 Stegosaurus ungulatus , meaning " hoofed roof lizard " , was named by Marsh in 1879 , from remains recovered at Como Bluff , Wyoming ( Quarry 12 , near Robber 's Roost ) . It might be synonymous with S. stenops . At 9 m ( 29 @.@ 5 ft ) , it was the longest species within the genus Stegosaurus . A fragmentary Stegosaurus specimen discovered in Portugal and dating from the upper Kimmeridgian @-@ lower Tithonian stage has been tentatively assigned to this species . Stegosaurus ungulatus can be distinguished from S. stenops by the presence of smaller , more triangular plates and by several pairs of small , flat , pointed plates just before the spikes on the tail . These spine @-@ like plates appear to have been paired , due to the presence of at least one pair that are identical but mirrored . S. ungulatus also appears to have had longer legs ( femora ) and hip bones than other species . The type specimen of S. ungulatus was discovered with eight spikes , though they were scattered away from their original positions . These have often been interpreted as indicating that the animal had four pairs of tail spikes . No specimens have been found with complete or articulated sets of tail spikes , but no additional specimens have been found that preserve eight spikes together . It is possible the extra pair of spikes came from a different individual , and though no other extra bones were found with the specimen , these may be found if more digging were done at the original site . Specimens from other quarries ( such as a tail from Quarry 13 , now forming part of the composite skeleton AMNH 650 at the American Museum of Natural History ) , referred to S. ungulatus on the basis of their notched tail vertebrae , are preserved with only four tail spikes . The type specimen of S. ungulatus ( YPM 1853 ) was incorporated into the first ever mounted skeleton of a stegosaur at the Peabody Museum of Natural History in 1910 by Richard Swann Lull . It was initially mounted with paired plates set wide , above the base of the ribs , but was remounted in 1924 with two staggered rows of plates along the midline of the back . Additional specimens recovered from the same quarry by the United States National Museum of Natural History , including tail vertebrae and an additional large plate ( USNM 7414 ) , belong to the same individual as YPM 1853 . 
