Night of the Living Iguana

     Okay, so I'm back to only two blogs a week. The first will be a summary of an article I have found in my research, and the second will be an overview of what I did (and didn't) accomplish in the lab. So here is my literature blog.
     So I found this article on the adaptations in the hind limb of lizards due to their sprawling posture (Rewcastle, 1983). There are technically two "problems" with their sprawling posture. The first being a problem of support. Because the body of the lizard does not sit directly above the limb supporting it, there is a lack of support for the body. Pull on your physics here, guys. The second problem occurs because the limb is so far from the body. The limb cannot rotate completely around without the bones in the hind limb, primarily the femur, running in to the hip or the edge of the acetabulum. In response to these constraints, lizards have evolved some special features. First, the femur of the lizard is abnormally long. In most quadruped mammals, the tibia and fibula are longer than the femur. In lizards, this is almost universally untrue. The femur is longer than the tibia and fibula, creating a longer moment arm for limb movement. However, this creates another problem, the longer moment arm makes the limb heavier and requires a significantly larger muscle mass to move it. The muscle I talked about in my prior post -- the caudofemoralis longus -- is one of the major muscles in the hindlimb, a muscle abundantly developed to move the hip.
     Another adaptation occurs in the ankle and foot. The tarsals of the foot/pes, have fused together, to create a more stable base, while the proximal metatarsals have grown to overlap one another and allow for the foot to be used as another lever. The pes also became more asymmetrical, with the first three digits elongating and falling on essentially the same plane, while the fourth and fifth digit became more autonomous. This development is believed to reflect an adaptation to arboreal/tree environments. The limb adaptations do require that the body of the lizard be significantly reduced in weight.
     This author also took the time to mention that the lizards sprawling stance does afford the lizards some advantages. First of all, it allows the body to lay closer to the substrate on which it's moving while still letting the limbs move. Think about it like this, if a lion were to lay nearly on its stomach on the ground and try to walk forward, it would fall on its face and look ridiculous. But if a lizard did that (and they do quite often, probably in your backyard), it would be able to move its limbs freely. The hindlimb apparatus allows for short bursts of incredible speed while keeping the lizard close to the ground and away from danger. This indicates a propensity in lizards to live in/on the ground or in the trees.

AA

Rewcastle, Stephen Compton. "Fundamental Adaptations in the Lacertilian Hind Limb: A    Partial Analysis of the Sprawling Limb Posture and Gait." Copeia (1983) 1983.2: 476-487. Web. 14 Mar 2012.