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Captorhinids and multiple tooth rows + Crosbysaurus in Utah + turtle scutes + more

Ben Creisler

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

Aaron R. H. LeBlanc & Robert R. Reisz (2015)
Patterns of tooth development and replacement in captorhinid reptiles:
a comparative approach for understanding the origin of multiple tooth
Journal of Vertebrate Paleontology (advance online publication)

Captorhinids are inherently interesting Paleozoic reptiles because
they include the first terrestrial vertebrates to have multiple tooth
rows on the maxilla and dentary. This may have been a key innovation
that allowed captorhinids to diversify and disperse throughout the
Permian Period of Pangea. We provide the first comparison of tooth
development in captorhinids to determine how multiple rows of marginal
teeth evolved within this clade. By comparing thin sections of
multiple-rowed Captorhinus aguti from the Lower Permian of Oklahoma
with the contemporaneous, single-rowed Captorhinus magnus, we provide
evidence for variation in jaw growth, which establishes the number of
tooth rows. Comparisons with the basal captorhinid Concordia
cunninghami from the Upper Carboniferous of Kansas demonstrate that
early captorhinids retained the typical amniote condition of replacing
teeth in a manner similar to modern iguanian lizards. By comparing
tooth development in C. aguti with other single-rowed captorhinids, we
also demonstrate that the shedding of old teeth and the development of
new teeth are not linked developmental processes in captorhinids.
Instead, the fates of older generations of teeth are entirely
dependent on their proximity to the lingual surface of the dentary
where the tooth-producing organ, the dental lamina, would have been
present. These peculiar features of the dentitions of captorhinids
make them model taxa for examining patterns of tooth development and


Final version of article that already appeared in preprint form on the DML:

Robert J. Gay & Isabella St. Aude (2015)
The first occurrence of the enigmatic archosauriform Crosbysaurus
Heckert 2004 from the Chinle Formation of southern Utah.
PeerJ 3:e905
doi:  https://dx.doi.org/10.7717/peerj.905

Originally identified as an ornithischian dinosaur, Crosbysaurus
harrisae has been found in New Mexico, Arizona, and its type locality
in Texas, as well as in North Carolina. The genus has been reassessed
by other workers in light of reinterpretations about the postcrania of
another putative Triassic ornithischian, Revueltosaurus. The
understanding of Triassic dental faunas has become more complicated by
the extreme convergence between pseudosuchian archosaurs and
ornithischian dinosaur dental morphologies. We report here on a new
specimen of Crosbysaurus (MNA V10666) from the Chinle Formation at
Comb Ridge in southeastern Utah. This new specimen is assigned to
Crosbysaurus sp. on the basis of the unique compound posterior
denticles, labiolingual width, and curvature. While MNA V10666 does
not help resolve the affinities of Crosbysaurus, it does represent the
extension of the geographic range of this taxon for approximately 250
kilometers. This is the first record of the genus Crosbysaurus in Utah
and as such it represents the northernmost known record of this taxon.
This indicates that Crosbysaurus was not limited to the southern area
of the Chinle/Dockum deposition but instead was widespread across the
Late Triassic paleoriver systems of western Pangea. The reported
specimen was found in close association with a typical Late Triassic
Chinle fauna, including phytosaurs, metoposaurs, and dinosauromorphs.


Jacqueline E. Moustakas-Verho and Gennadii O. Cherepanov (2015)
The integumental appendages of the turtle shell: An evo-devo perspective.
Journal of Experimental Zoology Part B: Molecular and Developmental
Evolution 324(3): 221–229
DOI: 10.1002/jez.b.22619

The turtle shell is composed of dorsal armor (carapace) and ventral
armor (plastron) covered by a keratinized epithelium. There are two
epithelial appendages of the turtle shell: scutes (large epidermal
shields separated by furrows and forming a unique mosaic) and
tubercles (numerous small epidermal bumps located on the carapaces of
some species). In our perspective, we take a synthetic, comparative
approach to consider the homology and evolution of these integumental
appendages. Scutes have been more intensively studied, as they are
autapomorphic for turtles and can be diagnostic taxonomically. Their
pattern of tessellation is stable phylogenetically, but labile in the
individual. We discuss the history of developmental investigations of
these structures and hypotheses of evolutionary and anomalous
variation. In our estimation, the scutes of the turtle shell are an
evolutionary novelty, whereas the tubercles found on the shells of
some turtles are homologous to reptilian scales.


Tetsuto Miyashita (2015)
Fishing for jaws in early vertebrate evolution: a new hypothesis of
mandibular confinement.
Biological Reviews (advance online publication)
DOI: 10.1111/brv.12187

The evolutionary origin of the vertebrate jaw persists as a deeply
puzzling mystery. More than 99% of living vertebrates have jaws, but
the evolutionary sequence that ultimately gave rise to this highly
successful innovation remains controversial. A synthesis of recent
fossil and embryological findings offers a novel solution to this
enduring puzzle. The Mandibular Confinement Hypothesis proposes that
the jaw evolved via spatial confinement of the mandibular arch (the
most anterior pharyngeal arch within which the jaw arose). Fossil and
anatomical evidence reveals: (i) the mandibular region was initially
extensive and distinct among the pharyngeal arches; and (ii) with
spatial confinement, the mandibular arch acquired a common pharyngeal
pattern only at the origin of the jaw. The confinement occurred via a
shift of a domain boundary that restricted the space the mesenchymal
cells of the mandibular arch could occupy. As the surrounding domains
replaced mandibular structures at the periphery, this shift allowed
neural crest cells and mesodermal mesenchyme of the mandibular arch to
acquire patterning programs that operate in the more posterior arches.
The mesenchymal population within the mandibular arch was therefore no
longer required to differentiate into specialized feeding and
ventilation structures, and was remodelled into a jaw. Embryological
evidence corroborates that the mandibular arch must be spatially
confined for a jaw to develop. This new interpretation suggests neural
crest as a key facilitator in correlating elements of the classically
recognized vertebrate head ‘segmentation’.


David K. Carpenter, Howard J. Falcon-Lang, Michael J. Benton, and
Melissa Grey (2015)
Early Pennsylvanian (Langsettian) fish assemblages from the Joggins
Formation, Canada, and their implications for palaeoecology and
Palaeontology (advance online publication)
DOI: 10.1111/pala.12164

A review of all available specimens of fossil fishes from the classic
Pennsylvanian Joggins locality of Nova Scotia, Canada, reveals the
existence of a diverse community of chondrichthyans (xenacanthids,
ctenacanthids and the enigmatic Ageleodus), acanthodians
(gyracanthids), sarcopterygians (rhizodontids, megalichthyids,
rhizodopsids and dipnoans) and actinopterygians (haplolepids).
Reassessment of supposed endemic species (Ctenoptychius cristatus,
Sagenodus plicatus, Gyracanthus duplicatus) indicates they are
invalid, and overall, the assemblage comprises cosmopolitan taxa that
were widespread around the coasts of tropical Pangaea. Strontium
isotope analysis of fish remains and a critical study of their facies
context suggest that these fish communities occupied bodies of water
with salinities across the marine–freshwater spectrum. This
preponderance of euryhaline forms implies a community structure quite
distinct from that of today and might represent a transitory phase
prior to the establishment of fully freshwater fish communities.
Interpretation of fish ecology provides further evidence that the
Joggins Formation was deposited in a paralic setting, and the
recognition of one previously undetected brackish incursion
strengthens the link between sedimentary cycles at Joggins and
Milankovitch-induced glacio-eustatic change. Furthermore,
interregional correlation of these marine transgressions supports
palynostratigraphical arguments for an early Langsettian age for the
Joggins Formation. This places tighter constraints on the age of the
earliest known crown amniote, Hylonomus lyelli, an important
calibration point used in phylogenomic studies.