78 BULLETIN 110, UNITED STATES NATIONAL MUSEUM. 



OSTEOLOGY OF CERATOSAUKUS. 



Since the osteology of Antrodemus has been described in considerable detail in 

 the preceding pages, it is only necessary to treat briefly the various elements com- 

 prising the bony structure of the present Morrison genus. The chief similarities 

 and dissimilarities as compared with the homologous parts of other membei's of 

 the Theropoda are pointed out and correction of such erroneous statements and 

 incorrect restoration as is now rendered possible by the more complete preparation 

 of the known material, and also on account of our greatly increased knowledge 

 of the skeletal structure of Theropodous dinosaurs in general. 



These observations are based entirely on the type specimen of Ceratosaurus 

 nasicornis. Prof. O. C. Marsh and Dr. O. P. Hay have been the chief contributors 

 to our knowledge of the skeletal anatoni}^ of this animal, and I have made free use 

 of their various contributions, although all of their work has been verified by per- 

 sonal examination of the specimen. 



SKULL. 



The skull of Ceratosaurus nasicornis, although constituting the most complete 

 cranium of a Morrison Theropod dinosaur yet found, is greatly distortcnl liy pressure 

 (fig. 53). 



This compression is largel}' from side to side, so that its present thickness is 

 only a little over 100 mm. The first restorations of the skull (pi. 7, Dinosaurs of 

 North America), were drawn under the supervision of Professor Marsh, and present 

 a somewhat restored view, and so far as representing the exact transverse propor- 

 tions, they must remain somewhat in doubt. It would appear, after a comparison 

 with the well-])reserved articidated skull of Tyrannosaurus,'- and with the skuU of 

 Antrodemus Xo. 4734 U.S.X.M. that the posterior portion is not wide enough as 

 restored. The restorations of the Ceratosaurus skull presented here (figs. 1 and 2, 

 pi. IS) are based upon the tj'pe specimen Xo. 4735, U.S.X.M., and althoiigh many 

 of the inaccuracies detected in the earlier restoration bj' Marsh have been eliminated, 

 it is anticipated that future discoveries will show the present restoration to be in 

 error in other particidars. The badly crushed condition of the skrdl (figs. 1 and 2, 

 pi. 17) makes it most difficult to determine the exact proportions of some parts, and 

 especially many of the mmor details. This restudy, however, in conjunction with 

 the beautifully preserved Antrodemus skull Xo. 4734, U.S.X.M., has cleared up many 

 apparent discrepancies, and has resulted, I trust, in giving a more correct concep- 

 tion of the skull of Ceratosaurus than coidd be obtained from the earlier repre- 

 sentations. 



In general, the skull of Ceratosaurus is light and open in its structure, excelluig 

 in this respect aU other of the larger members of the Theropodous Dinosauria. 



Its closest resemblances are with the skull of Antrodemus, though on comparison 

 many important structural differences are found. One especial distinctive feature 

 of the skuU and one which distinguishes it from all known Theropoda is the elevated, 

 trenchent horncore situated medially on the nasals. Other features are the elon- 

 gated quadrate, the relatively large size of the lateral opening's, reduced dentition, 

 and the slenderness of the posterior half of the lower jaw. 



1 Osbom, ii. F., Memoir American Museum Natural History, vol. 1, new ser., 1912, pt. 1, pi. 2. 



