Dawn of the Dinosaurs

     Alright guys, it was another day of research - a literature search to be exact. The article for today is "Caudefemoral Musculature and the Evolution of Theropod Locomotion," by  Gatesy (1990). Theropods are bipedal dinosaurs, and they eventually gave rise to some avian species. However, the researchers used iguanas as a comparative group and went into a discussion of the evolution of the iguana femur and the muscles the allow the iguana to move, with particular emphasis on the importance of tails in locomotion. 
     In this study, Dr. Stephen Gatesy was attempting to show how the caudofemoralis longus muscle of the dinosaurs - which allowed them to retract their leg and hence act as the major impetus for locomotion - has shrunken in their modern day descendants as their tails have grown smaller or disappeared. For those non-anatomy people, caudofemoralis longus is a muscle in the thigh area of prehistoric dinosaurs that extends from the tail to the femur. Its name gives much of its identity. 'Femoralis' obviously indicating that it is near or attached to the femur, 'caudo' meaning tail of toward the tail, and 'longus' referring to relative size (longer) compared to the muscle caudofemoralis brevis. 
     Iguanas are not Theropods. They do not walk on two feet and are not directly descended from dinosaurs. But, like I said, they were used as a comparative group along with a Savannah monitor, a horned lizard, an American alligator, a spectacled caiman, a bobwhite quail, a domestic fowl, a helmeted guinea fowl, and a domestic pigeon as well as the bones of several dinosaurs. 

     The CFL (caudofemoralis longus) of the iguana was 17 - 36% of the dry muscle mass of the hind limb. This is quite large, considering the amount of muscles in the hind limb. The CFL originates from the caudal vertebrae in the proximal 1/3 of the tail. The term ‘proximal’ refers to the part of the tail closest to the body.  Though this may seem like a weird attachment point, as the muscle then inserts on the trochanteric fossa of the femur, keep in mind that an iguana's tail is almost 2/3 of the iguana's length. The trochanteric fossa is located on the proximal end of the femur, which is why this muscle acts as the major mover of the femur. Iguanas, like many other lizards, have a hind limb that sits fairly far away from the body, and during movement, the femur is retracted 140-165 degrees. Though this sounds very scientific, it is easy to imagine. Picture a lizard and how it walks. There is a large upward movement of the hind limb as it pushes itself forward, almost as if it has a hitch in its gait. If you can't see it, watch this video of Lung, the green iguana, walking. On a leash (http://www.youtube.com/watch?v=iSSWvS_5Rvc). Pay particular attention to the orientation of the hind limb and how it moves as Lung walks. Enjoy the dramatic music :) 
    

The CFL is muscle number 3. 

     The CFL may also be responsible for the retraction of the entire hindlimb, not just the femur. It may be responsible for the rotation of the hind limb, the fixation and flexion of the knee joint, and the lateral movement of the tail. Cool stuff. 

AA


Gatesy, Stephen. "Caudefemoral Musculature and the Evolution of Theropod Locomotion." Paleobiology (1990)      16.2: 170-186. Web. 8 Mar 2012.