HALLOPUS, BAPTANODON, ATLANTOSAURUS BEDS 343 



Hatcher, and Darton. A resume of this discussion will be found in 

 Hatcher's recent paper on Haplocanthosaurus. 1 It is very evident 

 that the final solution of the problem must be left chiefly to the ver- 

 tebrate paleontologist, since the evidence presented by the inverte- 

 brates and the plants is not only scanty, but also, in the nature of 

 things, insufficient. Aside from the discussions of Marsh, we are 

 chiefly indebted to the late Mr. Hatcher for the presentation of the 

 vertebrate evidence, and it is the views and statements presented by 

 him that I wish to discuss here briefly. I will quote all of importance 

 that he has to say: 



Marsh was wont to correlate the Atlantosaurus beds with the Wealden, 

 which he regarded as of Upper Jurassic age. On just what evidence he relied 

 for this correlation is not quite clear. Nor does a comparison of the dinosaurian 

 faunas of these two horizons seem to warrant such correlation. While from the 

 fragmentary nature of much of the material upon which the different genera 

 and species are based it is clearly impossible to make satisfactory comparisons 

 in many instances between the more closely related genera and species of Amer- 

 ican and European dinosaurs, nevertheless when comparisons of the faunas as 

 a whole are instituted between the various American and European horizons, 

 most striking and important resemblances and dissimilarities are at once apparent. 

 Thus while in the Atlantosaurus beds the Sauropoda are the predominant forms 

 both as regards size and the number of genera, species and individuals, in the 

 Wealden they are almost entirely replaced by the Predentata and Theropoda. 

 And the Iguanodontia, so abundant in the latter formation, are quite unknown 

 in the former. It is not until we get down into the middle of the Oolite that we 

 find a dinosaurian fauna comparable even with that of the Upper and Middle 

 Atlantosaurus beds. 2 



The dinosaurian fauna of the Wealden is certainly quite different and more 

 modern than that of the Atlantosaurus beds. In the Wealden the Sauropod 

 dinosaurs, which form such a conspicuous feature in the faunas of the Middle 

 and Upper Jura, are on the wane, and that group of Predentate dinosaurs known 

 as the Iguanodontia has attained unusual importance, assuming to a certain 

 extent at least, the position formerly held by the Sauropoda. In the Altanto- 

 saurus beds, however, the Sauropoda predominate, and the Iguanodont group 

 of the Predentata are represented by smaller and less specialized forms. 3 



From the foregoing it will be seen that Hatcher believed that the 

 lower members of these beds are of real Jurassic age, that is below 



1 Memoirs of the Carnegie Museum, Vol. II (1903), p. 68. 



2 Ibid., p. 72. 



3 Proceedings of the American Philosophical Society, Vol. XLIII (November, 1903), 

 P- 353- 



