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Triceratops (Torosaurus) frill growth histology

From: Ben Creisler

A new advance paper:

John R. Horner  & Ellen-Thérèse Lamm (2011)
Ontogeny of the parietal frill of Triceratops: A preliminary histological
Comptes Rendus Palevol (advance online publication)
doi : 10.1016/j.crpv.2011.04.006

The parietal frill of Triceratops, one of the largest cranial ornamental
features known, undergoes extraordinary morphological changes late in
ontogeny -- progressing from a large, thickened, solid frill to a
substantially larger, thin, fenestrated frill. To understand how this
structure changed so dramatically we undertook a histological examination
of the caudal end of an ontogenetic series of Triceratops parietals.
Investigation revealed a histological progression that involved an initial
period of non-pathologic hyperostosis, followed by a phase of external
(dorsal and ventral sides of the parietal) resorption and border extension,
with a conclusive stage hypothesized to be dense fibrous connective tissues
mineralized through the process of metaplasia. These fibrous tissues form
the caudal end of the mature parietal as well as the epiparietals that fuse
to the caudal border of the frill late in ontogeny. Continued resorption
near the central parietal regions of the left and right lateral portions of
the parietal eventually results in a pair of large circular fenestrae. This
progression is somewhat similar to the parietal ontogeny of Centrosaurus .

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