But in the case of the well-known Jurassic dinosaur Stegosaurus, a
study published on Wednesday may provide a handy how-to guide on
telling the boys from the girls based on the shape of the big bony
plates protruding from its back.
Stegosaurus, which roamed the western United States about 150
million years ago, was a large, four-legged plant-eater with two
rows of plates along its back, as well as two pairs of spikes at the
end of its tail to clobber predators.
The largest Stegosaurus species reached about 30 feet (9 meters).
The species in this study, Stegosaurus mjosi, measured roughly 21
feet (6.5 meters).
A Montana Stegosaurus "graveyard" contained fossils of several
individuals, with plates coming in two distinct varieties: some
wide, others tall. The wide ones reached sizes 45 percent larger in
surface area than the taller ones, which were nearly 3 feet (90 cm)
high.
![](http://archives.lincolndailynews.com/2015/Apr/23/images/ads/current/best_friends_sda_010515.png) "Males typically invest more into their ornamentation than do
females, so the larger wide plates were likely from males," said
Evan Saitta, a 23-year-old paleontology graduate student at
Britain's University of Bristol whose study appears in the journal
PLOS ONE.
"The broad, thin structure of the plates and their positioning on
the back of the animal suggests that they were used in sexual
display, analogous to the tail of a peacock. The broad, wide plates
likely made a continuous display surface along the animal's back to
attract mates, like a billboard."
[to top of second column] |
![](http://archives.lincolndailynews.com/2015/Apr/23/images/ads/current/castlemanor_lda_032414.png)
To test whether the plate differences were instead because some
individuals were young and others old, CT scans and microscopic
analyses were performed that showed the bone tissue had ceased
growing, meaning both varieties came from full-grown adults.
Anatomical and other differences between the sexes of a single
species, like a male lion's mane or a male deer's antlers, are
called sexual dimorphism.
Sexual dimorphism examples have been proposed in other dinosaurs,
but many scientists find those inconclusive. Saitta said the
Stegosaurus plates may be "the most convincing evidence for sexual
dimorphism in dinosaurs to date."
University of Bristol paleontologist Michael Benton added, "It
suggests that many dinosaurs used sexual display, as birds and
mammals do today, usually the males displaying or mock fighting to
attract attention of females."
(Reporting by Will Dunham; Editing by Sandra Maler)
[© 2015 Thomson Reuters. All rights
reserved.]
Copyright 2015 Reuters. All rights reserved. This material may not be published,
broadcast, rewritten or redistributed.
![](http://archives.lincolndailynews.com/2015/Apr/23/images/ads/current/class_generic_sda.png) |