Paleoecological Aspects Research Articles

Paleoenvironmental insights from a middle Pennsylvanian trace-fossil assemblage during the late Paleozoic ice age in southern Brazil

Trace fossils play a fundamental role as biotic records in glacial deposits associated with the Late Paleozoic Ice Age, especially in the upper units of the Itararé Group in the Paraná Basin, where they are widely described and studied. The absence of ichnological studies for the lower interval of the Itararé Group, represented by the Campo do Tenente Formation, creates a significant gap in understanding the interaction between organisms and glacial environment during the middle Pennsylvanian period in the Paraná Basin. Addressing this gap provides new insights into adaptive strategies and paleoecological aspects related to extreme climatic events. Through macro and microscopic descriptions, we documented for the first time the occurrence of eight ichnotaxa in a siltstone interval of the Campo do Tenente Formation: Dimorphicnus isp., Diplichnites gouldi, Helminthoidichnites tenuis, Hormosiroidea meandrica, Irichnus saltatorius, Merostomichnites narragansettensis, Monomorphicnus lineatus, and Umfolozia sinuosa. This trace fossil association, dominated by arthropod trackways and burrows of wormlike organisms, indicates the coexistence of the Mermia and Scoyenia ichnofacies. Combined with the sedimentological data, these results reflect marginal continental conditions of shallow and restricted environments, with occasional input of glacial freshwater. These contributions not only provide new insights into the understudied ichnological content of this interval of the Itararé Group but also offer important paleoenvironmental and paleoecological perspectives on the middle Pennsylvanian during the most significant glaciation of the Phanerozoic.

Ultrastructure of the Jurassic serpulid tubes-phylogenetic and paleoecological implications.

The ultrastructural diversity of the Middle and Late Jurassic serpulid tubes from the Polish Basin has been investigated. The inspection of 12 taxa representing the two major serpulid clades allowed for the identification of three ultrastructure types-irregularly oriented prismatic structure (IOP), spherulitic prismatic structure (SPHP), and simple prismatic structure (SP). Six of the studied species are single-layered and six species possess two distinct layers. Ultrastructural diversity corresponds to certain serpulid clades. The members of Filograninae have single-layered tube walls composed of possibly plesiomorphic, irregularly oriented prismatic structure (IOP). Two-layered tubes occur solely within the clade Serpulinae, where the external, denser layer is built of either the ordered spherulitic (SPHP) or simple prismatic microstructure (SP), and the internal layer is composed of irregularly oriented prismatic structure (IOP). Apart from phylogenetic signals provided by the tube ultrastructure, it can be used in analyzing paleoecological aspects of tube-dwelling polychaetes. Compared to the more primitive, irregularly oriented microstructures of Filograninae, the regularly oriented microstructures of Serpulinae need a higher level of biological control over biomineralization. The advent of the dense outer protective layer (DOL) in serpulids, as well as the general increase in ultrastructure diversity, was likely a result of the evolutionary importance of the tubes for serpulids. Such diversity of the tube ultrastructural fabrics allowed for maximizing functionality by utilizing a variety of morphogenetic programs. The biomineralization system of serpulids remains more complex compared to other tube-dwelling polychaetes. Physiologically more expensive tube formation allows for mechanical strengthening of the tube by building robust, strongly ornamented tubes and firm attachment to the substrate. Contrary to sabellids, which perform a fugitive strategy, an increased tube durability allows serpulids a competitive advantage over other encrusters.

Cranium of Sipalocyon externus (Metatheria, Sparassodonta) with remarks on the paleoneurology of hathliacynids and insights into the Early Miocene sparassodonts of Patagonia, Argentina

In this contribution, we investigate two sparassodonts from the Sarmiento Formation (Colhuehuapian Age; Early Miocene) recovered at the Patagonian locality of Sacanana, Chubut Province, Argentina. The first specimen (MACN-Pv CH1911), identified as Sipalocyon externus, is an almost complete cranium with upper dentition. The second specimen (MACN-Pv CH40), referred to Borhyaena macrodonta, consists of a fragmentary rostral portion of the face with associated m3–m4. The cranium of S. externus was studied through µCT-scanning to investigate its internal anatomy and infer paleoecological aspects of olfaction and hearing. In general, the endocranial anatomy and encephalization quotient are like those of other metatherians. We report the presence of an accessory transverse diploic sinus that has not previously been described in marsupials. Elements of the nasal cavity (e.g., turbinals, ossified nasal septum, cribriform plate) of S. externus exhibit features that are widespread among marsupials. Sense of olfaction, as evaluated from the cribriform plate and the 3D models of the olfactory bulbs, appears to have grossly resembled that of the domestic cat, a well-researched therian proxy. The dimensions of the tympanic membrane, as estimated from the preserved ectotympanic, suggest that the optimal hearing frequency of S. externus would have been similar to that of extant carnivorous marsupials. In sum, our study suggests that S. externus was a typical small-bodied (2–3 kg) hypercarnivorous metatherian that primarily relied on vision to hunt its prey, complemented by other sensory capabilities (olfaction and hearing), in a similar manner to small felids.

Origin and Early Evolution of Hydrocharitaceae and the Ancestral Role of Stratiotes.

The combined morphological features of Stratiotes (Hydrocharitaceae) pollen, observed with light and electron microscopy, make it unique among all angiosperm pollen types and easy to identify. Unfortunately, the plant is (and most likely was) insect-pollinated and produces relatively few pollen grains per flower, contributing to its apparent absence in the paleopalynological record. Here, we present fossil Stratiotes pollen from the Eocene of Germany (Europe) and Kenya (Africa), representing the first reliable pre-Pleistocene pollen records of this genus worldwide and the only fossils of this family discovered so far in Africa. The fossil Stratiotes pollen grains are described and compared to pollen from a single modern species, Stratiotes aloides L. The paleophytogeographic significance and paleoecological aspects of these findings are discussed in relation to the Hydrocharitaceae fossil records and molecular phylogeny, as well as the present-day distribution patterns of its modern genera.

Trace element concentrations as proxies for diagenetic alteration in the African archaeofaunal record: Implications for isotope analysis

Isotope ratio analyses of trace elements are applied to tooth enamel, ostrich eggshell, and other archaeological hard tissues to infer mobility and other aspects of hominin and animal paleoecology. It has been assumed that these highly mineralized tissues are resistant to diagenetic alteration, but this is seldom tested and some studies document diagenetic alteration over brief time spans. Here, we build on existing research on Maximum Threshold Concentrations (MTCs) to develop screening tools for diagenesis that can inform heavy isotopic analyses. The premise of the MTC approach is that archaeological tissues are likely contaminated and unsuitable for isotope ratio analysis when they exceed characteristic modern concentration ranges of trace elements. Furthermore, we propose a new metric called the Maximum Threshold Ratio (MTR) of 85Rb/88Sr or whole element Rb/Sr, which can be measured simultaneously with 87Sr/86Sr during laser ablation (LA) MC-ICP-MS or applied during post hoc screening of specimens. We analyzed 56 enamel samples from modern Kenyan mammals and 34 modern ostrich eggshells from South Africa, Namibia, and the United States by solution ICP-MS, as well as a subset of shells using LA-MC-ICP-MS. Our results indicate that thresholds are consistent across taxa at a single location, but likely vary across locations. Therefore, MTCs and MTRs need to be tissue and locality specific, but not necessarily taxon-specific. Other important differences are observed between the inner and outer surfaces of the eggshells and between LA and solution ICP-MS. This exploratory study provides guidelines for building reference thresholds to screen enamel and eggshell for diagenesis potentially impacting biogenic isotope ratios.

Coexistence of Oligocene toothed and baleen-assisted mysticetes in the northwestern Pacific

Oligocene mysticetes display an unparalleled diversity and morphological disparity in the evolutionary history of Mysticeti. However, their paleoecological aspects, such as the patterns of coexistence of different morphotypes, remain poorly explored. Here we describe an aetiocetid (toothed mysticete) from the Jinnobaru Formation (lower upper Oligocene, about 28 million years ago) of Umashima Island, Kitakyushu, Japan. Our description of a toothed mysticete from the Oligocene of Umashima exemplifies the coexistence of toothed and baleen-assisted mysticetes in the northwestern Pacific. Hopefully, new finds of Oligocene mysticetes will lead to a well-sampled dataset for analyzing this and other related paleoecological traits to understand the demise of “archaic” Oligocene mysticetes and the subsequent rise of the modern-looking baleen-bearing whales in Miocene times.

A new toothless pterosaur from the Early Cretaceous Jehol Biota with comments on the Chaoyangopteridae

The Chaoyangopteridae is a clade of azhdarchoid pterosaurs that stands out in China, particularly in the Jehol Biota, as a Cretaceous group of medium-sized and high-crested pterosaurs. Herein, we describe a new species, Meilifeilong youhao gen. et sp. nov., based on two specimens, one tentatively referred to this taxon. This new species represents the most complete and well-preserved chaoyangopterid recorded to date. Along with a set of characters (low premaxillary crest above the nasoantorbital fenestra extending posteriorly, posterior premaxillary process arched and curving posteriorly, a slightly convex sternal articulation surface of coracoid, and a fibular shaft close to proximal articulation strongly arched posteriorly), this species also provides new information both on the unknown palatal region of this clade, and on the rarely preserved (in place) ear portion with stapes. Moreover, M. youhao sheds light on paleoecological aspects, while also giving new information about the taxonomic diversity of this peculiar group of Jiufotang pterosaurs.

Silurian Diploporitans as Substrata:

The middle Silurian Massie Formation of southeastern Indiana contains a rich stalked echinoderm fauna, of which diploporitan “cystoids” are a significant component. A small number of diploporitan thecae are encrusted by the dendritic radicular attachment structures of the monobathrid camerate crinoid Eucalyptocrinites. Recently, several encrusted specimens of the diploporitan Holocystites scutellatus were described from the Massie Formation of the Napoleon quarry (Ripley County) that are unusual in that the encrusting holdfasts display pronounced asymmetry with respect to radicle development. Due to settlement near the margin of the thecae, long, well-developed radicles are present on the side of the attachment structure where they could extend over the entire lateral surface of the theca, and short, poorly developed radicles are present on the side facing the margin of the theca. The anomalous nature of this attachment structure morphology is herein highlighted by comparison to more typical Eucalyptocrinites-encrusted diploporitan thecae from the same locality and stratigraphic interval. These display a much more radially symmetrical configuration of radicles due to a more central settlement position on the thecal lateral surface. Several additional morphological and paleoecological aspects of crinoid encrustation of diploporitans are described and illustrated, including an apparently bilaterally symmetrical radicle growth pattern and a rare occurrence of an encrusted Paulicystis.

Paleoecological aspects of the Southwestern portion of the Araripe Basin (Ipubi Formation, lower Cretaceous), Northeastern Brazil

The Araripe Basin in northeastern Brazil is known worldwide for the exceptionality of its fossils. Its Cretaceous sedimentary record (Santana Group), represented from the base to the top by the Barbalha, Crato, Ipubi, and Romualdo formations, has excellent paleontological content. The Ipubi Formation, previously described as devoid of fossils, has shown good paleontological potential in recent studies. This work presents the paleoecological aspects present in the shales immediately superimposed on the gypsum layer of this formation, aiming to recognize and identify changes over time that influenced the distribution and diversity. The taxonomic, morphometric, quantitative, and qualitative analyses presented here indicate a biota a with high probability of discovering of new taxa. The parameters of diversity, species richness, and evenness indicate a little diversified but abundant biota. Smaller total-length fish sizes were observed compared to specimens of the same species described for the other formations of the Santana Group. These data were visualized with box plots. This condition is possibly associated with variations in salinity and temperature, resulting in a high degree of environmental stress that limits the growth of organisms and could have caused mortality events in several species.

Potential pollinators and paleoecological aspects of Eocene Ludwigia (Onagraceae) from Eckfeld, Germany

Paleogene flower-insect interactions and paleo-pollination processes are, in general, poorly understood and fossil evidence for such floral and faunal interactions are rarely reported. To shed light on angiosperm flower-insect interactions, we investigated several hundred fossil flowers and insects from the middle Eocene Fossil Lagerstätte of Eckfeld, Germany. During our work, we discovered a unique fossil Ludwigia flower (bud) with in situ pollen. The ecological preferences (climate, biome, habitat, etc.) of extant Ludwigia and the paleoecological configurations of the fossil plant assemblage support the taxonomic affiliation of the flower bud and an Eocene presence of Ludwigia in the vicinity of the former Lake Eckfeld. Today’s Ludwigia are mostly pollinated by Hymenoptera (bees). Therefore, we screened all currently known hymenopteran fossils from Eckfeld but found no Ludwigia pollen adhering to any of the specimens. On the contrary, we discovered Ludwigia pollen adhering to two different groups of Coleoptera (beetles). Our study suggests that during the Eocene of Europe, Ludwigia flowers were visited and probably pollinated by beetles and over time there was a shift in primary flower visitors/pollinators, from beetles to bees, sometime during the late Paleogene to Neogene.

Taphonomy, paleoecology and chronology of a late Quaternary tank (natural reservoir) deposit from the Brazilian Intertropical Region

The Brazilian Intertropical Region (BIR) abounds with tank (natural reservoir) deposits, a primary source of late Quaternary megafauna remains. However, most of these important deposits lack comprehensive taphonomic analysis. In this study, we conducted a taphonomic analysis of Quaternary vertebrates from a specific tank deposit located at Fazenda Charco (Poço Redondo, Sergipe State), Brazil. We aimed to: (i) reconstruct the biostratinomic processes that influenced the deposition of vertebrate remains; (ii) interpret some fossildiagenetic features; and (iii) compare our findings with other tank deposits to highlight the main preservation patterns among these deposits. Additionally, we discuss the paleoenvironmental and paleoecological aspects of this vertebrate assemblage. The paleocommunity comprised eighteen individuals, including megamammals and reptiles, with a total of eleven taxa identified in the tank deposit, indicating a highly diversified assemblage. Eremotherium laurillardi and Toxodontinae indeterminate accounted for more than one individual each. Despite the high diversity, taphonomic features suggest the dominance of E. laurillardi in the assemblage and the preservation of bones transported from moderately distant locations to the tank deposit. Furthermore, Fazenda Charco exhibits a complex tank deposit characterized by various taphonomic signatures, including abrasion, trample marks, weathering, fragmentation, staining colors and bioerosions. These findings indicate that the bones underwent reworking events and were exposed to environmental conditions before their final burial. By integrating our taphonomic results with available isotopic, pollen, and speleothem data, we infer that a dry forest, resembling the extant Caatinga biome, prevailed during the past 42,000 years. This suggests a predominantly arid environment with a mosaic of phytophysiognomy dominated by herbs and shrubs. The further integration of taphonomic and paleoecological analyses of fossils from tank deposits will contribute to a more refined reconstruction of the paleoenvironmental scenario and the ecological interactions that occurred during the late Quaternary.

A microvertebrate assemblage from the Adamantina Formation (Bauru Group, Upper Cretaceous) in São Paulo State, Brazil

The Adamantina Formation is the most extensive and taxonomically rich unit within the Bauru Group (Upper Cretaceous). This unit is considered one of the most complete fossil records of vertebrate continental communities during the Cretaceous Gondwanan landmasses. However, this important fossil record is mainly based on large and articulated remains, and few works attempted to better understand its microvertebrate assemblages. This study reports a diverse microvertebrate assemblage from a new site in the Adamantina Formation in São Paulo, Brazil. The geological context in which the fossils were collected was analyzed, and all fossils were recovered in channel facies of the outcrop. The fossil assemblage described here includes elements commonly found in previous works in the Adamantina Formation, such as lepisosteiforms, amiids, dinosaurs, and crocodyliforms. But in this assemblage were also identified elements rarely recovered from Adamantina Formation, such as siluriforms, anurans, and a putative mammal. Furthermore, the taxa identified here indicate a humid environment, contributing to recognizing a diversity of paleoenvironments in the Adamantina Formation and highlighting the importance of microvertebrate assemblages to understanding the paleoecological aspects of fossil communities.

Колониальная Leptophragmidae (Porifera, Hexactinellida) из нижнего сантона Поволжья

Study of the skeletal morphology of a new representative of the Leptophragmidae family, with no suboscula in its structure, provides support for the earlierspecified regularities in generation of Hexactinellida modular forms. Good preservationstate of a majorcolony has made it possible to specify the aspects of paleoecology and taphonomy in the later representatives of the Middle Coniacian – Early Santonian succession of siliceous sponges.

Distribution and Tooth Morphoguilds of Mosasaurids (Squamata) of the Campanian Western Interior Seaway with Implications for Controls on Mosasaur Paleobiogeography

The Western Interior Seaway (WIS) of North America is well known for its mosasaurid squamate diversity, particularly during the Campanian of the Late Cretaceous. This diversity has historically been examined at a fine scale, with many studies investigating the faunal composition of specific assemblages. Mosasaur tooth morphology has also been extensively studied, with tooth characteristics commonly being used as phylogenetic characters. However, many studies examining mosasaur communities and tooth morphology have been focused on broader spatiotemporal or phylogenetic scales. This study investigates the spatial distribution and morphological disparity of Campanian WIS mosasaurs in relation to potentially limiting biotic and environmental factors as well as the importance of online, collections-based resources for paleontological data. 110 Campanian mosasaur occurrences recorded in online databases were categorized according to taxonomic rank and plotted on paleogeographic maps. Mosasaurines constitute approximately 45% of the total mosasaurid species within the seaway; russellosaurines are less common and halisaurines are scarce. Tooth morphoguilds indicative of feeding adaptations were also assigned to each taxon based on preexisting literature and novel measurements of tooth dimensions. The majority of Campanian WIS mosasaurids are found to belong to the 'Cut' guild. Mosasaurines display the highest amount of tooth disparity, with some guilds having a more spatially limited distribution potentially related to a combination of biotic and environmental factors. Many aspects of mosasaur paleoecology and evolution are still poorly understood; further additions to and expansions of online paleontological databases will help create a more complete picture of mosasaur paleobiogeography within the WIS.

Nuevo registro de Puma concolor Linnaeus, 1771 (Carnivora, Felidae) para el Pleistoceno Tardío de Uruguay y su importancia paleoecológica

Felidae entered South America from North America during the Ensenadan Stage/Age (Early to Middle Pleistocene). For Uruguay their fossil record is scarce but informative, although mostly correspond to large felids (Smilodon, Panthera onca). In this work describes fossil remain of a skull and a mandible assigned, based on morphology and statistical analysis, to Puma concolor. These materials were unearthed from Late Pleistocene sediments (Sopas Formation) from northern Uruguay. Based on these remains some paleobiological and
 paleoecological aspects are discussed. This specimen had a body mass of about 45 kg, with the potential capacity to hunt animals over 200 kg, which is in agreement with previous reports for other fossil puma remains. During Late Pleistocene, in the current territory of Uruguay, Puma concolor would have shared ecological niche with other large carnivore such as sabre-tooth cats (Smilodon populator, S. fatalis), the jaguar Panthera onca, the canid Protocyon troglodytes, and short-faced bears Arctotherium, feeding upon medium-sized animals in diverse environment.

A glimpse of a Gondwanan postglacial fossil forest

The rooted nature of vegetation allows for individual plants or entire communities to be buried in life position under exceptional geological conditions, thereby preserving their ecology and spatial distribution in the stratigraphic record. Upright lycopsids are not uncommon within paleoequatorial Carboniferous coal-bearing deposits, but they are rare in mid- to high-paleolatitude Gondwana, where they have only been found in lower Permian strata. An exceptionally well preserved in situ Brasilodendron-like lycopsid forest is described from an early Permian postglacial paleolandscape of western Gondwana (Paraná Basin, Brazil). The forest depicted here is unique given its extratropical location, as well as the exceptional preservation of abundant specimens and their morphological and paleoecological aspects. Over 150 lycopsid stumps, with a clustered spatial organization, were mapped. The host succession, overlying glaciomarine diamictites by a few tens of meters, captures the terminal deglaciation in the Paraná Basin, and shows that these forests could establish dense communities on poorly developed soils in postglacial times. Sedimentological data suggest that the death and burial of these lycopsids in life position were caused by crevasse splay progradation over the colonized interdistributary bay areas as a consequence of a major river flooding event.

Taxonomy, biostratigraphic and paleoecological aspects of non-marine ostracod fauna from the Jinju Formation (Albian) of the Gyeongsang Basin, South Korea

A total of seven species belonging to six genera of cypridoidean ostracods were recovered from three sections (Jeongchon, Hotan, and Tapri) of the Albian Jinju Formation from the Gyeongsang Basin, South Korea: Scabriculocypris yanbianensis, Cypridea khandae sp. nov., Cypridea samesi, Mongolocypris kohi, Lycopterocypris? cf. celsa, Candona sp., and Djungarica sp. Based on its morphology, C. khandae sp. nov. is considered to be the first record of the Cypridea alta-group in Korea. Although many species are endemic to the Jinju Formation, the occurrence of Scabriculocypris yanbianensis indicates that this fauna was linked with the contemporaneous fauna of the Tongfosi Formation of the Yanji Basin, northeast China. Based on previous studies and newly collected specimens, the taphonomic features of the sections indicate the presence of two distinct thanatocoenoses: a low-energy autochthonous thanatocoenosis (Jeongchon and Tapri sections) and a slightly higher energy thanatocoenosis (Hotan section). Finally, the absence of cytheroidean and darwinuloidean ostracods could be explained by the presence of unstable lake/temporal waterbodies and their low competitiveness.

First fossil record in Tambería formation (Neogene) in Bolsón de Fiambalá, Catamarca province, Argentina: Palaeoenvironmental inferences through Leguminosae woods

The aim of this study is to report the first fossil wood record of Leguminosae in miocene sediments from Tambería Formation outcropping in the center-west of Catamarca province, Argentina. This Leguminosae specimen was found on levels of multi-colored sandstones that alternated with dark brown pelites and gray conglomerates. It is characterized by the presence of: semi-ring porous wood with vestured ornamented pits, helicoidal thickenings on the vessel walls, paratracheal parenchyma, homogeneous and multiseriate rays, all of which justify its assignment to Gleditsioxylon Müller-Stoll and Mädel. Six species are known and distributed in: Argentina, the United States, China and Japan in Miocene sediments coetaneous with sediments from Tambería Formation. The fossil wood specimen documented in this study is assigned to Gleditsioxylon fiambalense nov. sp. taking into account the combination of its anatomical features. Vulnerability and mesomorphy indices reveal its subtropical environmental condition which is not only typical of Gleditsia amorphoides, the current species, but also coincides with the palaeoenvironmental inferences derived from sedimentological research. This first paleontological record promises interesting analyses to understand the paleobiological and paleoecological aspects of the Tambería Formation and adds another new evidence to show the diversity of the neogene Leguminosae lignofloras of northern Argentina.

Paleoenvironmental contexts of South American Cretaceous sauropod tracks

The ichnological Cretaceous sauropod record of South America is analyzed for the first time in relation with skeletal and paleoenvironmental data. The updated database includes 39 tracksites and 71 valid species (53 titanosaurs and 18 non-titanosaurs) from Colombia, Ecuador, Peru, Chile, Brazil and Argentina. The track and bone records analyzed evidence a relationship with continental environments, specifically with fluvial ones. This is observed in all Sauropoda records, indicating an ecological association of the Cretaceous sauropods for these environments. In addition, the paleogeographic reconstruction integrating these records does not evidence any correlation between the distribution of sauropods and the latitudinal range. During the late Campanian–Maastrichtian interval, when the Atlantic transgression event was established, the titanosaur record started to show a singular panorama. The tracksites are preserved not only in continental paleoenvironments but also in marginal-marine ones, being the only last records of titanosaurs associated with that environment in South America. Both the paleoecological aspects based on sauropod Cretaceous record and the paleoenvironmental data collected in this work support the hypothesis that these tracksites were used by titanosaurs as ‘transit areas’ to move among the environments they inhabited.

Gregariousness in the giant sloth Lestodon (Xenarthra): multi-proxy approach of a bonebed from the Last Maximum Glacial of Argentine Pampas

Megamammals constituted an important component in the Pleistocene faunal communities of South America. Paleobiological and paleoecological studies involving different megamammal taxa have increased significantly in the last years, but there are still several poorly-known issues of its life history. In this work, we analyze an assemblage composed of 13 individuals of different ontogenetic stages, and possibly different sex, belonging to the giant ground sloth Lestodon armatus (Xenarthra, Folivora), recovered from Playa del Barco site (Pampean Region, Argentina). A dating of 19,849 years Cal BP allows assigning this assemblage to a period of the MIS (Marine Isotope Stage) 2 related to the end of the Last Glacial Maximum. Based on multiple lines of research (e.g. taphonomy, paleopathology, osteohistology, isotopy), we interpret the origin of the assemblage and diverse paleobiological and paleoecological aspects (e.g. social behavior, ontogenetic changes, sexual dimorphism, diseases, resource and habitat use, trophic relationships) of L. armatus. Evidence suggests that the assemblage was formed by a local single event of catastrophic mortality, which affected different members of a social group. This record represents the first accurate evidence of gregariousness for this ground sloth, providing new data on a poorly-known behavior among extinct Folivora.