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Pacific pelagic fish across the K/Pg mass extinction + ichnogenus Ichniotherium



Ben Creisler
bcreisler@gmail.com

A couple of non-dino papers that may be of interest:

Elizabeth C. Sibert, Pincelli M. Hull & Richard D. Norris (2014)
Resilience of Pacific pelagic fish across the Cretaceous/Palaeogene
mass extinction.
Nature Geoscience (advance online publication)
doi:10.1038/ngeo2227
http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2227.html

Open-ocean ecosystems experienced profound disruptions to biodiversity
and ecological structure during the Cretaceous/Palaeogene mass
extinction about 66 million years ago. It has been suggested that
during this mass extinction, a collapse of phytoplankton production
rippled up the food chain, causing the wholesale loss of consumers and
top predators. Pelagic fish represent a key trophic link between
primary producers and top predators, and changes in their abundance
provide a means to examine trophic relationships during extinctions.
Here we analyse accumulation rates of microscopic fish teeth and shark
dermal scales (ichthyoliths) in sediments from the Pacific Ocean and
Tethys Sea across the Cretaceous/Palaeogene extinction to reconstruct
fish abundance. We find geographic differences in post-disaster
ecosystems. In the Tethys Sea, fish abundance fell abruptly at the
Cretaceous/Palaeogene boundary and remained depressed for at least 3
million years. In contrast, fish abundance in the Pacific Ocean
remained at or above pre-boundary levels for at least four million
years following the mass extinction, despite marked extinctions in
primary producers and other zooplankton consumers in this region. We
suggest that the mass extinction did not produce a uniformly dead
ocean or microbially dominated system. Instead, primary production, at
least regionally, supported ecosystems with mid-trophic-level
abundances similar to or above those of the Late Cretaceous.

****

Marco Romano and Paolo Citton (2014)
Reliability of digit length impression as a character of tetrapod
ichnotaxobase: considerations from the Carboniferous–Permian
ichnogenus Ichniotherium.
Geological Journal (advance online publication)
DOI: 10.1002/gj.2601
http://onlinelibrary.wiley.com/doi/10.1002/gj.2601/abstract

Although the relative length of digit impressions is often adopted as
a binding character in ichnotaxa discrimination and trackmaker
identification, it cannot be considered unequivocally operative. The
reliability of this character has been evaluated by means of principal
component analysis on several well-preserved footprints (both manus
and pes) referred to as Ichniotherium sphaerodactylum from the Early
Permian Tambach Formation (Thuringia, Germany). The analysis reveals a
substantial variability of digit impression length (especially in the
manus), relativizing the validity of digit IV length as a diagnostic
character as practised in different ichnological studies. Regarding
the use of such a character, results clearly suggest the need to
preliminarily conduct explorative analysis on the whole available
ichnological material in order to detect which digit is the most
consistent from an ichnotaxonomical standpoint, thus avoiding an
arbitrary selection. Such a preliminary analysis should provide a
better control on ichnotaxonomical splitting/lumping, particularly in
the case of allied footprints, and can also be considered a valuable
tool, if associated to functionality analysis, in improving and
refining trackmaker identification.