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Ecosystem structure—that is the species present, the functions they represent, and how those functions interact—is an important determinant of community stability. This in turn affects how ecosystems respond to natural and anthropogenic crises, and whether species or the ecological functions that they represent are able to persist. Here we use fossil data from museum collections, literature, and the Paleobiology Database to reconstruct trophic networks of Tethyan paleocommunities from the Anisian and Carnian (Triassic), Bathonian (Jurassic), and Aptian (Cretaceous) stages, and compare these to a previously reconstructed trophic network from a modern Jamaican reef community. We generated model food webs consistent with functional structure and taxon richnesses of communities, and compared distributions of guild level parameters among communities, to assess the effect of the Mesozoic Marine Revolution on ecosystem dynamics. We found that the trophic space of communities expanded from the Anisian to the Aptian, but this pattern was not monotonic. We also found that trophic position for a given guild was subject to variation depending on what other guilds were present in that stage. The Bathonian showed the lowest degree of trophic omnivory by top consumers among all Mesozoic networks, and was dominated by longer food chains. In contrast, the Aptian network displayed a greater degree of short food chains and trophic omnivory that we attribute to the presence of large predatory guilds, such as sharks and bony fish. Interestingly, the modern Jamaican community appeared to have a higher proportion of long chains, as was the case in the Bathonian. Overall, results indicate that trophic structure is highly dependent on the taxa and ecological functions present, primary production experienced by the community, and activity of top consumers. Results from this study point to a need to better understand trophic position when planning restoration activities because a community may be so altered by human activity that restoring a species or its interactions may no longer be possible, and alternatives must be considered to restore an important function. Further work may also focus on elucidating the precise roles of top consumers in moderating network structure and community stability. 

Abstract. The shells of marine invertebrates can serve as high-resolution records ofoceanographic and atmospheric change through time. In particular, oxygen andcarbon isotope analyses of nearshore marine calcifiers that grow byaccretion over their lifespans provide seasonal records of environmental andoceanographic conditions. Archaeological shell middens generated byIndigenous communities along the northwest coast of North America containshells harvested over multiple seasons for millennia. These shell middens,as well as analyses of archival and modern shells, have the potential toprovide multi-site, seasonal archives of nearshore conditions throughout theHolocene. A significant volume of oxygen and carbon isotope data fromarchaeological shells exist, yet they are separately published in archaeological,geochemical, and paleoceanographic journals and have not been comprehensivelyanalyzed to examine oceanographic change over time. Here, we compiled adatabase of previously published oxygen and carbon isotope data fromarchaeological, archival, and modern marine mollusks from the CaliforniaCurrent System (North American coast of the northeast Pacific, 32 to55∘ N). This database includes oxygen and carbon isotope data from 598modern, archaeological, and sub-fossil shells from 8880 years before present(BP) to the present, from which there are 4917 total δ13C and7366 total δ18O measurements. Shell dating and samplingstrategies vary among studies (1–345 samples per shell, mean 44.7 samplesper shell) and vary significantly by journal discipline. Data are fromvarious bivalves and gastropod species, with Mytilus spp. being the most commonlyanalyzed taxon. This novel database can be used to investigate changes innearshore sea surface conditions including warm–cool oscillations, heatwaves, and upwelling intensity, and it provides nearshore calcium carbonateδ13C and δ18O values that can be compared to thevast collections of offshore foraminiferal calcium carbonate δ13C and δ18O data from marine sediment cores. Byutilizing previously published geochemical data from midden and museumshells rather than sampling new specimens, future scientific research canreduce or omit the alteration or destruction of culturally valued specimensand sites. The dataset is publicly available through PANGAEA athttps://doi.org/10.1594/PANGAEA.941373 (Palmer et al.,2021). 

We compiled a database of previously published oxygen and carbon isotope data from archaeological, archival, and modern marine molluscs from the North American coast of the Northeast Pacific (32oN to 50oN). This database includes oxygen and carbon isotope data from over 550 modern, archaeological, and sub-fossil shells from 8880 years before present (BP) to the present, from which there are 4,845 total δ¹³C and 5,071 total δ¹⁸O measurements. Database includes the following parameters: paper of original publication, publication year, unique shell identification, unique subsample identification, sample number (given by original authors), subsample number (given by original author), number of subsamples per shell (added here), age in years before present, species, source (midden or modern), latitude, longitude, calculated sea surface temperature (only if published by original authors), tidal height, life mode, habitat, archaeological trinomial (when applicable), oxygen isotope value, and carbon isotope value. Shell dating and sampling strategies vary among studies (1-118 samples per shell) and vary significantly by journal discipline. Data are from various bivalves and gastropod species, with Mytilus spp. being the most commonly analyzed taxon. This novel database can be used to investigate changes in nearshore sea surface conditions including warm-cool oscillations, heat waves, and upwelling intensity, and provides nearshore calcite δ¹³C and δ¹⁸O values that can be compared to the vast collections of offshore foraminifera calcite δ¹³C and δ¹⁸O data from marine sediment cores. By utilizing previously published geochemical data from midden and museum shells rather than sampling new specimens, future scientific research can reduce or omit the alteration or destruction of culturally valued specimens and sites.