OSTEOLOGY OF THE ARMORED DINOSATJRIA. 



97 



arrangement of the plates is shown and the original idea of four pairs of spines 

 retained. 



The type of Stegosaurus stenops (No. 4934) corroborates most conclusively Lucas's 

 interpretation of the arrangement of the dorsal armor, and, except in one or two 

 points, I would indorse his restoration (pi. 34, lower figure) as being in accord with the 

 evidence shown by the specimens in the United States National Museum collections. 



The reasons given by Lucas for the alternating position, as stated in an unpub- 

 lished manuscript, were twofold: First, that the plates did alternate as they lay 

 embedded in the rock, and, second, that no two of them were precisely similar in 

 shape or dimensions. Opposed to this argument, Lull has advanced the opinion 

 "that the position of the plates in the rock is hardly conclusive, for the series might 

 easily have shifted forward or backward slightly during maceration or in the sub- 

 sequent movement of the rock." 



A careful study of this series of plates leads to the belief that such a shifting 

 has not taken place. For example, pa,rt of this series, as shown 

 in plates 2, 4, and 14, has fallen to the left and lies under the 

 body of the animal, while the posterior plates are approxi- 

 mately in position above the pelvic region, yet both sections 

 show the same alternating arrangement. Moreover, there is a 

 remarkable uniformity of the overlapping of plates of one side 

 upon those of the opposite row — that is, the middle point of 

 the underlying plates, taken longitudinally, is, in nearly all 

 instances, in the center of the interspace between the plates of 

 the uppermost series (pi. 14). This exact spacing of the plates 

 would indicate that they remained attached to the skin until 

 becoming fixed in the position in which we now see them. 

 If this be true, it is difficult to explain the possibility of 

 bringing the plates of opposite sides into alignment, since in 

 order to do so, it would be necessary to shift the small ante- 

 rior ones only a few inches, while the larger plates would need 

 to be moved a foot or more. Certainly, if remaining attached 

 to the skin in sequential order, as the evidence appears to show, 

 had the plates of one side shifted, all would have moved in the same direction and 

 approximately similar distances. 



As to the argument that the shifting took place by the movement of the rock — 

 that view seems absolutely untenable, since nowhere, either in the specimen or 

 in attached rock, is there any indication of lateral shearing. 



This specimen is surely another example of the truth so aptly put by the 

 late Prof. Charles E. Beecher 1 when he observes that "the positive information 

 conveyed by the finding of a foot or of any other portion of a skeleton, with the bones 

 in a sequential position in the rock, is of far greater anatomical value than any number 

 of expert opinions." 



That the bases of the plates of opposite rows, anterior to the sacrum, were 

 nearer together on the median line of the back (fig. 61) than has been represented 

 in any of the restorations of Stegosaurus is indicated by the evenness of the bases 



Fig. 61. — Section of the 

 neck of stegosaurus. 

 pi, Dermal plate; r, 



CERVICAL KIB; V, VER- 

 TEBRA. Modified 

 from Lull. 



' Trans. Conn. Acad. Sci., vol. 11, 1902, p. 311. 



