Labelling pattern after eye injection in the LGN of Nycticebus
(slow loris), Pteropus (flying fox) and Macroderma (a carnivorous
microbat with the most highly-developed visual system known amongst the
17 living families of microbats).
Note that all LGNs have a convex outer surface next to the optic tract., including the prosimian primate Nycticebus. (The concave outer surface of the LGN is seen in "higher" primates but does not represent the condition found in all primates. The LGN of Pteropus is not so ventraly displaced as in the prosimian, but is otherwise similar, with an outer pair of magnocellular layers and a 2 inner pairs of layers with smaller cells like all other primates.
Macroderma has a primitive LGN, without differentitation of magno layers and without laminae. The strange "cookie cutter" appearance of the opposite eye's representation (we called this "lacunar differentiation") is unusual in mammals, but is seen in some edentates. The sister taxn of microbats (apart from the controversial link to the other kind of bat), is a mystery, so the hint from the LGN is worth noting, as preposterous as it seems. Is the microbat lineage to be found in an ancient South American lineage? This suggestion gains support from the high diversity of microbats in South America (more endemic genera than in the Paleotropics!) and the tooth of the Cretaceous South American Bondesius (Bonaparte) which looks just like an Archenycterid microbat.