232 PROCEEDINGS OF THE PALEONTOLOGICAL SOCIETY 



Tertiary and the Miocene of the United States of Colombia — a phase of the 

 Bowden fauna ; Mactra dariensis Dall, of the Gatun beds ; Turritella tristis 

 Brown and Pilsbry, of the Costa Rica Miocene, Tlie rest of this fauna con- 

 tains casts of forms which represent typical Bowden genera. The fauna, be- 

 yond doubt, is some phase of the Bowden or associated horizon, and straits 

 connecting the Atlantic and Pacific at this stage of the Tertiary is thus con- 

 clusively proven. 



Doctor Dall has compared the Bowden fauna to that of Bordeaux and the 

 Aquitanian. Guppy has also compared the fauna to the Dax Miocene and the 

 Bordeaux. The age of the Aquitanian has not yet been definitely settled. 

 De Lapparent places it as Lower Miocene and the Stampian and Tongrian in 

 the Oligocene. Most of the faunal comparisons made by Guppy indicate the 

 same stage, but the Antillean fauna may have developed by convergent evolu- 

 tion from an earlier somewhat cosmopolitan fauna of Upper Eocene age, or we 

 may be dealing with a case of parallel evolution. Most of the European forms 

 identified in the Antilles — the corals, for example — by early investigators have 

 been rejected by the investigators of today. Thus Vaughan rejects all Dun- 

 can's European species as occurring in the Antilles. It seems that an Atlantis 

 is quite unnecessary to account for the faunal relationship between the West 

 Indies and the Miocene of Europe. According to Hill, OrJritoides manteUi, a 

 characteristic Oligocene form, does not occur in the Bowden beds. Thus the 

 best evidence for Oligocene age has disappeared or is rendered doubtful. Hill 

 states the exact date of this fauna as follows : "In my opinion, it was during 

 late Miocene and Pliocene time, beginning with the Bowden epoch of the 

 Jamaican sequence. Doctor Dall holds that the age of the Bowden beds is 

 late Oligocene. It is my opinion that the stratigraphic relations of these beds 

 in Jamaica indicate a later age. Deferring to Dall's opinion, I have tentatively 

 accepted his conclusions, however, until more field-work can be done. Thus 

 diastrophism indicates a Miocene age for Bowden fauna, as shown above. The 

 lack of relationship between Miocene mammalian faunas of North and South 

 America indicates a wide-spread submergence at this time. The Oligocene of 

 the Pacific contains no forms common to the Bowden fauna. All investigators 

 have recognized a number of living species in this fauna — Gabb, 30 to 40 per 

 cent; Moore, 8 to 9 per cent; Guppy, 20 per cent; Brown and Pilsbry, about 5 

 per cent." 



The following is a summary of the conclusions reached : 



(1) No connections between Atlantic and Pacific oceans in the vicinity of 

 Central America occurred during Cretaceous time. 



(2) The Panama and Tehuantepec portals were closed during the Lower 

 Eocene, but were open during the Middle or Upper Eocene. 



(3) Straits existed during that portion of the Tertiary which is character- 

 istically represented by the Bowden horizon. 



(4) The Bowden fauna was probably evolved in part from a somewhat 

 cosmopolitan Middle or Upper Eocene fauna and in part from Miocene or Oligo- 

 cene faunas of provincial Pacific origin. 



(5) The diastrophic record, the relations of Miocene mammalia of North 

 and South America, the stage of evolution of the Bowden fauna in terms of 

 the Recent, and the presence of several living species indicate that the age of 

 the Bowden is i^robably Miocene and not Oligocene of some authors. 



