PSYCHE 
Vol. 79 
September, 1972 
No. 3 
THE PROTHORAX OF COLEOPTERA: 
ORIGIN, MAJOR FEATURES OF VARIATION 1 
By T. F. H la vac 2 
Biological Laboratories, Harvard University, 
Cambridge, Massachusetts 
Introduction 
The unique evolutionary success of the order Coleoptera is a re- 
sult of great size combined with enormous biological diversity. The 
huge number of species (ca. 280,000) is arrayed across a broader 
ecological spectrum than that of any other group of terrestrial ar- 
thropods. Four adaptive zones have been extensively occupied : sur- 
face, substrate, aquatic, aerial. Higher categories of beetles are, 
with exceptions, very broad, overlapping adaptive radiations. This 
evolutionary complexity is associated with great structural variation 
and a small number of basic adaptations, particularly in the locomo- 
tory system. 
Because the Coleoptera are a series of replicated experiments in 
ecological differentiation, the group may be used for studying a suite 
of problems in the evolution of adaptation. And, because beetles are 
such a large, diverse and ubiquitous group of insects, they should 
have a place as subjects for developing and refining modern syste- 
matic methodologies. Work at these two superficially different levels 
has been hindered or made unfeasible (q. v. Brundin 1972: 72) by 
the lack of a firm foundation of comparative morphology. 
Most work on comparative structure of beetles suffers from one 
A preliminary version of this work was submitted as part of a Ph.D. 
thesis to the Biology Department, Harvard University. 
2 I thank Drs. R. A. Crowson, H. E. Evans, J. F. Lawrence, E. Mayr, 
and E. O. Wilson for many useful comments on the manuscript. Work on 
thoracic morphology has been supported by NSF grants GB 19922 (Reed 
C. Rollins, Harvard University, Principal Investigator), GB 12346 (P. J. 
Darlington, Jr., Harvard University, Principal Investigator), and GB 
31173 (F. M. Carpenter, Harvard University, Principal Investigator). 
Manuscript received by the editor October 1 , 1972 
123 
