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Turtle respiration + Eunotosaurus + non-dino papers
A number of new and recent non-dino papers that may be of interest:
Tyler R. Lyson, Emma R. Schachner, Jennifer Botha-Brink, Torsten M.
Scheyer, Markus Lambertz, G. S. Bever, Bruce S. Rubidge & Kevin de
Origin of the unique ventilatory apparatus of turtles.
Nature Communications 5, Article number: 5211
The turtle body plan differs markedly from that of other vertebrates
and serves as a model system for studying structural and developmental
evolution. Incorporation of the ribs into the turtle shell negates the
costal movements that effect lung ventilation in other air-breathing
amniotes. Instead, turtles have a unique abdominal-muscle-based
ventilatory apparatus whose evolutionary origins have remained
mysterious. Here we show through broadly comparative anatomical and
histological analyses that an early member of the turtle stem lineage
has several turtle-specific ventilation characters: rigid ribcage,
inferred loss of intercostal muscles and osteological correlates of
the primary expiratory muscle. Our results suggest that the
ventilation mechanism of turtles evolved through a division of labour
between the ribs and muscles of the trunk in which the abdominal
muscles took on the primary ventilatory function, whereas the
broadened ribs became the primary means of stabilizing the trunk.
These changes occurred approximately 50 million years before the
evolution of the fully ossified shell.
Embargo is off on presentation at SVP 2014
BEVER, G.S., ; LYSON, Tyler; BHULLAR, Bhart-Anjan
FOSSIL EVIDENCE FOR A DIAPSID ORIGIN OF THE ANAPSID TURTLE SKULL.
SVP 2014 Abstracts pg. 91
The reptile skull is an increasingly utilized model for understanding
the evolution and development of vertebrate adaptation. Turtles are an
important yet enigmatic piece of this puzzle. The earliest
uncontroversial stem turtles exhibit a fully anapsid skull with an
adductor chamber concealed by bone. If this lack of fenestration
reflects conservation of the ancestral condition, then turtles are an
extant remnant of an early reptile radiation that excludes the other
living forms. If turtles are nested within crown Diapsida, then their
anapsid skull is a secondary configuration built on a diapsid
structural plan. No direct paleontological evidence yet exists for
this reversal, a situation that epitomizes a general lack of
consilience between the fossil record and the molecular signature of
living taxa and one that obfuscates attempts to synthesize broad
evolutionary patterns across Reptilia.
Eunotosaurus africanus is a 260 Ma fossil reptile whose status as an
early stem turtle continues to be strengthened by new cranial and
postcranial synapomorphies. Here we use computed tomography (CT) to
study the temporal region of Eunotosaurus and to formulate a model for
the origin of the anapsid and diapsid skulls of modern amniotes.
Expression of a lower temporal fenestra (LTF) supports the hypothesis
that the closed cheek of modern turtles is secondary. The ventrally
unbounded nature of the LTF places Eunotosaurus at odds with
parareptiles, but also with pandiapsids where an unbounded LTF is
known only in conjunction with the more conservative upper temporal
fenestra (UTF). The region housing the diapsid UTF is overlain by an
elongate supratemporal in Eunotosaurus. In contrast to the
plesiomorphic condition, digitally removing the supratemporal reveals
a moderate-sized opening circumscribed by the same elements that
define the UTF. Additional evidence that this covering is secondary is
drawn from the observation that in Eunotosaurus the supratemporal
overlaps the postorbital, whereas plesiomorphically these two elements
are abutting or the postorbital overlaps the supratemporal. We propose
Eunotosaurus captures an early step in the evolution of the anapsid
turtle skull in which the UTF was secondarily covered by the
supratemporal before being obliterated through expansion of
neighboring dermal elements. The recognition of such a critical
transitional form facilitates the articulation of meaningful
transformational and functional models that can be tested with future
paleontological discoveries and rapidly emerging developmental data.
Also for Eunotosaurus
Sifelani Jirah & Bruce S. Rubidge (2014)
Refined stratigraphy of the Middle Permian Abrahamskraal Formation
(Beaufort Group) in the southern Karoo Basin.
Journal of African Earth Sciences 100: 121–135
Lithostratigraphic subdivision of South African lower Beaufort Group.
Recognition of refined stratigraphic ranges of Middle Permian tetrapod taxa.
Stratigraphic logging revealed that the Abrahamskraal Formation is
2565 m thick in this part of the Karoo Basin.
Last occurrence of dinocephalians is seen to be higher than previously
Fluvially deposited rocks of the Abrahamskraal Formation of the lower
Beaufort Group in the South African Karoo record sediment deposition
during the Middle Permian, the earliest terrestrial environment of
Gondwana. A rich diversity of fossil tetrapods from this Formation
provides a unique opportunity for understanding Middle Permian
biodiversity changes in Gondwanan terrestrial ecosystems, but this is
dependent on the existence of a robust stratigraphic framework that
has been hampered by lack of lateral continuity of lithological
markers combined with structural complexities relating to formation of
the Cape Fold Belt. Because the Abrahamskraal Formation covers a large
geographic area of the main Karoo Basin previous stratigraphic studies
have been undertaken over large areas. This study combines geology and
palaeontology to refine the stratigraphy of the Abrahamskraal
Formation in a part of the southwestern Karoo Basin and revealed
mappable lithological units with lateral continuity throughout the
study area. The measured stratigraphic section manifests a total
thickness of 2565 m for the Formation (the thickest occurrence of the
Abrahamskraal Formation in the Beaufort Group). For the first time
stratigraphic ranges of biostratigraphically important Middle Permian
index taxa which have restricted stratigraphic ranges have been
determined and, apart from dicynodonts, include the parareptile
Eunotosaurus and the biarmosuchid therapsid Hipposaurus. The
Abrahamskraal Formation comprises a 1104 m thick basal Eodicynodon
Assemblage Zone, overlain by a 1441 m thick Tapinocephalus Assemblage
Zone whose upper limit is 20 m below the Poortjie Member of the
Átila A.S. Da-Rosa (2014)
Geological context of the Dinosauriform-Bearing outcrops from the
Triassic of Southern Brazil.
Journal of South American Earth Sciences (advance online publication)
The contribution places all known Brazilian Triassic dinosaurian forms
into a geological context. There is a discussion on the type of
preservation, faciological subdivision and stratigrahic and tectonic
The Triassic of the western Gondwana (southern Brazil and northwestern
Argentina) records the oldest dinosaurs. The Southern Brazilian
Triassic fauna is subdivided into four assemblage zones (AZ’s),
recorded in alluvial (channel and floodplain) deposits, split into
three third-order sequences that comprise the Santa Maria
Supersequence. These deposits record dinosauriforms in three of these
AZ’s, mostly in near-channel environments (channel deposits, crevasse
splays, distal floodplains) with different types of preservation
(mostly partly articulated, with little carbonate deposition). There
is faciological homogeneity within the Dinodontosaurus, Santacruzodon
and Hyperodapedon AZ’s, whereas change in fluvial style is recorded at
the Riograndia AZ. So, further stratigraphic studies must include the
recognition of post-depositional tectonism, in order to better
understand the autogenic and allogenic mechanisms of deposition. It is
suggested here that there is a lateral change on main channel
deposition, with the areal restriction of the Santacruzodon AZ
probably linked to reactivation on the Passo do Sobrado lineament and
modification of the basin floor.
No Toxicofera? Venom evolved multiple times in reptiles
Adam D. Hargreaves, Martin T. Swain, Darren W. Logan & John F. Mulley (2014)
Testing the Toxicofera: Comparative transcriptomics casts doubt on the
single, early evolution of the reptile venom system.
Toxicon 92: 140–156
Transcripts encoding proposed venom toxins are expressed in multiple
Many hypothesised venom components are in fact housekeeping genes.
The complexity of snake venom has been overestimated by previous authors.
Venom has evolved multiple times in reptiles.
The identification of apparently conserved gene complements in the
venom and salivary glands of a diverse set of reptiles led to the
development of the Toxicofera hypothesis – the single, early evolution
of the venom system in reptiles. However, this hypothesis is based
largely on relatively small scale EST-based studies of only venom or
salivary glands and toxic effects have been assigned to only some
putative Toxicoferan toxins in some species. We set out to examine the
distribution of these proposed venom toxin transcripts in order to
investigate to what extent conservation of gene complements may
reflect a bias in previous sampling efforts. Our quantitative
transcriptomic analyses of venom and salivary glands and other body
tissues in five species of reptile, together with the use of available
RNA-Seq datasets for additional species, shows that the majority of
genes used to support the establishment and expansion of the
Toxicofera are in fact expressed in multiple body tissues and most
likely represent general maintenance or “housekeeping” genes. The
apparent conservation of gene complements across the Toxicofera
therefore reflects an artefact of incomplete tissue sampling. We
therefore conclude that venom has evolved multiple times in reptiles.