A lower jaw of a small Mammal was found in the Trias of North America by Emmons; and it has on one side three incisors, one long canine, then a diastema, three premolars, and seven molars with three points. It is therefore one of the Myrmecobius group.
After the age of the Trias, when there was much continuous land surface, Europe was broken up into a coral island tract, during the age of the collection of the Jurassic deposits. The islands were tenanted by many small Marsupials, four species of which have been discovered in the deposits of Stonesfield slate at the bottom of the Great Oolite. They belong to the extinct genera Amphitherium, Phascolotherium, and Stereognathus, and the first somewhat resembled the Myrmecobius of recent times; but all that can be said is that they belonged to Marsupial animals. Piled on the Stonesfield slates are many hundred feet of strata, and high up amongst them, in the Swanage and Purbeck districts, are deposits in which Messrs. Brodie and Beckles have found portions of the skeletons of numerous insectivorous Marsupials, of which the genera Spalacotherium, Plagiaulax, Triconodon, and Galestes are the most important. They were small, as a rule, and there has been much debate regarding their affinities with modern insectivorous forms, and they are still surrounded with doubt.
The appearance of the Mammalia without pouches took place in the Eocene age, and in the Old and New World, and contemporaneously with them lived in France a kind of Opossum, some of whose bones were found in the strata of Montmartre, near Paris; and in later Tertiary strata other relics have been found. These are the only instances of a fossil Didelphid occurring out of the New World; and there, where the Opossums are now characteristic animals, they were present in the last geological age, for in the Brazilian latest deposits remains of several species of Didelphys have been found. Remains of these fossil Opossums have been found in the North American Pliocene deposits. The more ancient deposits of Australia have not yielded the remains of any of the animals which are now so peculiar to the province, but in the bone caves of the Wellington Valley, some two hundred and ten miles west of Sydney, Sir Thomas Mitchell discovered a mass of bones, forming a breccia with limestone, which contained numerous and most interesting Marsupial remains. In deposits of the same late age, and in bogs and gravels in Queensland, other remains were found. They were described by Sir R. Owen in one of his greatest works, and they belong to the Australian families of Marsupials, and not to the American Didelphidæ. As was usual elsewhere before the appearance of man on the earth, and contemporaneously with him for awhile, many of the kinds which resemble more or less those now living, or would be classified in the same family, and perhaps in the same genus, are gigantic. Owen distinguished among the bones those of large fossil Marsupials which belong to the Macropodidæ, and which may be arranged as subdivisions of the genus Macropus or Kangaroos, and of a powerful creature called Thylacoleo, or Pouched Lion, which must be admitted as a new section of the Macropodidæ, and whose habits were probably carnivorous, although there is much diversity of opinion on the subject, some of the most distinguished anatomists believing the creature to have been of an innocent disposition, although appearances are much against it. It is more closely allied to Plagiaulax, of the English Purbeck beds, than to any other form, and they well fit in between the genera Macropus and Hypsiprymnus.
A huge Marsupial, with a skull three feet in length, with teeth, in front especially, on the Kangaroo plan, and with longer fore limbs and shorter hind ones than the last-named animal, was described by Owen. The pelvis, however, has but two sacral vertebræ, and its ilio-pubic process would ally it with the Macropodidæ. This Diprotodon was an herbivorous animal, and was of the size of a Rhinoceros. This great Marsupial had fore limbs which possessed the power of rotation, and it was not without some characters which are seen amongst the Wombats. It appears to have had a great range, for its remains have been found in the caverns in the Wellington Valley, at Welcome Springs, South Australia, Hergolt’s Springs, 500 miles north of Adelaide, near Melbourne, in the valley of the Condamine River, and widely over Queensland. A slightly smaller animal, called the Nototherium, also existed with the larger one.
The species of this genus have no lower incisive tusks, and a very short chin; the angle of the jaw is curved inwards, and there were only four molar teeth on each side in both jaws, and they were with two strong roots or fangs. It was probably one of the Macropodidæ. Others of this family are allied to Dendrolagus, and form the genera Protemnodon and Sthenurus. The Wombat was represented in the age of the great Marsupials; and both large and small species, one being of the size of the Tapir, have been described from bones and teeth which were found in the cave deposits of Australia. Remains of a Marsupial animal, probably of the Vulpine Phalanger, were found in the same caves, as were also some referable to the genus Perameles, or Bandicoots, and to the Potoroos. Several fossil species of the family Dasyuridæ have been found in the Australian caves, and one of them is referable to a section of the genus Dasyurus, which at present is restricted to Van Diemen’s Land, it being somewhat like Dasyurus ursinus; moreover, probably, there was a species of Thylacinus present also. So far as is known from the researches of Owen amongst this wonderful cave fauna, no members of the family Didelphidæ occur there. They were American then, as they are now.
CHAPTER IV.
SUB-ORDER—MONOTREMATA.[129]
THE PORCUPINE OR LONG-SPINED ECHIDNA AND DUCK-BILLED PLATYPUS.[130]
Why the Monotremata are formed into a Sub-order—The lowest of the Mammalian Class—[THE PORCUPINE OR LONG-SPINED ECHIDNA]—An Ant-eater, but not an Edentate—Its Correct Name—Description of the Animal—Habits and Disposition—Manner of Using the Tongue—Where it is Found—Anatomical Features: Skull, Brain, Marsupial Bones—The Young—Species of Van Diemen’s Land and New Guinea—[THE WATER-MOLE, OR DUCK-BILLED PLATYPUS]—The most Bird-like Mammal—Various Names—Description—Their Appearance and Movements in Water—Their Burrows—Habits of an Individual kept in Confinement—Used by Natives as Food—How they are Captured—The Young—A Family in Captivity—The Snout—Jaws—Teeth—Tongue—Fore and Hind Feet—Heel—Spur—The Shoulder Girdle—Breastbone—Concluding Remarks on the Sub-orders—Postscript on the Monotremes.