PROFESSOR OWEN ON THE FOSSIL MAMMALS OF AUSTRALIA. 



319 



may have existed in the upper jaw as much longer and larger than that below, as the 

 upper canine is in the extinct Machairodus. But sufficient is demonstrated in the above- 

 described fossils to make known the most anomalous dental system in carnivorous Mam- 

 malia, whether placental or marsupial. 



There is an interesting resemblance between the known dentition of the lower jaw of 

 Thylacoleo and that of the small extinct mammal from the Purbeck strata called Pla- 

 giaulax by Dr. Falconer * ; and the resemblance would be closer should the broken 

 tooth in the lower jaw of Thylacoleo here described prove to be the foremost one. 

 Certainly no other known mammal shows two posterior tubercular teeth so similar to 

 those in Plagiaulax minor, in their relative size to each other, to the trenchant tooth in 

 front and to the ramus of the jaw, as does the Thylacoleo. 



The anterior orifice of the dentary canal (Plate XI. fig. 3, o) appears, in the cast, to 

 have been in the fossa, on the outside of the jaw, between the socket of the sectorial 

 tooth and the one anterior to it. As much of the lower border of the jaw as is preserved 

 is straight. Not enough of the back part of the jaw remains to indicate the form or 

 direction of the angle. But the lower jaw oi Thylacoleo must have been singularly short 

 in proportion to its depth and breadth, and a like extreme shortness of the muzzle or 

 facial part of the skull may be inferred. 



With the above-described portions of the cranium of the Thylacoleo, I received from 

 my friend Dr. Hobson a portion of a sectorial tooth with one of the fangs. It was so 

 similar in the character of the crown to the great sectorial in place, that I had no doubt 

 about the genus to which it belonged, but only as to whether it was a smaller anterior 

 sectorial of the upper jaw, or the sectorial of the lower jaw. Mr. Stutchbury's speci- 

 men has settled that doubt. The tooth (Plate XI. figs. 4, 5 and 6) is the hinder half, 

 with the hinder fang of the left sectorial of the lower jaw. The characteristic markings 

 and undulations or grooves of the enamel, and the thickness of this substance where it 

 is exposed by the abrasion of the trenchant edge, are carefully shown in the figures. 



In existing carnivorous mammals the ferocity of the species is in the ratio of the 

 ' carnassiality' of the sectorial molar, i. e. of the predominance of the 'blade' over the 

 ' tubercle ;' and this ratio is shown more particularly in the upper sectorial, in which, as 

 the tubercular part enlarges, the species becomes more of a mixed feeder, and is less 

 devoted to the destruction of living prey. From the size and form of the carnassials of 

 Thylacoleo, especially of the upper one, we may infer that it was one of the fellest and 

 most destructive of predatory beasts. 



The metacarpal bone (Plate XIII. figs. 6, 7 and 8) is here figured, as it resembles in 

 its shape that of a large carnivorous animal, and may possibly belong to the Thylacoleo. 

 The figures preclude the necessity of verbal description. It is from a freshwater deposit 

 in Darling Downs, Australia. 



On the occasion of a visit to London, in 1848, by the able comparative anatomist and 

 palaeontologist M. Paul Gervais, at the period when the supposed marsupial character 



* Proceedings of the Geological Society, March, 1857. 



2 u 2 



