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Triassic climates: Lydekkerina (stereospondyl) growth patterns + Mid-Carnian “Wet Intermezzo” global event



Ben Creisler
bcreisler@gmail.com



Two new papers:



Aurore Canoville and Anusuya Chinsamy (2015)
Bone microstructure of the stereospondyl Lydekkerina huxleyi reveals
adaptive strategies to the harsh post Permian-extinction environment.
The Anatomical Record (advance online publication)
DOI: 10.1002/ar.23160
http://onlinelibrary.wiley.com/doi/10.1002/ar.23160/abstract

The small-bodied stereospondyl Lydekkerina huxleyi, dominated the
amphibian fauna of the South African Lower Triassic. Even though the
anatomy of this amphibian has been well described, its growth
strategies and lifestyle habits have remained controversial. Previous
studies attributed the relative uniformity in skull sizes to a
predominance of subadult and adult specimens recovered in the fossil
record. Anatomical and taphonomic data suggested that the relatively
small body-size of this genus, compared to its Permo-Triassic
relatives, could be linked to a shortened, rapid developmental period
as an adaptation to maintain successful breeding populations under
harsh environmental conditions. Moreover, Lydekkerina's habitat has
been hypothesized to be either aquatic or mainly terrestrial. The
current study utilizes bone microstructure to re-assess previous
hypotheses pertaining to the biology and ecology of Lydekkerina.
Various skeletal elements of different-sized specimens are analyzed to
understand its growth dynamics, intra-skeletal variability and
lifestyle adaptations. Bone histology revealed that our sample
comprises individuals at different ontogenetic stages i.e., juveniles
to mature individuals. Our results show that these amphibians, despite
exhibiting plasticity in growth, experienced an overall faster growth
during early ontogeny (thereby attaining sexual maturity sooner), as
compared to most other temnospondyls. The microanatomy of the long
bones with their thick bone walls and distinctive medullary cavity
suggests that Lydekkerina may have been amphibious with a tendency to
be more terrestrial. Our study concludes that Lydekkerina employed a
peculiar growth strategy and lifestyle adaptations, which enabled it
to endure the harsh, dry conditions of the Early Triassic.


==

James G. Ogg (2015)
The mysterious Mid-Carnian “Wet Intermezzo” global event
Journal of Earth Science 26(2): 181-191
DOI: 10.1007/s12583-015-0527-x
http://link.springer.com/article/10.1007/s12583-015-0527-x

Approximately 230 million years ago in the middle of the Carnian stage
of the Upper Triassic, the sedimentary records in different regional
basins display dramatic changes. Tropical carbonate platforms abruptly
ended, and engorged river systems left widespread sand-rich layers
across inland basins and coastal regions. This pulse lasted less than
a million years in some basins, but constituted a permanent shift in
others. Following this event, the Late Carnian has the earliest record
of significant dinosaurs on land and the emergence of the calcareous
nannoplankton in the oceans that now govern Earth’s carbon cycle. This
"most distinctive climate change within the Triassic" has been
interpreted by some geoscientists as a global disruption of the
Earth’s land-ocean-biological system. The eruption of the Wrangellia
large igneous province may have been the trigger for a sudden
carbon-dioxide-induced warming and associated increased rainfall in
some of these regions. Indeed, some workers have proposed that this
"wet intermezzo" warming event is a useful analog to aid in predicting
the effects of our future greenhouse on land ecosystems and ocean
chemistry. However, the understanding of the onset, duration, global
impacts and relatively rapid termination of this postulated warming
pulse has been hindered by lack of a global dataset with
inter-calibrated terrestrial and marine biostratigraphy, precise
radio-isotopic ages, stable isotope records of temperature and the
carbon system, and cycle-calibrated rates of regional and global
change.