Anthropologists in the Fayum (where else?) of Egypt have uncovered several interesting fossils that shed some light on the origins of anthropoids (old and new world monkies). Unlike previous finds, these fossils were found at a relatively new locality in the Fayum.
According to paper coauthor Elwyn Simons:
"...analyses of the teeth of the two species clearly place them as members of a group called parapithecoids, known as "stem" anthropoids because they constitute the species of early creatures from which the subsequent "crown" anthropoid line arose. "The finding of these parapithecoids from such an ancient time confirms that crown anthropoids -- a group including all modern anthropoids -- have their earliest known beginnings in Africa," said Simons. "They show that findings by other researchers of isolated examples of possible higher primate fossils in Asia do not constitute evidence of an ancestral crown anthropoid lineage there."
Leaving the cladistic terminology aside, what this means is that these fossils are on the main line of anthropoid evolution. One of the species, Biretia megalopsis, may have been nocturnal - also important for understanding anthropoid evolution. How do we know B. megalopsis was nocturnal and why is this important?
"...a tooth root from the species Biretia megalopsis is truncated, indicating that it had to make room for the larger eyesocket of a nocturnal animal."
"These finds seem to indicate that Biretia megalopsis must have had very large eyes, and so was likely nocturnal," said Seiffert. "This has never been documented in an early anthropoid. The simplest explanation is that Biretia's nocturnality represents an evolutionary reversal from a diurnal ancestor, but that conclusion is based solely on the probable pattern of relationships. If down the road we find out that our phylogeny was wrong, Biretia could end up being very significant for our understanding of the origin of anthropoid activity patterns."
In other words, being diurnal (active during the day) is the ancestral condition for anthropoids, apes and humans and B. megalopsis evolved away from that condition.