FOSSIL REPTILES. 631 



character on which too much weight must be placed. As we 

 see in the Lacertilia, dermal ossifications are subject to great 

 variation in even allied forms. 



, Another group to which the Pseudosuchians seem to have 

 affinities as suggested by Newton, is the Ornithosauria. In general 

 proportions the Pterodactyles differ very greatly, but the form 

 fi'om which they arose must have been very much like that seen 

 in Pseudosuchians. The Pterodactyl and Pseudosuchian skulls are 

 almost exactly similar in essentials. As pointed out by Newtou, 

 tlie skull in Scyphognathus resembles pretty closely that of Ornitho- 

 sachiis. The Pterodactyl manus is simply an ordinary reptilian 

 manus with the 5th digit lost and the 4th greatly specialised, 

 and there can be no doubt that the 5th digit was lost before the 

 wing-membrane was developed. Tlie pelvis of the Pterodactyl 

 is not thoroughly known beyond doubt, but seems to be a modi- 

 fication of the ordinary plate-like type with the prepubis ossified, 



Scleromochlus is a very lightly built Pseudosuchian evidently 

 adapted for taking leaps, and not for bipedal progression on the 

 ground. The limbs are long and slender, and the length and 

 slenderness of the fore limb suggest that possibly there was a 

 membrane stretched between the fore and hind limbs and pei-liaps 

 between the hind limbs and tail, which would enable the little 

 animal to take sustained leaps like Petaiirus. 



Although Sderomochhis is already too specialised in the hind 

 foot structure to have been in any way ancestral to the Ptero- 

 dactyls, it may suggest how they liave arisen, just as Galeoiyithecus 

 suggests how the bats arose. 



There is still another group to which some Pseudosuchian has 

 probably been ancestral, namely, the Biixls. For a time one or 

 other of the Dinosaurs was regarded as near the avian ancestor. 

 The resemblance of the hind limb and pelvis seemed to make this 

 extremely probable, and Huxley, Marsh, Cope, and others have 

 all favoured this view. Otliers, however, were more impi'essed by 

 the apparently avian characters in the skeleton of the Ptero- 

 dactyls, and especially in the striking avian appearances in the 

 brain, and have argued in favour of a close affinity between 

 the Birds and the Pterodactyls. Osborn, while recognising 

 the affinities to both groups, and especially to the Dinosaurs, 

 believed that the Birds and the Dinosaurs had a common ancestor, 

 probably in the Permian. Seven years ago, when describing the 

 skeletogenesis of the Ostrich, I argued that the bird had come 

 from a group immediately ancestral to the Theropodous Dinosaurs, 

 The Pseudosuchia, now that it is better known, proves to be just 

 such a group as is required. In those points where we find the 

 Dinosaur too specialised we see the Pseudosuchian still pi'imitive 

 enough. The bird pelvis has probably developed from a tyyie 

 like that of Ornithosiickus by the pubis turning fui-ther back a.nd 

 the symphysis becoming lost. Whether the union of the meta- 

 tarsals is a pi'imaiy or a secondaiy character is a debatable point. 

 The question is really whether the bird ancestor was a hopping 



