S the thrombin-generated fibrin clot. Thrombin, the key proteolytic enzyme, presides over the conversion of the soluble plasma glycoprotein fibrinogen into fibrin monomers. These monomers spontaneously aggregate, forming, in conjunction with the platelets, the mesh of the hemostatic fibrin clot. In search for the evolution of vertebrateblood coagulation Davidson et al. [2] draws a 450 million year