INTRODUCTION 
Original Descriptions 
Professor Marsh's original description of Barosaurus was published in the Ameri- 
can Journal of Science for January, 1890, pp. 85-86, Figs. 1 and 2, and reads as 
follows : 
Barosaurus lentus, gen. et sp. nov. 
A new genus of the Sauropoda is indicated by various remains of a very large reptile secured by 
the writer during the past season. The most characteristic portions examined are the caudal vertebrae, 
which in general form resemble those of Diplodocus. They are concave below, as in the caudals of 
that genus, but the sides of the centra are also deeply excavated. 
In the anterior caudals, this excavation extends nearly or quite through the centra, a thin septum 
usually remaining. In the median caudals, a deep cavity on each side exists, as shown in Figs. 1 and 
2 '[Fig. 1, A, B] on page 86. 
Figure 1.— A, Caudal vertebra of Barosaurus lentus, after Marsh. Median vertical section, 
lateral aspect of the same bone. C, Ventral aspect. All one-eighth natural size. 
B, Left 
On the distal caudals, the lateral cavity has nearly or quite disappeared. All the caudal vertebrae 
are proportionately shorter than in Diplodocus, and their chevrons have no anterior projection, as in 
that genus. 
The remains on which the present description is based are from the Atlantosaurus beds of Dakota, 
about two hundred miles further north than this well-marked horizon has hitherto been recognized. 
A supplementary description by Professor Marsh is found in his Dinosaurs of 
North America, 1896, pp. 174-175, Figs. 24-26: 
Barosaurus 
Another genus of the Sauropoda is indicated by various remains of a gigantic reptile described 
in 1890 by the writer. The most characteristic portions examined are the caudal vertebrae, which in 
general form resemble those of Diplodocus. They are concave, below, as in the caudals of that genus, 
but the sides of the centra are also deeply excavated. 
In the anterior caudals this excavation extends nearly or quite through the centra, a thin septum 
usually remaining. In the median caudals a deep cavity on each side exists, as shown in Figs. 24-26 
below [like those of the original description except that a ventral view of the caudal vertebra is shown 
(Fig. 1, C)]. 
On page 241 of the same publication the genus Barosaurus is placed under the 
family Atlantosauridse, which is thus defined : 
A pituitary canal; large fossa for nasal gland. Distal end of scapula not expanded. Sacrum 
hollow ; ischia directed downward, with expanded extremities meeting on median line. Anterior caudal 
vertebrae with lateral cavities ; remaining caudals solid. 
Genera Atlantosaurus, Apatosaurus, Barosaurus, Brontosaurus. Include the largest known land 
animals. Jurassic, North America. 
