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Herpetology papers in International Journal of Developmental Biology (free pdfs)
The new issue of International Journal of Developmental Biology
contains a number of papers of interest to vertebrate paleontology.
Some of the papers are currently in open access. Many thanks to
Tomasz Skawiński for bringing this to my attention.
International Journal of Developmental Biology 58 (10/11/12):
Isabel Guerreiro & Denis Duboule (2015) 
Snakes: hatching of a model system for Evo-Devo?
International Journal of Developmental Biology 58 (10-12): 727-732.
Evo-Devo studies rely on a collection of animal model systems
belonging to different phylogenetic branches to try and understand how
organisms carrying a similar set of genes and pathways can develop
into such a variety of shapes and sizes. The squamate clade, however,
has only recently started to receive the attention it deserves in
particular due to extreme morphological and metabolic aspects and,
consequently, the important insights that it could bring in different
fields. The recent sequencing of several squamate genomes as well as
the generation of high quality trancriptomes for different snake
tissues now provide the necessary tools to complement biological
studies. Here, we briefly report on recent work involving developing
snake embryos to illustrate their interest to assess vertebrate
developmental mechanisms. We also discuss the relevance to use snake
species as Evo-Devo model systems and potential ways to cross the
important limitations intrinsically associated with developmental and
genetic studies of these fascinating animals.
Lorenzo Alibardi (2015) 
Transition from embryonic to adult epidermis in reptiles occurs by the
production of corneous beta-proteins.
International Journal of Developmental Biology 58 (10-12): 829-839.
The adaptation of the epidermis in amniote vertebrates to life on land
took place by a drastic change from an embryonic epidermis made of
two-four periderm layers to a terrestrial-proof epidermis. This
transition occurred by the increase in types and number of specialized
corneous proteins coded by genes of the Epidermal Differentiation
Complex. The prevalent types of corneous proteins produced in the
reptilian epidermis contain a beta-sheet region of high amino acid
homology which allows their polymerization into a meshwork of
filaments forming the hard corneous material of scales and claws. The
present immunogold ultrastructural study shows that this transition
occurs with the synthesis of glycine-rich corneous beta-proteins
(formerly indicated as beta-keratins) that are added to the initial
framework of acidic intermediate filaments produced in the embryonic
epidermis of lizards, snake, alligator and turtle. These corneous
beta-proteins are accumulated in the transitional and definitive
layers of reptilian epidermis formed underneath the transitory
two-four layered embryonic epidermis. In the more specialized reptiles
capable of shedding the epidermis as a single unit, such as lizards
and snakes, special glycine-cysteine rich beta-proteins are initially
produced in a single layer immediately formed beneath the embryonic
epidermis, the oberhautchen. The latter layer allows the in ovo
shedding of the embryonic epidermis in preparation for hatching, and
in the following shedding cycles of the adult epidermis. The
production of specialized corneous-specific beta-proteins in addition
to intermediate filament keratins was probably an essential addition
for terrestrial life during the evolution of reptiles into different
lineages, including birds. The increase of glycine and cysteine in
epidermal proteins enhanced the hydrophobicity, insolubility and
mechanical strength of the stratum corneum in these amniotes.
Marc Tollis, Elizabeth D. Hutchins & Kenro Kusumi (2015) 
Reptile genomes open the frontier for comparative analysis of amniote
development and regeneration.
International Journal of Developmental Biology 58 (10-12): 863-871.
Developmental genetic studies of vertebrates have focused primarily on
zebrafish, frog and mouse models, which have clear application to
medicine and well-developed genomic resources. In contrast, reptiles
represent the most diverse amniote group, but have only recently begun
to gather the attention of genome sequencing efforts. Extant reptilian
groups last shared a common ancestor ?280 million years ago and
include lepidosaurs, turtles and crocodilians. This phylogenetic
diversity is reflected in great morphological and behavioral diversity
capturing the attention of biologists interested in mechanisms
regulating developmental processes such as somitogenesis and spinal
patterning, regeneration, the evolution of “snake-like” morphology,
the formation of the unique turtle shell, and the convergent evolution
of the four-chambered heart shared by mammals and archosaurs. The
complete genome of the first non-avian reptile, the green anole
lizard, was published in 2011 and has provided insights into the
origin and evolution of amniotes. Since then, the genomes of multiple
snakes, turtles, and crocodilians have also been completed. Here we
will review the current diversity of available reptile genomes, with
an emphasis on their evolutionary relationships, and will highlight
how these genomes have and will continue to facilitate research in
developmental and regenerative biology.
Richard P. Elinson, James R. Stewart, Laurie J. Bonneau & Daniel G.
Blackburn (2015) 
Amniote yolk sacs: diversity in reptiles and a hypothesis on their origin.
International Journal of Developmental Biology 58 (10-12): 889-894.
Oviparous amniotes produce a large yolky egg that gives rise to a
free-living hatchling. Structural characteristics and functional
attributes of the egg are best known for birds, which have a large
mass of fluid yolk surrounded by an extraembryonic yolk sac. Yolk
nutrients are delivered to the embryo via the vascular yolk sac. This
developmental pattern and nutrient transport mechanism is thought to
be representative of all other lineages of amniotes. Recent discovery
of a snake with cellularized yolk organized around a meshwork of blood
vessels reveals an additional pattern for yolk mobilization, which may
also occur in other squamate reptiles (lizards and snakes). This
complex yolk sac raises interesting questions about developmental
mechanisms and suggests a possible model for the transition between
the egg of anamniotes and that of amniotes.
Daniel G. Blackburn & Christian A. Sidor (2015) 
Evolution of viviparous reproduction in Paleozoic and Mesozoic reptiles.
International Journal of Developmental Biology 58 (10-12): 935-948.
Although viviparity (live-bearing reproduction) is widely distributed
among lizards and snakes, it is entirely absent from other extant
Reptilia and many extinct forms. However, paleontological evidence
reveals that viviparity was present in at least nine nominal groups of
pre-Cenozoic reptiles, representing a minimum of six separate
evolutionary origins of this reproductive mode. Two viviparous clades
(sauropterygians and ichthyopterygians) lasted more than 155 million
years, a figure that rivals the duration of mammalian viviparity.
Circumstantial evidence indicates that extinct viviparous reptiles had
internal fertilization, amniotic fetal membranes, and placentas that
sustained developing embryos via provision of respiratory gases,
water, calcium, and possibly organic nutrients. Production of
offspring via viviparity facilitated the invasion of marine habitats
in at least five reptilian lineages. Thus, this pattern of embryonic
development and reproduction was central to the ecology and evolution
of these ancient animals, much as it is to numerous extant species of
Tomasz Skawiński & Mateusz Tałanda (2015) 
Integrating developmental biology and the fossil record of reptiles.
International Journal of Developmental Biology 58 (10-12): 949-959.
Numerous new discoveries and new research techniques have influenced
our understanding of reptile development from a palaeontological
perspective. They suggest for example that transition from mineralized
to leathery eggshells and from oviparity to viviparity appeared much
more often in the evolution of reptiles than was previously thought.
Most marine reptiles evolved from viviparous terrestrial ancestors and
had probably genetic sex determination. Fossil forms often display
developmental traits absent or rare among modern ones such as
polydactyly, hyperphalangy, the presence of ribcage armour, reduction
of head ornamentation during ontogeny, extreme modifications of
vertebral count or a wide range of feather-like structures. Thus, they
provide an empirical background for many morphogenetic considerations.