Achillobator was a large dromaeosaurid from late cretaceous mongolia. Achillobator was discovered in 1989 and described in 1999. Achillobator is considered to be one of the largest dromaeosaurids, only being smaller than utahraptor, dakotaraptor, and austroraptor. Like all dromaeosaurids, achillobator had plumage covering its body. Achillobator had an unusually robust skeleton for a dromaeosaur.