The Paris Biota decapod (Arthropoda) fauna and the diversity of Triassic decapods
Christopher P. A. SmithSylvain CharbonnierJames F. JenksKevin G. BylundGilles EscarguelNicolas OlivierEmmanuel FaraArnaud Brayard
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Abstract We describe here the early Spathian (Early Triassic) Paris Biota decapod fauna from the western USA basin. This fauna contains two taxa of Aegeridae (Dendobranchiata), namely Anisaeger longirostrus n. sp. and Aeger sp. that are the oldest known representatives of their family, thus extending its temporal range by 5 Myr back into the Early Triassic. This fauna also includes two representatives of Glypheida (Pleocyemata) with Litogaster turnbullensis and Pemphix krumenackeri n. sp., confirming for the former and extending for the latter the temporal ranges of their respective superfamilies back to the Early Triassic. Overall, the Paris Biota decapods are some of the oldest known representatives of Decapoda, filling in an important gap in the evolutionary history of this group, especially during the Triassic that marks the early diversification of this clade. Additionally, we compile and provide overviews for all known Triassic decapods, which leads to the revision of four species of Middle and Late Triassic Aegeridae, and to a revised family assignment of a Middle Triassic Glypheida. Based on this refined dataset, we also investigate decapod diversity throughout the Triassic. We show that the apparent increase in decapod taxonomic richness is probably driven by the heterogeneity of the fossil record and/or sampling effort, and that the decapod alpha diversity is actually relatively high as soon as the Early Triassic and remains rather stable throughout the Triassic. UUID: http://zoobank.org/0f435f27-1767-473d-955c-57fe869faa0fKeywords:
Biota
Early Triassic
Biochronology
Paleoecology
Biochronology
Early Triassic
Ladinian
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Conodont
Early Triassic
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Biochronology
Paleoecology
Neogene
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The global Triassic timescale based on tetrapod biochronology remains a robust tool for both global and regional age assignment and correlation. The Lootsbergian and Nonesian land-vertebrate faunachrons (LVFs) are of
Early Triassic age; cross correlation of part of the Lootsbergian to the Olenekian and all or part of the Nonesian to the Anisian lacks support. In the South African Karoo basin, both the Lootsbergian and the Nonesian can and should be subdivided into sub-LVFs. The upper part of the South African Cynognathus zone, previously considered Nonesian in age, is younger, of Perovkan age. We redefine the beginning of the Perovkan as the first appearance datum of the temnospondyl Eocyclotosaurus, which resolves uncertainties in the correlation of Eocyclotosaurus assemblages and shansiodont assemblages. The Berdyankian LVF equates to parts of Ladinian and Carnian time. Rejection of recent cladotaxonomy of phytosaurs and an incorrect claim of a Revueltian record of the temnospondyl
Metoposaurus, as well as newly established stratigraphic ranges and new taxonomy of aetosaurs, have improved correlation and temporal resolution within the interval Otischalkian-Apachean. This further supports separation
of the Otischalkian and Adamanian and runs contrary to suggestions to merge the two LVFs as a single Ischigualastian LVF. Though readily recognized and correlated in western North America, the Apachean LVF remains the most problematic LVF for global correlation. A recent purported test of the Triassic LVFS based on GIS is rejected as invalid because it is replete with internal inconsistencies, factual errors and questionable interpretations. Continued careful biostratigraphy in the field and improved alpha taxonomies that are not cladotaxonomies will further develop, elaborate and test the Triassic timescale based on tetrapod evolution.
Biochronology
Tetrapod (structure)
Early Triassic
Ladinian
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Two extensive collections retrieved from Exotic Blocks from West Timor have yielded several astonishingly well-preserved and highly diversified Smithian (Early Triassic) ammonoid faunas (Kashmirites fauna, Owenites fauna, Anasibirites fauna).A population approach on this material, with an emphasis on ontogeny and covariation of morphological characters, led to the unprecedented assessment of intraspecific variation for many species.Based on this, their synonymy is thoroughly discussed whenever possible.One new genus (Roopnarinites) and five new species (Paraspidites bicarinatus, Flemingites lidakensis, Subflemingites bihatiense, Baidites obesus and Churkites warei) are described.These results have a direct impact on the resolution and accuracy of biochronological correlations, as well as on the accuracy of diversity counts at the species level, which is important for potential future broad-scale diversity analyses.This material also provides highly valuable data for comprehensive biogeographical and phylogenetic studies hopefully to come.Finally, these new Timor data strengthen the singularly uniform biogeographical distribution of the Smithian ammonoid faunas within the Tethys.
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Early Triassic
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A distinctive mobile pebble and cobble rockground biota of Late Eocene age is described from volcaniclastic sediments between Oamaru and Kakanui, North Otago, New Zealand. Thousands of subangular to subrounded basaltic pebbles and cobbles are encrusted with a diverse range of very well-preserved epibionts including crustose coralline algae, serpulids, bivalves, foraminifera, brachiopods, and more than 70 species of cyclostome and cheilostome bryozoans. The preservation of thin sediment layers beneath and between encrusting bryozoan colonies indicates the probable occurrence, during life, of agglutinating microbial mats. The abundance of subspherical rhodoliths, the diversity of epibionts, and their occurrence on all faces of the volcanic clasts reflect intermediate levels of overturning and rolling in a moderately current-swept channel adjacent to small volcanic islands and seamounts. The occurrence of large foraminifera (Asteroclyna), bryozoans (including two extant species), and brachiopods with warm-water affinities indicates subtropical sea temperatures and water depths of 25-50 m for this community, which represents one of the few described Cenozoic examples of a mobile rockground biota.
Paleoecology
Biota
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Triassic vertebrate tracks are known from the beginning of the 19th century and have a worldwide distribution.Several Triassic track ichnoassemblages and ichnotaxa have a restricted stratigraphic range and are useful in biochronology and biostratigraphy.The record of Triassic tracks in the Iberian Peninsula has gone almost unnoticed although more than 25 localities have been described since 1897.In one of these localities, the naturalist Longinos Navás described the ichnotaxon Chirotherium ibericus in 1906.The vertebrate tracks are in two sandy slabs from the Anisian (Middle Triassic) of the Moncayo massif (Zaragoza, Spain).In a recent revision, new, previously undescribed vertebrate tracks have been identified.The tracks considered to be C. ibericus as well as other tracks with the same morphology from both slabs have been classified as Chirotherium barthii.The rest of the tracks have been assigned to Chirotheriidae indet., Rhynchosauroides isp.and undetermined material.This new identification of C. barthii at the Navás site adds new data to the Iberian record of this ichnotaxon, which is characterized by the small size of the tracks when compared with the main occurrences of this ichnotaxon elsewhere.As at the Navás tracksite, the Anisian C. barthii-Rhynchosauroides ichnoassemblage has been found in other coeval localities in Iberia and worldwide.This ichnoassemblage belongs to the upper Olenekian-lower Anisian interval according to previous biochronological proposals.Analysis of the Triassic Iberian record of tetrapod tracks is uneven in terms of abundance over time.From the earliest Triassic to the latest Lower Triassic the record is very scarce, with Rhynchosauroides being the only known ichnotaxon.Rhynchosauroides covers a wide temporal range and gives poor information for biochronology.The record from the uppermost Lower Triassic to the Middle Triassic is abundant.The highest ichnodiversity has been reported for the Anisian with an assemblage composed of Dicynodontipus, Procolophonichnium, Rhynchosauroides, Rotodactylus, Chirotherium, Isochirotherium, Coelurosaurichnus and Paratrisauropus.The Iberian track record from the Anisian is coherent with the global biochronology proposed for Triassic tetrapod tracks.Nevertheless, the scarcity of track occurrences during the late Olenekian and Ladinian
Biochronology
Peninsula
Tetrapod (structure)
Early Triassic
Yucatan peninsula
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Biochronology
Early Triassic
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The end-Permian mass extinction is the biggest known crisis in life history and wiped out more than 90% of all marine species. In its aftermath, the Early Triassic was a time of profound instabilities in the sedimentary, geochemical and climatic evolution. Full recovery of many marine, essentially benthic clades as well as pre-crisis level of marine ecosystem complexity was not reached until the Middle Triassic (e.g. reefal communities). On the contrary, at least some faunal groups such as ammonoids and conodonts recovered much faster than other marine clades. However, the evolution of Early Triassic ammonoids was not a smooth, nor a gradual process. It was characterized by the following main features: (i) a very low diversity in the Griesbachian (early Induan), (ii) a moderate diversity increase in the Dienerian (late Induan), (iii) an explosive radiation in the early Smithian (early Olenekian), (iv) a late Smithian extinction event followed by (v) a second explosive radiation in the early Spathian (late Olenekian). In the first part of this thesis, the first report of reasonably well preserved Griesbachian and Dienerian ammonoids from South China is provided. Since localities yielding ammonoids of this time interval are rare in the low palaeolatitude record, our report is a significant contribution to the biostratigraphy and biogeography of the evolutionary recovery of ammonoids. However, the record of Griesbachian and Dienerian ammonoid still remains far from complete in the Tethyan realm. Second, the Lower Triassic sedimentary record from the Tulong area in South Tibet is entirely documented for the first time. New age control is provided by ammonoid and conodont biostratigraphy. Comparison of the Tulong record with other Tethyan localities reveals striking similar facies in parts of the Lower Triassic record. Deciphering such large-scale patterns may provide new insights into the climatic control that regulated sedimentation and the Early Triassic biotic recovery, as well. High-resolution sampling leads to a new carbonate carbon isotope record for the Early Triassic in South Tibet, which provides additional evidence for the global character of the carbon cycle instabilities during the recovery interval, thus confirming the well-documented perturbations of the global carbon cycle in the aftermath of the Permian–Triassic mass extinction event. The main part of this dissertation focuses on the taxonomic revision and biostratigraphy of Smithian ammonoid faunas from several basins of the Northern Indian Margin. We conducted extensive field studies in two classical regions for the Early Triassic, namely the Salt Range (Pakistan) and Spiti (Indian Himalayas). Additionally, we studied a section at Tulong (South Tibet) as well as extremely ammonoid-rich exotic blocks of Hallstatt Limestone in the Oman Mountains. Our abundant, bed-rock-controlled and well-preserved material enables us to revise many classical ammonoid taxa that were previously only poorly known. Each species is analyzed to account for its intraspecific variation and its ontogenetic changes. Moreover, a large number of new taxa was found, which enables us to define one new family, 23 new genera and 41 new species.
Finally, biochronological data for the three well-documented basins Salt Range, Spiti and Tulong are analysed by means of the Unitary Associations Method, resulting in a biochronological scheme of unprecedented high resolution for the Smithian of the Northern Indian Margin. Analysis of ammonoid diversity dynamics based on this new high-resolution 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 rather low spatial and temporal resolutions, the evolutionary tempo of Early Triassic ammonoids appears surprisingly high, as highlighted by a recent study. We show here that at the finest possible scale, the Smithian recovery peak of
ammonoids is characterized by extremely high turnover rates.
Early Triassic
Biochronology
Ladinian
Tethys Ocean
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Paleoecological investigations can be undertaken on a single species, or they may examine the interactions of animals and plants that are preserved as fossil communities. Paleontologists use multiple sources of evidence to reconstruct the paleoecology of an individual animal and the interactions of that animal within its community. The exceptionally well-preserved fossil biota of Chengjiang provides one of the most important windows on the complexity of the ecosystem involving early metazoans. Arthropods dominate the Chengjiang biota, comprising more than one-third of species, followed by sponges and priapulid worms and relatives, each representing some 10% of species. In general the ecological structure of the Chengjiang biota is comparable to that of the middle Cambrian Burgess Shale of British Columbia. Echinoderms are typically stenohaline, requiring normal salinities, and their absence has been attributed to abnormal salinity or possibly due to the absence of hard substrates on the Chengjiang seabed.
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