Troodon

Kingdom: Animalia

Phylum: Chordata

Class: Reptilia

Order: Saurischia

Family: Troodontidae

Genus:Troodon

Species:formosus

Introduction

Troodon was a small carnivorous or omnivorous dinosaur from the Late Cretaceous forests of North America. Troodon's discovery was important because it sparked an ongoing debate about the intelligence and potential social behavior of dinosaurs.

During the Triassic and Early Jurassic periods, the continents of the world were united in a single landmass, known as Pangaea, and dinosaurs spread around the globe and diversified into several species. Pangaea broke apart during the Jurassic, giving rise to two supercontinents, Gondwana in the south and Laurasia in the north.

During the Cretaceous period, the supercontinents of the Jurassic began to split into the present continental forms. Western Laurasia supported a wide variety of dinosaurs, many descended from species that migrated into the region during the Jurassic period. Troodon was a member of a widespread group of small- to medium-sized predatory dinosaurs that included Velociraptor and other common predators of the Cretaceous.

Classification

Scientists use two major methods to classify organisms. Linnaean taxonomy categorizes organisms based on overall physical similarity and is the basis for the current system of kingdom, phylum, family, etc. A more modern method called “cladistics” groups organisms based on evolutionary relationships, indicated by the inheritance of key traits. Cladistics creates “clades,” or groups of organisms related to a common ancestor, by examining a few key traits and trying to pinpoint the origin of the trait in evolutionary history.

Troodon belonged to a suborder of the saurischian or “lizard-hipped” dinosaurs called Theropoda, which were generally bipedal predatory animals. Theropods were characterized by the arrangement of the spine and pelvic bones and developments of the skull. Troodon is a member of Maniraptora, a division of the order Theropoda containing small, birdlike predators with grasping hands. Maniraptora are among the groups considered most closely related to birds.

Anatomy

Troodon was a small dinosaur, measuring about 2 meters (6 ft) long from nose to tail and standing about 1 meter (3 ft) at the hip. The adult animal weighed 27 to 50 kilograms (59–110 lbs). It was bipedal, with two long back legs terminating in clawed, four-toed feet. The second toe of each foot was modified with a larger, sickle-shaped claw. The slimmer, shorter forelimbs ended in three thin, clawed fingers on each hand, including one finger that was turned toward the other two, forming a partially opposable digit that may have given the dinosaur a dexterous grip.

Troodon had a long neck and a short muzzle, with long jaws of sharp, pointed teeth. Its head was large compared to its overall body size and its large, forward-facing eyes indicate sharp, binocular vision. Troodon, like its close relatives, might have been partly covered in simple feathers.

Intelligence

Troodon had an EQ level more than six times higher than other similarly-sized dinosaurs. Paleontologist Dale Russell used Troodon as evidence that the EQ values for dinosaurs were rising through the Mesozoic. Russell suggested that, if the Troodon lineage had continued, descendants might have developed human-like intelligence.

Russell's suggestion of sentient dinosaur evolution caused a major controversy, and many paleontologists argued that this theory was unsupported science fiction. Though Troodon might never have evolved into dinosaur humanoids, it was likely more intelligent than most dinosaurs of the Cretaceous and other periods.

Reproduction and Population

Paleontologists found skeletons of adult Troodon in close proximity to nests with eggs and juvenile animals, suggesting that the species may have brooded its eggs and displayed some form of parental care. By comparing the size and bone development of Troodon found near nest sites to living animals, researchers found that it was most likely male animals that were brooding the eggs. In addition, analyses of juvenile and hatchling Troodon indicated that the young may have required some parental care after hatching.

According to paleontologists, Troodon constructed circular nests from dirt and other debris, with raised edges to keep the eggs contained. Some evidence suggests that Troodon did not lay all of its eggs at once, but returned to the nest several times to add to the clutch. Species closely related to Troodon have been found to have two oviducts, meaning that the animals could lay eggs two at a time. This characteristic might have been common to the group.

Diet

Troodon was closely related to other groups of predatory dinosaurs, but Troodon's dentition indicates that it may also have eaten plants. It was first thought that Troodon used its unique serrated teeth to kill larger prey, creating large wounds that would cause terminal bleeding. Examinations of the jaws and teeth later led some to suggest that Troodon was an herbivore, using its sharp teeth to strip vegetation.

Troodon possessed other features, such as binocular vision, that are common in omnivorous, predatory animals. Some paleontologists suggest that Troodon's unusual dentition allowed it to eat plants as well as small animals, insects, and potentially larger dinosaurs if the animal hunted in groups.

Behavior

Because Troodon and its relatives were closely related to modern birds, paleontologists sometimes use birds as the general model when trying to infer information about the behavior of Troodon and similar species.

Troodon may have lived and/or hunted in groups. Elements of the animal's reproductive behavior also suggest some degree of social behavior. The animal had one of the largest brains of any dinosaur, which may have aided in predation, but is also characteristic of animals with complex social systems.

Habitat andOther Life Forms

During the Late Cretaceous, the center of North America was covered by a shallow inland sea surrounded by tidal marshes, flood plains, and lush forests. Ferns and gymnosperms, like conifers and cycads, were the dominant plants, though the first angiosperms were beginning to spread around the continent. A wide variety of insects, small reptiles, amphibians, and mammals lived in Cretaceous North America, many resembling living species.

Though birds were present, the dominant flying vertebrates were still the flying reptiles, or pterosaurs, ranging in size from small insect hunters to massive dinosaur-eating predators. Troodon was one of many successful theropods living in Cretaceous North America. The closely-related dromaeosaur predators were present, including Bambiraptor and Dromaeosaurus. There were also carnosaurs, large carnivorous theropods that had existed since the Jurassic period, including Tyrannosaurus and Albertosaurus.

North America was also home to a wide variety of herbivorous dinosaurs, including the hadrosaurs, or “duck-billed” dinosaurs, like Maiasaura and Parasaurolophus, and the ceratopsians, or “horned dinosaurs,” like Triceratops, Styracosaurus, and Pentaceratops. Other groups of herbivores included the pachycephalosaurids, bipedal herbivores distinguished by bony plates on the tops of their skulls, and the ankylosaurs, large herbivores with armored plates along their backs and weaponry on the ends of their tails.

Research

The first Troodon fossil was discovered by American paleontologist Joseph Leidy and described in 1856, from a single tooth. The bones of the species were not matched with the teeth until the 1980s. Before this time, paleontologists had named the bones as part of a dinosaur called Stenonychosaurus, which, along with Pectinodon, was later merged with the genus Troodon as Troodon inequalis and Troodon bakkeri, respectively.

In 1997, paleontologist David Varricchio began publishing papers on his analysis of Troodon nests and eggs uncovered from a fossil bed in Montana, forming the basis for theories that Troodon brooded its eggs and possibly provided basic parental care to its offspring.

In 2014, a paleontology student at the University of Alberta, Aaron van der Reest, was doing field work in Alberta's Dinosaur Provincial Park, when he found the remains of what he initially thought was a Troodon formosus. Van der Reest noticed that the pelvis and pubis bone differed from other troodontid remains, prompting him to examine the remains of other specimens from southern Alberta. In a 2017 study, he and paleontologist Philip J. Currie argued that the troodontid remains found in the Dinosaur Park Formation should not be assigned to Troodon, but to the resurrected troodontid species Stenonychosaurus inequalis and a novel troodontid species, Latenivernatrix mcmasterae.

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