Bird-like lungs found in Iguanas, is this further proof that reptiles and birds are more similar then we think?

A new discovery by Collen Farmer of the University of Utah demonstrates that iguanas have lungs alike to those found in bird species which, were believed to be present only in birds as a way of combating the high energy levels needed for flight but as iguanas do not fly, this can no longer be the case.
Mammals including humans, have lungs that have a branched structure, when we breathe in, the diaphragm ( a dome shaped muscle under your lungs) contracts expanding your chest cavity, intercostal muscles (located between your ribs) also help to further expand the chest cavity allowing for expansion of the lungs; this causes air to enter your body via the nose and mouth, down the trachea (windpipe) and into the lungs, once inside the lungs the windpipe divides into bronchial tubes (one for each lung), which divide into bronchioles and then further into alveoli. The alveoli are covered in capillaries (blood vessels) which connect to the arteries and veins of the bloodstream. When we breathe out the diaphragm and intercostal muscles relax reducing the amount of space in the chest cavity and therefore lungs causing air to exit the body in the opposite way to which it entered.

 

 Note: Cardiac notch is where the heart sits against the lung.

For birds, iguanas and some other reptiles including alligators and monitor lizards, they have a lung system in which air flows through a one way loop, they lack a diaphragm and have air sacs instead which fill a role similar to bellows to pump air through the lungs. When a bird breathes in they need inhale twice to get air to pass through the whole respiratory system  instead of singularly like mammals, on the first inhalation air enters the trachea then into the air sac below the lungs (caudal air sac), the bird then exhales and the air enters the lungs and into the bloodstream; the bird then inhales a second time forcing air from the lungs into the second set of air sacs in front of the lungs (cranial air sacs), the bird then exhales and the air leaves the body via the trachea.

Note: Posterior air sac = Caudal air sac, Anterior air sac = Cranial air sac.

The team of scientists at Utah university discovered this method of breathing in iguanas, by using a surgical scope to observe the lungs of live specimens as they inhaled harmless smoke from a fog machine. They then used 3D x-ray imaging images to make a computer model showing airflow which matched closely the observations seen in the real iguana lungs which showed that shapes and angles within the lungs of iguanas direct air in one direction. This discovery therefore points to the possibility that this method of breathing came from a common ancestor of crocodiles, lizards and dinosaurs (birds), further suggesting that reptiles and birds are more alike then we originally thought.

 3D x ray images of the iguana lungs

What are your thoughts on this new discovery? Do you think that birds and reptiles will be reclassified into a new group together in the future? As always leave your comments in the box below and thanks for reading.

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To view a previous post regarding the similarity between reptiles and birds Click here