E. 8. Biggs — BracMosaurus altithorax. 299 



Art. XXX. — BracMosaurus altithorax, the largest known 

 Dinosaur; by Elmer S. Riggs. 



The writer some time since called attention* to a partial 

 skeleton of an herbivorous dinosaur of unusual proportions 

 obtained from the Jurassic of western Colorado. On account 

 of the difficulty in distinguishing between a number of genera 

 already referred to the Sauropoda, it did not then appear 

 advisable to further complicate the problem by proposing a 

 new generic name. But as the unique characters of this animal 

 have become more and more evident it now seems desirable to 

 give it a name, even though it ultimately be found to fall within 

 one of the three or four uncertain genera proposed by Marsh 

 and Cope. The term BracMosaurus altithorax is therefore 

 proposed in recognition of the great size and unusually long 

 humerus of this specimen. 



The generic characters are : humerus longer than femur ; 

 thorax unusually deep ; centra of posterior thoracic vertebrae 

 longer than wide ; anterior caudal vertebrae amphicoelian and 

 their diapophyses not vertically expanded ; coracoid elongate 

 in direction of scapular suture and having glenoid cavity facing 

 antero-externally. 



The specimen upon wmich this genus is based was collected 

 by the Field Columbian Museum paleontological expedition 

 of 1900, from the Grand River valley of western Colorado. 

 Credit for its discovery is due to Mr. H. W. Menke of this 

 Museum. The specimen consists of the humerus, coracoid, 

 femur and ilium, all from the right side ; the sacrum, seven 

 thoracic and two caudal vertebrae, together with a number of 

 ribs and other bones. The parts were, with the exception of 

 the ribs, preserved in their relative positions, and as the speci- 

 men was isolated there can be no question that all belonged 

 to one individual. 



The distal end of the humerus was exposed, broken and dis- 

 placed as surface fragments. Associated with its proximal 

 end was the fairly well-preserved coracoid. Some fifteen feet 

 farther along the hillside the sacrum and pelvic bones appeared 

 lying with spines downward. Two partially weathered caudals 

 were closely connected with the posterior end of the sacrum. 

 The thoracic vertebrae stretched forward in an unbroken series 

 with the ribs scattered on either side and more or less displaced. 

 Up to this point there seemed every reason to hope that the 

 whole anterior portion of the skeleton would be found. But 

 at the end of the seventh presacral vertebra the thin clay 

 * Science, April 5, 1901. 



