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Supraspinous ligament in sauropod dinosaurs (free pdf)

Ben Creisler

A new paper in open access:

Ignacio A. Cerda, Gabriel A. Casal, Rubén D. Martinez &  Lucio M. Ibiricu (2015)
Histological evidence for a supraspinous ligament in sauropod dinosaurs.
Royal Society Open Science 2: 150369
DOI: 10.1098/rsos.150369

Supraspinous ossified rods have been reported in the sacra of some
derived sauropod dinosaurs. Although different hypotheses have been
proposed to explain the origin of this structure, histological
evidence has never been provided to support or reject any of them. In
order to establish its origin, we analyse and characterize the
microstructure of the supraspinous rod of two sauropod dinosaurs from
the Upper Cretaceous of Argentina. The supraspinous ossified rod is
almost entirely formed by dense Haversian bone. Remains of primary
bone consist entirely of an avascular tissue composed of two types of
fibre-like structures, which are coarse and longitudinally (parallel
to the main axis of the element) oriented. These structures are
differentiated on the basis of their optical properties under
polarized light. Very thin fibrous strands are also observed in some
regions. These small fibres are all oriented parallel to one another
but perpendicular to the element main axis. Histological features of
the primary bone tissue indicate that the sacral supraspinous rod
corresponds to an ossified supraspinous ligament. The formation of
this structure appears to have been a non-pathological metaplastic
ossification, possibly induced by the continuous tensile forces
applied to the element.