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More turtle evolution papers
From: Ben Creisler
The paper about the shoulder girdle of turtles in Biology Letter is
one of a number of recent papers about turtle evolution.
John Wilkins brought this one to my attention, which fits well with
the new Biology Letters paper.
The pdf is free!
Hiroshi Nagashima, Shigehiro Kuraku, Katsuhisa Uchida, Yoshie
Kawashima-Ohya, Yuichi Narita and Shigeru Kuratani (2012)
Body plan of turtles: an anatomical, developmental and evolutionary perspective.
Anatomical Science International 87(1): 1-13
The evolution of the turtle shell has long been one of the central
debates in comparative anatomy. The turtle shell consists of dorsal
and ventral parts: the carapace and plastron, respectively. The basic
structure of the carapace comprises vertebrae and ribs. The pectoral
girdle of turtles sits inside the carapace or the rib cage, in
striking contrast to the body plan of other tetrapods. Due to this
topological change in the arrangement of skeletal elements, the
carapace has been regarded as an example of evolutionary novelty that
violates the ancestral body plan of tetrapods. Comparing the spatial
relationships of anatomical structures in the embryos of turtles and
other amniotes, we have shown that the topology of the musculoskeletal
system is largely conserved even in turtles. The positional changes
seen in the ribs and pectoral girdle can be ascribed to
turtle-specific folding of the lateral body wall in the late
developmental stages. Whereas the ribs of other amniotes grow from the
axial domain to the lateral body wall, turtle ribs remain arrested
axially. Marginal growth of the axial domain in turtle embryos brings
the morphologically short ribs in to cover the scapula dorsocaudally.
This concentric growth appears to be induced by the margin of the
carapace, which involves an ancestral gene expression cascade in a new
location. These comparative developmental data allow us to hypothesize
the gradual evolution of turtles, which is consistent with the recent
finding of a transitional fossil animal, Odontochelys, which did not
have the carapace but already possessed the plastron.
Review in Nature of microRNA controversy for phylogeny. Last year,
microRNA evidence was cited to support turtles as close relations of
lizards. The text and pdf are free.
Another new paper. Not available for free as yet.
Ingmar Wernburg (2012)
Temporal Bone Arrangements in Turtles: An Overview.
Journal of Experimental Zoology Part B: Molecular and Developmental
Evolution 318(4): 235–249
The temporal region of turtles is characterized by significant
anatomical diversity. Turtles show a pure anapsid morphotype that
exhibits various different marginal reductions known as emarginations.
As a result of this diversity, turtles can be taken as a model by
which to understand the processes that may have resulted in the highly
debated anatomy of the amniote temporal region in general. In this
review on almost forgotten literature, I summarize ten potential
factors that may act on the skull to shape the temporal region of
turtles. These are: (1) phylogenetic constraints, (2) skull weights,
(3) type of food, (4) skull dimensions, (5) muscle bulging, (6) ear
anatomy and jaw muscle bending mechanisms, (7) extent and nature of
muscle attachment sites, (8) internal forces within the jaw adductor
chamber, (9) environmental pressure, and (10) neck bending mechanisms.
Particular focus is laid on the interrelationship of the jaw
musculature and the dermatocranial armour, which were assumed to
influence each other to a certain degree. In the literature, cranial
dimensions were assumed to influence temporal bone formation within
major tetrapod groups. Among these, turtles seem to represent a kind
of intermixture, a phenomenon that may be reflected in their specific
anatomy. The references presented should be understood as product of
the scientific environment in which they developed and the older
literature does not always insist current empirical demands. However,
the intuitive and creative ideas and the comprehensive anatomical
considerations of these authors may inspire future studies in several
fields related to this topic.