A collection of new papers...

[Guy Leahy <xrciseguy@sbcglobal.net>]

Apologies if these have been previously discussed...
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1: Trends Ecol Evol. 2006 Apr;21(4):217-24. Epub 2006
Jan 25. Links 

Ecological and evolutionary implications of dinosaur
feeding behaviour.

Barrett PM, Rayfield EJ.

Department of Palaeontology, The Natural History
Museum, Cromwell Road, London, UK, SW7 5BD.

Dinosaurs had a wide variety of feeding mechanisms
that strongly impacted on their ecology and evolution.
Here, we show how novel application of technologies
borrowed from medicine and engineering, such as CT
scanning and Finite Element Analysis, have recently
been combined with traditional approaches to result in
significant advances in our understanding of dinosaur
palaeobiology. Taxon-specific studies are providing
quantitative data that can be used to generate and
test functional hypotheses relating to jaw mechanics
and feeding behaviour. In turn, these data form a
basis for investigating larger scale patterns of
ecological and macroevolutionary change, such as
possible coevolutionary interactions and the influence
of feeding adaptations on species richness, which are
of more general interest to ecologists and
evolutionary biologists.
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1: An Acad Bras Cienc. 2006 Mar;78(1):175-82. Epub
2006 Mar 8. Related Articles, Links  

Description of a sauropod dinosaur braincase from the
Late Cretaceous Rio Colorado Subgroup, Patagonia.

Calvo JO, Kellner AW.

Centro Paleontologico Lago Barreales, Universidad
Nacional del Comahue, 8300 Neuquen, Argentina.

The fossil record of cranial material from
titanosaurid sauropods is very poor and no complete
skull has been described so far. Here we describe a
new braincase (MUCPv-334) that was recovered from
reddish sandstones of the Rio Colorado Subgroup (Late
Cretaceous) of the region of Bajo del Anelo,
approximately 20 km north of the town Anelo (Neuquen
Province, Argentina). This specimen is attributed to
the Titanosauridae based on the ventrally projected
basipterygoid processes, a common condition shared by
other titanosaurids. The robustness of MUCPv-334
together with an unusually expanded crista prootica
and the presence of an anterior prolongation of the
parasphenoid reaching the basal tubera were not
reported in other members of the Titanosauridae,
indicating a larger diversity in the braincase
morphology of this sauropod clade than previously
thought.

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1: Proc Biol Sci. 2006 Jan 7;273(1582):119-26. Related
Articles, Links  

High lift function of the pteroid bone and forewing of
pterosaurs.

Wilkinson MT, Unwin DM, Ellington CP.

Department of Zoology, University of Cambridge,
Downing Street, Cambridge CB2 3EJ, UK. mtw21@cam.ac.uk

The pteroid bone is a rod-like element found only in
pterosaurs, the flying reptiles of the Mesozoic. It
articulated at the wrist, and supported a membranous
forewing in front of the inner part of the wing spar.
The function of this bone, particularly its
orientation, has been much debated. It is widely
believed that it pointed towards the body, and that
the forewing was relatively narrow. An alternative
hypothesis states that it was directed forwards during
flight, resulting in a much broader forewing that
acted as a leading edge flap. We tested scale models
in a wind tunnel to determine the aerodynamic
consequences of these conflicting hypotheses, and
found that performance is greatly improved if the
pteroid is directed forwards: the lift: drag ratios
are superior and the maximum lift is exceptionally
high in comparison with conventional aerofoils. This
high lift capability may have enabled even the largest
pterosaurs to take off and land without difficulty.

---------------------------------------------------
1: J Anat. 2006 Mar;208(3):287-308. Related Articles,
Links  

 
Insight into the evolution of avian flight from a new
clade of Early Cretaceous ornithurines from China and
the morphology of Yixianornis grabaui.

Clarke JA, Zhou Z, Zhang F.

Department of Marine, Earth and Atmospheric Sciences,
North Carolina State University, Raleigh, 27695, USA.
Julia_Clarke@ncsu.edu

In studies of the evolution of avian flight there has
been a singular preoccupation with unravelling its
origin. By contrast, the complex changes in morphology
that occurred between the earliest form of avian
flapping flight and the emergence of the flight
capabilities of extant birds remain comparatively
little explored. Any such work has been limited by a
comparative paucity of fossils illuminating bird
evolution near the origin of the clade of extant (i.e.
'modern') birds (Aves). Here we recognize three
species from the Early Cretaceous of China as
comprising a new lineage of basal ornithurine birds.
Ornithurae is a clade that includes, approximately,
comparatively close relatives of crown clade Aves
(extant birds) and that crown clade. The morphology of
the best-preserved specimen from this newly recognized
Asian diversity, the holotype specimen of Yixianornis
grabaui Zhou and Zhang 2001, complete with finely
preserved wing and tail feather impressions, is used
to illustrate the new insights offered by recognition
of this lineage. Hypotheses of avian morphological
evolution and specifically proposed patterns of change
in different avian locomotor modules after the origin
of flight are impacted by recognition of the new
lineage. The complete articulated holotype specimen of
Yixianornis grabaui, from the Early Cretaceous
Jiufotang Formation of Liaoning Province, in
north-eastern China, arguably the best-preserved basal
ornithurine specimen yet discovered, provides the
earliest evidence consistent with the presence of
extant avian tail feather fanning.
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1: Mol Phylogenet Evol. 2006 Apr;39(1):16-32. Epub
2006 Feb 21. Related Articles, Links  

 
Are crocodiles really monophyletic?--Evidence for
subdivisions from sequence and morphological data.

McAliley LR, Willis RE, Ray DA, White PS, Brochu CA,
Densmore LD 3rd.

Department of Biological Sciences, Texas Tech
University, P.O. Box 43131, Lubbock, TX 79409-313,
USA. rexmcaliley@excite.com

Recently, the phylogenetic placement of the African
slender snouted crocodile, Crocodylus cataphractus,
has come under scrutiny and herein we address this
issue using molecular and morphological techniques.
Although it is often recognized as being a "basal"
form, morphological studies have traditionally placed
C. cataphractus within the genus Crocodylus, while
molecular studies have suggested that C. cataphractus
is very distinct from other Crocodylus. To address the
relationship of this species to its congeners we have
sequenced portions of two nuclear genes (C-mos 302bp
and ODC 294bp), and two mitochondrial genes
(ND6-tRNA(glu)-cytB 347bp and control region 457bp).
Analyses of these molecular datasets, both as
individual gene sequences and as concatenated
sequences, support the hypothesis that C. cataphractus
is not a member of Crocodylus or Osteolaemus.
Examination of 165 morphological characters supports
and strengthens our resurrection of an historic genus,
Mecistops (Gray 1844) for cataphractus.
----------------------------------------------------
1: J Mol Evol. 2005 Nov;61(5):620-6. Epub 2005 Oct 6.
Related Articles, Links  

 
Mitogenomic analyses place the gharial (Gavialis
gangeticus) on the crocodile tree and provide pre-K/T
divergence times for most crocodilians.

Janke A, Gullberg A, Hughes S, Aggarwal RK, Arnason U.

Department of Cell and Organism Biology, Division of
Evolutionary Molecular Systematics, University of
Lund, Solvegatan 29, S-223 62 Lund, Sweden.
axel.janke@cob.lu.se

Based on morphological analyses, extant members of the
order Crocodylia are divided into three families,
Alligatoridae, Crocodylidae, and Gavialidae.
Gavialidae includes one species, the gharial, Gavialis
gangeticus. In this study we have examined crocodilian
relationships in phylogenetic analyses of seven
mitochondrial genomes that have been sequenced in
their entirety. The analyses did not support the
morphologically acknowledged separate position of the
gharial in the crocodilian tree. Instead the gharial
joined the false gharial (Tomistoma schlegelii) on a
common branch that was shown to constitute a sister
group to traditional Crocodylidae (less Tomistoma).
Thus, the analyses suggest the recognition of only two
Crocodylia families, Alligatoridae and Crocodylidae,
with the latter encompassing traditional Crocodylidae
plus Gavialis/Tomistoma. A molecular dating of the
divergence between Alligatoridae and Crocodylidae
suggests that this basal split among recent
crocodilians took place approximately 140 million
years before present, at the Jurassic/Cretaceous
boundary. The results suggest that at least five
crocodilian lineages survived the mass extinction at
the KT boundary.
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1: J Anat. 2006 May;208(5):621-42. Related Articles,
Links  

 
Cell structure of developing downfeathers in the
zebrafinch with emphasis on barb ridge morphogenesis.

Alibardi L, Sawyer RH.

Dipartimento di Biologia evoluzionistica sperimentale,
University of Bologna, Italy.

The present ultrastructural and immunocytochemical
study on the embryonic feathers of the zebrafinch, an
altricial passerine bird, describes cellular
differentiation of developing downfeathers. Barb
ridges are folds of the original epidermis of the
embryonic feather germ in which the basal-apical
polarity of epidermal cells is upset. The result is
the loss of most germinal activity of basal cells of
the barb ridges so that only the embryonic epidermal
layers remain. The more external layer is the primary
periderm, followed by 4-6 layers of inner-periderm
cells that mature into feather sheath and barb vane
ridge cells. The following layer, the subperiderm,
produces a small type of beta-keratin typical of
feathers. In barb ridges, the subperiderm layer is
displaced to form barbule plates and barb cells. The
formation of branching barbules occurs by the presence
of barb vane ridge cells that function as spacers
between barbule cells. The fourth layer is homologous
to the germinal layer of the epidermis, but in barb
ridges it rapidly loses the germinal capability and
becomes the cyclindrical layer of marginal plates. The
study indicates that a necrotic process determines the
carving out of the final feather shape, although
apoptosis may also play a role. In fact, after barb
and barbule cells have formed a keratinized syncitium,
retraction of the vascular bed determines anoxia with
the resultant necrosis of all feather cells. Only
those of the keratinized syncitium remain to form the
feather while supportive cells disappear. The sheath
covering the barb and barbule syncitium is lost by the
formation of a sloughing layer following degeneration
of external barb ridge vane cells and loss of the
sheath. It is proposed that the evolution of the
morphogenetic process of barb ridge formation was
peculiar to tubular outgrowths of the integument of
archosaurian reptiles that evolved into birds. Once
established in the embryonic programmes of skin
morphogenesis of ancient birds, variations in the
process of barb ridge morphogenesis allowed the fusion
of ridges into large or branched ridges that
originated the rachis. This process produced
pennaceous feathers, among which were those later used
for flight. The present study stresses that the
morphogenetic process of barb ridge formation
determines the concomitant appearance of barbs and
barbules. As a consequence, intermediate forms of
evolving feathers with only barbs but not barbules are
unlikely or are derived from alteration of the above
basic morphogenetic mechanism.
----------------------------------------------------
Guy Leahy