Others again inclined the balance of probability towards the artiodactyle.

Finally, it appears that this very recently extinct beast presents a highly generalized type of structure, uniting in one organic form both artiodactyle and perissodactyle characters, and that in a manner not similarly found in any other known creature living, or fossil.

At the same time the differentiation of artiodactyle and perissodactyle forms existed as long ago as in the period of the Eocene ungulata, and that in a marked degree, as has been before observed.
Again, no armadillo _now living_ presents nearly so remarkable a speciality of structure as was possessed by the _extinct_ glyptodon.

In that singular animal the spinal column had most of its joints fused together, forming a rigid cylindrical rod, a modification, as far as yet known, absolutely peculiar to it.
[Illustration: DENTITION OF THE SABRE-TOOTHED TIGER (MACHAIRODUS).] In a similar way the _extinct_ machairodus, or sabre-toothed tiger, is characterized by a more highly differentiated and specially carnivorous dentition than is shown by any predacious beast of the _present day_.

{111} The specialization is of this kind.