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

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

troodontid Troodontidae is a clade of bird-like theropod dinosaurs. During most of the 20th century, troodontid fossils were few and incomplete and they have therefore been allied, at various times, with many dinosaurian lineages. More recent fossil disco ...

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 The Dinosaur Park Formation is the uppermost member of the Belly River Group (also known as the Judith River Group), a major geologic unit in southern Alberta. It was deposited during the Campanian stage of the Late Cretaceous, between about 76. ...

. 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. inequ ...

'' or ''

Troodon ''Troodon'' ( ; ''Troödon'' in older sources) is a wastebasket taxon and a dubious genus of relatively small, bird-like dinosaurs known definitively from the Campanian age of the Late Cretaceous period (about 77 mya). It includes at leas ...

'' for a significant time, before being declared a '' nomen dubium''. 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 sever ...

and only known specimen of ''Polyodontosaurus'' was collected in 1928 by

Charles Mortram Sternberg Charles Mortram Sternberg (1885–1981) was an American-Canadian fossil collector and paleontologist, son of Charles Hazelius Sternberg. Late in his career, he collected and described '' Pachyrhinosaurus'', '' Brachylophosaurus'', '' Parksosaur ...

, and includes only a left

dentary In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower teeth in place. The mandible sits beneath the maxilla. It is the only movable bone ...

, 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 ''

'' 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

. 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 deri ...

''. This specimen, CMN 12340, was from the

Oldman Formation The Oldman Formation is a stratigraphic unit of Late Cretaceous (Campanian stage) age that underlies much of southern Alberta, Canada. It consists primarily of sandstones that were deposited in fluvial channel and floodplain environments. It was ...

of Alberta, which lies directly above the Dinosaur Park Formation. This specimen was later named ''

Latenivenatrix ''Latenivenatrix'' (meaning "hiding huntress") is a genus of troodontid known from one species, ''L. mcmasterae''. Along with the contemporary ''Stenonychosaurus'', it is known from the non-tooth fossils formerly assigned to the genus ''Troodon ...

'' 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 '' nomen dubium'', 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 ''

'' 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 (ecology ...

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

Centrosaurus ''Centrosaurus'' ( ; ) is a genus of herbivorous ceratopsian dinosaur from the Late Cretaceous of Canada. Their remains have been found in the Dinosaur Park Formation, dating from 76.5 to 75.5 million years ago. Discovery and naming The firs ...

'', '' Styracosaurus'', 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 (Greek ''grypos'') lizard"; sometimes incorrectly translated as "griffin (Latin ''gryphus'') lizard") was a genus of duckbilled dinosaur that lived about 80 to 75 million years ago, in the Late Cretaceo ...

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

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 ''Gorgosaurus'' ( ; ) is a genus of tyrannosaurid theropod dinosaur that lived in western North America during the Late Cretaceous Period (Campanian), between about 76.6 and 75.1 million years ago. Fossil remains have been found in the Ca ...

'', and

armored Armour (British English) or armor (American English; see spelling differences) is a covering used to protect an object, individual, or vehicle from physical injury or damage, especially direct contact weapons or projectiles during combat, or f ...

Edmontonia ''Edmontonia'' is a genus of panoplosaurin nodosaurid dinosaur from the Late Cretaceous Period. It is part of the Nodosauridae, a family within Ankylosauria. It is named after the Edmonton Formation (now the Horseshoe Canyon Formation in Ca ...

'' 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 w ...

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 swampy and influenced by marine conditions over time as the

Western Interior Seaway The Western Interior Seaway (also called the Cretaceous Seaway, the Niobraran Sea, the North American Inland Sea, and the Western Interior Sea) was a large inland sea that split the continent of North America into two landmasses. The ancient sea ...

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 meteorologi ...

was warmer than present-day Alberta, without frost, but with wetter and drier seasons. Conifers were apparently the dominant

canopy Canopy may refer to: Plants * Canopy (biology), aboveground portion of plant community or crop (including forests) * Canopy (grape), aboveground portion of grapes Religion and ceremonies * Baldachin or canopy of state, typically placed over an ...

plants, with an

understory In forestry and ecology, understory (American English), or understorey (Commonwealth English), also known as underbrush or undergrowth, includes plant life growing beneath the forest canopy without penetrating it to any great extent, but abo ...

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 exce ...

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 angiosperms.

References

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