Dan Gebo has had a lifelong fascination with fossils -- ever since he took a high school biology class in South Carolina and read Louis Leakey's work on human evolution.
The Elgin anthropologist has spent nearly 20 years studying and identifying nearly 500 minuscule finger and toe bones as belonging to 45-million-year-old tiny primates from the mid-Eocene Period.
It's the largest collection of primate fossils -- many as tiny as a mustard seed -- ever assembled. Most of the phalanges are 1 to 2 millimeters in length; the smallest is 1.37 millimeters.
Protected in gelatin capsules, the entire collection is contained in small plastic boxes taking up one drawer in Gebo's office at Northern Illinois University in DeKalb.
"This is the biggest sample that has ever been put together," said Gebo, 62, a professor of anatomy and evolution at NIU, where he's worked the last 30 years. "We have way more than anybody else has ever had by hundreds of specimens. Most of them are the size of mice or smaller. They are the smallest fossil primates ever recorded. They are way tinier than any of the living primates recorded today."
These early primates lived in tree canopies and fed on fruit and insects in a tropical rain forest in what is now China, according to Gebo's study.
Gebo started visiting China and collecting fossils in the mid-1990s and discovered his first primate bones on a dig in 1998. He has been publishing articles on his research periodically, culminating in a groundbreaking study to be featured in the December issue of the Journal of Human Evolution.
Gebo's wife, Marian Dagosto, a professor of cell and molecular biology at Northwestern University's Feinberg School of Medicine, also is an author on the research paper.
The fossils Gebo identified were originally recovered from a quarry near the village of Shanghuang in the southern Jiangsu province of China, about 100 miles west of Shanghai. Shanghuang is well-known among paleontologists as a treasure trove for a variety of fossil specimens.
Gebo discovered bones from nine primate families -- some related to lemurs and other wet-nosed primates known as Strepsirhini and others related to dry-nosed primates or Haplorhini, to which monkeys, apes and humans belong.
"These are the two major groups of primates both living and fossils," Gebo said. "Most fossil sites don't have that kind of diversity ... this is the oldest evidence for them. This is the first record of some of these groups at 45 million years ago, and that includes our group. So the very first anthropoids -- monkeys, apes and humans -- come from this site."
There's documented evidence of the species' evolution as the site includes specimens from advanced anthropoids that look more like monkeys living today, as well as their earliest ancestors, Gebo said.
"Our ancestors were tiny mice-sized primates 45 million years ago," Gebo said.
Primate phalanges are distinctive with nails for grasping on both the hands and feet.
Gebo believes primitive primates' phalanges were developed for climbing trees, whereas their more evolved kin walked on the tops of branches rather than grasping the sides of tree trunks.
"The advanced anthropoid finger and toe bones look more like spears. They are much narrower than all the other fossil groups," Gebo said.
Another discovery is Gebo found grooming nails on many of the wet-nosed primate fossils, also found in living lemurs, which has evolutionary implications.
Gebo's collection of primate digits eventually will be returned to the Institute of Vertebrate Paleontology and Paleoanthropology, a division of the Chinese Academy of Sciences in Beijing, where other paleontologists can access and study the bones.
"It has been a long road to get here," said Gebo, relieved that the project that has consumed all of his research time for decades is finally complete.
His goal now is to find the common ancestor for all primates.
"The beginnings of primate evolution could be at least 60 million years old," Gebo said. "It looks like the answer is definitely in Asia."
Meanwhile, "there's always fossils to work on" at home, Gebo said of his next endeavor studying primate fossils found in Wyoming.