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Stegosaurus sexually dimorphic dermal plates



Ben Creisler
bcreisler@gmail.com


New in PLoS ONE:

Evan Thomas Saitta  (2015)
Evidence for Sexual Dimorphism in the Plated Dinosaur Stegosaurus
mjosi (Ornithischia, Stegosauria) from the Morrison Formation (Upper
Jurassic) of Western USA.
PLoS ONE 10(4): e0123503.
doi:10.1371/journal.pone.0123503
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0123503



Conclusive evidence for sexual dimorphism in non-avian dinosaurs has
been elusive. Here it is shown that dimorphism in the shape of the
dermal plates of Stegosaurus mjosi (Upper Jurassic, western USA) does
not result from non-sex-related individual, interspecific, or
ontogenetic variation and is most likely a sexually dimorphic feature.
One morph possessed wide, oval plates 45% larger in surface area than
the tall, narrow plates of the other morph. Intermediate morphologies
are lacking as principal component analysis supports marked size- and
shape-based dimorphism. In contrast, many non-sex-related individual
variations are expected to show intermediate morphologies. Taphonomy
of a new quarry in Montana (JRDI 5ES Quarry) shows that at least five
individuals were buried in a single horizon and were not brought
together by water or scavenger transportation. This new site
demonstrates co-existence, and possibly suggests sociality, between
two morphs that only show dimorphism in their plates. Without evidence
for niche partitioning, it is unlikely that the two morphs represent
different species. Histology of the new specimens in combination with
studies on previous specimens indicates that both morphs occur in
fully-grown individuals. Therefore, the dimorphism is not a result of
ontogenetic change. Furthermore, the two morphs of plates do not
simply come from different positions on the back of a single
individual. Plates from all positions on the body can be classified as
one of the two morphs, and previously discovered, isolated specimens
possess only one morph of plates. Based on the seemingly
display-oriented morphology of plates, female mate choice was likely
the driving evolutionary mechanism rather than male-male competition.
Dinosaur ornamentation possibly served similar functions to the
ornamentation of modern species. Comparisons to ornamentation involved
in sexual selection of extant species, such as the horns of bovids,
may be appropriate in predicting the function of some dinosaur
ornamentation.

==

News:

http://news.discovery.com/animals/dinosaurs/what-a-male-and-female-stegosaurus-looked-like-150422.htm

http://phys.org/news/2015-04-stegosaurus-plates-differed-male-female.html


http://www.theguardian.com/science/2015/apr/22/stegosaurus-back-plates-differed-between-genders-new-study-reveals





>From last December:

Stegosaurus plates study

http://www.princeton.edu/main/news/archive/S39/82/82K53/index.xml?section=featured