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Creodonta

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'CREODONTA,Carnivora). In many respects the Lower Eocene creodonts come very close to the primitive ungulates, or Condylarthra (see Phenacodus), from which, however, they are distinguished by the approximation in the form of the skull to the carnivorous type, the more trenchant teeth (at least in most cases) and the more claw-like character of the terminal joints of the toes. The general character of the dentition in the more typical forms,such as Hyaenodon (see fig.), recalls that of the carnivorous marsupials, this being especially the case with the Patagonian species, which have been Dentition of Hyaenodon leptorhynchus, from the Lower Oligocene of France. The last upper molar is concealed by the penultimate tooth.

separated as a distinct group under the name of Sparassodonta. The skull, however, is not of the marsupial type, and in the European forms at any rate there is a complete replacement of the milk-molars by pre-molars, while the minute structure of the enamel of the teeth is of the carnivorous as distinct from the marsupial type. The head is large in proportion to the body, the lumbar region is unusually rigid, owing to the complexity of the articulations, and the tail and hind-limbs are relatively long and powerful. In life the tail probably passed almost imperceptibly into the body, as in the Tasmanian thylacine.

That the Creodonta are the ancestors of the modern Carnivora is now generally admitted. They are apparently the most generalized and primitive of all (placental?) mammals, and probably the direct descendants of the mammal-like anomodont or theromorphous reptiles of the Triassic epoch; the evolution from that group having perhaps taken place in Africa or in the lost area connecting that continent with India. The relationship of the creodonts to the carnivorous marsupials is not yet determined, but it seems scarcely probable that the remarkable resemblance existing between the teeth of the two groups can be solely due to parallelism; and it has been suggested by Dr L. Wortman that both creodonts and marsupials are descended from a common non-placental stock. In other words, the latter are a side-branch from the anomodont-creodont line of descent. Dr C. W. Andrews has pointed out that certain of the Egyptian creodonts appear to have been aquatic or subaquatic in their habits; and it is possible that from such types are derived the true seals, or Phocidae. With the exception of Australasia, and perhaps South Africa, creodonts (on the supposition that the Patagonian forms are rightly included) appear to have had a nearly world-wide distribution. In Europe and North America they date from the Lowest Eocene and lived till the early Oligocene, while in India they apparently survived till a much later epoch. Some of the Oligocene forms, alike as regards dentition, the union of the scaphoid and lunar of the carpus, and the complexity of the brain, approximated to modern Carnivora.

As regards classification Mr W. D. Matthew includes in the typical family Hyaenodontidae not only the widely spread genera Hyaenodon and Pterodon, but likewise Sinopa (Stypolophus), Cynohyaenodon and Proviverra; but Viverravus (Didymictis) and Vulpavus (Miacis) are assigned to a separate family (Viverravidae). It is these latter forms which come nearest to modern Carnivora, most of them being of Oligocene age. The American and European Oxyaena apparently represents a family by itself, as does the American Oxyclaena; and Palaeonictis and Patriofelis are assigned to yet another family; while the North American Lower Eocene and Eocene Arctocyon typifies a family characterized by the somewhat bear-like type of dentition. Mesonyx is also a very distinct type, from the North American Eocene and Oligocene. Some of the species of Patriofelis and Hyaenodon attained the size of a tiger, although with long civet-like skulls. In the earlier forms the claws often retained somewhat of a hooflike character.

The South American Borhyaenidae include Borhyaena, Prothylacinus, Amphiproviverra, and allied forms from the Santa Cruz beds of Patagonia, and have been referred to a distinct group, the Sparassodonta, mainly on account of the alleged replacement of some only of the milk-molars by premolars. By their first describer, Dr F. Ameghino, they were regarded as nearly related to the marsupials, to which group they were definitely referred in 1905 by Mr W. J. Sinclair, by whom they are considered near akin to Thylacinus, but this view seems to be disproved by the investigations of Mr C. S. Tomes into the structure of the dental enamel.

It should be added that Dr J. L. Wortman transfers Viverravus and its allies, together with Palaeonictis, to the true Carnivora, the latter genus being regarded as the ancestral type of the sabretoothed cats (see Machaerodus).

Authorities.-J. L. Wortman, "Eocene Mammalia in the Peabody Museum, pt. i. Carnivora," Amer. J. Sci. vols. xi.-xiv. (1901-1902); W. D. Matthew, "Additional Observations on the Creodonta," Bull. Amer. Illus. vol. xiv. p. i. (1901); C. W. Andrews, Descriptive Catalogue of the Tertiary Vertebrata of the Fayum, British Museum (1906); W. J. Sinclair, "The Marsupial Fauna of the Santa Cruz Beds," Proc. Amer. Phil. Soc. vol. xlix. p. 73 (1905).

(R. L.*)