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Polydactyly in Jurassic salamander + lepidosaur body sizes and diversification rates + more
Some recent non-dino papers:
Yuan Wang, Liping Dong & Susan E. Evans (December 2015)
Polydactyly and other limb abnormalities in the Jurassic salamander
Chunerpeton from China.
Palaeobiodiversity and Palaeoenvironments (advance online publication)
Polydactyly and other malformations such as supernumerary limbs are
relatively common in extant salamander populations. They generally
result from biotic or abiotic disruption of normal regeneration
following non-lethal predator or conspecific bite injury. Here, we
record, for the first time, similar malformations in a fossil
salamander. Fourteen specimens of the perennibranchiate Jurassic
salamander Chunerpeton tianyiensis (Urodela, Cryptobranchidae),
recovered from Jianping County, Liaoning Province, China, display
polydactyly or abnormal phalangeal counts in one or more limbs, and
two also possess supernumerary hind limbs. Polydactyly in Chunerpeton
is mainly post-axial, occurring on the feet more often than the hands,
and on the right side of the body more often than on the left. The
extra legs also occurred on the right side of the body. Similar
conditions can be observed in living salamanders, so these specimens
suggest that the challenges faced by aquatic salamanders, and the
developmental processes triggered in response, have changed relatively
little in 160 million years.
Anat Feldman, Niv Sabath, R. Alexander Pyron, Itay Mayrose and Shai
Body sizes and diversification rates of lizards, snakes,
amphisbaenians and the tuatara.
Global Ecology and Biogeography (advance online publication)
Size is one of the most important and obvious traits of an organism.
Both small and large sizes have adaptive advantages and disadvantages.
Body size–frequency distributions of most large clades are unimodal
and right skewed. Species larger than the mean or range midpoint of
body sizes are relatively scarce. Theoretical models suggest
evolutionary rates are higher in small organisms with short generation
times. Therefore diversification rates are usually thought to be
maximal at relatively small body sizes. Empirical studies of the rates
of molecular evolution and clade diversification, however, have
usually indicated that both are unrelated to body size. Furthermore,
it has been claimed that because snakes are longer than lizards, the
size–frequency distribution of all squamate species is bimodal
overall. We examined the shape of the size–frequency distribution of
nearly all Squamata and Rhynchocephalia species, and investigated how
size affected diversification rates.
We collected data on maximum body length for 9805 lepidosaur
(squamates and the tuatara) species (99.7% of all species) and
converted them to mass using clade-specific allometric equations.
Using methods that test for relationships between continuous traits
and speciation and extinction rates on a large, dated phylogeny (4155
species), we investigated the relationship between diversification
rates and body size.
Living squamates span six orders of magnitude in body size, eight when
giant extinct snakes and mosasaurs are included. The body
size–frequency distributions of snakes and lizards separately, and of
all lepidosaur species combined, are unimodal and right skewed.
Nonetheless, we find neither linear nor hump-shaped relationships
between size and diversification rates, except in snakes, where
speciation and diversification are hump shaped.
Despite a clear modality and skew in the body sizes of lepidosaurs, we
find little evidence for faster diversification of modal-sized taxa,
perhaps implying that larger-sized clades are relatively young.
Raymond J. Carpenter, Michael K. Macphail, Gregory J. Jordan and
Robert S. Hill (2015)
Fossil evidence for open, Proteaceae-dominated heathlands and fire in
the Late Cretaceous of Australia.
American Journal of Botany (advance online publication)
PREMISE OF THE STUDY: The origin of biomes is of great interest
globally. Molecular phylogenetic and pollen evidence suggest that
several plant lineages that now characterize open, burnt habitats of
the sclerophyll biome, became established during the Late Cretaceous
of Australia. However, whether this biome itself dates to that time is
problematic, fundamentally because of the near-absence of relevant,
appropriately aged, terrestrial plant macro- or mesofossils.
METHODS: We recovered, identified, and interpreted the ecological
significance of fossil pollen, foliar and other remains from a section
of core drilled in central Australia, which we dated as Late
KEY RESULTS: The sediments contain plant fossils that indicate
nutrient-limited, open, sclerophyllous vegetation and abundant
charcoal as evidence of fire. Most interestingly, >30 pollen taxa and
at least 12 foliage taxa are attributable to the important Gondwanan
family Proteaceae, including several minute, amphistomatic, and
sclerophyllous foliage forms consistent with subfamily Proteoideae.
Microfossils, including an abundance of Sphagnales and other wetland
taxa, provided strong evidence of a fenland setting. The local
vegetation also included diverse Ericaceae and Liliales, as well as a
range of ferns and gymnosperms.
CONCLUSIONS: The fossils provide strong evidence in support of
hypotheses of great antiquity for fire and open vegetation in
Australia, point to extraordinary persistence of Proteaceae that are
now emblematic of the Mediterranean-type climate southwestern
Australian biodiversity hotspot and raise the profile of open habitats
as centers of ancient lineages.
Devon Parkos, Alina Alexeenko, Marat Kulakhmetov, Brandon C. Johnson &
H. Jay Melosh (2015)
NOx Production and Rainout from Chicxulub Impact Ejecta Reentry.
Journal of Geophysical Research: Planets (advance online publication)
The Chicxulub impact 66.0 million years ago initiated the second
biggest extinction in the Phanerozoic Eon. The cause of the concurrent
oceanic nitrogen isotopic anomaly, however, remains elusive. The
Chicxulub impactor struck the Yucatán peninsula, ejecting 2x1015 kg of
molten and vaporized rock that reentered globally as circa 1023
microscopic spherules. Here we report that modern techniques indicate
this ejecta generates 1.5x1014 moles of NOx, which is enough to cause
the observed nitrogen enrichment of the basal layer. Additionally,
reentry based NO production would explain the anomalously heavy
isotopic composition of the observed nitrogen. We include N, O, N2,
O2, and NO species in simulations of nonequilibrium chemically
reacting flow around a reentering spherule. We then determine the net
production of NO from all the spherules and use turbulence models to
determine how quickly this yield diffuses through the atmosphere. Upon
reaching the stratosphere and troposphere, cloud moisture absorbs the
NOx and forms nitric acid. We model this process and determine the
acidity of the resulting precipitation, which peaks about 1 year after
the impact. The precipitation ultimately reaches the upper ocean,
where we assume the well mixed surface layer is 100 m deep. We then
model the naturally occurring carbonate/bicarbonate buffer and
determine the net pH. We find that insufficient NOx reaches the ocean
to directly cause the observed end-Cretaceous oceanic extinction via
acidification and buffer removal. However, the resulting nitrates are
sufficient to explain the concurrent nitrogen isotopic anomaly and
facilitate an end-Cretaceous algae bloom.
A.B. Rutherford, B.S. Rubidge, and P.J. Hancox (2015)
Sedimentology and Palaeontology of the Beaufort Group in the Free
State Province Supports A Reciprocal Foreland Basin Model for the
Karoo Supergroup, South Africa
South African Journal of Geology 118(4): 355-372
Various different models have been proposed for the style of fill of
the Karoo Basin in South Africa. One of these proposes that the Karoo
Basin behaved as a partitioned entity, with reciprocal fills on either
side of a hinge line separating proximal and distal facies. Detailed
sedimentological, palaeontological, stratigraphic and geophysical data
for the Beaufort Group in the central Free State lends credence to
this model. In the study area fossils assignable to the Dicynodon,
Lystrosaurus and Cynognathus assemblage zones occur in the Balfour,
Katberg and Burgersdorp formations respectively. This data shows that
certain parts of the Beaufort Group stratigraphic succession that are
present in the southern part of the Karoo Basin, are absent in the
central Free State, indicating either a depositional hiatus or a
period of erosion at the beginning and the end of Lystrosaurus
Assemblage Zone, as well as the end of Cynognathus Assemblage Zone
times. During these depositional hiatuses or periods of erosion,
deposition or preservation of the rock record was restricted to the
proximal sector (south of the hinge line). Study of the geophysical
data has also allowed for the definition of a basement high north-east
of Thaba Nchu, which probably accounts for the provenance of the
informally named Musgrave unit (upper Balfour Formation), which also
has an anomalous south-westerly palaeocurrent direction.