Didymoconidae

The type genus of Didymoconidae, Didymoconus, was first described in W. D. Matthew and W. Granger in 1924 based on a fairly complete skull and mandibles; all of these being found within the sediments of the Hsanda Gol Formation. Since this original publication, didymoconids would be occasionally published on with all records of the family being located in Central Asia. Similar to a large amount of other early Cenozoic mammal groups, the exact placement of Didymoconidae within Eutheria has not remained consistent. In their original publication, Matthew and Granger would place it within Carnivora though compare the family to other groups such as Leptictidae and Mesonychidae. Other authors would place the family close to a number of other groups such as Creodonta, Lagomorpha, Hapalodectidae, and Macroscelidea though the suggestions made in the 1924 publication would still be brought up from time to time. One example of this is when authors such as Gingerich and Wang would push towards Didymoconidae having a close relationship with Mesonychidae. Authors would go as far as placing the mesonychid Yantanglestes as the ancestor of Didymoconidae. Another genus, Wyolestes, would also be suggested to be part of the family and would even be placed within its own subfamily, Wyolestinae, during this time but authors such as Meng would argue against the assignment. Men specifically argued against the genus being placed as a member of Didymoconidae due to a lack of shared, more derived features. This would be corroborated not only when more complete material of Wyolestes would be described in 1987 and 1991 but also when a 2025 study by Shawn P. Zack and coauthors would place the genus as a hyeanodont based on both cranial and postcranial material. A number of features in the cranium also suggested that Didymoconidae could have been closely related to the now obsolete orders Insectivora and Lipotyphla. A third subfamily, Kennatheriinae, would be named by Lopatin in a 2006 publication based on differences in the dentition along with the shape of the angular and coronoid processes on the mandible. The first and only cladistic analysis of the family would be done by Pieter Missiaen and coauthors in 2016 which would test the relationships within Didymoconidae along with a number of other groups that it has been suggested to be placed near. These groups included Zalambdalestidae, Nyctitheriidae, and Leptictida along with a similar Asian mammal group from the same time, Sarcodontidae. This analysis would show that Ardynictinae was a paraphyletic group of stem didymoconids though would find the other two subfamilies as monophyletic. Below is the cladogram from the 2016 publication. }} }}|style=font-size:90%;line-height:40%|label1=}}The type genus Didymoconus would be included in a cladogram within the 2025 publication by Shawn P. Zack and coauthors and would find it in a number of positions such as being close to Mesonyx and Afrosoricida though both of these results were weakly supported. Even with this being the case, the most parsimonious tree in the publication would place Didymoconus as sister to Mesonyx, agreeing with a number of previous papers that suggested a close relationship between Didymoconidae and Mesonychidae. Though not common, Didymoconidae is sometimes assigned to the order Didymoconidae with it being the only group within it. == Description ==

Skull Members of Didymoconidae have been generally described as being medium to large 'insectivores' with larger members of the family like Archaeoryctes euryalis having skull lengths of . The rostrum of the skull was made up of the premaxilla and nasal bones with this potentially leading to a very mobile nose in genera like Archaeoryctes. Sexual dimorphism has been noted as a possibility in at least some members of Didymoconidae like Ardynictis due to a number of features such as differences in the length of cheek tooth row and the anatomy of the horizontal ramus. == Paleoecology ==

Based on both cranial and postcranial anatomy, some members of Didymoconidae such as Didymoconus have been considered as being fossorial with the much more robust forelimbs with large claws being good tools for digging. A combination of the stronger skull and better low frequency hearing caused by the expansion of the middle ear space is also a trend seen in burrowing mammals. This lifestyle along with their cheek teeth that are specialized to puncture lead Xiaoming Wang and coauthors to suggest an insectivorous diet in their 2001 publication on Didymoconus. One member of the family, Erlikotherium, has been suggested to have been specialized in eusocial insects like anteaters due to the loss of its incisors with its still present canines being used to break open mounds. The limb bones of Erlikotherium have also been noted to be much larger than other didymoconids like Khaichinula. Kennatherium is also notable due to the fact that though the animals humerus proportions were similar to Didymoconus, it was much more developed which suggests a more fossorial ecology for the animal. ==References==