August 5, 1909J 



NATURE 



161 



lliem are feeding along the marshes, one is startled by 

 the approach of a carnivorous enemy, Tyrannosaurus, 

 and stands on tip-toe better to overlook the foliage ; 

 the other, unaware of danger, continues browsing. 

 On the base of the group are shown impressions of 

 leaves, fruit, wood, and shells, replicas of fossils 

 actually associated with the bones of Trachodon. The 

 leaves of the ginkgos, natives of China, were mingled 

 with the cones of Sequoia, or big tree of California. 

 Horsetail (Equisetum) rushes were abundant and 

 luxuriant in growtli, an imperfect specimen here re- 

 presented measuring sixteen feet in length. Fruit and 

 leaves of the Ing are also abundant, and with the 

 leaves of a species of banana and numerous palms 

 attest a warm climate in the northern United States 

 during the period. 



Hardly was this carefully studied group completed 

 late in 1907 when the fortunate discovery was made 

 in Converse County, Wyoming, in .August, igo8, by 

 Messrs. Charles and George Sternberg, father and 

 son, of another specimen of Trachodon with the epi- 

 dTmal impressions very extensively preserved. This 

 completes our knowledge of the animal, .\mongmany 

 other new features it especially brings out the very 

 important difference between the fore feet of Trachodon 

 and of Iguanodon. .As noted above, the manus of 



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Fu, 



-.\ portion of the t lil of rra:!todon iiiirabUis pr . 



Iguanodon is a short organ with grasping function. 

 In Trachodon the manus is long and very slender; the 

 thumb, or first digit, is not free, but closely appressed 

 to the side, and still more remarkable is the fact that 

 the entire hand was encased in an epidermal web, so 

 that the digits are not freely movable, but closely 

 united, and thus strongly indicative of a paddle func- 

 tion while moving in the water. This bears directly 

 on the question whether these animals were aquatic, 

 amphibious, or terrestrial. The terrestrial theory may 

 apply to Iguanodon, but certainly not to these animals. 

 The littoral or amphibious theory was that held by 

 Prof. Cope. The familiar restoration bv Charles R. 

 Knight, which was made under his personal direction, 

 represents one Trachodon on the shore in a sitting 

 position, a second wading and feeding in shallow 

 water. The enormously powerful hind limbs, pro- 

 vided with three large digits incased in hoofs, together 

 with the long lines of osseous tendons connecting the 

 vertebrae of the back with the vertebrae of the tail, both 

 point to capacity for land progression on the hind 

 limbs, with the use of the tail as a balancing organ. 

 NO. 2075, VOL. 81] 



No habitually swimming animal would retain siioh 

 limbs or acquire such infiexibilitv of a large region 

 of the backbone as is suggested by the ossification of 

 the tendons. On the other hand, river-frequenting or 

 littoral habits are indicated first by the webbed nature 

 of the epidermis on the fore feet, as well as bv the 

 observation of Mr. Brown that of all Upper Cretaceous 

 dinosaurs these are the only ones the remains of which 

 are found in off-shore marine deposits. This fact 

 may be cited as a proof, either that they frequented 

 shallow- and still-water bays of the sea, or that their 

 remains were carried seaward in rivers. 



The position selected for the group accordingly re- 

 presents these animals as on a ripple-marked shore ; 

 one, the Cope speciinen, in the quadrupedal position, 

 with the tips of the digits of the manus lightly resting 

 on the ground rather as balancers than as supporters. 

 This is the first time an iguanodont has ever been 

 mounted or represented in this position, and the justi- 

 fication for it is found in the fact that the fore limbs 

 do readily reach the ground and terminate in expanded 

 ph.alanges, which indicates the retention and occa- 

 sional use of hoofs. If the "trachodons in this phylum 

 had never assumed a quadrupedal position, or used 

 the fore limbs in this way, it is safe to infer that the 

 limbs would have been either still more reduced and 

 degenerate, or else the dibits would 

 have spread or expanded into true 

 swimming paddles. 



This method of mounting two or 

 more specimens together, but in 

 different poses to illustrate the sup- 

 posed habits of feeding and of loco- 

 motion, is one which is being 

 generally adopted. In the present 

 case it brings out in side and rear 

 views every important feature in 

 the osteology of these animals. By 

 an accident the tail in both thete 

 specimens terminates at the same 

 point, but in other specimens in 

 the Yale and National Museums 

 smaller terminal vertebras have 

 been found which would add about 

 five feet to the tail beyond the parts 

 preserved in these specimens. 



The actual height of the head 

 above the giound in the standing 

 Trachodon is seventeen feet; the 

 total length of the body is thirty 

 feet. Remains of still larger in- 

 dividuals of this species have been found which indi- 

 cate greater height and length. 



It is first of all evident from these skeletons and 

 models that these Trachodons, like all the iguanodons, 

 were full-chested and slim-wasted, to use the terms 

 of fashion ; while the longitudinal diameter of the 

 pelvic region is enormous, the vertical diameter is 

 very slight. Thus the proportions of the abdominal 

 girdle directly reverse those of the Sauropoda and car- 

 nivorous dinosaurs, in which the vertical diameter is 

 the greatest. The shape of the chest is exactly pre- 

 served in the new Sternberg specimen, as well as in 

 the indications of the muscular outlines of the limbs 

 and of the presence of a dermal frill on the neck and 

 anterior part of the back. >The neck and chest regions 

 are relatively short, .l^ie gape of the mouth is placed 

 exactly at tiM front of the great rows of grinding 

 teeth, 'as in the mammals. There is evidence that the 

 skin was thrown into loose folds at the junction of the 

 arms and legs with the body, as well as on the sides 

 of the chest. 



The Trachodon with the epidermal impressions was 



/.ng the pavement epidermal scales. 



