Assemblage Zones Research Articles

New constraints on the timing and nature of metamorphism in the eastern Meguma terrane, Nova Scotia, Canada

The Meguma terrane in Nova Scotia consists mainly of Cambrian to Ordovician metasedimentary rocks intruded by abundant peraluminous granite, granodiorite and minor diorite-tonalite-plutons between ca. 380 Ma and 360 Ma. The metasedimentary rocks were variably metamorphosed to greenschist- to amphibolite- facies during the early Devonian. In the eastern Meguma terrane, the regional M1 chlorite- and biotite- zone assemblages are overprinted by two types of high-temperature low-pressure M2 metamorphism. In contact aureoles around plutons the regional M1 assemblages are overprinted by cordierite- and andalusite-bearing M2 contact metamorphic assemblages, and away from plutons chlorite-bearing, (or biotite-bearing) regional M1 assemblages are overprinted by staurolite-, garnet-, and/or cordierite-bearing M2 regional assemblages that represent metamorphism driven by a regional elevated thermal gradient. The interpreted metamorphic conditions in the eastern Meguma terrane range from ca. 480 – 550 °C and pressures below 2.5 kbar up to 550 – 650 °C with pressures between 4 and 5 kbar. Based on a new garnet Lu-Hf age, regional metamorphism was ongoing at ca. 372 Ma, hence broadly coeval with pluton emplacement. Metamorphism and pluton emplacement took place in a largely transpressional tectonic setting during the collision of the Meguma terrane with Avalonia. After pluton emplacement, peak metamorphic assemblages were variably overprinted with retrograde chlorite and sericite M3 assemblages while deformation continued. Regional structures were transposed into a composite transposition foliation as a result of continued motion along the terrane-bounding Minas Fault Zone and associated ductile shear zones.

Ancient Species of the Genus <i>Dvinosaurus</i> (Temnospondyli, Dvinosauria) from the Permian Sundyr Tetrapod Assemblage of Eastern Europe

From the Sundyr-1 reference locality of the Sundyr faunal assemblage of Eastern Europe (Upper Permian, Upper Severodvinian Substage, Suchonica vladimiri Assemblage Zone), the oldest species of the genus Dvinosaurus Amalitzky, 1921 Dvinosaurus gubini sp. nov. The diagnostic criterions for the new species are its smaller size compared to other dvinosaurs, the narrowest skull, short and wide zygomatic bone, parasphenoid body with a more wide base of the cultriform process and a well ossified basisphenoid, a strongly curved dentary with a well-defined symphyseal crest extending downward from the labial side of the symphysis and, in a several cases, with a single symphyseal canine, a large angle (135–152°) between the clavicular plate and the dorsal process of the clavicle, narrow areas of the interclavicle for insertion of the clavicles, narrow entepicondylus of the humerus. The size, narrowness of the skull, the presence of a single symphyseal canine, and hypocentrum structure bring together a new form closer to the basal Dvinosauria, in particular, with ancestral Trimerorhachidae.

First record of rhynchosaurs (Archosauromorpha: Rhynchosauria: Hyperodapedontinae) from the early Late Triassic Santacruzodon Assemblage Zone of the Santa Maria Supersequence, Brazil.

Rhynchosauria is a group of extinct, exclusively Triassic, terrestrial, and herbivorous archosauromorphs, characterized by a peculiar maxillary-mandibular apparatus. They reached global distribution during the Carnian, with the Hyperodapedontinae clade. The rhynchosaurian record from South America is included in the Ladinian-?earliest Carnian Dinodontosaurus Assemblage Zone (Pinheiros-Chiniquá Sequence, Brazil) and Tarjadia Assemblage Zone (Chañares Formation, Argentina), and for strictly Carnian Hyperodapedon Assemblage Zone (Lower Candelária Sequence, Brazil) and Ischigualasto Formation (Argentina). Here, we present the first record of Hyperodapedontinae from the Brazilian Early Carnian Santacruzodon Assemblage Zone (Santa Cruz Sequence). The most diagnostic elements belong to a nearly complete left pes, which presents a combination of hyperodapedontine traits. The presence of a second individual of cf. Hyperodapedontinae is based on a fragmentary, isolated left metatarsal IV. An isolated fragment of premaxilla could belong to the second specimen (based on preservation mode) or to a third individual. This new report fills a gap within the South American rhynchosaurian distribution, strengthening biostratigraphic correlation with other regions from Gondwana (i.e., Madagascar), where similar and coeval faunas are known. The inclusion of these specimens in a phylogenetic dataset resulted in low resolution results, due to missing data because postcranial characters for rhynchosaurs are still poorly explored.

Stratigraphy, Microfacies, Paleoenvironments and Paleoecology of Asmari Formation (Oligocene - Miocene), Zagros Basin, Western Iran

The present work involves the study of the Asmari Formation from the viewpoint of the stratigraphy, microfacies, and depositional environment. The Khorramabad area, Zagros basin, west Iran, has been investigated for the first time. For this purpose, seventy-three samples were taken from the Shurab section. Eight microfacies have been identified in the Asmari Formation: Sandy wackestone (MF1), Peloidal Mudstone (MF2), Bioclastic milina Wackestone-Packstone (MF3), Bioclastic imperforate foraminifera Wackestone-Packstone (MF4), Coral boundstone (MF5), Bioclastic packstone - grainstone (MF6), Bioclastic imperforate foraminifera grainstone (MF7), Mudstone microfacies (MF8). Two benthic foraminiferal biozones were recognized, which are Archaias asparagus- Archaias Henson Assemblage Zone, which is restricted to Chattian, and the Eulepidina- Miogypsina Assemblage Zone, which is restricted to Aquitanian. The biostratigraphic correlation with other studies in and outside Iran, executed across the studied section, enveloping the Chattian to Aquitanian, divulges a progression in the biozone thickness, indicating a migration of the depositional center towards the northwest of the basin. The Asmari Formation is deposited from an outer ramp and open shelf lagoon and is defined as a tropical environment.

Biostratigraphic significance of a new record of Protuberum cabralense, a bizarre traversodontid cynodont from the Middle‑Late Triassic of Southern Brazil

ABSTRACT Traversodontid cynodonts are one of the most abundant and diverse groups of tetrapods in the Triassic assemblages of Brazil. These cynodonts are distributed across four Brazilian Assemblage Zones (AZ), ranging from the late Ladinian to the early Norian. The most taxonomically diverse record comes from the Dinodontosaurus AZ, which has so far yielded at least six traversodontid genera. Among these taxa, Protuberum cabralense represents one of the most bizarre forms. This cynodont is characterised by the presence of enlarged and rounded protuberances along the dorsal surface of the ribs, the vertebral neural spines and dorsal portion of the iliac blades. These structures have been suggested to serve as a defensive mechanism or related to burrowing/digging habits. We report the first occurrence of P. cabralense at the Linha Várzea 1 site, located in the municipality of Paraíso do Sul, Brazil. This site is considered late Ladinian to early Carnian in age. The new material consists of five rib fragments, which possess the characteristic protuberances on their dorsal surface. A biostratigraphic investigation demonstrates the absence of P. cabralense in fossiliferous sites that yielded the cynodonts Luangwa. This observation contributes to the discussion regarding a potential subdivision within the Dinodontosaurus AZ.

A new cynodont concentration from the Brazilian Triassic: Insights into the genesis and paleobiological significance of a highly productive fossil site

Bonebeds, concentrations of fossilized vertebrates, provide valuable insights into paleoecological, biostratigraphic, and macroevolutionary contexts, though they are often influenced by taphonomic processes. Brazilian Triassic rocks are notable for such fossil assemblages. Among these, the Várzea do Agudo site is remarkable for its abundance of fossils of the traversodontidae cynodont Exaeretodon riograndensis. Initial studies suggested that biogenic factors, especially scavenging and predation, were key to the formation of these bonebeds. This study aims to describe a new fossiliferous concentration from this site, analyzing the taphonomic and biostratinomic processes involved in its genesis. Our findings indicate that multiple factors, including biogenic actions and environmental conditions such as floodplain dynamics, contributed to the accumulation and preservation of the abundant bonebeds. This integrative approach enhances our understanding of the paleoecology of Exaeretodon riograndensis, which was probably a gregarious animal, and the environmental context of Hyperodapedon Assemblage Zone.

DASYCLADALES (GREEN ALGAE) AND SOME BENTHIC FORAMINIFERA FROM THE UPPER CRETACEOUS ILAM FORMATION (LATE CONIACIAN–SATONIAN), SW IRAN (ONSHORE AND OFFSHORE)

New data (onshore, offshore) on the Upper Cretaceous Ilam Formation of southwestern Iran are provided concerning the common presence of dasycladalean green algae (families Triploporellaceae, Polyphysaceae) that have so far been treated mostly in open nomenclature. The assemblage consists of the five taxa Salpingoporella ubaiydhi Radoičić, 1979, Dissocladella ondulata (Raineri, 1922), Trinocladus tripolitanus Raineri, 1922, Clypeina cf. dusanbrstinai Radoičić, 1997, and gen. et sp. indet. The taxa typically prevail in wackestones-packstones but exhibit different distributional patterns. While S. ubaiydhi and T. tripolitanus, rarely associated with D. ondulata, form a characteristic assemblage in a distal infralittoral facies (more diverse assemblage; zone no. 31 of Wynd, 1965), C. cf. dusanbrstinai occurs in a proximal infralittoral facies associated with miliolids among also complex forms (rhapydioninids) (assemblage zone no. 30 of Wynd, 1965). It is concluded that the two assemblage zones refer to different palaeoenvironments, instead of different ages (‘lower’ and ‘upper’). Based on benthic foraminifera, the main part of the Ilam Formation can be ascribed to the Santonian. For the lower part, a late Coniacian age is suggested implied indirectly by the comparably long vertical range of the rotaliid Orbitokathina vonderschmitti Hottinger, 1966 of the studied core. This would be in conformity with the K 150 Arabian Plate K 150 sequence boundary referring to a late Turonian?–early Coniacian hiatus. From a palaeobiogeographic perspective, T. tripolitanus is a cosmopolitan species, S. ubaiydhi is restricted to the area of the former Arabian Plate (subsurface Iraq, Saudi Arabia and Egypt), while C. dusanbrstinai has been recorded only from Serbia (type-locality). In addition to the algae, the stratigraphic discussion includes the occurrence of the benthic foraminifera Reticulinella? kaeveri Cherchi, Radoičić & Schroeder, 1989 and Orbitoides mid-orientalis (Eames & Smout, 1956) in the Ilam Formation.

Biostratigraphy of the early Cambrian small skeletal fossils from the Niuniuzhai section of southern Sichuan in China

The Niuniuzhai section in Leibo County, southern Sichuan, China, is part of the western carbonate platform of the Yangtze Block. The section is crucial for correlating early Cambrian successions in the eastern Yunnan and southern Sichuan areas. A comprehensive biostratigraphic analysis of small skeletal fossils (SSFs) from this section identifies three SSF assemblages: (1) the oldest from an interval of uncertain age affinity in the middle and upper Dahai Member of the Zhujiaqing Formation; (2) the Watsonella crosbyi Assemblage Zone (Zone Ⅲ) in the upper Dahai Member of the Zhujiaqing Formation; and (3) the Sinosachites flabelliformis–Tannuolina zhangwentangi Assemblage Zone (Zone IV) in the middle Shiyantou Formation. These SSF assemblage zones in the Niuniuzhai section correlate well with sections from eastern Yunnan and southern Sichuan, indicating a coherent Terreneuvian succession on the the Yangtze Platform and in other continents.

A new “silesaurid” from the oldest dinosauromorph-bearing beds of South America provides insights into the early evolution of bird-line archosaurs

Investigations regarding the early evolutionary history of bird-line archosaurs have undergone significant advancements in recent years. However, controversies remain, especially regarding the phylogenetic position of “silesaurids”. Whereas some hypotheses place these archosaurs as the sister-group to dinosaurs, others suggest that “silesaurids” are early ornithischian dinosaurs. Despite the phylogenetic disputes, “silesaurids” are a crucial group for comprehending the origins and early evolution of dinosaurs. In the present study, a new “silesaurid” from the Middle-Upper Triassic of Southern Brazil is described. Gondwanax paraisensis gen. et sp. nov. comes from the Dinodontosaurus Assemblage Zone of the Santa Maria Formation (Ladinian-Carnian boundary), representing one of the oldest “silesaurids” worldwide. Furthermore, Gondwanax paraisensis gen. et sp. nov is the oldest “silesaurid” with three sacral vertebrae, a feature usually observed in more derived forms. In addition, distinct from any other Triassic Pan-Aves, the new taxon bears an incipient fourth trochanter of the femur. This unique combination of features indicates a high diversity of locomotor strategies among early pan-avians. The co-occurrence of Gondwanax paraisensis gen. et sp. nov. and Gamatavus antiquus in the same Assemblage Zone represents the oldest evidence of sympatry among “silesaurids” in South America. Indeed, the unique combination of sacral and hindlimb features may suggest distinct behaviors for these species, potentially leading to niche differentiation within the same ecosystems.

Impact of the 2011 Tohoku Earthquake on the species diversity of rocky intertidal sessile assemblages.

The impacts of large-scale disturbance events on the species diversity of rocky intertidal sessile assemblages across multiple spatial scales are not well understood. To evaluate the influence of the 2011 Tohoku Earthquake on alpha and beta diversities of rocky intertidal sessile assemblages, we surveyed sessile assemblages in the mid-shore zone from 2011 to 2019 and compared the data with those collected from 2003 to 2010 before the earthquake at the same region. The census was conducted across 22 study plots on five rocky shores along 30 km of the Sanriku Coast of Japan, which is located 150-160 km north-northwest of the earthquake epicenter. Alpha diversity was measured with three Hill numbers (H 0, H 1, and H 2), which represent the number of equally common species that would exist in a community with the same diversity as the sampled community, with higher values of the subscript indicating more weight placed on abundant species. Beta diversity was measured with two metrics (BD total at two spatial scales). Values were compared between the post-earthquake period (2011-2019) and the pre-earthquake period (2003-2010). The results show that the Tohoku Earthquake significantly altered the species diversity of intertidal sessile assemblages across multiple spatial scales. All diversity metrics obtained at multiple spatial scales (i.e., alpha diversities: H 0, H 1, and H 2; beta diversities: BD total at the shore and regional scales) decreased immediately after the earthquake and then increased in subsequent years. At 2 years after the earthquake, H 0 recovered to within the range of pre-earthquake values and H 1 and H 2 became significantly higher than pre-earthquake values. Most metrics of alpha and beta diversities recovered to pre-earthquake levels after several years, but regional BD total remained low for a longer period.

Correlation and stratigraphic implications of the lowermost Cambrian small shelly fossils from new sites of South China

Early Cambrian small shelly fossils (SSFs) represent some of the earliest biomineralized examples of metazoans and are often extremely abundant and diverse, so can be useful for regional and intercontinental correlation in pre-trilobitic carbonate or phosphorite deposits. New SSF assemblages chemically extracted from the Cambrian Yangjiagou Member carbonates in the Fucheng area, southern Shaanxi Province, China. The SSFs include anabaritids, protoconodonts, hyolitheminths, maikhanellids, Quadrapyrgites , Archaeooides , Olivooides and Siphogonuchites . The recovered SSFs represent two previously identified SSF assemblage zones: the Anabarites trisulcatus – Protohertzina anabarica assemblage zone and the succeeding Paragloborilus subglobosa – Purella squamulosa assemblage zone. The early Cambrian fossil assemblage zones described from this locality are correlated on a regional scale across the Yangtze Platform from eastern Yunnan, the Three Gorge region of western Hubei, northern Sichuan, the Ningqiang and Xixiang regions of southern Shaanxi and the Nemakit–Daldynian Stages of Siberia. The results reveal that the Yangjiagou Member is provisionally equivalent to the Zhongyicun Member of Yunnan, the Yanjiahe Formation of Hubei, the Maidiping Formation of Sichuan and the Kuanchuanpu Formation of Shaanxi. This paper offers new evidence and fossil data for the location of the Precambrian–Cambrian boundary in the Micangshan area of South China.

Eocene larger benthic Foraminifera from the Jahrum Formation (Kalbibak Section, Boldaji Region) in High Zagros, Iran: an approach on paleontology and biostratigraphy

The Jahrum Formation is a major Eocene carbonate deposit of High Zagros in the west of Iran. It consists of thin bedded to thick massive limestone, accumulated on a shallow marine platform within the Neo-Tethys Ocean realm. Fifty-five surface samples were collected throughout a 215 m section in the Kalbibak area (Boldaji region, Chahar Mahal Bakhtiari province). The stratigraphic distribution of benthic foraminifers allows characterizing five foraminiferal biozones, which are in the following order: Alveolina aff. schwageri Taxon Range Zone, A. decastroi Taxon Range Zone, A. aff. frumentiformis–A. cf. stercusmuris Interval Zone, A. aff. stercusmuris–A. aff. fusiformis Interval Zone and Nummulites–Alveolina Assemblage Zone. The benthic foraminiferal associations in the studied area are similar to those recorded in Tethys realms and enable us to correlate the Jahrum Formation with the early to middle Eocene. Keywords: benthic foraminifers, biostratigraphy, Jahrum Formation, Kalbibak section, West Iran.

Seasonal patterns of juvenile fish assemblages in the surf zones of tropical sandy beaches along Gaolong Bay, Hainan Island, China

AbstractAimSurf zones are crucial nursery habitats for the early life stages of fish species associated with typical coastal ecosystems. However, little is known about the temporal patterns and drivers of fish assemblages in tropical surf zones. This study aimed to assess the (1) main changes in fish community structure throughout 1 year, (2) seasonal dynamic patterns in fish assemblages, and (3) key factors influencing fish assemblages in the tropical surf zones.LocationGaolong Bay, Wenchang City, Hainan Island, China.MethodsFish sampling was conducted monthly from June 2021 to May 2022 using a beach seine net. Fish species were identified using both morphological and molecular analyses. Kruskal–Wallis test, analysis of similarity, non‐metric multidimensional scaling analysis, and similarity percentage analysis were used to investigate the temporal fish assemblage patterns. Generalised additive models and canonical correspondence analysis were used to assess how environmental variables influence fish assemblages.ResultsWe identified 83 fish species, which were grouped into three ecotypes based on their primary habitat: coral reef‐seagrass‐associated species (CS) (35), mangrove‐estuarine‐associated species (ME) (30), and common coastal‐estuarine‐associated species (CE) (18). Most captured individuals were juveniles, and fish abundance and diversity were highest in May. Most CS species were abundant between March and May. ME and most CE species were dominant from June to August, and Mugilidae (CE) was abundant between October and February. Furthermore, surf fish assemblages were substantially influenced by tidal level, water temperature, conductivity, pH, turbidity, and dissolved oxygen.ConclusionsJuvenile fish were abundant in May and fish species with three ecotypes alternate in the surf zones throughout the year. Counter to much current thinking, March maybe the spawn peak of most fish species in the studied area, and we suggest that the fishing ban period could start from March instead of May in the inshore areas of Hainan Island.

New archosauromorph remains provide data on the age of a unique Late Triassic assemblage from southern Brazil

The Santa Maria Supersequence, an important stratigraphic unit in the Paraná Basin, yielded a diverse range of Triassic tetrapod assemblages, providing valuable insights into the evolutionary history of southwestern Pangea. This study focuses on the Candelária Sequence of the Santa Maria Supersequence, which includes the Hyperodapedon Assemblage Zone (AZ) and the Riograndia AZ. The Hyperodapedon AZ is characterized by the presence of Hyperodapedon rhynchosaurs alongside a diverse array of other taxa, including dinosaurs, pseudosuchians, and cynodonts. In contrast, the Riograndia AZ preserves mostly small cynodonts, lepidosauromorphs, and sauropodomorph dinosaurs. Whereas biostratigraphic correlations between several localities of the Candelária Sequence have been firmly established, certain sites, like the Niemeyer complex in the Agudo municipality of southern Brazil, present challenges because of their unusual assemblage composition, which result in ambiguous depositional ages. Despite yielding thousands of fossil specimens, the Niemeyer complex lacks index fossils typical of the known Brazilian AZs, making reliable correlation with other sites challenging. This study presents and describes new archosauromorph specimens discovered at the upper portion of the Niemeyer complex. The new materials include a rhynchosaur, a saurischian dinosaur, and a possible silesaurid, which represent the first record of these groups for the site. A phylogenetic analysis of the rhynchosaur material provides insights into its taxonomic affinities, offering valuable data for biostratigraphic comparisons. The new data reinforces an age (early Norian?) that is younger than that of the typical outcrops assigned to the Hyperodapedon AZ. Furthermore, these new specimens contribute to the unique assemblage of the Niemeyer complex, shedding light on its significance within the context of the Santa Maria Supersequence and the broader landscape of southern Brazil during the Triassic Period.

Cross-boundary effects of human impacts on animal assemblages in the coastal zone

Human impacts on ecosystems often transcend ecosystem boundaries and environmental realms, complicating ecosystem assessment, conservation, and management. Whether and how different impacts affect ecosystems in distinct but adjacent domains remains untested in many settings, and is rarely tested concurrently at the same spatial scales. In this study, we quantified the effects of coastal urbanisation on the structure of terrestrial coastal vertebrate assemblages (including birds, reptiles and mammals using baited trail cameras) and marine surf zone fish assemblages (using baited underwater videography) at 100 sites along 50 km of beach in eastern Australia. Sites occurred along a gradient of intensities of urban land conversion in the hind dunes. While the effects of urbanisation on the species sampled were pervasive across both ecosystems, the area of urbanised land mattered more for the coastal vertebrates observed, while proximity to urbanised land was more important for the surf zone fish observed. Here, fewer individuals and species of coastal vertebrates were found at sites with a greater extent of urbanised land within 5 km. Conversely, fish assemblages were more diverse in the surf zones abutting urban areas and more abundant at sites approximately 150 m from urbanised land. The spatial properties of these landscapes, including proximity to headlands for coastal vertebrates and reefs for fish, modified the effects of urbanisation. Our findings suggest that urbanisation can have ecologically nuanced effects that are detectable across the land-sea boundary, and stress the importance of landscape context when assessing and conserving animal assemblages in and around coastal cities.

Environmental factors influencing the abundance and spatial distribution of modern dinoflagellate cysts in Izmir Bay (Eastern Mediterranean)

We analyzed surface sediments from 12 stations located in Izmir Bay to determine the impact of anthropogenic pollution on dinoflagellate cysts. Forty-three dinoflagellate cyst taxa and two cyst assemblage zones were identified. Zone 1 is characterized by the dominance of cysts of Gymnodinium nolleri, Selenopemphix nephroides, and Operculodinium centrocarpum from the oligotrophic part of Izmir Bay. Zone 2 is in the highly productive inner part of the bay and is characterized by the high abundances of Lingulodinium machaerophorum, Spiniferites ramosus, cysts of Scrippsiella spp., cysts of Polykrikos spp. and Quinquecuspis concreta. We used multivariate statistical analysis (DCA and CCA) on dinoflagellate cysts and environmental variables to support the identification of Zones 1 and 2. Our analyses also revealed that summer and winter chlorophyll-a as well as elevated nitrate and nitrite concentrations are significant parameters in controlling dinoflagellate cyst distribution in Izmir Bay.

Palynostratigraphy and Paleoenvironment of Afikpo Well_3, Afikpo Syncline, Nigeria

The Afikpo Syncline constitutes the western segment of the southern part of the Benue Trough. The syncline orients in the northeast-southwest direction and unconformably overlies the pre-Santonian strata of the Benue Trough. This study investigates the sediments of Afikpo Well_3, drilled within the syncline, identifies its different palynozones, and interprets their paleoenvironments of deposition. Forty-two ditch-cutting samples recovered from the well at a 150 ft interval consist of mudstones, calcareous mudstones, carbonaceous shales, and calcareous shales. These samples were subjected to palynological analysis following the conventional acid maceration technique. A total of 637 palynomorph counts were recovered. These comprise 316 pollen grains, which make up 49.61%; 129 spores, which make up 20.25%; 9 fungi spores, which make up 1.41%; 17 microforaminifera wall linings, which make up 2.67%; and 166 dinoflagellate cysts, which make up 26.06%. Two palynozones were identified within the well. These include zone AF-01 (Monocolpites marginatus assemblage zone), which ranges from depths of 1500–1320 ft and is Campanian in age; and zone AF-2 (Dinogymnium sp. assemblage zone), which extends from depths of 50 ft–1320 ft and dates back to the Maastrichtian period. Based on the predominance of palmae pollen, together with the subordinate occurrence of dinoflagellate cysts, and the fair representations of spores (Cyathidite minor), the environment of deposition of the sediments ranges from a nearshore brackish water to a shallow marine environment. The shallow environment is further confirmed by the frequent occurrence of microforaminifera wall lining and the dominance of the peridinoid dinoflagellate cysts over the gonyaulacinoids.

A new small-sized predatory pseudosuchian archosaur from the Middle-Late Triassic of Southern Brazil

Before the rise of dinosaurs and pterosaurs, pseudosuchians—reptiles from the crocodilian lineage—dominated the Triassic land ecosystems. This lineage diversified into several less inclusive clades, resulting in a wide ecomorphological diversity during the Middle and Late Triassic. Some giant pseudosuchians occupied the top of the trophic webs, while others developed extensive bony armor as a defense mechanism, which later evolved as a convergence in the avemetatarsalian lineage. On the other hand, there were groups like the Gracilisuchidae, which was composed of carnivorous forms with lightweight build and less than 1 m in length. The fossil record of gracilisuchids is geographically restricted to China and Argentina, with one ambiguous record from Brazil. In the present study, the first unambiguous gracilisuchid from Brazil is described. Parvosuchus aurelioi gen. et sp. nov. comes from the Dinodontosaurus Assemblage Zone of the Santa Maria Formation, which is associated with the Ladinian-Carnian boundary. Composed of a complete cranium, vertebrae, pelvic girdle and hindlimbs, the new species nests with Gracilisuchus stipanicicorum and Maehary bonapartei in a phylogenetic analysis. Its discovery fills a taxonomic gap in Brazilian pseudosuchian fauna and reveals the smallest known member of this clade from the Dinodontosaurus Assemblage Zone, highlighting the diversity of pseudosuchians during the moment that preceded the dawn of dinosaurs.

Overview on the tetrapods from Faixa Nova-Cerrito I site (Hyperodapedon Assemblage Zone), Upper Triassic of southernmost Brazil

ABSTRACT The Faixa Nova-Cerrito I site, in the municipality of Santa Maria, Rio Grande do Sul, Brazil, displays rock layers from the Hyperodapedon Assemblage Zone (AZ), Carnian age of 233.23 ± 0.73 Ma (based on data collected in the nearby and correlated ‘Alemoa’ area), Santa Maria Supersequence, Upper Triassic, Paraná Basin. The new postcranial remains studied are referred to as Dinosauriformes indet., Silesauridae indet., Gnathovorax cabreirai (Herrerasauridae), and a Chiniquodontidae cynodont, all collected between 1996 and 2002, during the Pro-Guaíba project. The identification of specific groups like silesaurids, herrerasaurids and chiniquodontids for the first time in this outcrop adds valuable nuances to the biostratigraphical framework of the Brazilian Upper Triassic record. These findings straighten the correlation of the basal layers of Faixa Nova-Cerrito I Site with other Hyperodapedon Acme Subzone outcrops and provide some insights on the diversity of the upper Teyumbaita-layers. Our result in part corroborates the current hypothesis for the subdivision of the Hyperodapedon AZ, but the probable silesaur occurrence within the Teyumbaita-layers does not yet indicate that those levels are equivalent to those from the Exaeretodon Subzone. Our results highlight the importance of even fragmentary specimens in biostratigraphy and diversity estimations.

First Sauropodomorpha (Dinosauria) for the Vila Botucaraí site (Hyperodapedon Assemblage Zone, Candelária Sequence), Rio Grande do Sul, Brazil

The Vila Botucaraí site is located west of the municipality of Candelária, Rio Grande do Sul State, southern Brazil, and is particularly important because it represents the type locality of the species Exaeretodon riograndensis (Cynodontia, Traversodontidae), Charruodon tetracuspidatus (Cynodontia, Probainognathia) and Proterochampsa nodosa (Archosauriformes, Proterochampsidae). The site is correlated to the Hyperodapedon Assemblage Zone whose fossiliferous content allows to correlate it to the lower half of the Ischigualasto Formation (Ischigualasto-Villa Unión Basin), of late Carnian age, in Argentina. The aim of this study is to record the first remains of dinosaurs from this locality, found in 2001 during the Pró-Guaiba Project and stored in the Scientific Collection of the Paleontology Section of the Museu de Ciências Naturais, Secretaria Estadual do Meio Ambiente e Infraestrutura, Porto Alegre, RS. In addition to the taxa mentioned at the Vila Botucaraí site, the archosauromorph Hyperodapedon sp. was also preliminarily recorded. The Dinosauria specimen includes four dorsal vertebrae (MCN-PV 10347a, b, c, d). The general characteristics observed are: (i) absence of a ventral keel in the vertebral centra, shared with Guaibasaurus, Bagualosaurus, Pampadromaeus; (ii) amphicoelic centra with concave ventral surface, shared with Bagualosaurus, Guaibasaurus, and most non-sauropod sauropodomorphs (exceptions are, for example, Riojasaurus; also, this character does not appear in herrerasaurids); (iii) vertebral laminae connected to the diapophysis, and their arrangement results in different fossae, as in Bagualosaurus, Buriolestes, Guaibasaurus, and herrerasaurids; (iv) neural spine anteroposteriorly elongated and transversely narrow, as in Bagualosaurus, Pampadromaeus, Buriolestes, Macrocollum, differing from herrerasaurids and theropods. This set of characters is similar to that observed in basal sauropodomorphs, quite different from the neural spine with a spine table, such as the observed in herrerasaurids. Specimen MCN-PV 10347 is here considered a member of the Sauropodomorpha clade and tentatively identified as cf. Bagualosauria. The features of this specimen are shared among Carnian (e.g., Buriolestes schultzi, Bagualosaurus agudoensis) and Norian (e.g., Unaysaurus tolentinoi, Guaibasaurus candelariensis) sauropodomorphs. In addition to this, the new material expands the knowledge regarding the number of outcrops with the occurrence of sauropodomorphs for the Triassic in Brazil, as well as about the paleofauna of the Vila Botucaraí site, allowing us to infer its biostratigraphic correlation with one of the sub-divisions already proposed for the Hyperodapedon AZ, the Exaeretodon Subzone, interpreted as the top of this AZ. Despite the abundance of sauropodomorphs in Rio Grande do Sul, this record confirms the occurrence of this clade at the Hyperodapedon AZ in the Candelária region.