STRUCTURE AND RELATIONSHIPS OF OPISTHOCCLIAN 
DINOSAURS. 
PART I. 
APATOSAURUS* MARSH. 
Diba ore kl GG. 
The genus Brontosaurus Marsh was described Tf in 1879 from a 
well preserved skeleton found near Lake Como, Wyoming. The 
completeness of this specimen and the widely published restorations 
based upon it have caused this genus to be long regarded as the best 
known of all the American Opisthoccelia.f However, many questions 
of morphology were left in doubt by this famous specimen. No skull 
which could be identified with the genus has ever been described; that 
figured in Marsh’s restoration is based upon a comparison with the 
skull of Morosaurus. The structure of the hind feet was not made 
clear until figured by Osborn in 1899,§ while the structure of the fore 
foot remained a matter of conjecture until figured by Hatcher in rgoz.|| 
The vertebral formula of the dorsal and caudal series, as well as many 
sacral and pelvic characters, has remained to be determined by an 
unusually well preserved skeleton just placed upon exhibition in the 
Field Columbian Museum. | 
The specimen under consideration (Mus. No. 7163) was collected 
by the Museum Paleontological Expedition of rogoz, in charge of the 
writer, ably assisted by Mr. H. W. Menke. It was found in the Grand 
River Valley near Fruita, Colorado, ina geological horizon 4 probably 
equivalent to the Como Beds of Wyoming. The specimen was discov- 
ered in the fall of 1900, but owing to the lateness of .the season, its 
removal was deferred until the following spring. 
When found the last cervical vertebra was projecting from a steep 
hillside. ‘The thoracic series led diagonally into the face of the hill, 
leaving the distal ends of a number of ribs exposed and partially broken 
* Brontosaurus, Marsh, is shown to be a synonym of Af#atosaurus. 
+ Am. Jour. Sc. Vol. xviii, p. 503. 
¢ Sauropoda and Cetiosauria are shown to be synonyms of Opisthoccelia. 
§ Bull. Am. Mus. of Nat. Hist., Vol. xii, pp. 161-172. 
| Annals of the Carnegie Museum, Vol. i, pp. 156-76. 
- "See ‘The Dinosaur Beds of the Grand River Valley of Colorado,” this publication, 
Geol. Series, No. 9. 
FIELD COL. Mus., GEOL. SER., Vol. II, No. 4. 
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