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Cyamodus and pachypleurosaurid papers

From: Ben Creisler

More articles about Triassic marine reptiles:

Cajus G. Diedrich (2011)
The shallow marine placodont Cyamodus of the central European Germanic
Basin: its evolution, paleobiogeography and paleoecology. 
Historical Biology: An International Journal of Paleobiology (advance
online publication)
DOI: 10.1080/08912963.2011.575938 
The oldest record of Cyamodus is a skull of Cyamodus tarnowitzensis (Grich
1884, Zt dt Geol Ges. 36:125-144) from Pelsonian shallow marine deposits.
During the middle Illyrian, placodonts disappeared from the Germanic Basin.
With renewed upper Illyrian transgression, Cyamodus rostratus (Mnster 1839,
ber einige ausgezeichnete fossile Fischzhne aus dem Muschelkalk bei
Bayreuth. Birner, Bayreuth, p. 14) appeared which was found in terebratulid
shell-rich shallow marine deposits. Abundant remains of Cyamodus muensteri
(Agassiz 1839), traditionally referred to as Cyamodus hildegardis and here
synonymised with C. muensteri, have been reported from the upper
Illyrian/middle Fassanian. Skeletal remains of this species are from the
Grenzbitumenzone of the Monte San Giorgio lagoons. The youngest species,
Cyamodus kuhnschnyderi (Nosotti and Pinna 1993, Compt Rend Acad Sci Paris.
317:847-850), has been found in the upper Fassanian/lower Longobardian of
the southern Germanic Basin or Burgundian Gate when marine facies in the
Germanic Basin had nearly disappeared. These successive species provide
evidence of monophylogenetic development with a trend towards anterior
upper and lower jaw teeth reduction, along with a shortening of the
rostrum, over an interval of five million years (243-238 Ma). This
evolutionary trend most probably reflects adaptation to specialised feeding
on seaplants. The Cyamodus osteoderm carapace was not fused to the
vertebral column, and appears to have been primarily a body enhancement
that produced neutral or negative buoyancy to facilitate long-period

Jasmina Hugi, Torsten M. Scheyer, P. Martin Sander, Nicole Klein and
Marcelo R. Sánchez-Villagra (2011)
Long bone microstructure gives new insights into the life of
pachypleurosaurids from the Middle Triassic of Monte San Giorgio,
Comptes Rendus Palevol (advance online publication)

The long bone microstructure of four pachypleurosaurid taxa from Monte San
Giorgio (Switzerland/Italy) was studied. Pachypleurosaurids are secondarily
aquatic reptiles that lived during the Middle Triassic in varying marine
environments of the Tethys. All four pachypleurosaurids show high
compactness values in their long bones based on a thick cortex and a
calcified cartilaginous core, which remains in the medullary region
throughout the ontogeny. Parts or even the entire embryonic bone layer
composed of a mixture of woven-fibered bone tissue and parallel-fibered
bone tissue is preserved in both pachypleurosaurid genera. The rest of the
cortex consists of lamellar-zonal bone tissue type. Differences in the
microstructure of the bones between the pachypleurosaurids are reflected in
the occurrence of remodelling processes, which, if present, affect the
innermost growth marks of the cortex or the calcified cartilaginous core.
Further variation is present in the spacing pattern of the growth cycles,
as well as in the degree of vascularisation of the lamellar-zonal bone
tissue type. Our data on the microstructure of the long bones support
previous studies on morphology and facies distribution, which indicated
different habitats and adaptation to a secondary aquatic lifestyle for each
pachypleurosaurid taxon. Life history data furthermore reflect different
longevities and ages at sexual maturity. The bone histological data of the
stratigraphically youngest and oldest pachypleurosaurid species might
indicate possible climate-dependant reproductive seasons similar to Recent
lacertilian squamates.

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