Fig. 223.—Rhombus minimus, a small fossil Turbot from the Eocene Tertiary, Monte Bolca. order of the "Bony Fishes" (Teleosteans), so that in the main the forms of Fishes characterising the Eocene are similar to those which predominate in existing seas. In addition to the above, a few Ganoids and a large number of Placoids are known to occur in the Eocene rocks. Amongst the latter are found numerous teeth of true Sharks, such as Otodus (fig. 224) and Carcharodon. The pointed and serrated teeth of the latter sometimes attain a length of over half a foot, indicating that these predaceous fishes attained gigantic dimensions; and it is interesting to note that teeth, in external appearance very similar to those of the early Tertiary genus Carcharodon, have been dredged from great depths during the recent expedition of the Challenger. There also occur not uncommonly the flattened teeth of Rays (fig. 225), consisting of flat bony pieces placed close together, and forming "a kind of mosaic pavement on both the upper and lower jaws" (Owen).
In the class of the Reptiles, the disappearance of the
Fig. 224.—Tooth of Otodus obliquus. Eocene.
Fig. 225.—Flattened dental plates of a Ray (Myliobatis Edwardsii). Eocene. characteristic Mesozoic types is as marked a phenomenon as the introduction of new forms. The Ichthyosaurs, the Plesiosaurs, the Pterosaurs, and the Mosasaurs of the Mesozoic, find no representatives in the Eocene Tertiary; and the same is true of the Deinosaurs, if we except a few remains from the doubtfully-situated "Lignitic formation" of the United States, On the other hand, all the modern orders of Reptiles are known to have existed during the Eocene period. The Chelonians are represented by true marine Turtles, by "Terrapins" (Emydidœ), and by "Soft Tortoises" (Trionycidœ). The order of the Snakes and Serpents (Ophidia) makes its appearance here, for the first time under several forms—all of which, however, are referable to the non-venomous group of the "Constricting Serpents" (Boidœ). The oldest of these is the Palœophis toliapicus of the London Clay of Sheppey, first made known to science by the researches of Professor Owen. The nearly-allied Palœophis typhœus of the Eocene beds of Bracklesham appears to have been a Boa-constrictor-like Snake of about twenty feet in length. Similar Python-like Snakes (Palœophis, Dinophis, &c.) have been described from the Eocene deposits of the United States. True Lizards (Lacertilians) are found in some abundance in the Eocene deposits,—some being small terrestrial forms, like the common European lizards of the present day; whilst others equal or exceed the living Monitors in size. Lastly, the modern order of the Crocodilia is largely represented in Eocene times, by species belonging to all the existing genera, together with others referable to extinct types. As pointed out by Owen, it is an interesting fact that in the Eocene rocks of the south-west of England, there occur fossil remains of all the three living types of Crocodilians—namely, the Gavials, the true Crocodiles, and the Alligators (fig. 226)—though at the
Fig. 226.—Upper jaw of Alligator. Eocene Tertiary, Isle of Wight. present day these forms are all geographically restricted in their range, and are never associated together.
Almost all the existing orders of Birds, if not all, are represented in the Eocene deposits by remains often very closely allied to existing types. Thus, amongst the Swimming Birds (Natatores) we find examples of forms allied to the living Pelicans and Mergansers; amongst the Waders (Grallatores) we have birds resembling the Ibis (the Numenius gypsorum of the Paris basin); amongst the Running Birds (Cursores) we meet with the great Gastornis Parisiensis, which equalled the African Ostrich in height, and the still more gigantic Dasornis Londinensis; remains of a Partridge represent the Scratching Birds (Rasores); the American Eocene has yielded the bones of one of the Climbing Birds (Scansores), apparently referable to the Woodpeckers; the Protornis Glarisiensis of the Eocene Schists of Glaris is the oldest known example of the Perching Birds (Insessores); and the Birds of Prey (Raptores) are represented by Vultures, Owls, and Hawks. The toothed Birds of the Upper Cretaceous are no longer known to exist; but Professor Owen has recently described from the London Clay the skull of a very remarkable Bird, in which there is, at any rate, an approximation to the structure of Ichthyornis and Hesperornis. The bird in question has been named the Odontopteryx totiapicus, its generic title being derived from the very remarkable characters of its jaws. In this singular form (fig. 227) the margins of both jaws are furnished with tooth-like denticulations, which differ from true teeth in being actually portions of the bony substance of
