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Aquatic origin of turtles plus Mesozoic turtle stuff

From: Ben Creisler

A new PLoS ONE article about turtles, with a couple of recent Mesozoic
turtle articles thrown in:

Katie L. Willis, Jakob Christensen-Dalsgaard, Darlene R. Ketten &
Catherine E. Carr (2013)
Middle Ear Cavity Morphology Is Consistent with an Aquatic Origin for
PLoS ONE 8(1): e54086

The position of testudines in vertebrate phylogeny is being
re-evaluated. At present, testudine morphological and molecular data
conflict when reconstructing phylogenetic relationships. Complicating
matters, the ecological niche of stem testudines is ambiguous. To
understand how turtles have evolved to hear in different environments,
we examined middle ear morphology and scaling in most extant families,
as well as some extinct species, using 3-dimensional reconstructions
from micro magnetic resonance (MR) and submillimeter computed
tomography (CT) scans. All families of testudines exhibited a similar
shape of the bony structure of the middle ear cavity, with the
tympanic disk located on the rostrolateral edge of the cavity. Sea
Turtles have additional soft tissue that fills the middle ear cavity
to varying degrees. When the middle ear cavity is modeled as an
air-filled sphere of the same volume resonating in an underwater sound
field, the calculated resonances for the volumes of the middle ear
cavities largely fell within testudine hearing ranges. Although there
were some differences in morphology, there were no statistically
significant differences in the scaling of the volume of the bony
middle ear cavity with head size among groups when categorized by
phylogeny and ecology. Because the cavity is predicted to resonate
underwater within the testudine hearing range, the data support the
hypothesis of an aquatic origin for testudines, and function of the
middle ear cavity in underwater sound detection.


The pdf is free (open access journal):

E.V. Syromyatnikova, I.G. Danilov and V.B. Sukhanov (2012)
A redescription and phylogenetic position of Adocus planus, an adocid
turtle from the Late Cretaceous of Mongolia.
Proceedings of the Zoological Institute 316 (4): 380-391

In this paper we present a detailed description of the holotype of
Adocus (orig. Shineusemys) planus from the Late Cretaceous of
Mongolia. The holotype, originally reported to be a plastron, is
actually represented by a partial shell with an almost complete
plastron and few carapace fragments on the steinkern. The
reexamination of the holotype of A. planus allows us to present new
images of this specimen, improve its diagnosis and include it in a
phylogenetic analysis of Adocusia (Adocidae + Nanhsiungchelyidae) for
the first time. The phylogenetic analysis places A. planus within the
Adocus clade in polytomy with other species of this genus. This result
confirms our previous suggestion that Shineusemys should be considered
a junior subjective synonym of Adocus.


A. Pérez-García & X. Murelaga (2012)
Camerochelys vilanovai gen. et sp. nov., a new pan-cryptodiran turtle
in the Early Cretaceous of the Iberian Range (Spain).
Cretaceous Research (advance online publication)
http://dx.doi.org/10.1016/j.cretres.2012.12.002, How to Cite or Link Using DOI

A new turtle taxon, Camerochelys vilanovai gen. et sp. nov., from
Hauterivian–Barremian levels of the eastern Cameros Basin (La Rioja,
Iberian Range, Spain), is proposed here. Elements of the shell
corresponding to five individuals are assigned to it. Camerochelys
vilanovai is a turtle with a low, oval and longer than wide shell. It
is diagnosed by a combination of characters that includes, among
others, the presence of an ornamentation pattern, restricted to the
medial area of the vertebral scutes, and composed of thin, numerous
and poorly developed radiating striations; shallow nuchal notch;
short, and more than four times wider than long cervical scute; five
vertebral scutes, all of them substantially wider than long, the
second and third ones being more than two times wider than long, and
the fourth one two times wider than long; sagittal contact of the last
pair of costal plates; presence of inframarginal scutes; absence of
mesoplastra. Camerochelys vilanovai is identified as a member of
Pan-Cryptodira not assigned to Eurysternidae, to the clade including
representatives of Paracyptodira and Plesiochelyidae, or to the crown
group Cryptodira. This new taxon could be a representative of
Xinjiangchelyidae, a clade belonging to the stem group of Cryptodira,
and identified in the Asian and European record. The description of
this new taxon further increases the known diversity of turtles in the
Early Cretaceous of the Iberian Range, a region where members of
several clades of the stem group of Testudines, Pan-Pleurodira and
Pan-Cryptodira have been previously identified.