Triassic recovery and extinction papers

[Ben Creisler <bcreisler@gmail.com>]

From: Ben Creisler
bcreisler@gmail.com

A number of recent papers about the Triassic--no new taxa, but some
interesting  info about the world early dinosaurs evolved in.

Zhong-Qiang Chen & Michael J. Benton (2012)
The timing and pattern of biotic recovery following the end-Permian
mass extinction.
Nature Geoscience 5: 375–383
doi:10.1038/ngeo1475
http://www.nature.com/ngeo/journal/v5/n6/abs/ngeo1475.html


The aftermath of the great end-Permian period mass extinction 252 Myr
ago shows how life can recover from the loss of >90% species globally.
The crisis was triggered by a number of physical environmental shocks
(global warming, acid rain, ocean acidification and ocean anoxia), and
some of these were repeated over the next 5–6 Myr. Ammonoids and some
other groups diversified rapidly, within 1–3 Myr, but extinctions
continued through the Early Triassic period. Triassic ecosystems were
rebuilt stepwise from low to high trophic levels through the Early to
Middle Triassic, and a stable, complex ecosystem did not re-emerge
until the beginning of the Middle Triassic, 8–9 Myr after the crisis.
A positive aspect of the recovery was the emergence of entirely new
groups, such as marine reptiles and decapod crustaceans, as well as
new tetrapods on land, including — eventually — dinosaurs. The
stepwise recovery of life in the Triassic could have been delayed
either by biotic drivers (complex multispecies interactions) or
physical perturbations, or a combination of both. This is an example
of the wider debate about the relative roles of intrinsic and
extrinsic drivers of large-scale evolution.

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Sofie Lindström, Bas van de Schootbrugge, Karen Dybkjær, Gunver Krarup
Pedersen,
Jens Fiebig, Lars Henrik Nielsen and Sylvain Richoz (2012)
No causal link between terrestrial ecosystem change and methane
release during the end-Triassic mass extinction.
Geology 40(6): 531-534
doi: 10.1130/G32928.1
http://geology.gsapubs.org/content/40/6/531.abstract


Profound changes in both marine and terrestrial biota during the
end-Triassic mass extinction event and associated successive carbon
cycle perturbations across the Triassic-Jurassic boundary (T-J, 201.3
Ma) have primarily been attributed to volcanic emissions from the
Central Atlantic Magmatic Province and/or injection of methane. Here
we present a new extended organic carbon isotope record from a cored
T-J boundary succession in the Danish Basin, dated by high-resolution
palynostratigraphy and supplemented by a marine faunal record.
Correlated with reference C-isotope and biotic records from the UK, it
provides new evidence that the major biotic changes, both on land and
in the oceans, commenced prior to the most prominent negative
C-isotope excursion. If massive methane release was involved, it did
not trigger the end-Triassic mass extinction. Instead, this negative
C-isotope excursion is contemporaneous with the onset of floral
recovery on land, whereas marine ecosystems remained perturbed. The
decoupling between ecosystem recovery on land and in the sea is more
likely explained by long-term flood basalt volcanism releasing both
SO2 and CO2 with short- and long-term effects, respectively.


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Abdallah M.B. Abu Hamad, André Jasper& Dieter Uhl (2012)
The record of Triassic charcoal and other evidence for
palaeo-wildfires: Signal for atmospheric oxygen levels, taphonomic
biases or lack of fuel?
International Journal of Coal Geology  96–97: 60–71
http://dx.doi.org/10.1016/j.coal.2012.03.006
http://www.sciencedirect.com/science/article/pii/S0166516212000791


As wildfires are today important sources of disturbance in many
terrestrial ecosystems, it is of great interest to understand how
different environmental parameters and fire-activity interacted during
past periods of the Earth history. Fossil charcoal, inertinites, and
pyrogenic polycyclic aromatic hydrocarbons (PAHs) represent the only
direct evidence for the occurrence of such palaeo-wildfires. In the
present study, a review of published data, together with new data on
the occurrence of fossil charcoal for the Permian and the Triassic is
presented. For a long time, it has been speculated, that an assumed
lack of evidence for palaeo-wildfires during the Triassic should be
explained by a large drop in atmospheric oxygen concentration
following or during the end-Permian mass extinction event, preventing
the occurrence of wildfires. However, evidence for palaeo-wildfires is
relatively common in many middle and late Triassic strata, whereas
such evidence is almost totally lacking from early Triassic sediments.
The interpretation of this “charcoal gap” or depression is difficult,
as many factors (e.g. atmospheric oxygen concentration, taphonomical
biases, lack of sediments suitable for the preservation of macroscopic
charcoal, lack of fuel, and “ignorance” of scientists) may have
influenced not only the production, but also the preservation and
recovery of evidence for palaeo-wildfires during this period. Thus, it
is not clear whether this Early Triassic “charcoal gap” can also be
seen as evidence for an assumed “wildfire gap” or not. Without any
doubt further investigations on the early Triassic record of charcoal
and other evidence for palaeo-wildfires will be necessary before this
problem can be solved. In fact, it can be expected that the number of
published records of (early) Triassic evidence for palaeo-wildfires
will increase in the future as more and more scientist working on
sediments of this age may become aware of the interest in fires from
this time. This will certainly make it possible to give a much better
picture of the temporal and regional distribution of wildfires during
this period in the future.

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Adam Bodzioch & Monika Kowal-Linka (2012)
Unraveling the origin of the Late Triassic multitaxic bone
accumulation at Krasiejów (S Poland) by diagenetic analysis.
Palaeogeography, Palaeoclimatology, Palaeoecology (advance online publication)
http://dx.doi.org/10.1016/j.palaeo.2012.05.015
http://www.sciencedirect.com/science/article/pii/S0031018212002817?v=s5



A study of aquatic and terrestrial vertebrate remains from a bonebed
in the Late Triassic continental succession near Krasiejów (S Poland)
shows it was deposited by a single catastrophic event, perhaps a
flood. Hardparts of Metoposaurus, Paleorhinus, and Stagonolepis show
sedimentary infill and geochemical evidence for early diagenesis at
different times and in different microenvironments. The infills in the
aquatic animal bones (sediment, pyrite, calcite) show deposition in a
freshwater environment, while those in the terrestrial Stagonolepis
remains (mainly barite) point to an arid terrestial environment. The
trace element content of the remains, together with the absence of a
distinct pattern of element distribution, supports the conclusion that
individual hardparts underwent diagenesis in various microenvironments
and at different times. The accumulation of multitaxic vertebrate
remains in a single bed clearly indicates event deposition. The
hardparts must originally have been deposited at various locations
during different times, but were later transported and deposited
together in a pond by a short-lived, high-energy event, probably a
flood after catastrophic rainfall.


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