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Hi all,
I have read that Galton reported a dimorphism in the structure of the sacrum
of Hypsilophodon.
The text is from "The Dinosauria":
Some specimens  have 16 dorsal and 5 sacral vertebrae, but the centrum of
the last dorsal is expanded caudally and forms extensive sutural contacts
with the first sacral ribs.
By contrast certain individuals have 15 dorsal and 6 sacral vertebrae; the
first vertebra is a sacral because its ribs are sutured to both centrum and
neural arch.
Does someone tell me if this is a sexual dimorphism from male to female or
if this is an ontogenetic stage?

Thank you in advanced and sorry for the English
Alessandro Marisa
Via A. Grandi n18 ROVERETO (TN) ITALY
Tel: 039-0464-434658 Email: amaris@tin.it