li)10.] The " Sparassodonts." 207 



The Tasnianian Wolf {ThijJacynus) is represented in the Santa Cruz 

 formation of Patagonia by a series of genera Avhich were set apart as an 

 order, the "Sparassodonta" by Ameghino but which have been proven by 

 Sinclair (1904, pp. 333-408) to belong to the family Thylacinidfe. The 

 family shows a remarkable series of resemblances in general proportions and 

 dental characters to some of the Creodonts among Placentals. 



In Borhi/(i'7ia, the largest and most specialized genus, the incisors are 

 reduced to |, the upper molars have long metastyle blades and reduced 

 protocones. In the lower molars the metaconid is absent, the talonid is very 

 small, and the large compressed proto- and paraconids form a compressed 

 blade. The enamel departs from the normal Marsupial type with enamel 

 tubules entering the dentine and resembles the Carnivore type (Tomes, 

 1906). 



The zygomata arch widely and there is a high sagittal crest; the brain 

 case is narrow, especially back of the orbits, and the face is very broad and 

 heavy in top view. All these features are paralleled in the Mesonychid 

 and Oxyclaenid Creodonts (pp. 300-302). According to Ameghino and 

 Lydekker (1900) BorJu/a^na differs conspicuously from other Marsupials in 

 the replacement of the canine as well as of the ultimate premolar, while in 

 the related genera ProtJii/laci/nus and Amphiproviverra the canine, the ulti- 

 mate and the penultimate premolars are all replaced. According to Sinclair 

 this may mean merely that these Miocene Polyprotodonts had not advanced 

 so far as the modern forms in the suppression of the permanent, and reten- 

 tion of the milk, dentition. 



Among the true Marsupial characters retained by Borliijmia are the 

 following, recorded by Sinclair: the nasals spread posteriorly excluding the 

 maxillaries from contact with the frontals, the angle of the jaw is sharply 

 inflected, the atlantal intercentrum is not fused with the base of the neural 

 arch, the transverse processes of the seventh as well as of the second to sixth 

 cervicals are perforated by the vertebral artery, the ectocuneiform is displaced 

 beneath the cuboid as in Thylacipius. 



Amphiproviverra, the smallest and least specialized member of the 

 family retains a large opposable hallux. The cranial foramina and skull 

 structure are much as in Dasyurus. The peculiar family characters in the 

 dentition, namely the absence of the metaconid, the reduced metacone and 

 the vestigial external styloid cusps, are already established. The family 

 Thylacinidffi is thus seen to be a specialized cursorial ofFshoot either of very 

 primitive Dasyuridse or more directly from the Dideli)hiidfe. 



The Patagonian Thylacynes are further discussed below (pp. 302, 303). 



