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“Troodon” (Troödon in older sources) (Greek for "wounding tooth") is a dubious and former wastebasket taxon of relatively small avian-like dinosaurs known definitively from the Campanian age of the Cretaceous period (about 77 MYA). It includes at least one species, Troodon formosus, is known from Alberta and Montana. Discovered in 1855, T. formosus was among the first dinosaurs found in North America, although it was thought to be a lizard until 1877. The genus name is Greek for "wounding tooth", referring to the teeth, which were different from those of most other theropods known at the time of their discovery. The teeth bear prominent, apically oriented serrations. These "wounding" serrations, however, are morphometrically more similar to those of herbivorous reptiles, and suggest a possibly omnivorous diet.[1][2]

Description[]

Stenonychosaurus-scale

Size compared to a human

Troodon were small dinosaurs, up to 2.4 metres (7.9 ft) in length, and up to 50 kilograms (110 lb) in mass. The largest specimens are comparable in size to Deinonychus and Unenlagia. It is expected to have been able to run at faster speeds with its light body-weight and powerful back legs. It had a long claw on the second toe and long clawed fingers, as suggested by other members in the family. "Troodon" teeth in Alaska show that Alaskan "Troodons" could grow up to be 4 meters (13 feet), some scientists suggest that these teeth represent a new genus of Troodontid. Despite being very well known, the teeth have not been described properly.

Their eyes were very large (perhaps suggesting a partially nocturnal lifestyle), and slightly forward facing, giving Troodon some degree of depth perception. Their light skulls contained a capsule similar to those found in ostrich dinosaurs.

Brain and inner ear[]

Troodon had some of the largest known brains of any dinosaur group, relative to their body mass (comparable to modern birds). Troodon's cerebrum-to-brain-volume ratio was 31.5% to 63% of the way from a nonavian reptile proportion to a truly avian one. Troodon had bony crista supporting their tympanic membranes that were ossified at least in their top and bottom regions. The rest of the crista were either cartilaginous or too delicate to be preserved. The metotic strut of Troodon was enlarged from side-to-side, similar to Dromaeosaurus and primitive birds like Archaeopteryx and Hesperornis.

Discovery[]

Troodon formosus

1860 illustration of the T. formosus holotype tooth

The name was originally spelled Troödon (with a diaeresis) by Joseph Leidy in 1856, which was officially amended to its current status by Sauvage in 1876. The type specimen of Troodon has caused problems with classification, as the entire genus is based only on a single tooth from the Judith River Formation. Troodon has historically been a highly unstable classification and has been the subject of numerous conflicting synonymies with similar theropod specimens.

The dinosaur book - the ruling reptiles and their relatives (1951) (20406663741)

Troodon was mistaken as a pachycephalosaur Like the film Fantasia.

The “Troodon” tooth was originally classified as a "lacertilian" (lizard) by Leidy, but reassigned as a megalosaurid dinosaur by Nopcsa in 1901 (Megalosauridae having historically been a wastebasket taxon for most carnivorous dinosaurs). In 1924, Gilmore suggested that the tooth belonged to the herbivorous pachycephalosaur Stegoceras, and that Stegoceras was in fact a junior synonym of “Troodon” (the similarity of troodontid teeth to those of herbivorous dinosaurs continues to lead many paleontologists to believe that these animals were omnivores). The classification of Troodon as a pachycephalosaur was followed for many years, during which the family Pachycephalosauridae was known as Troodontidae. In 1945, Charles Mortram Sternberg rejected the possibility that Troodon was a pachycephalosaur due to its stronger similarity to the teeth of other carnivorous dinosaurs. With Troodon now classified as a theropod, the family Troodontidae could no longer be used for the dome-headed dinosaurs, so Sternberg named a new family for them, Pachycephalosauridae.

Naming of related species[]

Troodontid teeth

Comparison of troodontid teeth; A is the T. formosus holotype

The first specimen currently assigned to Troodon that was not a tooth was named Stenonychosaurus by Sternberg in 1932, based on a foot, fragments of a hand, and some tail vertebrae from the Dinosaur Park Formation of Alberta. A remarkable feature of these remains was the enlarged claw on the second toe, which is now recognized as characteristic of early paravians. Sternberg initially classified Stenonychosaurus as a member of the family Coeluridae. Later, in 1951, Sternberg speculated that since Stenonychosaurus had a "very peculiar pes" and Troodon "equally unusual teeth", they may be closely related. Unfortunately, no comparable specimens were available at that time to test the idea.

A more complete skeleton of Stenonychosaurus was described by Dale Russell in 1969 from the Dinosaur Park Formation, which eventually formed the scientific foundation for a famous life-sized sculpture of Stenonychosaurus accompanied by its fictional, humanoid descendant, the "dinosauroid". Stenonychosaurus became a well-known theropod in the 1980s, when the feet and braincase were described in more detail. Along with Saurornithoides, it formed the family Saurornithoididae. Based on differences in tooth structure, and the extremely fragmentary nature of the original Troodon formosus specimens, saurornithoidids were thought to be close relatives while Troodon was considered a dubious possible relative of the family. Phil Currie, reviewing the pertinant specimens in 1987, showed that supposed differences in tooth and jaw structure among troodontids and saurornithoidids were based on age and position of the tooth in the jaw, rather than a difference in species. He reclassified Stenonychosaurus inequalis as well as Polyodontosaurus grandis and Pectinodon bakkeri as junior synonyms of Troodon formosus. Currie also made Saurornithoididae a junior synonym of Troodontidae. In 1988, Gregory S. Paul went farther and included Saurornithoides mongoliensis in the genus Troodon as T. mongoliensis, but this reclassification, along with many other unilateral synonymizations of well known genera, was not adopted by other researchers. Currie's classification of all North American troodontid material in the single species Troodon formosus became widely adopted by other paleontologists, and all of the specimens once called Stenonychosaurus were referred to as Troodon in the scientific literature through the early 21st century.

Dissolution of the one species model[]

The Childrens Museum of Indianapolis - Troodon teeth

Teeth from South Dakota assigned to T. formosus, with a US dime coin for scale, Children's Museum of Indianapolis

However, the concept that all Late Cretaceous North American troodontids belong to one species began to be questioned soon after Currie's 1987 paper was published, including by Currie himself. Currie and colleagues (1990) noted that, while they believed the Judith River troodontids were all T. formosus, troodontid fossils from other formations, such as the Hell Creek Formation and Lance Formation, might belong to different species. In 1991, George Olshevsky assigned the Lance formation fossils, which had first been named Pectinodon bakkeri but later synonymized with Troodon formosus to the species Troodon bakkeri, and several other researchers (including Currie) have reverted to keeping the Dinosaur Park Formation fossils separate as Troodon inequalis (formerly Stenonychosaurus inequalis).

In 2011, Zanno and colleagues reviewed the convoluted history of troodontid classification in Late Cretaceous North America. They followed Longrich (2008) in treating Pectinodon bakkeri as a valid genus, and noted that it is likely the numerous Late Cretaceous specimens currently assigned to Troodon formosus almost certainly represent numerous new species, but that a more thorough review of the specimens is required. Because the holotype of T. formosus is a single tooth, this may render Troodon a nomen dubium.

Classification[]

Small theropod tooth morphotypes

Assigned teeth (G, M) among those of other small theropods

Troodon is considered to be one of the most derived members of its family. Along with Zanabazar, Saurornithoides and Talos it forms a clade of specialized troodontids.[3]

Below is a cladogram of Troodontidae by Zanno et al.

Troodontidae

Sinovenator changii





Sinovenator changii



Mei long





IMG 100/44




Sinornithoides youngi




Talos sampsoni




Byronosaurus jaffei




Talos sampsoni





Talos sampsoni



Saurornithoides mongoliensis





Zanabazar junior



Troodon formosus











Habitats[]

“Troodons” lived in many different environments from woods, to forests, tundras, fields, meadows, grasslands, plains and lowlands. Like Coyotes, the "Troodon" was a likely very adaptable dinosaur that could survive in different habitats, as suggested by the remains of its relatives. This dinosaur has had presumed material found in Alaska, Alberta, Montana, Wyoming, Texas and New Mexico, though it is still unknown how much of this material belonged to "Troodon."

Paleobiology[]

Troodon at night

Hypothetical restoration based on related animals

Troodon likely ate baby dinosaurs, but its main prey were birds, lizards, snakes, and small mammals. The form of the teeth suggests that Troodon may have been opportunistic, snatching whatever scraps of food were left behind by larger animals, based on the fact that Troodon would have been lower down the food chain. Troodon teeth were not adapted to crunch down on hard-shelled food, instead favouring soft prey rather than tough plants or shelled animals.

Paleoecology[]

Alaskan troodont

Restored skeleton of an unnamed Alaskan troodontid, Perot Museum

The type specimen of Troodon formosus was found in the Judith River Formation of Montana. The rocks of the Judith River Formation are equivalent in age with the Oldman Formation of Alberta, which has been dated to between 77.5 and 76.5 million years ago.

In the past, remains have been attributed to the same genus as the Judith River Troodon from a wide variety of other geological formations. It is now recognized as unlikely that all of these fossils, which come from localities hundreds or thousands of miles apart, separated by millions of years of time, represent a single species or genus of troodontid dinosaurs. Further study and more fossils are needed to determine how many species of Troodon existed. It is questionable that, after further study, any additional species can be referred to Troodon, in which case the genus would be considered a nomen dubium.

Additional specimens currently referred to Troodon come from the upper Two Medicine Formation of Montana, the Dinosaur Park Formation and Horseshoe Canyon Formation of Alberta, and the Prince Creek Formation of Alaska. There is some evidence that Troodon favored cooler climates, as its species seem to have been particularly abundant in northern and even arctic areas and during cooler intervals, such as the early Maastrichtian. Possible Troodon teeth have been found in the lower Javelina Formation of Texas and the Naashoibito Member of the Kirtland Formation in New Mexico. It lived alongside of rich myriad of dinosaurs such as the hadrosaurs Edmontosaurus and Maiasaura, the armoured Zuul and Edmontonia, the ceratopsians Centrosaurus and Pachyrhinosaurus, as well as the ferocious tyrannosaurid Gorgosaurus, Albertosaurus, and Daspletosaurus.

JPInstitute.com Description[]

Troodon may have been the smartest of all the dinosaurs.

It had a very large brain when compared to its overall body size, which would have given it huge hunting advantage. It also had large eyes, long legs for speedy pursuit of prey, and sharp teeth.

Troodon is one of the most well known dinosaurs, with over 20 known specimens, including an egg with a Troodon embryo inside. It was actually one of the first North American dinosaurs to be named, originally described in 1856. However, the fragmentary remains were attributed to a number of dinosaurs before the original genus became accepted. It wasn't until Dr. Dale Russell described a fairly complete specimen that the pieces fell into place.

Troodon is also used as evidence in the bird/dinosaur debate, as it shares a number of common characteristics with birds.

Dinosaur Field Guide Description[]

Troodon ("wounding tooth") is a small bird-like theropod. It has very long legs with specialized feet, in which the middle long bone was pinched out at the top to form a shock-absorbing wedge. This allowed it to run very fast. Troodon had very large eyes that faced mostly forward, so that could focus better. It is famous for having one of the largest brains (for its body size) of any dinosaur. Troodon had a jaw full of many small teeth, but they were not like the teeth of typical meat-eaters. Instead of little serrations running up and down the back of the teeth (as in most meat-eaters), there were much bigger bumps running along the side, as in many plant-eating dinosaurs and lizards. Some paleontologists speculate that Troodon may have eaten not only small mammals, lizards, and baby dinosaurs, but also insects, eggs, and even plants. Paleontologist Dave Varricchio discovered the first Troodon nests. Like oviraptorosaurs and ground-dwelling birds, Troodon would make a nest on the ground. It would then curl up on top of the nest to brood its eggs.

Fun Facts[]

When the first Troodon tooth was found, paleontologists thought it was from a lizard!

Trivia[]

Paleontologist Dale Russell once made a model of what he thought a modern, intelligent, tool-using descendant of Troodon would look like. He named this creature "dinosauroid."

Gallery[]

Appearance in other media[]

Jurassic Park[]

  • Troodon is mentioned in The Lost World novel. John Roxton discovered what he believed to be a Velociraptor skeleton in Mongolia. However, it was actually a Troodon skeleton (even though the Troodon genus is only found in North America, although there are troodontids in Asia). The fossil discovered had impressions of its skin.
  • Troodon is one of the available dinosaurs on the IOS application, Jurassic Park Builder. The Troodon uses the same animations of Compsognathus and Velociraptor.
  • Troodon was added to Jurassic World: The Game on January 4, 2016, but is a limited tournament dinosaur. It is a legendary carnivore. While it is accurately portrayed with a coat of feathers, it is shown inaccurately to be able to pronate it's hands.
  • A pack of Troodons can be seen in Jurassic Park: The Game at the beginning and in other parts of the game. They are said to be venomous in the game, which is very unlikely. It is important to note that the species of Troodon in the game is the fictional species "Troodon pectinodon" (the name is combined with the genus Pectinodon for the species name) and not an existing species. The Troodons in the game, even though claimed to be created only using Troodon DNA, but still have pronated wrists and minimal quill-like feathers.
  • Troodon was added to Jurassic World: Evolution on November 20 2018. It will inaccurately have a poisonous bite, much like Jurassic Park: The Game. It is also lacked the feathers which in real life they have and made sounds of Compsognathus.


The Land Before Time[]

It appears in The Land Before Time: Dinosaur Q&A.


Links[]

http://web.archive.org/web/20040606034106/http://www.jpinstitute.com/dinopedia/dinocards/dc_trood.html

References[]

  1. Holtz, Thomas R., Brinkman, Daniel L., Chandler, Chistine L. (1998) Denticle Morphometrics and a Possibly Omnivorous Feeding Habit for the Theropod Dinosaur Troodon. Gaia number 15. December 1998. pp. 159-166.
  2. Template:Cite journal
  3. Cite error: Invalid <ref> tag; no text was provided for refs named Talos
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