NO. 5 MAMMALS Ol' I'ANAMA (.()I,I>MAN 2^ 



autumii.'il appc.'iraiKC, relieved to some exleiil ahjiij^ llic horrlers of 

 slrcanis. It is in this dry forest that oik; notes the strange hahit, 

 |)OSsesscd hy various unrelated species, of prodiiciii)^ flowers and 



ripening friiils while the trees are in a leafless condition. 



I'AIJNAL RELATIONS 



The /ideological structure and history of Panama and Central 

 America in j.jcneral arc, as yet, very imperfectly known. The at- 

 tenuation of the isthmian reji^ion and the slight elevation of various 

 trans-isthmian passes, irrespective of other data, suj.(^est the proh- 

 ahle former isolation of the two {.greater Americas, Some of the 

 j)asses are less than 500 fe<'t above sea level, and a subsidence fjf 1,000 

 feet of the present continental mass would establish interocean con- 

 nections at various jjoints. licf^innin^ on the south some of these 

 are marked by j^aps in the mountains at the source of the Rio 

 Napijji, a tributary of the Rio Atrato, at the Sucubti, an affluent of the 

 Rio Chucunaquc, at the Canal Zone, and farth(;r north at Lake 

 Nicaragua and at the Isthmus of TehauntejK-c. Such a division 

 wouM leave a chain of islands, .several r/f the more southern of which 

 would be 3,(XK) to 4,ocx) f(rct hi^h, and it would isolate the lii}.,di 

 mountains of Costa Rica and Guatemala. 



Geolop[ical investigations, especially tho.se pursucfl in eonneelion 

 with Panama Canal construction, indicate that oceanic waters did in 

 fact extend across, at least at the Canal Zone, durinj.^ the C^Iij^^oeenc 

 period ; but the dale of land emerj^ence has not been very definitely 

 determinerl. The slif.,dit depth of the water to a submarine; escarp- 

 ment far out alonj.^ the coasts of Panama, anrl the present rapifl rate 

 of erosion, indicate that the Isthmus was formerly much broarler 

 than at present. The encroachment of \hr. sea is well shown alon^ 

 much of the northern coast line, where cli/Ts receive the full battering 

 effect of the waves swept in by the northerly trade winds. Southerly 

 winds are less dr>minant, but the southern coast is constantly sub- 

 jected to the erosive influence of tremendous tid(;s, 



Coiba Island atul the large islands of the Pearl Archipelago lie in 

 shallow water uprm the continental shelf and inay have fornied jjarts 

 of an ancient mairdanrl. The excessive rainfall and tendency of 

 isthmian rocks in general to flisintcgrate rapidly on exposure to the 

 elements also greatly accelerate the redneiif>n of the gcnerrd laiul 

 mass. 



The Miocene mammalian faunas of sf»uthem South America and 

 of North .America arc known to have been wid<'ly different, but a 



