Over the winter break I took three weeks to visit my family and friends in Portland, OR. I think I saw pretty much EVERYONE I usually promise to see on such holiday visits. Usually I have a 50% attrition rate, but by staying for a prolonged period of time I met all my people, rest, and work goals.
However, meeting so many people made me realize how few people knew what I was doing and, more importantly, WHY I was doing it. They were usually not asking about the larger philosophical reasons why I am in Paleontology or a Masters program in Texas (let’s save that for a later post), but why, as a paleontologist, I am studying the skulls of modern lizards. Good question. Let’s get into it.
I am studying Australian agamid lizards (heretofore referred to as ‘AA lizards’), specifically the osteology (skeleton, bones) of these lizards. These lizards are highly variable and some are crazy enough to appear on popular nature shows. If you’ve ever seen a frilled lizard running upright (i.e. Chlamydosaurus kingii) or a spiky lizard that slowly walks and gorges itself on ants (Moloch horridus), you’ve seen one of my study organisms.
Fun fact: Jurassic Park’s Dilophosaurus has more in common with the frill-necked lizard (C. kingii) than the actual reconstruction of the dinosaur. Represent!
Agamids are part of Squamata, the largest living order of reptiles (a group of animals long thought to be the domain of naturalists and 8 year old boys, which is, in fact, a myth). The ancestors of modern agamids differentiated pretty early from the rest of Squamata. Agamids, iguanids, and chameleons form the Order Iguana (appropriately named). Iguanids and chameleons are probably more closely related to each other than to agamids. After that… the picture gets rather hazy.
Like most of the current dominant orders, squamates are thought to diversify during the Jurassic. After this the agamids die off in the Americas when Pangea splits, but they slowly invade Africa, Asia, and, eventually, Australia. Recent genetic analyses1 have shown AA lizards have been in Australia for much longer than their slow invasion would have allowed. Remember that.
Behold, Pangea! If ever there was time for a road trip…
The fossil record? Sparse and mostly jaws, which is actually pretty cool. Agamids and chameleons have teeth that literally fuse to their jaw bones (acrodont dentiton)2
. They literally can’t lose their teeth. Instead, they are worn down gradually and eventually the jaw is used as a cutting surface if no tooth is left. For chameleons, all teeth are irreplaceable, whereas for agamids only the side teeth are irreplaceable and the front teeth are replaced with wear (pleurodont dentition). So, their teeth are pretty cool, but that means most of what is known about the osteology of agamids centers around the jaw (or the ribs, if you are Draco volans, but I digress).
So what is the problem? Currently, most of the work on modern agamids is genetic, which is awesome, but it means there is no way to directly compare what we know about modern agamids with their fossil ancestors (which lack genetic data). Fossil DNA has been sequenced, but only for fossils that were well preserved and only thousands of years old. In other words, the babies of the fossil record. Babies. DNA duplicates and changes easily, which is how evolution can occur, but that means it also easily degrades once death occurs. What paleontologists are mostly left with is bones.
Genetics can overestimate the divergence times of different groups of animals, and accuracy decreases the farther back in time you go. Often, fossils are used to calibrate or check phylogenies, but if no one knows what a fossil agamid would look like… And that’s where I come in!
What I have done so far: collected all osteological characters used to describe agamids, rewritten characters, coded characters on my lovely AA lizard skeletal collection*, and recorded all the weird stuff I’ve noticed along the way.
*skeletal collection not actually mine, but we’ve bonded a bit
Currently: I am running tree analyses, taking pictures through a microscope to definitively record these characters (you’re welcome, five interested people), and writing.
In a few months I will be able to tell you what makes the skeletons of different species of AA lizards unique, what these characters can contribute to a phylogeny, and one of the many critical gaps between the past and the present will be a little smaller. I am adding information not only to the past, but the current state of these lizards, which is becoming more and more critical in our extinction-centric world.
What more do agamids have to offer? That, my friend, will have to wait for a later post…
1. Smirina, Ella M., and Natalia B. Ananjeva. “Growth layers in bones and acrodont teeth of the agamid lizard Laudakia stoliczkana (Blanford, 1875)(Agamidae, Sauria).” Amphibia-Reptilia 28.2 (2007): 193-204.
2.Hugall, Andrew F., and Michael SY Lee. “Molecular claims of Gondwanan age for Australian agamid lizards are untenable.” Molecular biology and evolution21.11 (2004): 2102-2110.