Prof. Owen on the Skull 0/ Thylacoleo carnifex. 131 



peculiarly modified shear-blade teeth in the mammalian class. Al- 

 though the tusks are incisors — not, as in placental carnivora, canines 

 — they possess, through the singular shortness of the facial part of 

 the skull in Thylacoleo, the same mechanical advantage, in their 

 proximity to the biting-power of the enormously developed temporal 

 muscles, as in Felis. In the lower jaw there is, anterior to the car- 

 nassial, either a socket for a small double-rooted premolar, or two 

 approximate sockets for as many single-rooted ones ; and, as in the 

 upper jaw, these cavities do not range in the same longitudinal line 

 with the carnassial, but extend obliquely inward and forward, from 

 the inner side of its fore part. There is no other alveolus in the 

 lower jaw between the premolar one and that of the large lower 

 tusk. The small 'tubercular' molar on the inner side of the hind 

 end of the upper carnassial, and the two ' tuberculars ' behind the 

 lower carnassial, are indicated by their sockets in the present speci- 

 men. The author sums up, from acquired data, the dental formula 

 of Thylacoleo as follows : — Incisors ~ x , Canines ^, Premolars ^ 



or ^—# Carnassials -^r, Tuberculars ~ 2 - Of the incisors, the fore- 

 most above are long and large tusks, like the pair below : of the 

 other teeth, the carnassials, of unusually large size, are functioned as 

 flesh-cutters, and the small tuberculars would serve for pounding 

 gristle or tendon, as in Felis : the premolars indicated by sockets, 

 and the small upper incisors, represent a remnant of the dental 

 family type under its extreme adaptive modifications in Thylacoleo. 



In the rest of the skull of the subject of the present Part, many 

 particulars are yielded in addition to those deduced from the frag- 

 mentary fossils which indicate the genus. They confirm the deduc- 

 tions of the marsupial nature of the large extinct Australian carnivore, 

 determine the alternative expressed in the author's first communica- 

 tion as to the homologies of the inferior tusks, and show that the 

 genus Thylacoleo ranges, not with the series now including Didel- 

 phys, Dasyurus, and Thylacynus, but with the Diprotodont group, 

 more eminently characteristic of the Australian continent, and which 

 is at present represented by, or reduced to, the genera Phascolarctos, 

 Phalangista with its subgenera, Macropus with its subgenera, and 

 Phascolomys. The carnassial of Thylacoleo, in its large propor- 

 tional size, absence of the tubercular part, and indications of subver- 

 tical groovings of the enamel, most closely resembles that tooth of 

 the more ancient marsupial carnivore Playiaulax, and is associated, 

 in the lower jaw, as in that genus, with two small posterior tuber- 

 culars, one or two small premolars, and one large incisive tusk, simi- 

 larly directed obliquely upward and forward. Few facts in mamma- 

 lian palaeontology are more interesting and suggestive than the 

 occurrence in our hemisphere, during secondary geological periods, of 

 Marsupial forms, which find their nearest representatives in existing 

 or tertiary extinct Marsupialia of the continent of our Antipodes. 



The present Part of the author's series of Papers on Extinct Aus- 

 tralian Mammals is illustrated with drawings of the entire skull of 

 the Thylacoleo carnifex. 



