other dromaeosaurids. For instance, the pubis is aligned vertically and has a relatively large pubic boot (a wide expansion at the end), unlike most other dromaeosaurids, where a generally a much smaller boot is seen. The preserved vertebrae are very robust and feature a series of pleurocoels. The above differences led Burnham and team in 2000 to suggest that the holotype of Achillobator, in fact, represents a paleontological chimera, and only the pedal unguals may have come from a dromaeosaurid-grade dinosaur. However, given that the specimen was actually found in semiarticulation, and all elements have the same color and preservation quality, the assignment of remains to a single individual is supported. Despite the fact that Achillobator features unusual and primitive characteristics compared to other dromaeosaurids, it is commonly recovered as a taxon falling within the Dromaeosauridae in cladistic analyses. Description Achillobator represents one of the largest described dromaeosaurid taxa, reaching in length, in hip height, and in body mass. In 2007, Turner and his colleagues gave a higher mass estimate of about based on the femur length estimate by Perle and his colleagues in 1999, but they later criticized the 1999 study due to its uninformative diagnosis; they did note that the body mass of Achillobator might be potentially over . Although the holotype was found lacking traces of feather integument, strong evidence coming from other relatives suggests the likely presence of plumage on Achillobator. According to the revised diagnosis by Turner and colleagues in 2012, Achillobator can be distinguished based on the following combination of characteristics and autapomorphies: The promaxillary fenestra is completely exposed; the promaxillary and maxillary fenestrae are elongated and vertically oriented at same level in the maxilla; metatarsal III is wide on the upper end; the femur is longer than the tibia; the pelvis is propubic (pubis extends forward towards the head of the animal); the obturator process on the ischium is large and triangular situated on the upper half of ischial shaft; and the boot at distal symphysis of the pubis is developed in a cranial and caudal aspect. Skull The maxilla was deep and robust, and measured about in length. Its lateral side was smooth compared to the dorsal areas, but had a robust constitution. It had approximately 11 alveoli (sockets that held the roots of teeth). The teeth of Achillobator displayed marked homodonty (teeth of similar shape and size) and they were serrated