Microbialite Accretion and Growth: Lessons from Shark Bay and the Bahamas.

Microbialites provide geological evidence of one of Earth's oldest ecosystems, potentially recording long-standing interactions between coevolving life and the environment. Here, we focus on microbialite accretion and growth and consider how environmental and microbial forces that characterize living ecosystems in Shark Bay and the Bahamas interact to form an initial microbialite architecture, which in turn establishes distinct evolutionary pathways. A conceptual three-dimensional model is developed for microbialite accretion that emphasizes the importance of a dynamic balance between extrinsic and intrinsic factors in determining the initial architecture. We then explore how early taphonomic and diagenetic processes modify the initial architecture, culminating in various styles of preservation in the rock record. The timing of lithification of microbial products is critical in determining growth patterns and preservation potential. Study results have shown that all microbialites are not created equal; the unique evolutionary history of an individual microbialite matters.

Assessing siliceous sinter matrices for long-term preservation of lipid biomarkers in opaline sinter deposits analogous to Mars in El Tatio (Chile).

Subaerial hydrothermal systems are of great interest for paleobiology and astrobiology as plausible candidate environments to support the origin of life on Earth that offer a unique and interrelated atmosphere-hydrosphere-lithosphere interface. They harbor extensive sinter deposits of high preservation potential that are promising targets in the search for traces of possible extraterrestrial life on Hesperian Mars. However, long-term quality preservation is paramount for recognizing biosignatures in old samples and there are still significant gaps in our understanding of the impact and extent of taphonomy processes on life fingerprints. Here, we propose a study based on lipid biomarkers -highly resistant cell-membrane components- to investigate the effects of silicification on their preservation in hydrothermal opaline sinter. We explore the lipid biomarkers profile in three sinter deposits of up to ~3000 years from El Tatio, one of the best Martian analogs on Earth. The lipid profile in local living biofilms is used as a fresh counterpart of the fossil biomarkers in the centuries-old sinter deposits to qualitatively assess the taphonomy effects of silicification on the lipid's preservation. Despite the geological alteration, the preserved lipids retained a depleted stable-carbon isotopic fingerprint characteristic of biological sources, result highly relevant for astrobiology. The data allowed us to estimate for the first time the degradation rate of lipid biomarkers in sinter deposits from El Tatio, and to assess the time preservation framework of opaline silica. Auxiliary techniques of higher taxonomic resolution (DNA sequencing and metaproteomics) helped in the reconstruction of the paleobiology. The lipids were the best-preserved biomolecules, whereas the detection of DNA and proteins dropped considerably from 5 cm depth. These findings provide new insights into taphonomy processes affecting life fingerprints in hydrothermal deposits and serves as a useful baseline for assessing the time window for recovering unambiguous signs of past life on Earth and beyond.

Soft-Tissue, Rare Earth Element, and Molecular Analyses of Dreadnoughtus schrani, an Exceptionally Complete Titanosaur from Argentina.

Evidence that organic material preserves in deep time (>1 Ma) has been reported using a wide variety of analytical techniques. However, the comprehensive geochemical data that could aid in building robust hypotheses for how soft-tissues persist over millions of years are lacking from most paleomolecular reports. Here, we analyze the molecular preservation and taphonomic history of the Dreadnougtus schrani holotype (MPM-PV 1156) at both macroscopic and microscopic levels. We review the stratigraphy, depositional setting, and physical taphonomy of the D. schrani skeletal assemblage, and extensively characterize the preservation and taphonomic history of the humerus at a micro-scale via: (1) histological analysis (structural integrity) and X-ray diffraction (exogenous mineral content); (2) laser ablation-inductively coupled plasma mass spectrometry (analyses of rare earth element content throughout cortex); (3) demineralization and optical microscopy (soft-tissue microstructures); (4) in situ and in-solution immunological assays (presence of endogenous protein). Our data show the D. schrani holotype preserves soft-tissue microstructures and remnants of endogenous bone protein. Further, it was exposed to LREE-enriched groundwaters and weakly-oxidizing conditions after burial, but experienced negligible further chemical alteration after early-diagenetic fossilization. These findings support previous hypotheses that fossils that display low trace element uptake are favorable targets for paleomolecular analyses.

Neoichnology of mygalomorph spiders: improving the recognition of spider burrows in the geological record

The female Mygalomorphae spiders are sedentary and long-lived organisms that spend most of their lives inside their burrows. Neoichnological studies provide relevant information that can help the recognition of these structures in paleosols. Body fossils of spiders are known since the Carboniferous and burrowing is a primitive behavior in Mygalomorphae spiders. However, trace fossils attributable to ground-dwelling spiders are still poorly documented in the geological record. In this work, we examine the burrows and burrowing behavior of Rachias intermedius Soares, 1944 (Araneae: Mygalomorphae: Nemesiidae) in its natural environment and discuss the characteristics that can be used as ichnotaxobases for recognition of fossil spider burrows. Three major architectures, straight shaft with a terminal ovoid chamber, J-shaped winding shaft with the terminal chamber, and Y-shaped with a terminal teardrop-shaped chamber, are described and compared to morphologically similar ichnogenera, like Capayanichnus, Loloichnus, Macanopsis, and Psilonichnus. Differences in burrow shape and architecture are linked with the spider's sex and ontogenetic stage. Pedipalps, chelicerae, and fangs are used for soil excavation, forming a variety of burrow wall ornaments represented by delicate sub-horizontal parallel ridges, irregular knobby micro-relief surface with soil structures attached to the wall, rounded pits, and millimeter-scale vertical striations along the burrow length. A thick inorganic clay lining covers the inner burrow wall, a feature that has not been described for spider burrows yet. These characteristics allow distinguishing spider burrows from burrows produced by other soil-dwelling arthropods. They should be used for spider burrow recognition in paleosols, mainly the millimeter-scale vertical striations that had not been documented before. The data discussed herein improve the knowledge about spider burrowing behavior and the mechanism that play the main role in preserving these burrows' features in the fossil record.

Neoichnology of mygalomorph spiders: Improving the recognition of spider burrows in the geological record

The female Mygalomorphae spiders are sedentary and long-lived organisms that spend most of their lives inside their burrows. Neoichnological studies provide relevant information that can help the recognition of these structures in paleosols. Body fossils of spiders are known since the Carboniferous and burrowing is a primitive behavior in Mygalomorphae spiders. However, trace fossils attributable to ground-dwelling spiders are still poorly documented in the geological record. In this work, we examine the burrows and burrowing behavior of Rachias intermedius Soares, 1944 (Araneae: Mygalomorphae: Nemesiidae) in its natural environment and discuss the characteristics that can be used as ichnotaxobases for recognition of fossil spider burrows. Three major architectures, straight shaft with a terminal ovoid chamber, J-shaped winding shaft with the terminal chamber, and Y-shaped with a terminal teardrop-shaped chamber, are described and compared to morphologically similar ichnogenera, like Capayanichnus, Loloichnus, Macanopsis, and Psilonichnus. Differences in burrow shape and architecture are linked with the spider's sex and ontogenetic stage. Pedipalps, chelicerae, and fangs are used for soil excavation, forming a variety of burrow wall ornaments represented by delicate sub-horizontal parallel ridges, irregular knobby micro-relief surface with soil structures attached to the wall, rounded pits, and millimeter-scale vertical striations along the burrow length. A thick inorganic clay lining covers the inner burrow wall, a feature that has not been described for spider burrows yet. These characteristics allow distinguishing spider burrows from burrows produced by other soil-dwelling arthropods. They should be used for spider burrow recognition in paleosols, mainly the millimeter-scale vertical striations that had not been documented before. The data discussed herein improve the knowledge about spider burrowing behavior and the mechanism that play the main role in preserving these burrows' features in the fossil record.

Description and ontogeny of Pattersoncypris minima sp. nov. (Crustacea: Ostracoda), Araripe Basin, Northeast Brazil.

Representatives of the Class Ostracoda are widely used as tools in applied paleoecological and biostratigraphical studies in all continents. In the Araripe Basin, located in the northeastern of Brazil, the Romualdo Formation is one of the most studied, not only for the preservation but also for the abundance of its fossils. The ostracod genus Pattersoncypris Bate, 1972 is well-represented in this formation and it is the most abundant, which reinforces the importance of its taxonomic study. In this work, Pattersoncypris minima sp. nov. is described for the Romualdo Formation as a contribution to the knowledge on Brazilian Cretaceous non-marine ostracods. Taphonomic aspects are also presented, considering the complete ontogenetic stages of the material.

Metodología de Binford para la categorización tafonómica de marcas de dientes animales en superficies óseas: una revisión con búsqueda sistemática / Binford methodology for taphonomic classification of animal tooth marks on bone surfaces: a systematic search review

La Tafonomía, concepto reconocido en paleontología y antropología, permite estimar tiempo y circunstancias de muerte mediante el estudio de condiciones post-mortem y factores relativos a la supervivencia de restos óseos. Entre las diferentes variables tafonómicas, Binford (1981) propuso una categorización de marcas de mordedura, hoy reconocido estándar para estos estudios. Sin embargo, su diseño original en inglés podría llevar a malinterpretaciones o informes erróneos por no poseer una traducción validada. Se realizó una revisión con búsqueda sistemática de artículos en español, sin límite temporal, que citaran a Binford ("Bones: Ancient Men and Modern Myths") en Google Scholar. Fueron incluidos aquellos que mencionaran esta metodología para categorizar marcas de mordedura como agente tafonómico. Se excluyeron tesis, libros, pósters y resúmenes de congresos. Se identificaron 349 documentos y se seleccionaron 83 según criterios. El 65,12 % refirió sólo a huellas de mordedura animal sin especificar categorías; el 26,51 % mostró traducciones libres o categorizaciones parciales, y el 8,43 % realizó categorizaciones sin traducción. La mayor cantidad de citas fueron realizadas por autores de Argentina y España (54,22 % y 24,10 % respectivamente, como única filiación). Las categorías con más traducciones libres fueron "pitting" y "puncture" (11 y 8 términos diferentes respectivamente). Si bien la categorización de Binford es citada profusamente en países de habla hispana para definir las marcas de mordedura animal en hueso, la ausencia de transculturización conlleva falta de consenso para la comunidad científica. Más allá de una traducción literal, la adaptación y estandarización de estos términos es necesaria para validar esta metodología.

Taphonomy, a concept recognized in paleontology and anthropology, allows the estimation of time and circumstances of death by studying post-mortem conditions and factors related to the survival of bone remains. Among the different taphonomic variables, Binford (1981) proposed a categorization of bite marks, now recognized as standard for these studies. However, its original design in English could lead to misinterpretations or erroneous reports for not having a validated translation. A scoping review was conducted for articles in Spanish, without a time limit, that cited Binford ("Bones: Ancient Men and Modern Myths") in Google Scholar. Those who mentioned this methodology to categorize bite marks as taphonomic agent were included. Theses, books, posters and conference proceedings were excluded. We identified 349 documents, and 83 were selected according to criteria. 65.12 % referred only to animal bite marks without specifying categories; 26.51 % showed free translations or partial categorizations, and 8.43 % made categorizations without translation. The largest number of citations were made by authors from Argentina and Spain (54.22 % and 24.10 % respectively, as the only affiliation). The categories with the most free translations were "pitting" and "puncture" (11 and 8 different terms respectively). While Binford's categorization is widely cited in Spanish-speaking countries to define animal bite marks in bone, the absence of transculturation implies a lack of consensus for the scientific community. Beyond a literal translation, the adaptation and standardization of these terms is necessary to validate this methodology.

African helminth infection out of Africa: Paleoparasitological and paleogenetic investigations in Pretos Novos cemetery, Rio de Janeiro, Brazil (1769-1830).

Pretos Novos cemetery (PNC), Rio de Janeiro, Brazil (1769-1830) was created exclusively to bury enslaved Africans who died upon arrival at the city or before being sold in the slave market. The PNC site may be unique in the Americas in allowing the study of African parasite infections acquired in Africa. We aimed to identify parasites infecting PNC individuals through paleoparasitological and paleogenetic analyses. The bodies had been dismembered, placed in mass graves, and burned, and most human remains collected from the site are highly fragmented and show extensive degradation. Sacrum and pelvic sediments were collected from five individuals along with seven samples of sediment from other areas of the body, as controls. Samples were submitted to three parasitological techniques and, in paleogenetic analysis, to four molecular targets. Larvae, mites, pollen grains, and structure suggestive of plants and fungus were observed, but we found no evidence of helminth infection. Ascaris sp. cytb sequence was recovered in one individual. We emphasize that, even with the extensive degradation of PNC human remains and the process of curation of samples, it was possible to recover helminth aDNA. The origin of PNC individuals confirms that these infections were brought to Brazil from western and central Africa during the colonial era.

Study of marsh foraminifera from the coastal plain of Buenos Aires (Argentina) and its ecological implications.

The objective of this work was determinate the diversity and abundance of benthic foraminifers from recent sediments of Channel 15, Samborombón Bay (35º57´-35º58´S and 57º25´-57º22´W). From this analysis, we identified 31 species grouped within 17 genera. The assemblages were composed mainly of hyaline and agglutinated forms characterized by Elphidium aff. poeyanum, Elphidium gunteri, Ammonia parkinsoniana, Arenoparella mexicana and Trochammina inflata, reflecting an environment of marsh or floodplain. The foraminifer's tests were generally well preserved, with morphologies that indicate predominantly epifauna and epifauna-infauna. The present work shows that despite having a general fauna characteristic of these environments, there are small microenvironments that are characterized by the state of preservation, diversity and abundance of the found specimens. In that context, three associations were recognized; A, dominated by Astrononion sp.1 that was registered in the central part of the channel; association B, characterized mainly by E. aff. poeyanum that was founded in the internal and external areas of the channel and association C, characterized by a considerable increase of mentioned agglutinated species (close to 50%) registered in the center of the channel. This study represents one of the first contributions on the distribution of foraminifera and their ecological characteristics from recent sediments in Samborombón Bay.

Scavenging Activity of Dermestes maculatus (Coleoptera: Dermestidae) on Burned Cadaveric Tissue.

The aim of this work was to study the effect that fire exposure in tissues may have on Dermestes maculatus DeGeer (Dermestidae: Dermestini) taphonomic behaviour under controlled conditions. Two different times of fire exposure (treatments) were evaluated, 15 min and 30 min, after spraying pig trotters with gasoil. The pig trotters were provided to adult hide beetles and both were maintained at 24 ± 0.1°C, 55.4% ± 2% relative humidity, and a 12:12 h day/night cycle. An unburned pig trotter was used as a control for each treatment. Observations were made and photographs were taken every 4-5 days for 4 months. Qualitative and quantitative analyses were performed. Dermestes maculatus was able to feed and reproduce on burned tissues. Beetles in adult and larvae stages produced different types of marks in several kinds of tissues such as integumental, connective, and muscular, in the controls and treatments. Apparently, 15 min of burning the pig trotters were not sufficient enough to cause differences in the taphonomic marks with respect to the control, but post mortem burning for 30 min may have implicated changes (lesser insect damage represented by lesser number and surface of both depressions and holes were found with respect to the control; greater surfaces and diameters were noticed compared to those found in the unburned pig trotters). The shape of the marks was equal in the controls and treatments.

Large mammal burrows in late Miocene calcic paleosols from central Argentina: paleoenvironment, taphonomy and producers.

Large cylindrical sediment-filled structures interpreted as mammal burrows occur within the loess-paleosol sequence of the late Miocene Cerro Azul Formation of central Argentina. A total of 115 burrow fills from three localities were measured. They are typically shallowly dipping, subcylindrical, unbranched structures with rounded ends and lacking enlargements. The horizontal diameter of the burrows range between 0.15 and 1.50 m, with most of the burrows in the interval of 0.39 to 0.98 m. Geometric morphometric analysis of transverse cross-sections support their distinct subcircular and elliptical (horizontally flattened) shapes. Burrow fills are typically laminated in the lower part and massive in the upper part. The laminated intervals reflect pulses of flowing water entering the abandoned burrow during moderate rains, whereas massive intervals reflect mass flow input of dense sediment-water mixtures during heavy rains that produced sheet floods. Approximately 1% of the burrows contained fragmentary, disarticulated and weathered mammal bones that were introduced in the open burrow by currents along with other sedimentary particles. Analysis of the tetrapod burrow fossil record suggests that Miocene burrows, including those studied herein, reflect a remarkable increase in the average size of the fossorial fauna. We conclude that large late Miocene mammals dug burrows essentially as a shelter against environmental extremes and to escape predation. The simple architecture of the burrows suggests that the producers essentially foraged aboveground. Several mammal groups acquired fossorial habits in response to cold and seasonally dry climatic conditions that prevailed during the late Miocene in southern South America. The considerable range of horizontal diameters of the studied burrows can be attributed to a variety of producers, including dasypodids, the notoungulate Paedotherium minor, Glyptodontidae and Proscelidodon sp.

A new giant titanosaur sheds light on body mass evolution among sauropod dinosaurs.

Titanosauria was the most diverse and successful lineage of sauropod dinosaurs. This clade had its major radiation during the middle Early Cretaceous and survived up to the end of that period. Among sauropods, this lineage has the most disparate values of body mass, including the smallest and largest sauropods known. Although recent findings have improved our knowledge on giant titanosaur anatomy, there are still many unknown aspects about their evolution, especially for the most gigantic forms and the evolution of body mass in this clade. Here we describe a new giant titanosaur, which represents the largest species described so far and one of the most complete titanosaurs. Its inclusion in an extended phylogenetic analysis and the optimization of body mass reveals the presence of an endemic clade of giant titanosaurs inhabited Patagonia between the Albian and the Santonian. This clade includes most of the giant species of titanosaurs and represents the major increase in body mass in the history of Titanosauria.

Study of infectious diseases in archaeological bone material - A dataset.

Bones of human and ground sloth remains were analyzed for presence of Trypanosoma cruzi by conventional PCR using primers TC, TC1 and TC2. Sequence results amplified a fragment with the same product size as the primers (300 and 350pb). Amplified PCR product was sequenced and analyzed on GenBank, using Blast. Although these sequences did not match with these parasites they showed high amplification with species of bacteria. This article presents the methodology used and the alignment of the sequences. The display of this dataset will allow further analysis of our results and discussion presented in the manuscript "Finding the unexpected: a critical view on molecular diagnosis of infectious diseases in archaeological samples" (Pucu et al. 2017) [1].

Early Devonian (Late Emsian) shark fin remains (Chondrichthyes) from the Paraná Basin, southern Brazil

ABSTRACT We report on the pioneering discovery of Devonian fish remains in the Paraná Basin, which represents the southernmost record of fishes from that period in mainland South America. The material comes from an outcrop at the lower portion of the São Domingos Formation, within Sequence C of the Paraná-Apucarana sub-basin in Tibagi, State of Paraná. Marine invertebrates are abundant in the same strata. The dark colored fish remains were collected in situ and represent natural moulds of partially articulated shark fin rays (radials). No elements such as teeth or prismatic cartilage have been preserved with the fins rays. This can be attributed to the dissolution of calcium-phosphatic minerals at the early stages of fossilization due to diagenetic processes possibly linked to strong negative taphonomic bias. This may have contributed to the fact that fishes remained elusive in the Devonian strata of this basin, despite substantial geological work done in the Paraná State in recent decades. In addition, the scarcity of fish fossils may be explained by the fact that the Devonian rock deposits in this basin originated in a vertebrate impoverished, cold marine environment of the Malvinokaffric Realm, as previously suspected.

Largest baleen whale mass mortality during strong El Niño event is likely related to harmful toxic algal bloom.

While large mass mortality events (MMEs) are well known for toothed whales, they have been rare in baleen whales due to their less gregarious behavior. Although in most cases the cause of mortality has not been conclusively identified, some baleen whale mortality events have been linked to bio-oceanographic conditions, such as harmful algal blooms (HABs). In Southern Chile, HABs can be triggered by the ocean-atmosphere phenomenon El Niño. The frequency of the strongest El Niño events is increasing due to climate change. In March 2015, by far the largest reported mass mortality of baleen whales took place in a gulf in Southern Chile. Here, we show that the synchronous death of at least 343, primarily sei whales can be attributed to HABs during a building El Niño. Although considered an oceanic species, the sei whales died while feeding near to shore in previously unknown large aggregations. This provides evidence of new feeding grounds for the species. The combination of older and newer remains of whales in the same area indicate that MMEs have occurred more than once in recent years. Large HABs and reports of marine mammal MMEs along the Northeast Pacific coast may indicate similar processes in both hemispheres. Increasing MMEs through HABs may become a serious concern in the conservation of endangered whale species.

Deciphering the preservation of fossil insects: a case study from the Crato Member, Early Cretaceous of Brazil.

Exceptionally well-preserved three-dimensional insects with fine details and even labile tissues are ubiquitous in the Crato Member Konservat Lagerstätte (northeastern Brazil). Here we investigate the preservational pathways which yielded such specimens. We employed high resolution techniques (EDXRF, SR-SXS, SEM, EDS, micro Raman, and PIXE) to understand their fossilisation on mineralogical and geochemical grounds. Pseudomorphs of framboidal pyrite, the dominant fossil microfabric, display size variation when comparing cuticle with inner areas or soft tissues, which we interpret as the result of the balance between ion diffusion rates and nucleation rates of pyrite through the originally decaying carcasses. Furthermore, the mineral fabrics are associated with structures that can be the remains of extracellular polymeric substances (EPS). Geochemical data also point to a concentration of Fe, Zn, and Cu in the fossils in comparison to the embedding rock. Therefore, we consider that biofilms of sulphate reducing bacteria (SRB) had a central role in insect decay and mineralisation. Therefore, we shed light on exceptional preservation of fossils by pyritisation in a Cretaceous limestone lacustrine palaeoenvironment.

New occurrences of fossilized feathers: systematics and taphonomy of the Santana Formation of the Araripe Basin (Cretaceous), NE, Brazil.

Here we describe three fossil feathers from the Early Cretaceous Santana Formation of the Araripe Basin, Brazil. Feathers are the most complex multiform vertebrate integuments; they perform different functions, occurring in both avian and non-avian dinosaurs. Despite their rarity, fossil feathers have been found across the world. Most of the Brazilian feather fossil record comes from the Santana Formation. This formation is composed of two members: Crato (lake) and Romualdo (lagoon); both of which are predominantly reduced deposits, precluding bottom dwelling organisms, resulting in exceptional preservation of the fossils. Despite arid and hot conditions during the Cretaceous, life teemed in the adjacency of this paleolake. Feathered non-avian dinosaurs have not yet been described from the Crato Member, even though there are suggestions of their presence in nearby basins. Our description of the three feathers from the Crato laminated limestone reveals that, despite the small sample size, they can be referred to coelurosaurian theropods. Moreover, based on comparisons with extant feather morphotypes they can be identified as one contour feather and two downy feathers. Despite their rareness and low taxonomic potential, fossilized feathers can offer insights about the paleobiology of its owners and the paleoecology of the Araripe Basin.

Postmortem Changes in Animal Carcasses and Estimation of the Postmortem Interval.

A thorough understanding of the physical and chemical changes that occur in the body after death is critical for accurate interpretation of gross and microscopic pathology at autopsy. Furthermore, knowledge of the postmortem processes and the factors that affect them will aid in the estimation of the postmortem interval (PMI). The estimation of the PMI is important in many human and animal death investigations. Despite many decades of research, accuracy in estimation of the time of death has not significantly improved, and no single method can be reliably used to accurately estimate the time of death. Great care should be taken when formulating such an estimate, for it is dependent on multiple circumstantial and environmental factors, and the accuracy and precision of the estimate decrease as the PMI increases. The majority of the research in the field has been conducted on human bodies, but many relevant conclusions may be drawn regarding the expected postmortem changes in animals and the estimation of the PMI. The veterinary pathologist must use great caution when attempting to extrapolate data and apply formulas designed for use in humans. Methods reviewed include gross changes, microscopic changes, temperature-based methods, postmortem chemistry, molecular methods, microbial assay, ocular changes, radiography, entomology, and others. Although only several of these methods are currently practical for use in the workup of cases, it is expected that future research will result in improved techniques with enhanced accuracy in the estimation of the PMI, which will benefit both human and veterinary forensic investigations.

Symbolic bones and interethnic violence in a frontier zone, northwest Mexico, ca. 500-900 C.E.

Although extensive deposits of disarticulated, commingled human bones are common in the prehispanic Northern Frontier of Mesoamerica, detailed bioarchaeological analyses of them are not. To our knowledge, this article provides the first such analysis of bone from a full residential-ceremonial complex and evaluates multiple hypotheses about its significance, concluding that the bones actively represented interethnic violence as well as other relationships among persons living and dead. Description of these practices is important to the discussion of multiethnic societies because the frontier was a context where urbanism and complexity were emerging and groups with the potential to form multiethnic societies were interacting, possibly in the same ways that groups did before the formation of larger multiethnic city-states in the core of Mesoamerica.

Repeated mass strandings of Miocene marine mammals from Atacama Region of Chile point to sudden death at sea.

Marine mammal mass strandings have occurred for millions of years, but their origins defy singular explanations. Beyond human causes, mass strandings have been attributed to herding behaviour, large-scale oceanographic fronts and harmful algal blooms (HABs). Because algal toxins cause organ failure in marine mammals, HABs are the most common mass stranding agent with broad geographical and widespread taxonomic impact. Toxin-mediated mortalities in marine food webs have the potential to occur over geological timescales, but direct evidence for their antiquity has been lacking. Here, we describe an unusually dense accumulation of fossil marine vertebrates from Cerro Ballena, a Late Miocene locality in Atacama Region of Chile, preserving over 40 skeletons of rorqual whales, sperm whales, seals, aquatic sloths, walrus-whales and predatory bony fish. Marine mammal skeletons are distributed in four discrete horizons at the site, representing a recurring accumulation mechanism. Taphonomic analysis points to strong spatial focusing with a rapid death mechanism at sea, before being buried on a barrier-protected supratidal flat. In modern settings, HABs are the only known natural cause for such repeated, multispecies accumulations. This proposed agent suggests that upwelling zones elsewhere in the world should preserve fossil marine vertebrate accumulations in similar modes and densities.