442 



NATURE 



\_Scpt. 6, 1 88^ 



pelvis is no doubt directly connected with the muscular 

 requirements concerned in the erect posture, originated 

 probably in the Dinosauria, and transmitted to birds, in 

 which it has been improved upon by the elimination, 

 almost complete, of the original pubis through disuse. 



M. Dollo takes the view that the post-pubis is a bone 

 peculiar to Dinosaurians and birds. As he pointed out to 

 me in the mounted specimen, probably a male, the aper- 

 ture inclosed between the two ischiatic bones posteriorly 

 is a very narrow slit through which, if the Iguanodon was 

 by any chance oviparous, no egg of size proportionate to 

 the animal could have passed, and it is, he thinks, just 

 possible that in females he may find the ischia bowed 

 so as to inclose a widely open passage above the 

 symphysis. 



In a separate memoir M. Dollo has pointed out an 

 additional resemblance in the femur of Iguanodon to that 

 of birds to those already pointed out by former observers, 

 namely that the third trochanter present in the former 

 is represented, though feebly, in the femur of many birds. 

 This third trochanter in birds, as he has shown by dis- 

 section in the duck serves for the origin of a small 

 muscle first described by Meckel, which is attached to 

 the tail, and by which the lateral movements of the tail 

 are performed; he terms the muscle " caudo-femoral." 

 The great development of the third trochanter in Iguan- 

 odon must, he concludes, have been in relation with very 

 large similar caudo-femoral muscle concerned in the 

 movement of the immense tail of the animal in the act of 

 swimming. For reasons which he gives, he proposes to 

 call the trochanter in future the fourth trochanter. It is 

 not necessary to enter here into the further well known 

 details in which the hind limb of Iguanodon shows inti- 

 mate resemblance to that of birds, and especially in 

 birds in the young condition. 



The reduction of the anterior limbs in proportion to 

 the posterior and their difference in structure are further 

 evidence, though not conclusive, of the erect posture of 

 the Iguanodons. In /. Mantelli the fore limbs are of abcut 

 half the length of the hinder, whilst in /. Bernissartensis 

 the difference is less, the proportion in length being two- 

 thirds to one. 



The reduction in the volume of the head and thorax as 

 compared with those of quadruped reptiles is further 

 evidence on the same side. The head is comparatively 

 small and very narrow in Iguanodon, the neck flexible 

 and light as in birds. 



One of the most remarkable new points discovered in 

 the Bernissart Iguanodons, also a strongly birdlike feature, 

 is the presence in them of a series of completely ossified 

 ligaments stretching along the sides of the dorsal spines 

 or the vertebra; (see figure), and binding the whole 

 dorso-lumber region into a rigid mass as in birds, whilst 

 the region of the neck and hinder region of the tail are 

 free from any such ligaments. No traces of ossified 

 tendons, such as occur in birds, have been found in con- 

 nection with the limbs of the Iguanodons. 



M. Dollo sums up as follows : — " In short the position 

 of the occipital condyle, the length and the mobility of 

 the neck, the rigid attachment of the dorso-lumbar region 

 to the pelvis, the number of the sacral vertebrae, the 

 massive nature of the tail, in fact, the entire structure of 

 the vertebral column, agree in demonstrating that 

 Iguanodon was biped in its gait. " But the most convincing 

 proof of all, perhaps, lies in the evidence afforded by the 

 footprints of Iguanodon in the Wealden strata. Of the 

 eight Dinosauria known from the Wealden, Iguanodon is 

 the only one which could leave tridactyle footprints. M. 

 Dollo obtained a series of casts of the tridactyle Wealden 

 footprints from Mr. Struchman from the neighbourhood 

 of Hanover ; choosing one of the right size, he intro- 

 duced the three toes of the corresponding foot of one of 

 the Bernissart /. Mantelli, and also the three metataisals 

 still united together, giving them a digitigrade position, 



the only one in which they would enter the impression, 

 and an exact fit of the whole was the result. There can 

 remain no doubt as to the complete correspondence of the 

 two in the mind of any one who has seen the foot and impres- 

 sion thus fitted together. The hand of Iguanodon (see fig.) 

 is pentadactyle, with the thumb transformed into a huge 

 spur which must have been covered with a horny spine when 

 the animal was living. If the animal had walked on all fours, 

 it is impossible but that pentadactjle impressions should 

 have occurred with the tridact\le, but such is not the case. 

 Long series of the tridactyle prints are found without a 

 trace of pentadactyle marks. The arrangement of the 

 tridactyle tracks shows that Iguanodon walked on its hind 

 feet, and did not spring like a kangaroo with the aid of its 

 tail. This merely dragged lightly behind and has left no im- 

 pression in connection with the foot tracks. The spur-like 

 thumbs were formerly supposed to be the cores of horny 

 appendages of the head. They are much smaller in 

 J. Mantelli than in /. Bernissartensis, and M. Dol.o 

 thinks it will possibly turn out that they are larger in 

 the males than the females. 



M. Dollo has not \et published a preliminary account 

 of the skull of Iguanodon, he is now at work on this sub- 

 ject, and a notice of it will shortly appear. In a popular 

 account of the Iguanodons (the last cited in the list) he 

 writes briefly as follows : — 



"The head is relatively small, and very much compressed 

 from side to side " (this is a most striking feature when 

 the mounted skeleton is viewed from in front). " The 

 nostrils are spacious and chambered in their anterior 

 region, the orbits are of moderate size, elongated in a 

 vertical direction. The temporal fossa is limited above 

 and below by a bony arch, an arrangement which occurs 

 else only in Hatteria. The distal extremities of both upper 

 and lower jaws are devoid of teeth. They were no doubt 

 during life covered by a horny beak ; in the hinder part of 

 the jaws are ninety-two teeth." One of the most remarkable 

 features of the skull is the presence at the symphysis of the 

 lower jaw of a curious separate mass of bone shaped 

 somewhat like a horse's hoof (see figure) which forms 

 the distal extremity of the mandible, fitting in to an ex- 

 cavation on the upper surface of the symphysis. Along 

 its upper rounded margin this bone is dentated. This is 

 believed by M. Dollo to be a bone special to Iguanodon, 

 but not without homologues elsewhere which he will in 

 the future point out, and forming part of the lower jaw. 

 Other observers have considered the bone as the inter- 

 maxillary, and have thus concluded that the opening of 

 the mouth lay between the bone and the distal extremity 

 of i he lower jaw, and that thus the upper jaw was shaped 

 something like a parrot's beak, shutting into a depression 

 at the symphysis of the lower. A slight inspection of the 

 complete cranium and lower jaw cleared completely 

 of the matrix, which M. Dollo has befoie him, seems 

 sufficient to carry conviction that his view as to the 

 position of the bone and mouth aperture is the correct 

 one. 



The roof of the mouth of Iguanodon in its anterior 

 region is moulded into rounded, ridge-like prominences, 

 which as M. Dollo pointed out have some curious resem- 

 blances in form to those occurring in the corresponding 

 position in a duck. The animal was an inhabitant of 

 marshes — as far as yet known apparently of freshwater 

 marshes only — and fed probably largely on ferns, abund- 

 ance of which were found with the Bernissart specimen. 

 No results of importance as to this question have as yet 

 been obtained from the examination or their coprolites. 



The outline of the body shown in the prestnt figure 

 was roughly sketched in by M. Dollo on request, in order 

 to give an idea of his present conjecture as to the probable 

 shape of the living Iguanodon. It is most distinctly to be 

 regarded as merely tentative he reserves any expression 

 of final opinion till the whole material has passed through 

 his hands. On examining the outline, it will be seen that tte 



