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Machimosaurus teeth + other non-dino papers



Ben Creisler
bcreisler@gmail.com

A number of recent non-dino papers that may be of interest:

In open access:


Mark T. Young, Lorna Steel, Stephen L. Brusatte, Davide Foffa & Yves
Lepage (2014)
Tooth serration morphologies in the genus Machimosaurus
(Crocodylomorpha, Thalattosuchia) from the Late Jurassic of Europe.
Royal Society Open Science 1: 140269.
DOI: 10.1098/rsos.140269
http://rsos.royalsocietypublishing.org/content/1/3/140269



Machimosaurus was a large-bodied durophagous/chelonivorous genus of
teleosaurid crocodylomorph that lived in shallow marine and brackish
ecosystems during the Late Jurassic. Among teleosaurids, Machimosaurus
and its sister taxon ‘Steneosaurus’ obtusidens are characterized by
having foreshortened rostra, proportionally enlarged supratemporal
fenestrae and blunt teeth with numerous apicobasal ridges and a
shorter anastomosed ridged pattern in the apical region. A recent
study on ‘S.’ obtusidens dentition found both true denticles and false
serrations (enamel ridges which contact the carinae). Here, we
comprehensively describe and figure the dentition of Machimosaurus,
and find that Machimosaurus buffetauti and Machimosaurus hugii have
four types of serration or serration-like structures, including both
denticles and false denticles on the carinae. The denticles are
irregularly shaped and are not always discrete units, whereas the
false denticles caused by the interaction between the superficial
enamel ridges and the carinae are restricted to the apical region.
Peculiarly, the most ‘denticle-like’ structures are discrete, bulbous
units on the apicobasal and apical anastomosed ridges of M. hugii.
These ‘pseudo-denticles’ have never, to our knowledge, previously been
reported among crocodylomorphs, and their precise function is unclear.
They may have increased the surface area of the apical region and/or
strengthened the enamel, both of which would have been advantageous
for a durophagous taxon feeding on hard objects such as turtles.

===


Walter G. Joyce, Juliana Sterli, and Sandra D. Chapman (2014)
The skeletal morphology of the solemydid turtle Naomichelys speciosa
from the Early Cretaceous of Texas.
Journal of Paleontology 88(6):1257-1287. 2014
doi: http://dx.doi.org/10.1666/14-002
http://www.bioone.org/doi/abs/10.1666/14-002

The fossil record of solemydid turtles is primarily based on isolated
fragments collected from Late Jurassic to Late Cretaceous sediments
throughout North America and Europe and little is therefore known
about the morphology and evolutionary history of the group. We here
provide a detailed description of the only known near-complete
solemydid skeleton, which was collected from the Lower Cretaceous
(Aptian–Albian) Antlers Formation of Texas during the mid-twentieth
century, but essentially remains undescribed to date. Though
comparison is limited, the skeleton is referred to Naomichelys
speciosa, which is based on an isolated entoplastron from the Lower
Cretaceous (Aptian–Albian) Kootenai (Cloverly) Formation of Montana.
The absence of temporal emarginations, contribution of the jugals to
the orbits, and a clear subdivision of the middle and inner cavities,
and the presence of elongate postorbitals, posteriorly expanded
squamosals, a triangular fossa at the posterior margin of the
squamosals, an additional pair of tubercula basioccipitale that is
formed by the pterygoids, foramina pro ramo nervi vidiani (VII) that
are visible in ventral view, shell sculpturing consisting of high
tubercles, a large entoplastron with entoplastral scute, V-shaped
anterior peripherals, and limb osteoderms with tubercular sculpture
diagnose Naomichelys speciosa as a representative of Solemydidae. The
full visibility of the parabasisphenoid complex in ventral view, the
presence of an expanded symphyseal shelf, and the unusual ventromedial
folding of the coronoid process are the primary characteristics that
distinguish Naomichelys speciosa from the near-coeval European taxon
Helochelydra nopcsai.

===



P. M. Gignac and G. M. Erickson (2014)
Ontogenetic changes in dental form and tooth pressures facilitate
developmental niche shifts in American alligators.
Journal of Zoology (advance online publication)
DOI: 10.1111/jzo.12187
http://onlinelibrary.wiley.com/doi/10.1111/jzo.12187/abstract
Between hatching and late adulthood American alligators Alligator
mississippiensis show up to 7000-fold increases in body mass.
Concurrent with such changes in body size are absolute and relative
modifications in rostral proportions, dental form, feeding capacities
and dietary preferences. How these major anatomical changes
accommodate prey-resource shifts is poorly understood. In this study,
we focus on the effects of ontogenetic changes in bite-force
capacities and dental form to address how these factors relate to
tooth-pressure generation and diet. We derive absolute values of tooth
pressure along the crowns of the most prominent teeth (the first
documentation of tooth pressures throughout ontogeny and after initial
tooth contact for any animal) and show that these pressures increase
with positive allometry during ontogeny. In addition, we discuss how
American alligator tooth-pressure values explain their capacities for
seizure and oral processing of typical prey, and how tooth-pressure
changes facilitate developmental niche shifts in this large-bodied
taxon.

===

In open access:


Hans A. Schnyder, Dieter Vanderelst, Sophia Bartenstein, Uwe Firzlaff
& Harald Luksch (2014)
The Avian Head Induces Cues for Sound Localization in Elevation.
PLoS ONE 9(11): e112178.
doi:10.1371/journal.pone.0112178
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0112178


Accurate sound source localization in three-dimensional space is
essential for an animal’s orientation and survival. While the
horizontal position can be determined by interaural time and intensity
differences, localization in elevation was thought to require external
structures that modify sound before it reaches the tympanum. Here we
show that in birds even without external structures like pinnae or
feather ruffs, the simple shape of their head induces sound
modifications that depend on the elevation of the source. Based on a
model of localization errors, we show that these cues are sufficient
to locate sounds in the vertical plane. These results suggest that the
head of all birds induces acoustic cues for sound localization in the
vertical plane, even in the absence of external ears.