implicationsThe undulating body of the shark balances the lateral motion ofthe tail with the lateral motion of the anterior body in the oppositedirection. And the downward and posteriorly directed forces pro-duced by the tail are balanced by the lift provided by the 8–14◦bodyangle maintained during forward swimming (Wilga and Lauder,2002). It was previously thought that the fact that sharks producedownward oriented thrust forces was primarily a factor of theirtail shape. Using two-dimensional hydrodynamic analysis methods