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Placodont growth (free pdf) + archosaur unidirectional breathing and muscle attachments

Ben Creisler

A number of recent papers:

Nicole Klein, James M. Neenan, Torsten M. Scheyer & Eva Maria Griebeler (2015)
Growth patterns and life-history strategies in Placodontia (Diapsida:
Royal Society Open Science 2015 2 140440
DOI: 10.1098/rsos.140440

Free pdf:

Placodontia is a clade of durophagous, near shore marine reptiles from
Triassic sediments of modern-day Europe, Middle East and China.
Although much is known about their primary anatomy and palaeoecology,
relatively little has been published regarding their life history,
i.e. ageing, maturation and growth. Here, growth records derived from
long bone histological data of placodont individuals are described and
modelled to assess placodont growth and life-history strategies.
Growth modelling methods are used to confirm traits documented in the
growth record (age at onset of sexual maturity, age when asymptotic
length was achieved, age at death, maximum longevity) and also to
estimate undocumented traits. Based on these growth models,
generalized estimates of these traits are established for each taxon.
Overall differences in bone tissue types and resulting growth curves
indicate different growth patterns and life-history strategies between
different taxa of Placodontia. Psephoderma and Paraplacodus grew with
lamellar-zonal bone tissue type and show growth patterns as seen in
modern reptiles. Placodontia indet. aff. Cyamodus and some Placodontia
indet. show a unique combination of fibrolamellar bone tissue
regularly stratified by growth marks, a pattern absent in modern
sauropsids. The bone tissue type of Placodontia indet. aff. Cyamodus
and Placodontia indet. indicates a significantly increased basal
metabolic rate when compared with modern reptiles. Double lines of
arrested growth, non-annual rest lines in annuli, and subcycles that
stratify zones suggest high dependence of placodont growth on
endogenous and exogenous factors. Histological and modelled
differences within taxa point to high individual developmental
plasticity but sexual dimorphism in growth patterns and the presence
of different taxa in the sample cannot be ruled out.


C. G. Farmer (2015)
Similarity of Crocodilian and Avian Lungs Indicates Unidirectional
Flow Is Ancestral for Archosaurs.
Integrative and Comparative Biology (advance online publication)
doi: 10.1093/icb/icv078

Patterns of airflow and pulmonary anatomy were studied in the American
alligator (Alligator mississippiensis), the black caiman (Melanosuchus
niger), the spectacled caiman (Caiman crocodilus), the dwarf crocodile
(Osteolaemus tetraspis), the saltwater crocodile (Crocodylus porosus),
the Nile crocodile (Crocodylus niloticus), and Morelet’s crocodile
(Crocodylus moreletii). In addition, anatomy was studied in the
Orinoco crocodile (Crocodylus intermedius). Airflow was measured using
heated thermistor flow meters and visualized by endoscopy during
insufflation of aerosolized propolene glycol and glycerol. Computed
tomography and gross dissection were used to visualize the anatomy. In
all species studied a bird-like pattern of unidirectional flow was
present, in which air flowed caudad in the cervical ventral bronchus
and its branches during both lung inflation and deflation and craniad
in dorsobronchi and their branches. Tubular pathways connected the
secondary bronchi to each other and allowed air to flow from the
dorsobronchi into the ventrobronchi. No evidence for anatomical valves
was found, suggesting that aerodynamic valves cause the unidirectional
flow. In vivo data from the American alligator showed that
unidirectional flow is present during periods of breath-holding
(apnea) and is powered by the beating heart, suggesting that this
pattern of flow harnesses the heart as a pump for air. Unidirectional
flow may also facilitate washout of stale gases from the lung,
reducing the cost of breathing, respiratory evaporative water loss,
heat loss through the heat of vaporization, and facilitating crypsis.
The similarity in structure and function of the bird lung with
pulmonary anatomy of this broad range of crocodilian species indicates
that a similar morphology and pattern of unidirectional flow were
present in the lungs of the common ancestor of crocodilians and birds.
These data suggest a paradigm shift is needed in our understanding of
the evolution of this character. Although conventional wisdom is that
unidirectional flow is important for the high activity and basal
metabolic rates for which birds are renowned, the widespread
occurrence of this pattern of flow in crocodilians indicates
otherwise. Furthermore, these results show that air sacs are not
requisite for unidirectional flow, and therefore raise questions about
the function of avian air sacs.


B.M. Rothschild, D.R. Wilhite, D.S. McLeod & H. Ting (2015)
Evidence from surface microscopy  for recognition of fleshy and
tendinous muscle insertion in extant vertebrate femora: implications
for muscle reconstruction in fossils.
Historical Biology (advance online publication)

Recognition of muscle attachment sites and their modification has been
an important tool in anthropologic and paleontologic research, but has
been compromised by limited ability to recognise sites of tendinous
attachments. We investigated bone–tendon (three sites) and bone–muscle
(six sites) interfaces in six pairs of femora across a broad taxonomic
spectrum of higher amniote archosaurs (both recent and fossil) by
epi-illumination microscopy. Direct fleshy and indirect tendinous
muscle attachments were identified by dissection of fresh specimens
and examination of fossils and the surface microscopic changes
identified at those locations. Examination revealed bone modifications
specific to each type of muscle insertion, allowing them to be
identified and distinguished. Application of a surface microscopy
technique not only permits more confident localisation of tendinous
attachments, but for the first time allows recognition of sites of
direct fleshy muscle attachments – in a reproducible manner across
phylogenetic lines.