Maryland Geological Survey 175 



the centra of the vertebrae. The teeth, which are slender, slightly flat- 

 tened cylinders, sometimes nearly straight, again spoon-shaped, with 

 blunt cutting edges, imply a very soft vegetable food, probably in the 

 form of an aquatic plant, which grew in sufficient profusion to enable 

 these creatures to satisfy their needs. The Sauropoda were apparently 

 of wading habits though, with such small types as this, land locomotion 

 was doubtless not only possible but probable. Pleuroccelus nanus has 

 allies so near akin as to be nearly indistinguishable, both in the Morrison 

 beds of the West and the Upper Jurassic ( ? Kimmeridgian) near Havre, 

 France, while somewhat more remotely related types are reported from the 

 Kimmeridgian of Sussex and of the Isle of Wight. 



Another species of Pleuroccelus, to which Professor Marsh gave the 

 name of alius in allusion to its greater size, is also found in Maryland, 

 though its known remains are very few compared Avith those of its ally. 

 In size it exceeded that of Pleuroccelus nanus by about two and a half 

 times, giving it an estimated length of at least 30 feet. Its limb bones 

 were much slenderer than those of a Morosaurus of equivalent length, 

 indicating an animal of greater activity. Another genus, Asfrodon, 

 described years ago by Dr. Leidy from one or two teeth, is a near ally, 

 if not identical with Pleuroccelus alius. Judgment is suspended, how- 

 ever, until further light is forthcoming in the way of more material, 

 for the teeth of Asirodon are extremely rare. 



To the orthopod or predentate dinosaurs may be referred two genera 

 of Potomac forms, one a lightly built, agile, plant-feeding type, differing 

 from Pleuroccelus in many respects, of which two are perhaps the most 

 striking. One is the character of the mouth armament, for, while in 

 Pleuroccelus the teeth were fragile structures situated along the jaws, 

 but especially in the front of the mouth, in the form under considera- 

 tion, Dryosaurus, the anterior portion of the mouth was toothless, and 

 doubtless sheathed with horn like that of a turtle, while the teeth were 

 contained in magazines in the cheek portion of the jaws, a relatively 

 simple mechanism, however, when compared with the later Cretaceous 

 types. The other distinctive feature is the bipedal gait, shown by the 

 great difference in size of the fore and hind limbs. Doubtless, however, 

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