NOVEMBBB 1, 1892.] 



KNOWLEDGE. 



213 



during a visit to the museum at Oxford, was shown two 

 minute jaws, carrying a nuraber of eusped teeth, which 

 had been obtained in the neighbouring quarries of Stones- 

 field, from the rock known as the Stonesfield slate, be- 

 longing to the lower part of the great Jurassic, or oohtic, 

 system. After careful examination, the French anatomist 

 pronounced eonfidentlj- that these two tiny little jaws, 

 neither of which exceeded au inch in length, were those of 

 mammals, and he further suggested that they would prove 

 to belong to a species of opossum. Although this opinion 

 was given ip the year 1818, it does not appear that it was 

 published till the year 1825, when the second edition of 

 the fifth volume of the immortal " Ossements Fosiles " 

 saw the light. In publishing this epoch-making notice of 

 the occurrence of mammals in the secondary period, 

 Cnvier, with the usual caution of naturalists, was careful 

 to add the proviso that everything depended on whether 

 the specimens he saw had really been obtained from the 

 Stonesfield slate. Unfortunately, there does not appear 

 to be any record stating by whom, or at what date, these 

 original specimens — now forming some of the most valued 

 treasures of the Oxford Museum — were obtained from the 

 Stonesfield slate ; but that they did come from that forma- 

 tion is perfectly certain. Indeed, other specimens have 

 been subsequently obtained from the same beds, showing 

 certain characteristic Stonesfield shells embedded in the 



fragments of 

 rock in which 

 the mammalian 

 jawa are con- 

 tained. Here 

 we may men- 

 tion that the 

 Stonesfield 

 slate is the 

 equivalent of 

 the lower portion of the great, or Bath, oolite — a deposit 

 which is separated from the underlying lias by the beds 

 known as the inferior oolite. Consequently, the mammal- 

 yielding beds are separated from the rocks of the tertiary 

 period, not only by the immense series of cretaceous deposits 

 (chalk, gault, greensands, and wealden), but Ukewise by a 

 large thickness of those belonging to the Jurassic system, 

 such as the Purbeck and Portland oolites, the Kimeridge 

 clay, the coral rag, and the Oxford clay. 



Needless to say, no sooner was the existence of mammals 

 in the Stonesfield slate announced than it was received 

 with a howl of incredulity. First of all it was attempted 

 to show that the specimens themselves did not come from 

 Stonesfield ; and no sooner was this objection knocked on 

 the head than doubts were raised as to the Jurassic age of 

 the Stonesfield slate itself. These, however, were equally 

 soon disposed of, and the only thing then remaining was 

 to dispute the mammalian nature of the fossils. This task 

 was undertaken by the French naturalist, De Blainville, 

 who attempted to show that the mammalian character of 

 the specimens was not proved by the double roots of their 

 molar teeth. In the course of the argument, great stress 

 was laid on the chcumstauce that two-rooted molars were 

 found in a gigantic animal from the eocene of the United 

 States, then known as BasiluMunis, and regarded as a 

 reptile. De Blain\'ille was, however, here treading on very 

 dangerous ground, for it subsequently turned out that 

 Basihsauius itself was really a mammal, which is now 

 generally placed among the whales, under the name of 

 Zeutjlodon. The correctness of Cuvier's original determi- 

 nation was thus in the end triumphantly sustained, and the 

 existence of Jurassic mammals became henceforth an 

 estabhshed fact in geology, although the suggestion that 



Fig. 1. — One half of the lower ja«" of .i 

 Stouesfield Mammal; twice uatui-al size. The 

 restoration of the front teeth is conjectural. 



these fossils belonged to opossums was, of course, 

 imfounded. 



Passing on to the consideration of the specimens them- 

 selves, we find that the great pecuUarity of the jaws of 

 these Stonesfield mamnils(for one of which D^ Blainville 

 proposed the name of amphithere) is the excessive number 

 of their cheek-teeth, a feature now paralleled (as we have 

 mentioned in an earlier article on " Pouched Mammals '') 

 only in the little banded ant-eater of AustraUa. This 

 multiplicity of teeth is well shown in the jaw represented 

 in Fig. 1, which is preserved in the museum at York, 

 and shows upwards of nine cheek-teeth still remaining, 

 whereas in practically all existing mammals with complex 

 teeth, except the banded ant-eater, the number does not 

 exceed seven. Other jaws were, however, subsequently 

 discovered in Stonesfield, in which the number of 

 cheek-teeth was considerably less; but one of these 

 later specimens (described as the phascolothere), revealed 

 the important fact that there were four pairs of front or 

 incisor teeth in the lower jaw. Now since (as stated in 

 the article cited) it is only among pouched mammals, or 

 marsupials, that more than three pairs of incisor teeth are 

 found, while the banded ant-eater, with its numerous cheek- 

 teeth, is a member of the same group, it became a very 

 natural conclusion that the Stonesfield mammals were 

 likewise marsupials. Support was lent to this conclusion 

 by the circumstance that, with the exception of the egg- 

 laving mammals, or monotremes (to which a special 

 article in Knowledge has likewise been devoted), the 

 marsupials are the lowest of all living mammals. And in- 

 directly som3 further support to this view is afibrded by 

 the fact that Australia still retains other forms of 

 animal hfe alhed to those which were living in Europe 

 during the period of the Stonesfield slate. For instance, 

 it is in the Australian seas alone that there still survives 

 the solitary representative of the beautiful genus of bivalve 

 shells known as Trhjoiiid, which were so especially abundant 

 in the oolites ; while it is also there alone that swims 

 the Port Jackson shark, whose mouth is armed with a 

 pavement of crushing teeth, recalling those of many of its 

 Jurassic forerunners. Moreover, in the presence of 

 numerous cicads among its flora, Australia again recalls 

 the Jurassic epoch of Europe ; and it has accordingly been 

 suggested that modern Austraha might ba regarded as a 

 kind of direct survival from Jurassic times. Before, how- 

 ever, we can say anything more as to the affinities of 

 the Stonesfield mammals, we must turn our attention to 

 subsequent discoveries of mammalian remains in other 

 formations. 



The first of these discoveries was made in the year 1847, 

 by Professor PUeninger, of Stuttgart, who obtained certain 

 minute teeth from a bone-bed near that town belonging to 

 the upper part of the triassic period, which were declared 



Fig. 



-Lower jaw of an Aiueriuan Jura.-*sic Mammal ; twice 

 natural size. (After Marsh.) 



to be mammalian, and for the owner of which the name 

 Microlestes was proposed. Now, as the trias lies below the 

 lias, the existencj of mammaUau life was by this discovery 



