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Kentrosaurus sexual dimorphism and Tarbosaurus juvenile skull

From: Ben Creisler

In addition to the new dinosaurs Arcusaurus and Haya, the May JVP has two
other dinosaur-related papers:

I had an earlier posting on this one based on news stories and press

Takanobu Tsuihiji; Mahito Watabe; Khishigjav Tsogtbaatar; Takehisa
Tsubamoto; Rinchen Barsbold; Shigeru Suzuki; Andrew H. Lee; Ryan C.
Ridgely; Yasuhiro Kawahara; Lawrence M. Witmer  (2011)
Cranial osteology of a juvenile specimen of Tarbosaurus bataar (Theropoda,
Tyrannosauridae) from the Nemegt Formation (Upper Cretaceous) of Bugin
Tsav, Mongolia.
Journal of Vertebrate Paleontology 31(3): 497 - 517 
DOI: 10.1080/02724634.2011.557116 

A juvenile skull of the tyrannosaurid Tarbosaurus bataar found in the Bugin
Tsav locality in the Mongolian Gobi Desert is described. With a total
length of 290 mm, the present specimen represents one of the smallest
skulls known for this species. Not surprisingly, it shows various
characteristics common to juvenile tyrannosaurids, such as the rostral
margin of the maxillary fenestra not reaching that of the external
antorbital fenestra and the postorbital lacking the cornual process. The
nasal bears a small lacrimal process, which disappears in adults. Lacking
some of the morphological characteristics that are adapted for bearing
great feeding forces in adult individuals, this juvenile specimen suggests
that T. bataar would have changed its dietary niches during ontogeny. The
numbers of alveoli in the maxilla (13) and dentary (14 and 15) are the same
as those in adults, suggesting that they do not change ontogenetically in
T. bataar and thus are not consistent with the hypothesis that the numbers
of alveoli decreases ontogenetically in tyrannosaurids. 

Holly E. Barden & Susannah C. R. Maidment (2011)
Evidence for sexual dimorphism in the stegosaurian dinosaur Kentrosaurus
aethiopicus from the Upper Jurassic of Tanzania. 
Journal of Vertebrate Paleontology 31(3): 641--651
DOI: 10.1080/02724634.2011.557112 

Sexual dimorphism, the condition whereby males and females differ from one
another physically, is one of the most fundamental aspects of the biology
of any animal. However, sexually dimorphic characters can be subtle and are
mainly related to soft tissue anatomy. They are, therefore, difficult to
identify reliably in the fossil record particularly when dealing with small
sample sizes and osteology alone. The first geometric morphometric analysis
of dimorphism in a thyreophoran (armored) dinosaur shows that the femora of
the stegosaurian dinosaur Kentrosaurus aethiopicus (Upper Jurassic,
Tanzania) bear a statistically significant shape difference of the proximal
end, which is independent of size and is therefore proposed to be a sexual
difference. Although the disarticulated nature of the material means that
intraspecific variation in other skeletal elements, such as the enigmatic
dermal armor, cannot be identified as sexual dimorphism at this time, this
study provides a methodology for further work on articulated stegosaurian
specimens and has the potential to reveal additional information regarding
the palaeobiology and population dynamics of this poorly understood clade. 

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