Last February, when presenting to the Zoological Society an account of the skin of a Ground-Sloth discovered in a cavern in Southern Patagonia, Dr. Moreno mentioned that further excavations were being made in the hope of finding other remains of the same animal. The task referred to was undertaken by Dr. Rudolph Hauthal, geologist of the La Plata Museum, who met with complete success.[40] He not only found another piece of skin, but also various broken bones of more than one individual of a large species of Ground-Sloth in a remarkably fresh state of preservation. Moreover, he discovered teeth of an extinct horse and portions of limb-bones of a large feline carnivore, in association with these remains; he likewise met with traces of fire, which clearly occurred in the same deposits as the so-called Neomylodon. All these remains were found beneath the dry earth on the floor of an enormous chamber which seemed to have been artificially enclosed by rude walls. In one spot they were scattered through a thick deposit of excrement of some gigantic herbivore, evidently the Ground-Sloth itself; in another spot they were associated with an extensive accumulation of cut hay. Dr. Hauthal and his colleagues, indeed, concluded that the cavern was an old corral in which the Ground-Sloths had been kept and fed by man.
As the result of these explorations, Dr. Moreno has now the gratification of exhibiting to the Society complete proof that the piece of skin described on the former occasion belongs to a genuine Pampean Ground-Sloth, not Mylodon itself, but a very closely related genus Grypotherium, of which skulls are already known from Pampean deposits in the Province of Buenos Aires.[41] The collection which we now have the privilege of examining distinctly supports his contention that the large quadruped in question belongs to an extinct fauna, though contemporary with man. The discovery is thus unique in the history of palæontology, on account of the remarkably fresh state of preservation of all the remains. Some of the new specimens exhibit no indication whatever of having been buried. Many of the bones retain their original whitish colour, apparently without any loss of gelatine; while both these and other bones, which have evidently been entombed in brownish dust, bear numerous remnants not only of the dried periosteum, but also of shrivelled muscles, ligaments, and cartilages. Very few of the bones are fossilised, in the ordinary sense of the term.
An admirable brief description of this collection has already been published (op. cit.) by Dr. Roth, who was the first to recognise the generic identity of Neomylodon with Grypotherium. Some of the specimens, however, are worthy of a more detailed examination; and Dr. Moreno has kindly entrusted them to me for study in connection with the collections in the British Museum and the Royal College of Surgeons. The following notes, supplementing Dr. Roth's original memoir, are the result of this further investigation.
1. Remains of Grypothrium listai.
Number of Individuals.
Among the fragmentary bones of the Ground-Sloth, it is easy to recognise evidence of three individuals, which do not differ much in size. There are three distinct examples of the occiput and fragments of the dentigerous portion of three mandibles. It is also noteworthy that the three malar bones preserved are all different in shape, while three corresponding fragments of the acromial process of the scapula differ in size. One portion of maxilla seems to represent a fourth individual, being probably too small for either of the skulls to which the occiputs belong. Finally, as Dr. Roth has pointed out, one shaft of a humerus, which appears to be the bone of an adult, belongs to a much smaller animal than is indicated by any other specimen in the collection.
Remains of three individuals are thus recognisable with certainty; two others can probably be distinguished; while some of the fragments may even belong to a sixth specimen. It must also be noted that other portions of jaws are said to have been discovered by E. Nordenskjöld.[42]
Skull and Mandible.
The largest portion of cranium (No. 1) is not stained in any way, and does not retain a trace of the material in which it was buried in any hollow or crevice. It does not appear to have been damaged during excavation, but exhibits fractures which were almost certainly made when the animal was freshly killed. The cranial roof near the occipital region is battered in four places, though the injuries do not affect the brain-case itself; while the right occipital condyle is partly removed by a sharp, clean cut. There can, indeed, be no doubt that the animal was killed and cut to pieces by man.
This skull is evidently that of an adult animal, all the sutures in the hinder region being closed. The inner wall of the temporal fossa is much flattened, without any irregular convexities, but marked with the characteristic reticulately-decussating, fine ridges of bone, and studded with adherent patches of muscle-fibre. The upper border of the fossa is a remarkably sharp edge, while the narrow flattened cranial roof is only marked by a faint longitudinal median furrow and by a diminutive tuft of fibre in a small median pit near the occipital edge.[43] The fractures exhibit the very large cancellated chambers surrounding the brain-case dorso-laterally; while a median longitudinal section shows both these cells and others in the basi-sphenoid. The basi-cranial axis is nearly straight, inclining a little upwards in front. The anterior condyloid foramina piercing the basi-occipital are remarkably large, as usual; the basi-sphenoid is very long and narrow, flattened mesially on its lower face, but with one slight median prominence near its hinder end; the pre-sphenoid forms a short acute rostrum, above which there are remains of the vomer. The hinder ends of the pterygoids are shown to be inflated with large cancellæ, but the sides of the base of the skull are somewhat obscured by the dried soft parts. The mastoid process of the periotic, with its articular facette for the stylohyal, seems to be rather smaller than in Mylodon. The tympanic bone is preserved on the right side, though wanting on the left. It is an irregular curved plate only slightly bullate, but forming a complete floor to the tympanic cavity. As usual in Edentata, it is not produced into an auditory meatus.