Monday, June 17, 2013
Synapomorphies as tree slices
A phylogenetic tree is usually drawn as a stick diagram showing the historical lines of descent; and if the tree has been constructed from phenotypic data then the characters are often plotted onto the tree as cross-bars at the place where they are postulated to have arisen.
This creates an artistic problem if the phylogenetic tree is to be drawn as a real tree. Rob DeSalle & David Lindley (1997. The Science of Jurassic Park and the Lost World; or, How to Build a Dinosaur. Basic Books, ISBN 0-465-07379-4) have dealt with this issue by representing the synapomorphies as slices taken from the tree branches, as shown below.
Not all of the synapomorphies are shown, of course (birds have several more, and mammals do have some), but this is an intriguing artistic solution to a problem that Ernst Haeckel never conceived of when he first drew a phylogeny as a real tree. It is certainly more interesting than the more conventional representation (by Steven M. Carr), as shown below. (Note that mammals do acquire a synapomorphy in this version of the tree.)
Update note from Rob DeSalle:
"The figure was drawn by one of our artists here at the museum [American Museum of Natural History] and it was a collaborative effort to get the drawing done. In the conversation with the artist when outlining what I wanted in the figure I explained synapomorphy to him, and we went back and forth for an hour and settled on the slices. If I remember right it was the artist's idea. But the idea of representing synapomorphy as slices might have appeared before that."