Rogerio R. Rubert, Ana Maria Pimentel Mizusaki, Agustín G. Martinelli & Camile Urban (2017)
Paleoenvironmental reconstruction and evolution of an Upper Cretaceous lacustrine-fluvial-deltaic sequence in the Parecis Basin, Brazil.
Journal of South American Earth Sciences (advance online publication)
Study of poorly known Cretaceous lacustrine-fluvial-deltaic sequence Central Brazil.
Detailed faciologic characterization and paleoenvironmental reconstruction.
Tectonic and sedimentary evolution of the Alto Xingu Sub-basin, Parecis Basin.
Inferred-age correlation with other South American basins.
Cretaceous vertebrate fossil record, extremely rare in this area of Brazil, within a paleoenvironmental study.
The Cretaceous in the Brazilian Platform records events of magmatism, tectonism and sedimentation coupled to the Gondwana breakup. Some of these events are registered as sedimentary sequences in interior basins, such as in the Cretaceous sequence of the Alto Xingu Sub-basin, Parecis Basin, Central Brazil. This article proposes the faciologic characterization and paleoenvironmental reconstruction of the Cretaceous sequence of the eastern portion of the Parecis Basin and its relation with some reactivated structures as, for instance, the Serra Formosa Arch. Based on both data from outcrops and core drillings a paleoenvironmental and evolutionary reconstruction of the sequence is herein presented. The base of the studied section is characterized by chemical and low energy clastic sedimentation of Lake Bottom and Shoreline, in a context of fast initial subsidence and low sedimentation rate. As the subsidence process decreased, a deltaic progradation became dominant with deposition in a prodelta environment, followed by a deltaic front and deltaic plain interbedded with fluvial plain, and aeolian deposition completing the sequence. The inferred Coniacian–Santonian age is based on vertebrate (fishes and notosuchians) and ostracod fossils with regional chrono-correlates in the Adamantina (Bauru Group), Capacete (Sanfranciscana Basin), and Bajo de la Carpa (Neuquén Group, in Argentina) formations. The formation of a Coniacian depocenter in the Alto Xingu Sub-basin is associated to the Turonian–Coniacian reactivation event in the Peruvian Orogenic Phase of the Andean Orogeny, with the transference of stresses to interplate setting, reactivating Proterozoic structures of the basement.
Pia A. Viglietti, Bruce S. Rubidge & Roger M. H. Smith (2017)
New Late Permian tectonic model for South Africa’s Karoo Basin: foreland tectonics and climate change before the end-Permian crisis.
Scientific Reports 7, Article number: 10861 (2017)
Late Permian Karoo Basin tectonics in South Africa are reflected as two fining-upward megacycles in the Balfour and upper Teekloof formations. Foreland tectonics are used to explain the cyclic nature and distribution of sedimentation, caused by phases of loading and unloading in the southern source areas adjacent to the basin. New data supports this model, and identifies potential climatic effects on the tectonic regime. Diachronous second-order subaerial unconformities (SU) are identified at the base and top of the Balfour Formation. One third-order SU identified coincides with a faunal turnover which could be related to the Permo-Triassic mass extinction (PTME). The SU are traced, for the first time, to the western portion of the basin (upper Teekloof Formation). Their age determinations support the foreland basin model as they coincide with dated paroxysms. A condensed distal (northern) stratigraphic record is additional support for this tectonic regime because orogenic loading and unloading throughout the basin was not equally distributed, nor was it in-phase. This resulted in more frequent non-deposition with increased distance from the tectonically active source. Refining basin dynamics allows us to distinguish between tectonic and climatic effects and how they have influenced ancient ecosystems and sedimentation through time.
Saurichthys spinosa sp. nov.
WU Fei-Xiang, SUN Yuan-Lin & FANG Geng-Yu (2017)
A new species of Saurichthys from the Middle Triassic (Anisian) of southwestern China.
Vertebrate PalAsiatica (advance online publication)
The saurichthyiform fishes were effective predators and hence the significant consumers in the aquatic ecosystems during the Early Mesozoic. They showed a notable diversification in the Anisian (Middle Triassic) Lagerstätten of southwestern China. In this contribution, we report a new species of Saurichthys from the Anisian of Yunnan, China, that displays some peculiar modifications of the axial skeleton and the longate body of the group. This new species, Saurichthys spinosa is a small-sized saurichthyid fish characterized by a very narrow interorbital region of the skull roof, an anteriorly expansive and ventrally arched cleithrum, proportionally large abdominal vertebrae lacking neural spines and alternately bearing laterally-stretching paraneural plates, few fin rays in the median fins, and two paralleling rows of needle-like flank scales with strong thorns. This fish has slimmed down the body by reducing the depth of the head and the epaxial part of the trunk. The elongate paraneural plates inserted in the horizontal septum and the rigid interlocking of the flank scales render the fish a very stiff body, which is compatible with the functional consequence of the obvious decrease of the body (vertebral) segments. This discovery reveals the variability of the axial skeleton and the hydrodynamic properties of the saurichthyiform fishes. These factors, together with the innovations in the locomotion and feeding habit, might have intrinsically effected the evolutionary burst of the eastern Tethyan saurichthyiform fishes during the Anisian, a marked signature of the rapid radiation stage of the biotic recovery after the end-Permian extinction.
Foreyia maxkuhni gen. et sp. nov.
Lionel Cavin, Bastien Mennecart, Christian Obrist, Loïc Costeur & Heinz Furrer (2017)
Heterochronic evolution explains novel body shape in a Triassic coelacanth from Switzerland.
Scientific Reports 7, Article number: 13695 (2017)
A bizarre latimeriid coelacanth fish from the Middle Triassic of Switzerland shows skeletal features deviating from the uniform anatomy of coelacanths. The new form is closely related to a modern-looking coelacanth found in the same locality and differences between both are attributed to heterochronic evolution. Most of the modified osteological structures in the new coelacanth have their developmental origin in the skull/trunk interface region in the embryo. Change in the _expression_ of developmental patterning genes, specifically the Pax1/9 genes, may explain a rapid evolution at the origin of the new coelacanth. This species broadens the morphological disparity range within the lineage of these ‘living fossils’ and exemplifies a case of rapid heterochronic evolution likely trigged by minor changes in gene _expression_.
Special Issues on Mesozoic Fishes in Thai journal Research & Knowledge Meeting on Mesozoic Fishes at Mahasarakham University (August 2017). All the papers are open access:
Research & Knowledge 3(1):
Research & Knowledge 3(2):
Alexander M. Dunhill, William J. Foster, James Sciberras & Richard
J. Twitchett (2017)
Impact of the Late Triassic mass extinction on functional diversity
and composition of marine ecosystems.
Palaeontology (advance online publication)
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.
The six largest known impact craters of the last 250 Myr (≥70 km in
diameter), which are capable of causing significant environmental damage,
coincide with four times of recognized extinction events at 36 (with 2
craters), 66, and 145 Myr ago, and possibly with two provisional extinction
events at 168 and 215 Myr ago. These impact cratering events are accompanied by
layers in the geologic record interpreted as impact ejecta. Chance occurrences
of impacts and extinctions can be rejected at confidence levels of 99.96% (for
4 impact/extinctions) to 99.99% (for 6 impact/extinctions). These results argue
that several extinction events over the last 250 Myr may be related to the
effects of large-body impacts.
Robert G. Jenkins, Andrzej Kaim, Kei Sato, Kazuhiro Moriya, Yoshinori
Hikida, and Ren Hirayama (2017)
Discovery of chemosynthesis-based association on the Cretaceous basal leatherback sea turtle from Japan.
Acta Palaeontologica Polonica (in press)
We report a Late Cretaceous chemosynthetic community fueled by decomposing basal leatherback sea turtle on the ocean floor in the western Pacific. The fossil association representing this community has been recovered from the matrix of a concretion containing a single carapace of Mesodermochelys sp. from Late Cretaceous outer shelf to upper slope deposit of northern Hokkaido, Japan. The carapace displays boreholes most likely performed by boring bivalves, and is associated with molluscan shells, mainly Provanna cf. nakagawensis and Thyasira tanabei. Since this association is similar to fauna already known from Late Cretaceous hydrocarbon seeps, sunken wood, and plesiosaur-falls in Hokkaido, it is suggested that all types of chemosynthesis-based communities in the Late Cretaceous of western Pacific may have belonged to the same regional pool of animals and were not yet fully differentiated into three independent types of communities as it is known today. This finding also indicates that the sulfophilic stage of the vertebrate-fall communities was supported not only by plesiosaur carcasses, which were previously reported, but also by sea turtle carcasses. It highlights the possibility of surviving vertebrate-fall communities through the end-Cretaceous mass extinction event on carcasses of sea turtles which are the only large marine vertebrates surviving this event.