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Ankylosaur Long Bone Histology and Growth Patterns

From: Ben Creisler

New in PLoS ONE:

Martina Stein, Shoji Hayashi & P. Martin Sander (2013)
Long Bone Histology and Growth Patterns in Ankylosaurs: Implications
for Life History and Evolution.
PLoS ONE 8(7): e68590.

The ankylosaurs are one of the major dinosaur groups and are
characterized by unique body armor. Previous studies on other dinosaur
taxa have revealed growth patterns, life history and evolutionary
mechanisms based on their long bone histology. However, to date
nothing is known about long bone histology in the Ankylosauria. This
study is the first description of ankylosaurian long bone histology
based on several limb elements, which were sampled from different
individuals from the Ankylosauridae and Nodosauridae. The histology is
compared to that of other dinosaur groups, including other Thyreophora
and Sauropodomorpha. Ankylosaur long bone histology is characterized
by a fibrolamellar bone architecture. The bone matrix type in
ankylosaurs is closest to that of Stegosaurus. A distinctive mixture
of woven and parallel-fibered bone together with overall poor
vascularization indicates slow growth rates compared to other
dinosaurian taxa. Another peculiar characteristic of ankylosaur bone
histology is the extensive remodeling in derived North American taxa.
In contrast to other taxa, ankylosaurs substitute large amounts of
their primary tissue early in ontogeny. This anomaly may be linked to
the late ossification of the ankylosaurian body armor. Metabolically
driven remodeling processes must have liberated calcium to ossify the
protective osteodermal structures in juveniles to subadult stages,
which led to further remodeling due to increased mechanical loading.
Abundant structural fibers observed in the primary bone and even in
remodeled bone may have improved the mechanical properties of the
Haversian bone.