Having been engaged for several years in the investigation of American Mesozoic birds, it became important for me to study the European forms, and I have recently examined with some care the three known specimens of Archæopteryx. I have also studied in the Continental museums various fossil reptiles, including Compsognathus, which promised to throw light on the early forms of birds.
During my investigation of Archæopteryx, I observed several characters of importance not previously determined, and I have thought it might be appropriate to present them here. The more important of these characters are as follows:
1. The presence of true teeth, in position, in the skull.
2. Vertebræ biconcave.
3. A well-ossified, broad sternum.
4. Three digits only in the manus, all with claws.
5. Pelvic bones separate.
6. The distal end of fibula in front of tibia.
7. Metatarsals separate, or imperfectly united.
These characters, taken in connection with the free metacarpals, and long tail, previously described, show clearly that we have in Archæopteryx a most remarkable form, which, if a bird, as I believe, is certainly the most reptilian of birds.
If now we examine these various characters in detail, their importance will be apparent.
The teeth actually in position in the skull appear to be in the pre-maxillary, as they are below or in front of the nasal aperture. The form of the teeth, both crown and root, is very similar to the teeth of Hesperornis. The fact that some teeth are scattered about near the jaw would suggest that they were implanted in a groove. No teeth are known from the lower jaw, but they were probably present.
The presacral vertebræ are all, or nearly all, biconcave, resembling those of Ichthyornis in general form, but without the large lateral foramina. There appear to be twenty-one presacral vertebræ, and the same, or nearly the same, number of caudals. The sacral vertebræ are fewer in number than in any known bird, those united together not exceeding five, and probably less.
The scapular arch strongly resembles that of modern birds. The articulation of the scapula and coracoid, and the latter with the sternum is characteristic; and the furculum is distinctly avian. The sternum is a single broad plate, well ossified. It probably supported a keel, but this is not exposed in the known specimens.
In the wing itself the main interest centers in the manus and its free metacarpals. In form and position these three bones are just what may be seen in some young birds of to-day. This is an important point, as it has been claimed that the hand of Archæopteryx is not at all avian, but reptilian. The bones of the reptile are indeed there, but they have already received the stamp of the bird.