Kansaignathus () is an extinct genus of dromaeosaurid theropod from the Late Cretaceous Yalovach Formation (or Ialovachsk Formation) of Tajikistan. The genus contains only one species, the type species, K. sogdianus. The generic name of Kansaignathus comes from near the town of Konsoy ("Kansai" in Russian) where it was discovered and the Greek word "gnathos" meaning "jaw". The specific epithet "sogdianus" is derived from the historical region of Sogdiana, which was an ancient name for the Fergana Valley region where the fossil was discovered. Kansaignathus is known from a single right dentary bone and a few post-cranial bone fragments. It was the first, and so far the only, dinosaur from Tajikistan to be described and named.
Discovery
The holotype of Kansaignathus was found at the Kansai locality, about 22 km to the North of the town of Khujand (sometimes spelled "Khudzhand") in the Sughd Region of Tajikistan. This locality was discovered in 1940 by O.S. Vialov, but fossils were not excavated from the area until the Paleontological Institute of the Academy of Sciences of the USSR sent large-scale expeditions to the area in 1963 and 1964. Exact dates and times of when the holotype was excavated is not known, but references to dromaeosaurs known from the locality were made by L.A. Nesov in a publication in 1995. The type specimen is reposited at the Borissiak Paleontological Institute at the Russian Academy of Sciences in Moscow. It was given the designation PIN 2398/15 and consists of a single partial dentary bone. Additional material, which was also collected in the 1963-1964 expeditions, was described by A.K. Rozhdestvensky in 1977. This additional material included PIN 2398/16 and 2398/1 (fragments of a sacrum), PIN 2398/4 and 2398/17 (two ungual phalanges), PIN 2398/18 (a manual ungual), and PIN 2398/19 (a fragmentary metatarsal). This material was referred to the new genus in January 2023 by the same authors who described the holotype. A dorsal vertebra found in association with these specimens was previously considered to belong to Kansaignathus, but is now believed to belong to a crocodyliform.
Description Kansaignathus is a small-bodied dromaeosaur which was probably similar in size to Velociraptor. The authors of its description estimate that it was probably about 2 metres (6.6 ft) long, which is similar to size estimates for Velociraptor and Dineobellator. In their description of the holotype, Averianov and Lopatin distinguish Kansaignathus from other dromaeosaurs by the presence of several autapomorphies. It has a thin and deep profile of the dentary, parallel edges along the dentary's length (rather than tapering towards the front of the snout), a facet on the posterior-ventral process of the dentary to articulate with the splenial bone, two rows of vascular foramina on the outside edge of the jawbone, and interdental plates which have merged completely with the jaw. The additional post-cranial material described by the authors in their subsequent publication was not included as part of the holotype specimen. However, the authors are confident in their assignment of the material to the same genus, and the anatomical characters from this material is used in their phylogenetic analysis.
Skull
The only portion of the skull which was preserved is the right dentary, which is almost complete. It preserves 12 alveoli, which is fewer than most other velociraptorines (which usually have 14-16 dentary teeth). The dentary itself has several distinct features including a rectangular shape when viewed from the side, a down-turned process on the anterior side of the bone, and a small prominence in the symphysis area at the front of the bone where it would have met with the left dentary. The two dentaries were probably joined at a relatively acute angle, which is common in dromaeosaurs. However, the holotype is relatively unique in preserving several rows of nutrient foramina, which imparts a rugose texture to the lateral surface of the bone in some areas. None of the teeth are preserved, but the shape of the alveoli indicates that the teeth would have likely been mediolaterally flattened and increase in size towards the anterior end of the jaw until the ninth tooth position, when they decrease in size again. Two partially-grown teeth are preserved in the sixth and twelfth tooth positions, but they were in the early stages of growth when the animal was fossilized, so they do not convey much information about the in-life nature of the animal's teeth.
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