The low diversity of marine fishes, particularly shell-crushing predators (durophages), at the beginning of Romer's gap is supported by the sudden abundance of hard-shelled crinoid echinoderms during the same period. The Tournaisian has even been called the "Age of Crinoids". Once the number of shell-crushing ray-finned fishes and sharks increased later in the Carboniferous, coincident with the end of Romer's gap, the diversity of crinoids with Devonian-type armor plummeted, following the pattern of a classic predator-prey (Lotka-Volterra) cycle. There is increasing evidence that lungfish and stem tetrapods and amphibians recovered quickly and diversified in the rapidly changing environment of the end-Devonian and Romer's Gap.