Andrew Taylor wrote: 
 
  I don't understand how you can tell from Markgraf's rendering of words
in Latin what language his informant(s) spoke.
   
 
Well Portuguese is a form of vulgar Latin ... but in any case
his "jacana" is otherwise coincidentally identical in form to the
Portuguese rendering of the Tupi-Guarani word jaçanã, except
that the cedilha and nasal a were lost in unaccented Latin.   
 
If he had tried rendering it phonetically into Latin, jacana
wouldn't work (c in his time would have been pronounced like k - in
modern Anglicised Latin it can be like s) - maybe jasana/yasana? 
zasana? chasana? 
 
L. 
 
-- 
Lawrie Conole
28 Reid St
Northcote, Victoria 3070
Australia
0419 588 993
lconole[at]gmail.com
 
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