Death Assemblages Research Articles

Trace element taphonomy of the Hanson Ranch Edmontosaurus bonebed supports its origin via transportation of a mass death assemblage

Trace element taphonomy of the Hanson Ranch Edmontosaurus bonebed supports its origin via transportation of a mass death assemblage

Shell strength of Eucallista purpurata (Bivalvia) from life and death assemblages on sandy beaches of the Bonaerense coast, southwest Atlantic Argentina

ABSTRACT Mollusc shells are among the most abundant and well-preserved organisms in sediments worldwide, but their shells are usually subject to fragmentation due to exposure time in the TAZ, which compromises their preservation potential. The shell strength of valves from life and death assemblages from the sandy beaches of Santa Clara (37°50′49″S, 57°30′16″W) and Mar Chiquita (37°44′45″S, 57°25′1.5″W) on the Bonaerense coast, southwest Atlantic Argentina, was analysed to capture the effect of taphonomic processes over time and to determine how intrinsic properties and taphonomic variables influence their shell strength. To achieve this, the mechanical resistance profile of the bivalve Eucallista purpurata was assessed using point load and microindentation tests, and the mineralogical composition and organic matter content of the shell, as well as morphological variables, were measured. We concluded that, as expected, shells from life assemblages were more resistant to compression than those from death assemblages, but surprisingly, right valves were more resistant to compression than left valves in both Mar Chiquita and Santa Clara death assemblages. No differences were observed between broken and unbroken shells.

A sea of change: Tracing parasitic dynamics through the past millennia in the northern Adriatic, Italy

Abstract Our study uses data from Holocene core samples and modern death assemblages to understand how human-induced environmental change in the northern Adriatic Sea (Italy) may have affected parasite-host dynamics in the economically important bivalve Chamelea gallina. Thirty-one radiocarbon dates confirm temporal distinctness between the periods before and after the onset of significant human influence and confirm that trematode prevalence has decreased by an order of magnitude over the past ~2 k.y. The median number of parasite-induced pits per bivalve host and parasite aggregation has also decreased significantly, signaling a substantial decrease in the effective population size of digenean trematodes. Gaussian finite mixture modeling of pit size does not support the hypothesis of parasite extinction. Combined, these results indicate the (potentially ongoing) collapse of parasite-host interactions in C. gallina in concert with human influence on the Adriatic and its transition to an “urban sea.”

Ecological baselines in the Eastern Mediterranean Sea shifted long before the availability of observational time series.

Native biodiversity loss and invasions by nonindigenous species (NIS) have massively altered ecosystems worldwide, but trajectories of taxonomic and functional reorganization remain poorly understood due to the scarcity of long-term data. Where ecological time series are available, their temporal coverage is often shorter than the history of anthropogenic changes, posing the risk of drawing misleading conclusions on systems' current states and future development. Focusing on the Eastern Mediterranean Sea, a region affected by massive biological invasions and the largest climate change-driven collapse of native marine biodiversity ever documented, we followed the taxonomic and functional evolution of an emerging "novel ecosystem", using a unique dataset on shelled mollusks sampled in 2005-2022 on the Israeli shelf. To quantify the alteration of observed assemblages relative to historical times, we also analyzed decades- to centuries-old ecological baselines reconstructed from radiometrically dated death assemblages, time-averaged accumulations of shells on the seafloor that constitute natural archives of past community states. Against expectations, we found no major loss of native biodiversity in the past two decades, suggesting that its collapse had occurred even earlier than 2005. Instead, assemblage taxonomic and functional richness increased, reflecting the diversification of NIS whose trait structure was, and has remained, different from the native one. The comparison with the death assemblage, however, revealed that modern assemblages are taxonomically and functionally much impoverished compared to historical communities. This implies that NIS did not compensate for the functional loss of native taxa, and that even the most complete observational dataset available for the region represents a shifted baseline that does not reflect the actual magnitude of anthropogenic changes. While highlighting the great value of observational time series, our results call for the integration of multiple information sources on past ecosystem states to better understand patterns of biodiversity loss in the Anthropocene.

Modern coral range expansion off southeast Florida falls short of Late Holocene baseline

As thermal stress and disease outbreaks decimate coral reefs throughout the tropics, there is growing evidence that higher latitude marine environments may provide crucial refuges for many at-risk, temperature-sensitive coral species. However, our understanding of how coral populations expand into new areas and sustain themselves over time is constrained by the limited scope of modern observations. Here, we provide geological insights into coral range expansions by reconstructing the composition of a Late Holocene-aged subfossil coral death assemblage on the southeast Florida reef tract and comparing it to modern reefs throughout the region. Our findings show that the Late Holocene coral assemblages were dominated by now critically endangered Acropora species between ~3500 and 1800 years before present, mirroring classic zonation patterns characteristic of healthy pre-1970s Caribbean reefs. In contrast, the modern reefs off southeast Florida are becoming increasingly dominated by stress-tolerant species like Porites astreoides and Siderastrea siderea despite modest expansions of Acropora cervicornis over the past several decades. Our results suggest that ongoing anthropogenic stressors, not present during the Late Holocene, are likely limiting the ability of modern higher latitude reefs in Florida to function as long-term climate refugia.

Taxonomic, phylogenetic, and functional diversity of mollusk death assemblages in coral reef and seagrass sediments from two shallow gulfs in Western Cuban Archipelago.

Mollusk death assemblages are formed by shell remnants deposited in the surficial mixed layer of the seabed. Diversity patterns in tropical marine habitats still are understudied; therefore, we aimed to investigate the taxonomic, phylogenetic, and functional diversity of mollusk death assemblages at regional and local scales in coral reef sands and seagrass meadows. We collected sediment samples at 11 sites within two shallow gulfs in the Northwestern Caribbean Sea and Southeastern Gulf of Mexico. All the shells were counted and identified to species level and classified into biological traits. We identified 7113 individuals belonging to 393 species (290 gastropods, 94 bivalves, and nine scaphopods). Diversity and assemblage structure showed many similarities between gulfs given their geological and biogeographical commonalities. Reef sands had higher richness than seagrasses likely because of a more favorable balance productivity-disturbance. Reef sands were dominated by epifaunal herbivores likely feeding on microphytobenthos and bysally attached bivalves adapted to intense hydrodynamic regime. In seagrass meadows, suspension feeders dominated in exposed sites and chemosynthetic infaunal bivalves dominated where oxygen replenishment was limited. Time averaging of death assemblages was likely in the order of 100 years, with stronger effects in reef sands compared to seagrass meadows. Our research provides evidence of the high taxonomic, phylogenetic, and functional diversity of mollusk death assemblages in tropical coastal sediments as result of the influence of scale-related processes and habitat type. Our study highlights the convenience of including phylogenetic and functional traits, as well as dead shells, for a more complete assessment of mollusk biodiversity.

Taphofacies of coastal lakes based on mollusk death assemblages: a case study of Mirim Lake

Mirim Lake is the second-largest lacustrine body in Brazil, stretching for some 185 km and covering about 375 thousand hectares of water surface. This lake is part of the Patos-Mirim System, one of the world’s largest complexes of coastal lagoons, which is the result of the rise and fall of sea level over transgressive-regressive cycles triggered by glacio-eustasy during the Late Pleistocene and Holocene. Its characteristics and dynamics give it singular importance for studies on the genesis of shell accumulation in lagoons. This study aims to improve the knowledge of how the taphonomic signatures reflect the environmental characteristics and dynamics of Mirim Lake. Categorization of the arrangement and packing of death assemblages, as well as the orientation of shells, supported the biostratinomical approach. The taphonomic signatures included disarticulation, fragmentation, and corrosion of shells. Corrosion is the primary damage observed in the bioclasts, varying from a single loss of color to complete degradation. Differences in the characteristics of death assemblages observed in the dune fields and the lacustrine plain led to the recognition of two taphofacies. A more significant number of whole shells was observed in the dune field taphofacies, while sharp fragments and open-articulated bivalves in hydrodynamic unstable positions characterize the lacustrine plain taphofacies. The genesis of death assemblages and the taphonomic signatures of bioclasts were linked to three sedimentary dynamics attributed to the environment of Mirim Lake. Keywords: biostratinomy, taphonomic signatures, shell deposits, dune field, lacustrine plain.

Taphonomic significance of Aristotle's 'Wheel Paradox': an example with the cerithid gastropod Cerithium atratum (Born, 1778) from Conceição Lagoon, Santa Catarina State, Southern Brazil

In the book Mechanical Problems, attributed to Aristotle, the author relates the differential degrees of wearing and rounding of pebbles and shells moved by waves on the seashore to the variable radii and diameters of these particles. This phenomenon, which became known as Aristotle’s ‘Wheel Paradox,’ seems to explain the pattern of abrasion observed in shells of gastropods Cerithium atratum (Born) found in Conceição Lagoon, on the Island of Santa Catarina, Brazil. In situ observations show that the elongated turriform shells of C. atratum deposited at shallow (< 30 cm) depths on a sandy bottom with pavements of disarticulated valves of Anomalocardia flexuosa Gmelin are subject to bidirectional wave-generated currents under fairweather conditions. The 47 specimens analyzed exhibit a pattern of abrasion characterized by the loss of the shell wall, apparently proceeding from the wider last whorl toward the narrow apex, culminating in the exposure of the columella. Experiments designed to test whether this pattern could be related to the ‘Wheel Paradox’ principle show that under bidirectional flow, the shells describe circles on the vertical plane around the longitudinal axis (rolling) and a pendulum movement (revolution) on the horizontal plane centered on the apex. The whorls located farther from the apex have larger diameters and describe broader arc segments. Thus, they have higher tangential velocities and travel longer paths, which could explain why they are abraded earlier than the narrower whorls. Recognizing similar abrasion features in fossil shells can provide information on the local paleo-currents, hydrodynamics, and relative time-averaging of death assemblages and allow distinguishing between natural or anthropogenic modification in archaeological specimens. Although the effects vary between shells with different shapes, Aristotle’s ‘Wheel Paradox’ principle explains the general abrasion pattern among gastropods under certain hydrodynamic conditions. Keywords: Actualistic Taphonomy, Aktuopaläontologie, shell abrasion, shell orientation, biostratinomy, hydrodynamics

Putting the dead to work: A new method to assess the autochthony of marine Ostracoda death assemblages

Sedimentary and paleontological records can be powerful means of reconstructing ecological and physical environmental changes, by using a variety of records extending proxies to extend chronologies beyond the reach of instrumental or manual records. Ostracods are often used as paleoenvironmental proxies. Estimating the population age structure could be a useful tool for assessing the influence of some environmental parameters on death assemblages and for determining the autochthoneity or allochthoneity of the species that make up the thanatocoenosis. In the literature, several methods based on population age structure have been proposed to distinguish autochthonous and allochthonous components of life/death ostracod assemblages.The Adult:Juveniles ratio analysis of a rich and well-preserved ostracod assemblage from one site in the circalittoral zone of Pontine Archipelago, in the central-eastern Tyrrhenian Sea, is presented. The new Specific Population Stage Index (SPS) is proposed, built upon the measurements of all growth stages in the assemblage. The population structure using the new SPS Index on three different grain sizes is tested against a list of putative in situ and transported ostracod specimens. The analysis on the small grain size (maximum heigth >63 µm) proved the most effective in describing the putative life ostracod assemblage, whereas in the largest grain size (maximum height >180 µm) the young instars of the smaller species are under-represented. This includes species generally under-represented in the fossil record of the Mediterranean, probably due to sample processing bias and not to the rarity of the species itself. Assessing the autochthoneity of modern/fossil assemblages has great potential for acquiring baseline information on ecosystems before the onset of human activities, making this an extremely powerful approach essential to evaluating anthropogenic impacts. This approach seeks to identify the in situ life assemblages within an ostracod population to ensure that paleoenvironmental interpretations are not biased by transported allochthonous elements.

Taphonomic damage of molluscan shells in the Nile Delta under natural and anthropogenic sources of environmental variability

Environmental reconstruction can benefit from the interpretation of the postmortem history of shell remains. The molluscan death assemblages obtained from grab samples at forty-nine sites in the Manzala lagoon, the largest lagoon in the Nile Delta, were analyzed to infer the taphonomic alteration. The preservation of shells at each site has been semi-quantitatively ranked based on the taphonomic features formed by encrustation, bioerosion, abrasion, dissolution, precipitation, fragmentation, discoloration, and loss of sheen (low, moderate, high). A significant difference has been observed between sites of low and high environmental stress. Water depth and substrate type (hydrodynamics) correlate significantly to the percent number of altered shells. The southern parts of the lagoon, which are characterized by lower water energy and higher rates of sedimentation, are highly polluted by heavy metals (Cd, Pb, Zn) and organic pollutants. The southern parts receive much sediment from the agricultural drains, which increases burial of shelly material and decreases their time on the TAZ. The northern parts of the lagoon have slower rates of sedimentation, so that the molluscan shells remain longer at the sediment-water interface (Taphonomic Active zone; TAZ), where fragmentation is enhanced by winnowing under higher water-energy. The long residence in the TAZ also favored both bioerosion (Trypanites and Oichnus) and encrustation by bryozoan colonies, polychaetes, and oysters. Therefore, the taphonomic processes have the potential to cause severe damage and taphonomic loss of shell materials. Chemical dissolution and precipitation of shell remains may be related to acidic pore water. Moreover, high alkalinities in the southern polluted parts may also reduce the dissolution in contrast to the acidic water in the northern parts of the lagoon.

Temporal and spatial comparisons of ocean quahog (Arctica islandica) growth and lifespan on the mid-Atlantic continental shelf during inshore transgressions of their range from the Neoglacial through the twentieth century

Arctica islandica provide long-term records of climate change on the U.S. northeast continental shelf transgressing and regressing across the shelf numerous times synchronously with cold and warm climatic periods. The availability of A. islandica in the death assemblage over a wide geographic and temporal range makes this species well suited for documenting both spatial and temporal influences of climate change in the Mid-Atlantic through the correlation of growth rates in response to changing water conditions. This study focuses on comparing regional growth of subfossil ocean quahogs obtained offshore of the Delmarva Peninsula (Delmarva), and living during the cold periods since the Holocene Climate Optimum, with living A. islandica from offshore New Jersey, offshore Long Island, and Georges Bank. These populations exhibited different growth rates, with subfossil individuals from Delmarva death assemblages, representing previous Holocene cold periods, having growth rates as greater than or equal the growth rates of living individuals. Moreover, the growth rates for subfossil A. islandica from Delmarva that were alive from 1740 to 1940 were more rapid than contemporaneous individuals of the same age alive today. Higher growth rates for A. islandica from off Delmarva suggest that conditions supported near maximum growth during the cold periods after the Holocene Climate Optimum, possibly due to increased food supply in water shallower than that inhabited today. Unlike many bivalves, evidence for range recession of A. islandica as bottom water temperatures warm is found first in juvenile abundance, suggesting that recruitment ceases long before the population's demise: range recession in this species is a 100+ year process determined by the survivorship of the oldest and largest individuals. This study is the largest spatial and temporal growth comparison of A. islandica ever recorded and the first record of the process by which this species' inshore range regresses as temperatures rise.

A natural death assemblage of fishes from an early modern archeological context in Antwerp (Belgium)

AbstractAn unusual concentration of tens of thousands small fish remains discovered during rescue excavations in the town of Antwerp, Belgium, is described. The material was found in a small depression with no associated archeological material but could be dated to the first half of the 16th century based on its stratigraphic position. About 3500 freshwater fish were found in articulating position and it is shown that they died naturally during a single depositional event after an exceptional flood. The species spectrum and the reconstructed fish lengths make it possible to document the season when the catastrophic mortality occurred. This assemblage differs from the few assemblages of natural mortality reported in the literature, which are all of the attritional type.

Abandoned Quaternary gastropod shells: Incrustation, bioerosion, and fragmentation approaches

At the beach, death assemblages are constantly reworked by wind and waves. One of the various consequences of this shore dynamic is the constant burial and exhumation of the shells, making them inappropriate for epibionts. However, some gastropod shells collected in the death assemblages arranged on the foreshore of the coastal plain of south Brazil were hardly encrusted. Olivancillaria urceus corresponds to 48.8% of all encrusted taxa, suggesting that some shell species may play a more striking role than others as available bioclasts. Therefore, the research aims to discuss the taphonomic implications for epibionts and bioerosion in gastropod shells. Abandoned gastropod shells were collected on 27 sites along a 150 km coastal strip in southernmost Brazil. Epibionts and bioerosion traces were identified, and their frequency was calculated considering their abundance, which taxa they occurred in, and their settlement on the different parts of the shells. At least 13 of 21 taxa were colonized by epibionts, of which 97% were by bryozoans. Other epibionts recognized were serpulid tubes, bivalves, and balanids. Fifteen taxa were bioeroded, showing traces made by worms (cf. Caulostrepsis), bryozoans (cf. Pennatichnus), balanids (cf. Rogerella), bivalves (cf. Gastrochaenolites), and sponges (cf. Entobia). The results reached in this survey suggest that the bryozoans have an advantage over other epibionts at colonizing the gastropod shells.

Age variability and decadal time-averaging in oyster reef death assemblages

Abstract Using paleoecological data to inform resource management decisions is challenging without an understanding of the ages and degrees of time-averaging in molluscan death assemblage (DA) samples. We illustrate this challenge by documenting the spatial and stratigraphic variability in age and time-averaging of oyster reef DAs. By radiocarbon dating a total of 630 oyster shells from samples at two burial depths on 31 oyster reefs around Florida, southeastern United States, we found that (1) spatial and stratigraphic variability in DA sample ages and time-averaging is of similar magnitude, and (2) the shallow oyster reef DAs are among the youngest and highest-resolution molluscan DAs documented to date, with most having decadal-scale time-averaging estimates, and sometimes less. This information increases the potential utility of the DAs for habitat management because DA data can be placed in a more specific temporal context relative to real-time monitoring data. More broadly, the results highlight the potential to obtain decadal-scale resolution from oyster bioherms in the fossil record.

THE ROLE OF DRILLING PREDATION IN ISOLATED, NUTRIENT-POOR ECOSYSTEMS: FIRST INSIGHTS FROM RAPA NUI, POLYNESIA

Abstract As a biotic interaction, drilling predation is affected by the evolutionary histories of the predator and prey, as well as the environment. A unique location with distinctive evolutionary histories and environmental conditions is the remote island of Rapa Nui. For mollusks, an evolutionary history in relative isolation has led to high rates of endemism (35–40%), in an area that has some of the most nutrient-poor waters of the global ocean. Here, we use death assemblages collected in Rapa Nui to answer two main questions: (1) How does a pervasive interaction like drilling predation play out in an isolated, oligotrophic marine system? and (2) What role do the environment (exposed vs. sheltered sites) and species traits (feeding, mobility, life habit) play in ‘protecting' the prey? We predicted that predation would be low relative to other tropical and subtropical islands given the oligotrophic conditions and found that the average drilling frequency (DF) was 5.67% (n = 6122). We observed no significant differences in DF between feeding guilds, mobility types, or life habits. Sheltered sites dominated by the infaunal bivalve Ctena bella had higher predation. In terms of passive defenses for C. bella, larger body size was not an effective defense against drilling predators. We show that drilling predation in Rapa Nui is lower than in high-latitude regions, and it is dependent on how sheltered or exposed sites are. Historically and currently, Rapa Nui has been subject to multiple anthropogenic stressors, including over-extraction and tourism, making efforts to understand its endemic species and their interactions fundamental.

Shell injuries, repair and malformation in the early Cambrian mollusc Helcionella antiqua from Scania, Sweden

ABSTRACT Three cases of repaired injuries and malformation in specimens of the helcionelloid mollusc Helcionella antiqua (Kiær, 1917) from the lower Cambrian (Cambrian Series 2, Stage 4) Gislöv Formation of southern Sweden document some of the oldest known durophagous attacks on Palaeozoic molluscs. Two of the injuries are developed as clefts, of which one had a severe effect on the continued growth of the shell. The third example is a large embayment removing large portions of the supra-apical part of the shell. A similar repaired injury is known in the slightly older mollusc Marocella mira Geyer, 1986. from Antarctica and Australia. The morphology of the injuries and the hydrodynamically quiet depositional setting suggests that the shell damage was caused by failed predatory attacks. The location of the repaired injuries suggests that the attacks may have targeted the head region of the molluscs, thus supporting an endogastrically coiled orientation of the shell in Helcionella. Only three repaired injuries in 252 Helcionella specimens were found, giving a shell repair frequency of 1.2%. All three examples occur in the larger size classes. The size-frequency distribution (N = 182) is strongly right skewed, which could suggest high input of juvenile specimens into the assemblage. The assemblage is interpreted as a time averaged and mixed death assemblage, albeit with good correspondence with the living shelly assemblage, due to a relatively thin, homogenous unit that may suggest within-habitat time averaging.

MILLENIAL-SCALE TIME AVERAGING INFERRED BY DISCOLORED SHELLS IN BEACH DEATH ASSEMBLAGES

ABSTRACT Molluscan death assemblages occurring on present-day beaches frequently consist of secondary-colored shells, with yellow to brown and gray to black colors. It is hypothesized that this secondary coloration can be related to postmortem age and to conditions in the taphonomically active zone, altering shells to black and gray tones in reducing conditions, and then becoming yellowish or brownish in oxidizing settings. In this study, we assessed whether the variability in the degree of shell discoloration of two species of the infaunal bivalve Mactra collected in beach death assemblages from a temperate siliciclastic beach in Uruguay is a function of postmortem age, and whether this variability in discoloration can be linked to differences in their elemental composition, microstructure, and provenance. Although we did not detect any differences in mineralogy or elemental composition among shells differing in discoloration, we show that modern (younger than a century) beach shells are not secondary-colored, but have remained white, but some white shells are also old (millennial). In contrast, yellow and gray shells are consistently older than 1,000 years, indicating that this degree of discoloration requires millennial residence times in the taphonomically active zone and suggesting that discoloration can be used as an indicator of time averaging. Discolored shells are derived from subtidal death assemblages.

TAPHONOMIC INDICATORS OF DEAD OCEAN QUAHOG (ARCTICA ISLANDICA) SHELL AGE IN THE DEATH ASSEMBLAGE OF THE MID-ATLANTIC BIGHT CONTINENTAL SHELF

ABSTRACT Taphonomic indicators are often used to assess time-since-death of skeletal remains. These indicators frequently have limited accuracy, resulting in the reliance of other methodologies to age remains. Arctica islandica, commonly known as the ocean quahog, is a relatively widespread bivalve in the North Atlantic, with an extended lifespan that often exceeds two hundred years; hence, their shells are often studied to evaluate climate change over time. This report evaluates taphonomic age using 117 A. islandica shells collected from the Mid-Atlantic Bight offshore of the Delmarva Peninsula with radiocarbon dates extending from 60–4,400 cal years BP. These shells had varying degrees of taphonomic alteration produced by discoloration and degradation of periostracum. To determine if a relationship exists between taphonomic condition and time-since-death, radiocarbon ages were compared with the amount of remaining periostracum and type of discoloration. Old shells (individuals that died long ago) were discolored orange with no periostracum while younger shells (individuals that died more recently) had their original color, with some periostracum. Both the disappearance of periostracum and appearance of discoloration followed a logistic process, with 50% of shells devoid of periostracum and 50% discolored in about 1,000 years. The logistic form of long-term taphonomic processes degrading shell condition is first reported here, as are the longest time series for taphonomic processes in death assemblages within the Holocene record. This relationship can be utilized for triage when deciding what shells to age from time-averaged assemblages, permitting more efficient application of expensive methods of aging such as radiocarbon dating.

The quality of the fossil record across higher taxa: compositional fidelity of phyla and classes in benthic marine associations.

Although the fossil record preserves a wealth of historical data about past ecosystems, the current paradigm, which postulates that fossils provide faithful archives of ecological information, stems from research primarily focused on a single group of organisms known for their high fossilization potential: molluscs. Here, we quantify the fidelity of higher taxa (six phyla and 11 classes) by comparing live communities and sympatric dead remains (death assemblages) using comprehensive surveys of benthic marine invertebrates from coastal habitats in North Carolina (U.S.A). We found that although community composition differed between the two assemblages across phyla and classes, these differences were predictable with an overabundance of robust and more preservable groups. In addition, dead molluscs appear to be an excellent proxy for all taxa when tracking spatio-temporal patterns and shifts in community structure using a variety of ecological metrics, including measures of α, γ, and β diversity/evenness. This suggests that despite filters imposed by differential preservation of taxa and time-averaging, the fossil record is likely to be reliable with respect to relative comparisons of composition and diversity in shallow benthic marine paleocommunities. This is consistent with previous work indicating that shallow marine death assemblages can yield robust ecological estimates adequate for assessing the variability of ecosystems that existed under natural, pre-anthropogenic conditions.

Dead Shells Bring to Life Baselines for Conservation: Case Studies from The Bahamas, Southern California, and Wisconsin, USA

We are living in a time of rapid biodiversity loss. Numerous studies have shown that modern extinction rates are higher than pre-human background rates. However, these studies of biodiversity decline almost exclusively focus on large vertebrates. The scientific community lacks the sufficient long-term records necessary to track biodiversity loss for many invertebrate taxa. However, aquatic, benthic, and skeletonized invertebrates have the advantage of leaving a long-term record that can readily be sampled in conjunction with living communities because the mineralized skeletons accumulate in the very same sediments in which the animals that produced them once lived. These not-quite-fossil “death assemblages” contain an underutilized record for long-term monitoring. Here, we leverage three case studies of calcareous micro- and macro-faunal remains from three aquatic environments spanning two gradients: freshwater to fully marine and polluted to pristine and remediated. We compared the death assemblages to living assemblages in these case studies using Spearman’s rho and the Jaccard–Chao agreement to determine the degree of fidelity. Death assemblages of lacustrine, calcareous microcrustaceans (Ostracoda), collected from lakes in The Bahamas and Wisconsin, USA, faithfully record human impacts, both for degradation and remediation, as determined by a mismatch in the live–dead comparisons. Likewise, the live–dead comparisons of calcareous marine macrofauna (Bivalvia) from the southern California shelf also indicate human impact, including pollution and remediation. These case studies demonstrate how death assemblages can be used to gauge the changes in community assembly and population structures at local and regional scales, even in the absence of a systemic monitoring program. Conservation, restoration, and biomonitoring efforts would benefit from the inclusion of live–dead comparisons of taxa with easily fossilized, identifiable parts. Live–dead studies, such as those presented in these case studies, can be used as tools for recognizing targets and establishing baselines for conservation, tracking community responses to remediation efforts, and identifying local species extinctions.