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Panchetocynodon, new cynodont from Triassic of India; Tritylodon jaw histology



From: Ben Creisler
bcreisler@gmail.com

A couple of new papers about cynodonts.

D. P. Das and Abir Gupta (2012)
New cynodont record from the lower Triassic Panchet Formation, Damodar valley.
Earth and Environmental Science Journal of the Geological Society of India
Volume 79, Number 2, 175-180
DOI: 10.1007/s12594-012-0022-2
http://www.springerlink.com/content/u85484576365lp51/


This paper reports the find of a new non-mammalian cynodont from the
Lower Triassic Panchet Formation of the Damodar valley, West Bengal,
India. The fossil, recovered from a clay pellet rich calcareous
sandstone bed, is a part of left lower jaw having five post canines
that are damaged to various extents. A combination of mammal-like
advanced characters such as much enlarged dentary, reduced post
dentary bones, high coronoid process, large masseteric fossa, each
post canine with a large central cusp flanked by a distal and a mesial
accessory cusps with two additional lingually positioned cingular
cusps, incipient root division and clearly demarcated crown-root
juncture prompted to erect a new taxon Panchetocynodon damodarensis
gen. et sp. nov.

===
Jasinoski, S. C. and Chinsamy, A. (2012)
Mandibular histology and growth of the nonmammaliaform cynodont Tritylodon.
Journal of Anatomy (advance online publication).
doi: 10.1111/j.1469-7580.2012.01494.x
http://onlinelibrary.wiley.com/doi/10.1111/j.1469-7580.2012.01494.x/abstract

An investigation of bone microstructure of nonmammalian therapsids has
revealed distinctive signals pertaining to their ontogenetic growth
and biology. Until now, histological studies of the nonmammaliaform
cynodonts have focused only on postcranial material. Through the
examination of micro-computed tomography (micro-CT) scans and serial
thin sections, the current study provides a novel perspective on the
structure and growth of the mandible of Tritylodon, a derived
herbivorous cynodont from southern Africa. By tracking histological
features across the serial thin sections, trends in relocation and
modelling are documented for the growing Tritylodon mandible. For
example, during growth, localized changes in the cross-sectional shape
of the mandible occurred. Localized deposits of new lamellar and
fibrolamellar bone on the lateral edge indicate widening of the
mandible during different episodes of growth. The presence of radial
channels indicates the deepening of the mandible at its anterior and
posterior ends. The relocation of the paired mental foramina suggests
that the mandibular body lengthened mainly in the posterior direction.
The medial movement of a posterior postcanine tooth during growth and
eruption is recorded in the histology. This histological assessment
also documents the presence of Sharpey’s fibres in the cellular
cementum of the first incisor, providing novel and unequivocal
evidence that it was attached to the Tritylodon jaw by a periodontal
ligament. This is the first comprehensive study that uses histological
analysis to document the growth dynamics of the mandible of a
nonmammalian therapsid, thus providing a unique perspective of
localized mandibular growth in a fossil animal.