At least 50 features unite the family Ceratopsidae as a monophyletic clade. The large Neoceratopsians are only known from North America (Serreno, 1999). There were many important modifications of ceratopsian teeth after the lineage separated fron that of Protoceratops.  In the members of the family Ceratopsidae, there were 2-3 teeth per tooth position as opposed to one, there were no longer teeth on the premaxillary bone, the teeth were located farther back in the jaws for greater power when chewing, and their teeth became adapted for slicing as opposed to grinding.  Highly fibrous material is better chewed by slicing than grinding and ceratopsians were probably specialized for eating cycads and palms rather than softer leaves and fruits (Lambert, 1990, Fastovsky, 1996).

triceratops dental battery
     The heads of the post-Protoceratops ceratopsians are enormous.  Even without the frill, the head is never less than 1/3 the length of the back (Tyrannosaurus is the only other dinosaur which approaches this ratio) and in Pentaceratops the head length is actually greater than the back length.  Most had either two long brow horns and a short nose horn, or two short brow horns and a long nose horn.  The horns were probably covered with keratin in life.  The neck vertebrae were often fused to help support the weight of the head.  There are two subfamilies: Chasmosaurinae and Centrosaurinae (Lambert, 1990, Fastovsky, 1996).
torosaurus arrhinoceratops
triceratops skel various species
triceratops species
    In the Chasmosaurinae, the squamosal bones were long.  In Triceratops, “three horn face”, the skull was 1/3 body length.  The humerus indicates that posture might have been slightly sprawling while footprints suggest that walked upright.  Based on skull variations, there is disagreement regarding the number of Triceratops species that should be recognized.  “Lumpers” feel that there were only 1 or 2 variable species while “splitters” may recognize as many as 16 different species. triceratops sepcies 2
     In the Centrosaurinae, the squamosal bones are short.   Pachyrhinosaurus possessed a large, rough bone ridge from nose to eye.  This species lived in NW North America–even onto Alaska’s North Slope–5 degrees from the North Pole of the Late Cretaceous (Lambert, 1990, Fastovsky, 1996).
pachyrhinosaurus styracosaurus