Richardoestesia is a medium-sized (~100 kg) genus of theropod dinosaur from the late Cretaceous Period of what is now North America. It is known from a single pair of lower jaw bones and a large number of isolated teeth.
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. In the eighties it became clear that Chirostenotes was a 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. The genus is named for Richard Estes, 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 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.
The holotype, NMC 343, consists of the pair of lower jaws found in the Judith River Formation, dating from the Campanian. 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. Richardoestesia type teeth are also found in the Late Cretaceous Horseshoe Canyon Formation, and the Scollard Formation. Its teeth are extremely common in the Lance Formation. Paronychodon teeth may come from Richardoestesia. Similar teeth have been referred to this genus from as early as the Barremian age (Cedar Mountain Formation, 125 million years ago). Because of the disparity in location and time of the many referred teeth, Richardoestesia is often seen as a form taxon, in this case actually functioning as the name of a tooth type.
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. The teeth of R. isosceles have also been identified as crocodyliform in shape, possibly belonging to a sebecosuchian.
It has been suggested that Richardoestesia was a fish eater, like a heron. Because so little is known of the animal, its relationships are unclear, the original authors classifying it as Theropoda incertae sedis. However, the jaws resemble Archaeopteryx, Troodontidae and some Dromaeosauridae, in having a strong groove on the lateral surface.