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Re: Draco-Stygi-Pachy paper
Horner JR, Goodwin MB (2009) Extreme Cranial Ontogeny in the Upper
Cretaceous Dinosaur Pachycephalosaurus. PLoS ONE 4(10): e7626.
Coronal histological sections of the frontoparietal
dome of an adult Pachycephalosaurus wyomingensis reveal a dense
structure composed of metaplastic bone with a variety of extremely
fibrous and acellular tissue. [...] These dinosaurs employed
metaplasia to rapidly grow and change the size and shape of their
horns, cranial ornaments and frontoparietal domes, resulting in
extreme cranial alterations during late stages of growth.
And here's what that means:
John Horner & Ellen Lamm (2009): Metaplasia provided dinosaur skulls
extreme morphological plasticity during ontogeny, online-only supplement
to JVP 29(3), 117A
Arguably, one of the most interesting characteristics of the Dinosauria
is the incredible
morphological variety of their skulls. Numerous species in both the
Saurischia sport some sort of cranial display feature on one or more of
their cranial elements.
In addition, these features undergo considerable alteration during
ontogeny, so much so that
ontogenetic stages of some species have been described as different
species. In each case
these major alterations appear to have occurred very rapidly during late
stages of ontogeny.
In an attempt to determine how such changes could occur in short periods
of time, numerous
dinosaur skull bones were histologically examined. Surprisingly, every
revealed tissues produced by metaplasia. Metaplastic bone is the result
of fibrous tissues
having been transformed directly into bone without the presence of a
osteoblasts. The metaplastic tissues observed in this study revealed a
wide variety of tissue
types, most often extremely fibrous, acellular and/or avascular, or
sometimes highly cellular
(fibrocytes rather than osteocytes) and highly vascularized. Mature
are much denser than ordinary bone. Because these tissue types do not
contain cells with
canaliculi their initial thickness is limited, although at depth they
are often remodeled by
secondary reconstruction. In many of the bones sectioned there was
evidence of deposition,
erosion, and subsequent deposition indicative of continuous shape
tissues found in the skulls of extant avian taxa form and alter very
quickly, a characteristic
apparently acquired from their dinosaurian ancestors.
Bone formed without osteoblasts!?! Wow.
Unfortunately I missed the talk.
Metaplasia has already been described for *Majungasaurus* (SVP Memoir 8).