Here, we describe a juvenile Triceratops sp. skull, UCMP 136306, from the Hell Creek Formation, McCone County, Montana. The relative completeness and superb preservation of this skull contribute to an improved understanding of the cranial ontogeny, morphology, and individual variation in Triceratops. Total skull length is 120 cm long (est.). UCMP 136306 is one of the most complete Triceratops skulls of this ontogenetic stage yet known. The cranial sutures are patent, and most are overlapping with minimal sinuosity, modest interdigitation, and overlapping flat sutural surfaces. The following cranial elements are preserved and described in this study: epinasal, rostral, quadrate, quadratojugal, jugal, pterygoid, dentary, surangular, postorbital horn, parietal, squamosal, epiparietal, episquamosal, occipital condyle, supraoccipital, and exoccipital.

For decades following the initial description of Triceratops by O.C. Marsh in 1889, the typical collector attitude was “bigger is better.” Emerging scientific institutions and museums with newly constructed exhibit halls demanded the biggest and newest dinosaurs. We hypothesize that this historical practice, influenced by facies and taphonomic factors in the Upper Cretaceous Hell Creek Formation, Montana (and contemporaneous formations in neighboring states), resulted in the underrepresentation of nonadult Triceratops in museum collections. This practice contributed to the false notion that nonadult Triceratops specimens are rarely preserved in the fossil record, until now.