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[dinosaur] Choerosaurus (Therapsida) cranial bosses + tetrapod palatal dentition + archosaur teeth from Cretaceous of India




Ben Creisler
bcreisler@gmail.com


Some recent papers:


Free pdf:

Julien Benoit, Paul R. Manger, Vincent Fernandez & Bruce S. Rubidge (2016)
Cranial Bosses of Choerosaurus dejageri (Therapsida, Therocephalia): Earliest Evidence of Cranial Display Structures in Eutheriodonts. 
PLoS ONE 11(8): e0161457. 
doi:10.1371/journal.pone.0161457
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0161457



Choerosaurus dejageri, a non-mammalian eutheriodont therapsid from the South African late Permian (~259 Ma), has conspicuous hemispheric cranial bosses on the maxilla and the mandible. These bosses, the earliest of this nature in a eutheriodont, potentially make C. dejageri a key species for understanding the evolutionary origins of sexually selective behaviours (intraspecific competition, ritualized sexual and intimidation displays) associated with cranial outgrowths at the root of the clade that eventually led to extant mammals. Comparison with the tapinocephalid dinocephalian Moschops capensis, a therapsid in which head butting is strongly supported, shows that the delicate structure of the cranial bosses and the gracile structure of the skull of Choerosaurus would be more suitable for display and low energy combat than vigorous head butting. Thus, despite the fact that Choerosaurus is represented by only one skull (which makes it impossible to address the question of sexual dimorphism), its cranial bosses are better interpreted as structures involved in intraspecific selection, i.e. low-energy fighting or display. Display structures, such as enlarged canines and cranial bosses, are widespread among basal therapsid clades and are also present in the putative basal therapsid Tetraceratops insignis. This suggests that sexual selection may have played a more important role in the distant origin and evolution of mammals earlier than previously thought. Sexual selection may explain the subsequent independent evolution of cranial outgrowths and pachyostosis in different therapsid lineages (Biarmosuchia, Dinocephalia, Gorgonopsia and Dicynodontia).

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Ryoko Matsumoto and Susan E. Evans (2016)
The palatal dentition of tetrapods and its functional significance.
Journal of Anatomy (advance online publication)
DOI: 10.1111/joa.12534
http://onlinelibrary.wiley.com/doi/10.1111/joa.12534/full


The presence of a palatal dentition is generally considered to be the primitive condition in amniotes, with each major lineage showing a tendency toward reduction. This study highlights the variation in palatal tooth arrangements and reveals clear trends within the evolutionary history of tetrapods. Major changes occurred in the transition between early tetrapods and amphibians on the one hand, and stem amniotes on the other. These changes reflect the function of the palatal dentition, which can play an important role in holding and manipulating food during feeding. Differences in the arrangement of palatal teeth, and in their pattern of loss, likely reflect differences in feeding strategy but also changes in the arrangement of cranial soft tissues, as the palatal dentition works best with a well-developed mobile tongue. It is difficult to explain the loss of palatal teeth in terms of any single factor, but palatal tooth patterns have the potential to provide new information on diet and feeding strategy in extinct taxa.


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An earlier paper not yet mentioned:

Guntupalli V.R. Prasad, Vishal Verma, Pooja Grover, Rajkumari Priyadarshini, Ashok Sahni and Ranjit S. Lourembam (2016)
Isolated Archosaur teeth from the green sandstone capping the Coralline Limestone (Bagh Group) of the Narmada valley: Evidence for the presence of pre-Late to Late Maastrichtian abelisaurids in India.
Island Arc (advance online publication)
DOI: 10.1111/iar.12142
http://onlinelibrary.wiley.com/doi/10.1111/iar.12142/full


https://www.researchgate.net/publication/303771935_Isolated_Archosaur_teeth_from_the_green_sandstone_capping_the_Coralline_Limestone_Bagh_Group_of_the_Narmada_valley_Evidence_for_the_presence_of_pre-Late_to_Late_Maastrichtian_abelisaurids_in_India_Cre

Recent field prospecting in the Cretaceous sequences of the lower Narmada valley has led to the discovery of three isolated archosaur teeth from the upper part of marine Cretaceous rocks of the Bagh Group. The specimens were recovered by surface prospecting from an oyster-bearing green sandstone bed occurring at the top of the Coralline Limestone (Coniacian) from a site near Phutibawri village, Dhar District, Madhya Pradesh, India. Of the three teeth recovered from this horizon, two are identified with abelisaurid dinosaurs and the third one with an indeterminate crocodile. The abelisaurid teeth conform to the premaxillary and maxillary tooth morphology of Majungasaurus and Indosuchus. Earlier reports of abelisaurid dinosaurs from India are from the Upper Cretaceous (Maastrichtian) Lameta Group of Jabalpur, Pisdura (Central India) and Balasinor (Western India) and Upper Cretaceous (Late Maastrichtian) Kallamedu Formation (South India). As no associated age diagnostic fossils are found, the specimens described here are considered to represent pre-Late to Late Maastrichtian age based on the known ages of the underlying and overlying formations. The new finds, therefore, document stratigraphically the oldest occurrence of abelisaurid dinosaurs known from the Indian subcontinent.


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