i6o 



NA TURE 



[August 5, 19^9 



T" 



THE UPPER CRETACEOUS IGUANODONT 

 DINOSAURS. 



DISCOVERIES of the last few years in Wyoming 

 and Montana have thrown a flood of light upon 

 the great herbivorous dinosaurs of the Upper Cre- 

 taceous which Joseph Leidy named Trachodon, so 

 that now they are by far the most completely under- 

 stood group of the dinosaurs, not excepting- the famous 

 iguanodonts of the Wealden or Lower Cretaceous of 

 Bernissart. 



It has long been known that Trachodon is readily 

 distinguished bv the elaborate and compound nature 

 of its multiple grinding teeth, which 

 present as great an advance upon 

 those of Iguanodon as the teeth of 

 Equus do upon those of the Eocene 

 Orohippus ; but there prove to be 

 other characters indicative of the 

 fact that Trachodon followed a 

 fundamentally dilferent line of evolu- 

 tion from that initiated by Iguano- 

 don, or by the nearly contemporary, 

 closely related Camptosaurus of 

 America. These true Lower Cre- 

 taceous iguanodons are probably 

 tvpical terrestrial forms, as shown in 

 the familiar restorations of the Ber- 

 nissart specimens, possessing a short 

 manus with the first digit set well 

 apart, as if adapted to grasping the 

 branches of trees or shrubs, or to 

 supporting the animal while brows- 

 ing. 



Trachodon also has been repre- 

 sented as a terrestrial animal. One 

 of the skeletons mounted under the 

 direction of Mr. F. A. Lucas in the 

 L'nited States National Museum, 

 and another mounted under the 

 direction of the late Frof. Charles E. 

 Beecher in the Yale Museum, repre- 

 sent the animal in a walking or run- 

 ning position, using the tail as a 

 balancing organ. On the other 

 hand, Mr. Barnum Brown, who has 

 been the leader of the American 

 Museum expeditions, under the 

 writer's direction, to the Laramie or 

 L'pper Cretaceous of northern Mon- 

 tana since 1902, is convinced that 

 these animals were principally 

 aquatic or swimming forms, which 

 used the tail chiefly for propulsion 

 through the water, a view shared by 

 Mr. Charles H. Sternberg, another 

 field explorer. It may De added 

 parenthetically that observation in 

 the field often affords the most im- 

 portant indications as to mode of life. 



It will be interesting to discuss the question of the 

 appearance and habits of these animals from materials 

 in the .American Museum, which are being very 

 thoroughly studied by Mr. Brown in preparation for 

 a memoir. Of the two skeletons represented in the 

 accompanying photograph (Fig. i), this museum has 

 acquired three skeletons. The one mounted in the quad- 

 rupedal pose (Fig. i) was discovered in South Dakota, 

 norih-east of the Black Hills, by Dr. J. L. Wortman, 

 in 1882, while collecting for Prof. Cope. It had been 



served on the broad bill, showing an interlocking, 

 tooth-like series of points on the horny sheath. .As 

 the skeleton lav in the rocks a stream had cut through 

 it, carrying away both femora, most of the pelvis, and 

 twelve presacral vertebrae. The erect specimen (Fig. i) 

 was found in central Montana by Mr. Oscar Hunter in 

 1904, and originally " swapped " for a " six-shooter " 

 revolver. In 1906 it was purchased by the .American 

 .Museum and excavated by Mr. Brown. An important 

 feature of this skeleton was that the vertebral colunm 

 was connected throughout, and all the bones which 

 the Cope specimen lacked were preserved, together 

 with both lower jaws and two bones of the skull ; the 



Fig. 1. — Oblique front view of two specimens of Tiachodon mirahitis as mounted in tli-- Amci j. .ni 

 Museum of Na'.ural History. 



rest of the skull is restored after the Cope specimen. 

 In both specimens the tip of the tail is missing. 



The difference in the preservation of these two 



animals partly controlled the design which has been 



adopted for the mounting; the animal with the perfect 



head, well known through the descriptions and figures 



of Cope as DicJoniiis inirabilis, is represented in a 



feeding posture, which brings the head where it can 



readily be examined, while the imperfect skull of the 



second skeleton is " skied " where it cannot be seen. 



complete, .and the skeleton was surrounded bv im- The conception of this group takes us back to the 



pressions of the skin, most of which were destroyed \ close of the Cretaceous period, when trachodons were 



during excavation. Some epidermal parts were pre- among the most numerous of dinosaurs; as two of 



NO. 2075, VOL. 81] 



