Research

My research explores the constraints that influence the evolution of the vertebrate body plan. I believe convergent lineages, or lineages that have independently evolved to look the same, provide a natural experiment. Each lineage that evolves a similar body plan is a different trial and these trails can be examined for patterns. My studies focus on the evolution of the elongate, limbless body plan most well known in snakes that has evolved at least four times in amphibians, 20 times in teleost fish, and almost 40 times in lizards.

Shoulder Bones

In most tetrapods, the arms are supported by a complex of bones called the pectoral girdle (e.g. collar bones, shoulder blade, sternum), but these are often reduced in species with reduced or absent limbs. To learn more about how pectoral girdles are reduced during the evolution of limblessness, I used a genus of skinks, Lerista, which contains species that range from pentadactyl to completely limbless. I CT scanned specimens of Lerista and used geometric morphometrics to compare their pectoral girdles. I found that girdle shape was associated with degree of limb reduction to a certain extent, but found variation, especially among highly limb reduced specimens.

Neck-Trunk Boundary

I have also been using a wider variety of legless lizards to examine what happens to the boundary between the neck and the torso during the evolution of limblessness. I have been using CT data to compare the position along the body axis of a number of traits that occur at the neck-trunk boundary in limbed lizards.

Smell

Recently, I have been working on a project investigating smelling ability in legless lizards with an international group of volunteer mentees through the Society of Vertebrate Paleontology. Smells are processed in a part of the brain called the olfactory bulb and the bigger the olfactory bulb is, the better an animal is at smelling. When lizards evolve to lose their legs, they often evolve to have poor eyesight as well. We hypothesize that these groups evolve to have better senses of smell and thus, bigger olfactory bulbs. We are using CT data of endocasts (the cavity in the skull the brain occupies) to estimate smelling ability of extinct and living lizards to test this hypothesis. The mentees have learned how to process CT scans, have written a literature review, collected ecology data, and made decisions about methods and our research approach.

A series of lizards with varying degrees of limb reduction lined up from pentadactyl to limbless.

A human hand holding a tiny lizard. The lizard has three fingers on its hand.

All thats left of this lizard's arm is a tiny humerus. The pectoral girdle is visible in the CT scan

The skeleton of a long lizard with no limbs. It still has tiny remnant hip bones.

The CT scan of a lizard's skeleton superimposed on its photo. In the right photo, we can see a claw is the entirety of this animal's external forelimb, but with the CT scan, we can see the claw is a small protrusion of the humerus (blue) which is anchored to a pectoral girdle (green).

Lizards that have evolved to move underground are often small, elongate and have reduced limbs and digits, or no limbs at all.