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In possessing true teeth, the Hesperornis differs from every existing bird, and from every bird yet discovered in the tertiary formations, the tooth-like serrations of the jaws in the Odontopteryx of the London clay being mere processes of the bony substance of the jaws, and not teeth in the proper sense of the word.
Before the discovery of Hesperornis, the definition of the class Aves based upon our knowledge of existing birds might have been extended to all birds; it might have been said that the absence of teeth was characteristic of the class of birds; but the discovery of an animal which, in every part of its skeleton, closely agrees with existing birds, and yet possesses teeth, shows that there were ancient birds, which, in respect of possessing teeth, approached reptiles more nearly than any existing bird does, and, to that extent, diminishes the hiatus between the two classes.
By his kindness, I am enabled to place before you a restoration of one of these extraordinary birds, every part of which can be thoroughly justified by the more or less complete skeletons, in a very perfect state of preservation, which he has discovered. But Hesperornis differs from all existing birds, and so far resembles reptiles, in one important particular it is provided with teeth.
By his kindness, I am enabled to place before you a restoration of one of these extraordinary birds, every part of which can be thoroughly justified by the more or less complete skeletons, in a very perfect state of preservation, which he has discovered. But Hesperornis differs from all existing birds, and so far resembles reptiles, in one important particular it is provided with teeth.
Apart from the few fragmentary remains from the English greensand, to which I have referred, the Mesozoic rocks, older than those in which Hesperornis and Ichthyornis have been discovered have afforded no certain evidence of birds, with the remarkable exception of the Solenhofen slates.
Before the discovery of Hesperornis, the definition of the class Aves based upon our knowledge of existing birds, might have been extended to all birds; it might have been said that the absence of teeth was characteristic of the class of birds; but the discovery of an animal which, in every part of its skeleton, closely agrees with existing birds, and yet possesses teeth, shows that there were ancient birds which, in respect of possessing teeth, approached reptiles more nearly than any existing bird does, and, to that extent, diminishes the hiatus between the two classes.
One of these lines the pelicans, cormorants, etc. seems to be a continuation of the Ichthyornis type of the Cretaceous, with the Odontopteryx as an Eocene offshoot; the divers, penguins, grebes, and petrels represent another ancient stock, which may be related to the Hesperornis group of the Cretaceous. Dr.
Side and upper views of half the lower jaw; and side and end views of a vertebra. Apart from the few fragmentary remains from the English greensand, to which I have referred, the Mesozoic rocks, older than those in which Hesperornis and Ichthyornis have been discovered, have afforded no certain evidence of birds, with the remarkable exception of the Solenhofen slates.
The absence of any keel on the breast-bone and some other osteological peculiarities, observed by Professor Marsh, however, suggest that Hesperornis may be a modification of a less specialised group of birds than that to which these existing aquatic birds belong.
Other fossil forms like Hesperornis and Ichthyornis, whose remains occur in the strata of a later date, fill in the gap between Archæopteryx and the birds at the present time, for among other things they possess teeth which indicate their origin from forms like Archæopteryx, while in other respects they are far nearer the birds of later epochs.
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