It is not every day that one goes out looking for dinosaur bones, but instead finds a fossil that may not be as glamorous, but is even more important to science than yet another dinosaur. University of Michigan paleontologist Iyad Zalmout found that out for himself last year, when he went exploring western Saudi Arabia for dinosaur fossils, but instead discovered what may be one of the last common ancestors of apes and Old World monkeys.
What Dr. Zalmout found was the partial skull of Saadanius hijazensis, a primitive primate that displayed all the shared characteristics of both Old World monkeys, such as baboons, macaques, and colubus monkeys, and apes, such as gibbons, orangutans, gorillas, chimpanzees, and, oh, yes, humans, but lacked the specialized distinguishing features of either group. This combination of traits is exactly what a common ancestor of both groups would have.
Note only does Saadanius hijazensis fill in a chapter in the fossil history leading to humans that scientists had long suspected to have existed but never had read before, it puts a date on that chapter with greater precision than scientists working from previously available evidence had been able to infer. Paleontologits working from fossil evidence speculated that the split between the apes and Old World monkeys could have occurred as recently as 23 million to 25 million years ago (National Science Foundation). On the other hand, analysis of DNA from living apes and monkeys indicted the same event happened as long ago as 30 million to 35 million years ago (Scientific American and Red Orbit). The preliminary age for Saadanius hijazensis of 28 million to 29 million years narrows down the timing of the divergence between apes and Old World monkeys to no earlier and not much later than 29 million years ago, splitting the difference between the two estimates.
In a press release from the National Science Foundation (NSF), University of Michigan anthropologist William Sanders said, “This new primate gives researchers a better idea of the time of the divergence of Old World monkeys and apes, and a better knowledge about what the ancestor of Old World monkeys and apes looked like. This discovery also helps identify difficult-to-recognize early apes, which had few features of modern apes.”
Zalmout, a postdoctoral fellow working with University of Michigan paleontologist Philip Gingerich, found the fossil in 2009 during a trip focused on finding fossil whales and dinosaurs. Working with the Saudi Geological Survey (SGS), he was exploring an area where geological maps indicated the rocks might contain fossils from the Cretaceous period (65 to 145 million years ago), a time when dinosaurs dominated the land. His first clue that the maps were wrong came when he saw a jawbone sticking out of the sediments and realized it was from a hippo-like animal that lived more recently—around 35 to 33 million years ago.
The next day, he explored a nearby area that seemed more likely to yield older fossils, but again the first thing he found was another fossil from a more recent hippo-like creature.
“I didn’t know whether to be disappointed or not, but I thought, well, maybe something interesting will pop up here, so I started looking around,” Zalmout said in a press release from the University of Michigan. “Within minutes, I found teeth sticking out of the ground, and when I realized what they were I was shocked. I had worked with Phil [Gingerich] on terrestrial mammals in the Bighorn Basin, and my first look at the size and shape of these teeth told me I had found a primitive primate.”
Zalmout e-mailed a photo to Gingerich, an expert on early primates as well as ancient whales.
In the same University of Michigan press release, Gingerich said, “I knew right away what it was, and I was thrilled.” As a student, Gingerich had worked with paleontologist Elwyn Simons, who studied Aegyptopithecus, a primitive member of the group that gave rise to both apes and Old World monkeys from the early Oligocene (30 million to 34 million years ago). “Here was something very much like it looking up at me,” Gingerich said.
In a press release from the NSF, Gingerich added that “the new primate was found while searching for geological strata that might yield fossil whales, which shows the importance of ongoing exploration in new areas.”
Significance of the Find
In addition to confirming the existence of an organism that scientists had long known had to exist and settling a dispute between fossil and genetic evidence over the age of the split between apes and Old World monkeys, Saadanius hijazensis helps resolve a dispute over what the early apes looked like. Working from fossils, paleontologist deduced that the ancestors of modern apes and Old World monkeys developed long faces, such as are seen in modern Old World monkeys. Zoologists working with living apes and monkeys thought that their ancestors had rounder faces to begin with and developed longer faces in the monkey line later. In Nature, Erik Seiffert, an anatomist at Stony Brook University in New York, said, “This evidence very clearly supports the palaeontological view,” that longer faces developed before the divergence of the two groups.
Richard Lane, program manager in NSF’s earth sciences division, explained in the NSF press release that the “discovery of Saadanius hijazensis is a side benefit of NSF supported research in non-hominid vertebrate paleontology. It emphasizes the need for strong field support in the historical geosciences.”
Nature published the discovery, description, and significance of Saadanius hijazensis this past Wednesday. In addition to Zalmout, Walker, and Gingerich, Laura M. MacLatchy, Gregg F. Gunnell, and Jeffrey A. Wilson from the University of Michigan and Yahya A. Al-Mufarreh, Mohammad A. Ali, Abdul-Azziz H. Nasser, Abdu M. Al-Masari, Salih A. Al-Sobhi, Ayman O. Nadhra, and Adel H. Matari of the Saudi Geological Survey were listed as authors. The National Science Foundation and the Saudi Geological Survey both sponsored the research.