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Ratite leg muscles + other non-dino papers

Ben Creisler

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

Ratite pelvic muscles and limb motion

John R Hutchinson, Jeffery W Rankin, Jonas Rubenson, Kate H
Rosenbluth, Robert A Siston & Scott L Delp (2014)
Musculoskeletal modeling of an ostrich (Struthio camelus) pelvic limb:
Influence of limb orientation on muscular capacity during locomotion.
PeerJ PrePrints 2:e513v1
doi: http://dx.doi.org/10.7287/peerj.preprints.513v1

We developed a three-dimensional, biomechanical computer model of the
36 major pelvic limb muscle groups in an ostrich (Struthio camelus) to
investigate muscle function in this, the largest of extant birds and
model organism for many studies of locomotor mechanics, body size,
anatomy and evolution. Combined with experimental data, we use this
model to test two main hypotheses. We first query whether ostriches
use limb orientations (joint angles) that optimize the
moment-generating capacities of their muscles during walking or
running. Next, we test whether ostriches use limb orientations at
mid-stance that keep their extensor muscles near maximal, and flexor
muscles near minimal, moment arms. Our two hypotheses relate to the
control priorities that a large bipedal animal might evolve under
biomechanical constraints to achieve more effective static weight
support. We find that ostriches do not use limb orientations to
optimize the moment-generating capacities or moment arms of their
muscles. We infer that dynamic properties of muscles or tendons might
be better candidates for locomotor optimization. Regardless, general
principles explaining why species choose particular joint orientations
during locomotion are lacking, raising the question of whether such
general principles exist or if clades evolve different patterns (e.g.
weighting of muscle force-length or force-velocity properties in
selecting postures). This leaves theoretical studies of muscle moment
arms estimated for extinct animals at an impasse until studies of
extant taxa answer these questions. Finally, we compare our model’s
results against those of two prior studies of ostrich limb muscle
moment arms, finding general agreement for many muscles. Some flexor
and extensor muscles exhibit self-stabilization patterns
(posture-dependent switches between flexor/extensor action) that
ostriches may use to coordinate their locomotion. However, some
conspicuous areas of disagreement in our results illustrate some
cautionary principles. Importantly, tendon-travel empirical
measurements of muscle moment arms must be carefully designed to
preserve 3D muscle geometry lest their accuracy suffer relative to
that of anatomically realistic models. The dearth of accurate
experimental measurements of 3D moment arms of muscles in birds leaves
uncertainty regarding the relative accuracy of different modelling or
experimental datasets such as in ostriches. Our model, however,
provides a comprehensive set of 3D estimates of muscle actions in
ostriches for the first time, emphasizing that avian limb mechanics
are highly three-dimensional and complex, and how no muscles act
purely in the sagittal plane. A comparative synthesis of experiments
and models such as ours could provide powerful synthesis into how
anatomy, mechanics and control interact during locomotion and how
these interactions evolve. Such a framework could remove obstacles
impeding the analysis of muscle function in extinct taxa.

Luis P Lamas, Russell P Main & John R. Hutchinson (2014)
Ontogenetic scaling patterns and functional anatomy of the pelvic limb
musculature in emus (Dromaius novaehollandiae).
PeerJ PrePrints 2:e508v1
doi: http://dx.doi.org/10.7287/peerj.preprints.508v1

Emus (Dromaius novaehollandiae) are exclusively terrestrial, bipedal
and cursorial ratites with some similar biomechanical characteristics
to humans. Their growth rates are impressive as their body mass
increases eighty-fold from hatching to adulthood whilst maintaining
the same mode of locomotion throughout life. These ontogenetic
characteristics stimulate biomechanical questions about the strategies
that allow them to cope through these changes. To answer such
questions, in this study we have collected pelvic limb anatomical data
(muscle architecture, tendon length, tendon mass and bone lengths) and
calculated muscle physiological cross sectional area (PCSA) and
average tendon cross sectional area from emus across an ontogenetic
series (n=17, body masses from 3.6 to 42 kg). The data were analysed
by reduced major axis regression to determine scaling relationships
with body mass. Muscle mass and PCSA showed a marked trend towards
positive allometry (26 and 27 out of 34 muscles respectively) and
fascicle length showed a more mixed scaling pattern. The long tendons
of the main digital flexors scaled with positive allometry for all
characteristics whilst other tendons demonstrated a less clear scaling
pattern. Finally, the two longer bones of the limb (tibiotarsus and
tarsometatarsus) also exhibited positive allometry for length and the
other two (femur and first phalanx of the pes) had trends towards
isometry. These results indicate that emus increase their muscle
force-generating capacities, as well as potentially increasing the
force-sustaining capacities of their tendons, as they grow.
Furthermore, we have clarified anatomical descriptions and provided
illustrations of the pelvic limb muscle-tendon units in emus.

Origin of angiosperms

Liping Zeng, Qiang Zhang, Renran Sun, Hongzhi Kong, Ning Zhang & Hong Ma (2014)
Resolution of deep angiosperm phylogeny using conserved nuclear genes
and estimates of early divergence times.
Nature Communications 5, Article number: 4956

Angiosperms are the most successful plants and support human
livelihood and ecosystems. Angiosperm phylogeny is the foundation of
studies of gene function and phenotypic evolution, divergence time
estimation and biogeography. The relationship of the five divergent
groups of the Mesangiospermae (~99.95% of extant angiosperms) remains
uncertain, with multiple hypotheses reported in the literature. Here
transcriptome data sets are obtained from 26 species lacking sequenced
genomes, representing each of the five groups: eudicots, monocots,
magnoliids, Chloranthaceae and Ceratophyllaceae. Phylogenetic analyses
using 59 carefully selected low-copy nuclear genes resulted in highly
supported relationships: sisterhood of eudicots and a clade containing
Chloranthaceae and Ceratophyllaceae, with magnoliids being the next
sister group, followed by monocots. Our topology allows a
re-examination of the evolutionary patterns of 110 morphological
characters. The molecular clock estimates of Mesangiospermae
diversification during the late to middle Jurassic correspond well to
the origins of some insects, which may have been a factor facilitating
early angiosperm radiation.


K-Pg extinction and recovery at Hell Creek, Montana

Courtney J. Sprain, Paul R. Renne, Gregory P. Wilson, and William A.
Clemens (2014)
High-resolution chronostratigraphy of the terrestrial
Cretaceous-Paleogene transition and recovery interval in the Hell
Creek region, Montana.
Geological Society of America Bulletin (advance online publication)
doi: 10.1130/B31076.1

Detailed understanding of ecosystem decline and recovery attending the
Cretaceous-Paleogene boundary (KPB) mass extinctions is hindered by
limited constraints on the pace and tempo of environmental events near
the boundary. To mitigate this shortcoming, high-resolution 40Ar/39Ar
geochronology was performed on tephras intercalated between
fossiliferous terrestrial sediments of the upper Hell Creek and lower
Fort Union Formations in the western Williston Basin of northeastern
Montana (USA). Tephra samples were collected from 10 stratigraphic
sections spanning an area of ~5000 km2. Several distinctive tephras
can be correlated between sections separated spatially by as much as
~60 km. The tephras are thin distal deposits generally preserved only
in lignite beds, which are interbedded with clastic deposits yielding
vertebrate faunas of Lancian (late Maastrichtian) to Torrejonian
(early Danian) North American Land Mammal Ages. Sanidine from 15
tephra samples was analyzed in 1649 total fusion experiments (1597 on
single crystals) and 12 incremental heating analyses of multigrain
aliquots. Ages were determined for 13 distinct tephras, ranging from
66.289 ± 0.051 to 64.866 ± 0.023 Ma, including only analytical
uncertainties. This level of precision is sufficient to resolve the
ages of all of the coal beds that have served as a basis for a
regional stratigraphic framework. The data confirm that the Hell
Creek–Fort Union formational contact is diachronous, and further
support the age of the KPB impact layer at 66.043 ± 0.010 Ma (or ±
0.043 Ma considering systematic uncertainties). Application of the new
results to previous magnetostratigraphic data indicates an appreciably
compressed time interval between the base of chron C29r and the top of
chron C28r, with a maximum duration estimate of 1.421 ± 0.066 Ma. Most
notable is the implied brevity of chron C29r, with a maximum estimate
of 457 ± 54 ka, and possibly as brief as 345 ± 38 ka, compared to the
710 ka estimate from the Geologic Time Scale 2012 (GTS2012). Further,
application of new results to terrestrial biostratigraphy adds higher
precision to the timing and tempo of biotic change before and after
the KPB. Our results indicate that the timing of pre-KPB ecological
decline is constrained to the last ~200 ka of the Cretaceous, adding
further support to the press-pulse extinction hypothesis.
Additionally, the duration of the depauperate basal Paleogene Puercan
1 disaster fauna is confined to a 70 ka interval. Faunal recovery in
this region, indicated by the appearance of primitive members of the
placental mammal radiation and the restoration of taxonomic richness
and evenness, occurred within ~900 ka after the KPB. These results
show that biotic recovery after the mass extinction in the terrestrial
realm was more rapid than in the marine.