Richardoestesia is a medium-sized (about 100 kilograms (220 lb)) genus of theropod dinosaur from the late Cretaceous Period of what is now North America. It currently contains two species, R. gilmorei and R. isosceles.

Temporal range: Late Cretaceous, 76.5–66 Ma
Tooth of cf. R. gilmorei with close up of denticles
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Order: Saurischia
Suborder: Theropoda
Clade: Coelurosauria
Genus: Richardoestesia
Currie, Rigby & Sloan, 1990
Type species
Richardoestesia gilmorei
Currie, Rigby & Sloan, 1990
  • R. gilmorei Currie, Rigby & Sloan, 1990
  • R. isosceles Sankey, 2001


Richardoestesia isosceles
Tooth of cf. R. isosceles with close up of denticles

The holotype specimen of Richardoestesia gilmorei (NMC 343) consists of the pair of lower jaws found in the upper Judith River Group, dating from the Campanian age, about 75 million years ago. The jaws are slender and rather long, 193 millimeter, but the teeth are small and very finely serrated with five to six denticles per millimeter. The serration density is a distinctive trait of the species.

In 2001, Julia Sankey named a second species: Richardoestesia isosceles, based on a tooth, LSUMGS 489:6238, from the Texan Aguja Formation, which is of a longer and less recurved type.[1] The teeth of R. isosceles have also been identified as crocodyliform in shape, possibly belonging to a sebecosuchian.[2]


The jaws were found in 1917 by Charles Hazelius Sternberg and sons in the Dinosaur Provincial Park in Alberta at the Little Sandhill Creek site. In 1924 Charles Whitney Gilmore named Chirostenotes pergracilis and referred the jaws to this species.[3] In the eighties it became clear that Chirostenotes was an oviraptosaur to which the long jaws could not have belonged. Therefore in 1990 Phillip Currie, John Keith Rigby and Robert Evan Sloan named a separate species: Richardoestesia gilmorei.[4] The genus is named for Richard Estes, to honor his important work[5] on small vertebrates and especially theropod teeth of the Late Cretaceous. The naming authors actually intended to use the spelling Ricardoestesia, Ricardus being the normal latinisation of "Richard". However, except in one overlooked figure caption, the editors of the paper altered the spelling to include the 'h'.[1] Ironically, in 1991 George Olshevsky in a species list also used the spelling Richardoestesia, and indicated Ricardoestesia to be the misspelling, unaware that the original authors actually intended the name to be spelled this way. As a result, under ICZN rules, he acted as "first revisor" choosing between the two spelling variants of the original publication and inadvertently made the misspelt name official. Subsequently, the original authors have adopted the spelling Richardoestesia. The specific name honors Gilmore.

Age range

Richardoestesia teeth
Referred teeth from the San Juan Basin

Richardoestesia-like teeth have been found in many Late Cretaceous geological formations, including the Horseshoe Canyon Formation, the Scollard Formation, Hell Creek Formation, Ferris Formation, and the Lance Formation (dated to about 66 million years ago). Similar teeth have been referred to this genus from as early as the Barremian age (Cedar Mountain Formation, 125 million years ago).[6]

Because of the disparity in location and time of the many referred teeth, researchers have cast doubt on the idea that they all belong to the same genus or species. A comparative study of the teeth published in 2013 demonstrated that both R. gilmorei and R. isosceles were only definitively present in the Dinosaur Park Formation, dated to between 76.5 and 75 million years ago. R. isosceles was also present in the Aguja Formation, roughly the same age. All other referred teeth most likely belong to different species, which have not been named due to the lack of body fossils for comparison.[7]

Fossils of Richartoestesia have also been found in the Tremp Formation of northeastern Spain.[8]


  1. ^ J.T. Sankey, 2001, "Late Campanian southern dinosaurs, Aguja Formation, Big Bend, Texas", Journal of Paleontology 75(1): 208-215
  2. ^ Company, J.; Suberbiola, X.P.; Ruiz-Omenaca, J.I.; Buscalioni, A.D. (2005). "A new species of Doratodon (Crocodyliformes: Ziphosuchia) from the Late Cretaceous of Spain" (PDF). Journal of Vertebrate Paleontology. 25 (2): 343–353. doi:10.1671/0272-4634(2005)025[0343:ANSODC]2.0.CO;2.
  3. ^ Gilmore, C.W., 1924, "A new coelurid dinosaur from the Belly River Cretaceous of Alberta", Canada Department of Mines Geological Survey Bulletin (Geological Series) 38(43): 1-12
  4. ^ Currie, P. J., K. J. Rigby, and R. E. Sloan. 1990. "Theropod teeth from the Judith River Formation of southern Alberta, Canada". Pp. 107–125. In P. J. Currie, and K. Carpenter, eds. Dinosaur Systematics: Perspectives and Approaches. Cambridge University Press, Cambridge.
  5. ^ Estes, R., 1964, Fossil vertebrates from the Late Cretaceous Lance Formation, eastern Wyoming. University of California Publications in Geological Sciences 49: 1-180
  6. ^ Kirkland, Lucas and Estep, (1998). "Cretaceous dinosaurs of the Colorado Plateau." in Lucas, Kirkland and Estep (eds.). Lower and Middle Cretaceous Terrestrial Ecosystems. New Mexico Museum of Natural History and Science Bulletin, 14, 79-89.
  7. ^ Larson DW, Currie PJ (2013) Multivariate Analyses of Small Theropod Dinosaur Teeth and Implications for Paleoecological Turnover through Time. PLoS ONE 8(1): e54329. doi:10.1371/journal.pone.0054329
  8. ^ Blasi 2 at

Further reading

  • Baszio, S. 1997. Investigations on Canadian dinosaurs: systematic palaeontology of isolated dinosaur teeth from the Latest Cretaceous of Dinosaur Provincial Park, Alberta, Canada. Courier Forschunginstitut Senckenberg 196:33-77.
  • Sankey, J. T., D. B. Brinkman, M. Guenther, and P. J. Currie. 2002. Small theropod and bird teeth from the Late Cretaceous (Late Campanian) Judith River Group, Alberta. Journal of Paleontology 76(4):751-763.

External links


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Camadas de Guimarota

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Foremost Formation

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The Kirtlandian is a North American land-vertebrate faunal age of the Cretaceous period, following the Judithian and succeeded by the Edmontonian. It lasted about 2 million years, ca 74.8 to 72.8 Mya and is characterized by the ceratopsian Pentaceratops sternbergii, which lived throughout the Kirtlandian. It was first named by R.M. Sullivan and S.G. Lucas in 2003 as a faunal age for the Kirtland and Fruitland formations. Previously, only five land-vertebrate ages were identified from the Late Cretaceous. as identified by Loris S. Russell in 1975, they include the Paluxian, Aquilan, Judithian, Edmontonian, and the Lancian. Before the naming of the Kirtlandian, three gaps, between the Paluxian and Aquilan, the Aquilan and the Judithian, and the Judithian and Edmontonian, were identified but not named.

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List of the Mesozoic life of Montana

This list of the Mesozoic life of Montana contains the various prehistoric life-forms whose fossilized remains have been reported from within the US state of Montana and are between 252.17 and 66 million years of age.

List of the Mesozoic life of South Dakota

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List of the Mesozoic life of Utah

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List of the prehistoric life of Montana

This list of the prehistoric life of Montana contains the various prehistoric life-forms whose fossilized remains have been reported from within the US state of Montana.

List of the prehistoric life of North Dakota

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List of the prehistoric life of South Dakota

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Lourinhã Formation

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Ojo Alamo Formation

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Paronychodon (meaning "beside claw tooth") was a theropod dinosaur genus. It is a tooth taxon, often considered dubious because of the fragmentary nature of the fossils, which include "buckets" of teeth but no other remains.

The type species, named by Edward Drinker Cope in 1876, is Paronychodon lacustris, from the Judith River Formation of Montana, dating to 75 million years ago, during the Campanian stage. The holotype is specimen AMNH 3018. It is a tooth about one centimetre long, elongated, recurved, lacking serrations, possessing low vertical ridges and with a D-shaped cross-section, the inner side being flattened. Cope at first thought the tooth belonged to a plesiosaur, but the same year realised it represented a carnivorous dinosaur.A second species, Paronychodon caperatus, is known from the Hell Creek Formation of North Dakota, Montana, and South Dakota and Lance Formation of Wyoming (latest Maastrichtian stage, 66 million years ago) and was originally referred to the mammal genus Tripriodon by Othniel Charles Marsh in 1889, but placed in Paronychodon by George Olshevsky in 1991. It is based on holotype YPM 10624, a tooth close in form to the holotype of P. lacustris but somewhat larger. In 1995 Olshevsky renamed Laelaps explanatus Cope 1876 into a Paronychodon explanatus; today the taxon is seen as based on Saurornitholestes teeth.

A very large number of other specimens matching these teeth in some or all aspects of their anatomy have been referred to Paronychodon. Some of these included serrated teeth, low teeth and teeth without a flattened side. These teeth of the general "Paronychodon" type have been reported from a wide variety of times and places, including the Early Cretaceous Una Formation of Spain, dating to the late Barremian age 125 million years ago.

Paronychodon has been considered a coelurid, an ornithomimosaur, a dromaeosaurid, an archaeopterygid, and a troodontid, though it could also be another kind of coelurosaurian theropod. While most researchers have therefore considered it simply represents indeterminate theropod teeth, a small consensus has found them to be Deinonychosauria. The teeth assigned to Paronychodon are all small, and may have come from various juvenile deinonychosaurs. Jaws from adult individuals bearing identical teeth have never been found. Marsh already suggested such teeth were pathological, having formed when the first teeth of the lower jaws by accident grew back-to-back to each other on the mandible suture. Philip J. Currie in 1990 also concluded to a malformation, thinking the flattened side resulted from the tooth remaining attached too long to the inner wall of the tooth-socket. Serrated specimens of the type would thus simply be deviant dromaeosaurid teeth; however, unserrated teeth might represent a separate taxon or taxa. One study, by Sunny Hwang, showed that the tooth enamel is identical to that found in Byronosaurus, a troodontid known from juveniles with serration-less teeth.Several taxa have on occasion been considered synonyms of Paronychodon, though there is little consensus. Paronychodon was in 1876 by Cope described as being similar to Zapsalis, another tooth taxon, itself often considered synonymous with Richardoestesia, a possible dromaeosaurid. Richardoestesia isosceles would, according to a study by Julia Sankey e.a., be synonymous with the elongated, so-called "Type A", teeth of Paronychodon, to which also the Paronychodon holotype belongs. The Eurasian Euronychodon tooth genus is also sometimes considered a (junior) synonym of Paronychodon.

Udurchukan Formation

The Udurchukan Formation is a geological formation located in Amur Region, Far East Russia. Based on palynomorphs such as Wodehouseia spinata the Udurchukan is considered of Maastrichtian age of the Late Cretaceous, during the Cretaceous Period.


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