My primary academic interest is the comparative anatomy, evolution, and development of the skeleton. In particular, I study the biology of the musculoskeletal system with a focus on the interactions between soft tissue structures such as ligament, tendon, and even neural tissue with bone. My past and current research focuses on the knee and the ways it has changed in the evolutionary shift from arboreal quadruped to biped. My ultimate goal is to gain a more thorough understanding of human evolution, with emphasis on elucidating the way in which bony tissues are shaped so that we may more accurately interpret the life histories of extinct taxa. Additionally, my research informs the way in which we collect data from skeletal and paleontological specimens by assessing the validity of these structures in interpreting locomotion. A common theme in my research has been to analyze not only anatomical structures in a comparative context, but to critically examine the ways in which biological anthropologists make inferences about fossil taxa.

deer gorilla
Gross anatomy of the ACL in Deer (A) and Gorilla (B) compared with microscopic anatomy of the ACL in deer (C) and gorilla (D).

Evolution of the Knee

My dissertation research is focused on the human knee in terms of its novelty, as well as its shared primate evolutionary past- and how both of these aspects leave it vulnerable to injury. I used quantitative polarized light microscopy to demonstrate that animals with a smaller range of motion have subdivisions of the ACL that are farther apart from one another than animals with a greater range of motion, yet are more uniform in collagen fiber orientation. These data inform a prominent debate in current orthopedic surgery- whether double-bundle ACL reconstruction is more appropriate than the standard single-bundle reconstruction- as well the anthropological literature on the evolution of the human knee.

I also explore the proximate structures of the ACL, such as the lateral meniscus. Humans have a unique lateral meniscus in that ours has two attachment points to the tibia- one anterior, and one posterior. It is common for paleoanthropologists to describe traits unique to humans as adaptations to bipedality, and the posterior meniscotibial ligament is no exception. However, I examined the possibility that this trait is a consequence of the geometry of our knee and found that humans and orangutans have each independently evolved similar but unique morphologies in the lateral meniscus, despite their widely divergent locomotion patterns. I argue that this supports a developmental hypothesis in which the shape of the menisci is a consequence of the pattern formation of the condyles, and reassess the fossil evidence of its presence in several australopithecine fossils.

Figure3 Two groups of rodents
Skulls of (top, left to right) dipodid rodents Napaeozapus insignus and Jaculus jaculus, and (bottom, left to right) heteromyid rodents Chaetodipus hispidus, Dipodomys spectabilis, and Microdipodops pallidus in norma basalis (Not to scale; the distances between basion and prosthion have been made equal). Note the grossly inflated auditory bullae in the three bipeds (J. jaculus, D. spectabilis, and M. pallidus) vs. those in the two quadrupeds (N. insignus and C. hispidus ). Taxa in both dipodid and heteromyid rodents share adaptations for desert living, including large auditory bullae and bipedal, saltatory locomotion. The immediate proximity of the bullae to the FM obviously influences both its position and orientation.

Foramen Magnum Position

In addition to my work on the postcranium, I also conduct research using cranial morphometrics as they relate to brain size and other factors. A traditional hypothesis in physical anthropology posits that the foramen magnum is located more anteriorly in humans as an adaptation to bipedality- i.e., in order to balance the head atop a bipedal spine. My research tested this hypothesis against the hypothesis that foramen magnum position is the result of developmental interactions between the brain and cranium. I tested this hypothesis first in bats, which do not vary with regard to locomotion, but do vary with regard to brain size. I was able to use relatively simple linear morphometrics to demonstrate that neocortex size is a determining factor in foramen magnum position in bats. I expanded this research to primates, rodents, and marsupials, and expanded my hypotheses to include masticatory size and the size of the auditory bullae. My paper on the position of the foramen magnum in rodents, marsupials, and primates is in the May 2016 volume the Journal of Human Evolution.