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Hindlimb segment mass proportions in neognath birds and other non-dino papers

Ben Creisler

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

Free pdf:

Brandon M. Kilbourne (2014)
Scale effects and morphological diversification in hindlimb segment
mass proportions in neognath birds.
Frontiers in Zoology (advance online publication)
DOI: 10.1186/1742-9994-11-37

In spite of considerable work on the linear proportions of limbs in
amniotes, it remains unknown whether differences in scale effects
between proximal and distal limb segments has the potential to
influence locomotor costs in amniote lineages and how changes in the
mass proportions of limbs have factored into amniote diversification.
To broaden our understanding of how the mass proportions of limbs vary
within amniote lineages, I collected data on hindlimb segment masses –
thigh, shank, pes, tarsometatarsal segment, and digits – from 38
species of neognath birds, one of the most speciose amniote clades. I
scaled each of these traits against measures of body size (body mass)
and hindlimb size (hindlimb length) to test for departures from
isometry. Additionally, I applied two parameters of trait evolution
(Pagel’s lambda and delta) to understand patterns of diversification
in hindlimb segment mass in neognaths.
All segment masses are positively allometric with body mass. Segment
masses are isometric with hindlimb length. When examining scale
effects in the neognath subclade Land Birds, segment masses were again
positively allometric with body mass; however, shank, pedal, and
tarsometatarsal segment masses were also positively allometric with
hindlimb length. Methods of branch length scaling to detect
phylogenetic signal (i.e., Pagel’s lambda) and increasing or
decreasing rates of trait change over time (i.e., Pagel’s delta)
suffer from wide confidence intervals, likely due to small sample size
and deep divergence times.
The scaling of segment masses appears to be more strongly related to
the scaling of limb bone mass as opposed to length, and the scaling of
hindlimb mass distribution is more a function of scale effects in limb
posture than proximo-distal differences in the scaling of limb segment
mass. Though negative allometry of segment masses appears to be
precluded by the need for mechanically sound limbs, the positive
allometry of segment masses relative to body mass may underlie scale
effects in stride frequency and length between smaller and larger
neognaths. While variation in linear proportions of limbs appear to be
governed by developmental mechanisms, variation in mass proportions
does not appear to be constrained so.


Tatsuya Hirasawa, Juan Pascual-Anaya, Naoki Kamezaki, Mari Taniguchi,
Kanako Mine and Shigeru Kuratani (2014)
The evolutionary origin of the turtle shell and its dependence on the
axial arrest of the embryonic rib cage.
Journal of Experimental Zoology Part B: Molecular and Developmental
Evolution (advance online publication)
DOI: 10.1002/jez.b.22579

Turtles are characterized by their possession of a shell with dorsal
and ventral moieties: the carapace and the plastron, respectively. In
this review, we try to provide answers to the question of the
evolutionary origin of the carapace, by revising morphological,
developmental, and paleontological comparative analyses. The turtle
carapace is formed through modification of the thoracic ribs and
vertebrae, which undergo extensive ossification to form a solid bony
structure. Except for peripheral dermal elements, there are no signs
of exoskeletal components ontogenetically added to the costal and
neural bones, and thus the carapace is predominantly of endoskeletal
nature. Due to the axial arrest of turtle rib growth, the axial part
of the embryo expands laterally and the shoulder girdle becomes
encapsulated in the rib cage, together with the inward folding of the
lateral body wall in the late phase of embryogenesis. Along the line
of this folding develops a ridge called the carapacial ridge (CR), a
turtle-specific embryonic structure. The CR functions in the marginal
growth of the carapacial primordium, in which Wnt signaling pathway
might play a crucial role. Both paleontological and genomic evidence
suggest that the axial arrest is the first step toward acquisition of
the turtle body plan, which is estimated to have taken place after the
divergence of a clade including turtles from archosaurs. The
developmental relationship between the CR and the axial arrest remains
a central issue to be solved in future.


Emma Sherratt, David J. Gower, Christian Peter Klingenberg & Mark
Wilkinson (2014)
Evolution of Cranial Shape in Caecilians (Amphibia: Gymnophiona).
Evolutionary Biology (advance online publication)
DOI: 10.1007/s11692-014-9287-2

Insights into morphological diversification can be obtained from the
ways the species of a clade occupy morphospace. Projecting a phylogeny
into morphospace provides estimates of evolutionary trajectories as
lineages diversified information that can be used to infer the
dynamics of evolutionary processes that produced patterns of
morphospace occupation. We present here a large-scale investigation
into evolution of morphological variation in the skull of caecilian
amphibians, a major clade of vertebrates. Because caecilians are
limbless, predominantly fossorial animals, diversification of their
skull has occurred within a framework imposed by the functional
demands of head-first burrowing. We examined cranial shape in 141
species, over half of known species, using X-ray computed tomography
and geometric morphometrics. Mapping an existing phylogeny into the
cranial morphospace to estimate the history of morphological change
(phylomorphospace), we find a striking pattern: most species occupy
distinct clusters in cranial morphospace that closely correspond to
the main caecilian clades, and each cluster is separated by unoccupied
morphospace. The empty spaces in shape space are unlikely to be caused
entirely by extinction or incomplete sampling. The main caecilian
clades have different amounts of morphological disparity, but neither
clade age nor number of species account for this variation. Cranial
shape variation is clearly linked to phyletic divergence, but there is
also homoplasy, which is attributed to extrinsic factors associated
with head-first digging: features of caecilian crania that have been
previously argued to correlate with differential microhabitat use and
burrowing ability, such as subterminal and terminal mouths, degree of
temporal fenestration (stegokrotaphy/zygokrotaphy), and eyes covered
by bone, have evolved and many combinations occur in modern species.
We find evidence of morphological convergence in cranial shape, among
species that have eyes covered by bone, resulting in a narrow
bullet-shaped head. These results reveal a complex history, including
early expansion of morphospace and both divergent and convergent
evolution resulting in the diversity we observe today.