THE RIGHT INTERPRETATION OF THE CHEEKTEETH TUBERCLES OP TITANOMYS.

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1 XXIII. ANNALES MUSEI NATIONALIS HUNGARICI. 96. THE RIGHT INTERPRETATION OF THE CHEEKTEETH TUBERCLES OP TITANOMYS. By Dr. J. ÉHIK. (With 5 figures.) The lophodont character of the upper molars of Titanomys was established first by FORSYTH MAJOR, as well as the fact that these teeth present a much more bunodont appearance in an unworn condition. According to the same author it has five cheek-teeth in the upper jaw : three premolars and two molars, and two premolars and two or three molars in the mandibles. By a closer inspection of the third premolar on fig.., we see at first glance the tooth can be divided into three parts, separated by small grooves filled up with cement. Numbering these enamel-coated parts, which are folded over each other, and have a rather lamina like shape, we have lamina, the highest and centrally placed part (fig.. ), lamina, the anterior lingual and posterior portion of the tooth (fig.. ), lamina, its buccal portion (fig.. ). By examining these portions one by one, we shall find that lamina is the most remarkable and typical in all the upper cheek-teeth, conserving its characteristic salient angle in all of them, even in the posterior molar m, inspite of the fact, that the lamina of that tooth is in a reduced condition. It is remarkable, that, while the antero-external lobe in p does not reach the buccal border of the tooth, it does in the other cheek teeth. Its posterior lobe extends buceally and joins the buccal lobe of lamina. This lobe is missing on m, where it is represented by only a stunted remnant (seefig..). A F O R S Y T H M A J O R C. J. : On Fossil and Recent Lagomorpha. Trans. L i n. Soc, London, 899. (ser. ) vol. VII. p As above, p. 45. I have to remark that F O R S Y T H M A J O R begins the numbering of the premolars and molars from m\ while I apply the more generally adopted method of numbering backward, where p preceeds m. This characteristic salient angle of lamina on m can be seen very distinctly by holding i t obliquely (fig..). 4,

2 Lamina of p ' folded over lamina, separated from it by a groove filled up with cement. (Fig.. z.) The lamina on the anterior part of the tooth is low and thin, it is suddenly raised and widens on its lingual part into three cusps, then bends buceally and narrows until the border of the tooth is reached. The anterior part of the lamina on pfi (fig.. c) is well developed, and by extending to the level of the other portions of the tooth, constitutes a considerable part of the triturating surface. The process of transformation in this portion takes place in the following way: the lingual intermediate portion of lamina of p (fig.., &), extends transversely. Its internal portion shifts the denticle (fig.. p c), Fig.. Titanomys Fontannesi DEP. Left upper set of teeth. (0:.) On the trituration surface: cement=*dotted, dentin=hatches, enamel=left plain. protoloph with protocone; a hypoloph with hypocone; b -f- c paraloph (b paracone; c cingulum and parastyle); ectoloph ( a metacone; b mesostyle; c metastyle). forward so that the latter is compressed due to the stress exerted. In p 4 * it flattens transversely, increases, and coalesces with the anterior portions (fig.., c) extending buccaly. The inner enemal border of the lingual intermediate part of lamina pushes ahead a part of the cement by embracing it, until it becomes attached to the anterior marginal parts extend buccaly. The homology of these portions on p and p* is incontrovertible, for in p 4 even the spot of coalescence can be found on the triturating surface of the tooth in the form of a transversal fossa, which extends in the center in a triangular shape, and that triangular notch is filled up, with cement, a remnant of the cement separating originally laminae and. The lingual posterior portion of lamina retains almost its original shape. All these portions of lamina can be *

3 found under exactly similar conditions on m ; with the sole difference that a slight film of cement is deposited secondarily on the buccal, anterior portion of its surface. This secondary deposit of cement is missing on m, and the lingual posterior portion of the lamina is retained in the shape of a lobe ; besides that, an enamel peg can be found, slid down fairly deep on the back side of the tooth, as a degeneration of its further portions. Lamina on p is less a lamina than a minor folding of the toothcrust, considering that on laminae and the folding of the toothcrust has made only erect, lamina-like enamel cusps forming considerable enamel folds due to wear; on lamina there have grown only enamel tubercles three in number, placed in the shape of clover leaves (fig.. a, &, e). Only the third of these tubercles (a) was raised so high that it was exposed to wear, so that it may be considered as a true cusp. Two degrees of attrition can be discovered on the right and left p, while there is an independent, pear-like fold formed on the right one, the neck of the fold has coalesced with the enamel fold of lamina on the left one. Only two of the three enamel cusps can be found on p*, the two external ones (6, c) while the internal one (a) disappeared, or, more properly said, it has coalesced with the antero-exterior lobe of lamina, so that the latter extends to the buccal border of the tooth. The same formations can be found on m also. The buccal posterior tubercle is entirely missing on m, for the posterior part of the tooth has been reduced. We have next to consider the part played by the roots on the single teeth. We do not intend to give a detailed description of these roots ; the less so since a classical description of then has been given by FORSYTH MAJOR, SO that it will suffice to refer to his description. Every tooth has two small buccal roots, and one lingual with a persistent pulp. The specimen under investigation lacks p the alveolus is decaying, so that the number and arrangement of roots cannot be established with certainty. The anterior small root on p (fig.. A) serves as a support for lamina ; the posterior root (fig.. B) supports lamina ; the large root is below lamina. The two small roots on p* and m are below the two tubercles of lamina ; the large root supports the other parts. The posterior small root on m (fig.. B) having been originally It is only for simplicity's sake, that I use the denomination lamina. On Fossil and Recent Lagomorpha, p This part of the tooth is really rootles, but i t may be considered also as having a root (see F O R S Y T H M A J O R as quoted above); I call i t third root for simplicity's sake. FORSYTH MAJOR:

4 below lamina, is shifted below lamina l, the anterior small root (fig.. A) which originally was under lamina, remains on its original place, as on jp 4 and m ; the large root serves to support the other portions. As we have seen, the roots of the tooth change their place, due to their being adopted to the special trituration mechanism of the tooth. This shifting is independent of the development of the homologous portions of the crown. It takes places under a long concatantion of exterior mechanical influences in a manner which results in their being placed below parts which are the most exposed to pressure and wear during trituration ; so that in the case of the Titanomys the disposition of the roots of the tooth is entirely independent from the homologous parts of the crown. p* m Fig.. Anterior side view of buccal of Fig.. Posterior side view of buccalporportion p sin. A buccal anterior small tion of m sin. A buccal anterior small root ; 5 buccal posterior small root. 0 :. root ; B buccal posterior small root. 0 : The question arises, how could we apply the tritubercular theory of OSBORN to Titanomys. OSBORN treats the teeth of the Duplicidentata on the base of the Titanomys Fontannesi. 5 His exposition, though it seems to be convincing, is based on an error, which consists mainly in the denomination of the cusps.. What he calls the metacone is the cement substance (fig.. x) The degree of shifting is not so considerable as to be remarkable at first glance, but it is distinctly visible in side view, that it cannot support any other portion but lamina. Of course, it is not only this degenerate small root which supports lamina. OSBORN (Evolution of mammalian molar teeth, p. 50) says the following: we have here a tooth with three originally subequal roots disposed in a triangle, and a trigonal and probably tritubercular crown." This supposition proved to be inexact in this form on the base of facts as above. Evolution ot mammalian molar teeth, p and 4, illustration A.

5 to be found to the anterior of the buccal anterior tubercle of lamina on m (fig,. b), and in the best case the tubercle ( b) itself; it is difficult to establish from OSBORN 'S drawing, which one.. What he calls the protocone (on the drawing) without any doubt is the groove separating laminae and, or more properly said the cement (fig.. Z) filling it.. W hat he calls the paracone is the worn cusp of lamina. It is evident, that among the parts called cusps by him, there is only one real cusp, the other two being nothing else but grooves filled with cement. Nevertheless, considering the striking analogies found when analysing the teeth of the Titanomys, I cane to the conclusion that the trituber cular theory can be applied on the molars of the Titanomys. According to OSBORN'S opinion, every mammalian molar tooth had to pass through the triconodont state in its evolution, or more properly, the most compli cated mammalian molar tooth can be brought back to a triconodont predecessor. He is able to prove that however only with those groups, where the lower mandible has a chiefly vertical motion without any accessory movement. On the other hand, the application of that theory neets with serious obstacles in species where the movement of the mandibles changes, and becomes complicated with other movements. The hares move the mandible transversely, which is complicated by a slight longitudinal movement at the same time. It is very likely that with animals where the process of trituration consists in a transverse movement of the mandibles, the three main cusps of the triconodont type are not disposed longitudinally, but transversely. I consider p of Titanomys to be such a triconodont tooth placed transversely where, however, certain other accessory parts already make their appearance. The may be considered as representing a higher degree in evolution, where the main cusps are arranged as in the primitive triangle, but transverselly ; we see the same on the true molars as well. T s Considering the facts detailed above, I adopted the following The same observations were made b y GREGORY (The orders of Mammals. B u l l. A m. Mus. Nat. Hist. V o l. X X V I I p. 8) i n studying theeth of Paramijs, the most p r i m i t i v e rodent. He explains the atypical evolution of the teeth of said a n i m a l f r o m the transverse m o v i n g of the mandible. TULLBERG : System d. Nagethiere, p- 48. I have to emphasize however, that m y interpretation is based o n the postulate that the three m a i n cusps of the triconodont type are to be considered as disposed transversely, a n d n o t l o n g i t u d i n e l l y. The question, whether this supposition be admissible or more properly said whether it be w i l l tounded i n the actual state of o u r knowledge, could be decided only on the base of a more thorough knowledge and study of the milk-teeth.

6 terminology. (Fig. 4.) I consider the cusp of lamina a p r o t o c o n e and I call its worn enamel fold p r o t o l o p h. The highest cusp of lamina, the lingual intermediate part, is a p a r a c o n e in my opinion, the small cusp in front of it a p a r a s t y l e, and the one behind it a h y p o c o n e. I call the paracone, the parastyle, and the cingulum in front of it, p a r a l o p h. I call the depressed heel or talon connected with the hypocone h y p o l o p h ; the buccal extension of the hypoloph is the h y p o s t y l e. I consider the highest worn cusp of lamina m et ac one; the interior enamel tubercle a m e s o s t y l e, the exterior one a m e t a s t y l e ; the combination of the three last is the e c t o o p h. The description of the teeth will be modified on the base of the above terminology as follows: The ectoloph consists of three enamel tu bercles disposed in the shape of clover leaves, where only one, the metacone, extends high enough to form an enamel fold after having been worn ; the fold is ellipsoid, longitudinal ; it is iso lated on the right tooth, while it extends to the posterior lobe of the protoloph on the left. The mesostyle has the shape of a less developed meta style, in a well developed enamal tubercle. The protoloph is V shaped so that its point is inwards, its anterior lobe extends toward the exterior end of the mesostyle, and its posterior lobe, after having coalesced with the ectoloph, has a broad end Fig- 4. Terminology of tbe parts of p sin. toward the hypoloph. The hypoloph extends trans versely, having an extension towards the buccal border of the tooth the hypostyle. It widens inwards and coalesces, through a slight constric tion, with the paraloph. The highest part of the paraloph the paracone, extending in an egg-like shape after its narrowing, is connected for the while with the parastyle only by the continuity of the enamel coating. There is a cingulum of enamel between the parastyle and meso style, paying an important part in the building up of the other teeth. The highest parts of p is the salient angle of the protoloph, then the lingual side of the paracone, and finally the portion of the fold formed by the metacone, opposite to the narrowing part of it. By connecting the points mentioned, we get a roof edge" having the parts to its left sloping to the left, and those on its right sloping to the right. On the narroving between the para- and hypoloph, on the side of the tooth there is a vertical groove visible, filled with cement. The para- and hypoloph are separated from the protoloph by a cement deposit (fig.. x, z\ just as is the protoloph

7 from the ectoloph ; cement can be found also between the metacone, metastyle and hypostyle. As for the general appearance of the tooth, I have to remark furthermore, that the hypoloph is transversely concave. P is formed by lateral pressure from a tooth of the general type as p *) so that the whole tooth is modified correspondingly. The ectoloph slopes outward under the pressure, the mesostyle is placed on the exterior anterior portion, the metastyle is placed on the exterior posterior part. The fold of the metacone unites with the anterior lobe of the protoloph, so that this lobe seems to be extending to the exterior border of the tooth. The protoloph conserves its original shape, its anterior lobe is prolonged together with the metacone and its posterior lobe has a narrow extension into the hypoloph. The hypoloph narrows and the hypostyle extends forward; the narrowing between the proto- and hypoloph extends further forward, so that the hypocome becomes more strongly marked. The parts of the paraloph undergo a peculiar transformation due to strong increase and to side pressure. The paracone increases by pushing two lobelike extensions forwards, and folds around the cement deposit between the parastyle, cingulum and portoloph. The parastyle flattens by extending forward, and unites in a broad surface with the enlarged cingulum. The combination of the enlarged paracone, parastyle and cingulum constitutes the anterior triturating surface of the tooth. The place of coalescing is distinct between the enlarged paracone on one side, and the parastyle and cingulum on the other, in the form of a fossa, which extendes into a triangular notch near the center of the tooth, where cement is deposited. On the lingual side of the tooth, it is bicuspid, instead of being tricuspid, due to coalescing. The posterior cusp corresponds to the hypocone, and the anterior to the paracone and parastyle. The two cusps are separated by a vertical groove filled with cement on the side of the tooth. The cement deposit between the hypo- and protoloph unites in a broad surface with the cement between the ectoloph and protoloph, separating the paraand hypoloph from the protoloph on one hand, and surrounding the mesostyle on two interior sides, on the other. The cement deposit, wich is between the metacone, metastyle and hypostyle on p, gets between the V shaped lobes of the protoloph on p, and surrounds the metastyle on two interior sides. The roof edge" is the line connecting the narrow strip between the hypoloph and paraloph with the proto cone and the metacone. The paraloph and hypoloph are transversely concave. 4 4 l l Conditions in m are indentical with those in p, with the sole difference, that both the paraloph and hypoloph are narrower due to FOBSYTH MAJOR : On Fossil and Recent Lagomorpha. p. 44.

8 the increased lateral pressure. A secondary deposit of cement can be found on the buccal part of the paraloph, which is however very slight. m is degenerate; the posterior part of the tooth does not take part in the process of trituration, so it has degenerated through being super fluous. Among the parts of the ectoloph the metastyle is missing; the cement surrounding the metastyle is shifted on the posterior side of the tooth. The posterior part of the protoloph has but a very short lobe. The paraloph is retained intact, even if extented. The only remnant of the hypoloph, which serves a function, is the hypocone, and the cement substance separating the hypoloph from the protoloph extends freely over the exterior side of the tooth. On the posterior side of the tooth a small cingulum-like, enamelled belt is visible, which is really the remnant of the posterior part of the hypoloph. The roof edge" connects the metacone, the protocone and the hypocone, and while the portions sloping to the right and the left from the roof edge are developed almost uniformly in the case of the other teeth, here only remnants are left of the portion bending backward. To give a short summary of the facts mentioned, we may suppose, that. The main cusps of tooth of Titanomys (proto-, para- and metacone) are placed transversely, and not longitudonally.. Therefore we find yet the vestiges of the transitory form of the triconodont type upon it.. The parts of p and ^) can be considered homologous without any difficulty. 4. The structure of p* is entrielly identical with that of m. 5. The parts of m and m can be considered homologous just as well. 6. Taking into consideration the facts mentioned under, the relation of the main cusps on p m and m is like that in a normal tritubercular set of teeth. These description are correct only in case we accept the premolar analogy theory. In my opinion, there is no reason in this case to doubt its correctness. The principal objections of OSBORN are really nullified, if we have to consider the original triconodont state a distribution of different kind. The correctness of the theory of premolar analogy has been demonstrated by R. BROOM in Chrysochloris; ) that is on a species in which OSBORN considered its inadmissibility as beyond any doubt. The question arises, whether the theory of premolar analogy should be 4 l i l! ') Some observations on the dentition of Chrysochloris and on the tritubercular theory. (Annals Natal. Gov. Mus. Vol. I I. p Pl. II.) He says on p. the following: The premolars are practically identical in structure with the molars in both upper and lower jaws. Even the incisors and canines seem to foreshadow the cusp development of the molars and one is irresistibly driven to the conclusion that the main cusps are homologous throughout".

9 entirely rejected, like it is in OSBORN'S opinion, or whether it be valid in its entirety for all mammalian species? According to my conviction the theory is acceptable, but only in connection with species in which the premolars have the same function in trituration as the molars. Considering these, the structure of the molars can be studied very well on the base of the premolars in all cases, in which they have not been specialised for performing a different function. I see that this is the case in Titanomys. We come thereby to the conclusion, that the premolar analogy theory may stand beside the tritubercular theory without affe cting its main prin ciples, and it can be an excellent means by which to interpret cor rectly the cusps of the teeth. Finally, I wish to present some data from a palaeontological point Fig. 5. Titanomys Fontannesi DEP. Left and right upper jaw frag of view regarding ment. Upper Miocene, Felső-Tárkány, county Heves, Hungary. (4 :.) Titanomys fossils in my hands. I received from the outskirts of the community FelsőTárkány in the county of Heves, in Hungary, from the upper Miocene strata, several mammalian fossils for indentification. Mammalian fossils from the upper Miocene are rarely known in Hungary and there is only one locality where different mammalian fossils have been excavated in considerable numbers. Great was therefore my joy, when the fauna in question came to me for determination. I was able therefrom to determine the remnants of the Titanomys Fontannesi DEP., which meant an increase of one to the number of fossil species in Hungary, adding also to the extension of our biological knowledge. I determined a left and a right upper jaw fragment belonging probably to the same specimen as T. Fontannesi; I had besides two separate pieces of lower molars from the same animal. Budapest, Hungarian National Museum, the 8 t h of January, 94. GREGORY, who cannot be said to be one of the adhérants of premolar analogy, also considers this theory to be very adaptable in certain cases. (Cf. The orders of Mammals, p. 8.)

Fig. 12 Trigonias?osborni Lucas, SMNH PI637.2, left maxillary fragment with pi to MI; occlusal view, x I. DESCRIPTION

Fig. 12 Trigonias?osborni Lucas, SMNH PI637.2, left maxillary fragment with pi to MI; occlusal view, x I. DESCRIPTION SMNH P1637.1 has the teeth somewhat cracked but otherwise well preserved. p 2 is very