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BAMBACH—SUPPORTING PREDATORSmean of the maximum and minimum range ofdiversity of predators was calculated, along withthe turnover appropriate for the boundary-crossingdiversities, and they are shown in Figure 3a.At this time this is the best estimate we can makeof the genus diversity of predators represented inthe fossil record. Because of uncertainty about howmany genera in many groups are actually predatorsthis estimate is necessarily a compromise, greaterthan the minimum possible number but less thanthe maximum reasonable number. However, it islikely to be closer to the actual value than either themaximum or minimum estimates. The only otherfactor that could alter the pattern of diversity ofpredators would be secular change in the proportionof predators within those groups that have a mixof predator and non-predator taxa. An example atthe class level will be shown below for gastropods,where we can follow change in the proportion ofdiversity contributed by different orders, each witha different proportion of predator genera. Althoughsuch changes in proportion did occur within someor all groups, this would not alter the generalpatterns, even if the change in each group was fromits minimum to maximum proportion as calculatedhere.The diversity of non-predator metazoan genera(calculated simply by subtracting the data onestimated predator diversity from the total of allmetazoa) is shown in Figure 3b at the same scaleas Figure 3a for predators. As expected, nonpredatorsconsistently outnumber predator taxa.The relationship between them will be discussedin the concluding section of this paper.DIVERSITY HISTORIES OFPREDATOR GROUPSBecause constant proportions were used inestimating maximum and minimum diversity ofpredators within each taxon, only the average(mean) of the range of estimated diversities ofpredators was used in the following examples,except for the anthozoa. This mean, or average, isnecessarily parallel to the maximum and minimumpossible numbers of predator genera, but midwaybetween them, as is illustrated by the data on theanthozoa (Fig. 4). Unless a significant shift in theproportion of taxa having predatory habits occurredwithin a taxon during the Phanerozoic, the patternof actual diversity change in predators should berecorded reliably by the average estimateddiversity. If the proportion of predator taxa changedin the same direction as overall diversity (forexample, if both increased), then the real changewould be exaggerated compared to the pattern seenusing a constant proportionality. Only if theproportion of predators in a taxon changed inopposition to the change in overall diversity of thetaxon, and at a greater rate than the change inoverall diversity (both unlikely), would the generaltrend of predator diversity in a taxon be obscuredor misrepresented by the method used here.Anthozoa.—Although anthozoans aresedentary organisms, many use their nematocystsand tentacles to entrap animals (Parker, 1982;Hyman, 1940). Some even extend parts of theseptal filaments out through the mouth and begindigestion externally. However, hermatypic reefbuildingcorals gain most nutrition fromphotosymbionts (zooxanthellae), and many smallpolypanthozoans use mucus and cilliary currentsin suspension-feeding, so many anthozoans are notpredators. But long-tentacled and large-polypanthozoa must be regarded as predators eventhough sedentary. The large polyps of manyrugosans and some tabulates, plus doubts thatPaleozoic corals were hermatypic, suggest thatmany of them had similar “passive-predator” lifehabits to those of living predatory anthozoans.From a survey of the distribution of polyp sizes,between ten and fifty percent of anthozoan generacan be regarded as predators. Figure 4 shows therange in number of genera of anthozoa that couldhave been predators through the Phanerozoic.Although there is a wide range of possible diversityof predatory anthozoans, three features are clear:1) the slow recovery from the Permian extinction,which eliminated the Tabulata and Rugosa, createda low-diversity interval from the start of the Triassicto the mid-Jurassic; 2) Cretaceous and Cenozoicdiversity is not dramatically higher than Devonian325