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Ampelosaurus (Titanosauria) laminar bone
From: Ben Creisler
A new paper in PLoS ONE:
Klein, N., Sander, P.M., Stein, K., Le Loeuff, J., Carballido, J.L.,
et al. (2012)
Modified Laminar Bone in Ampelosaurus atacis and Other Titanosaurs
(Sauropoda): Implications for Life History and Physiology.
PLoS ONE 7(5): e36907.
Long bone histology of the most derived Sauropoda, the Titanosauria
suggests that titanosaurian long bone histology differs from the
uniform bone histology of basal Sauropoda. Here we describe the long
bone histology of the titanosaur Ampelosaurus atacis and compare it to
that of basal neosauropods and other titanosaurs to clarify if a
special titanosaur bone histology exists.
Ampelosaurus retains the laminar vascular organization of basal
Sauropoda, but throughout most of cortical growth, the scaffolding of
the fibrolamellar bone, which usually is laid down as matrix of woven
bone, is laid down as parallel-fibered or lamellar bone matrix
instead. The remodeling process by secondary osteons is very extensive
and overruns the periosteal bone deposition before skeletal maturity
is reached. Thus, no EFS is identifiable. Compared to the atypical
bone histology of Ampelosaurus, the large titanosaur Alamosaurus shows
typical laminar fibrolamellar bone. The titanosaurs Phuwiangosaurus,
Lirainosaurus, and Magyarosaurus, although differing in certain
features, all show this same low amount or absence of woven bone from
the scaffolding of the fibrolamellar bone, indicating a clear
reduction in growth rate resulting in a higher bone tissue
organization. To describe the peculiar primary cortical bone tissue of
Phuwiangosaurus, Ampelosaurus, Lirainosaurus, and Magyarosaurus, we
here introduce a new term, “modified laminar bone” (MLB).
Importantly, MLB is as yet not known from extant animals. At least in
Lirainosaurus and Magyarosaurus the reduction of growth rate indicated
by MLB is coupled with a drastic body size reduction and maybe also a
reduction in metabolic rate, interpreted as a result of dwarfing on
the European islands during the Late Cretaceous. Phuwiangosaurus and
Ampelosaurus both show a similar reduction in growth rate but not in
body size, possibly indicating also a reduced metabolic rate. The
large titanosaur Alamosaurus, on the other hand, retained the
plesiomorphic bone histology of basal neosauropods.