April 27, 1876] 



NATURE 



515 



On passing to the internal organs, and the mode of 

 development, we find far greater points of resemblance ; 

 as to the latter, in fact, the correspondence is wonderful, 

 the account given of the development of a reptile (Nature, 

 vol. xiii., p. 429), applying in every respect to that of a 

 bird. 



On the whole it is certain, from anatomical characters 

 alone, that birds are modificatons of the same type as that 

 on which reptiles are formed, and if this similarity of 

 structure is the result of community of descent, we should 

 expect to find, in the older formations, birds more like 

 reptiles than any existing bird, and reptiles more like 

 birds than any existing reptile. If the Geological record 

 were sufficiently extensive, and the conditions of preser- 

 vation favourable, we ought to find an exact series of 

 links, but this, of course, is hardly to be expected, and it 

 will be a great step if we can show that certain forms tend 

 to bridge over the gulf between the two groups. 



Let us see, then, what the facts of Palseontology tell us 

 in this matter : and first, as to birds. 



It is a curious fact that, just as in the case of Croco- 

 diles, all the birds found in the Tertiary deposits differ in 

 no essential respects from those of the present clay. 

 Great numbers of remains have been found in beds of 

 Miocene age— beds found at the bottoms of great lakes 

 — and the very peifectly preserved specimens show, be- 

 yond any doubt, that the Miocene birds are referable to 

 precisely the same groups as those of our own time. Our 

 knowledge of the Eocene forms is less perfect, but enough 

 is known to show that the same fact held good at the 

 commencement of the Tertiary epoch. 



Throughout the secondary period remains of birds are 

 very rare ; until lately, in fact, there were none at all. 

 But within the last ten or fifteen years some remarkable 

 discoveries have been made — one or two in Europe, and 

 a whole series in America, which give us some very pre- 

 cise i:;formation as to the nature of the Mesozoic birds. 



Two of the most interesting of these— the genera Hes- 

 perornis and Ichthyornis — occur in certain beds in the 

 United States, corresponding in age to our later Cre- 

 taceous. Hesperornis is stated, by its describer, to have 

 had nearly the organisation of our Northern Diver 

 {Colymbus) ; it was five or six feet in length, of swimming 

 habits, had small wings, like those of the Penguin or 

 Auk, and a long beak like the Diver. But — and this is 

 the interesting feature in its organisation — both jaws were 

 beset with teeth : not mere serrations of the jaw, such as 

 many existing birds have, but true teeth like those of a 

 reptile. Here then we have the appearance of a true 

 reptilian character. 



Ichthyornis was, in some respects, even more curious. 

 It was about as large as a good-sized pigeon, had large 

 wings adapted for powerful flight, and teeth in both jaws, 

 like Hesperornis. In another character it showed a still 

 greater approximation to the lower reptilian type : the 

 bodies of its vertebrae, instead of having the cylmdroidal 

 or saddle-shaped form so characteristic of nearly all birds,^ 

 were bi-concave. Thus, in tracing birds back in time, we 

 find a parallel series of modifications to those described in 

 the Crocodilia. 



Beyond this point, the history of birds is almost a 

 blank, the only other remains being — curiously enough — 

 one or two feathers, and the Archaopteryx of the Solen- 

 hofen slates, a formation which has been of great service 

 in the preservation of organic remains, the same qualities 

 which make it so useful for purposes of lithography 

 having fitted it for the preservation of even such perish- 

 able structures as jelly-fish. 



Archajopteryx, known only by a single specimen now 

 in the British Museum, was a bird about the size of a 



' In this peculiarly avian form of vertebra, the front face of the centrum 

 is convex from above downwards, and concave from side to side, the binder 

 face being concave from above downwards, and convex from side to side. 

 The Penguins have the dorsal vertebrae opisth»ccelous, i e., with a ball in 

 front and a cup behind. 



crow. Its head is unfortunately wanting ; its tail is 

 quite unlike that of any existing bird, being long, com- 

 posed of a great number of vertebrae, and having two 

 rows of feathers attached, one to each side of it. The 

 leg is quite like that of any ordinary perching bird. Un- 

 luckily, the bones of the wing are detached, so that the exact 

 structure of the manus is not known, but it is quite certain 

 that the metacarpal bones were not united together, but 

 were separate and terminated by distinct claws ; there 

 was thus an approximation in structure to a true fore- 

 paw. Long quills were attached to the wings, and both 

 they and the tail-feathers are in an exquisite state of pre- 

 servation. 



With Archceopteryx we come to the end of all precise 

 information as to the history of birds, and the only pos- 

 sible trace of the group in earlier formations are certain 

 footprints found in the Trias of Connecticut, and referred 

 to the genus Brontozotitn. These were prints of some 

 gigantic three-toed animal, which certainly walked on its 

 hind legs, and was always supposed to be an ostrich-like 

 bird until some recent discoveries, presently to be men- 

 tioned, have shown that Brontozoum may have been a 

 reptile. 



It would at first seem easy to show an equally striking 

 approximation of reptiles to birds, for we have, throughout 

 the greater part of the secondary rocks, and notably in the 

 Solenhofen slates, remains of a group of reptiles known as 

 Fterodactyles. These remarkable creatures had teeth 

 set in distinct sockets, sometimes extending to the end of 

 the long snout, sometimes stopping short, and having 

 their place taken by a horny beak. The neck was long ; 

 the sacrum consisted of from three to six vertebras ; the 

 tail was short in some, long in other genera. The breast- 

 bone had a great keel, like that of a bird, the shoulder- 

 girdle was also quite birdlike, as also were the humerus 

 and tha bones of the fore-arm. The manus, on the other 

 hand, was quite different to anything found in birds ; the 

 first, second, and third digits were of the usual reptilian 

 character and bore claws, but the fourth was immensely 

 prolonged, produced downwards, and clawless. The 

 pelvis was, in some respects, birdlike, in others quite 

 peculiar : the hind-limb was reptilian. 



It is certain that the Fterodactyles were animals of 

 flight, and that there was a membrane, like a bat's wing, 

 stretched between the fourth finger and the sides of the 

 body ; it is also certain that it was unable to walk, though 

 it may have used its hind-limbs, as bats do, for hanging 

 itself head downwards from branches. 



Although these creatures are, in many respects, very 

 birdlike, yet it can hardly be said that they give us any 

 direct help, or that they connect reptiles and birds any 

 more than bats connect birds and mammals. Their avian 

 characters seem to have been purely adaptive, or pro- 

 duced in relation to their peculiar mode of life, and we 

 must therefore try some other line of reptiles for the 

 origin of birds. 



In the rocks from the Trias to the later Cretaceous there 

 are, in many places, abundant remains of a group of 

 wholly extinct terrestrial reptiles known as Dinosauria. 

 Most of these are of great size, the genus Igtianodon, for 

 instance, must have attained a length of fully thirty feet. 

 Our knowledge of most of them is imperfect, but many 

 points of the greatest possible interest are perfectly well 

 known. 



Some genera have the snout turned downwards like a 

 turtle's beak, and both it and the large lower jaw were 

 ensheathed in horn. In some the vertebras are slightly ex- 

 cavated on both faces, and are penetrated with air cavities. 

 The shoulder-girdle consists of a long blade-bone and a 

 short coracoid like that of many lizards. Of the fore- 

 limb nothing is known for certain in the larger species. 

 The sacrum is composed of as many as six vertebrae, 

 which often take on a remarkably birdlike character. 

 More curious still, the ilium has a great forward process, 



