44-615: Troodon ( / ˈ t r oʊ . ə d ɒ n / TROH -ə-don ; Troödon in older sources) is a former wastebasket taxon and a potentially dubious genus of relatively small, bird -like theropod dinosaurs definitively known from the Campanian age of the Late Cretaceous period (about 77 mya ). It includes at least one species, Troodon formosus , known from Montana . Discovered in October 1855, T. formosus
88-503: A nomen dubium . In 2017, Evans and colleagues further discussed the undiagnostic nature of the holotype of Troodon formosus and suggested that Stenonychosaurus be used for troodontid skeletal material from the Dinosaur Park Formation. Later in the same year, Aaron J. van der Reest and Currie came to a similar conclusion as Evans and colleagues and also split much of the material assigned to Stenonychosaurus into
132-593: A wastebin taxon , dustbin taxon or catch-all taxon ) is a term used by some taxonomists to refer to a taxon that has the purpose of classifying organisms that do not fit anywhere else. They are typically defined by either their designated members' often superficial similarity to each other, or their lack of one or more distinct character states or by their not belonging to one or more other taxa. Wastebasket taxa are by definition either paraphyletic or polyphyletic , and are therefore not considered valid taxa under strict cladistic rules of taxonomy. The name of
176-442: A formal phylogenetic definition in 2015, when it was defined as all species more closely related to Coelurus fragilis than to Proceratosaurus bradleyi , Tyrannosaurus rex , Allosaurus fragilis , Compsognathus longipes , Ornithomimus edmontonicus , or Deinonychus antirrhopus by Hendrickx, Hartman and Mateus. It remains unclear whether or not this group contains any species other than Coelurus itself, and while Tanycolagreus
220-465: 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
264-734: A new genus: Latenivenatrix . In 2018, Varricchio and colleagues disagreed with Evans and colleagues, citing that Stenonychosaurus had not been used in the thirty years since Currie and colleagues synonymized it with Troodon and they indicated that " Troodon formosus remains the proper name for this taxon". This conclusion by Varricchio was agreed upon by Sellés and colleagues in their 2021 description of Tamarro . Varricchio's comments were later addressed by Cullen and colleagues in their 2021 review of Dinosaur Park Formation biodiversity, where they noted that, while Stenonychosaurus has indeed not been used for 30 years, Currie's original hypothesis of subjective synonymy (based on tooth and jaw morphology)
308-505: A possibly omnivorous diet. 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 one single tooth from the Judith River Formation . Troodon has historically been a highly unstable classification and has been
352-554: A single species or even a single genus of troodontid. 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 . Remains referred to Troodon are known from the Prince Creek Formation , a rock layer in Alaska that dates from
396-426: A wastebasket taxon may in some cases be retained as the designation of an evolutionary grade , however. The term was coined in a 1985 essay by Stephen Jay Gould . There are many examples of paraphyletic groups, but true "wastebasket" taxa are those that are known not to, and perhaps not intended to, represent natural groups, but are nevertheless used as convenient groups of organisms. The acritarchs are perhaps
440-446: Is generalist , leading to generally similar body shapes by convergent evolution . The term wastebasket taxon is sometimes employed in a derogatory fashion to refer to an evolutionary grade taxon. Coeluridae Coeluridae is a historically unnatural group of generally small, carnivorous dinosaurs from the late Jurassic Period . For many years, any small Jurassic or Cretaceous theropod that did not belong to one of
484-523: 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. Below is a cladogram of Troodontidae by Zanno et al. in 2011. Sinovenator changii Sinovenator changii Mei long IGM 100/44 Sinornithoides youngi Talos sampsoni Byronosaurus jaffei Talos sampsoni Talos sampsoni Saurornithoides mongoliensis Zanabazar junior Troodon formosus One study
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#1732771905978528-625: Is currently uncertain due to a paucity of sufficient remains of the latter genus. A 2023 study using presumed Troodon eggshells from the Oldman Formation used clumped isotope thermometry to determine their formation and development. The study found that in contrast to the accelerated mineralization of eggs in modern birds, Troodon and likely other non-avian maniraptorans had slowed egg calcification akin to other reptiles. This would indicate that, unlike birds, Troodon and other maniraptorans had two functional ovaries that would limit
572-466: Is often included, support for this relationship has been weak in most of the studies that recovered it. In 2024, Cau recovered Coeluridae as the basalmost family of maniraptoromorphs , including few of its traditional members; in addition to Coelurus , it contains Shishugounykus (traditionally a basal alvarezsaur ), Phuwiangvenator and Vayuraptor (sometimes considered to be early megaraptorans ), Fukuivenator (sometimes considered to be
616-406: 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
660-620: 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 (now Stenonychosaurus inequalis ). In 2011, Zanno and colleagues reviewed
704-541: The coelophysids . A wastebasket Coeluridae lingered into the early 1990s in some sources (and appears in at least one 2006 source) but since then it has only been recognized in a much reduced form. In 2003, O.W.M. Rauhut, using a cladistic analysis, found Coeluridae to include Coelurus ( Late Jurassic , North America), Compsognathus (Late Jurassic, Europe), Sinosauropteryx ( Early Cretaceous , Asia) and an unnamed Compsognathus -like form (Early Cretaceous, South America; this dinosaur has since been placed in
748-455: The metatherian mammal Unnuakomys hutchisoni . Based on the amount of teeth found, this troodontid was the most common theropod of the formation , making up 2/3 of all specimens, which is a stark contrast to more southern deposits in Montana, where troodontids only comprise 6% of all theropod remains. This, along with evidence that Troodon was more abundant during cooler intervals, such as
792-412: The taxonomic name contains too much unrelated "baggage" to be successfully salvaged. As such, it is usually dumped in favour of a new, more restrictive name (for example, Rhynchocephalia ), or abandoned altogether (for example, Simia ). A related concept is that of form taxon , "wastebasket" groupings that are united by gross morphology. This is often result of a common mode of life, often one that
836-499: 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 , but that a more thorough review of the specimens is required. Because the holotype of T. formosus is a single tooth, this renders Troodon
880-434: The crocodile-like Triassic group Rauisuchia . One of the roles of taxonomists is to identify wastebasket taxa and reclassify the content into more natural units. Sometimes, during taxonomic revisions, a wastebasket taxon can be salvaged after doing thorough research on its members, and then imposing tighter restrictions on what continues to be included. Such techniques "saved" Carnosauria and Megalosaurus . Other times,
924-480: The early 1930s in the Dinosaur Park Formation of Alberta . The first was named Stenonychosaurus inequalis by Sternberg in 1932 based on a foot, fragments of a hand, and some tail vertebrae. 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
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#1732771905978968-604: The early Maastrichtian, may indicate that Troodon favored cooler climates. Additional specimens currently referred to Troodon come from the upper Two Medicine Formation of Montana. Troodon -like teeth have been found in the lower Javelina Formation of Texas and the Naashoibito Member of the Ojo Alamo Formation in New Mexico . Wastebasket taxon Wastebasket taxon (also called
1012-468: The family Coeluridae . The second, a partial lower jaw bone, was described by Gilmore (1932) as a new species of lizard which he named Polyodontosaurus grandis . In 1951, Sternberg later recognized P. grandis as a possible synonym of Troodon and 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
1056-419: The genus Latenivenatrix , and some to the genus Pectinodon . The genus name is Ancient 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
1100-402: 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 time the family Pachycephalosauridae
1144-447: The holotype could allow the direct testing of the synonymy hypothesis, but re-affirmed that, for now, given the lack of supporting evidence, the synonymy of Troodon and Stenonychosaurus cannot be maintained and that merely remaining untested for 30 years is insufficient justification to accept a proposed lumping of taxa lacking overlapping diagnostic materials. However, Varricchio and others still insist on their naming method. Troodon
1188-455: The idea. In a recent revision of the material by van der Reest & Currie, Polyodontosaurus was determined to be a nomen dubium , not fit for synonymy with other taxa. 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,
1232-475: The late Cretaceous, the area faced 120 or so days of winter darkness. This maniraptoran lived alongside many other reptiles, like the centrosaurine Pachyrhinosaurus perotorum , a species of the saurolophine hadrosaurid Edmontosaurus , the pachycephalosaurin Alaskacephale gangloffi , an unnamed azhdarchid pterosaur , and the tyrannosaurine Nanuqsaurus hoglundi . It also lived alongside
1276-454: The latest Campanian to Maastrichtian ages of the Late Cretaceous . Based on the presence of gypsum and pyrite in the rocks, it suggests that the formation was bordered by a large body of water. It seems that, based on the presence of pollen fossils, the dominant plants were trees , shrubs , herbs , and flowering plants . The temperature ranged from possibly 2-12°C, which roughly correlates to 36-54°F, and based on Alaska's position in
1320-433: The more specialized families recognized at the time was classified with the coelurids, creating a confusing array of 'coelurid' theropods that were not closely related. Although they have been traditionally included in this family, there is no evidence that any of these primitive coelurosaurs form a natural group with Coelurus , the namesake of Coeluridae, to the exclusion of other traditional coelurosaur groups. Before
1364-400: The most famous example. Wastebasket taxa are often old (and perhaps not described with the systematic rigour and precision that is possible in the light of accumulated knowledge of diversity) and populous. Fossil groups that are poorly known due to fragmentary remains are sometimes grouped together on gross morphology or stratigraphy , only later to be found to be wastebasket taxa, such as
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1408-444: The new genus Mirischia ). Rauhut considered coelurids to be a monophyletic group of basal coelurosaurs , characterized by evolutionary reversals in some aspects of the vertebrae to the more primitive theropod condition. However, he and other authors have not since found this result. Phil Senter proposed in 2007 that Coelurus and Tanycolagreus were the only coelurids, and were actually tyrannosauroids . Coeluridae received
1452-449: The number of eggs produced. Thus, the study concluded that the large clutches of fossilized eggs present in the formation, despite the limited egg production each individual had, would indicate that Troodon had communal nesting behavior, where eggs would be laid together at a single nest by multiple females, forming large clutches. This is a strategy also used by some modern birds, such as ostriches . The type specimen of Troodon formosus
1496-558: The specimens once called Stenonychosaurus were referred to as Troodon in scientific literature through the early 21st century. However, the concept that all Late Cretaceous North American troodontids belong to one single 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
1540-402: The subject of numerous conflicting synonymies with similar theropod specimens. The Troodon tooth was originally classified as a "lacertilian" ( lizard ) by Leidy, but reassigned as a megalosaurid dinosaur by Franz Nopcsa von Felső-Szilvás in 1901 (Megalosauridae having historically been a wastebin taxon for most carnivorous dinosaurs). In 1924, Gilmore suggested that the tooth belonged to
1584-424: The use of phylogenetic analyses, Coeluridae and Coelurosauria were taxonomic wastebaskets used for small theropods that did not belong to other groups; thus, they accumulated many dubious genera. As late as the 1980s, popular books recognized over a dozen "coelurids", including such disparate forms as the noasaurid Laevisuchus and the oviraptorosaurian Microvenator , and considered them descendants of
1628-406: The wear patterns of all Troodon teeth suggest a diet of soft foods - inconsistent with bone chewing, invertebrate exoskeletons, or tough plant items. This study hypothesizes a diet primarily consisting of meat. A pellet possibly belonging to Troodon suggests it hunted early mammals such as Alphadon . In 2011, another derived troodontid, Linhevenator , was described from Inner Mongolia. It
1672-563: Was among the first dinosaurs found in North America , although it was thought to be a lizard until 1877. Several well-known troodontid specimens from the Dinosaur Park Formation in Alberta were once believed to be members of this genus. However, recent analyses in 2017 have found this genus to be undiagnostic and referred some of these specimens to the genus Stenonychosaurus (long believed to be synonymous with Troodon ) some to
1716-446: Was based on multiple Troodon teeth that have been collected from Late Cretaceous deposits in northern Alaska. These teeth are much larger than those collected from more southern sites, providing evidence that northern Alaskan populations of Troodon grew to larger average body size, hinting at Bergmann's rule . This study also provides an analysis of the proportions and wear patterns of a large sample of Troodon teeth. It proposes that
1760-485: Was considered a dubious possible relative of the family. Phil Currie , reviewing the pertinent 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 , Polyodontosaurus grandis , and Pectinodon bakkeri as junior synonyms of Troodon formosus . Currie also made Saurornithoididae
1804-690: 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
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1848-493: Was known as Troodontidae . In 1945, Charles Mortram Sternberg rejected the possibility that Troodon was a pachycephalosaur thanks 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 . The first specimens assigned to Troodon that were not teeth were both found by Sternberg in
1892-429: Was never directly tested and, given that later research found that teeth were not diagnostic below the family level in troodontids, Currie's original hypothesis is therefore not supported by the available data, regardless of the amount of time since it was originally proposed. They suggested that the description of more complete skeletal material (i.e. containing dental, frontal, and postcranial elements) that can be tied to
1936-480: Was noted by the authors as having relatively short and robust forelimbs, along with an enlarged second pedal ungual akin to that of the dromaeosaurids compared to more basal troodontids. It was proposed that derived troodontids had convergently evolved dromaeosaurid-style large second pedal unguals, likely as an adaptation relating to predation. The authors noted that it is plausible that this may be applicable to other derived troodontids, including Troodon , although this
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