 Early members of the ceratopsian group , such as Psittacosaurus , were small bipedal animals . Later members , including ceratopsids like Centrosaurus and Triceratops , became very large quadrupeds and developed elaborate facial horns and frills extending over the neck . While these frills might have served to protect the vulnerable neck from predators , they may also have been used for display , thermoregulation , the attachment of large neck and chewing muscles or some combination of the above . Ceratopsians ranged in size from 1 meter ( 3 ft ) and 23 kilograms ( 50 lb ) to over 9 meters ( 30 ft ) and 5 @,@ 400 kg ( 12 @,@ 000 lb ) . 
 Early members of the ceratopsian group , such as Psittacosaurus , <a href='uninflect' title='1'><mark>were</mark></a> small bipedal animals . Later members , including ceratopsids like Centrosaurus and Triceratops , became very large quadrupeds and developed elaborate facial horns and frills extending over the neck . While these frills might <a href='been_done' title='2'><mark>have</mark></a> served to protect the vulnerable neck from predators , they may also <a href='been_done' title='3'><mark>have</mark></a> been used for display , thermoregulation , the attachment of large neck and chewing muscles or some combination of the above . Ceratopsians ranged in size from 1 meter ( 3 ft ) and 23 kilograms ( 50 lb ) to over 9 meters ( 30 ft ) and 5 @,@ 400 kg ( 12 @,@ 000 lb ) . 
Early members of da ceratopsian group , such as Psittacosaurus , was small bipedal animals . Later members , including ceratopsids like Centrosaurus and Triceratops , became very large quadrupeds and developed elaborate facial horns and frills extending ova tdaneck . While these frills might done served to protect the vulnerable neck from predators , they may also done been used for display , thermoregulation , thdattachment of large neck and chewing muscles or some combination of the above . Ceratopsians ranged in size from 1 meter ( 3 ft ) and 23 kilograms ( 50 lb ) to oova9 meters ( 30 ft ) and 5 @,@ 400 kg ( 12 @,@ 000 lb ) .