Farming is a behavior in which an organism promotes the growth and reproduction of other organisms in or on a substrate as a food source. A number of trace fossils have been suggested to record the occurrence of farming behavior. These include the deep-sea graphoglyptid trace fossils, proposed to be microbial farms on the seafloor, and terrestrial fossil social insect nests thought to represent fungicultural behavior. The presumed farming behavior of graphoglyptids is the basis of the ethological category agrichnia. Four criteria have been proposed as diagnostic of farming behavior, and these can be applied to both observed modern and proposed trace fossil examples of farming behavior. The evidence for farming behavior in the social insect trace record is strong but is much weaker in the case of graphoglyptids. The use of agrichnia as an ethological category should be limited to well-supported cases.

Organismal metabolic rates reflect the interaction of environmental and physiological factors. Thus, calcifying organisms that record growth history can provide insight into both the ancient environments in which they lived and their own physiology and life history. However, interpreting them requires understanding which environmental factors have the greatest influence on growth rate and the extent to which evolutionary history constrains growth rates across lineages. We integrated satellite measurements of sea-surface temperature and chlorophyll-a concentration with a database of growth coefficients, body sizes, and life spans for 692 populations of living marine bivalves in 195 species, set within the context of a new maximum-likelihood phylogeny of bivalves. We find that environmental predictors overall explain only a small proportion of variation in growth coefficient across all species; temperature is a better predictor of growth coefficient than food supply, and growth coefficient is somewhat more variable at higher summer temperatures. Growth coefficients exhibit moderate phylogenetic signal, and taxonomic membership is a stronger predictor of growth coefficient than any environmental predictor, but phylogenetic inertia cannot fully explain the disjunction between our findings and the extensive body of work demonstrating strong environmental control on growth rates within taxa. Accounting for evolutionary history is critical when considering shells as historical archives. The weak relationship between variation in food supply and variation in growth coefficient in our data set is inconsistent with the hypothesis that the increase in mean body size through the Phanerozoic was driven by increasing productivity enabling faster growth rates.

The warm, equable, and ice-free early Eocene Epoch permits investigation of ecosystem function and macro-ecological patterns during a very different climate regime than exists today. It also provides insight into what the future may entail, as anthropogenic CO₂ release drives Earth toward a comparable hothouse condition. Studying plant–insect herbivore food webs during hothouse intervals is warranted, because these account for the majority of nonmicrobial terrestrial biodiversity. Here, we report new plant and insect herbivore damage census data from two floodplain sites in the Wind River Basin of central Wyoming, one in the Aycross Formation (50–48.25 Ma) at the basin edge (WRE) and the second in the Wind River Formation in the interior of the basin (WRI). The WRI site is in stratigraphic proximity to a volcanic ash that is newly dated to 52.416 ± 0.016/0.028/0.063 (2σ). We compare the Wind River Basin assemblages to published data from a 52.65 Ma floodplain flora in the neighboring Bighorn (BH) Basin and find that only 5.6% of plant taxa occur at all three sites and approximately 10% occur in both basins. The dissimilar floras support distinct suites of insect herbivores, as recorded by leaf damage. The relatively low-diversity BH flora has the highest diversity of insect damage, contrary to hypotheses that insect herbivore diversity tracks floral diversity. The distinctiveness of the WRE flora is likely due to its younger age and cooler reconstructed paleotemperature, but these factors are nearly identical for the WRI and BH floras. Site-specific microenvironmental factors that cannot be measured easily in deep time may account for these differences. Alternatively, the Owl Creek Mountains between the two basins may have provided a formidable barrier to the thermophilic organisms that inhabited the basin interiors, supporting Janzen's hypothesis that mountain passes appear higher in tropical environments.

To assess evolutionary processes in deep time, it is essential to understand the roles of development and environment, both recorded through the morphological variability of fossil assemblages. Thanks to their great abundance and the high temporal resolution of their fossil record, conodont elements are ideal to address this issue. In this paper, we present the first quantitative study of a Carnian–Norian (Late Triassic) assemblage of closely related P₁ conodont elements. Using geometric morphometrics (landmarks, sliding landmarks, and elliptic Fourier analysis), we explore the main axes of phenotypic variation and relate them to classically used taxonomic characters. We show that some important taxonomic features follow laws of covariation, hence highlighting developmental constraints. Furthermore, the intraspecific variation within all considered species, either Carnian or Norian forms, is similarly restricted, emphasizing, for the first time in conodont P₁ elements, a common line of least resistance to evolution, which means that similar intrinsic (developmental) factors were acting on these taxa and likely biased the evolutionary trajectories of all these taxa in a similar way. Because the evolution between Carnian and Norian forms is known to have followed a trajectory that is significantly different from the line of least resistance, strong extrinsic pressures, such as environmental disturbances, were probably at play around the Carnian/Norian boundary to counteract the effects of these intrinsic, developmental constraints.

Conodonts are among the first vertebrates to have evolved mineralized tooth-like structures. Among these, the so-called P₁ elements are known to have been used to break down food and display a wide variety of morphologies. In particular, the repeated independent evolution of platform-like P₁ elements have been suggested to correspond to similar functional constraints linked to diet. To test this hypothesis of convergence, we measured size (as element length) for various conodont taxa and used it as a proxy for trophic level. We then tested the correlation between size and platform presence/absence, both on raw data and in a phylogenetic context. Retaining or excluding the platform traits from the character matrix has limited impact on the resulting phylogeny. Contrary to platform presence/absence, size shows no phylogenetic signal. Using the raw data, size and platform presence appear positively correlated. That correlation, however, is no longer significant if one corrects for the phylogeny. We conclude that platform presence cannot be explained by an enlargement of the conodont element, be it via a trophic-level change or developmental constraints. This suggests that conodonts as a whole, and in particular platform-bearing conodonts, were an ecologically diverse group and that the various known platform types are likely to reflect different, rather than convergent, ecological niches.

The coastal environment of the Changjiang delta has been influenced by recent anthropogenic activities such as dam construction and increased sewage and fertilizer inputs. Previous work examined the compositional shift of marine plankton to assess ecological impacts of these activities on marine ecosystems in the Changjiang discharge area. Here we used benthic marine ostracodes collected in the Changjiang estuary and the adjacent East China Sea in the 1980s and the 2010s, respectively, to investigate temporal changes of the benthic community and controlling factors for the benthic fauna. Our results revealed more shoreward distribution of some well-known offshore ostracode species in the 2010s compared with the 1980s and a relatively more important role for environmental processes (e.g., bottom-water temperature, bottom-water salinity, and eutrophic conditions of surface water) than spatial processes (e.g., the flow of ocean currents) in structuring ostracode compositions. The temporal changes in the ostracode community are likely attributable to the combined effects of reduced fresh water and sediment discharge and eutrophic conditions of the Changjiang due to the many dams constructed along the Changjiang and population expansion in the Changjiang Basin. Results of redundancy analysis and variation partitioning suggest that ocean currents facilitated environmental filtering of ostracode species such that they could disperse to preferred environmental conditions. These findings highlight the potential uses of marine microfossils to better understand ecological impacts on benthic ecosystems in vulnerable Asian mega-deltas and provide insights into the integration of metacommunity concepts in disentangling dynamics of marine benthic communities.

Approximately 50,000–11,000 years ago many species around the world became extinct or were extirpated at a continental scale. The causes of the late Pleistocene extinctions have been extensively debated and continue to be poorly understood. Several extinction models have been proposed, including two nutritionally based extinction models: the coevolutionary disequilibrium and mosaic-nutrient models. These models draw upon the individualistic response of plant species to climate change to present a plausible scenario in which nutritional stress is considered one of the primary causes for the late Pleistocene extinctions.

In this study, we tested predictions of the coevolutionary disequilibrium and mosaic-nutrient extinction models through the study of dental wear and enamel hypoplasia of Equus and Bison from various North American localities. The analysis of the dental wear (microwear and mesowear) of the samples yielded results that are consistent with predictions established for the coevolutionary disequilibrium model, but not for the mosaic-nutrient model. These ungulate species show statistically different dental wear patterns (suggesting dietary resource partitioning) during preglacial and full-glacial time intervals, but not during the postglacial in accordance with predictions of the coevolutionary disequilibrium model. In addition to changes in diet, these ungulates, specifically the equid species, show increased levels of enamel hypoplasia during the postglacial, indicating higher levels of systemic stress, a result that is consistent with the models tested and with other climate-based extinction models. The extent to which the increase in systemic stress was detrimental to equid populations remains to be further investigated, but suggests that environmental changes during the late Pleistocene significantly impacted North American equids.