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Triassic archosauromorphs in new JVP



From: Ben Creisler
bh480@scn.org

In the new JVP:

Da-Yong Jiang, Olivier Rieppel, Nicholas C. Fraser, Ryosuke Motani,
Wei-Cheng Hao, Andrea Tintori, Yuan-Lin Sun & Zuo-Yu Sun (2011)
New information on the protorosaurian reptile Macrocnemus fuyuanensis Li et
al., 2007, from the Middle/Upper Triassic of Yunnan, China.
Journal of Vertebrate Paleontology 31(6):, 2011-1237 
DOI:10.1080/02724634.2011.610853
http://www.tandfonline.com/doi/abs/10.1080/02724634.2011.610853


A new specimen of the protorosaur Macrocnemus fuyuanensis, from the
Zhuganpo Member of the Falang Formation at Fuyuan (Yunnan Province,
southwestern China), is described and compared with Macrocnemus bassanii.
The new specimen is the first in the genus Macrocnemus that clearly shows
details of the preorbital region of the skull. A large, plate-like lacrimal
is located in front of the tall, columnar prefrontal that defines the
anterior margin of the orbit. A longitudinally oriented nasal groove
extends along the anterior two-thirds of the snout, accommodating the
external naris at its anterior part. A similar preorbital depression has
previously been described for Dinocephalosaurus and it is also reported
here for the first time in Tanystropheus. The new specimen confirms the
status of Macrocnemus fuyuanensis as a species distinct from Macrocnemus
bassanii on the basis of a humerus that significantly exceeds the radius in
length. The occurrence of both Macrocnemus and Tanystropheus in
southwestern China further underscores the close faunal affinities of the
eastern and western Tethyan realms during the Middle and early Late
Triassic.

--


Jennifer Botha-Brink & Roger M. H. Smith (2011)
Osteohistology of the Triassic archosauromorphs Prolacerta, Proterosuchus,
Euparkeria, and Erythrosuchus from the Karoo Basin of South Africa.
DOI:10.1080/02724634.2011.621797
http://www.tandfonline.com/doi/abs/10.1080/02724634.2011.621797


The South African non-archosauriform archosauromorph Prolacerta and the
archosauriforms Proterosuchus, Erythrosuchus, and Euparkeria were important
constituents of the Early to early Middle Triassic Karoo ecosystem
following the end-Permian mass extinction. We present new data on the
osteohistology of these stem archosaurs and provide insight into their
paleobiology. Bone tissues of the Early Triassic Prolacerta contain a
poorly defined fibro-lamellar complex, with parallel-fibered bone in some
regions, whereas the contemporaneous Proterosuchus exhibits rapidly forming
uninterrupted fibro-lamellar bone early in its ontogeny, which becomes slow
forming lamellar-zonal bone with increasing age. The early Middle Triassic
Erythrosuchus deposited highly vascularized, uninterrupted fibro-lamellar
bone throughout ontogeny, whereas the growth of the contemporaneous
Euparkeria was relatively slow and cyclical. When our data are combined
with those of previous studies, preliminary results reveal that Early and
Middle Triassic non-crown group archosauromorphs generally exhibit faster
growth rates than many of those of the Late Triassic. Early rapid growth
and rapid attainment of sexual maturity are consistent with life history
expectations for taxa living in the unpredictable conditions following the
end-Permian mass extinction. Further research with larger sample sizes will
be required to determine the nature of the environmental pressures on these
basal archosaurs.



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