This animation sequence comes out of my more than a quarter of a century of teaching comparative anatomy to students at Brown, and the frustration (for both me and the students) of teaching students who have difficulty in visualizing objects in three dimensions. This always came easily to me, but I understand that it is an innate ability that is present in a minority of people (even if someone who initially has difficulty can improve with practice). A particular difficulty for students was visualizing the formation of these arches in 3D space ----- 2D pictures show either a side (lateral) view or a view from the top, but many students were unable to integrate these into a holistic picture. Thus my idea of doing reconstructions in a three-quarter view of the animal, so that both sides could be seen simultaneously, and also how transitions from one form to another could occur.

Full Overview of Animation

These series of illustrations take the viewer through an evolutionary history of the form of the aortic arches in vertebrates, in a three-quarter view fashion where both left and right sides can be seen simultaneously. The illustrations show how the system seen in mammals today, where separate vessels supply the lungs and the body, had its origins in the supply of arteries to the gills in more primitive vertebrates (ancestral fishes). The animation also shows the passage of blood through the system, changing from deoxygenated to oxygenated. This change in the form of the arteries, a basic pattern of six arches resulting in the three major ones seen today (carotids, systemic [i.e., the aorta], and pulmonary), is also mirrored in human development, so this animation sequence is also of potential interest to medical students as well as to people interested in evolutionary comparative anatomy.

The evolutionary stages encompass the following depictions: hypothetical primitive vertebrate, generalized gnathostome (jawed fish), generalized lobe-finned fish (fish with lungs, shown both breathing water and breathing air), primitive tetrapod (i.e., land vertebrate), more derived tetrapod (proto-amniote; i.e., the group containing reptiles, mammals and birds), basal synapsid ("mammal-like reptile", or mammal ancestor), and mammal.

The sequence can be viewed either as a continuous stream, or each stage can be viewed in a more static format. In the static format, there are buttons that enable the viewer to see labels identifying the various structures and blood vessels shown, and there is also the opportunity to access information explaining issues about the anatomy portrayed.

Some of the "stages" here represent the condition seen today in actual animals: the "generalized gnathostome" is basically the dogfish shark of comparative anatomy dissection labs, and the "mammal" is the condition seen in mammals today (including humans). Other "stages" have been extrapolated from a combination of embryological information from living vertebrates, and/or comparison with the condition in adult living vertebrates. For example, the "primitive lobe-finned fish" does not show the condition in any actual living lungfish, as the three living species are variously specialized in their own right, but the anatomy of living lungfish and primitive ray-finned fishes is used to infer what must have been the generalized condition from which either the living lungfish or living tetrapods could have been derived. Information about how these hypothetical evolutionary intermediate stages have been inferred is available in the information that can be accessed for each stage.

Individual Stages

Primitive Vertebrate (Jawless) Basal Gnasthostome (Jawed Fish) Generalized Lobefinned Fish (Water) Generalized Lobefinned Fish (Air) Primitive Tetrapod More Derived Tetrapod (Anamniote) Basal Synapsid "Mammal-Like" Animal Mammal