1905.] 



SINCLAIR— FAUNA OF SANTA CRUZ BEDS. 



THE MARSUPIAL FAUNA OF THE SANTA CRUZ BEDS. 



(Plates I and II.) 



BY WM. J. SINCLAIR. 



[Read April 13, fcpoj. ) 



The Patagonian marsupials of the Santa Cruz epoch are of pecu- 

 liar interest from the relationship which they bear to certain Aus- 

 tralian and Tasmanian forms. This relationship establishes the 

 reality of a former land connection between the Australian region 

 and South America, so plainly indicated by the distribution of the 

 Tertiary marine mollusks, fishes, land shells, decapod Crustacea and 

 plants. 1 



These marsupials are referable to three families, remnants of 

 which survive in widely separated parts of the world. The Thyla- 

 cynidas are represented by at least four genera in the Santa Cruz 

 fauna, where they occupy the place of the placental carnivora. The 

 Didelphyidae include the genus Microbioiherium and several other 

 imperfectly known forms, comparable in size to some of the smaller 

 South American opossums. The Santa Cruz diprotodonts belong 

 to a third family which may be called the Casnolestidae. A single 

 representative of this family, dznolestes, survives in Ecuador and 

 Colombia. 



The Thylacynid.e. 



This family is sharply separated from the Dasyuridse and all other 

 existing carnivorous marsupials by the absence of the metaconid in 

 the lower molars and by the great reduction of the outer cingulum 



'Ortmann, A. E., Reports of the Princeton University Expeditions to Pata- 

 gonia, iSqb-iSqq, Vol. IV, pp. 299-302, 1902. 



Ortmann, A. E., "The Geographical Distribution of Freshwater Decapods 

 and its Bearing upon Ancient Geography," Proc. Amer. Phil. Soc, Vol. XLI, 

 pp. 267-400, 1902. 



Pilsbry, H. A., "Distribution of Helices in Time and Space," Manual of 

 Conchotomy, Series 2, Vol. IX, pp. xxxviii et set/., 1894. 



Lydekker, R., "A Geographical History of Mammals." 



Hedley, C, " Considerations on the surviving refugees in Austral lands of 

 ancient Antarctic life," Proc. Roy. Soc. A r . S. Wales, August, 1895, p. 3, foot- 

 note 1. 



