Impact of the Late Triassic mass extinction on functional diversity and composition of marine ecosystems

Mass extinctions have profoundly influenced the history of life, not only through the death of species but also through changes in ecosystem function and structure. Importantly, these events allow us the opportunity to study ecological dynamics under levels of environmental stress for which there are no recent analogues. Here, we examine the impact and selectivity of the Late Triassic mass extinction event on the functional diversity and functional composition of the global marine ecosystem, and test whether post‐extinction communities in the Early Jurassic represent a regime shift away from pre‐extinction communities in the Late Triassic. Our analyses show that, despite severe taxonomic losses, there is no unequivocal loss of global functional diversity associated with the extinction. Even though no functional groups were lost, the extinction event was, however, highly selective against some modes of life, in particular sessile suspension feeders. Although taxa with heavily calcified skeletons suffered higher extinction than other taxa, lightly calcified taxa also appear to have been selected against. The extinction appears to have invigorated the already ongoing faunal turnover associated with the Mesozoic Marine Revolution. The ecological effects of the Late Triassic mass extinction were preferentially felt in the tropical latitudes, especially amongst reefs, and it took until the Middle Jurassic for reef ecosystems to fully recover to pre‐extinction levels.     

High-resolution biochronology and diversity dynamics of the Early Triassic ammonoid recovery: The Smithian faunas of the Northern Indian Margin

Based on new collections of abundant and well preserved material from the Salt Range (Pakistan), Spiti (Northern India) and Tulong (South Tibet), several recent studies focused on the taxonomic revision and detailed biostratigraphy of Smithian ammonoids. In this work, biochronological data for these three well-documented basins are analyzed by means of the Unitary Associations method, resulting in a biochronological scheme of unprecedented high-resolution for the Smithian of the Northern Indian Margin (NIM). Data for each basin are first processed separately, thus yielding three local biochronological zonations. Then, the three sequences are processed together as a regional three-section data set for the construction of an inter-basin sequence at the NIM level. The latter zonation comprises 16 Unitary Associations grouped into 13 zones for the entire Smithian. Analysis of ammonoid diversity dynamics based on this new highly resolved time frame highlights (i) a marked diversification during the early Smithian, (ii) a severe extinction during the late Smithian, and (iii) an overall very high turnover throughout the Smithian. At a global spatial scale and stage resolution, the diversity of Smithian ammonoid genera appears surprisingly high, as highlighted by a previous study. It is shown that at a smaller geographic scale and with the most highly resolved time frame, Smithian ammonoids of the NIM reached their explosive diversity peak essentially through extremely high turnover rates rather than through a classic diversification process of high origination rates coupled with low extinction rates. Based on recently published U/Pb ages, regional apparent total rates of origination and extinction of more than 100 species per My can be inferred for the Smithian ammonoids of the NIM.     

Geographical distribution and extinction risk: lessons from Triassic–Jurassic marine benthic organisms

Aim To evaluate the influence of geographical distribution on the extinction risk of benthic marine invertebrates using data from the fossil record, both during times of background extinction and across a mass‐extinction episode. Total geographical range is contrasted with proxies of global abundance to assess the relationships between the two essential components of geographical distribution and extinction risk. Location A global occurrence data base of fossil benthic macro‐organisms from the Triassic and Jurassic periods was used for this study. Methods Geographical distributions and biodiversity dynamics were assessed for each genus (all taxa) or species (bivalves) based on a sample‐standardized data set and palaeogeographical reconstructions. Geographical ranges were measured by the maximum great circle distance of a taxon within a stratigraphic interval. Global abundance was assessed by the number of localities at which a taxon was recorded. Widespread and rare taxa were separated using median and percentile values of the frequency distributions of occurrences. Results The frequency distribution of geographical ranges is very similar to that for modern taxa. Although no significant correlation could be established between local abundance and geographical range, proxies of global abundance are strongly correlated with geographical range. Taxon longevities are correlated with both mean geographical range and mean global abundance, but range size appears to be more critical than abundance in determining extinction risk. These results are valid when geographical distribution is treated as a trait of taxa and when assessed for individual geological stages. Main conclusions Geographical distribution is a key predictor of extinction risk of Triassic and Jurassic benthic marine invertebrates. An important exception is in the end‐Triassic mass extinction, which equally affected geographically restricted and widespread genera, as well as common and rare genera. This suggests that global diversity crises may curtail the role of geographical distribution in determining extinction risk.     

The biogeography of Early Triassic ammonoid faunas: Clusters, gradients, and networks

The aim of this paper is to quantitatively investigate the spatial and temporal biogeographical relationships of the recovery of ammonoid faunas after the Permian-Triassic mass extinction using three complementary numerical approaches among which is a new, non-hierarchical clustering strategy. The faunal data set consists of a taxonomically homogenised compilation of the spatial and temporal occurrences of ammonoid genera within 20 Early Triassic Tethyan and Panthalassic sites ranging from 40°S to 70°N in palaeolatitudes. In addition to hierarchical cluster analysis (hCA) and nonmetric multidimensional scaling (NMDS), we introduce a third, new non-hierarchical clustering technique allowing the visualisation of a nonmetric interassemblages similarity structure as a connected network constructed without inferring additional internal nodes. The resulting network, which we call a “Bootstrapped Spanning Network” (BSN), allows the simultaneous identification of partially or totally nested as well as gradational linear or reticulated biogeographical structures.The identified interlocalities relationships indicate that the very beginning of the Early Triassic (Griesbachian) corresponds to a very simple biogeographical context, representing a time of great cosmopolitanism for ammonoids. This context shifts rapidly to a more complex configuration indicative of a more endemic and latitudinally-restricted distribution of the ammonoids during the middle and late Early Triassic (Smithian and Spathian). From an evolutionary dynamic point of view, our results illustrate a very rapid (less than ca. 1.4 myr) Early Triassic recovery of the ammonoid faunas, in contrast to many other marine organisms. This recovery is linked with a marked increase in the overall biogeographical heterogeneity, and parallels the formation of a latitudinal gradient of taxonomic richness, which may be essentially controlled by the progressive intensification of the gradient of sea surface temperature. From a methodological point of view, we show that a BSN is a simple, intuitively legible picture of the nested as well as gradational taxonomic similarity relationships, hence providing a good synthesis (and additional insights) between hierarchical clustering and ordination in reduced space results.     

Phanerozoic survivors: Actinopterygian evolution through the Permo‐Triassic and Triassic‐Jurassic mass extinction events

Actinopterygians (ray‐finned fishes) successfully passed through four of the big five mass extinction events of the Phanerozoic, but the effects of these crises on the group are poorly understood. Many researchers have assumed that the Permo‐Triassic mass extinction (PTME) and end‐Triassic extinction (ETE) had little impact on actinopterygians, despite devastating many other groups. Here, two morphometric techniques, geometric (body shape) and functional (jaw morphology), are used to assess the effects of these two extinction events on the group. The PTME elicits no significant shifts in functional disparity while body shape disparity increases. An expansion of body shape and functional disparity coincides with the neopterygian radiation and evolution of novel feeding adaptations in the Middle‐Late Triassic. Through the ETE, small decreases are seen in shape and functional disparity, but are unlikely to represent major changes brought about by the extinction event. In the Early Jurassic, further expansions into novel areas of ecospace indicative of durophagy occur, potentially linked to losses in the ETE. As no evidence is found for major perturbations in actinopterygian evolution through either extinction event, the group appears to have been immune to two major environmental crises that were disastrous to most other organisms.     

Taphonomy and palaeoecology of Late Triassic (Carnian) ammonoid concentrations from the Taurus Mountains,Turkey

The deposits of the Carnian Kas?mlar Formation within the Taurus Platform Units of south‐western Turkey represent an important archive of a Late Triassic ecosystem. New palaeontological information was obtained by analysing the Kasimlarceltites mass occurrence, located within the Kas?mlar Formation and named after the Lower Carnian (Julian) ammonoid genus Kasimlarceltites. This is the dominant taxon (> 94%) within the mass occurrence: nearly 775 million ammonoids and 50 million gastropods were extrapolated for the whole extension (at least 5 km²) of the Kasimlarceltites beds. This calculation is one of the main findings within this study, as it is the first time that such a fossil mass occurrence was quantified. Additionally, orientation measurements of the planispiral ammonoids and the helical gastropods enabled reconstructing the history of the mass occurrence and interpreting the underlying transport mechanisms. Further taphonomic aspects (e.g. biofabric, preservation, bioerosion or genetic classification) as well as comparisons with samples of the same acme zone from different localities near A?a?iyaylabel (AS IV, KA I‐II) point to a two‐phased genetic history. Accordingly, local mass mortality within the Kasimlarceltites fauna due to oxygen fluctuations or methane degassing may have initially led to a primary accumulation. These deposits were then reworked and redeposited basinward by gravity flows to create the present‐day secondary allochthonous concentrations.     

The Luoping biota: exceptional preservation, and new evidence on the Triassic recovery from end-Permian mass extinction

The timing and nature of biotic recovery from the devastating end-Permian mass extinction (252 Ma) are much debated. New studies in South China suggest that complex marine ecosystems did not become re-established until the middle–late Anisian (Middle Triassic), much later than had been proposed by some. The recently discovered exceptionally preserved Luoping biota from the Anisian Stage of the Middle Triassic, Yunnan Province and southwest China shows this final stage of community assembly on the continental shelf. The fossil assemblage is a mixture of marine animals, including abundant lightly sclerotized arthropods, associated with fishes, marine reptiles, bivalves, gastropods, belemnoids, ammonoids, echinoderms, brachiopods, conodonts and foraminifers, as well as plants and rare arthropods from nearby land. In some ways, the Luoping biota rebuilt the framework of the pre-extinction latest Permian marine ecosystem, but it differed too in profound ways. New trophic levels were introduced, most notably among top predators in the form of the diverse marine reptiles that had no evident analogues in the Late Permian. The Luoping biota is one of the most diverse Triassic marine fossil Lagerstätten in the world, providing a new and early window on recovery and radiation of Triassic marine ecosystems some 10 Myr after the end-Permian mass extinction.     

Body size changes in bivalves of the family Limidae in the aftermath of the end‐Triassic mass extinction: the Brobdingnag effect

Reduction in body size of organisms following mass extinctions is well‐known and often ascribed to the Lilliput effect. This phenomenon is expressed as a temporary body size reduction within surviving species. Despite its wide usage the term is often loosely applied to any small post‐extinction taxa. Here we assess the size of bivalves of the family Limidae (Rafineque) prior to, and in the aftermath of, the end‐Triassic mass extinction event. Of the species studied only one occurs prior to the extinction event, though is too scarce to test for the Lilliput effect. Instead, newly evolved species originate at small body sizes and undergo a within‐species size increase, most dramatically demonstrated by Plagiostoma giganteum (Sowerby) which, over two million years, increases in size by 179%. This trend is seen in both field and museum collections. We term this within‐species size increase of newly originated species in the aftermath of mass extinction, the Brobdingnag effect, after the giants that were contemporary with the Lilliputians in Swift's Gulliver's Travels. The size increase results from greater longevity and faster growth rates. The cause of the effect is unclear, although it probably relates to improved environmental conditions. Oxygen‐poor conditions in the Early Jurassic are associated with populations of smaller body size caused by elevated juvenile mortality but these are local/regional effects that do not alter the long‐term, size increase. Although temperature‐size relationships exist for many organisms (Temperature‐Size Rule and Bergmann's Rule), the importance of this is unclear here because of a poorly known Early Jurassic temperature record.     

Bivalves and evolutionary resilience: old skills and new strategies to recover from the P/T and T/J extinction events

Diversity dynamics among bivalves during the Triassic and Early Jurassic provides the opportunity to analyse the recovery patterns after two mass extinctions: Permian/Triassic and Triassic/Jurassic (T/J). The results presented here are based on a newly compiled worldwide genus-level database and are contrasted to the main morphological characters of the different taxonomical (orders and their constituent families and genera) and ecological groups. Many of such morphological characters are innovations appearing during the time span considered. Diversity and evolutionary rates were assessed and compared between these groups. During the Early Triassic there was a slow recovery, dominated by epifaunal taxa, the order Pectinida being the most diverse. The major post-Permian radiation took place during the Anisian, with several morphological and ecological innovations appearing and/or diversifying. The Late Triassic was a time of great diversification and ecological specialisation. Although the T/J was a true mass extinction for bivalves, it was not indiscriminate as its impact was stronger on specialised orders and not all ecological categories were equally affected. Recovery during earliest Jurassic was fast, confirming the high-evolutionary resilience of bivalve molluscs, except for groups with thick shells and tropical distribution, probably because of a biocalcification crisis.     

Microbes,mud and methane: cause and consequence of recurrent Early Jurassic anoxia following the end‐Triassic mass extinction

The end‐Triassic mass extinction (c. 201.6 Ma) was one of the five largest mass‐extinction events in the history of animal life. It was also associated with a dramatic, long‐lasting change in sedimentation style along the margins of the Tethys Ocean, from generally organic‐matter‐poor sediments during the Triassic to generally organic‐matter‐rich black shales during the Jurassic. New core material from Germany provides biomarker evidence of persistent photic‐zone euxinia during the Hettangian, the onset of which is associated with a series of both negative and positive carbon isotope excursions. Combined inorganic and organic geochemical and micropalaeontological analyses reveal strong similarities between the Hettangian and the better‐known Toarcian anoxic event. These events appear to be the most clearly expressed events within a series of anoxic episodes that also include poorly studied black shale intervals during the Sinemurian and Pliensbachian. Both the Hettangian and Toarcian events are marked by important changes in phytoplankton assemblages from chromophyte‐ to chlorophyte‐dominated assemblages within the European Epicontinental Seaway. Phytoplankton changes occurred in association with the establishment of photic‐zone euxinia, driven by a general increase in salinity stratification and warming of surface waters. For both events, the causes of large negative carbon isotope excursions remain incompletely understood; evidence exists for both variation in the δ¹³C of atmospheric CO₂ and variation in the sources of organic carbon. Regardless of the causes of δ¹³C variability, long‐term ocean anoxia during the Early Jurassic can be attributed to greenhouse warming and increased nutrient delivery to the oceans triggered by flood basalt volcanism.     

Middle and Late Triassic radiolarians from northern Tibet: Implications for the Bayan Har Basin evolution

During the Triassic, the Bayan Har Basin is a huge triangular basin surrounded by the North China Platform, South China Platform and Qingtang Terrane. It is filled by a Triassic turbidite sequence, the Bayan Har Group. For a long time, the series of Bayan Har Group in the eastern part of the basin were considered to be a Lower to Upper Triassic sequence, and in the western part, was attributed to the Upper Triassic. A well-preserved diversified radiolarian fauna was recovered from radiolarian chert and tuffite interbeds of the Bayan Har Group turbidites and adjacent stratigraphic units in the Hoh Xil area, northern Tibet. Sixty-seven species are identified and subdivided into two assemblages: late Anisian and early Carnian. Combined with the discovery of the Late Permian and Early Triassic turbidite in the Bayan Har Group in this area by Huang et al., it proves that all the Triassic is also present in the Bayan Har Group sequence in the western part. The evolution of the Bayan Har Basin may be traced back to the Late Permian. The massive sequence of the Bayan Har Group and its provenance indicate that the Kunlun and Qinling orogenic belts rapidly rise during the Middle-Late Triassic. The basin extended to the end of the Triassic, possibly locally to the Jurassic.     

New and little-known grylloblattids of the family Geinitziidae (Insecta: Grylloblattida) from the Triassic and Jurassic of Europe,Asia, and South Africa

The fossil history of the family Geinitziidae is reviewed. New taxa are described in the family: Shurabia hissarica, sp. nov. (Lower Jurassic of Tajikistan), Sh. shartegica, sp. nov. (Upper Jurassic of Mongolia), Sh. serrata, sp. nov. and Ginitzia sagulensis, sp. nov. (both Lower Jurassic of Kyrgyzstan). The subfamily Stegopterinae Sharov, 1961 is synonymized under Geinitziinae Handlirsch, 1906. The genera Minesedes Fujiyama, 1973 and Ominea Fujiyama, 1973 (Upper Triassic of Japan) are synonymized under Shurabia Martynov, 1937 and Geinitzia Handlirsch, 1906, respectively. Geinitzia varia Bode, 1953 (Lower Jurassic of Germany) and Fletchizia picturata Riek, 1976 (Upper Triassic of South Africa) are redescribed from their holotypes. F. kapokraalensis Wappler, 2001 and F. aleda Wappler, 2001 (both Upper Triassic of South Africa) are transferred to the genus Shurabia.     

Middle Triassic Xingyi Fauna: Showing turnover of marine reptiles from coastal to oceanic environments

The late Ladinian (Middle Triassic) Xingyi Fauna from the Zhuganpo Member of the Falang Formation yields abundant and well-preserved marine reptiles. Bed-by-bed excavation at Wusha in Xingyi of Guizhou Province reveals two marine vertebrate assemblages in a fossiliferous horizons that span 5.1 m in total thickness. The lower assemblage is marked by the near-shore sauropterygians, including the pachypleurosaur Keichousaurus, the nothosaurians Nothosaurus and Lariosaurus, with a strong paleobiogeographic affinity to western Tethys. The upper assemblage consists of oceanic ichthyosaurs and pistosaurs, including the large shastasaurid ichthyosaur Guizhouichthyosaurus, the euichthyosaur Qianichthyosaurus, pistosaurs Yunguisaurus and Wangosaurus, and the thalattosaur Xinpusaurus, with a closer paleobiogeographic affinity to North America. The coastal pachypleurosaur and nothosaurid sauropterygians disappeared in the upper assemblage, suggesting that they were replaced by an oceanic marine reptile community that emerged. The reptilian composition of the upper assemblage is similar to that of the Guanling Biota, which is of the Early Carnian (Late Triassic) in age and thus somewhat younger than the Xingyi Fauna. The ecological turnover of marine reptiles from near-shore to the open ocean community corresponds to the paleoenvironmental changes indicated by lithofacies analysis, δ¹³C and the global sea level changes.     

Late Jurassic sea-level fluctuations in NW Switzerland (Late Oxfordian to Late Kimmeridgian): closing the gap between the Boreal and Tethyan realm in Western Europe

In Late Jurassic times, the Swiss Jura carbonate platform occupied the transition between the Paris Basin and the Tethys and thus connects the Boreal and Tethyan realm. Up to now, the lack of index fossils in the Reuchenette Formation prevented a reliable correlation between both areas (its sediments are characterised by a prominent sparseness of index fossils). Now, seven recently in situ collected species of ammonites helped to establish a new sequence-stratigraphical frame for the platform sediments of the Reuchenette Formation in NW Switzerland. Based on biostratigraphical data, five third-order sedimentary sequences were assigned to the Late Oxfordian to Late Kimmeridgian. The upper three third-order sequences correspond to the Boreal sequences Kim3–5 of Hardenbol et al. (1998). The deduced large-scale sea-level fluctuations match those from other European regions (Spain, Russia). This biostratigraphically based sequence-stratigraphical frame is a prerequisite to refine correlations within a wider area covering the Swiss Jura and parts of adjacent France and Germany. Electronic Supplementary Material Supplementary material is available for this article at     

A review of the chronostratigraphical ages of Middle Triassic to Late Jurassic dinoflagellate cyst biozones of the North West Shelf of Australia

The chronostratigraphical ages of the 20 dinoflagellate cyst zones and one dinoflagellate cyst assemblage for the Middle Triassic (Ladinian) to the Jurassic-Cretaceous transition of the North West Shelf of Australia are comprehensively reviewed. Evidence from macro- and micropalaeontology, palynology and strontium isotopes made available after the establishment of these biozones in the 1980s has been used to reassess the ages of this important zonal scheme and to calibrate it to the international stratigraphical stages. The Shublikodinium Superzone is renamed herein as the Rhaetogonyaulax Superzone, and based on conodont evidence is determined to span the Ladinian to Early Sinemurian. This is significantly shorter in duration than was originally envisaged (Late Anisian to Late Pliensbachian). The Luehndea Assemblage is a low diversity dinoflagellate cyst association which marks a eustatic rise; it is subdivided into two subzones. It is of latest Pliensbachian to Early Toarcian age, based largely on palynological evidence. The Bajocian to earliest Oxfordian Pareodinia ceratophora Superzone represents the inception of a continuous Mesozoic-Cenozoic dinoflagellate cyst record in Australia. It comprises seven zones, which are considered to be slightly older than originally interpreted. The overlying Pyxidiella Superzone is characterised by diverse dinoflagellate cyst associations. It is Early Oxfordian to Kimmeridgian in age, and comprises three zones. The bases of the Wanaea spectabilis and Wanaea clathrata zones are reinterpreted as being slightly older than originally proposed. The superjacent Fromea cylindrica Superzone is Tithonian to earliest Valanginian and modified ages are indicated for four of the nine zones. This unit is dominated by endemic dinoflagellate cysts, reflecting a global trend towards provincialism at this time due to a regressive eustatic regime.     

Linking taphonomy to community-level abundance: Insights into compositional fidelity of the Upper Triassic shell concentrations (Eastern Alps)

Although actualistic live/dead comparisons lead to robust estimates of fidelity of modern death assemblages, quantitative evaluation of fidelity of fossil assemblage remains uncertain. In this paper, effects of storm reworking on compositional fidelity of the Upper Triassic shell concentrations (Eastern Alps, Austria) are evaluated. An exploratory approach is based on comparison of reworked and non-reworked assemblages in ordination analyses. Non-reworked assemblages of one or more communities provide a baseline for evaluation of fidelity of reworked assemblages. In siliciclastic-rich intervals of the Kössen Formation, shell concentrations are represented by (1) packstones with small, shallow infaunal bivalves, (2) floatstones and pavements with large semi-infaunal bivalves, and (3) bioclastic marlstones. In carbonate-rich intervals, bioclastic floatstones with bivalves and brachiopods occur. Analyzing all shell concentrations, eight sample groups sharing similar species composition are discriminated. Limited effect of storm reworking on composition of shell concentrations is indicated by (1) a general persistence of six sample groups when only non-reworked assemblages are analyzed, (2) similarity in composition between reworked and non-reworked assemblages within sample groups, and (3) compositional segregation between non-reworked assemblages of distinctive sample groups, mostly without any reworked assemblages of intermediate composition.Depth-related variations in dead-shell production, shell destruction and body size governed preservation and distribution of the shell concentrations along onshore-offshore gradient in the Kössen Basin. First, at times when environmental conditions were unfavorable for shell producers, coupled with high background shell destruction rates, limestone beds formed during storm events were shell-poor. Second, less common shell concentrations in upper than in lower parts of siliciclastic intervals can be related to higher environmental stress in shallower habitats. Third, the difference between shell concentrations dominated by small and large bivalves is driven by between-habitat differences in body size and is not due to a differential sorting of small and large shells. Combining community analysis based on species abundances with taphonomic analysis can thus be helpful in tracking fidelity of fossil assemblages.     

From success to persistence: Identifying an evolutionary regime shift in the diverse Paleozoic aquatic arthropod group Eurypterida,driven by the Devonian biotic crisis

Mass extinctions have altered the trajectory of evolution a number of times over the Phanerozoic. During these periods of biotic upheaval a different selective regime appears to operate, although it is still unclear whether consistent survivorship rules apply across different extinction events. We compare variations in diversity and disparity across the evolutionary history of a major Paleozoic arthropod group, the Eurypterida. Using these data, we explore the group's transition from a successful, dynamic clade to a stagnant persistent lineage, pinpointing the Devonian as the period during which this evolutionary regime shift occurred. The late Devonian biotic crisis is potentially unique among the “Big Five” mass extinctions in exhibiting a drop in speciation rates rather than an increase in extinction. Our study reveals eurypterids show depressed speciation rates throughout the Devonian but no abnormal peaks in extinction. Loss of morphospace occupation is random across all Paleozoic extinction events; however, differential origination during the Devonian results in a migration and subsequent stagnation of occupied morphospace. This shift appears linked to an ecological transition from euryhaline taxa to freshwater species with low morphological diversity alongside a decrease in endemism. These results demonstrate the importance of the Devonian biotic crisis in reshaping Paleozoic ecosystems.     

A new juvenile specimen of Yunnanosaurus robustus (Dinosauria: Sauropodomorpha) from Early to Middle Jurassic of Chuxiong Autonomous Prefecture,Yunnan Province,China

An almost complete skeleton with partial cranial material (ZMNH-M8739) is recovered from the Early or Middle Jurassic of southwest China. ZMNH-M8739 is identified as a juvenile individual of basal sauropodomorph dinosaur, Yunnanosaurus robustus Young, 1951. The revised diagnoses are as follows: absence of anteroposterior expansion on the medial end of astragalus and dorsoventrally compressed medium shaft of the metatarsal IV. Unfused neural arch and finely grooved long bone surface texture indicate that this individual is in the immature growth stage. ZMNH-M8739 possesses the tooth–tooth wear facet on its mesial maxillary and dentary teeth. However, the distal maxillary teeth have coarse serrations. Such a characteristic dentition could represent a unique feeding mechanism of this animal. Finally, ZMNH-M8739 constitutes a monophyletic group with Y. robustus (holotype), and Y. huangi is nesting this clade in the phylogenetic tree of the present analysis. Comparison of juvenile and adult specimen reveals distinctive growth changes of Y. robustus. This clade is positioned in an unnamed clade at a sister taxon of Sauropoda. Finally, some members of the so-called prosauropod dinosaurs constitute a monophyletic group in the present result.     

From shallow to deep water: an ecological study of the Hirnantia brachiopod Fauna (Late Ordovician) and its global implications

A large brachiopod fauna collected through the upper Wanyaoshu Formation (middle Hirnantian), West Yunnan, China displays, for the first time, a vertical transition within the Hirnantia fauna. The inner to mid-shelf Fardenia–Hirnantia association segues into the deeper water Aegiromena–Anisopleurella association during the Metabolograptus persculptus marine transgression. This transition parallels the pattern apparent in onshore–offshore gradients within the Hirnantian, imitating Walther’s Law for facies, instead predicting the seaward transitions between community types within a single transgressive sequence. In addition, large-sized brachiopods such as Hirnantia and Eostropheodonta become rarer and small-sized brachiopods, for example, Aegiromena and Anisopleurella more common. It is a rare opportunity to view transformations in community composition and structure within the Hirnantia fauna together with changes in both the size of individuals and populations (from large to small) during the transgression.