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On the Morphology of the Gallinaceœ

1891; Linnean Society of London; Volume: 5; Issue: 6 Linguagem: Inglês

10.1111/j.1096-3642.1891.tb00172.x

1945-9343

William Kitchen Parker,

Amphibian and Reptile Biology

Amongst the higher Vertebrata, the Bird Class is by far the most potent in genera and species, about twelve thousand species being found in the existing avifauna. If, instead of this abundance of living forms, this were an extinct Class and we knew of its members merely by the recovery of a few fossil forms, the value and importance of such relics would be accounted exceedingly great. Now I contend that the interest attached to this group is not in the least lessened by the numbers it contains, and the fact that they are still living, are present everywhere, and can be obtained for morphological purposes at every stage of their growth. The acknowledged fact that these warm-blooded types are, in a sense, merely Reptiles in a high degree of modification, greatly increases the interest in their structure, and especially as the linking on of the Class is not to the existing Reptilian forms, but to various groups that once held sway, but that are only known to us now by their bony remains. Thus in themselves, as a Class, when we study them from an ornithological standpoint and for ornithological purposes, they are a group rich in interest, but their ontology takes them far outside the ornithological territory. A bird is not merely a modified Reptile; and no true abranchiate amniotic Reptile ever gave birth to, or was metamorphosed into, a bird, either slowly or by an evolutional “leap.” Those branchiate, non-amniotic forms, the Amphibia and Dipnoi, have a prior quasi-parental claim on the bird; its development clearly suggests this, and it seems to me that we must seek for the origin of both Reptiles and Birds amongst imagined forms of those half-fishy sort of creatures. The resemblance in its structure and development of a Bird to a Reptile is not at first to be understood off-hand easily, it is a very complex matter; for a bird is like one kind of Reptile in one thing, and resembles others in other things. Note one thing, namely, that a bird is extremely unlike a flying Reptile (Pterosaur), and that the types that help most in this comparison are the Ichthyosaur, the Plesiosaur, and the Dinosaur. If anatomists had gone on in the old way, simply comparing the adult of one type of Vertebrates with the adult of another, the whole subject must have still slept in darkness; the study of the development forces the mind into evolutional speculation. Nearly half a century has elapsed since my own attention was arrested by this subject, and to-day, instead of finding any place of rest, the necessity for renewed labour is felt by me more strongly than ever. In the beginning of this part of my morphological work, which has been taken up again and again, the labourers mere few indeed; now one is almost lost amongst a host of esteemed fellow-workers, whose researches are ever shedding new light upon this difficult but delightful subject. In the present paper I have only lightly touched those regions of the skeleton of the Fowl which have already been figured and described. Nevertheless, the whole skeleton of the Chick is shown, just at the end of the first or beginning of the second week of incubation. The Fowl is but a halfway kind of bird, between an Ostrich and one of the highest types of a songster; and yet the rate of development in it is marvellously rapid, for even this medium kind of bird ripens its young in the egg at four times the rate of that of an embryo Crocodile; three weeks serves for the Chick, three months are required for that Reptile, and six months for a Skate. It can be seen, even at the beginning of the second week of incubation, that the embryo is that of a bird, for it combines, in one, characters that are diagnostic of three, at least, of the most remarkable types of extinct Reptiles. Thus the upper and lower jaws are growing forwards into a long beak, and the extension of the basi-facial axis is just like what is seen in all rostrate types, e.g., in the Skate, Sturgeon, and Lepidosteus, and the embryonic skull of Ichthyosaurus must have had the same intense “prognathism.” But the elongation of the neck and the shortening of the tail remind us of the Plesiosaurus, which type, if it had possessed a long beak, might have done duty, hypothetically, for an early pupal form which was destined to become a bird. But that water-monster never attained to such a dignity. The newest evolutional candidates for birdship are the Ornithoscelida—the Iguanodon and his kindred; I need not say that none of these ever became a bird; they did grow into something wonderful, and their hind-quarters were modified in the same manner as those of an embryo Humming-bird; but a creature weighing twenty tons would have required, in the atmosphere of this planet, wings that would have reached “from sea to sea.” Was the bird developed from some small kind of Ornithoscelidan? I think not, nor do I imagine that the fan-tailed normal birds—toothed or with horny jaws—are the proper descendants, slowly or more rapidly modified, of the mysterious Archœopteryx. That Oolitic form did duty, hypothetically, for a short time as a parental bird; hut Marsh's Toothed Birds of the Cretaceous period suggest that this is a fallacy. The fact that Hesperornis had cylindroidal vertebræ up to its pelvis, and that it had existed as a type long enough for the abortion of its wings and sternal keel, is proof surely that this short-tailed type had existed for an enormous period of time; that is, if our evolutional speculations have any solid truth in them. Anyhow, however long the period has been in which the Bird has arisen from some low form, the time taken, now, in the egg, for the whole of its pre-natal transformation is extremely short—an hour, now, stands for an age, in the past. At this stage—my first in this paper (see p. 215)—the hind-quarters are already essentially Ornithoscelidan; the ilium embraces a long series of sacral vertebrae, and the pubis and ischium have rotated backwards as in those extinct Reptiles. The hind limbs correspond very closely at this time with those of the Iguanodon, yet they are very partially ossified, and in some things they are evidently in harmony with what existed in the early young, not the adult, of that large extinct Reptile. The Wing, at first, has only three digits; the foot has a proximal rudiment of the fifth, with the first arrested at its upper end. But the ends of the digits are flat and soft, there is no claw at present; they are in an amphibian stage at this early date; all Reptiles pass through that stage, and one Amphibian, namely. Dactylethra, does acquire claws. The Hemipod comes in as a very instructive type, tending to connect the Fowls with the Ostrich tribe; it is evidently archaic. In the present short and very imperfect summary, I, of necessity, refer to the other piece of work on the Fowl and the Hemipod, and also to other papers of mine on the morphology of this bird. There is no finality about work of this kind; all the old work serves but as the beginning of new; and I have sought here rather to offer suggestions than to repeat the detailed facts:—they have but Little interest except as links in a long and tortuous chain; they are not things on which we can rest—they serve, however, as stimulants to further research.