Classification of the Dinosauria. 81 



Dinosanrian remains from other formations of this country, and like- 

 wise, during the past summer, have visited most of the museums of 

 Europe that contain important specimens of this group. Although 

 the investigation is not yet completed, I have thought the results 

 already attained of sufficient interest to present to the Academy at 

 this time. 



In previous classifications, vs^hich were based upon very limited 

 material compared with what is now available, the Dinosaurs were very 

 generally regarded as an order. Various characters were assigned 

 to the group by Von Meyer, who applied to it the term Fachypoda ; 

 by Owen, who subsequently gave the name Dinosauria, now in 

 general use ; and also by Huxley, who more recently proposed the 

 name Ornithoscelida, and who first appreciated the great importance 

 of the group, and the close relation it bears to Birds. The researches 

 of Leidy and Cope in this country, and Hnlke, Seeley, and others in 

 Europe, have likewise added much to our knowledge of the subject. 



An examination of any considerable portion of the Dinosaurian 

 remains now known will make it evident to any one familiar with 

 reptiles, recent or extinct, that this group should be regarded, not as 

 an order, but as a sub-class, and this rank is given it in the present 

 communication. The great number of subordinate divisions in the 

 group, and the remarkable diversity among those already discovered, 

 indicate that many new forms will yet be found. Even among those 

 now known, there is a much greater difference in size and in osseous 

 structure than in any other sub-class of vertebrates, with the single 

 exception of the placental Mammals. Compared with the Marsupials, 

 living and extinct, the Dinosauria show an equal diversity of 

 structure, and variations in size from by far the largest land animals 

 known — fifty or sixty feet long — down to some of the smallest, a few 

 inches only in length. 



According to present evidence, the Dinosaurs were confined 

 entirely to the Mesozoic age. They were abundant in the Triassic, 

 culminated in the Jurassic, and continued in diminishing numbers 

 to the end of the Cretaceous period, when they became extinct. The 

 great variety'- of forms that flourished in the Triassic render it more 

 than probable that some members of the group existed in the 

 Permian period, and their remains may be brought to light at any 

 time. 



The Triassic Dinosaurs, although so very numerous, are known 

 to-day mainly from footprints and fragmentary osseous remains. 

 Not more than half a dozen skeletons, at all complete, have been 

 secured from deposits of this period ; hence, many of the remains 

 described cannot at present be referred to their appropriate divisions 

 in the group. 



From the Jurassic period, however, during which Dinosaurian 

 reptiles reached their zenith in size and numbers, representatives of 

 no less than four well-marked orders are now so well known that 

 different families and genera can be very accurately determined, and 

 almost the entire osseous structure of typical examples, at least, be 

 made out with certainty. The main difficulty at present with the 



DECADE II. — VOL. IX. — NO. II. 6 



