Paleontology Zorritos Formation 27 



far available, and can not be proven through mere dissimil- 

 arity of faunas in regions which might have offered differ- 

 ent habitats for any one of a number of reasons involving 

 the disposition of coastal land and the distributions of ocean 

 currents, or which might have been faunally isolated from 

 one another for similar reasons. 



There is evidence, on the other hand, which is difficult of 

 explanation if a sea-barrier separated two continental masses 

 according to von Ihering. The upper Cretaceous flora of 

 Argentina, according to Kurtz ^' is derived from that of 

 North America. It could hardly have passed the sea-barrier. 

 The Miocene flora of the Xavidad beds, Chile shows close 

 affinity to floras of similar age found in Ecuador and Peru, 

 and extremely close relatives of the Xavidad plants are 

 living today in the upper Amazon country, in Peru and 

 Bolivia, according to Berry.^® These facts do not support 

 but contradict the theory of a central seaway. 



The remaining part of this discussion will be concerned 

 with the age relations of the fauna. A survey of the table 

 of distribution and affinities, will show at once the relation- 

 ships of the separate species, and the discussion to follow 

 will embody merely the grouping of the evidence, with 

 remarks on pertinent points and without repetition of faunal 

 lists. 



The fauna as a whole, shows affinities so stronglv Bur- 

 digalian that much discussion is not necessary. The term 

 Burdigalien is used not to indicate that the age determin- 

 ation has been made through European comparisons, but 

 because the European units are more expressive of exact 

 age relationship, and are standard; the fauna is closest to 

 Panamanian-Antillean-Floridian assemblages of well-estab- 

 lished Burdigalien age. 



"Kurtz, F., Rev. Mus. La Plata, vol. 10, pp. 43-60, (1899) I902- 

 "Berry, E. W., personal communication; also Proc. U. S. 

 Nat. Mus., vol. 55, Xo. 2270. p. 283, 1919. 



