BY R. BROOM. 73- 



Also in Burramys is lost the upper p^ which is retained in Thyln- 

 coleo. Still Burramys is probably very closely allied to the 

 small Phalanger from which TJbylacoleo is descended. 



As already shown, small mammals which are normally 

 herbivorous veiy frequently are partly insectivorous, and the 

 type of dentition in Burramys is not more typically herbivorous 

 than that in Macroscelides. Hence there is reason to suppose 

 that the Burramys-like ancestor of Thylacoleo not improbably 

 varied its herbivorous diet by the addition of insects; as we know 

 the living Phalangers most nearly allied to Burratnys do to a 

 considerable extent. Such a slight modification of the diet would 

 probably afford the starting point for the new line by which 

 Thylacoleo arose. From an animal occasionally partaking of 

 insects it is not difficult to derive one more or less habitually 

 insectivorous. In such a form, the following changes would pro- 

 bably be found. The anterior incisors would be strengthened 

 and become less procumbent. The large premolars would pro- 

 bably be but little altered, being as well suited for the new as 

 for the old function, while the molars would become markedly 

 cuspid. The jaw would be shortened and strengthened; and we 

 should have a condition not very dissimilar to that found in the 

 larger Shrews, where a diprotodont type of dentition becomes 

 specialised to an insectivorous life. From such a shrew-like form 

 it would not be difficult to derive a larger animal, which would, 

 like the diprotodont Hedgehog, be more or less carnivorous; and 

 in such a type, as the carnivorous habits became more developed, 

 the characteristic features of Thylacoleo would soon arise. The jaw 

 would become gradually more powerful, the temporal muscles 

 greatly enlarged, and the whole face broadened and shortened to 

 bring the piercing teeth nearer the pulling force. The gi^eat pre- 

 molar would become more powerful and more specialised for 

 cutting flesh, while the molars, being but little required, would 

 gradually become reduced. 



All that would thus be required to bridge over the gap between 

 the more or less herbivorous Burramyinoe and the carnivorous 



