For Immediate Release Contact: Greg Borzo (312) 665-7100 gborzo@fieldmuseum.org New dates for calibrating trees Many scientists use inferred dates of origin provided by paleontologists as temporal anchors for their work. In particular, molecular biologists have relied heavily on these derived dates when constructing a timescale for evolutionary trees of animals. Molecular biologists estimate the length of time along branches between related species on these trees by estimating the number of changes in DNA sequences. However, there is no known way of deriving a timescale from molecular data alone. In order to attach a timescale to a molecular tree, the standard practice has been to calibrate it using usually only one date derived from the fossil record. If the date of origin of a group derived from the fossil record is seriously underestimated, the same must be true for any molecular tree calibrated using that date. “We hope our research will help reconcile the discrepancies between the various dates suggested by paleontologists and molecular biologists, not just for primates but for other groups of organisms, too,” Dr. Martin says. Earliest common ancestor of all primates Existing primates can be divided into six subgroups: lemurs, lorises, tarsiers, New World monkeys, Old World monkeys, and apes and humans. Their 85-million-year-old earliest common ancestor probably looked like a primitive, small-brained version of today’s dwarf lemur, according to Dr. Martin, who has studied primate evolution from many different perspectives for the past 30 years. That animal would probably have been a nocturnal, tree-living creature weighing about 1-2 pounds, with grasping hands and feet, also used by the infant to cling to the mother’s fur. It probably had large forward-facing eyes for stereovision and a shortened snout (reflecting a reduction of the anterior dentition). It would have inhabited tropical/subtropical forests, feeding on a mixed diet composed mainly of fruit and insects. Like humans, it probably had a slow pace of breeding characterized by heavy investment in a relatively small number of offspring. The research to be published in Nature represents an unusual combination of mathematicians’ statistical expertise with biologists’ knowledge of primate evolution. In addition to Dr. Martin, the authors are Dr. Simon Tavaré and Dr. Oliver Will (University of Southern California in Los Angeles), Dr. Charles Marshall (Harvard University), and Dr. Christophe Soligo (Natural History Museum in London). Download Images To download a 200 dpi tif image directly to your computer, click on the thumbnail image(s) below. Caption information may be found under "file/file info" of the Adobe® Photoshop® file. Evolutionary Tree for Primates file size: 2.9 MB Earliest Common Ancestor file size: 2.9 MB Robert D. Martin, Ph.D Vice President of Academic Affairs at The Field Museum file size: 3.6 MB