A new analysis of an old fossil yields evolutionary insights. By Nancy Yang.
It’s been said that fossils aren’t something we find; rather, they find us. Such was the case back in 2002, when workers at a construction site in the Catalan region of Spain came upon a long, sharp tooth that turned out to be a canine. A team of paleontologists on site returned the next day and excavated fossilized segments of a face. Over the following year, the scientists unearthed 83 bones and fragments that allowed them to piece together a partial skeleton of a male ape thought to be 11.9 million years old.
The discovery, Pierolapithecus catalaunicus, created a sensation. Important parts of the skull, rib cage, hands, feet and pelvis were well preserved, offering clues that could further our understanding of how apes and humans evolved. Until then, fossil evidence from this period had been sparse, and scientists were eager to recover evidence of ancestors that evolved after great and lesser apes diverged. Writing in the journal Science in 2004, a member of the Spanish team that found the specimen suggested that P. catalaunicus was either the last common ancestor or close to it.
Ashley Hammond, a Life Sciences Fellow in the MU Department of Pathology and Anatomical Sciences, supports that latter claim. “Pierolapithecus catalaunicus was a particularly important fossil ape,” she says. “We don’t think it was the last common ancestor of modern great apes. That’s a pretty big claim. But it was probably pretty close in time.”
Paleontologists are interested in the evolution of this group of primates because it ultimately helps answer the age-old questions of where we came from and why we’re here, Hammond says.
Hammond’s findings on the fossil specimen, “Middle Miocene Pierolapithecus provides a first glimpse into early hominid pelvic morphology,” was published in the Journal of Human Evolution in March 2013. In this study and other work, Hammond has used a laser scanner and advanced software to help scientists piece together portions of the evolutionary puzzle in ways that hadn’t been possible until recently. Technology, it seems, is changing many aspects of life — even the study of 12-million-year-old fossils.
“What I do, as well as other scientists like me, is look at fossil anatomy and compare it to things that are alive today,” says Hammond. “That gives us an idea of how they were built, what kinds of locomotion they were built for using.” She says she’s like a detective, piecing together fossil fragments to come up with a cohesive story about a specimen.
Hammond was the first scientist to examine fragments of the Pierolapithecus pelvis and compare its anatomy to other species. She scanned the fossil fragments and used modeling software to produce three-dimensional representations of what the original pelvis would have looked like. Her findings were consistent with some features of Pierolapithecus that the Spanish team were beginning to unravel.
“We were lucky that Ashley was visiting Barcelona to participate in our 2012 fieldwork season, an occasion that allowed her to inspect the original fossils,” writes Sergio Almécija, research instructor at the Department of Anatomical Sciences at Stony Brook University of Medicine, in an e-mail.
“Ashley had spent several years laser-scanning pelves of extant primates and that allowed her to compare the preserved portions of Pierolapithecus with homologous regions of extant taxa as well as the other well-preserved fossil pelvis of the early hominoid Proconsul.”
Modern great apes, or hominids, include orangutans, gorillas, chimpanzees, bonobos and humans. The great apes evolved from a line of primates that diverged from lesser apes, today’s gibbons and siamangs, about 16-18 million years ago. Orangutans were thought to have split off about 14 million years ago, followed by gorillas, chimps and humans. During the Miocene era, between 5 and 23 million years ago, apes lived in Europe as well as Africa and Asia, giving rise to a diverse group of primates.
Hammond says that paleontologists are interested in the evolution of this group of primates, because it ultimately helps answer the age-old question of where we came from and why we’re here. She and her colleagues place Pierolapithecus between the appearance of the orangutan lineage and the group of hominids that led to humans.
“The exact relationship of fossil apes is a matter of contentious debate among scientists,” says Hammond. “There are so many different fossil ape species out there, and so many different scientists have different interpretations. Pierolapithecus ended up being quite controversial because of some of the assertions by the Spanish team that found it. It had a number of different pieces of the face, the teeth, and the post crania — things that are below the neck — so they were able to make a number of inferences about quite a number of things.”
But time allowed better, more in-depth analyses. Examination by the Spanish researchers revealed that, like living species of great apes, Pierolapithecus was built for tree climbing. Its ribs, shoulder blades and lower spine would have allowed it to assume an upright posture useful for climbing. However, other aspects of its anatomy were quite primitive. It had monkey-like features such as a sloped face, and its short fingers and toes suggested it didn’t swing in trees like the great apes today.
These findings came as a surprise, says Hammond, because modern great apes prefer to swing by their forelimbs rather than walk on the ground with their hands. It’s a behavior that distinguishes them from other species like monkeys, which have tails and a more primitive skeletal structure. Pierolapithecus, which was probably a fruit eater and slightly smaller than today’s chimpanzees, was therefore quite primitive given where it appears on the ape family tree.
“We’ve always assumed that because all of the living species of apes swing around by their arms, that it must have been something they all inherited from a species long ago — that it came from a common ancestor,” she says. “It probably means that these swinging behaviors, which we thought had always been present in the great apes, are probably something that evolved more than once. It’s not something they all inherited.”
In an effort to build on this information, the Spanish scientists working on Pierolapithecus brought Hammond on board in 2012. They were interested in her use of digital technologies and her ability to create virtual anatomical structures from fossil fragments. They were also interested in her data on different anatomies of the pelvis, and how these vary according to locomotor behaviors. She had presented her work at conferences, and it appeared later in the American Journal of Physical Anthropology.
“This paper was attracting the interest of these researchers,” says Hammond. “They knew I was using some novel techniques to do things like estimate joint size by fitting spheres to the hip joint surface. So they asked me to have a look at their fossil and see if I could apply some of those methods to Pierolapithecus. The hip joint was too small and fragmentary to apply my methods, but we were able to come up with some other things on the pelvis that were really interesting and worthy of analysis.”
Hammond determined that the ilium of Pierolapithecus was slightly wider than that of Proconsul nyanzae, a more primitive ape that lived approximately 18 million years ago. She says that the wider pelvis might have allowed the ape greater lateral balance and stability while climbing.
“Her findings support previous findings on other anatomical regions of Pierolapithecus,” writes Almécija. “This new evidence suggests mosaic evolution of the skeleton in our family, and more importantly, that living great apes do not represent good models of what our ancestors would look like. Overall a really important message. These results would have not been possible without the use of 3-D models and the novel morphometric techniques used by Ashley.”
Hammond’s techniques and research have opened doors. This summer, she accepted a postdoctoral position as a research instructor at Stony Brook University. Getting this kind of job before graduating is quite an honor, she says. For her dissertation, she received funding from three prominent institutions: the National Science Foundation, the Leakey Foundation and the Wenner-Gren Foundation.
Hammond’s dissertation involves using digital technologies to explore range-of-motion, specifically in the hip joints of fossil primates. By gathering data from anesthetized zoo animals, she was able to test the accuracy of three-dimensional simulations that she created from museum specimens. When she compared the live-animal measurements to the simulations, the results were similar.
“That was a great validation of this modeling technique,” she says. “Because it worked in the live animals — the species of animals that we know the real range-of-motion for — I could then model range-of-motion in fossil primates.” The next step was to determine which aspects of a specimen’s anatomy related to range-of-motion and what allowed one animal to have a greater range-of-motion than another, she says. In quantifying these different morphologies, she has been able to begin piecing together what some fossil primates were capable of doing.
“Ashley’s dissertation is a very good example of how you can combine different kinds of data and test hypotheses,” says Michael Plavcan, professor of Anthropology at the University of Arkansas. “In the grand scheme of things, she’s doing a project that’s helping us understand how the post-cranial skeleton is adapted for different forms of locomotion. The technology here is allowing her to ask questions by looking at the anatomy in ways that were difficult to look at with traditional techniques.”
The new technologies don’t change the questions, says Plavcan, but they allow researchers to answer them in ways that they couldn’t before.
Hammond’s use of these technologies came about through a collaboration with Plavcan’s lab at the University of Arkansas. Plavcan has worked on a number of projects with Hammond’s advisor, Carol Ward, a professor of pathology and anatomical sciences at MU. Plavcan and Ward have received several grants together, which has allowed them to work with the Center for Advanced Spatial Technologies, an academic center at the University of Arkansas.
CAST owns the license for the three-dimensional modeling software, and its staff offers technical support as well. “That turns out to be very, very important, because the software and the technology can be difficult to use,” says Plavcan. “There’s a steep learning curve. When you have questions, you definitely need somebody to help you with these things.”
Hammond says that the technologies she and her colleagues use are not unlike medical imaging or the CAD software that architects, prototyping engineers and others use. She says that she would like to continue working with fossils in the future while discovering what new technologies will bring.
“I am at this really great intersection of paleontology, live animal research and anatomical research using these 3-D technologies,” she says.
Hammond’s enthusiasm for her work was evident last spring at the Missouri Life Sciences Week seminar. She was voted best speaker for a presentation entitled “Novel 3-D approaches to understanding the evolution of ape locomotion.”
“I’m proud of this,” she says. “It’s nice to be recognized at your own institution.” She praises Ward, whose lab has a number of projects using new technologies, and says that Ward had a lot to do with her coming to MU.
Among other projects, Hammond and Ward have worked with the Leakey family, a renowned family of paleontologists. In addition to field work, they’re currently working with the Leakeys on an academic paper about a fossil hominin pelvis. Hammond had worked with the Leakeys before: Back in 2009, she participated in field work in East Lake Turkana, Kenya, under the direction of Meave Leakey.
“I was learning from the best of the best,” she says. It was a really rugged environment. It was definitely a life-changing experience.”
Hammond recalls that, even as a child, she was fascinated with fossils and where they came from. This youthful fascination led to what she calls a “gateway experience,” taking anthropology classes for fun in college.
“I wasn’t sure that I would become an anthropologist or paleontologist, because probably it’s not the most sensible of careers, but I just loved it, so I pursued it,” she says. “I get to wake up in the morning and go to school, and I work really hard. But I love what I’m doing. I don’t mind putting in the 70 hours a week.”