126 Reviews — Bono's Dinosanria of Bernissart. 



birds. M. Dollo has already elected to dismiss for tlie present botli 

 of these questions, but the subject is one which must eventually be 

 faced, and I venture to urge that the functional development of avian 

 characters is the safest basis of interpretation ; first, because func- 

 tional conditions are the primary directing cause of structural 

 variations; and, secondly, because the modifications of structure in 

 any Dinosaur vs^hich would be necessary to convert it into a bird, are 

 not less considerable than would be required to convert a Crocodile 

 into a Dinosaur, If Dinosaurs and Birds are supposed to descend 

 from an ancient common stock, then the functional evolution of some 

 avian characters in certain families of Dinosaurs becomes more 

 intelligible. M. Dollo's chief inference, however, from the avian 

 resemblances is, that the Iguanodon also must consequently be 

 inferred to have been a biped. He quotes Sir Eichard Owen to 

 show that the mere difference in size between the fore and hind 

 limbs would not establish this conclusion, since the difference, as 

 marked in the Crocodile and in Iguana, is relatively almost the same 

 as in Iguanodon MantelU. The proof of the biped condition is made 

 to rest upon the greatly reduced size of the anterior extremities, the 

 difference in number of digits on the anterior and posterior limbs 

 (both of which characters are common to the Crocodile) ; and, 

 thirdly, divergences of structure which show a different physiological 

 use for these members. Here a good deal is assumed. The presence 

 in Iguanodon of a powerful offensive spine on the inner anterior digit, 

 which has no parallel in the hind limb, is surely a doubtful argument 

 that the animal was a biped. The argument would have been much 

 stronger if the author had been content to show that the weight of the 

 tail would necessitate the trunk being thrown into a forward position, 

 so that the body could only have been carried when balanced on the 

 pelvic axis. The author goes on to contest Sir Richard Owen's ai-gu- 

 ments against the upright position, in the course of which he states that 

 the neck is relatively long, containing ten or twelve vertebrae, while 

 in the dorso-lumbar region there are sixteen or eighteen. The 

 opisthocoelous articulation of the centrum, and the nature of the 

 zygapophyses give great mobility to the neck ; and, although 

 the number of vertebra in the sacrum is smaller than that in birds, 

 yet this number may be apparently reduced, since the number of 

 sacral vertebrae in Archceopteryx is probably fewer than in Iguanodon 

 Bernissartensis. M. Dollo remarks that the position of the occipital 

 condyle is interesting as having an intermediate position between 

 the horizontal arrangement of quadruped reptiles and the condition 

 in birds, in which the head is carried at right angles to the neck. 

 The foot-prints which have been attributed to Iguanodon MantelU 

 are discussed, with the result that the author finds evidence of no 

 other known Wealden Dinosaur which could have produced these 

 tridactyle impressions, while the bones of the three digits are super- 

 imposed successfully on the natural cast ; and hence it follows that 

 the animal walked as a biped, without leaving any impression of its 

 tail upon the shore. The author agrees with Sir Eichard Owen that 

 the resemblance of the tail to that of a Crocodile, and the develop- 



