''Richardoestesia'' is a

morphogenus Form classification is the classification of organisms based on their morphology (biology), morphology, which does not necessarily reflect their biological relationships. Form classification, generally restricted to palaeontology, reflects uncer ...

theropod Theropoda (; ), whose members are known as theropods, is a dinosaur clade that is characterized by hollow bones and three toes and claws on each limb. Theropods are generally classed as a group of saurischian dinosaurs. They were ancestrally c ...

dinosaur teeth, originally described from the

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''creta'', the ...

of what is now

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...

. It currently contains two species, ''R. gilmorei'' and ''R. isosceles''. It has been used as a morphotaxon to describe other theropod teeth widely displaced in time and space from the type species. If all teeth assigned to the genus are truly reflective of the animals biology and taxonomic state, it would have been one of the longest lasting dinosaur genera, prehaps also being the most widely distributed.

Species

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 ...

specimen of ''Richardoestesia gilmorei'' (NMC 343) consists of a pair of lower jaws found in the upper

Judith River Group The Judith River Group is a group of geologic formations in western North America dating from the late Cretaceous and noted as a site for the extensive excavation of dinosaur fossils. The formation is named after the Judith River in Montana. The ...

, dating from the

Campanian The Campanian is the fifth of six ages of the Late Cretaceous Epoch on the geologic timescale of the International Commission on Stratigraphy (ICS). In chronostratigraphy, it is the fifth of six stages in the Upper Cretaceous Series. Campanian s ...

age, about 75 million years ago. The jaws are slender and rather long, 193 millimeters, 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 Julia is usually a feminine given name. It is a Latinate feminine form of the name Julio and Julius. (For further details on etymology, see the Wiktionary entry "Julius".) The given name ''Julia'' had been in use throughout Late Antiquity (e.g ...

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. The teeth of ''R. isosceles'' have also been identified as

crocodyliform Crocodyliformes is a clade of crurotarsan archosaurs, the group often traditionally referred to as "crocodilians". They are the first members of Crocodylomorpha to possess many of the features that define later relatives. They are the only pseudo ...

in shape, possibly belonging to a sebecosuchian.

Research

The jaws were found in 1917 by Charles Hazelius Sternberg and sons in the

Dinosaur Provincial Park Dinosaur Provincial Park is a UNESCO World Heritage Site situated a two hour drive east of Calgary, Alberta, Canada; or , about a half-hour drive northeast of Brooks. The park is situated in the Red Deer River valley, which is noted for its stri ...

Alberta Alberta ( ) is one of the thirteen provinces and territories of Canada. It is part of Western Canada and is one of the three prairie provinces. Alberta is bordered by British Columbia to the west, Saskatchewan to the east, the Northwest Ter ...

at the Little Sandhill Creek site. In 1924

Charles Whitney 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 ...

named ''

Chirostenotes ''Chirostenotes'' ( ; named from Greek 'narrow-handed') is a genus of oviraptorosaurian dinosaur from the late Cretaceous (about 76.5 million years ago) of Alberta, Canada. The type species is ''Chirostenotes pergracilis''. History of discover ...

pergracilis'' and referred the jaws to this species. In the 1980s it became clear that ''Chirostenotes'' was an

oviraptorosaur Oviraptorosaurs ("egg thief lizards") are a group of feathered maniraptoran dinosaurs from the Cretaceous Period of what are now Asia and North America. They are distinct for their characteristically short, beaked, parrot-like skulls, with or w ...

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''. The genus is named for

Richard Estes Richard Estes (born May 14, 1932 in Kewanee, Illinois) is an American artist, best known for his photorealist paintings. The paintings generally consist of reflective, clean, and inanimate city and geometric landscapes. He is regarded as one of ...

, to honor his important work 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

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 International Code of Zoological Nomenclature, 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''-like teeth have been found in many Late Cretaceous geological formations, including the

Horseshoe Canyon Formation The Horseshoe Canyon Formation is a stratigraphic unit of the Western Canada Sedimentary Basin in southwestern Alberta. It takes its name from Horseshoe Canyon, an area of badlands near Drumheller. The Horseshoe Canyon Formation is part of th ...

, the

Scollard Formation The Scollard Formation is an Upper Cretaceous to lower Palaeocene stratigraphic unit of the Western Canada Sedimentary Basin in southwestern Alberta. Its deposition spanned the time interval from latest Cretaceous to early Paleocene, and it inclu ...

Hell Creek Formation The Hell Creek Formation is an intensively studied division of mostly Upper Cretaceous and some lower Paleocene rocks in North America, named for exposures studied along Hell Creek, near Jordan, Montana. The formation stretches over portions of ...

Ferris Formation The Ferris Formation is a Late Cretaceous (~66 Ma) to Paleocene (66-63 Ma), fluvial-deltaic geological formation in southern Wyoming. It contains a variety of trace and body fossils, preserved in sandy fluvial channel deposits and overbank units. ...

, and the

Lance Formation The Lance (Creek) Formation is a division of Late Cretaceous (dating to about 69 - 66 Ma) rocks in the western United States. Named after Lance Creek, Wyoming, the microvertebrate fossils and dinosaurs represent important components of the late ...

(dated to about 66 million years ago). Similar teeth have been referred to this genus from as early as the

Barremian The Barremian is an age in the geologic timescale (or a chronostratigraphic stage) between 129.4 ± 1.5 Ma (million years ago) and 121.4 ± 1.0 Ma). It is a subdivision of the Early Cretaceous Epoch (or Lower Cretaceous Series). It is precede ...

age (

Cedar Mountain Formation The Cedar Mountain Formation is the name given to a distinctive sedimentary geologic formation in eastern Utah, spanning most of the early and mid- Cretaceous. The formation was named for Cedar Mountain in northern Emery County, Utah, where Will ...

, 125 million years ago).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. 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, and the genus is best considered a

form taxon Form classification is the classification of organisms based on their morphology, which does not necessarily reflect their biological relationships. Form classification, generally restricted to palaeontology, reflects uncertainty; the goal of s ...

. 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 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. ...

, 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.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 Fossils of ''Richardoestesia'' have also been found in the

Tremp Formation The Tremp Formation ( es, Formación de Tremp, ca, Formació de Tremp), alternatively described as Tremp Group ( es, Grupo Tremp), is a geological Formation (geology), formation in the comarca Pallars Jussà, Lleida Province, Lleida, Spain. Th ...

of northeastern Spain (Blasi 2 member).Blasi 2
at

Fossilworks Fossilworks is a portal which provides query, download, and analysis tools to facilitate access to the Paleobiology Database The Paleobiology Database is an online resource for information on the distribution and classification of fossil animals ...

.org

Biology

At least a few studies have speculated a piscivorous lifestyle for ''Richardoestesia'', due to its vast distribution as well as predominance in marine sites.Longrich, N., 2008, Small theropod teeth from the Lance Formation of Wyoming, USA, in Sankey, J.T., Baszio, S. (eds.), Vertebrate microfossil assemblages: their role in paleoecology and paleobiogeography: Bloomington, Indiana, Indiana University Press, 135-158. (5) (PDF) Presence of a maniraptoriform dinosaur in the Late Cretaceous (Maastrichtian) of Chiapas, Southern Mexico. Available fro
www.researchgate.net
ccessed March 14, 2021

References

External links