Paleontological research on predation has been expanding rapidly in scope, methods, and goals. The growing assortment of research strategies and goals has led to increasing differences in sampling strategies, types of data collected, definition of variables, and even reporting style. This methodological overview serves as a starting point for erecting some general methodological guidelines for studying the fossil record of predation. I focus here on trace fossils left by predators in the skeleton of their prey, arguably one of the most powerful sources of direct data on predator-prey interactions available in the fossil record. A critical survey of sampling protocols (data collecting strategy, sieve size, and sample size) and analytical approaches (predation intensity metrics, strategies for evaluating behavioral selectivity of predators, and taphonomic tests) reveals that various approaches can be fruitful depending on logistic circumstances and scientific goals of paleoecological projects. Despite numerous caveats and uncertainties, trace fossils left by predators on skeletons of their prey remain one of the most promising directions of research in paleoecology and evolutionary paleobiology.

The fossil record contains far more coprolites produced by carnivorous animals than by herbivores. This inequity reflects the fact that feces generated by diets of flesh and bone (and other skeletal materials) contain chemical constituents that may precipitate out under certain conditions as permineralizing phosphates. Thus, although coprolites are usually less common than fossil bones, they provide a significant source of information about ancient patterns of predation. The identity of a coprolite producer often remains unresolved, but fossil feces can provide new perspectives on prey selection patterns, digestive efficiency, and the occurrence of previously unknown taxa in a paleoecosystem. Dietary residues are often embedded in the interior of coprolites, but much can be learned from analyses of intact specimens. When ample material is available, however, destructive analyses such as petrography or coprolite dissolution may be used to extract additional paleobiological information.

Archeological interest in predation ranges from studies of the earliest evidence for human meat-eating, to attempts to understand the fossil record's ambiguity about the meaning of associated animal bones and human artifacts. A number of quantitative measures are used to find the meaningful patterns in archeological assemblages, and taphonomic research has also provided analogs and comparative standards for interpreting human behavior based on the evidence for predation. The most important methods, approaches, and interests are discussed here, using case studies to illustrate the way archeologists have thought about the record of humans as predators.

Microorganisms (prokaryotes and protists) seldom fossilize, but they form much of the trophic structure in marine pelagic and benthic environments, chiefly as primary producers and secondary consumers. The fossil record of unskeletonized groups is meager or non-existent. Skeletonized groups have excellent records but represent a small portion of the total microbial diversity.

The evolution of trophic structures and roles of microorganisms can be reconstructed broadly for most of geologic history. When life first evolved, it had a trophic structure. The first microbial fossils appear to be benthic mats; these are abundant in the Precambrian but sparse later; body fossils are very rare. The Archean saw pelagic and benthic prokaryotes and possibly protists later on. Proterozoic trophic structures became increasingly complex as protists entered pelagic environments. Benthic assemblages likewise became complex, as prokaryotes and protists formed mats and stromatolites in many environments. At the end of the eon, animals appeared; microbial primary producers and predation on microorganisms and among animals fueled these assemblages. The fundamental trophic structures that developed then persisted with modification into modern times. Phanerozoic ecosystems became very complex as skeletonized animals and protists evolved. Among the important trophic developments in the Phanerozoic history of microorganisms were the early diversification of phytoplankton and siliceous micro-zooplankton (Cambrian), algal endosymbiosis with benthic metazoans (Cambrian to Recent) and rock-forming foraminifera (late Paleozoic to Recent), the radiation of pelagic skeletal primary producers and micro-zooplankton (mid-Mesozoic), and radiations in the deep sea, reefs, and shallow areas (Mesozoic and Cenozoic). Each evolutionary change increased trophic complexity by adding more species at each level, while episodic mass extinctions decreased species diversity and trophic complexity.

Marine trophic structures evolved over immense intervals of geologic time, growing complex and then suffering destruction at major extinction events. The effects of human impact on these structures should be examined, for without them, Earth may change dramatically.

The Paleozoic body fossil record of potential benthic predators includes nautiloid and ammonoid cephalopods, phyllocarids, decapods, and several lineages of gnathostomes. The latter group, in particular, radiated rapidly during the Devonian. In the pelagic realm, predator-prey interactions involving cephalopods and some nektonic arthropods probably appeared in the Ordovician. Again, evidence indicates intensification of pelagic predation, much of it by arthrodires and sharks on other fishes, during the Devonian radiation of gnathostomes.

Trace fossils provide direct evidence of predatory attack from the Ediacarian and Early Cambrian onward, but with a substantial increase in the Siluro-Devonian. Brachiopod and molluscan shells and trilobite exoskeletons show evidence of healed bite marks and peeling from the Cambrian onward, but with an increased frequency in the Devonian. Predatory drill holes with stereotypical position and prey-species preference are found in brachiopods (Cambrian onward) and mollusks (Ordovician onward); boreholes also show increased frequency in the middle Paleozoic. Certain of these boreholes are tentatively attributable to platyceratid gastropods.

Hard-shelled benthic organisms with thicker, more spinose skeletons may have had a selective advantage as durophagous predators increased. Brachiopods, gastropods, trilobites, and crinoids show an abrupt increase in spinosity beginning in the Siluro-Devonian. But spinosity decreases after the early Carboniferous. Late Paleozoic benthos may have taken refuge in smaller size and resistant, thick-walled skeletons, as well as endobenthic and cementing modes of life. Conversely, in the pelagic realm, external armor was reduced, while more efficient, fast-swimming modes of life (e.g., in sharks) increased in the post-Devonian.

Mesozoic and Cenozoic evolution of predators involved a series of episodes. Predators rebounded rather rapidly after the Permo-Triassic extinction and by the Middle Triassic a variety of new predator guilds had appeared, including decapod crustaceans with crushing claws, shell-crushing sharks and bony fish, as well as marine reptiles adapted for crushing, smashing, and piercing shells. While several groups (e.g., placodonts, nothosaurs) became extinct in the Late Triassic crises, others (e.g., ichthyosaurs) survived; and the Jurassic to Early Cretaceous saw the rise of malacostracan crustaceans with crushing chelae and predatory vertebrates—in particular, the marine crocodilians, ichthyosaurs, and plesiosaurs. The late Cretaceous saw unprecedented levels of diversity of marine predaceous vertebrates including pliosaurids, plesiosaurs, and mosasaurs. The great Cretaceous-Tertiary extinction decimated marine reptiles. However, most invertebrate and fish predatory groups survived; and during the Paleogene, predatory benthic invertebrates showed a spurt of evolution with neogastropods and new groups of decapods, while the teleosts and neoselachian sharks both underwent parallel rapid evolutionary radiations; these were joined by new predatory guilds of sea birds and marine mammals. Thus, although escalation is sometimes cast as an ongoing “arms race,” in actuality the predatory record shows long interludes of relative stability puncturated by episodes of abrupt biotic reorganization during and after mass extinctions. This pattern suggests episodic, but generally increasing, predation pressure on marine organisms through the Mesozoic-Cenozoic interval. However, review of the Cenozoic record of predation suggests that there are not unambiguous escalatory trends in regard to antipredatory shell architecture, such as conchiolin and spines; nor do shell drilling and shell repair data show a major increase from the Late Mesozoic through the Cenozoic. Most durophagous groups are generalists, and thus it may be that they had a diffuse effect on their invertebrate prey.

The paleontological literature on marine invertebrates is rich in supposed examples of parasitism and our tabulation shows a nearly even distribution of reported cases through the post-Cambrian Phanerozoic. Slightly lower frequencies characterize the Triassic and Jurassic and higher frequencies the Cretaceous and Tertiary, and the pattern roughly mirrors Sepkoski's (1984) marine diversity curve. The total number of parasitic associations for any geologic period rarely exceeds a dozen, yet few of the reported examples provide explicit criteria distinguishing parasitism from predation, commensalism, or mutualism. We evaluated the published examples using the following criteria: (1) evidence of a long-term relationship between two organisms, (2) benefit of interaction to supposed parasite, and (3) detriment of interaction to the host We found that only in exceptional cases were these criteria fulfilled. One example that provides much information on parasitic interactions involves platyceratids and crinoids and we summarize the evidence for the parasitic interaction between these two groups of organisms.

Carnivory is the consumption of one animal by another animal; among invertebrates in terrestrial and freshwater ecosystems this type of feeding can take three forms: predation, parasitoidism, and parasitism. Differences among these three functional modes involve (i) whether the duration of feeding on the prey item is quick or there is an accommodation, coevolutionary or otherwise, between the carnivore and the host prey; (ii) whether the prey or host is killed; (iii) whether single or multiple prey or host items are consumed during the carnivore's lifespan, and (iv) the relative sizes of the carnivore and its prey or host. Uniformitarian and nonuniformitarian evidence directly relating to the history of carnivory can be found in exceptionally preserved deposits from the mid-Paleozoic to the Recent, but such evidence is relatively rare because carnivores are the least represented trophic group in ecosystems. Six types of paleobiological data provide evidence for carnivory: taxonomic affiliation, fossil structural and functional attributes, organismic damage, gut contents, coprolites, and indications of mechanisms for predator avoidance.

Only 12 invertebrate phyla have become carnivorous in the continental realm. Six are lophotrochozoans (Acanthocephala, Rotifera, Platyhelminthes, Nemertinea, Mollusca, and Annelida) and six are ecdysozoans (Nematoda, Nematomorpha, Tardigrada, Onychophora, Pentastoma, and Arthropoda). Most of these groups have poor continental fossil records, but the two most diverse—nematodes and arthropods—have comparatively good representation. The record of arthropods documents (i) the presence of predators among primary producers, herbivores, and decomposers in early terrestrial ecosystems; (ii) the addition later in the fossil record of the more accommodationist strategies of parasitoids and parasites interacting with animal hosts; (iii) the occurrence of simpler food-web structures in terrestrial ecosystems prior to parasitoid and parasite diversification; and (iv) a role for mass extinction in the degradation of food-web structure that ultimately affected carnivory. Future research should explore how different modes of carnivory have brought about changes in ecosystem structure through time. Despite numerous caveats and uncertainties, trace fossils left by predators on skeletons of their prey remain one of the most promising research directions in paleoecology and evolutionary paleobiology.

Predatory theropod dinosaurs can usually be identified as such by features of their jaws, teeth, and postcrania, but different clades of these reptiles differed in their adaptations for prey handling. Inferences about theropod diets and hunting behavior based on functional morphology are sometimes supported by evidence from taphonomic associations with likely prey species, bite marks, gut contents, coprolites, and trackways. Very large theropods like Tyrannosaurus are unlikely to have been pure hunters or scavengers, and probably ate whatever meat they could easily obtain, dead or alive. Theropods were not the only dinosaur hunters, though; other kinds of large reptiles undoubtedly fed on dinosaurs as well The taxonomic composition of dinosaurian predator-prey complexes varies as a function of time and geography, but an ecologically remarkable feature of dinosaurian faunas, as compared with terrestrial mammalian faunas, is the very large size commonly attained by both herbivorous and carnivorous dinosaurs. The K/T extinction event(s) did not end dinosaurian predation, because carnivorous birds remained prominent predators throughout the Cenozoic Era.

Synapsids include modern mammals and their fossil ancestors, the non-mammalian synapsids, or ‘mammal-like reptiles' of old classifications. The synapsid fossil record extends from the Late Carboniferous to the present, a span of nearly 300 million years. However, it can be broken into two distinct phases of diversification, separated by about 150 million years. The first phase extends from the Late Carboniferous to the mid-Triassic, includes the first large land predators on Earth, and is almost entirely non-mammalian. The second phase begins about 65 million years ago after the demise of the dinosaurs, includes only mammals, and extends to the present. In this overview of synapsid predators, we emphasize terrestrial species of large size, and their adaptations for killing and feeding, rather than locomotion. Despite fundamental differences in jaw mechanics and tooth morphology, there are significant parallels in the non-mammalian and mammalian radiations of synapsid predators. Both groups evolve sabertooth forms more than once, and both evolve short-snouted, powerful biting forms. In addition, both the Late Carboniferous—Triassic and Cenozoic phases are characterized by repeated patterns of clade replacement, in which one or a few clades evolve large size and seem to dominate the carnivore guild for several million years, but then decline and are replaced by new taxa. Moreover, within both ancient and Cenozoic predator clades, there are parallel trends over time toward increased body size and hypercarnivory that likely result from a combination of interspecific competition and energetic constraints.

Predation, in the broad sense of an organism killing another organism for nutritional purposes, is probably as old as life itself and has originated many times during the history of life. Although little of the beginnings is caught in the fossil record, observations in the rock record and theoretical considerations suggest that predation played a crucial role in some of the major transitions in evolution. The origin of eukaryotic cells, poorly constrained to about 2.7 Ga by geochemical evidence, was most likely the ultimate result of predation among prokaryotes. Multicellularity (or syncytiality), as a means of acquiring larger size, is visible in the fossil record soon after 2 Ga and is likely to have been mainly a response to selective pressure from predation among protists. The appearance of mobile predators on bacteria and protists may date back as far as 2 Ga or it may be not much older than the Cambrian explosion, or about 600 Ma. The combined indications from the decline of stromatolites and the diversification of acritarchs, however, suggest that such predation may have begun around 1 Ga. The Cambrian explosion, culminating around 550 Ma, represents the transition from simple, mostly microbial, ecosystems to ones with complex food webs and second- and higher-order consumers. Macrophagous predators were involved from the beginning, but it is not clear whether they originated in the plankton or in the benthos. Although predation was a decisive selective force in the Cambrian explosion, it was a shaper rather than a trigger of this evolutionary event.

This paper presents new estimates of the genus diversity of predators in each major taxon containing predators, as well as an estimate of the total genus diversity of predators through the Phanerozoic. Predators have never been numerically abundant compared to prey. However, the diversity of predators and the proportion of total faunal diversity composed of predators have both increased over time, implying that ecosystems have increased their ability to support either more predators or more specialization among predators. Also, turnover in diversity dominance among predator groups, with more energetic predator taxa replacing or being added to a fauna of less energetic groups, implies that the energy available in marine food webs has increased. The apparent increase in diversity and biomass of primary producers plus patterns of diversity change in prey taxa supports these inferences based on patterns of change in predators alone.

Arms races between predators and prey may be driven by two related processes—escalation and coevolution. Escalation is enemy-driven evolution. In this top-down view of an arms race, the role of prey (with the exception of dangerous prey) is downplayed. In coevolution, two or more species change reciprocally in response to one another; prey are thought to drive the evolution of their predator, and vice versa. In the fossil record, the two processes are most reliably distinguished when the predator-prey system is viewed within the context of the other species that may influence the interaction, thus allowing for a relative ranking of the importance of selective agents. Detailed documentation of the natural history of living predator-prey systems is recommended in order to distinguish the processes in some fossil systems. A geographic view of species interactions and the processes driving their evolution may lead to a more diverse array of testable hypotheses on how predator-prey systems evolve and what constraints interactions impose on the evolution of organisms. Scale is important in evaluating the role of escalation and coevolution in the evolution of species interactions. If short-term reciprocal adaptation (via phenotypic plasticity or selection mosaics among populations) between predator and prey is a common process, then prey are likely to exert some selective pressure over their predators over the short term (on ecological time scales), but in the long run predators may still exert primary “top-down” control in directing evolution. On the scale of evolutionary time, predators of large effect likely control the overall directionality of evolution due to the inequalities of predator and prey in control of resources.

Three properties of predation make this form of consumption an important agency of evolution: universality (all species have predators), high frequency (encounters of prey with predators test both parties often), and imperfection (many predatory attacks fail, enabling antipredatory selection to take place). On long time scales, predators have two principal effects: they influence their victims' phenotypes, and prey species that are highly vulnerable to all phases of predatory attacks are evolutionarily restricted to environments where predators are rarely encountered. Although predator and prey can affect each other's behavior and morphology on timescales commensurate with individual lifespans, predators have the evolutionary upper hand over the long run, especially in the expression of sensory capacities, locomotor performance, and the application of force. Only in passive defenses (armor, toxicity, large body size) does escalation favor the prey. In a review of methods for inferring predation in the geological past, I argue against the use of whole assemblages, which combine species of contrasting adaptive type, Instead, I strongly favor species-level and clade-level approaches (including examples of clade replacement) in which comparisons among places and among time intervals are made within the same adaptive types and the same physical environments. The available evidence, much of which comes from studies of shell drilling and shell breakage, points to temporal increases in both predator power and prey defenses. Escalation between species and their enemies, including predators, has proceeded episodically against a backdrop of generally increasing productivity and increasing top-down evolutionary control by high-energy predators during the Phanerozoic, the consumer age.