humans do. The evolution of the brain would have also changed the appearance of the dinosaurs, molding them into more of a human figure. The dinosauroid would of developed an upright posture, but maintained the reptilian features such as the lack of external genitals and the scaly skin. Figure 5 identifies characteristics that would ve remained similar to the Troodon and those that resemble more of a human appearance. Russell also believed that the dinosauroids would ve interacted with humans today as much as humans interact with any other animal today. However paleontologist dismissed Russells idea because it was too improbable.

13 Figure 5: Comparison of Troodon to Dinosauroid (Gopinath, 2015) Conclusion The discovery of the original tooth of the Troodon in 1856 by Leidy lead to over 150 years of study of the genus Troodon, attempting to establish what all species fit under the umbrella. The environment that Troodon typically lived in was on what is now the Alaskan North Slope, primarily herbaceous vegetation, during the late Campanian- early Maestrichitan time, approximately 76 million years ago. These non-migrant dinosaurs had serrated teeth, forward-facing eyes, long legs, light build, claw on each foot, a wide, U shaped jaw suggesting it was a predator, however

14 the Troodon would've been incapable of eating large bones and hard material so it is likely it ate small rodents and vegetation. had characteristics about them that made them possibly the most intelligent dinosaur to ever roam the earth. The brain size of the Troodon is one what the small dinosaur is most known for, leading researchers to believe that the creature was smartest of all dinosaurs. This level of intelligence lead to the dinosauroid theory by Dale Russell, who believed that if the Troodon had not gone extinct perhaps it could of evolved into an animal similar to a human both physically and intellectually. Overall the Troodon was a reptilian-like dinosaur that is well known for its intelligence and the first dinosaur to lead to a theory of a human-like dinosaur.

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16 Clemens, William A. "Continental Vertebrates From the Late Cretaceous of the North Slope, Alaska." Boem.gov. University of Paleontology, University of California, Berkeley, Web. 3 Dec Spector, Mitchell. "Troodon Fact Sheet." Troodon Fact Sheet. EnchantedLearning, Sept Web. 03 Dec Allred, Laura. "Troodon." Dinosaurs For Kids. Kids Dinos, Dec Web. 03 Dec Daniels, Jeffrey. "Plush-ifying Jurassic Park - Feathered Dinosaurs." UA Magazine. United Academics, 18 June Web. 03 Dec Currie, Philip J. "Dinosaur Systematics." Google Books. N.p., n.d. Web. 03 Dec