By Andy Pasternack
They say a good man is hard to find. Change that to "a good fossil hominid," and it's just about impossible to find one of those. It's not that there aren't plenty of human fossils in museums. But museum curators would have to have rocks in their heads to part with a rare and fragile fossil skull, even for scientific study. Thanks to computer graphics, however, researchers are learning reams about human origins without having to damage or alter valuable specimens.
A paleoanthropologist's work often requires figuring out how to glean maximum information about human origins from a minimum of fossil fragments. Among the questions scientists ponder are how our ancestors might have looked, how they got around (by climbing or walking), how they developed and matured, and what their environment was like. Increasingly, these researchers are using techniques such as computer tomography to acquire fossil data; three-dimensional computer graphics to analyze and visualize surfaces, volumes, and internal structures; and rapid prototyping technology to create specimens for further study and public exhibition.
Biologist Christoph Zollikofer and anthropologist Marcia Ponce de Leon, both at the University of Zurich, are among those using computer-aided paleoanthropology (CAP) to expand our understanding of human origins. In fact, one project brought them face to face with a 30,000- to 50,000-year-old Neanderthal. "Just 10 years ago, research into Nean derthals was considered marginal," says Zollikofer. "In the last five to seven years, there has arisen a lot of debate about them. Did they become extinct? Were they assimilated? It's a very big debate in Europe."
|To create a life-like physical sculpture of the so-called "Devil's Tower" Neanderthal child (below), artist Elisabeth Daynes used a 3D stereolithography model that was built from scans of 30,000- to 50,000-year-old fossil fragments. Comparing the skulls o|
Zollikofer and Ponce de Leon were asked to apply their computer-based techniques and take a new look at a rare set of skull fragments from a Neanderthal child. The Devil's Tower Child, as the fragments have been known, were discovered in 1926 by archaeologist Dorothy Guard in Gibraltar.
Using a CT scanner, the scientists made a full series of one-millimeter serial cross sections of all the fragments. Each pixel in a CT image conveys the object density at that location, allowing thresholding, or the defining of specific object regions. From the CT data, they were able to construct contours to create 3D surfaces. Then, running their own software, called Forces Reconstruction and Morphometry Interactive Toolkit (or FORMIT), on a Silicon Graphics Onyx II, they were able to fit the fragments together into a single skull. "The most exciting moment was when we put those parts together, and they just fit perfectly," Zollikofer says.
Next, the researchers created a stereolithographic replica using a 3D Systems SLA machine. They then morphed data collected from CT scans of modern human children to the Neanderthal skull and sent both the skull replica and the facial imagery to sculptor Elisabeth Daynes in France. "We didn't want to constrain her too much-we wanted to let her follow her own human intuition about how the child should look," Zollikofer says.
Daynes selected eye color, hair color, hair length, and other characteristics, and using the replica and imagery created a statue of a four-year-old that ended up having the facial maturity you'd expect in a six-year-old. This supports the theory that Neanderthals, and other pre-historic humans, developed more quickly than modern humans do, possibly as an adaptation to harsher ice age environments. Conversely, our slower development may have facilitated the development of culture and civilization. "That's completely hypothetical," says Zollikofer. "We don't really have a clue as to why we develop more slowly." The resulting statue is on exhibit in the National History Museum, London, England.
|To make a nearly complete reconstruction of a Neanderthal skull, University of Zurich researchers Christoph Zollikofer and Marcia Ponce de Leon assembled CG images of fragments of bone and teeth. They filled in missing regions by morphing or mirroring exi|
Out on a Limb
Did our earliest ancestors climb upright or hang suspended from branches? That's one of the questions asked about Proconsul Heseloni, a hominoid that roamed East Africa some 18 million years ago. Many scientists believe Proconsul represents the beginning of the line that ends with human beings. It lived at the exact evolutionary moment when monkeys and apes split into different families, and while Proconsul shares some features with modern apes, such as skull shape and the lack of a tail, it moved more like a monkey. That makes the creature interesting to study, says Dana L. Duren, an anthropologist at Wright State University School of Medicine in Dayton, Ohio.
Duren has been studying the long arm and leg bones of juvenile Proconsuls, using fossil remains found at the National Museums of Kenya. She has focused on the metaphyses, or bone ends. Forces or stresses on the growth plates are believed to affect the pattern of growth, and therefore the morphology of the bones adjacent to the growth plates. "The stresses across the growth plate tell you how it moved," Duren explains. In a human leg bone, the majority of pressure on the knee goes straight down. But a monkey in a tree never extends its knee all the way when it walks, so its bones exhibit different morphology and different stresses, she says.
|Zollikofer and Ponce de Leon developed a software toolkit called FORMIT to simplify the process of piecing together 3D surfaces of fossil fragments.|
Image courtesy Christoph Zollikofer and Marcia Ponce de Leon.
Using 3D graphics, she has been able to resolve the question of how Proconsul got around. First, she made molds of the bone ends with the kind of silicone putty dentists use to take molds of their patients' teeth. From these she made epoxy casts, which were then scanned using a Laser Design 3D scanner. Data from the scans were imported as XYZ coordinates into geographic information systems software, ESRI's ArcView, and its 3D Analyst extension. "ArcView was originally developed to reconstruct and analyze geographic landscapes. But it is ideal for the kinds of analyses I do because to the computer the surface of the metaphyses resembles mountain ranges," says Duren. "The units of measure are just a whole lot smaller."
Once a 3D rendering was created in ArcView, Duren calculated the surface and planimetric areas and other features of the bone ends. "It is virtually impossible to measure surface area without a 3D rendering of these surfaces, especially since some of them are so small," she says. By using both surface area and planimetric area, Duren was then able to compute a roughness index for the bone-end surfaces. When she compared the roughness of the bone end surfaces of Proconsul limbs to that of modern primates, it was clear that the species climbed and moved around on all fours.
|Anthropologist Dana Duren created 3D models of the bones of an early hominid and used geographic software to analyze their surfaces. Because the bone ends were rougher than those of upright-walking modern primates, she believes that the species walked on |
Duren is now using ArcView and 3D surfacing to compare humans with other primates and ancient australopithecenes to evaluate the same kind of bone stress patterns. During the last century, only a handful of bone end surfaces were analyzed. "With the GIS software, you can do a comprehensive analysis," she says. "This technique will open up this area of study."
Remains of long-gone modern humans are also undergoing more in-depth analyses, thanks to 3D graphics. Arthur Andersen-whose Virtual Surfaces computer-aided design shop in Downers Grove, Illinois, specializes in reverse engineering-has brought his skills to bear on behalf of museums that want to electronically reexamine their human specimens. One of these was a 2200-year-old mummy.
Just a few things were known about the mummy. His name was Padu-Hari. Possibly a priest, he died at about the age of 20, around 200 BC. He was found in Akmen, Egypt, from which his remains made their way to the Milwaukee Public Museum in the mid-nineteenth century. When the museum decided to add a high-tech touch to its mummy exhibit, it contracted with Mobil Scanning Laboratories to perform CT scans of the specimens, head to toe. The data for Padu-Hari's head was handed over to Andersen to see what he could do in the way of analyzing and visualizing the skull and face.
|Using Mimics software, consultant Arthur Andersen assigned opacity thresholds to various density values in a 3D model of the resin-impregnated head (far left) of Padu-Hari, thought to be an Egyptian priest living in 200 BC. He extracted a solid model of t|
Andersen brought the data into Mimics, a PC-based 3D modeling program from Materialise, which allowed him to edit the scan data. The image could be manipulated, and the brightness and contrast could be adjusted as needed. Mimics allowed him to set a threshold for a particular density of pixels, which would then come up as a solid model of the skull. Once the skull was established, he selected less dense material for the mummified skin. "I was working on it at night," he recalls. "I created a threshold and the skull popped right up. I changed the thresholding and up popped his face. I realized I was the first person in 2200 years to look at this guy."
Medical device and supply manufacturer Baxter Corp. loaned its resources to create a prototype of the skull. Baxter's process uses technology from Z Corp., which is different from stereolithography. Z Corp.'s plaster-like material is treated with a curing agent, and there are no internal supports in the prototype, as is the case with stereolithography. Thus, cavities such as the sinuses, which might otherwise have had supports intruding on the structure, are rendered intact.
The mummy skull replica had a few surprises of its own that hadn't shown up in the CT slices. Using Z Corp.'s rapid prototyping technology, Andersen created a physical model. From there, he was able to establish that the brain had been removed from the skull, a practice common to mummy pre paration. The model also re vealed the presence of bone chips in the occipital (back) region of the skull. He also discovered that some kind of liquid resin had been poured into the skull, where it dried and crusted.
|After building a complete 3D CG model of Padu-Hari's skull (left), Andersen used rapid prototyping systems to produce a realistic-looking physical model (right) for the Milwaukee Public Museum.|
Image courtesy Arthur Andersen.
The experience of using 3D modeling and rapid prototyping to reconstruct mum my remains left Andersen thinking of other ways the technology could benefit paleoanthropologists. For example, researchers could take 3D models of two skulls, compare the point clouds, and digitally see how they differ, he says. "If you're comparing Paleoindians and Euro peans or a Neander thal and Cro-Magnon, for example, it could really aid in paleontological studies."
That a CAD operator like Andersen is conjuring up paleoanthropological CG applications shows how this technology is transforming the study of human origins. It's also bringing nonscientists into the realm. Zollikofer, who spends most of his time in a multimedia lab, sees great promise in the teaming of CG experts and scientists. He hopes that, eventually, these cross-disciplinary partners will team up to compile 3D quantitative data on the hu man body. "Normal human variation of anatomy isn't documented in 3D graphics, and it needs to be for these kinds of studies," he says. "That's one of the big projects for the future."
Andy Pasternack is a freelance writer based in Richmond, California.
|MultiMedia Laboratory and Anthropological Institute