Troodon
| Troodon Temporal range: Late Cretaceous
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| File:Troodont.jpg | |
Fossil
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| Genus: | Troodon
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| Troodon formosus Leidy, 1856
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Troodon was a relatively small, bird-like dinosaur from the Late Cretaceous Period (75-65 mya). Discovered in 1855, it was among the first dinosaurs found in North America.
Its name (pronounced "Tro-odon") is Greek for "wounding tooth", referring to the dinosaur's serrated teeth (although these may actually have been adapted for a herbivorous diet).
Characteristics
Troodon was a small dinosaur, around 2 m (6.5 ft) in length, 1 m (3 ft) tall, and weighed 60 kg (130 lb). It had very long, slender limbs, suggesting that the animal was able to move quickly. It had long 'arms' that folded back like a bird's and its 'hands' possessed partially opposable thumbs. It had large, sickle-shaped claws on its second toes, which were raised off the ground when running. Because of these features scientists regard Troodon as a member of the Maniraptora. Its eyes were large (perhaps suggesting nocturnal activity) and slightly forward facing, giving Troodon some depth perception. In fact most reconstructions give Troodon eyes which point in a more forwards direction than almost any other dinosaur, which implies that it had better binocular vision than most dinosaurs. Troodon had one of the largest known brains of any dinosaur, relative to its body mass (comparable to modern birds). Hence it is believed to have been one of the most intelligent dinosaurs. Eggs have also been discovered, in nests.
Distribution
Troodon is known from the Judith River Formation of Montana, the Judith River Group of Alberta, the Horseshoe Canyon Formation of Alberta, the North Slope of Alaska and in the famous Hell Creek Formation of the USA. There is some evidence that Troodon favored cooler climates, as it seems to have been particularly abundant in northern areas and during cooler intervals, such as the Early Maastrichtian.
It seems 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 of Troodon. However, further study and more fossils are needed to determine how many species of Troodon existed.
Paleobiology
Troodon was originally thought to have been a predator, feeding mainly on smaller animals including invertebrates and mammals - this view was based on its Maniraptoran features (sickle claw on foot; bird-like folding arms) and apparently good binocular vision. However, there is some evidence that Troodon may either have been an omnivore or a herbivore. The jaws met in a broad, U-shaped symphysis similar to that of an iguana, a lizard species adapted to a plant-eating lifestyle. Additionally, the teeth of Troodon were leaf-like, bearing large serrations like those of herbivorous dinosaurs; short but broad, with wear facets on their sides. In these respects Troodon was more like plant eating dinosaurs than carnivores such as Dromaeosauridae.
A specimen of Troodon is known from Montana, sitting atop a clutch of eggs.
History
Troodon 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 Troodon tooth was originally classified as a "lacertian" (lizard) by Leidy, but re-assigned as a megalosaurid dinosaur by Nopsca in 1901 (Megalosauridae having historically been a wastebin 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). In 1945, Charles Hazelius Sternberg rejected the possibility that Troodon was a pachycephalosaur due to its stronger similarity to the teeth of other carnivorous dinosaurs.
The first specimen of Troodon that was not a tooth, then referred to its own genus (Stenonychosaurus), was named by Sternberg in 1932, based on a foot, fragments of a hand, and some caudal vertebrae from Alberta. A remarkable feature of these remains was the enlarged claw on the second toe, which is now recognized as characteristic of Deinonychosauria. Sternberg initially classified Stenonychosaurus as a member of the family Coeluridae. Later, Sternberg (1951) 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, which eventually formed the scientific foundation for a famous life-sized sculpture of Stenonychosaurus accompanied by its fictional, human-like descendant, the "dinosauroid". Stenonychosaurus became a well-known theropod in the 1980s, when the feet and braincase were described in more detail. Phil Currie, reviewing the known Troodontidae in 1987, reclassified Stenonychosaurus inequalis as a junior synonym of Troodon formosus. This synonymy has been widely adopted by other paleontologists, and therefore all of the specimens once called Stenonychosaurus are now referred to as Troodon in the recent scientific literature.
Classification
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. Since the discovery of the original tooth, postcranial material from a related animal were given the name Stenonychosaurus. More complete remains of Stenonychosaurus convinced most paleontologists that it in fact was the same animal as the original tooth, so the name Stenonychosaurus was replaced with its senior synonym, Troodon. Other genera, including Polyodontosaurus and Pectinodon, have also been assigned to Troodon based on the assumption that this particular tooth type is limited to only a single type of dinosaur. For this reason, the future of the name Troodon itself is dubious--in similar situations, genera based on teeth have been abandoned in favor of names based on better remains. Familiar names like Deinodon and Trachodon have been abandoned in this way, and further research may require Troodon be replaced with Stenonychosaurus. In a chapter of the 2005 book Dinosaur Provincial Park, Phil Currie (one of the leading experts on North American troodontids) resurrects the type species of Stenonychosaurus (S. inequalis) within the genus Troodon as Troodon inequalis (Currie, 2005).
The "Dinosauroid"
In 1982, paleontologist Dale Russell, curator of vertebrate fossils at the National Museum of Canada in Ottawa, speculated on how evolution would have proceeded if the troodonts had survived the extincton of the dinosaurs. Russell speculated that a species like Troodon would have grown smarter and taken on a human-like appearance. Russell partnered with taxidermist and artist Ron Sequin and together they made a model of what a derived, intelligent Troodon would look like, naming their fantasy creation a "Dinosauroid" (Russell & Séguin, 1982). While a few paleontologists, such as David Norman (1985) and Cristiano dal Sasso (2004) have regarded this as a plausible line of reasoning, others, such as Gregory S. Paul (1988) and Thomas R. Holtz Jr., consider it "suspiciously human" (Paul, 1988) and argue that a large-brained, highly intelligent troodontid would retain a more standard theropod body plan. Darren Naish has suggested the ground hornbill as a better model for a hominid-mimicking terrestrial theropod.[1][2]
In popular culture
Troodon also featured in ITV's Prehistoric Park in 2006. It was shown as a highly intelligent scavenger.
Troodon are shown in two episodes Dinosaur Planet. In one, a pack of dwarf Troodon make "friends" with a Pyroraptor, in another, a pack of Troodon attack a flock of Orodromeus.
Troodon also featured in Science Channel's Dino Lab 2006.
Troodon also made an appearence in the video game Dino Stalker in which the mother computer called one "Trinity" which could control other dinosaurs.
An intelligent saurian species very like the Troodons, called the saurs, appears in Ken MacLeod's "Engines of Light" series of books.
References
- Currie, P. J. (1987). "Bird-like characteristics of the jaws and teeth of troodontid theropods (Dinosauria, Saurischia)." Journal of Vertebrate Paleontology, 7: 72-81.
- Currie, P. J. (2005). "Theropods including birds." In: Currie & Koppelhus, Dinosaur Provincial Park, Indiana University Press, Bloomington. Pp 367-397.
- Norman, D. B. (1985). The Illustrated Encyclopedia of Dinosaurs. Salamander Books, London.
- Russell, D. A. and Séguin, R. (1982). "Reconstruction of the small Cretaceous theropod Stenonychosaurus inequalis and a hypothetical dinosauroid." Syllogeus, 37, 1-43.
- Russell, D. A. (1987). "Models and paintings of North American dinosaurs." In: Czerkas, S. J. & Olson, E. C. (eds) Dinosaurs Past and Present, Volume I. Natural History Museum of Los Angeles County/University of Washington Press (Seattle and Washington), pp. 114-131.