Modeling durophagous predation and mortality rates from the fossil record of gastropods

Abstract

Gastropods often show signs of unsuccessful attacks by durophagous predators in the form of healed scars in their shells. As such, fossil gastropods can be taken as providing a record of predation through geological time. However, interpreting the number of such scars has proved to be problematic—Would a low number of scars mean a low rate of attack or a high rate of success, for example? Here we develop a model of population dynamics among individuals exposed to predation, including both lethal and nonlethal attacks. Using this model, we calculate the equilibrium distributions of ages and healed scars in the population and among fossilized specimens, based on the assumption that predation is independent of age or scar number. Based on these results, we formally show that the rates of attack and success cannot be disambiguated without further information about population structure. Nevertheless, by making the assumptions that the non-durophagous predatory death rate is both constant and low, we show that it is possible to use relatively small assemblages of gastropods to produce accurate estimates of both attack and success rates, if the overall death rate can be estimated. We consider likely violations of the assumptions in our model and what sort of information would be required to solve this problem in these more general cases. However, it is not easy to extract the relevant information from the fossil record: a variety of important biases are likely to intervene to obscure the data that gastropod assemblages may yield. Nonetheless, the model provides a theoretical framework for interpreting summary data, including for comparison between different assemblages.

Biomechanical analyses of Cambrian euarthropod limbs reveal their effectiveness in mastication and durophagy

“…Durophagous predation-the consumption of prey with hard biomineralized shells or exoskeletons-is an effective feeding mode exploited by various metazoan groups across the Phanerozoic [1][2][3][4]. Euarthropods in particular have effectively used mandibles and other modified appendages to crush cuticle and biomineralized structures, such as a shell.…”

Macroevolutionary patterns of body plan canalization in euarthropods

“…This issue is commonly conveyed by the notions of “stem” and “crown” groups (Jefferies 1979; Budd and Jensen 2000). While some authors chose to assign macroevolutionary properties (such as having or not having a body plan) to all stem and crown lineages based on the sole property of being respectively extinct or extant (Budd and Jensen 2000; Budd and Mann 2019), cladistic stem and crown groups are arguably different from “ontological” stem and crown groups (Aria 2019). Although this distinction is first conceptual (description of the form vs. property of the content), it also follows from the simple observation that any lineage is subject to extinction independent of intrinsic limiting factors.…”

Community evenness and sample size affect estimates of predation intensity and prey selection: A model-based validation

“…Theoretical investigations also demonstrated the effect of sample size on inferred predation intensity (Smith et al 2018, 2022). Analytical techniques to evaluate and compare predation measures across groups often impact the inferences (Kowalewski 2002; Leighton 2002; Grey et al 2006; Stafford and Leighton 2011; Dietl and Kosloski 2013; Smith et al 2018; Budd and Mann 2019).…”