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Apatosaurus tail malformation

From: Ben Creisler

A new online paper:

David M. Lovelace (2014)
Developmental Failure of Segmentation in a Caudal Vertebra of
Apatosaurus (Sauropoda).
The Anatomical Record (advance online publication)
DOI: 10.1002/ar.22887

A vertebral element assigned to an Apatosaurus cf. ajax from the Late
Jurassic Morrison Formation is described. The specimen exhibits an
unusual morphology where two vertebrae are nearly seamlessly fused
together, including the haemal arch that spans them. This morphology
is thought be the result of a developmental abnormality. CT scans of
the specimen reveal a thin zone of dorsoventral thickening between the
two neural arches consistent with cortical bone. Contrast in internal
morphology differentiates the anterior and posterior vertebral bodies
with the anterior expressing greater porosity, which increased
accommodation for barite-rich calcite precipitation. No vacuities are
observed to suggest the former presence of an intervertebral disk or
intervertebral joints: the absence of an intervertebral disc or
intervertebral joints is indicative of a condition known as block
vertebra. Block vertebrae occur with the loss, or inhibition, of
somitocoele mesenchyme early in embyogenesis (i.e., during
resegmentation of the somites responsible for the formation of the
affected vertebra). The derivatives of somitocoele mesenchyme include
the intervertebral disc and joints. Although vertebral
paleopathologies are not uncommon in the fossil record, this specimen
is the first recognized congenital malformation within Sauropoda.