Nodosaurus textilis Marsh. 121 



Deep blood-vessel impressions on the superior inner 

 portion of each ilium, which appear somewhat abruptly 

 along a definite line, seem to indicate that beyond that 

 line the dermal armor ceased and the cutaneous invest- 

 ment was closely applied to the surface of the ilia 

 themselves (see above, page 105, and pi. 11). Thus the 

 latter formed an endoskeletal continuation of the median 

 dermal carapace. The actual dermal scutes are not 

 preserved for the full width of their former extent (see 

 pi. II). The nodular prominences over the sacrum are 

 almost obsolete, increasing apparently in height forward 

 toward the dorsal region and laterally in that region from 

 the neural series outward. There is no preserved trace 

 of subdermal ossicles in the pelvic region of Nodosaurus. 

 The evidence afforded by Nodosaurus emphasizes 

 Wieland's statements concerning the dinosaur-turtle 

 analogy. In the crocodile-like reptiles, the outer dermo- 

 gene-producing layer only is present;^ the turtles had 

 originally both outer and nether dermogene layers. The 

 latter early tended to strengthen and use the under layer 

 only. The dinosaurs developed both body and cranial 

 armature in both upper and nether dermogene layers. 

 The latter, Wieland thinks, gave rise to the huge plate 

 roofing the entire skull in Ankylosaurus and the hip 

 armature of Polacanthus. However the greater portion 

 of the Polacanthus carapace may have originated, the 

 occasional keeled plates which arise above the level of 

 the main structure seem to be homologous with the 

 nodular scutes of Nodosaurus and thus to be, like those 

 of the crocodiles, of outer dermal origin. Thus the 

 dinosaurs, as "Wieland says, instead of eventually 

 confining extensive dermal development to but a single 

 nether layer, covering the body region only as in the 

 turtles, tended to develop both the nether and outer 

 layers in body or skull, or both. 



^Scutes from Deinosuchus hatclwri, a Judith Eiver crocodile, described 

 and figured by Holland (Ann. Carnegie Mus., 6, 291, 1909) ^'show on the 

 under surface numerous fine straight lines decussating with each other at 

 an angle of about 45°, indicating the structure of the dermal tissues in 

 which they were embedded and to which they adhered. ' ' Sir Eichard Owen 

 (Eept. British Assoc.^ 1841, p. 71) calls attention to a similar feature in 

 the scutes of Gonio'pholis crassidens Owen. The figure (fig. 10) published by 

 Holland shows a very distinct layer, in part broken away from the overlying 

 cancellous bone, which bears the intersecting lines. This would seem to 

 indicate that the scute as a whole is of dual origin, derived in part from 

 the outer dermal and in part from the subdermal layers. 



