tarsiers: giant eyes 45 million years ago
A fossil discovered in China shows that giant eyes dominated the facial features of tarsiers as early as 45 million years ago. The nose region also corresponds to that of modern relatives - the appearance of the nocturnal animals has hardly changed over the course of the earth's history. The skull fragment discovered is of Tarsius eocaenus, a mid-Eocene dwarf species from which only five single molars were previously known.
The large eyes of the fossil tarsier and also of the recently described ape ancestor Biretia megalopsis provide new material for the discussion of whether the last common ancestor of prosimians and apes was also nocturnal. However, the researchers led by James Rossie from the University of Stony Brook conclude that the common ancestor was still diurnal and had no tapetum lucidum. This reflective layer behind the retina of many nocturnal animals reflects the incoming radiation, which stimulates the sensory cells again. In this way, the animals can orientate themselves in poor light conditions without having to enlarge their eyes.
The remains of the skull cannot, however, contribute to clarifying the exact relationships between apes and prosimians. However, a comparison with other prosimian fossils at least shows that the nocturnal lifestyle within this group must have evolved several times independently of one another in the Eocene - because some of the other fossil Tarsius species have hardly enlarged eye sockets.
