A new gomphodont cynodont (Traversodontidae) from the Middle–Late Triassic Dinodontosaurus Assemblage Zone of the Santa Maria Supersequence,Brazil

The tetrapod faunas from the terrestrial Middle–Late Triassic basins of Africa and South America are among the richest in the world, especially in non‐mammalian cynodonts. Despite the great abundance of cynodont specimens found in these basins, there are few known taxa that exhibit interbasinal distributions. Here we describe a new species of traversodontid cynodont of the genus Scalenodon from the Triassic Dinodontosaurus Assemblage Zone of the Santa Maria Supersequence, from the state of Rio Grande do Sul, Brazil. Scalenodon ribeiroae sp. nov. is based on a partial skull that possesses a combination of features not observed in any other South American traversodontid: ellipsoid upper postcanines with the transverse crest formed by three cusps, lacking a mesiobuccal accessory cusp, and with lingual cusp projected lingually creating a concave lingual surface on the upper postcanines; the paracanine fossa is positioned medially to the upper canine, and jugal lacks a suborbital process. A phylogenetic analysis places the new taxon in a basal position within the Family Traversodontidae, with the African Scalenodon angustifrons as sister‐taxon. The new specimen of Scalenodon represents the first record of this genus outside of the Manda Beds of Tanzania, and reinforces the biostratigraphical and biogeographical connection between Gondwanan Middle–Late Triassic tetrapod faunas. Although recent advances have been made, our current knowledge of these faunas is limited by the lack of absolute dates for most units and by uncertainties in the taxonomy and stratigraphical provenance of key fossils.     

First 'Rauisuchian' archosaur (Pseudosuchia,Loricata) for the Middle Triassic Santacruzodon Assemblage Zone (Santa Maria Supersequence), Rio Grande do Sul State,Brazil

The ‘Rauisuchia’ are a group of Triassic pseudosuchian archosaurs that displayed a near worldwide distribution. In Brazil, their fossils are found only in the Santa Maria Formation (Paraná Basin) of the Rio Grande do Sul State, specifically in the Middle Triassic Dinodontosaurus assemblage zone (AZ) and the Late Triassic Hyperodapedon AZ (Rauisuchus tiradentes). Between these two cenozones is the Santacruzodon AZ (Middle Triassic), whose record was, until now, restricted to non-mammalian cynodonts and the proterochampsian Chanaresuchus bonapartei. Here we present the first occurrence of a rauisuchian archosaur for this cenozone, from the Schoenstatt outcrop, located near the city of Santa Cruz do Sul and propose a new species, based on biostratigraphical evidence and a comparative osteological analysis.     

Dinosaur remains from the ‘Botucaraí Hill’ (Caturrita Formation), Late Triassic of south Brazil,and their stratigraphic context

Vertebrate fossils recovered from sites nearby the Botucaraí Hill and Candelária (Caturrita Formation) depict a diverse Late Triassic tetrapod fauna from south Brazil. These records are of key importance to the biostratigraphy of the upper sections of the Rosario do Sul Group. A lithological and biostratigraphic survey on the main fossil localities of the Botucaraí Hill area confirms the occurrence of the lower Hyperodapedon and the upper Riograndia Assemblage Zones in the region, the latter yielding early saurischians. In this paper, three incomplete dinosaur specimens, an isolated sacral vertebra, an articulated left pubis–ischium and an isolated right ischium, from the ‘Botucaraí Hill’ site are described. A comparative survey suggests that these specimens have sauropodomorph affinities, but probably more primitive than typical ‘prosauropods’ from the Norian-Early Jurassic. Regardless of the phylogenetic position of Guaibasaurus as theropod or sauropodomorph, their occurrence in the Caturrita Formation, which also yielded ‘core prosauropods’ from the Santa Maria region, suggests either the survival of early members of the clade with more derived ‘prosauropods’ or that heterochronous faunas are sampled from that stratigraphic unit.     

Taxonomic and biochronological significance of specimens of the Triassic dicynodontDinodontosaurus Romer 1943 in the Tübingen collection

Two species of the dicynodontDinodontosaurus from the Middle Triassic interval of the Santa Maria Formation in Rio Grande do Sul, southern Brazil,D. tener (von Huene 1935) andD. turpior (von Huene 1935), are based on undiagnostic lectotypes and thus arenomina dubia. The oldest valid, available name for a species ofDinodontosaurus isD. oliveirai Romer 1943, the type species of the genus. (The unused senior subjective synonymDiodontosaurus pedroanum Caldas, 1936 has been suppressed by the International Commission on Zoological Nomenclature).Chanaria platyceps Cox 1968 andDinodontosaurus brevirostris Cox 1968 are junior subjective synonyms ofD. oliveirai Romer 1943.Dinodontosaurus thus is a monospecific genus known from the Santa Maria Formation and the Ischichuca (= Chañares) Formation of northwestern Argentina. This dicynodont and associated tetrapods characterize the Chanarian land-vertebrate faunachron, which is of Middle Triassic age, probably Ladinian.     

A New Species Of The Late Triassic Rhynchosaur Hyperodapedon From The Santa Maria Formation Of South Brazil

A new rhynchosaur, Hyperodapedon huenei sp. nov., is described from the Upper Triassic Santa Maria Formation of the Paraná Basin, Brazil. The holotype is an almost complete skull and mandible, collected at Inhamandá, in the state of Rio Grande do Sul, Brazil. The diagnosis of the genus Hyperodapedon Huxley is revised to include not only H. huxleyi Lydekker and H. gordoni Huxley (as generally accepted), but also the new species described here, various specimens usually assigned to ' Scaphonyx fischeri ' Woodward, and ' S '. sanjuanensis Sill. H. huenei sp. nov. exhibits a number of plesiomorphic features and appears to be the least derived species of Hyperodapedon , forming a sister taxon to the remaining members of the genus. A preliminary phylogenetic analysis for the more derived rhynchosaurs is presented. ' Scaphonyx ' sulcognathus Azevedo and Schultz represents the sister taxon of Hyperodapedon , while ' Rhynchosaurus ' spenceri Benton is considered to be a more derived Middle Triassic rhynchosaur. key words : Rhynchosauria, Hyperodapedon , Triassic, Brazil.     

Biostratigraphy and geometric morphometrics of conchostracans (Crustacea,Branchiopoda) from the Late Triassic fissure deposits of Cromhall Quarry,UK

The enigmatic fissure deposits of south‐western England and southern Wales are famous for their unique assemblage of Late Triassic vertebrates, although their age is contentious. While recent studies of palynomorphs have dated some as Rhaetian, their conchostracan (Crustacea, Branchiopoda) assemblages have not been described in detail nor used in biostratigraphy. We find that species determination of British Late Triassic conchostracans requires detailed observations of size, shape and ornamentation. We provide evidence that although Euestheria brodieana is invariably smaller than E. minuta, with some slight differences in carapace ornamentation, the traditional view that they are very similar is upheld. The use of conchostracans as a biostratigraphical tool is here tested by application to the British Triassic fissures at Cromhall quarry where the usual stratigraphical evidence provided by superposition is absent. We find no distinction between conchostracans from bedded Rhaetian deposits of the UK and specimens collected from the fissure deposits of Cromhall Quarry, Gloucestershire, supporting a late Rhaetian age for these deposits.     

Mammalian Carnivore Coprolites from the Sopas Formation (Upper Pleistocene,Lujanian Stage), Uruguay

Continental tetrapod coprolites from Uruguay are described for the first time. These remains come from the Piedra Pintada locality (Artigas Department), northern Uruguay, where the Sopas Formation crops out (Upper Pleistocene, Lujanian Stage). It was possible to identify several attributes indicative of a coprolitic origin, such as anisopolar shape, extrusion marks, pointed ends, sutures, gas bubbles, and inclusions. These specimens are assigned to carnivorous mammals, probably large felids, based on morphological attributes and inclusions of rodent bones and teeth.     

Vertebrate assemblages from the north‐central Main Karoo Basin,South Africa,and their implications for mid‐Permian biogeography

The rich fossil vertebrate record from the Beaufort Group, Main Karoo Basin, provides a global standard for mid‐Permian to Mid‐Triassic continental faunas. However, recent studies have demonstrated variability in the composition of contemporaneous faunas across Gondwana. This raises the question of how much the vertebrate faunas differ within the Karoo, where the taxonomic composition of vertebrate assemblage zones (AZs) is mostly considered to be uniform. Although fossil material is known from across the outcrop of the Beaufort Group, the lowest Beaufort strata have received little attention, particularly north of S31°10′. Here, we report two fossil tetrapod assemblages from the lowest Beaufort Group in the southern Free State Province, which represent the northernmost point at which the lowest Beaufort has been targeted for collecting. The lower assemblage is characterized by an abundance of the small dicynodont Eosimops and can thus be attributed to the Tapinocephalus AZ (Guadalupian), but the absence of dinocephalian or pareiasaurian material is unlike contemporaneous assemblages found further south. This suggests that the Tapinocephalus AZ was not uniform across the entire basin and highlights that the abundance, distribution and taxonomic composition of Karoo biozones may vary more than currently appreciated. The upper assemblage, characterized by the dicynodonts Oudenodon, Aulacephalodon and Dinanomodon, is attributable to the upper Cistecephalus AZ to lower Daptocephalus AZ. The juxtaposition of the lower Tapinocephalus AZ and upper Cistecephalus\lower Daptocephalus AZ in the southern Free State implies a stratigraphic gap from the Middle to Late Permian of up to 6 million years.     

OnStaurikosaums pricei,an early saurischian dinosaur from the Triassic of Brazil,with notes on the Herrerasauridae and Poposauridae

The anatomy of the saurischian dinosaurStaurikosaums pricei Colbert from the Santa Maria Formation (Middle or Upper Triassic) of Rio do Sul, Brazil is redescribed.Staurikosaurus has 9 (or possibly 10) short cervicals, 15 dorsals and 2 sacral vertebrae, a modified brachyiliac pelvic girdle and an elongate hindlimb with the tibia longer than the femur. The new family Staurikosauridae is erected, the Herrerasauridae is redefined, and both families are considered to be Saurischia incertae sedis. The distal part of the “femur” ofPoposaurus gracilis Mehl (Upper Triassic, North America) is the ventral part of the pubes with a footed distal end but, because some members of the Poposauridae have an imperforate acetabulum, this family is transferred from the Saurischia (Theropoda, Carnosauria) to the Thecodontia (Pseudosuchia).     

Middle–Late Permian tetrapods from the Rio do Rasto Formation,Southern Brazil: a biostratigraphic reassessment

Dias‐da‐Silva, S. 2011: Middle–Late Permian tetrapods from the Rio do Rasto Formation, Southern Brazil: a biostratigraphic reassessment. Lethaia, Vol. 45, pp. 109–120. The Rio do Rasto Formation (Permian of Southern Brazil) was previously regarded as Guadalupian–early Lopingian age. Three tetrapod‐based localities are known: the Serra do Cadeado area, Aceguá and Posto Queimado. The latest tetrapod‐based biostratigraphic contribution considers that the Posto Queimado and Aceguá faunas are coeval and Wordian (middle Guadalupian) in age, correlated to the Isheevo faunas from Eastern Europe and to the Tapinocephalus Assemblage Zone of South Africa; whereas the Serra do Cadeado fauna is Capitanian (late Guadalupian), correlated to the Kotelnich fauna of Eastern Europe and, from bottom to top, to upper Pristerognathus, Tropidostoma and lower Cistecephalus assemblage zones of South Africa. A re‐evaluation of the tetrapods from the Rio do Rasto Formation and new fossil discoveries in the localities of Posto Queimado and Serra do Cadeado area (melosaurine and platyoposaurine temnospondyls, a basal anomodont, a dinocephalian and a basal dicynodont) supports a new tetrapod‐based biostratigraphic scheme for the Rio do Rasto Formation. Accordingly, the age of the fauna at Aceguá is late Roadian‐early Wordian, whereas the locality of Posto Queimado is late Wordian‐Capitanian. The Serra do Cadeado Area is correlated with both southernmost ones (Guadalupian) but also Wuchiapinghian (early Lopingian). □Paraná Basin, Passa Dois Group, tetrapod biostratigraphy, Western Gondwana.     

Early Triassic Archosaur-Dominated Footprint Assemblage from the Argana Basin (Western High Atlas,Morocco)

An assemblage of abundant and well-preserved tetrapod footprints has been discovered in the Tanamert Member (T3) of the Triassic Timezgadiouine Formation (Argana basin, western High Atlas, Morocco). It is the first fossil record from T3. Surfaces from different localities show a uniform tetrapod ichnofauna that consists of chirotherian and small lacertoid forms. The chirotherians are assigned to the plexus Protochirotherium—Synaptichnium, their trackmakers interpreted as basal archosaurs. The lacertoid imprints show close affinities with Rhynchosauroides and may reflect archosauromorphs or lepidosauromorphs. Protochirotherium—Synaptichnium assemblages are characteristic of the Early Triassic and were known previously only from units of this age in central Europe. Biostratigraphically, the European record implies a wide-spread pre-Anisian Protochirotherium—Synaptichnium dominated assemblage preceding the first appearance of Chirotherium barthii near the Olenekian-Anisian boundary. The stratigraphic position of T3 between Late Permian (uppermost T2) and Middle Triassic (T4) and the European correlatives suggest an Early Triassic age of this unit. It is the first record of Early Triassic continental deposits in Morocco. The surfaces from T3 open up perspectives for further contributions to ecology, biogeography and locomotion of early archosaurs. Furthermore, excellent outcrops and quality of footprint preservation in the Argana basin offer a potential for clarification of ichnotaxonomic and biostratigraphic issues.     

The origin and early evolution of dinosaurs

The oldest unequivocal records of Dinosauria were unearthed from Late Triassic rocks (approximately 230 Ma) accumulated over extensional rift basins in southwestern Pangea. The better known of these are Herrerasaurus ischigualastensis, Pisanosaurus mertii, Eoraptor lunensis, and Panphagia protos from the Ischigualasto Formation, Argentina, and Staurikosaurus pricei and Saturnalia tupiniquim from the Santa Maria Formation, Brazil. No uncontroversial dinosaur body fossils are known from older strata, but the Middle Triassic origin of the lineage may be inferred from both the footprint record and its sister‐group relation to Ladinian basal dinosauromorphs. These include the typical Marasuchus lilloensis, more basal forms such as Lagerpeton and Dromomeron, as well as silesaurids: a possibly monophyletic group composed of Mid‐Late Triassic forms that may represent immediate sister taxa to dinosaurs. The first phylogenetic definition to fit the current understanding of Dinosauria as a node‐based taxon solely composed of mutually exclusive Saurischia and Ornithischia was given as “all descendants of the most recent common ancestor of birds and Triceratops”. Recent cladistic analyses of early dinosaurs agree that Pisanosaurus mertii is a basal ornithischian; that Herrerasaurus ischigualastensis and Staurikosaurus pricei belong in a monophyletic Herrerasauridae; that herrerasaurids, Eoraptor lunensis, and Guaibasaurus candelariensis are saurischians; that Saurischia includes two main groups, Sauropodomorpha and Theropoda; and that Saturnalia tupiniquim is a basal member of the sauropodomorph lineage. On the contrary, several aspects of basal dinosaur phylogeny remain controversial, including the position of herrerasaurids, E. lunensis, and G. candelariensis as basal theropods or basal saurischians, and the affinity and/or validity of more fragmentary taxa such as Agnosphitys cromhallensis, Alwalkeria maleriensis, Chindesaurus bryansmalli, Saltopus elginensis, and Spondylosoma absconditum. The identification of dinosaur apomorphies is jeopardized by the incompleteness of skeletal remains attributed to most basal dinosauromorphs, the skulls and forelimbs of which are particularly poorly known. Nonetheless, Dinosauria can be diagnosed by a suite of derived traits, most of which are related to the anatomy of the pelvic girdle and limb. Some of these are connected to the acquisition of a fully erect bipedal gait, which has been traditionally suggested to represent a key adaptation that allowed, or even promoted, dinosaur radiation during Late Triassic times. Yet, contrary to the classical “competitive” models, dinosaurs did not gradually replace other terrestrial tetrapods over the Late Triassic. In fact, the radiation of the group comprises at least three landmark moments, separated by controversial (Carnian‐Norian, Triassic‐Jurassic) extinction events. These are mainly characterized by early diversification in Carnian times, a Norian increase in diversity and (especially) abundance, and the occupation of new niches from the Early Jurassic onwards. Dinosaurs arose from fully bipedal ancestors, the diet of which may have been carnivorous or omnivorous. Whereas the oldest dinosaurs were geographically restricted to south Pangea, including rare ornithischians and more abundant basal members of the saurischian lineage, the group achieved a nearly global distribution by the latest Triassic, especially with the radiation of saurischian groups such as “prosauropods” and coelophysoids.     

New information about <Emphasis Type="Italic">Irajatherium hernandezi</Emphasis> Martinelli,Bonaparte, Schultz &; Rubert 2005 (Eucynodontia,Tritheledontidae) from the upper triassic (Caturrita Formation,Paraná Basin) of Brazil

In this contribution, new specimens of the tritheledontid eucynodont Irajatherium hernandezi, from the Late Triassic (Caturrita Formation) of southern Brazil, are analyzed. The new material provides significant information about incisor count, canine size and shape, basicranial morphology, and other previously unknown aspects of skull and dentition. A cladistic analysis with inclusion of the new data supports the assignment of Irajatherium to Tritheledontidae, basal to Chalimininae and Pachygenelinae. Previously unknown characters of Irajatherium revealed by the new material include: the presence of three lower incisors; the first lower incisor is enlarged; the presence of large upper and lower canines with deep paracanine fossa on the maxilla; almost complete upper and lower postcanine tooth row with a pattern similar to that of other tritheledontids (e.g. Pachygenelus and Chaliminia); there is a conspicuous crest on the inner surface of the maxilla for the attachment of the inferred maxillary turbinates; partially confluent jugular foramen and fenestra rotunda within the jugular fossa, separated by a finger-like projection of the posterolateral wall of the opisthotic; and hypoglossal foramina located outside the jugular fossa. Irajatherium is a key taxon for understanding the early evolution of ictidosaurs, a group of cynodonts closely related to mammaliaforms, during the cynodont–mammal transition from the Late Triassic to Early Jurassic.     

Evidence of osteomyelitis in the dentary of the late Triassic rhynchocephalian Clevosaurus brasiliensis (Lepidosauria: Rhynchocephalia) from southern Brazil and behavioural implications

Clevosaurus was a cosmopolitan Rhynchocephalia genus restricted to the Late Triassic and the Early Jurassic. In Brazil, C. brasiliensis is one of the most conspicuous species collected from the Candelária Sequence (Riograndia Assemblage Zone, Norian age) of the Santa Maria Supersequence. Several jaws of C. brasiliensis are housed in the Laboratório de Paleontologia de Vertebrados of the Instituto de Geociências-UFRGS. Some of these jaws bear a relatively small protuberant bony callus on the anterolateral margin of the dentary, evidenced by a different tissue pattern incorporating small pits and discrete grooves. This pattern closely resembles a common bone infection known in the mandible of the extant Sphenodon punctatus. Although this similarity, the infection may be the result of two possible processes: as consequence of orthal jaw shearing movements during feeding at the moments that the dentary impacts with the enlarged premaxillary tooth or due to injuries produced after fights between conspecific individuals (as is the case for S. punctatus). If the second hypothesis is correct, the same pathological processes probably occurred in the Late Triassic C. brasiliensis indicating that similar ethological conditions were already present at the beginning of the Mesozoic, during the initial radiation of the lepidosaurian clade.     

Large tetrapod burrows from the Middle Triassic of Argentina: a behavioural adaptation to seasonal semi‐arid climate?

Krapovickas, V., Mancuso, A.C., Marsicano, C.A., Domnanovich, N.S. & Schultz, C.L. 2013: Large tetrapod burrows from the Middle Triassic of Argentina: a behavioural adaptation to seasonal semi‐arid climate? Lethaia, Vol. 46, pp. 154–169. We report the discovery of large burrow casts in the early Middle Triassic Tarjados Formation, at Talampaya National Park, north‐western Argentina. Facies analysis indicates the burrows are preserved in sandbars deposited by an ephemeral river under semi‐arid and seasonal climatic conditions. The structures are mostly preserved in longitudinal cross‐section and consist of an opening, an inclined tunnel (ramp), and a terminal chamber. The ramp is 8–14 cm in height, up to 130 cm in length and penetrates 49–63 cm bellow the palaeosurface with an inclination of 22°–30°. We studied burrow cast dimensions, overall architectural morphology, surficial marks, and compared them with other large burrows of both invertebrate and vertebrate origin. A tetrapod origin of the burrow casts was established based on: distinctive architecture, and size, which is more than twice the most common size range for large terrestrial invertebrate burrows. Comparison with other Upper Permian and Triassic tetrapod burrows allows us to identify three general morphological groups: (1) simple inclined burrows; (2) helical burrows; and (3) burrow network complexes, representing different behaviours. A study of tetrapod body fossils preserved within other Upper Permian and Triassic burrows shows that the Tarjados structures were most likely produced by non‐mammalian cynodonts. The environmental and climatic context suggests that aridity and seasonality played a fundamental role selecting burrowing behaviour in therapsids and that by the Early–Middle Triassic their burrowing behaviour attained a complexity comparable to modern mammals. □Argentina, behaviour, palaeoclimate, Permo‐Triassic, Tarjados Formation, Tetrapod burrows.     

First record of Mesozoic scroll coprolites: classification,characteristics, elemental composition and probable producers

Multiple, small, cylindrical scroll coprolites having rounded and tapering ends and pertaining to a new ichnotaxon have been recovered from the Upper Triassic Tiki Formation of India. This is the first record of scroll coprolites from the Mesozoic. Based on cross‐sectional geometry, external surface textures, and internal morphology, these coprolites are subdivided into three morphotypes. The coprolites contain several kinds of undigested food material in the form of ganoid fish scales, teeth, lower jaw and skeletal remains of various osteichthyans, chondrichthyans, archosauriforms and indeterminate reptiles. These inclusions are embedded in the groundmass separated by thin mucosal layers. The groundmass contains abundant gas vesicles, and secondarily‐filled shrinkage cracks. EDS analysis shows that the overall composition of the coprolites reflects Ca, P, C and O, suggesting calcium phosphate mineralogy, though other elements such as Fe, Mn, Al, Si are present in lesser proportions. Based on their similarity with the scrolled faeces of extant euryhaline hammerhead sharks, it is deduced that these coprolites were produced by euryhaline hybodontid sharks. At least two hybodontid taxa, Lonchidion and Pristrisodus, show high prevalence in the Tiki vertebrate fauna, suggesting that these were the possible producers. As the coprolite inclusions contain remains of other aquatic animals, these carnivorous hybodonts constituted the dominant predators of the Tiki aquatic ecosystem.     

Biogeography of Triassic tetrapods: evidence for provincialism and driven sympatric cladogenesis in the early evolution of modern tetrapod lineages

Triassic tetrapods are of key importance in understanding their evolutionary history, because several tetrapod clades, including most of their modern lineages, first appeared or experienced their initial evolutionary radiation during this Period. In order to test previous palaeobiogeographical hypotheses of Triassic tetrapod faunas, tree reconciliation analyses (TRA) were performed with the aim of recovering biogeographical patterns based on phylogenetic signals provided by a composite tree of Middle and Late Triassic tetrapods. The TRA found significant evidence for the presence of different palaeobiogeographical patterns during the analysed time spans. First, a Pangaean distribution is observed during the Middle Triassic, in which several cosmopolitan tetrapod groups are found. During the early Late Triassic a strongly palaeolatitudinally influenced pattern is recovered, with some tetrapod lineages restricted to palaeolatitudinal belts. During the latest Triassic, Gondwanan territories were more closely related to each other than to Laurasian ones, with a distinct tetrapod fauna at low palaeolatitudes. Finally, more than 75 per cent of the cladogenetic events recorded in the tetrapod phylogeny occurred as sympatric splits or within-area vicariance, indicating that evolutionary processes at the regional level were the main drivers in the radiation of Middle and Late Triassic tetrapods and the early evolution of several modern tetrapod lineages.     

An unusual new archosauriform from the Middle–Late Triassic of southern Brazil and the monophyly of Doswelliidae

Until now the Doswelliidae was considered a monospecific family including Doswellia kaltenbachi from the Late Triassic of North America. The phylogenetic position of this taxon remained enigmatic until recently, when a sister‐group relationship with the Proterochampsidae was suggested. In the present contribution we describe the new doswelliid species Archeopelta arborensis gen. et sp. nov. from the Middle–Late Triassic of Brazil. A cladistic analysis recovered Archeopelta, Doswellia, and Tarjadia within a monophyletic group of basal archosauriforms, the Doswelliidae. The monophyly of this family is supported by the presence of osteoderm ornamentation that is coarse, incised, and composed of regular pits and the presence of an unornamented anterior articular lamina. Archeopelta is more closely related to Doswellia than to other archosauriforms by the presence of basipterygoid processes anterolaterally orientated, dorsal centra with a convex surface, width of the neural arch plus ribs of the first primordial sacral that are three times the length of the neural arch, and iliac blade laterally deflected, with strongly convex dorsal margin, and a length less than three times its height. The phylogenetic analysis indicates that Doswellidae is the closest large monophyletic entity to Archosauria, which achieved a wide palaeolatitudinal distribution during the late Middle and Late Triassic time span. © 2011 The Linnean Society of London, Zoological Journal of the Linnean Society, 2011, 161 , 839–871.     

Diversity and palaeoecology of a highly diverse Late Triassic marine biota from the Cassian Formation of north Italy

A sample of marine invertebrates from the Late Triassic Cassian Formation (north Italy) yielded one of the most diverse Early Mesozoic fossil assemblages ever reported (c. 170 species). The assemblage was found in basin clays, but was transported from nearby carbonate platforms as indicated by fragmentation, microbial encrustation and the presence of coated grains and ooids. Most of the specimens are small (< 1 cm) reflecting both, small adult sizes and size sorting during transport. Rarefaction analysis suggests that diversity of surface collection and bulk sampling is the same. However, rank abundance, species richness and taxonomic composition differ strongly according to sampling method. Low‐grade lithification of the sediments is the main reason that high diversity can be recognized, because it facilitates disaggregation and finding of small molluscs. Sample standardization shows that the studied assemblage is much more diverse than known Early Triassic assemblages. However, its diversity is similar to that of Anisian assemblages. This suggests that recovery from the end‐Permian mass‐extinction was quite advanced in the Middle Triassic and alpha‐diversity remained high until the Late Triassic. According to current models, Early Triassic and Anisian faunas match the niche overlap phase of recovery during which diversity is built up by increasing alpha‐diversity, whereas beta‐diversity rises slowly. Subsequently, habitat width of species contracts because of increasing competition, making beta‐diversity the principal drive of overall diversity increase. The diversity pattern of various Late Triassic Cassian associations meets the predictions for the transition from the niche overlap to the habitat contraction phase.: Triassic, Cassian Formation, palaeoecology, diversity, mollusc dominance.