Extinct forms of life are often so very different to the creatures inhabiting the world of to-day, that naturalists find it a hard task to assign them their places in the animal kingdom. The classes, orders, and families under which living forms are grouped are often found inadequate for the purpose, so much so that new orders and new families require to be made for them; and then it is often quite impossible to determine the relations of these new groups to the old ones we are accustomed to. Dinosaurs offer a good example of this difficulty. Were they related to ancient crocodiles? No one can say for certain; but it is quite possible, and even probable. Again, did certain long-legged Dinosaurs eventually give rise by evolution to the running birds, ostriches, emeus, etc.? This, although supported by weighty authority, is a matter of speculation: we ought to be very careful in accepting such conclusions. It may perhaps be safer to look upon the ancestry of birds as one of those problems on which the oracle of science cannot at present declare itself.
Various attempts have been made to classify Dinosaurs, and arrange them in family groups; but, considering our imperfect knowledge, it will be wise to regard all such attempts as purely temporary and provisional, although in some ways convenient. Professor Marsh, of Yale College, U.S., whose wonderful discoveries in the far West have attracted universal attention, has grouped the Dinosaurs into five sub-orders. It will, however, be sufficient for our purpose if we follow certain English authorities who divide them into three groups--taking the names given by Professor Marsh, only running together some which he would separate.
We shall first consider the very interesting and huge forms included in his sub-order the Sauropoda, or lizard-footed Dinosaurs. Various parts of the skeletons, such as vertebræ, leg-bones, etc., of these cumbrous beasts have long been known in this country; but Professor Marsh was the first person to discover a complete skeleton.
We shall, therefore, now turn our attention to the bony framework of the huge Brontosaurus (Fig. 9), a vegetable-feeding lizard. But it will be necessary to completely lay aside all our previous notions taken from lizards of the present day, with their short legs and snake-like scaly bodies, before we can come to any fair conclusion with regard to this monstrous beast.