OSTEOLOGY OF THE ARMORED DINOSAURIA. 



83 



armored Stegosaurus. I quite believe that the feeble ossification of the sternal apparatus and the low 

 degree of ossification of the distal carpals and tarsals in most Dinosaurs are much more likely to explain 

 the great cartilage caps on the femora of the Stegosauridte and similar animals than the hypothetical 

 aquatic habits. These features and the coarse structures of the bones indicate a low degree of ossification 

 in the whole body, and the great masses of cartilage were probably needed to ensure the continuous 

 increase of size throughout life. 



Lull ' says: 



The loss of this trochanter [the fourth] together with the slight development of the pubic peduncle 

 of the ilium precludes the possibility of a bipedal gait, though doubtless Stegosaurus is derived from a 

 bipedal ancestry, quadrupedalism being secondarily acquired as in the Ceratopsia, owing to the immense 

 weight of the creature's armament. 



A comparative study of the series of femora in the National Museum collections 

 shows the existence of two types of animal — one a distinctively slender, long- 

 limbed form, the other a short-limbed tj T pe. The former reaches its maximum 

 development in S. ungulatus as shown in the mounted skeleton (fig. 46 and pi. 36). 

 The latter is represented by a hind limb, No. 7380. The femur of this specimen 

 is of a fully adult animal, as evidenced by the rugose nature of the articulations 

 and areas of attachment for the more important muscles. The articular ends 

 and condyles are especially well defined and in every way have a more finished 

 appearance than any of the longer femora in the collection. A small humerus, 

 No. 7409, but not associated with the hind limb mentioned above, also exhibits 

 characteristics similar to those of the femur described above. 



Whether these bones represent an undescribed species, I am not prepared to 

 decide at this time, but that there are long and short limbed forms of the genus 

 Stegosaurus, the evidence before me appears most conclusive. 



The femora of S. stenops and S. longispinus show these species to be classed 

 as long-limbed animals. It is quite possible that when the femora of the other 

 described species are known it will be found that these short-limb bones pertain 

 to one of them. There is also the possibility that the matter of sex may account 

 for the difference in the size of the limbs. 



Measurements of femora . 





S. stenops, 

 type No. 4934. 



S. un- 

 gulatus. 



Stegosaurus sp. 



5. longi- 

 spinus, 

 type. 



Bight. 



Left. 



No. 

 6646, 

 right. 



No. 

 7370, 

 left. 



No. 

 7380, 

 right. 



No. 

 7380, 

 left. 



No. 

 7385, 

 right. 



Right. 





mm. 



1,080 

 283 

 276 

 145 



mm. 



1.010 

 307 

 269 

 140 



mm. 



1.200 

 329 

 263 

 147 



mm. 



977 



227 

 130 



mm. 

 908 

 245 

 246 

 12S 



mm. 



895 

 26S 

 242 

 128 



mm. 

 S50 

 225 

 192 

 117 



mm. 



1.082 

 275 

 242 

 132 



Greatest breadth at proximal end . . . 

 Greatest breadth at distal end 





1 Amer. Joum. Sei., vol. 30, 1910, p. 367. 



