Three new traits were discovered by peering closely at the specimens: the surface sculpting of the respiratory lamellae (the leaves of the book); the edges of the leaves, within a chamber called an atrium (the pre-chamber of the book lung); and the processes on the posterior valve-like edges of the spiracles (the point at which the book lung opens to the atmosphere). The tremendous diversity of structures documented by Kamenz and Prendini is matched only by the respiratory organs of air-breathing crabs.
These structures contain phylogenetically important variation at multiple branches in the scorpion tree. One striking example is the sculpting on the surface of the book lung's leaves. While all nonbuthid scorpions have papillate trabeculae (simple or branched hair-like projections) on the leaves' surfaces, the buthids (the venomous thick-tailed scorpions) and chaerilids have reticulate venation (a network of veins), a fundamental difference between these scorpion lineages that is independently supported by external morphology and DNA. The finding suggests that a significant change in the structure of the respiratory apparatus must have occurred early in the evolution of modern scorpions. Both conditions of the lamellar surface show additional variation that is informative higher up the branches of the scorpion tree. The data gathered by Kamenz and Prendini will be combined with DNA sequences and character traits from other parts of the scorpion anatomy to reconstruct the scorpion tree of life.
"The best way to understand the evolution of scorpions, like any group of organisms, is to investigate multiple lines of evidence, using the best techniques available. As the book lung study shows, we may not recognize the
|Contact: Kristin Elise Phillips|
American Museum of Natural History