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Sauropod caudal vertebrae from Niger with subchondral cysts



Ben Creisler
bcreisler@gmail.com

A new paper:

Florian Witzmann, Oliver Hampe, Bruce M. Rothschild, Ulrich Joger,
Ralf Kosma, Daniela Schwarz & Patrick Asbach (2016)
Subchondral cysts at synovial vertebral joints as analogies of
Schmorl's nodes in a sauropod dinosaur from Niger.
Journal of Vertebrate Paleontology (advance online publication)
DOI:10.1080/02724634.2016.1080719
http://www.tandfonline.com/doi/full/10.1080/02724634.2016.1080719



Several abnormal caudal vertebrae are described in an indeterminate
sauropod specimen from ?Middle–Late Jurassic strata of Niger. The
anterior and posterior articular surfaces of caudal vertebrae 7–11
exhibit erosive perforations (‘holes’) of the subchondral compact bone
into the trabecular bone of the vertebral centrum. Additionally, the
vertebral centra of caudal vertebrae 17 and 18 are fused and show a
bulging mass of abnormal bone growth, most probably caused by
infection. The erosive lesions of the anterior tail vertebrae closely
resemble the morphological and radiological characteristics of
Schmorl's nodes in humans and other mammals, in which the gel-like
nucleus pulposus of the intervertebral discs penetrates through the
endplate into the cancellous bone of the vertebral body and creates an
erosive cavity of mushroom-like shape. The diagnosis of Schmorl's
nodes in this sauropod, however, would be incompatible with the extant
phylogenetic bracket and osteological correlates that suggest that
dinosaurs had no intervertebral discs. Rather, they possessed synovial
joints with a joint space filled with synovial fluid between adjacent
vertebral centra. Therefore, the lesions can best be interpreted as
subchondral cysts and as an analog of Schmorl's nodes in synovial
joints. Similar to Schmorl's nodes, the regular pattern and location
of the lesions suggest that the cysts were caused by axial stress. One
may hypothesize that the fusion of caudals 17 and 18 led to altered
mechanical loading that may have facilitated rupture of the articular
cartilage and subchondral bone and forced synovial fluid into the
spongiosa of the vertebral centra.