OCR Text |
Show 184 MR. W. K. PARKER ON STEATORNIS CARIPENSIS. [Apr. 2, are only present in birds that have arrived at the highest state of ornithic modification and perfection. In the self-same skull we have then, as I have shown, a basis cranii with large backwardly placed " basi-pterygoids" that are nearly Struthious ; the only carinate bird that is a rival to Steatornis in this respect is Pallas's Sand-Grouse (Syrrhaptes paradoxus) (see Trans. Zool. Soc. vol. v. pi. xxxvi.). On the other hand, the "ethmo-nasal wall" has been completely broken through and thus a complete hinge of the face on the skull has been formed exactly as in the Parrots, where the mobility of the upper face is at its greatest possible perfection. But the basis cranii of the Parrots, in harmony with the "palato-quadrate" arcade, is in the highest state of modification ; no bird is so far from the old quasi-reptilian Ratitae in this respect as the Parrot. Yet, as a set-off against this, whilst the Archaic Ratitae have all their pre-sacral vertebrae in the highest ornithic perfection, namely, cylindroidal, in the Parrots the dorsals are opisthoccelian ; so they are as we have seen in Steatornis, which also has the rare condition, as in Hesperornis and the Grebes, of perfect rib-bars on the axis 1. In Wading and Water Birds this state of things is common, e.g. in the Penguins, Alcine Divers2, Gulls, and Limicolce ; but the Psit-tacidae and Steatornis are the only high-class arboreal birds in which I have found this character of opisthoccelous dorsals. Here I may remark upon a most puzzling fact with regard to both old and new kinds of birds, namely, a prolepsis, or anticipation, so to speak, of Mammalian characters, in certain birds-a similarity or isomorphism rather, for here "genetic affinity" has no place. The more Archaic the type of any one of the existing Ratitae, the more complex is the nasal labyrinth, quite similar in its complex "outgrowths" to what we see in a mammal. The very dorsal vertebrae that are ancient or opisthoccelian in a Parrot, are also like the vertebrae of a Mammal-they have thin terminal epiphyses. In by far the noblest of all birds, the Crows and Songsters, the form of palate which gives them their morphological name, " JE^i-thognathEe," is quite similar to what is seen in the Marsupials and low Insectivorous Mammals. In this very bird, Steatornis-as in Podargus, the larger Bucerotidae, and in certain Ducks and Swans-there is a degree of double Desmo-gnathism quite similar to that which exists in the Marsupialia. Hence we had better, at present, speak of these things as cases of isomorphism, or similarity-confessing our ignorance of their meaning-than rashly to set them down to genetic relationship. By taking this character or that, and closing the eyes to the other characters seen in Steatornis, we might find many a relation for it: it is, nevertheless, a friendless bird, I cannot find a near relation for it. And this is the more evident if we consider that the forms that apparently come nearest to it are Eastern and Australian types, 1 In typical Chenomorphce-Geese, Swan, Ducks-the atlas, also, has its rib-bar complete, and a separately ossified rib. a Not in the Loons and Q-rebes. |