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End-Triassic extinction + bird diversity across K-Pg + alligator vocalizations (free pdf) + more

Ben Creisler

A number of recent, mainly non-dino papers that may be of interest:

Alexander M. Dunhill & Matthew A. Wills (2015)
Geographic range did not confer resilience to extinction in
terrestrial vertebrates at the end-Triassic crisis.
Nature Communications 6, Article number: 7980

Rates of extinction vary greatly through geological time, with losses
particularly concentrated in mass extinctions. Species duration at
other times varies greatly, but the reasons for this are unclear.
Geographical range correlates with lineage duration amongst marine
invertebrates, but it is less clear how far this generality extends to
other groups in other habitats. It is also unclear whether a wide
geographical distribution makes groups more likely to survive mass
extinctions. Here we test for extinction selectivity amongst
terrestrial vertebrates across the end-Triassic event. We demonstrate
that terrestrial vertebrate clades with larger geographical ranges
were more resilient to extinction than those with smaller ranges
throughout the Triassic and Jurassic. However, this relationship
weakened with increasing proximity to the end-Triassic mass
extinction, breaking down altogether across the event itself. We
demonstrate that these findings are not a function of sampling biases;
a perennial issue in studies of this kind.







Bird Evolution

Daniel T. Ksepka and Matthew J. Phillips (2015)
Avian Diversification Patterns across the K-Pg Boundary: Influence of
Calibrations, Datasets, and Model Misspecification.
Annals of the Missouri Botanical Garden 100(4):300-328. 2015
doi: http://dx.doi.org/10.3417/2014032

Birds represent the most diverse extant tetrapod clade, with ca.
10,000 extant species, and the timing of the crown avian radiation
remains hotly debated. The fossil record supports a primarily Cenozoic
radiation of crown birds, whereas molecular divergence dating analyses
generally imply that this radiation was well underway during the
Cretaceous. Furthermore, substantial differences have been noted
between published divergence estimates. These have been variously
attributed to clock model, calibration regime, and gene type. One
underappreciated phenomenon is that disparity between fossil ages and
molecular dates tends to be proportionally greater for shallower nodes
in the avian Tree of Life. Here, we explore potential drivers of
disparity in avian divergence dates through a set of analyses applying
various calibration strategies and coding methods to a mitochondrial
genome dataset and an 18-gene nuclear dataset, both sampled across 72
taxa. Our analyses support the occurrence of two deep divergences
(i.e., the Palaeognathae/Neognathae split and the Galloanserae/Neoaves
split) well within the Cretaceous, followed by a rapid radiation of
Neoaves near the K-Pg boundary. However, 95% highest posterior density
intervals for most basal divergences in Neoaves cross the boundary,
and we emphasize that, barring unreasonably strict prior
distributions, distinguishing between a rapid Early Paleocene
radiation and a Late Cretaceous radiation may be beyond the resolving
power of currently favored divergence dating methods. In contrast to
recent observations for placental mammals, constraining all
divergences within Neoaves to occur in the Cenozoic does not result in
unreasonably high inferred substitution rates. Comparisons of nuclear
DNA (nDNA) versus mitochondrial DNA (mtDNA) datasets and NT- versus
RY-coded mitochondrial data reveal patterns of disparity that are
consistent with substitution model misspecifications that result in
tree compression/tree extension artifacts, which may explain some
discordance between previous divergence estimates based on different
sequence types. Comparisons of fully calibrated and nominally
calibrated trees support a correlation between body mass and apparent
dating error. Overall, our results are consistent with (but do not
require) a Paleogene radiation for most major clades of crown birds.


Jonathan S. Mitchell (2015)
Extant-only comparative methods fail to recover the disparity
preserved in the bird fossil record.
Evolution (advance online publication)
DOI: 10.1111/evo.12738

Most extant species are in clades with poor fossil records, and recent
studies of comparative methods show have low power to infer even
highly simplified models of trait evolution without fossil data. Birds
are a well-studied radiation, yet their early evolutionary patterns
are still contentious. The fossil record suggests that birds underwent
a rapid ecological radiation after the end-Cretaceous mass extinction,
and several smaller, subsequent radiations. This hypothesized series
of repeated radiations from fossil data is difficult to test using
extant data alone. By uniting morphological and phylogenetic data on
604 extant genera of birds with morphological data on 58 species of
extinct birds from 50 million years ago, the “halfway point” of avian
evolution, I have been able to test how well extant-only methods
predict the diversity of fossil forms . All extant-only methods
underestimate the disparity, although the ratio of within to between
clade disparity does suggest high early rates. The failure of standard
models to predict high early disparity suggests that recent radiations
are obscuring deep time patterns in the evolution of birds. Metrics
from different models can be used in conjunction to provide more
valuable insights than simply finding the model with the highest
relative fit.


Alligator Vocalizations

Reber, S. A., Nishimura, T., Janisch, J., Robertson, M. and Fitch, W. T. (2015)
A Chinese alligator in heliox: formant frequencies in a crocodilian.
Journal of Experimental Biology 218: 2442-2447

Free pdf:

Crocodilians are among the most vocal non-avian reptiles. Adults of
both sexes produce loud vocalizations known as ‘bellows’ year round,
with the highest rate during the mating season. Although the specific
function of these vocalizations remains unclear, they may advertise
the caller's body size, because relative size differences strongly
affect courtship and territorial behaviour in crocodilians. In mammals
and birds, a common mechanism for producing honest acoustic signals of
body size is via formant frequencies (vocal tract resonances). To our
knowledge, formants have to date never been documented in any
non-avian reptile, and formants do not seem to play a role in the
vocalizations of anurans. We tested for formants in crocodilian
vocalizations by using playbacks to induce a female Chinese alligator
(Alligator sinensis) to bellow in an airtight chamber. During
vocalizations, the animal inhaled either normal air or a helium/oxygen
mixture (heliox) in which the velocity of sound is increased. Although
heliox allows normal respiration, it alters the formant distribution
of the sound spectrum. An acoustic analysis of the calls showed that
the source signal components remained constant under both conditions,
but an upward shift of high-energy frequency bands was observed in
heliox. We conclude that these frequency bands represent formants. We
suggest that crocodilian vocalizations could thus provide an acoustic
indication of body size via formants. Because birds and crocodilians
share a common ancestor with all dinosaurs, a better understanding of
their vocal production systems may also provide insight into the
communication of extinct Archosaurians.


Kathryn Knight (2015)
Alligators use resonance for communication
Journal of Experimental Biology 218: 2315-2316
doi: 10.1242/jeb.128686

Free pdf:



C. G. Dacke, R. M. Elsey, P. L. Trosclair III, T. Sugiyama, J. G.
Nevarez and M. H. Schweitzer (2015)
Alligator osteoderms as a source of labile calcium for eggshell formation.
JOURNAL OF ZOOLOGY (advance online publication)
DOI: 10.1111/jzo.12272

The calcium (Ca) demand on alligators in active reproduction is
significant, yet the source of this additional Ca is unclear. Three
possible sources for Ca mobilization are endolymphatic deposits, as in
anurans and some lizards; short-lived skeletal medullary bone or
analogous deposits, as in birds; or some other source such as the
osteoderm layer of the integument or simply mobilization of structural
bone. Here, we investigate possible extra-skeletal sources for labile
Ca in the reproducing alligator, including endolymphatic Ca deposits,
by analogy with anuran amphibian and some reptiles and integumentary
osteodermal (scale) Ca deposits. We conducted X-ray image analyses of
skulls for the presence of significant endolymphatic Ca deposits. We
also examined dermal bone of scutes (osteoderm, scales) from the
dorsal integument using both X-ray and histological analyses. Tissues
from reproducing females containing mature but unovulated follicles
were compared with those from specimens that had nested (laid eggs) or
contained eggs within the oviduct at advanced stages of calcification.
A small number of immature specimens and an adult male were also
compared. No clear differences were observed in endolymphatic deposits
between pre- and post-ovulatory specimens. Scute (osteoderm) X-ray
density was significantly greater in females with ripe ovarian
follicles compared with those that had recently laid (nested) or
contained heavily calcified eggs within their oviducts. The latter
groups also showed histological evidence of scute resorption compared
with the former, suggesting that the scutes play a role in Ca storage
during egglay.


Viviana D. Barreda, Luis Palazzesi, Maria C. Tellería, Eduardo B.
Olivero, J. Ian Raine, and Félix Forest (2015)
Early evolution of the angiosperm clade Asteraceae in the Cretaceous
of Antarctica.
Proceedings of the National Academy of Sciences (advance online publication)


The flowering plant family Asteraceae (e.g. sunflowers, daisies,
chrysanthemums), with about 23,000 species, is found almost everywhere
in the world except in Antarctica. Asteraceae (or Compositae) are
regarded as one of the most influential families in the
diversification and evolution of a large number of animals that
heavily depends on their inflorescences to survive (e.g. bees,
hummingbirds, wasps). Here we report the discovery of pollen grains
unambiguously assigned to Asteraceae that remained buried in Antarctic
deposits for more than 65 million years along with other extinct
groups (e.g. Dinosaurs, Ammonites). Our discovery drastically pushes
back the assumed origin of Asteraceae, because these pollen grains are
the oldest fossils ever found for the family.


The Asteraceae (sunflowers and daisies) are the most diverse family of
flowering plants. Despite their prominent role in extant terrestrial
ecosystems, the early evolutionary history of this family remains
poorly understood. Here we report the discovery of a number of fossil
pollen grains preserved in dinosaur-bearing deposits from the Late
Cretaceous of Antarctica that drastically pushes back the timing of
assumed origin of the family. Reliably dated to ∼76–66 Mya, these
specimens are about 20 million years older than previously known
records for the Asteraceae. Using a phylogenetic approach, we
interpreted these fossil specimens as members of an extinct early
diverging clade of the family, associated with subfamily
Barnadesioideae. Based on a molecular phylogenetic tree calibrated
using fossils, including the ones reported here, we estimated that the
most recent common ancestor of the family lived at least 80 Mya in
Gondwana, well before the thermal and biogeographical isolation of
Antarctica. Most of the early diverging lineages of the family
originated in a narrow time interval after the K/P boundary, 60–50
Mya, coinciding with a pronounced climatic warming during the Late
Paleocene and Early Eocene, and the scene of a dramatic rise in
flowering plant diversity. Our age estimates reduce earlier
discrepancies between the age of the fossil record and previous
molecular estimates for the origin of the family, bearing important
implications in the evolution of flowering plants in general.

Dinosaurs and daisies