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No, nothing to do with what _Spinosaurus_ had for dinner; but some very
interesting paleoichthyological papers in the latest PNAS. (Although, for the
first paper, not necessarily mutually exclusive).
Matt Friedman (2009). Ecomorphological selectivity among marine teleost fishes
during the end-Cretaceous extinction. PNAS 106: 5218-5223.
"Despite the attention focused on mass extinction events in the fossil record,
patterns of extinction in the dominant group of marine vertebrates - fishes -
remain largely unexplored. Here, I demonstrate ecomorphological selectivity
among marine teleost fishes during the end-Cretaceous extinction, based on a
genus-level dataset that accounts for lineages predicted on the basis of
phylogeny but not yet sampled in the fossil record. Two ecologically relevant
anatomical features are considered: body size and jaw-closing lever ratio.
Extinction intensity is higher for taxa with large body sizes and jaws
consistent with speed (rather than force) transmission; resampling tests
indicate that victims represent a nonrandom subset of taxa present in the final
stage of the Cretaceous. Logistic regressions of the raw data reveal that this
nonrandom distribution stems primarily from the larger body sizes of victims
relative to survivors. Jaw mechanics are also a
significant factor for most dataset partitions but are always less important
than body size. When data are corrected for phylogenetic nonindependence, jaw
mechanics show a significant correlation with extinction risk, but body size
does not. Many modern large-bodied, predatory taxa currently suffering from
overexploitation, such billfishes and tunas, first occur in the Paleocene, when
they appear to have filled the functional space vacated by some extinction
An excerpt from the Results & Discussion:
"The clearest pattern delivered by this study is the complete
extirpation of large-bodied fishes with biomechanically fast jaws
... Elevated extinction intensity among teleosts appearing to occupy higher
trophic levels is consistent with the collapse of oceanic food webs,
corroborating earlier hypotheses implicating diet as an important determinant
of survivorship among fishes... The most prominent teleostean casualties of the
end-Cretaceous extinction include the predatory pachycormids,
pachyrhizodontids, ichthyodectiforms, enchodontids, and cimolichthyids, all of
which are equipped with high-aspect-ratio caudal fins and fusiform bodies that
imply fast swimming and sustained cruising."
That article is not open access, but the following article is:
Alan Pradel, Max Langer, John G. Maisey, Didier Geffard-Kuriyama, Peter
Cloetens, Philippe Janvier, and Paul Tafforeau (2009). Skull and brain of a
300-million-year-old chimaeroid fish revealed by synchrotron holotomography.
PNAS 106: 5224-5228.
"Living cartilaginous fishes, or chondrichthyans, include numerous elasmobranch
(sharks and rays) species but only few chimaeroid (ratfish) species. The early
history of chimaeroids, or holocephalans, and the modalities of their
divergence from elasmobranchs are much debated. During Carboniferous times,
358â300 million years (Myr) ago, they underwent a remarkable evolutionary
radiation, with some odd and poorly understood forms, including the enig
erygians that were known until now from poorly informative flattened
impressions. Here, we report iniopterygian skulls found preserved in 3
dimensions in â300-Myr-old concretions from Oklahoma and Kansas. The study
was performed by using conventional X-ray microtomography (ÎCT), as well as
absorption-based synchrotron microtomography (SR-ÎCT) [Tafforeau P, et al.
(2006) Applications of X-ray synchrotron microtomography for non-destructive 3D
studies of paleontological specimens. Appl Phys A
83:95â202] and a new holotomographic approach [Guigay P, Langer M, Boistel
R, Cloetens P (2007) Mixed transfer function and transport of intensity
approach for phase retrieval in the Fresnel region. Opt Lett 32:1617â1619],
which revealed their peculiar anatomy. Iniopterygians also share unique
characters with living chimaeroids, suggesting that the key chimaeroid skull
features were already established 300 Myr ago. Moreover, SR-ÎCT of an
articulated skull revealed a strikingly brain-shaped structure inside the
endocranial cavity, which seems to be an exceptional case of soft-tissue
mineralization of the brain, presumably as a result of microbially induced
postmortem phosphatization. This was imaged with exceptional accuracy by using
holotomography, which demonstrates its great potential to image preserved soft
parts in dense fossils."