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[dinosaur] Palacrodon from Arizona + from tracks from Korea + K-Pg seafloor eruptions + more

Ben Creisler

Some recent non-dino papers:

Free pdf:

Ben T. Kligman, Adam D. Marsh, and William G. Parker (2018)
First records of diapsid Palacrodon from the Norian, Late Triassic Chinle Formation of Arizona, and their biogeographic implications.
Acta Palaeontologica Polonica (in press)

Vertebrates from the Triassic Period have broadly disparate tooth shapes and dentition patterns, the result of intense morphospace experimentation following the Permo-Triassic extinction. Here, we describe fragmentary tooth-bearing jaw elements of the rare Gondwanan Middle Triassic taxon Palacrodon that represent first occurrences from the Upper Triassic Chinle Formation in northeastern Arizona. These specimens come from two notably diverse macrovertebrate and microvertebrate assemblages, the âcoprolite layerâ horizon in Petrified Forest National Park, and the Placerias Quarry near St. Johns, Arizona. Palacrodon is diagnosed by the presence of acrodont maxillary and dentary dentition of labiolingually-widened, bulbous teeth, which are fused to one another mesiodistally, and are pyramidal in lateral view. We agree with previous workers and refer Palacrodon to Diapsida based on the presence of a posterior jugal spur and a quadrate that has a quadratojugal foramen and a concave posterior surface. Formerly known only from the Cynognathus Assemblage Zone in southern Africa and Antarctica, the presence of Palacrodon in the Norian of North America represents a temporal range extension of at least 15 million years and represents the first tetrapod genus known to be present in the Karoo Basin, Fremouw Formation, and the Upper Triassic of the southwestern United States. Range extensions such as this suggest that some vertebrate biostratigraphic hypotheses for the Triassic may be less robust than previously believed and subject to significant sampling biases.


Won Mi Park, Martin G. Lockley, Jeong Yul Kim & Kyung Soo Kim (2018)
Anuran (frog) trackways from the Cretaceous of Korea.
Cretaceous Research (advance online publication)
doi: https://doi.org/10.1016/j.cretres.2018.02.002

Newly discovered frog tracks from the Cretaceous of Saok Island, South Korea, represent the first report of anuran (frog) tracks from the Phanerozoic of Asia and, only the second global report of Mesozoic anuran tracks. This is also the first global report of frog track assemblages with multiple trackways from multiple stratigraphic levels. The tracks occur in fine-grained lacustrine sediments and are generally well-preserved, showing a pentadactyl pes and a tetradacyl manus typical of modern anurans. The trackways indicate hopping locomotion, also typical of modern anurans, indicating that frog foot morphology and behavior have not changed significantly since the Late Cretaceous. The trackways reveal that some trackmakers possessed the ability to leap 6â7 times body (trunk) length. The material allows for the emendation of the diagnosis of the ichnogenus Ranipes and erection of the new ichnospecies Ranipes saokensis ichnosp. nov.. Associated tracks and traces of arthropods (cf. Diplichnites) and shorebirds are characteristic typical lacustrine margin paleoecology and the shorebird ichnofacies.


Free pdf:

John P Staub (2018)
Paleozoic geomagnetism shapes vertebrate evolution.
PeerJ Preprints 6:e26490v1
doi:Â https://doi.org/10.7287/peerj.preprints.26490v1

Background. Despite a fifty-year failure of paleontologists to find a viable connection between geomagnetic polarity reversals and evolutionary patterns, recent databases show that the early appearance, radiation, and diversification of Paleozoic vertebrates tend to occur during periods having frequent collapses of the Earthâs geomagnetic field. The transition time during the collapse of the Earthâs protective magnetic shield can last thousands of years, and the effects on biota are unknown. Solar and cosmic radiation, volcanism, weather alteration, low-frequency electromagnetic fields, depletion of ozone, and the stripping of atmospheric oxygen have been proposed as possible causes, but previous studies have found no effects.

Methods. Using published databases, we compiled a spreadsheet that shows the first appearance of 1809 age-dated genera with each genus assigned to one of 28 taxonomic groups. From Gradsteinâs Geologic Time Scale 2012, we delineated 17 Paleozoic zones with either high or low levels of polarity reversals.

Results. From our compilation, we counted 508 Paleozoic vertebrates that first appeared within 20 million-years of the origin of their clade or natural group. These genera represent the initial radiation and diversification of individual Paleozoic vertebrate clades. After compensating for sample-size and external geologic biases, the resulting Pearsonâs coefficient between these genera and polarity zones equals 0.781. Using 11 commonly accepted clades and assuming a natural competition existed between them, we counted each genus from a cladeâs inception until it was bypassed by a subsequent clade. Here, Pearson's equals 0.901 with a p-value of <0.000001. In a blindfold study, we separated the Paleozoic into a dozen equally-sized temporal bins, then 13 bins, up to 31 bins. The mean Pearson coefficient for these bins is 0.810. After calculating coefficients for four distinct taxonomies, two paleomagnetic systems, three systematics for age-dating within geologic stages, and seven independent spreadsheets, the results suggest a strong relationship exists between Paleozoic vertebrates and polarity reversals. In addition, the earliest species of the major divisions of Paleozoic vertebrates (jawless fish, armored fish, jawed fish, cartilage fish, fish with bones, lobe-finned fish, tetrapods, amphibians, reptiles, and synapsids) first appeared in zones with relatively high levels of polarity reversals.

Discussion. The question: is this apparent connection between geomagnetism and the evolution of Paleozoic vertebrate due to environmental or biologic factors. If biologic, why are vertebrates the only biota effected? And after an indeterminate period of time, how do vertebrate families become immune to the ongoing effects of polarity reversals?


Joseph S. Byrnes & Leif Karlstrom (2018)
Anomalous K-Pgâaged seafloor attributed to impact-induced mid-ocean ridge magmatism.
Science Advances 4(2): eaao2994
DOI: 10.1126/sciadv.aao2994 ,

Eruptive phenomena at all scales, from hydrothermal geysers to flood basalts, can potentially be initiated or modulated by external mechanical perturbations. We present evidence for the triggering of magmatism on a global scale by the Chicxulub meteorite impact at the Cretaceous-Paleogene (K-Pg) boundary, recorded by transiently increased crustal production at mid-ocean ridges. Concentrated positive free-air gravity and coincident seafloor topographic anomalies, associated with seafloor created at fast-spreading rates, suggest volumes of excess magmatism in the range of ~105 to 106 km3. Widespread mobilization of existing mantle melt by post-impact seismic radiation can explain the volume and distribution of the anomalous crust. This massive but short-lived pulse of marine magmatism should be considered alongside the Chicxulub impact and Deccan Traps as a contributor to geochemical anomalies and environmental changes at K-Pg time.





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