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species Z. apicalis has the apex of the spines dilated and sculptured on the superior or external surface, indicating the presence of a row of osseous shields covered by epidermis only, extending along the middle dorsal line. In the Trias, two such types have been previously known; viz., the genus Typothorax Cope, from New Mexico, and Aëtosaurus Fraas from Würtemberg.

The discovery of the Permian form in question is important from various points of view. The discovery confirms again a hypothesis proposed by me, several years previously (NATURALIST, 1885, p. 247, Transac. Amer. Philos. Soc., 1892, p. 24). It presents us with what had been previously wanting, forms ancestral not only to the Triassic Reptilia above referred to, but also ancestral to the order of the Testudinata, which according to Quenstadt and Baur appears first in the Trias. The discovery also brings to light an interesting case of homoplassy, since we have two families in no way allied to each other, the one a Batrachian, and the other a reptile, presenting an identical character, and which is so closely similar in the two, that the carapaces cannot be well distinguished on an external view. Internally, however, the characters differ widely. In the case of the Reptilian family (Otocolida) the structure is what one finds in the Testudinata and Pseudosuchia (Typothorax); while in the Batrachian it is constructed by an expansion of characters already known in other Stegocephalia.

For the accompanying illustrations I am indebted to the American Philosophical Society.

PLATE XXI.

Otocalus testudineus Cope, From above x.66.

PLATE XXII.

Dissorhophus articulatus Cope, x.82; 1 above; 2 below; 3 anterior view.-E. D. COPE.

Ameghino on the Evolution of Mammalian Teeth.'-The discoveries of M. Ameghino in Argentina have put him in a position to throw a great deal of light on the evolution of the Mammalia. Several problems which are presented by general Mammalian dentition should be greatly elucidated by his material, and some of those suggested by the Toxodont and Edentate types are within his reach almost to the exclusion of other investigators. He has already made important con

1 See l'Evolution des Dents des Mammiferes par Florentino Ameghino. From the Bull. Acad de Ciencias de Cordoba, XIV, p. 381; Buenos Ayres, 1896.

tributions to the histories of both these orders, while other problems remain open.

In the paper of about 1060 pages now before us, M. Ameghino gives his views on the general subject. It seems that in his work Filogenia, published in 1884, he adopted the view of Gaudry of 1878, (previously barely suggested by others), that complex teeth of Mammalia are produced by the fusion of a number of originally distinct simple teeth; a view which has been supported by Kükenthal and Röse on embryologic grounds. It had been previously believed that additional cusps are the product of plications of the dental crowns of simple teeth, and in 1873 and later I had constructed on that basis a phylogenetic system of dentition. This, as is well-known, proceeds from the simple to the complex, without the element of fusion entering at any point. The series is, for the upper jaw; the haplodont, triconodont, tritubercular,' (sectorial) quadritubercular, quinque and sextubercular, and the various lophodont forms; for the lower jaw; haplodont, triconodont, tritubercular, tuberculosectorial, (sectorial), quadritubercular, and the various lophodonts. This succession corresponds with the time order both in North America and Europe, and it is to be supposed that it must, therefore, do so in other parts of the earth, wherever the Mammalia have developed a dentition beyond primitive types.

I have never attempted to bring into this system the Monotrematous Prototheria, and have maintained that they constitute a distinct phylum. My discovery that the dentition of the Permian Cotylosaurian family of the Pariotichida consists of simple teeth arranged in transverse series,* induced me to remark"" that the only question that could arise" as to the hypothesis of dental fusion "is with regard to the Multituberculata." A fusion of the teeth of the Pariotichidæ could produce molars like those of the Multituberculata; but there is no evidence that such a fusion has ever occurred.

Returning to the Eutherian Mammalia, we observe that Ameghino believes that the complex molars have preceded the simple ones in the order of time, and that the tritubercular molar is the result of a loss of a tubercle of the quadritubercular; the quadritubercular the result of

2 Rütimeyer used the term trigonodont for triangular molars, without specification of the number of tubercles. This word cannot take the place of tritubercular, since the evolution is a question of tubercles, and not of shape. Some tritubercular teeth are quadrangular (Periptychus) and vice versa.

3 See Amer. Journal of Morphology, 1889, p. 146.

'Proceeds. Amer. Philos. Society, 1895, 439--444.

5

6 Primary Factors of Organic Evolution, 1896, p. 334. AMER. NATURALIST, 1896, Plate VIIa, p. 801.

reduction of a still more complex molar. Most of the evidence for this conclusion is derived from the fact, as he believes, that the Mammalia of Eocene and possibly earlier age, which are found in Argentina generally, have quadritubercular molars. In accordance with this view Cetacea and Edentata with numerous teeth, present a primitive type of dentition which has survived.

The reply which can be made to this fundamental proposition as to time-order, is, that M. Ameghino has probably affixed too great an age to his earlier beds. This is the opinion of Lydekker, and such extinct types as occur in those beds which occur elsewhere confirm this conclusion. Thus the Patagonian, which Ameghino regards as an Eocene formation, containing the Pyrotherium, contains also the primitive monkeys Anthropops, and the cetaceous Prosqualodon, Argyrocetus and Diaphorocetus. Now Diaphorocetus and forms closely allied to Arygocetus and Prosqualodon are characteristic of the middle Miocene in North America and Europe. It is highly improbable that the quadrumanous genera discovered by Ameghino are of Eocene age, since nothing of the kind occurs in Eocene beds in the Northern Hemisphere, where more primitive and ancestral lemuroid families represent them. The presence of supposed Condylarthra (not yet described) however, gives an Eocene character, and if the forms described by Ameghino as Multituberculata are really such, this character would be difficult to deny. However, recently Ameghino has recognized that these forms do do not belong to that order, but are true Marsupialia, and Lydekker assert that they do not belong to the Patagonian formation, but to the overlying Santa Cruz beds. But supposing that the Patagonian formation is upper Eocene, it does not furnish the material for an elucidation of the dental characters of the primitive Mammalia. These are only partly displayed in the lower Eocene, for it is in the Postcretaceous (Puerco and Laramie) that the true ancestral relation of the tritubercular molar is fully seen. These formations may be represented by the lower or dinosaurian beds which lie below the Patagonian formation in Argentina, but no Mammalian remains have been found there thus far by Ameghino. The oldest Mammal is said to be the Pyrotherium of the Patagonian formation, but it has an aspect more modern than Eocene. It is suspected by Ameghino to be a proboscidian, but it has not yet been shown that it is not a marsupial.

Dr. A meghino misinterprets North American fossils in more than one instance. He cites the Amblypoda in evidence of the proposition that the tritubercular molar is the result of a reduction of the quadri

6 Geographical History of Mammals, 1896, 115. Ameghino makes the same statement in Enum. Synopt. Mamm. Foss. Eocene de Patagonie, 1894, p. 10.

tubercular. His series is Uintatherium, Coryphodon, Pantolambda ; the last the most completely tritubercular. The time order is, however, the reverse, viz.: Pantolambda (Puerco), Coryphodon (Wasatch, and Uintatherium (Bridger); the first the most unmodified tritubercular. In accordance with his general position Dr. Ameghino believes (p. 72) that the quadritubercular genus Procyon is of great antiquity and prior to tritubercular types. This, however, cannot be believed. It has descended from a primitive plantigrade tritubercular, canine type, as have their allies the bears. The same modification is seen in the Mustelide in the badgers; and all such are modern forms. He states (p. 26) that in Periptychus and Mioclænus, Phenacodus and Achæn odon, the teeth are quadritubercular. The first two genera have tritubercular molars with insignificant rudiments of others both before and behind the protocone (Periptychus) or behind only (Mioclænus), and they belong to the primitive Puerco period. The other two genera are quadritubercular, but belong to later beds, Phenacodus being Wasatch, and Achænodon, Bridger, neither of which formations has any genus in common with the Puerco (except Didymictis of Puerco and Wasatch ages).

Dr. Ameghino believes the Typotherian suborder of the Toxodontia to be related to the Quadrumana. The digits resemble decidedly those of that suborder, but one important difference is overlooked by him. He has pointed out the striking alternation of the two rows of carpal bones in the Typotheria, in which they agree with the Toxodontia proper, and with the Amblypoda. Now in primitive Quadrumana this alternation does not exist, but the bones of the two carpal rows, like those of the tarsus, are directly juxtaposed, or taxeopodous. This characterizes the Condylarthra, which furnish the exact foot characters of the lemuroids, or ancestral Quadrumana.

Finally as to Dr. Ameghinos' views of the origin of the Cetacea, he again inverts the order of succession. He does this by assuming that the Archæoceti are not related to the Cetacea proper, and cannot be ancestral to them. He does not regard the presence of two rooted molars in the foetal Balæna as significant in this direction. The opinion of zoologists and paleontologists has been different from this, and I have confirmed the general view in my recent researches on the extinct Balænidæ of the Eastern United States. I have shown that a decided sagittal crest like that of the Zeuglodontidæ exists in some of the Miocene whalebone whales. In my estimation the simple teeth of many Cetacea are the result of a process of dental degeneration. 'Proceeds. Amer. Philos. Soc., 1895, p. 139; 1896, p 141.

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