Page:Encyclopædia Britannica, Ninth Edition, v. 18.djvu/53

 ORNITHOLOGY pithy -&quot;Birds are only glorified Reptiles.&quot; It is not intended here to enter upon their points of resemblance and differences. These may be found summarized with more or less accuracy in any text-book of zoology. We shall content ourselves by remarking that by the naturalist just named Birds and Reptiles have been brigaded together under the name of Sauropsida as forming one of the three primary divisions of the Vertebrata the other two being Ichtkyopsida and Mammalia. Yet Birds have a right to be considered a Class, and as a Class they have become so wholly differentiated from every other group of the Animal Kingdom that, among recent and even the few fossil forms known to us, there is not one about the assignation of which any doubt ought now to exist, though it is right to state that some naturalists have even lately refused a place among Aves to the singular Archxopteryx, of which the remains of two individuals most probably belonging to as many distinct forms 1 have been discovered in the quarries of Solenhofen in Bavaria. Yet one of them has been referred, without much hesitation, by Prof. Vogt to the Class Reptilia on grounds which seem to be mistaken, since it was evidently in great part if not entirely clothed with feathers. 2 The peculiar structure of Archceopteryx has already been briefly mentioned and partly figured in this work (BiEDS, vol. iii. p. 728-9), and, while the present writer cannot doubt that its Bird-like characters predomin ate over those which are obviously Reptilian, he will not venture to declare more concerning its relations to other Birds, and accordingly thinks it advisable to leave the genus as the sole representative as yet known of the Sub class Saurursef established for its reception by Prof. Hiickel, trusting that time may shew whether this pro visional arrangement will be substantiated. The great use of the discovery of Archxopteryx to naturalists in general is well known to have been the convincing testimony it afforded as to what is well called &quot; the imperfection of the Geological Record.&quot; To ornithologists in particular its chief attraction is the evidence it furnishes in proof of the evolution of Birds from Reptiles; though, as to the group of the latter from which the former may have sprung, it tells us little that is not negative. It throws, for instance, the Pterodactyls so often imagined to be nearly related to Birds, if not to be their direct ancestors completely out of the line of descent. Next to this its principal advan tage is to reveal the existence at so early an epoch of Birds with some portions of their structure as highly organized as the highest of the present day, a fact witnessed by its foot, which, so far as can be judged by its petrified relics, 1 See Prof. Seeley s remarks on the differences between the two specimens, in the Geological Magazine for October 1881. 2 Prof. Vogt lays much stress on the absence of feathers from certain parts of the body of the second example of Archxopteryx now, thanks to Dr Werner Siemens, in the museum of Berlin. But Prof. Vogt himself shews that the parts of the body devoid of feathers are also devoid of skin. Now it is well known that amongst most existing Birds the ordinary &quot;contour-feathers&quot; have their origin no deeper than the skin, and thus if that decayed and were washed away the feathers growing upon it would equally be lost. This has evidently happened (to judge from photographs) to the Berlin specimen just as to that which is in London. In each case, as Sir R. Owen most rightly suggested of the latter, the remains exactly call to mind the very familiar relics of Birds found on a seashore, exposed perhaps for weeks or even months to the wash of the tides so as to lose all but the deeply-seated feathers, and finally to be embedded in the soft soil. Prof. Vogt s paper is in the Revue Scienfifique, ser. 2. ix. p. 241, and an English translation of it in The Ibis for 1880, p. 434. 3 Prof. Ha ekel seems first to have spelt this word Sauriurie,, in which form it appears in his Attgemeine Entwickelungeschichte der Organismen, forming the second volume of his Generelle Morpholoyie {pp. xi. and cxxxix. ), published at Berlin in 1866, though on plate vii. of the same volume it appears as Sauriuri. Whether the masculine or feminine termination be preferred matters little, though the latter is come into general use, but the interpolation of the i in the middle of the word appears to be against all the laws of orthography. might well be that of a modern Crow. The fossil remains of many other Birds, for example Prof. SEELEY S Enaliornis (Quart, Journ. Geol. Society, 187G, pp. 496-512), Sir R. OWEN S Odontopteryx (BIRDS, vol. iii. p. 729), Gastorms, Prof. COPE S Diatryma (Proc. Acad. N. Sc. Philadelphia, April 1876), and some more, are too fragmentary to serve the purposes of the systematist ; but the grand discoveries of Prof. Marsh, spoken of above, afford plentiful hints as to the taxonomy of the Class, and their bearing deserves the closest consideration. First of all we find that, while Antiquity Birds still possess the teeth they had inherited from their of the Reptilian ancestors, two remarkable and very distinct types * of the Class had already made their appearance, and we ^ r i mite must note that these two types are those which persist at types. the present day, and even now divide the Class into Ratitse and Carinatse, the groups whose essentially distinct characters were recognized by Merrem. Furthermore, while the Ratite type (Hesperornis) presents the kind of teeth, arrayed in grooves, which indicate (in Reptiles at least) a low morphological rank, the Carinate type (Ich- thyornis) is furnished with teeth set in sockets, and shew ing a higher development. On the other hand this early Carinate type has vertebrae whose comparatively simple, biconcave form is equally evidence of a rank unquestion ably low ; but the saddle-shaped vertebrae of the con temporary Ratite type as surely testify to a more exalted position. Reference has been already made to this com plicated if not contradictory state of things, the true explanation of which seems to be out of reach at present. It has been for some time a question whether the Ratite is a degraded type descended from the Carinate, or the Carinate a superior development of the Ratite type. Several eminent zoologists have declared themselves in favour of the former probability, and at first sight most people would be inclined to decide with them ; for, on this hypothesis, the easiest answer to the question would be found. But the easiest answer is not always the true one ; and to the present writer it seems that before this question be answered, a reply should be given to another Was the first animal which any one could properly call a &quot; Bird,&quot; as distinguished from a &quot;Reptile,&quot; possessed of a keeled sternum or not 1 Now Birds would seem to have been differentiated from Reptiles while the latter had biconcave vertebrae, and teeth whose mode of attachment to the jaw was still variable. There is no reason to think that at that period any Reptile (with the exception of Pterodactyls, which, as has already been said, are certainly not in the line of Birds ancestors) had a keeled sternum. Hence it seems almost impossible that the first Bird should have possessed one ; that is to say, it must have been practically of the Ratite type. Prof. Marsh has shewn that there is good reason for believing that the power of flight was gradually acquired by Birds, and with that power would be associated the development of a keel to the sternum, on which the volant faculty so much depends, and with which it is so intimately correlated that in certain forms which have to a greater or less extent given up the use of their fore-limbs the keel though present has become pro portionally aborted. Thus the Carinate type would, from all we can see at present, appear to have been evolved from the Ratite. This view receives further support from a consideration of the results of such embryologies! research as has already been made the unquestionable ossification of the Ratite sternum from a smaller number of paired centres than the Carinate sternum, in which (with the doubtful exception of the Anatvlse] an additional, unpaired centre makes its appearance. Again the geographical dis tribution of existing, or comparatively recent, Ratite forms points to the same conclusion. That these forms Moa, Kiwi, Emeu and Cassowary, Rhea, and finally Ostrich