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Mesosaurus swimming speed + cynodont Trucidocynodon biomechanics + chelonioid turtles from Poland



Ben Creisler
bcreisler@gmail.com


Some recent non-dino papers:


Joaquín Villamil, Pablo Núñez Demarco, Melitta Meneghel, R. Ernesto
Blanco, Washington Jones, Andrés Rinderknecht, Michel Laurin &
Graciela Piñeiro (2015)
Optimal swimming speed estimates in the Early Permian mesosaurid
Mesosaurus tenuidens (Gervais 1865) from Uruguay.
Historical Biology (advance online publication)
DOI:10.1080/08912963.2015.1075018
http://www.tandfonline.com/doi/full/10.1080/08912963.2015.1075018#abstract

Mesosaurid biology has been subject of continuous debate since the
first description of Mesosaurus tenuidens by Paul Gervais in 1867.
Controversy surrounds their environmental and feeding preferences.
Most studies suggested that mesosaurids were marine reptiles and
perhaps piscivorous predators. Nonetheless, recent work suggests that
they inhabited a salty, eventually hypersaline shallow epicontinental
sea and that pygocephalomorph crustaceans were their preferred food
item. Here, we present results of the first biomechanical study about
optimal swimming capabilities in Mesosaurus tenuidens, which along
with the comparative analysis of the limb morphology support the
hypothesis that these animals were slow swimmers living in shallow
waters. The study is based on the revision of several almost complete
mesosaurid specimens and isolated, well-preserved bones housed in
palaeontological collections in Uruguay, Brazil, France and Germany.
We studied the relative size and proportions of the bones, as well as
their morphology and anatomical position to produce a
three-dimensional reconstruction of the original appearance of an
undamaged, complete skeleton. Our results suggest a fairly low optimal
swimming speed for mesosaurids, which is consistent with capture of
fairly slow prey like pygocephalomorphs, possibly by filter-feeding,
rather than by active pursuit of fast prey.


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Téo Veiga De Oliveira and Cesar Leandro Schultz (2015)
Functional morphology and biomechanics of the cynodont Trucidocynodon
riograndensis from the Triassic of Southern Brazil: Pectoral girdle
and forelimb.
Acta Palaeontologica Polonica (in press)
doi:http://dx.doi.org/10.4202/app.00171.2015
http://app.pan.pl/article/item/app001712015.html

Non-mammalian cynodonts provide insights on several points about
mammalian evolution, such as the postural change and locomotory
advances within the group. Unfortunately, complete skeletons of
Triassic cynodonts are not very common and where more complete
specimens are found they can offer a global vision on some traits not
available from partial specimens. This is the case of the cynodont
Trucidocynodon riograndensis, from the Triassic of Brazil, that has
its forelimbs and locomotory properties presented in this paper. The
movements between interclavicle and clavicle must have been limited,
as such as those occurring between the latter and the scapulocoracoid
although the long acromion process of this should have permitted a
greater degree of freedom. Some of the more significant movements were
those on the shoulder joint, in which the maximum adduction should
have been circa 35º relative to the parasagittal plane and the greater
abduction circa 55º. The maximum adduction occurred when the humerus
was in the more retracted position during stride and the variation in
the adduction/abduction should have been significant to the limb
posture during its recovery stroke. The long olecranon and the distal
overlapping between radius and ulna suggest the predominance of simple
flexion/extension on the forearm without significant
pronation/supination. The poorly preserved hand suggests that
Trucidocynodon could have evolved a slight semidigitigrad condition in
its forelimbs. All these features places Trucidocynodon as an
important actor on the evolution of the mammalian locomotory
properties indicating that some features, as the possibility of
greater humeral adduction, evolved early in cynodont lineage.

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Agnieszka Kapuścińska & Marcin Machalski (2015)
Upper Albian chelonioid turtles from Poland.
Geobios (advance online publication)
doi:10.1016/j.geobios.2015.07.002
http://www.sciencedirect.com/science/article/pii/S0016699515000613

Remains of chelonioid turtles assigned to Protostegidae are recorded
from the upper Albian (Early Cretaceous) sands at Annopol, Poland.
These are the first remains of Cretaceous marine turtles from Poland.
A semi-articulated partial carapace with an associated postorbital
bone is referred to as Protostegidae gen. et sp. indet. A. Scute sulci
are visible on each preserved costal and neural plate of this
specimen, which suggests hypertrophy and multiplication of vertebral
scutes, a unique feature among chelonioids. An isolated humerus from
the same level as the carapace is referred to as Protostegidae gen. et
sp. indet. B. The massive lateral process of this humerus extends
significantly onto the ventral surface of the bone, like in some
humeri of primitive protostegids from the European Cretaceous,
including the Albian “Lytoloma cantabrigiense” from England and
Turonian “Rhinochelys (?) cf. carusiana” from Germany.
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