Name: Troodon ‭(‬wounding tooth‭)‬.
Phonetic: Tru-don.
Named By: Joseph Leidy‭ ‬-‭ ‬1856.
Classification: Chordata,‭ ‬Reptilia,‭ ‬Dinosauria,‭ ‬Saurischia,‭ ‬Theropoda,‭ ‬Troodontidae,‭ ‬Troodontinae.
Species: T.‭ ‬formosus‭ (‬type‭)‬.
Diet: Carnivore.
Size: Unknown.
Known locations: USA,‭ ‬Monatana‭ ‬-‭ ‬Judith River Formation.
Time period: Campanian of the Cretaceous.
Fossil representation: Teeth.

       Remarkably when Troodon was first‭ '‬discovered‭' ‬it was only known from a tooth,‭ ‬and it was the description of this tooth that gave rise to the genus.‭ ‬Although naming a creature after only discovering its teeth is hard to imagine today,‭ ‬it was a common place practice in the nineteenth century,‭ ‬and at least in the case of Troodon the teeth were different to most others.‭ ‬Two problems arose from describing Troodon from only teeth.‭ ‬One,‭ ‬while these teeth were curved like in a carnivore,‭ ‬they had curved serrations similar to some herbivores.‭ ‬Two,‭ ‬because no one knew of any skeletal remains,‭ ‬no one knew what kind of dinosaur it actually was,‭ ‬or even if it really was a dinosaur for that matter.‭
       When named by Joseph Leidy in‭ ‬1856,‭ ‬Troodon was classed as a lizard.‭ ‬When classed as a dinosaur in‭ ‬1901,‭ ‬Troodon was assigned to the megalosauridae,‭ ‬a wastebasket group at the time that was used as a dumping ground for any carnivorous dinosaur whose kind and position among others was not known.‭ ‬In‭ ‬1924‭ ‬Troodon‭ '‬became‭' ‬a pachycephalosaur,‭ ‬a herbivorous kind of dinosaur known for having dome headed skulls,‭ ‬with the grouping made on the basis of similarities between their teeth,‭ ‬notably the serrations.‭ ‬It should also be mentioned that as Troodon was grouped with them,‭ ‬all pachycephalosaurs known at the time were classed under Troodontidae,‭ ‬until‭ ‬1945‭ ‬when Troodon was removed from the group on the basis that its teeth were for a carnivorous purpose.‭ ‬Because the group could not be called after a dinosaur that was no longer a part of it,‭ ‬they were re-named the pachycephalosuars after Pachycephalosaurus.

       Skipping back to‭ ‬1932,‭ ‬and another genus of dinosaur,‭ ‬Stenonychosaurus,‭ ‬was formally described to science.‭ ‬This‭ ‬was a small predator,‭ ‬later realised to have had teeth similar to Troodon.‭ ‬But for over fifty years Stenonychosaurus and Troodon were kept separate,‭ ‬until‭ ‬1987,‭ ‬when palaeontologist Philip J.‭ ‬Currie found Stenonychosaurus to be a synonym of Troodon.‭ ‬This was done on the basis that differences in tooth and jaw form of known troodonts seemed to‭ ‬have been down to age and growth and were probably representing a single species of dinosaur.
       The addition of this fossil material‭ ‬to Troodon allowed the first accurate reconstructions of the genus.‭ ‬As a small predator with a sickle shaped claw on each foot,‭ ‬Troodon was often recreated in popular science,‭ ‬as a small but fierce and deadly predator that terrorised Late Cretaceous North America.‭ ‬This depiction was common throughout the late twentieth/early twenty-first centuries.
       Now it seems things were not so clear cut,‭ ‬and questions over assigning all of this fossil material to Troodon began to be asked as to whether this was the correct thing to do.‭ ‬This questioning was not just done by some other palaeontologists,‭ ‬but by Philip Currie himself.‭ ‬Throughout the‭ ‬1990s and opening years of the twenty-first century new ideas that fossils from different formations could represents at least different species of Troodon,‭ ‬perhaps even different genera of troodontid dinosaurs,‭ ‬were often discussed.
       Ultimately the problem of Troodon always came down to the same issue.‭ ‬Troodon was established upon the basis of teeth,‭ ‬and like all creatures described by only teeth,‭ ‬it is almost impossible to refer fossils on bone material.‭ ‬On the principal of‭ ‬extra fossil bones later assigned to Troodon,‭ ‬there was just not a clear example to prove a connection,‭ ‬just superficial similarity.
       Thirty years after Troodon and Stenonychosaurus were synonymised together,‭ ‬they were split again in‭ ‬2017.‭ ‬Fossils of bones once used to reconstruct‭ ‬Troodon now either placed back into the resurrected Stenonychosaurus genus,‭ ‬or moved into an additional new genus called Latenivenatrix.‭ ‬This conclusion is the culmination of work by many palaeontologists again including Philip Currie.‭ ‬While some palaeontologists have not‭ ‬been quick to accept the removal of bone fossils from‭ ‬Troodon,‭ ‬at the time‭ ‬of writing‭ (‬2020‭) ‬most palaeontologists are working with the resurrection of Stenonychosaurus and description of Latenivenatrix as valid.
       With Troodon being dubbed a‭ ‘‬tooth taxon‭’ (‬known only from teeth‭)‬,‭ ‬Troodon itself is now once again regarded as a dubious genus of dinosaur.

Further reading
-‭ ‬Notices of remains of extinct reptiles and fishes,‭ ‬discovered by Dr.‭ ‬F.‭ ‬V.‭ ‬Hayden in the bad lands of the Judith River,‭ ‬Nebraska Territory.‭ ‬-‭ ‬Proceedings of the Academy of Natural Sciences of Philadelphia‭ ‬8:72-73.‭ ‬-‭ ‬J.‭ ‬Leidy‭ ‬-‭ ‬1856.
-‭ ‬The dentary of Troödon,‭ ‬a genus of theropod dinosaurs.‭ ‬-‭ ‬Journal of Paleontology‭ ‬22‭(‬5‭)‬:625-629.‭ ‬-‭ ‬L.‭ ‬S.‭ ‬Russel‭ ‬-‭ ‬1948.
-‭ ‬A new specimen of Stenonychosaurus from the Oldman Formation‭ (‬Cretaceous‭) ‬of Alberta.‭ ‬-‭ ‬Canadian Journal of Earth Sciences‭ ‬6:595-612.‭ ‬-‭ ‬D.‭ ‬A.‭ ‬Russel‭ ‬-‭ ‬1969.
-‭ ‬Reconstruction of the small Cretaceous theropod Stenonychosaurus inequalis and a hypothetical dinosauroid.‭ ‬-‭ ‬Syllogeus‭ ‬37:‭ ‬1‭–‬43.‭ ‬-‭ ‬D.‭ ‬A.‭ ‬Russel‭ & ‬R.‭ ‬Séguin‭ ‬-‭ ‬1982.
-‭ ‬Theropods of the Judith River Formation of Dinosaur Provincial Park,‭ ‬Alberta,‭ ‬Canada,‭ ‬by P.‭ ‬J.‭ ‬Currie.‭ ‬-‭ ‬In Fourth Symposium on Mesozoic Terrestrial Ecosystems.‭ ‬Tyrrell Museum of Paleontology,‭ ‬Drumheller,‭ ‬Alberta‭ ‬52-60.‭ ‬-‭ ‬P.‭ ‬J.‭ ‬Currie‭ & ‬E.‭ ‬H.‭ ‬Koster‭ (‬eds.‭) ‬-‭ ‬1987.
-‭ ‬Bird-like characteristics of the jaws and teeth of troodontid theropods‭ (‬Dinosauria,‭ ‬Saurischia‭)‬.‭ ‬-‭ ‬Journal of Vertebrate Paleontology‭ ‬7:‭ ‬72‭–‬81.‭ ‬-‭ ‬P.‭ ‬J.‭ ‬Currie‭ ‬-‭ ‬1987.
-‭ ‬Bone microstructure of the Upper Cretaceous theropod dinosaur Troodon formosus.‭ ‬-‭ ‬Journal of Vertebrate Paleontology‭ ‬13,‭ ‬99-104.‭ ‬-‭ ‬D.‭ ‬V.‭ ‬Varricchio‭ ‬-‭ ‬1993.
-‭ ‬Denticle Morphometrics and a Possibly Omnivorous Feeding Habit for the Theropod Dinosaur Troodon.‭ ‬-‭ ‬Gaia‭ ‬15.‭ ‬-‭ ‬Thomas R.‭ ‬Holtz,‭ ‬Daniel L.‭ ‬Brinkman‭ & ‬Christine L.‭ ‬Chandler‭ ‬-‭ ‬1998.
-‭ ‬Embryos and eggs for the Cretaceous theropod dinosaur Troodon formosus.‭ ‬-‭ ‬Journal of Vertebrate Paleontology‭ ‬22‭ (‬3‭)‬:‭ ‬564‭–‬576.‭ ‬-‭ ‬David J.‭ ‬Varricchio,‭ ‬John R.‭ ‬Horner‭ & ‬Frankie D.‭ ‬Jackson‭ ‬-‭ ‬2002.
-‭ ‬The last polar dinosaurs:‭ ‬high diversity of latest Cretaceous arctic dinosaurs in Russia.‭ ‬-‭ ‬Naturwissenschaften‭ ‬-‭ ‬P.‭ ‬Godefroit,‭ ‬L.‭ ‬Golovneva,‭ ‬S.‭ ‬Shchepetov,‭ ‬G.‭ ‬Garcia‭ & ‬P.‭ ‬Alekseev‭ ‬-‭ ‬2008.
-‭ ‬On the Occurrence of Exceptionally Large Teeth of Troodon‭ (‬Dinosauria:‭ ‬Saurischia‭) ‬from the Late Cretaceous of Northern Alaska.‭ ‬-‭ ‬Palaios volume‭ ‬23‭ ‬pp.322-328.‭ ‬-‭ ‬Anthony R.‭ ‬Fiorillo‭ ‬-‭ ‬2008.
-‭ ‬Description of two partial Troodon braincases from the Prince Creek Formation‭ (‬Upper Cretaceous‭)‬,‭ ‬North Slope Alaska.‭ ‬-‭ ‬Journal of Vertebrate Paleontology‭ ‬29‭(‬1‭)‬:178-187.‭ ‬-‭ ‬A.‭ ‬R.‭ ‬Fiorillo,‭ ‬R.‭ ‬S.‭ ‬Tykoski,‭ ‬P.‭ ‬J.‭ ‬Currie,‭ ‬P.‭ ‬J.‭ ‬McCarthy‭ & ‬P.‭ ‬Flaig‭ ‬-‭ ‬2009.
-A new species of troodontid theropod‭ (‬Dinosauria:‭ ‬Maniraptora‭) ‬from the Horseshoe Canyon Formation‭ (‬Maastrichtian‭) ‬of Alberta,‭ ‬Canada.‭ ‬Canadian Journal of Earth Sciences.‭ ‬54‭ (‬8‭)‬:‭ ‬813‭–‬826.‭ ‬-‭ ‬D.‭ ‬C.‭ ‬Evans,‭ ‬T.‭ ‬M.‭ ‬Cullen,‭ ‬D.‭ ‬W.‭ ‬Larson‭ & ‬A.‭ ‬Rego‭ ‬-‭ ‬2017.
-‭ ‬Troodontids‭ (‬Theropoda‭) ‬from the Dinosaur Park Formation,‭ ‬Alberta,‭ ‬with a description of a unique new taxon:‭ ‬implications for deinonychosaur diversity in North America‭ ‬.‭ ‬Canadian Journal of Earth Sciences‭ ‬54:919-935.‭ ‬-‭ ‬A.‭ ‬J.‭ ‬van der Reest‭ & ‬P.‭ ‬J.‭ ‬Currie‭ ‬-‭ ‬2017.


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