Lemur revealed in signs Darwin oddly ignored (5)
I believe the answer is:
indri
'lemur' is the definition.
(indri is a kind of lemur)
'signs darwin oddly ignored' is the wordplay.
'oddly ignored' means one should take alternating letters (letters in odd-numbered positions are removed).
'signs'+'darwin'='signsdarwin'
The alternating letters of 'signsdarwin' are 'INDRI'.
'revealed in' acts as a link.
(Other definitions for indri that I've seen before include "Species of lemur" , "Animal" , "Large Madagascan lemur" , "Short-tailed lemur of Madagascar" , "Madagascan mammal" .)