The big-headed pantanal swamp turtle (Acanthochelys macrocephala, cágado) was scientifically described as recent as 1984 (Rhodin et al., 1984); On these pictures is a young hatchling with an exposed head. When they grow older the shell overlaps the neck giving the turtle's head more protection. Note the big left-folded neck, hence part of the name.

They live in swamps and saline lakes and feed mostly on insect larvae. One of their main predators are crab-eating foxes (Cerdocyon thous, lobinho), like shown in this post: link

Photo by Adrian Testa