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Mesozoic papers in International Year of Planet Earth 2012



From: Ben Creiser
bcreisler@gmail.com

Some new articles in the publication International Year of Planet
Earth 2012, related to Mesozoic life and extinctions:


Federico Fanti (2012)
Cretaceous Continental Bridges, Insularity, and Vicariance in the
Southern Hemisphere: Which Route Did Dinosaurs Take?
International Year of Planet Earth 2012, Part IV: 883-911
DOI: 10.1007/978-90-481-3428-1_31
http://www.springerlink.com/content/n31686212842q724/


The history of dispersal of biota during the Mesozoic in the southern
hemisphere is much debated. Clearly, the sequential break-up of
Gondwana produced physical barriers that must, variously, have
hampered dispersal events, and therefore impacted the phylogenetic
hypotheses. Did various terrestrial organisms undergo dispersal via
recently claimed continental bridges? When were the geographic and
environmental conditions at an optimum for diffusion during Mesozoic
times? Dinosaurs are arguably the most relevant group for illuminating
the biogeography of the southern landmasses during the Cretaceous.
Their vast stratigraphic and geographic occurrence is intimately
linked to the evolution of Gondwana. Recent discoveries from all
southern landmasses challenge several vicariant models. This study
summarizses the most significant geologic, palaeogeographic,
palaeontologic, and phylogenetic data on Cretaceous Gondwanan dinosaur
evolution, with particular emphasis on the ephemeral land bridges that
bulk large in recently developed biogeographic models. Comparison
between different datasets accords with a complex and sequential mix
of vicariance and dispersal patterns characterizing the fabric of
dinosaurian faunas at that time. This study probes the significance of
ephemeral intercontinental connections with regard to the biotic
dispersal in the Late Cretaceous. An earlier peak in dinosaur
diversity and dispersals seems likely.


===

Sankar Chatterjee and R. Jack Templin (2012)
Palaeoecology, Aerodynamics, and the Origin of Avian Flight.
International Year of Planet Earth 2012, Part II: 585-612
DOI: 10.1007/978-90-481-3428-1_18
http://www.springerlink.com/content/h2754p7l24828n38/


Data from hundreds of small, exquisitely preserved feathered
coelurosaurs and early birds from the Early Cretaceous Jehol Group,
Liaoning Province, China, suggest that avian flight probably began in
the trees (arboreal or trees-down theory) rather than on the ground
(cursorial or ground-up theory). The quality of preservation of the
Jehol biota and the sediment in which they were preserved accords with
recurrent mass mortality events, the animals being asphyxiated, buried
by ash falls and swiftly preserved. The inferred palaeoecology of the
Jehol biota indicates they lived in a forest environment bordering a
large lake. New information on the origin of flight by the Jehol
fossils is presented; it includes various transitional stages of
flight—from wingless, tree climbing coelurosaurs to parachuting, to
gliding, to fully winged, active flying birds. The fossils show
development of adaptations necessary to enable wing-assisted climbing:
highly recurved claws on hands and feet; long fingers, wrist joints
that swivelled, and stiffened tails. Several feathered paravian
coelurosaurs, exemplified by Epidendrosaurus, Epidexipteryx, and
Scansoriopteryx with wings suitable for climbing, became arboreal, yet
were flightless. Their arboreal lifestyles contradict arguments
previously advanced supporting the cursorial (ground-up) theory of the
origin avian flight. The cursorial model fails to explain climbing
adaptations of protobirds, different stages of flight, and development
of neurosensory specializations in early birds. Rather, the climbing
adaptations of protobirds support an arboreal setting for the
evolution of flight. These adaptations include, for example, different
stages of flight from a perch, gradual brain enlargement for
three-dimensional orientation, acquisition of vision and acute sight,
and neurosensory specialization for hearing and balance. We have
identified six evolutionary stages of avian flight represented by
phylogeny and transitional fossils—arboreal leaping, parachuting,
biplane gliding, monoplane gliding, undulating flight, and manoeuvring
flapping flight. Arboreal life is suggested to have promoted
enlargement of the brain, increased visual acuity, and development of
more sophisticated vision. A computer model to simulate the flight
performance of protobirds and early birds has been developed that
corroborates the argument for the above evolutionary pathway.



==

Gerta Keller (2012)
The Cretaceous–Tertiary Mass Extinction, Chicxulub Impact, and Deccan Volcanism
International Year of Planet Earth 2012, Part III : 759-793
DOI: 10.1007/978-90-481-3428-1_25
http://www.springerlink.com/content/n275347t87g03547/



After three decades of nearly unchallenged wisdom that a large impact
(Chicxulub) on Yucatan caused the end-Cretaceous mass extinction, this
theory is facing its most serious challenge from the Chicxulub impact
itself, as based on evidence in Texas and Mexico and from Deccan
volcanism in India. Data generated from over 150 Cretaceous–Tertiary
(KT) boundary sequences to date make it clear that the long-held
belief in the Chicxulub impact as the sole or even major contributor
to the KT mass extinction is not supported by evidence. The
stratigraphic position of the Chicxulub impact ejecta spherules in NE
Mexico and Texas and the impact breccia within the crater on Yucatan
demonstrate that this impact predates the KTB by about 300,000 years.
Planktic foraminiferal and stable isotope analyses across the primary
impact ejecta layer reveal that not a single species went extinct as a
result of this impact and no significant environmental changes could
be determined. The catastrophic effects of this impact have been
vastly overestimated. In contrast, recent advances in Deccan volcanic
studies indicate three volcanic phases with the smallest at 67.5 Ma,
the main phase at the end of the Maastrichtian (C29r), and the third
phase in the early Danian C29r/C29n transition (Chenet et al. 2007).
The main phase of eruptions occurred rapidly, was marked by the
longest lava flows spanning 1500 km across India, and ended coincident
with the KT boundary. The KT mass extinction may have been caused by
these rapid and massive Deccan lava and gas eruptions that account for
~80% of the entire 3500 m thick Deccan lava pile.


==


Thomas H. Rich and Patricia Vickers-Rich (2012)
Palaeobiogeography of Mesozoic Mammals – Revisited
International Year of Planet Earth 2012, Part IV: 913-934
DOI: 10.1007/978-90-481-3428-1_32
http://www.springerlink.com/content/q59w6645t22hrpp0/


The fossil record of mammals in the Mesozoic is decidedly meagre in
comparison to that of the Cainozoic, but some useful generalisations
can be drawn about the biogeographic history of this group during the
Mesozoic. Compared with the Jurassic, when cosmopolitanism was
frequent among the mammalian families, regionalism became more
pronounced in the Cretaceous, particularly the Late Cretaceous,
probably reflecting the continental aggregation that produced Pangea
and, subsequently Gondwana as the Mesozoic progressed. The
conventional hypothesis that therians arose on the northern continents
and dispersed to the southern continents reflects the poor Mesozoic
mammalian record. Recent discoveries in Africa, South America and
Australia suggest that caution is warranted before accepting the
conventional hypothesis.


===


Jeffrey D. Stilwell and Eckart Håkansson (2012)
Survival, but…! New Tales of ‘Dead Clade Walking’ from Austral and
Boreal Post-K–T Assemblages.
International Year of Planet Earth 2012, Part III: 795-810
DOI: 10.1007/978-90-481-3428-1_26
http://www.springerlink.com/content/r011j02w61738456/


Our knowledge of postmass extinction biotic trajectories is at the
mercy of available data and detailed research on the governing factors
of differential extinction/survivorship patterns of fossil biotas.
Some taxa managed—barely—to survive major extinction events, but only
for the short-term, becoming extinct at variable times in the
following geologic stage, having succumbed to myriad natural forces
generated by severe paleoenvironmental perturbations. These ‘Dead
Clade Walking’ (DCW) organisms should be included in investigations on
the resultant effects of the extinction bottleneck and subsequent
rebound phase(s). Significantly, even though the ‘big five’ mass
extinctions of the Phanerozoic are distinguished primarily by their
overwhelming intensities, their magnitudes—and thus importance for
shaping the present-day biosphere—have been systematically
underestimated, when time frames including immediate, post-apocalyptic
DCW taxa are included in survivorship/extinction analyses. Our
research from recent studies of Austral and Boreal invertebrates and
vertebrates in relation to the Cretaceous–Tertiary (K–T) boundary
provides alluring new evidence of the DCW phenomenon, including the
short-term survivorship of ammonoid cephalopods and possible non-avian
dinosaurs into the dawn of the Cenozoic.