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Bony ancestors of sharks + Cretaceous Arctic cold snap (free pdfs)
Recent open access papers that may be of interest:
John A. Long , Carole J. Burrow, Michal Ginter, John G. Maisey, Kate
M. Trinajstic, Michael I. Coates, Gavin C. Young & Tim J. Senden
First Shark from the Late Devonian (Frasnian) Gogo Formation, Western
Australia Sheds New Light on the Development of Tessellated Calcified
PLoS ONE 10(5): e0126066.
Living gnathostomes (jawed vertebrates) comprise two divisions,
Chondrichthyes (cartilaginous fishes, including euchondrichthyans with
prismatic calcified cartilage, and extinct stem chondrichthyans) and
Osteichthyes (bony fishes including tetrapods). Most of the early
chondrichthyan (‘shark’) record is based upon isolated teeth, spines,
and scales, with the oldest articulated sharks that exhibit major
diagnostic characters of the group—prismatic calcified cartilage and
pelvic claspers in males—being from the latest Devonian, c. 360 Mya.
This paucity of information about early chondrichthyan anatomy is
mainly due to their lack of endoskeletal bone and consequent low
Here we present new data from the first well-preserved chondrichthyan
fossil from the early Late Devonian (ca. 380–384 Mya) Gogo Formation
Lägerstatte of Western Australia. The specimen is the first Devonian
shark body fossil to be acid-prepared, revealing the endoskeletal
elements as three-dimensional undistorted units: Meckel’s cartilages,
nasal, ceratohyal, basibranchial and possible epibranchial cartilages,
plus left and right scapulocoracoids, as well as teeth and scales.
This unique specimen is assigned to Gogoselachus lynnbeazleyae n. gen.
The Meckel’s cartilages show a jaw articulation surface dominated by
an expansive cotylus, and a small mandibular knob, an unusual
condition for chondrichthyans. The scapulocoracoid of the new specimen
shows evidence of two pectoral fin basal articulation facets,
differing from the standard condition for early gnathostomes which
have either one or three articulations. The tooth structure is
intermediate between the ‘primitive’ ctenacanthiform and symmoriiform
condition, and more derived forms with a euselachian-type base. Of
special interest is the highly distinctive type of calcified cartilage
forming the endoskeleton, comprising multiple layers of nonprismatic
subpolygonal tesserae separated by a cellular matrix, interpreted as a
transitional step toward the tessellated prismatic calcified cartilage
that is recognized as the main diagnostic character of the
In open access:
Jens O. Herrle, Claudia J. Schröder-Adams, William Davis, Adam T.
Pugh, Jennifer M. Galloway and Jared Fath (2015)
Mid-Cretaceous High Arctic stratigraphy, climate, and Oceanic Anoxic Events.
Geology (advance online publication)
Over the past decades, much research has focused on the mid-Cretaceous
greenhouse climate, the formation of widespread organic-rich black
shales, and cooling intervals from low- to mid-latitude sections. Data
from the High Arctic, however, are limited. In this paper, we present
high-resolution geochemical records for an ~1.8-km-thick sedimentary
succession exposed on Axel Heiberg Island in the Canadian Arctic
Archipelago at a paleolatitude of ~71°N. For the first time, we have
data constraints for the timing and magnitude of most major Oceanic
Anoxic Events (OAEs) in brackish-water (OAE1a) and shelf (OAE1b and
OAE2) settings in the mid-Cretaceous High Arctic. These are consistent
with carbon-climate perturbations reported from deep-water records of
lower latitudes. Glendonite beds are observed in the upper Aptian to
lower Albian, covering an interval of ~6 m.y. between 118 and 112 Ma.
Although the formation of glendonites is still under discussion, these
well-dated occurrences may support the existence of cool shelf waters
in the High Arctic Sverdrup Basin at this time, coeval with recent
geochemical data from the subtropical Atlantic indicating a drop in
sea-surface temperature of nearly 4 °C.