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Bird femurs and dinosaur tails + other papers and news

From: Ben Creisler

A number of recent papers, news, and blog items that may be of interest:

>From SVP meeting:

Flightless birds and long-tailed dinosaurs


Technical Session XIV (Saturday, November 2, 2013, 10:45 AM)
CHAN, Nicholas, Macquarie University, Sydney, Australia

The removal of flight as a constraint on size has led to the evolution
of gigantism in several lineages of birds. However, even they have not
attained the size of large nonavian (n-a) theropods. Predictions of
two hypotheses were tested to examine potential size constraints in
flightless birds. The first is that egg shell strength restricts the
size of the incubating bird and that the extreme sexual dimorphism
seen in the moa genera Dinornis and Pachyornis was an adaptation to
reduce the stresses placed upon eggs during incubation. If so, then
similarly large birds should also exhibit extreme dimorphism. This was
tested for in Genyornis newtoni (Aves: Dromornithidae), an anseriform
bird similar in size to Dinornis. Coefficients of variation in the
size of leg bones from a sample of adult Genyornis from Lake
Callabonna, South Australia are three times lower than that of
Dinornis, suggesting that extreme dimorphism was absent.

Alternatively, a mechanical constraint caused by femoral orientation
may restrict mass in flightless birds. Unlike n-a theropods, birds
lack a long counter-balancing tail, and a sub-horizontal orientation
of the femur places the knee under the center of mass. This restricts
femur morphology, with femoral length constrained to maintain the
position of the knee and robusticity increasing with body mass to
counteract greater torsional strains. Previous studies have suggested
that these restrictions may limit body mass in flightless birds. As a
result, avian scaling curves are expected to exhibit a lower
inflection point than is seen in n-a theropods. In addition, if this
is a universal constraint in birds then different avian phylogenetic
groups should scale similarly. Femoral length and circumference
measurements were taken for 43 species from 7 orders of flightless
terrestrial birds and regression results compared to a data set for 81
n-a theropods compiled from the literature. Polynomial regressions
reveal significant curvilinearity in avian femoral scaling, whilst
model II regressions show significant overlap of slope and intercept
confidence intervals (CIs) for ratite (n=19), gruiform (n=13), and
galloanseraean (n=8) birds. Conversely, n-a theropods show no
significant curvilinearity and the CIs of maniraptorans (n=17) and
tyrannosauroids (n=18) do not overlap. This suggests greater
flexibility in femoral proportions in n-a theropods than in flightless
birds, supporting previous suggestions that femoral scaling in birds
is constrained by the loading regime.

Evidence for Shiva crater?

J.F. Lerbekmo (2013)
The Chicxulub-Shiva extraterrestrial one-two killer punches to Earth
65 million years ago.
Marine and Petroleum Geology (advance online publication)
doi:  http://dx.doi.org/10.1016/j.marpetgeo.2013.05.014

Two large asteroids struck Earth at almost the same time, 65 million
years ago, causing the major extinctions recognized as ending the
Mesozoic Era. Although occurring close together in time, the Earth's
magnetic pole had moved from the South Pole to the North Pole in
between, allowing a time difference between the impacts to be
calculated. The first strike produced a ~180 km diameter crater named
Chicxulub on the Yucatan shelf of southern Mexico. The second hit the
shelf of the northward drifting Indian continent in the southern
Indian Ocean, producing a crater ~450 × 600 km named Shiva. Hitherto,
the main obstacle to verifying this scenario has been the paucity of
geological sections containing evidence of both impacts. Here, we
present such evidence, and conclude that the two impacts were
separated by about 40,000 years.


Turtle origins

M. S. Y. Lee  (2013)
Turtle origins: insights from phylogenetic retrofitting and molecular scaffolds.
Journal of Evolutionary Biology 26(12): 2729–2738
DOI:  10.1111/jeb.12268

Adding new taxa to morphological phylogenetic analyses without
substantially revising the set of included characters is a common
practice, with drawbacks (undersampling of relevant characters) and
potential benefits (character selection is not biased by
preconceptions over the affinities of the ‘retrofitted’ taxon).
Retrofitting turtles (Testudines) and other taxa to recent reptile
phylogenies consistently places turtles with anapsid-grade
parareptiles (especially Eunotosaurus and/or pareiasauromorphs), under
both Bayesian and parsimony analyses. This morphological evidence for
turtle–parareptile affinities appears to contradict the robust genomic
evidence that extant (living) turtles are nested within diapsids as
sister to extant archosaurs (birds and crocodilians). However, the
morphological data are almost equally consistent with a
turtle–archosaur clade: enforcing this molecular scaffold onto the
morphological data does not greatly increase tree length (parsimony)
or reduce likelihood (Bayesian inference). Moreover, under certain
analytic conditions, Eunotosaurus groups with turtles and thus also
falls within the turtle–archosaur clade. This result raises the
possibility that turtles could simultaneously be most closely related
to a taxon traditionally considered a parareptile (Eunotosaurus) and
still have archosaurs as their closest extant sister group.


Pterosaur tracks from Utah to be displayed at American Museum of
Natural History for pterosaur exhibit (click to enlarge photo)



Pterosaur tracks found in  Dongyang in Zhejiang Province, China, along
with dinosaur and bird tracks (in Chinese)



New hypsilophodont from Spain (in Spanish)



Glow-in-the-dark dinosaur coins wins award



"Jurassic" petrified forest found in Qijiang in Yunnan Province, China
(in Chinese)

Apparently the wood is carbonized and can burn. The date is given as
140 million years ago and said to be Jurassic. However, if the date is
correct, it would be Early Cretaceous I assume.