''Polyodontosaurus'' (meaning "many-toothed lizard") is a potentially dubious

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

of troodontid dinosaur named in 1932 by

Charles W. Gilmore Charles Whitney Gilmore (March 11, 1874 – September 27, 1945) was an American paleontologist who gained renown in the early 20th century for his work on vertebrate fossils during his career at the United States National Museum (now the N ...

for a left dentary from the Dinosaur Park Formation. Gilmore, C. W. (1932). A new fossil lizard from the

Belly River Formation The Belly River Group is a stratigraphical unit of Late Cretaceous age in the Western Canadian Sedimentary Basin. It takes the name from the Belly River, a tributary of the Oldman River in southern Alberta, and was first described in outcrop ...

of Alberta. ''Transactions of the Royal Society of Canada'', section 4, series 3 16:117-119 It had been considered a synonym of ''

Stenonychosaurus ''Stenonychosaurus'' (meaning "narrow claw lizard") is a genus of troodontid dinosaur from the Late Cretaceous Dinosaur Park Formation of Alberta, Canada, as well as possibly the Two Medicine Formation. The type and only species, ''S. inequalis ...

'' or '' Troodon'' for a significant time, before being declared a ''

nomen dubium In binomial nomenclature, a ''nomen dubium'' (Latin for "doubtful name", plural ''nomina dubia'') is a scientific name that is of unknown or doubtful application. Zoology In case of a ''nomen dubium'' it may be impossible to determine whether a s ...

''. The only known species is the type, ''P. grandis''.

History of discovery

The

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of several ...

and only known specimen of ''Polyodontosaurus'' was collected in 1928 by Charles Mortram Sternberg, and includes only a left dentary, lacking any teeth. Sternberg presented the dentary to Charles Gilmore, who identified it as a lizard. Gilmore thus named the binomial ''Polyodontosaurus grandis'' for the new taxon in 1932. Sternberg revisited the material in 1951 and determined that it represented a carnivorous dinosaur based on the general morphology of the bone, as well as the anatomy of the Meckelian groove, multiple nutrient foramina, and separation of teeth into multiple sockets. Sternberg compared this dentary to one referred to '' Troodon'' by Russel in 1948, and decided that they belonged to the same family, and potentially the same genus. While similar, there were a few differences, that might be shown to relate to age or variation within the genus. Sternberg, therefore, referred ''Polyodontosaurus'' to the family Troodontidae, until further material could be found. The name ''Polyodontosaurus'' has been misspelled as "Polydontosaurus" by some authors. ''Polyodontosaurus'', represented by the holotype CMN 8540, was found in the Steveville area in the Dinosaur Park Formation. It was found about below the highest layer of the formation, and comes from the MAZ (Megaherbivore assemblage zone)-2 portion of the fauna, which existed after MAZ-1. This exact stratigraphic location cannot be verified. MAZ-2 spans from 75.9 to 75.3 million years ago, CMN 8540 is from slightly above (younger) than the middle of the formation. In 1969

Dale Russell Dale Alan Russell (27 December 1937 – 21 December 2019) was an American-Canadian geologist and palaeontologist. Throughout his career Russell worked as the Curator of Fossil Vertebrates at the Canadian Museum of Nature, Research Professor a ...

described a new specimen of ''

'', a troodontid closely related to ''

Saurornithoides ''Saurornithoides'' ( ) is a genus of troodontid maniraptoran dinosaur, which lived during the Late Cretaceous period. These creatures were predators, which could run fast on their hind legs and had excellent sight and hearing. The name is deriv ...

''. This specimen, CMN 12340, was from the Oldman Formation of Alberta, which lies directly above the Dinosaur Park Formation. This specimen was later named '' Latenivenatrix'' and comes from the MAZ-2 level of the formation. Because of the similarities between ''Polyodontosaurus'', ''Stenonychosaurus'', and more complete ''Saurornithoides'', Russell concluded that ''Polyodontosaurus'' was a junior synonym of ''Stenonychosaurus'', and that they both might be synonyms of the tooth-taxon ''Troodon'', although the material of ''Troodon'' is very incomplete.

Classification

After being initially named as a lizard, ''Polydontosaurus'' was reclassified as a troodontid, a classification which stands today. Since 1969 ''Polyodontosaurus'' has been considered a synonym of ''Stenonychosaurus'', and later its senior synonym ''Troodon''. ''Polyodontosaurus'' is potentially a synonym of the taxon ''Latenivenatrix'', named in 2017, but they may come from separate regions of the formation. Van der Reest & Currie in 2017 determined that due to the lack of sufficient material in the holotype, and that the dentaries of troodontids to not bear unique, autapomorphic features, ''Polyodontosaurus'' was a ''

'', and could not be considered senior synonym of ''Latenivenatrix''. Below is the phylogenetic analysis of van der Reest & Currie (2017). ''Polyodontosaurus'' has been considered a synonym of the "Two Medicine troodontid" and '' Latenivenatrix'' previously.

Paleoecology

The single specimen of ''Polyodontosaurus'' was found in the central level of the Dinosaur Park Formation, and was a member of a diverse and well-documented

fauna Fauna is all of the animal life present in a particular region or time. The corresponding term for plants is ''flora'', and for fungi, it is '' funga''. Flora, fauna, funga and other forms of life are collectively referred to as '' biota''. Zoo ...

of prehistoric animals that included such well-known dinosaurs as the

horned A horn is a permanent pointed projection on the head of various animals that consists of a covering of keratin and other proteins surrounding a core of live bone. Horns are distinct from antlers, which are not permanent. In mammals, true horns ...

'' Centrosaurus'', ''

Styracosaurus ''Styracosaurus'' ( ; meaning "spiked lizard" from the Ancient Greek / "spike at the butt-end of a spear-shaft" and / "lizard") is a genus of herbivorous ceratopsian dinosaur from the Cretaceous Period (Campanian stage), about 75.5 to 74.5&nbs ...

'', and ''

Chasmosaurus ''Chasmosaurus'' ( ) is a genus of ceratopsid dinosaur from the Upper Cretaceous Period of North America. Its name means 'opening lizard', referring to the large openings ( fenestrae) in its frill (Greek ''chasma'' meaning 'opening' or 'hollow' ...

'', fellow duckbills ''

Prosaurolophus ''Prosaurolophus'' (; meaning "before ''Saurolophus''", in comparison to the later dinosaur with a similar head crest) is a genus of hadrosaurid (or duck-billed) dinosaur from the Late Cretaceous of North America. It is known from the remains of ...

'', ''

Gryposaurus ''Gryposaurus'' (meaning "hooked-nosed (Ancient Greek, Greek ''grypos'') lizard"; sometimes incorrectly translated as "griffin (Latin ''gryphus'') lizard") was a genus of hadrosaur, duckbilled dinosaur that lived about 80 to 75 million years ...

'', ''Corythosaurus'', and ''

Parasaurolophus ''Parasaurolophus'' (; meaning "near crested lizard" in reference to '' Saurolophus)'' is a genus of herbivorous hadrosaurid ornithopod dinosaur that lived in what is now North America and possibly Asia during the Late Cretaceous Period, abou ...

'',

tyrannosaurid Tyrannosauridae (or tyrannosaurids, meaning "tyrant lizards") is a family of coelurosaurian theropod dinosaurs that comprises two subfamilies containing up to thirteen genera, including the eponymous ''Tyrannosaurus''. The exact number of genera ...

'' Gorgosaurus'', and armored '' Edmontonia'' and ''

Euoplocephalus ''Euoplocephalus'' ( ) is a genus of very large, herbivorous ankylosaurid dinosaurs, living during the Late Cretaceous of Canada. It has only one named species, ''Euoplocephalus tutus''. The first fossil of ''Euoplocephalus'' was found in 1897 i ...

''. The Dinosaur Park Formation is interpreted as a low-relief setting of

river A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases, a river flows into the ground and becomes dry at the end of its course without reaching another body of wate ...

s and

floodplain A floodplain or flood plain or bottomlands is an area of land adjacent to a river which stretches from the banks of its channel to the base of the enclosing valley walls, and which experiences flooding during periods of high discharge.Goudi ...

s that became more

swamp A swamp is a forested wetland.Keddy, P.A. 2010. Wetland Ecology: Principles and Conservation (2nd edition). Cambridge University Press, Cambridge, UK. 497 p. Swamps are considered to be transition zones because both land and water play a role in ...

y and influenced by

marine Marine is an adjective meaning of or pertaining to the sea or ocean. Marine or marines may refer to: Ocean * Maritime (disambiguation) * Marine art * Marine biology * Marine debris * Marine habitats * Marine life * Marine pollution Military * ...

conditions over time as the Western Interior Seaway transgressed westward. The

climate Climate is the long-term weather pattern in an area, typically averaged over 30 years. More rigorously, it is the mean and variability of meteorological variables over a time spanning from months to millions of years. Some of the meteorologic ...

was warmer than present-day Alberta, without

frost Frost is a thin layer of ice on a solid surface, which forms from water vapor in an above-freezing atmosphere coming in contact with a solid surface whose temperature is below freezing, and resulting in a phase change from water vapor (a gas) ...

, but with wetter and drier seasons.

Conifer Conifers are a group of conifer cone, cone-bearing Spermatophyte, seed plants, a subset of gymnosperms. Scientifically, they make up the phylum, division Pinophyta (), also known as Coniferophyta () or Coniferae. The division contains a single ...

s were apparently the dominant canopy plants, with an understory of

fern A fern (Polypodiopsida or Polypodiophyta ) is a member of a group of vascular plants (plants with xylem and phloem) that reproduce via spores and have neither seeds nor flowers. The polypodiophytes include all living pteridophytes except t ...

tree fern The tree ferns are arborescent (tree-like) ferns that grow with a trunk elevating the fronds above ground level, making them trees. Many extant tree ferns are members of the order Cyatheales, to which belong the families Cyatheaceae (scaly tree ...

s, and

angiosperm Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (), commonly called angiosperms. The term "angiosperm" is derived from the Greek words ('container, vessel') and ('seed'), and refers to those plants th ...

References

{{Taxonbar, from=Q48834266 Troodontids Late Cretaceous dinosaurs Nomina dubia Cretaceous dinosaurs of North America