[D] Hesperosaurus mjosi [Su] [sG] [T]
Carpenter, Miles & Cloward, 2001
Jurassic Late Kimmeridgian Tithonian
Ornithischia Thyreophora Stegosauria Stegosauridae
Morrison Formation, Wyoming, US
Genus - Typespecies - Skull
A primitive stegosaur, discovered by Patrick McSherry in June, 1985, on the B.Smith Ranch in fine-grained sandstone just five meters above the base of the Morrison Formation, in Johnson County, south of Buffalo, Wyoming.
Greek hesper = \\\\\\\"western\\\\\\\" + Greek sauros = \\\\\\\"lizard\\\\\\\"
HMNH 001, partial skeleton including almost complete skull, hyoid, vertebrae (13 cervicals, 13 dorsals, three sacrals, and 44 caudals), most cervical and dorsal ribs, most chevrons, 10 dermal plates, ilia, ischia, pubus, partial left scapula, ossified tendons, semiarticulated.
Diagnosis of genus (as for the type species)
(Cranial) skull intermediate between Stegosaurus stenops and Huayangosaurus; medium-size antorbital fenestra, intermediate in size between Huayangosaurus taibaii and Stegosaurus stenops; frontoparietal domed (flat in all other known stegosaurs); basisphenoid short (long in S. stenops); mandible below coronoid process proportionally deeper to length than in S. stenops and H. taibaii; alveolar border of mandible not visible in lateral aspect as in S. stenops (visible in H. tabaii); foramen magnum wider than occipital condyle (narrower in Stegosaurus ungulatus, S. stenops and H. taibaii); teeth proportionally larger relatie to skull size than in S. stenops; (postcranial) vertebral formula of 13 cervical, 13 dorsal, three sacral, and ?45 caudal (10 cervical, 17 dorsals, and 47 caudal in S. stenops; eight cervical, 17-18 dorsal, three sacral, and 42 cuadal in Dacentrurus; ?eight cervical, ?17 dorsal, four sacral, and 43 caudal in Kentrosaurus; axis having tall, caudally inclined neural spine (as in S. stenops, low in H. taibaii); caudal cervical neural canal taller than wide, neural arch of midddorsals low (as in H.taibaii, not all as in Stegosaurus ungulatus and Stegosaurus stenops); cervical ribs with blades expanded distally (not expanded in S. stenops and H. tabaii); caudal neural spines not bifurcated as in S. stenops; ilia strongly divergent cranially (as in H. tabaii, straight in S. stenops); distal end of pubis expanded (as in H. taibaii, not expanding in S. stenops); cervical plates low, oval (tall, triangular in S. ungulatus, S. stenops, and H. taibaii); caudal spikes similar to those of S. stenops, but with more rugose base (Carpenter, Miles and Cloward, 2001)