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29

Note that the Yucatan Peninsula was close to what is now the coast of Honduras (before they cleaved apart). The whole of Central America was previously attached to the north west corner of South America. Similarly the Caribbean Islands were also attached to South America on its northern coast.

 

Rifting, as indicated by the yellow arrows could have separated the landmasses from South America simultaneously. Central America may have retained a tenuous northern connection with North America.

 

The Cocos Ridge, which is now a small ridge on the Pacific side of Central America may have, at one time, reached right across the Caribbean in the way indicated.

 

Subsequently, North America was pushed southwards again, as the Arctic Ocean bed formed and a land link with South America was made through Central America.

 

By studying the mammals of South America we can come to understand which species are descendents of those which migrated down from North America (very recently, in geological terms), which ones are decendents of the ‘old timers’ from the Gondwanan connection with Africa and Oceania, and which ones have ‘evolved on’.

 

By comparing brain morphologies it is easy to identify the basal mammals which inhabited both Gondwanan fragments - some 50 million years ago. The web-site brainmuseum.org catalogues the brain morphologies of many species of mammal and is a useful resource in this analysis.

 

1) The Old-timers of Gondwanan South America/Africa

 

Anteaters, sloths and rodents from South America show a brain architecture in common with many African species and this suggests a common ancestry from Gondwanan times when South America was continuous with Africa.

 

2) The Old-timers of Gondwanan South America/Oceania

 

There are 93 species of opossum within the Order Didelphimorpha and other marsupials in the Orders Paucituberculata and Microbiotheria in South America which show biological similarity with the marsupials of Australia. This suggests that there was a land link between 3) The less recent newcomers.

 

The llamas and Alpacas are derived versions of camelids which entered South America through Central America during the last 2 million years.

 

4) Recent Newcomers to South America from North America

 

These are the:-

 

Mustelidae, weasels and otters

Canidae, Bush dog, Speothos species

Cervidae, deer, Mazarama species

Lagomorphae,  rabbits, pikas

Felidae, Jaguars, ocelot etc, Pantera spp

Tapiridae, tapirs

 

5) Recently evolved types

 

Surprisingly, what appear to be very advanced species - the New World monkeys have brain morphologies which are more in common with the basal prosimians such as the bushbaby, (Otelemur crassicaudatus) of Africa, than the Old World monkeys, despite their superficial similarity. This may suggest that only bushbaby like species were common to both Gondwanan fragments at the time of separation, and their evolution into monkeys took place independently in South America and Africa. The Old World monkeys

are much more advanced than the New World monkeys and there is no equivalent of the African apes, in the South America continent.

 

 

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