Dicynodonts represent a speciose clade of non-mammalian synapsids that lived from the middle Permian to the Late Triassic, exhibiting a Pangaean distribution. The South American Norian fossil record is represented by two species: Jachaleria colorata from Argentina and J. candelariensis from Brazil. The Brazilian specimens come from a relatively small quarry located in the site known as Botucaraà or Botucaraà Hill (CandelÃria, Rio Grande do Sul). We describe here four dorsal vertebrae of a single individual referred to cf. Jachaleria candelariensis from a site named Alto Guarda Mor, located in the Faxinal do Soturno municipality, State of Rio Grande do Sul, Brazil. This taxonomic proposal and the lithological features of the site support that the outcrop belongs to the Riograndia Assemblage Zone (AZ; CandelÃria Sequence, Santa Maria Supersequence). Although the specimen cannot be referred unambiguously to Jachaleria candelariensis due to the lack of cranial material, it likely represents the second record of the genus in the Triassic of Brazil. We further discuss the faunal composition and relative age of some sites referred to the Riograndia AZ, which exhibit odd faunal context likely representing an AZ between the top of the Hyperodapedon AZ and the base of the Riograndia AZ.
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The density, or specific gravity (SG), of organisms has numerous important implications for their form, function, ecology, and other facets of beings living and dead, and it is especially necessary to apply SG values that are as accurate as practical when estimating their masses which is itself a critical aspect of living things. Yet a comprehensive review and analysis of this notable subject of anatomy has never been conducted and published. This is such an effort, being as extensive as possible with the data on hand, bolstered by some additional observations, and new work focusing on extinct animals who densities are least unknown: pterosaurs and dinosaurs with extensive pneumatic complexes, including the most sophisticated effort to date for a sauropod. Often difficult to determine even via direct observation, techniques for obtaining the best possible SG data are explained and utilized, including observations of floating animals. Neutral SG (NSG) is proposed as the most important value for tetrapods with respiratory tracts of fluctuating volume. SGs of organisms range from 0.08 to 2.6, plant tissues from 0.08 to 1.39, and vertebrates from about 0.75 (some giant pterosaurs) to 1.2 (those with heavy armor and/or skeletons). Tetrapod NSGs tend to be somewhat higher than widely thought, especially those theropod and sauropod dinosaurs and pterosaurs with airâsacs because diverticula volume is usually measured at maximum inhalation in birds. Also discussed is evidence that the ratio of the mass of skeletons relative to total body mass has not been properly assayed in the past.
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Free pdf:
T. J. Bralower, J. Cosmidis, M. S. Fantle, C. M. Lowery, B. H. Passey, S. P. S. Gulick,J. V. Morgan, V. Vajda, M. T. Whalen, A. Wittmann, N. Artemieva, K. Farley,S. Goderis, E. Hajek, P. J. Heaney, D. A. Kring, S. L. Lyons, C. Rasmussen,E. Sibert, F. J. RodrÃguez Tovar, G. TurnerâWalker, J. C. Zachos, J. Carte, S. A. Chen,C. Cockell, M. Coolen, K. H. Freeman, J. Garber, M. Gonzalez, J. L. Gray, K. Grice,H. L. Jones, B. Schaefer, J. Smit, and S. M. Tikoo (2020)
The Habitat of the Nascent Chicxulub Crater.
AGU Advances 1(4) (advance online publication)
doi:
https://doi.org/10.1029/2020AV000208https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2020AV000208Free pdf:
https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2020AV000208
An expanded sedimentary section provides an opportunity to elucidate conditions in the nascent Chicxulub crater during the hours to millennia after the CretaceousâPaleogene (KâPg) boundary impact. The sediments were deposited by tsunami followed by seiche waves as energy in the crater declined, culminating in a thin hemipelagic marlstone unit that contains atmospheric fallout. Seiche deposits are predominantly composed of calcite formed by decarbonation of the target limestone during impact followed by carbonation in the water column. Temperatures recorded by clumped isotopes of these carbonates are in excess of 70ÂC, with heat likely derived from the central impact melt pool. Yet, despite the turbidity and heat, waters within the nascent crater basin soon became a viable habitat for a remarkably diverse cross section of the food chain. The earliest seiche layers deposited with days or weeks of the impact contain earliest Danian nannoplankton and dinocyst survivors. The hemipelagic marlstone representing the subsequent years to a few millennia contains a nearly monogeneric calcareous dinoflagellate resting cyst assemblage suggesting deteriorating environmental conditions, with one interpretation involving low light levels in the impact aftermath. At the same horizon, microbial fossils indicate a thriving bacterial community and unique phosphatic fossils including appendages of pelagic crustaceans, coprolites and bacteriaâtunneled fish bone, suggesting that this rapid recovery of the base of the food chain may have supported the survival of larger, higher trophicâlevel organisms. The extraordinarily diverse fossil assemblage indicates that the crater was a unique habitat in the immediate impact aftermath, possibly as a result of heat and nutrients supplied by hydrothermal activity.
Plain Language Summary
The newly formed Chicxulub crater was rapidly filled by seawater then disturbed by tsunami and seiche waves. Sedimentary layers deposited as wave energy declined provide a unique window into the environment of the nascent crater in the months and years to millennia after the impact. Geochemical data show temperatures in hotter regions of the crater in excess of 70ÂC for the first few years with heat derived from the underlying melt sheet via hydrothermal circulation. Cooler regions of the crater became habitats soon after impact with a suite of fossils indicating diverse life on the seafloor and sea surface, ranging from microbes to marine arthropods, and possibly fish. We suggest that this community was sustained by nutrients and heat from the hydrothermal system. The rapid early recovery in the Chicxulub crater and ocean above demonstrates the resiliency of life under extraordinarily harsh conditions, which has important ramifications for early life on Earth and life on other planets.
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