Lions, Tigers, and Crocodiles

So the article for the week is about Crocodylian forelimb musculature. You may be asking yourself how that is related to iguanas, and well ... it's not really, other than it is yet another comparison. My interest of this article relates to its focus on why anybody is even studying Crocodylian forelimbs. The article, "Crocodylian Forelimb Musculature and its Relevance to Archosauria," discusses the forelimb of archosaurs as a functionally diverse anatomical unit, but one that has remained nearly the same through its evolutionary path (Meers, 2003).

Archosaurs are a group of creatures that evolved in the late Permian or early Triassic period. They are diapsid amniotes (meaning they have two holes in their skull, one on each side) and the most modern representatives are crocodiles and birds. This gives you a clue as to why their forelimbs are so interesting. The front limbs of an alligator (arms) vary quite significantly from the front limbs of birds (wings). But though they may look different, their musculature isn't all that distinct.

The author dissected 4 Alligator mississippiensis, 1 Crocodylus siamensis, 2 Crocodylus acutus, 2 Osteolaemus tetraspis, and 1 Gavialis gangeticus. They then compiled in depth muscle descriptions for all of the muscles in the forelimbs of the specimens. The muscles don't vary all that much from the iguanas. A part of this is because crocodylians are squamates, like iguanas, and hence their posture is very similar as are the muscles required to maintain this posture. The species dissected did have more extrinsic muscles on the ventral side. This means that they had more chest muscles (extrinsic meaning the muscles originate on the trunk and insert on the front limbs, and ventral being the side with the animal’s heart.) Also, the study named the deep muscles of the back differently than my sources did, but they were relatively the same.

The conclusion of the study was basically that the American alligator is representative of most Crocodylian species (re-enforcing that the forelimb musculature of Archosaurs has not changed much).

AA

Meer, Mason. "Crocodylian Forelimb Musculature and its Relevance to Archosauria." The Anatomical Records Part A: Discoveries in Molecular, Cellular, and Evolutionary Biology (2003) 274A.2: 891-916. Web. 28 Apr 2012.