Table 2.

The study set of Triceratops and the ontogenetic trends expressed within and across four growth stages. (Abbreviations: MOR, Museum of the Rockies; UCMP, University of California Museum of Paleontology. A, parietal–squamosal frill with scalloped posterior margin; B, posterior frill margin less scalloped to wavy; C, epoccipitals merged onto smooth caudal frill margin; D, fan-shaped frill; E, posterior postorbital horn curvature; F, excavation of postorbital horn internally; G, fusion of nasals; H, fusion of nasal horn onto the nasals; I, supraoccipital present between the exoccipitals; J, anterior postorbital horn recurvature.)

Triceratops	element	growth stage	ontogenetic trends
A	B	C	D	E	F	G	H	I	J
UCMP 154452	skull	baby	x								x
MOR 652	squamosal	baby	x
MOR 1098	postorbital horn	baby
MOR 1053	postorbital horn	baby
UCMP 158441	postorbital horn	baby
UCMP 399749	postorbital horn	baby
MOR 1199	skull	juvenile		x			x
UCMP 136306	skull	juvenile		x			x
MOR 1110	skull	juvenile		x			x	x
UCMP 159233	partial skull	juvenile
MOR 1129	partial skull	juvenile
UCMP 139292	postorbital horn, maxillary, braincase	juvenile
UCMP 150234	parietal	juvenile		x			x
MOR 539	postorbital horns	juvenile					x
UCMP 186583	epinasal	juvenile
MOR 989	epinasal	juvenile
MOR 1167	epinasal	juvenile
UCMP 137263	skull	subadult		x		x						x
MOR 1120	skull	subadult		x	x	x		x	x	x	x	x
MOR 699	skull	subadult		x		x					x	x
UCMP 136092	skull	subadult		x		x					x
UCMP 137266	partial skull and skeleton	subadult										x
UCMP 173739	postorbital horn	subadult										x
MOR 1604	skull	adult			x				x	x		x
MOR 004	skull	adult			x	x			x	x		x
MOR 1625	skull	adult			x				x	x		x
UCMP 113697	skull	adult			x	x		x	x			x
UCMP 174838	skull	adult			x				x	x		x
UCMP 136589	partial skull	adult			x							x
UCMP 140416	partial skull	adult				x						x
UCMP 129205	premaxillae, nasals, nasal horn	adult				x
			A	B	C	D	E	F	G	H	I	J