Lorenzo Marchetti, Andrea Tessarollo, Fabrizio Felletti, and Ausonio Ronchi (2017)
Tetrapod footprint paleoecology: behavior, taphonomy and ichnofauna disentangled. A case study from the Lower Permian of the Southern Alps (Italy).
PALAIOS 32(8): 506-527
Vertebrate tracks are linked to the depositional environment
where they were formed. Several studies hypothesized a paleoenvironmental
control on vertebrate track ichnocoenoses, although this issue was never
analyzed thoroughly. A new study of the sedimentology and tetrapod ichnology of
two key stratigraphic sections in the Pizzo del Diavolo Formation of the lower
Permian continental Orobic Basin of Southern Alps (Italy) tested the link
between tetrapod ichnocoenoses and depositional environment. Behavior,
taphonomy, and ichnocoenoses of three different lithozones (P-PDV, U-PDVa,
U-PDVb) were analyzed and compared, two new census methods for tetrapod tracks
were tested (“track/slab” and “weighting size”) and the first was applied to
our specimen sample. The possible biostratigraphic meaning of track
occurrences/relative proportions were discussed and excluded. Results indicate
a predominance of the ichnogenus Erpetopus in a distal floodplain environment
(P-PDV), a diverse ichnocoenosis in a proximal floodplain environment (U-PDVa),
and a predominance of the ichnogenus Dromopus in a scarcely diverse
ichnocoenosis in a floodplain/marginal lacustrine environment (U-PDVb). This
encourages further detailed studies on tetrapod track paleoecology, in order to
refine and give utility to the concept of tetrapod ichnofacies.
Jonathan P. Rio & Philip D. Mannion (2017)
The osteology of the giant snake Gigantophis garstini from the upper Eocene of North Africa and its bearing on the phylogenetic relationships and biogeography of Madtsoiidae.
Journal of Vertebrate Paleontology Article: e1347179 (advance online publication)
Madtsoiidae is a speciose family of extinct snakes that achieved a wide Gondwanan and trans-Tethyan distribution by the Late Cretaceous, surviving until the late Pleistocene. Gigantophis garstini, the first and largest described madtsoiid, was recovered from the upper Eocene of Fayum, Egypt. The 20 vertebrae that constitute the syntype have only received brief description, hindering the referral of specimens to this taxon and our understanding of madtsoiid interrelationships in general. A detailed redescription of the syntype material demonstrates the validity of Gigantophis, based on two autapomorphies (including a strongly depressed neural canal in posterior trunk vertebrae) and a unique combination of characters. Referred material from the lower Paleocene of Pakistan differs significantly, and we restrict Gigantophis to the middle–late Eocene of North Africa. Using a model of morphological variation in extant snakes, we estimate that Gigantophis was 6.9 ± 0.3 m long. A phylogenetic analysis using the largest sample of putative madtsoiids (20 operational taxonomic units) and a revised and augmented matrix (148 characters) places Gigantophis as sister taxon to the latest Cretaceous Indian snake Madtsoia pisdurensis. Whereas our topology might suggest that a dispersal route was present between India and North Africa in the latest Cretaceous–early Paleogene, an evaluation of putative dispersal routes leads us to conclude that the paleobiogeography of Madtsoiidae is best explained by a poorly sampled, earlier widespread distribution in Africa, Indo-Madagascar, and South America. In contrast, latest Cretaceous madtsoiid occurrences in Europe might be explicable by trans-Tethyan dispersal from Africa across the Apulian Route.
Sophie Macaulay, John R. Hutchinson and Karl T. Bates (2017)
A quantitative evaluation of physical and digital approaches to centre of mass estimation.
Journal of Anatomy (advance online publication)
Centre of mass is a fundamental anatomical and biomechanical parameter. Knowledge of centre of mass is essential to inform studies investigating locomotion and other behaviours, through its implications for segment movements, and on whole body factors such as posture. Previous studies have estimated centre of mass position for a range of organisms, using various methodologies. However, few studies assess the accuracy of the methods that they employ, and often provide only brief details on their methodologies. As such, no rigorous, detailed comparisons of accuracy and repeatability within and between methods currently exist. This paper therefore seeks to apply three methods common in the literature (suspension, scales and digital modelling) to three ‘calibration objects’ in the form of bricks, as well as three birds to determine centre of mass position. Application to bricks enables conclusions to be drawn on the absolute accuracy of each method, in addition to comparing these results to assess the relative value of these methodologies. Application to birds provided insights into the logistical challenges of applying these methods to biological specimens. For bricks, we found that, provided appropriate repeats were conducted, the scales method yielded the most accurate predictions of centre of mass (within 1.49 mm), closely followed by digital modelling (within 2.39 mm), with results from suspension being the most distant (within 38.5 mm). Scales and digital methods both also displayed low variability between centre of mass estimates, suggesting they can accurately and consistently predict centre of mass position. Our suspension method resulted not only in high margins of error, but also substantial variability, highlighting problems with this method.
Mercedes E. Belica, Eric Tohver, Miquel Poyatos-Moré, Stephen Flin, Luis A. Parra-Avila, Luca Lanci Steven Denyszyn & Sergei A Pisarevsky (2017)
Refining the chronostratigraphy of the Karoo Basin, South Africa: magnetostratigraphic constraints support an Early Permian age for the Ecca Group.
Geophysical Journal International (advance online publication)
The Beaufort Group of the Karoo Basin, South Africa provides an important chrono- and biostratigraphic record of vertebrate turnovers that have been attributed to the End-Permian mass extinction events at ca. 252 Ma and ca. 260 Ma. However, an unresolved controversy exists over the age of the Beaufort Group due to a large dataset of published U-Pb SHRIMP zircon results that indicate a ca. 274–250 Ma age range for deposition of the underlying Ecca Group. This age range requires the application of a highly diachronous sedimentation model to the Karoo Basin stratigraphy and is not supported by published paleontologic and palynologic data. This study tested the strength of these U-Pb isotopic datasets using a magnetostratigraphic approach. Here we present a composite ∼1500 m section through a large part of the Ecca Group from the Tanqua depocentre, located in the southwestern segment of the Karoo Basin. After the removal of two normal polarity overprints, a likely primary magnetic signal was isolated at temperatures above 450° C. This section is restricted to a reverse polarity, indicating that it formed during the Kiaman Reverse Superchron (ca. 318–265 Ma), a distinctive magnetostratigraphic marker for Early−Middle Permian rocks. The Ecca Group has a corresponding paleomagnetic pole at 40.8° S, 77.4° E (A95 = 5.5°). U-Pb SHRIMP ages on zircons are presented here for comparison with prior isotopic studies of the Ecca Group. A weighted mean U-Pb age of 269.5 ± 1.2 Ma was determined from a volcanic ash bed located in the uppermost Tierberg Formation sampled from the OR1 research core. The age is interpreted here as a minimum constraint due to a proposed Pb-loss event that has likely influenced a number of published results. A comparison with the Geomagnetic Polarity Time Scale as well as published U-Pb TIMS ages from the overlying Beaufort Group supports a ca. 290–265 Ma age for deposition of the Ecca Group.
Celina A. Suarez, Todd K. Knobbe, James L. Crowley, James I. Kirkland & Andrew R.C. Milner (2017)
A chronostratigraphic assessment of the Moenave Formation, USA using C-isotope chemostratigraphy and detrital zircon geochronology: Implications for the terrestrial end Triassic extinction.
Earth and Planetary Science Letters 475: 83–93
Detrital zircons reveal the 1st maximum depositional ages from the formation.
These ages are 201.33 ± 0.07/0.12/0.25 Ma for the upper Dinosaur Canyon Member and
201.28 ± 0.11/0.15/0.26 Ma for the middle sandstone of the Whitmore Point Member.
This correlates to bio- and magnetostratigraphy but not the C-isotope record.
C-isotope excursions occur in the Jurassic and the ETE occurs in the mid-lower DCM.
The Late Triassic is a period of abrupt climate change associated with a disruption to the global carbon cycle usually ascribed to the emplacement of the Central Atlantic Magmatic Province (CAMP). Geochronologic, paleontologic, and geochemical studies have shown that the CAMP was likely the major factor for the end-Triassic extinction (ETE), however, difficulties correlating and dating terrestrial strata has left the nature of the terrestrial extinction in question. The lacustrine Whitmore Point Member (WPM) of the Moenave Formation is ideal for investigating these details because it is reported to be Late Triassic to Early Jurassic. However, currently there are conflicting age constraints between biostratigraphy and magnetostratigraphy. In this study we attempt to elucidate the ETE by incorporating C-isotope chemostratigraphy and detrital zircon geochronology. Detrital zircon geochronology suggests the upper part of the Dinosaur Canyon Member (DCM) is younger (201.33 ± 0.07/0.12/0.25 Ma) than the ETE (201.564 Ma) suggesting the ETE is in the middle to lower DCM, in agreement with track biostratigraphy (first occurrence of Eubrontes, Anomoepus, and Batrachopus). Meanwhile a distinct negative carbon isotope (NCIE) excursion (−5.5‰) occurs at the base of the WPM at Potter Canyon, AZ with a more subtle NCIE at the base of the WPM at Black Canyon, UT (−2.0‰) that may correlate to the initial NCIE at the ETE. However, the WPM NCIE is correlated to the preservation of organic C (relative %C) suggesting it may be either related to local lake productivity and biases in organic matter preservation or may be a negative CIE in the Jurassic Hettangian stage. With the addition of the detrital zircon data, we suggest the M2r reversal at the base of the WPM is a reversal in the Hettangian (the H24r, H25r, or H26r) and the ETE is within the DCM. Additional C-isotope analysis of the DCM is necessary to determine if the initial NCIE that is the hallmark of the ETE occurs in terrestrial strata in western Pangea. However, our WPM C-isotope record is the most complete C-isotope record from terrestrial strata of western Pangea to date and in addition to detrital zircon geochronology, magnetostratigraphy, and biostratigraphy, will be used to provide a framework for future chronologic and paleoclimatic studies.
Adam B. Jost, Aviv Bachan, Bas van de Schootbrugge, Kimberly V. Lau, Karrie L. Weaver, Kate Maher & Jonathan L. Payne (2017)
Uranium isotope evidence for an expansion of marine anoxia during the end-Triassic extinction.
Geochemistry, Geophysics, Geosystems (advance online publication)
The end-Triassic extinction coincided with an increase in marine black shale deposition and biomarkers for photic zone euxinia, suggesting that anoxia played a role in suppressing marine biodiversity. However, global changes in ocean anoxia are difficult to quantify using proxies for local anoxia. Uranium isotopes (δ238U) in CaCO3 sediments deposited under locally well-oxygenated bottom waters can passively track seawater δ238U, which is sensitive to the global areal extent of seafloor anoxia due to preferential reduction of 238U(VI) relative to 235U(VI) in anoxic marine sediments. We measured δ238U in shallow-marine limestones from two stratigraphic sections in the Lombardy Basin, northern Italy, spanning over 400 m. We observe a ∼0.7‰ negative excursion in δ238U beginning in the lowermost Jurassic, coeval with the onset of the initial negative δ13C excursion and persisting for the duration of subsequent high δ13C values in the lower-middle Hettangian Stage. The δ238U excursion cannot be realistically explained by local mixing of uranium in primary marine carbonate and reduced authigenic uranium. Based on output from a forward model of the uranium cycle, the excursion is consistent with a 40–100-fold increase in the extent of anoxic deposition occurring worldwide. Additionally, relatively constant uranium concentrations point towards increased uranium delivery to the oceans from continental weathering, which is consistent with weathering-induced eutrophication following the rapid increase in pCO2 during emplacement of the Central Atlantic Magmatic Province. The relative timing and duration of the excursion in δ238U implies that anoxia could have delayed biotic recovery well into the Hettangian stage.
Michael R. Rampino & Ken Caldeira (2017)
Comparison of the ages of large-body impacts, flood-basalt eruptions, ocean-anoxic events and extinctions over the last 260 million years: a statistical study.
International Journal of Earth Sciences (advance online publication)
Many studies have linked mass extinction events with the catastrophic effects of large-body impacts and flood-basalt eruptions, sometimes as competing explanations. We find that the ages of at least 10 out of a total of 11 documented extinction events over the last 260 Myr (12 out of 13 if we include two lesser extinction events) coincide, within errors, with the best-known ages of either a large impact crater (≥70 km diameter) or a continental flood-basalt eruption. The null hypothesis that this could occur by chance can be rejected with very high confidence (>99.999%). The ages of large impact craters correlate with recognized extinction events at ~36 (two impacts), 66, 145 and 215 Myr ago (and possibly an event at ~168 Myr ago), and the ages of continental flood basalts correlate with extinctions at 66, ~94, ~116, 183, 201, 252 and 259 Myr ago (and possibly at ~133 Myr ago). Furthermore, at least 7 periods of widespread anoxia in the oceans of the last 260 Myr coincide with the ages of flood-basalt eruptions (with 99.999% confidence), and are coeval with extinctions, suggesting causal connections. These statistical relationships argue that most mass extinction events are related to climatic catastrophes produced by the largest impacts and large-volume continental flood-basalt eruptions.
Spencer G. Lucas (2017)
The best sections method of studying mass extinctions
Lethaia (advance online publication)
Phanerozoic mass extinctions have been studied primarily by analysing global diversity patterns compiled from the published literature. However, such compilations are beset by problems of incorrect correlation, imprecise age assignments and changing taxonomy. An alternative approach is to analyse mass extinctions by the ‘best sections’ method. This method identifies abundantly fossiliferous, well-studied, stratigraphically dense and temporally extensive fossil records in strata that contain geochemical and other relevant non-palaeontological data from a single depositional basin or geographically restricted outcrop area as the ‘best sections’ by which to analyse extinctions. A strength of the best sections method is that it allows the extinctions identified to be compared directly to changes in facies and other factors recorded in the best section. And, the hypothesis of a widespread extinction based on an extinction seen in a best section can be tested by its presence or absence in temporally equivalent sections. What we need are more field-based studies of the best sections that encompass mass extinctions (real and hypothetical) and less of a reliance on literature-based diversity compilations to produce a more reliable and comprehensive understanding of the history of extinctions.
Chadlin M. Ostrander, Jeremy D. Owens and Sune G. Nielsen (2017)
Constraining the rate of oceanic deoxygenation leading up to a Cretaceous Oceanic Anoxic Event (OAE-2: ~94 Ma).
Science Advances 3(8): e1701020
The rates of marine deoxygenation leading to Cretaceous Oceanic Anoxic Events are poorly recognized and constrained. If increases in primary productivity are the primary driver of these episodes, progressive oxygen loss from global waters should predate enhanced carbon burial in underlying sediments—the diagnostic Oceanic Anoxic Event relic. Thallium isotope analysis of organic-rich black shales from Demerara Rise across Oceanic Anoxic Event 2 reveals evidence of expanded sediment-water interface deoxygenation ~43 ± 11 thousand years before the globally recognized carbon cycle perturbation. This evidence for rapid oxygen loss leading to an extreme ancient climatic event has timely implications for the modern ocean, which is already experiencing large-scale deoxygenation.