One of the perks of using a digital xray system for morphological measurements is that I get to see all sorts of interesting things that are difficult to detect or are not visible to the naked eye. I picked out a few of my favorite xrays from my recent field trip to Puerto Rico. These are all Anolis cristatellus, the common endemic “Crested Anole” of Puerto Rico.
Adult male and female A. cristatellus are sexually dimorphic. The males are much larger than the females (60-70+ mm SVL males versus ~50mm svl for females), have larger dewlaps, and have a thick tail at the base where the hemipenes are located. This usually makes it easy to tell the sexes apart, except when the male is around 50mm in size. At that size a subadult or juvenile male will look very similar to a female in terms of body size, dewlap size, and tail appearance. This female above gave us a surprise when we put her on the xray. We thought we had caught a young male that had just had a big meal but the xray showed clearly a very large egg in this gravid female.
Occasionally, we also see broken bones on the xrays. Sometimes they are minor fractures or are healing, and sometimes the breaks are so bad I wince when I see them. I try to handle the animals with the bad double breaks or exposed bone breaks extra carefully. The amount of broken bones we see is actually fairly surprising and maybe I will do some analyses on fracture rates in these populations. Here are some of my favorite broken bones from this trip:
In contrast to these poor lizards, a nice healthy lizard with no broken bones looks something like the lizard below.
And this last lizard may not have any breaks, but compare the tail in this one to the one above. Notice how you can see the vertebrae all the way down the tail in the lizard above but not in the lizard below? Anoles can autotomize their tails (drop them willingly to escape predators). When this happens it occurs along a fracture plate in the vertebrae. A new tail then regrows from that point, but the regenerated tail is composed of cartilage instead of bone.