Wikipedia
Tatankaceratops (meaning " Bison horn face") is a controversial genus of herbivorous ceratopsian dinosaur. It is a small chasmosaurine ceratopsian which lived during the Late Cretaceous period (latest Maastrichtian stage) in what is now South Dakota. It is known from a single partial skull which was collected from the Hell Creek Formation, dating to 66 million years ago. Tatankaceratops was described by Christopher J. Ott and Peter L. Larson in 2010 and the type species is Tatankaceratops sacrisonorum.
In 2011, Nick Longrich published a paper containing a brief re-evaluation of Tatankaceratops. Longrich suggested that Tatankaceratops appeared to possess a bizarre mix of characteristics from adult and juvenile Triceratops specimens. Longrich noted that this animal could represent a dwarf Triceratops species or simply a Triceratops specimen with a developmental disorder which caused it to stop growing prematurely. Other paleontologists, including Thomas R. Holtz, Jr., have written that they "strongly suspect" Tatankaceratops is merely a juvenile specimen of Triceratops.