[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Megalophthalma, new Triassic plagiosaurid temnospondyl, and other non-dino papers



From: Ben Creisler
bcreisler@gmail.com

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

Megalophthalma, new Triassic plagiosaurid temnospondyl

Rainer R. Schoch, Andrew R. Milner & Florian Witzmann (2014)
Skull morphology and phylogenetic relationships of a new Middle
Triassic plagiosaurid temnospondyl from Germany, and the evolution of
plagiosaurid eyes.
Palaeontology (advance online publication)
DOI: 10.1111/pala.12101
http://onlinelibrary.wiley.com/doi/10.1111/pala.12101/abstract


A partial skull from the Lower Keuper (Middle Triassic) of Germany is
recognized as belonging to a new genus and species of plagiosaurid
temnospondyl. It is readily identified by the following
autapomorphies: (1) extremely large orbits medially extended to give
very thin interorbital region and cheek; (2) posterior skull table
abbreviated, with splint-like supratemporals, postparietals and
parietals; (3) supraorbital lateral line sulcus absent on frontal,
with blind ending on parietal, and continued at the anterior margin of
the postorbital; (4) occiput sloping posteriorly, with subtympanic
fossa exposed in ventral view; (5) cultriform process and basicranial
suture extremely narrow; (6) mandibular and maxillary teeth very long
with crowns markedly curved inwards. The new taxon shares the
following derived character states with Plagiosternum: (1) the
pentagonal shape of orbits; (2) the slender interorbital region and
cultriform process; (3) the small-scale, polygonal pit-and-ridge
ornament on posterior skull table, with single prominent tubercles
rising from ridges. Phylogenetic analysis finds plagiosaurids to be
monophyletic within a broad range of temnospondyls, nesting within a
clade of short-skulled stereospondyls. Plagiosuchus is the most basal
plagiosaurid, and Plagiosternum forms the sister group to the new
taxon. The biological significance of the large orbits of
plagiosaurids and their relationships to the eyeballs is discussed.
The only type of eyeball that would be feasible for all known
plagiosaurids would be a small spherical structure possibly situated
near the anterior edge of the orbit. For those plagiosaurs with
extremely large shallow orbits like Plagiosternum and Megalophthalma,
a possible adaptation would be a lens-less eye comprising a flat
retinal plate across the entire orbit.

===


Yanbin Wang, Deting Yang, Juan Han, Liting Wang, Jianxin Yao and Dunyi Liu
The Triassic U-Pb age for the aquatic long-necked protorosaur of Guizhou, China.
Geological Magazine (advance online publication)
DOI: http://dx.doi.org/10.1017/S001675681400003X
http://128.232.233.5/action/displayAbstract?fromPage=online&aid=9186559&fulltextType=RC&fileId=S001675681400003X

The ancient marine limestone beds of the upper part of the Guanling
Formation, Panxian County, Guizhou Province, SW China, yielded a wide
range of high-diversity well-preserved marine reptiles such as the
fully aquatic protorosaur with an extremely long neck
Dinocephalosaurus orientalis, the oldest mixosaurid ichthyosaurs and
lariosaurs. However, there is no precise isotopic age to study the
intriguing origin, evolution and emigration history of the important
fauna. We report a sensitive high-resolution ion microprobe (SHRIMP)
U-Pb zircon age for a volcanic tuff bed within the upper part of the
Guanling Formation. The result indicates that the age of the fossil
horizon is 244.0±1.3 Ma, 14 Ma earlier than the previously estimated
age based on conodont evidence. We consider that the marine reptiles
had a relatively rapid evolution during Middle Triassic time, some 8
Ma after the end-Permian mass extinction.

===

Ryan N. Felice & Patrick M. O'Connor (2014)
Ecology and Caudal Skeletal Morphology in Birds: The Convergent
Evolution of Pygostyle Shape in Underwater Foraging Taxa.
PLoS ONE 9(2): e89737.
doi:10.1371/journal.pone.0089737
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0089737

Birds exhibit a specialized tail that serves as an integral part of
the flight apparatus, supplementing the role of the wings in
facilitating high performance aerial locomotion. The evolution of this
function for the tail contributed to the diversification of birds by
allowing them to utilize a wider range of flight behaviors and thus
exploit a greater range of ecological niches. The shape of the wings
and the tail feathers influence the aerodynamic properties of a bird.
Accordingly, taxa that habitually utilize different flight behaviors
are characterized by different flight apparatus morphologies. This
study explores whether differences in flight behavior are also
associated with variation in caudal vertebra and pygostyle morphology.
Details of the tail skeleton were characterized in 51 Aequornithes and
Charadriiformes species. Free caudal vertebral morphology was measured
using linear metrics. Variation in pygostyle morphology was
characterized using Elliptical Fourier Analysis, a geometric
morphometric method for the analysis of outline shapes. Each taxon was
categorized based on flight style (flap, flap-glide, dynamic soar,
etc.) and foraging style (aerial, terrestrial, plunge dive, etc.).
Phylogenetic MANOVAs and Flexible Discriminant Analyses were used to
test whether caudal skeletal morphology can be used to predict flight
behavior. Foraging style groups differ significantly in pygostyle
shape, and pygostyle shape predicts foraging style with less than 4%
misclassification error. Four distinct lineages of underwater foraging
birds exhibit an elongate, straight pygostyle, whereas aerial and
terrestrial birds are characterized by a short, dorsally deflected
pygostyle. Convergent evolution of a common pygostyle phenotype in
diving birds suggests that this morphology is related to the
mechanical demands of using the tail as a rudder during underwater
foraging. Thus, distinct locomotor behaviors influence not only
feather attributes but also the underlying caudal skeleton,
reinforcing the importance of the entire caudal locomotor module in
avian ecological diversification.

===

James M. Neenan, Marcello Ruta, Jennifer A. Clack and Emily J. Rayfield (2014)
Feeding biomechanics in Acanthostega and across the fish-tetrapod transition.
Proceedings of the Royal Society. B. 281 no. 1781 20132689 (advance publication)
doi: 10.1098/rspb.2013.2689
http://rspb.royalsocietypublishing.org/content/281/1781/20132689.abstract

Acanthostega is one of the earliest and most primitive limbed
vertebrates. Its numerous fish-like features indicate a primarily
aquatic lifestyle, yet cranial suture morphology suggests that its
skull is more similar to those of terrestrial taxa. Here, we apply
geometric morphometrics and two-dimensional finite-element analysis to
the lower jaws of Acanthostega and 22 other tetrapodomorph taxa in
order to quantify morphological and functional changes across the
fish-tetrapod transition. The jaw of Acanthostega is similar to that
of certain tetrapodomorph fish and transitional Devonian taxa both
morphologically (as indicated by its proximity to those taxa in
morphospace) and functionally (as indicated by the distribution of
stress values and relative magnitude of bite force). Our results
suggest a slow tempo of morphological and biomechanical changes in the
transition from Devonian tetrapod jaws to aquatic/semi-aquatic
Carboniferous tetrapod jaws. We conclude that Acanthostega retained a
primitively aquatic lifestyle and did not possess cranial adaptations
for terrestrial feeding.

News story
http://phys.org/news/2014-02-jaw-mechanics-tetrapods-fed-underwater.html

==

Vivian de Buffrénil, Aurore Canoville, Susan E. Evans & Michel Laurin (2014)
Histological study of karaurids, the oldest known (stem) urodeles.
Historical Biology (advance online publication)
DOI:10.1080/08912963.2013.869800
http://www.tandfonline.com/doi/full/10.1080/08912963.2013.869800#.UwzQYvldXeI

Little is known about the initial phases of lissamphibian history
(before the Cretaceous), because their fossil record is quite scanty.
Only the morphology of the earliest members has been investigated,
although other sets of data, from bone microanatomy and histology, are
known to yield valuable paleobiological information. In the present
study, we provide the first histological and microanatomical data on
the oldest known stem-urodeles, the karaurids, from the Middle
Jurassic. Three humeri from the Upper Bathonian, Oxfordshire, referred
to juvenile or subadult individuals of Marmorerpeton and to an unnamed
caudate of undetermined (but obviously non-larval) ontogenetic stage,
were sampled in order to shed new light on the habitat and ontogeny of
these basal caudates. The great compactness of the three humeri
suggests that these salamanders were aquatic. The presence of
extensive amounts of calcified cartilage in the humeri greatly
strengthens the case for the presence of neoteny in these taxa, a
suggestion that had initially been made on the basis of a few
morphological characters. This constitutes the oldest known occurrence
of neoteny in lissamphibians. Finally, bone histology reveals that the
growth of Marmorerpeton and the related unnamed caudate was fairly
slow and cyclic, a characteristic of extant lissamphibians.

==

Ingmar Werneburg, Juliane K. Hinz, Michaela Gumpenberger, Virginie
Volpato, Nikolay Natchev & Walter G. Joyce (2014)
Modeling neck mobility in fossil turtles.
Journal of Experimental Zoology Part B: Molecular and Developmental
Evolution (advance online publication)
DOI: 10.1002/jez.b.22557
http://onlinelibrary.wiley.com/doi/10.1002/jez.b.22557/abstract

Turtles have the unparalleled ability to retract their heads and necks
within their shell but little is known about the evolution of this
trait. Extensive analysis of neck mobility in turtles using
radiographs, CT scans, and morphometry reveals that basal turtles
possessed less mobility in the neck relative to their extant
relatives, although the anatomical prerequisites for modern mobility
were already established. Many extant turtles are able to achieve
hypermobility by dislocating the central articulations, which raises
cautions about reconstructing the mobility of fossil vertebrates. A
3D-model of the Late Triassic turtle Proganochelys quenstedti reveals
that this early stem turtle was able to retract its head by tucking it
sideways below the shell. The simple ventrolateral bend seen in this
stem turtle, however, contrasts with the complex double-bend of extant
turtles. The initial evolution of neck retraction therefore occurred
in a near-synchrony with the origin of the turtle shell as a place to
hide the unprotected neck. In this early, simplified retraction mode,
the conical osteoderms on the neck provided further protection.