With high-speed DNA sequencing, scientists can look at slight genetic differences among humans, great apes and other primates to arrive at new estimates of when different ancestral groups split.
These findings provide invaluable insights into the evolutionary past, especially when the fossil record is sparse, as it is for the period when the ancestors of humans and great apes split from the Cercopithecoidea (or Old World monkey) lineage tens of millions of years ago.
DNA analysis has pegged this split some 35 million to 30 million years ago, but a new fossil specimen challenges that molecular data with rock-hard evidence.
The partial skull of an ancient primate, dubbed Saadanius hijazensis, seems to have trappings of both the Hominoidea and Cercopithecoidea lines. A group of researchers led by Iyad Zalmout of the Museum of Paleontology at the University of Michigan asserts that S. hijazensis is a catarrhine—a member of the common group before the two lineages split. The primate has been dated to the Oligocene between 29 million and 28 million years ago—indicating that the split between Old World monkeys and the ancestors of humans and great apes occurred more recently than genetic evidence has suggested.
The researchers used micro-computed tomography to scan the fossil fragments and compare the clues to other known ancestral great apes and Old World monkeys.
The skull belonged a male, weighing some 15 to 20 kilograms, with a "snout-like projection of the midface," and was found in a black-mangrove environment in what is now Saudi Arabia. The study was published online July 14 in Nature (Scientific American is part of Nature Publishing Group).
Although this ancient fragment cannot fill in all of the blanks in the human evolutionary tree, new primate species finds in this common, catarrhine line "are crucial for providing a method for recognizing basal hominoids," the authors concluded.
Image of cranium, found in 2009, courtesy of Iyad Zalmout/University of Michigan Museum of Paleontology