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Spinophorosaurus (Sauropoda) Braincase in PLoS ONE



From: Ben Creisler
bcreisler@gmail.com



New in PLoS ONE:


Knoll, F., Witmer, L.,M, Ortega, F., Ridgely, R.C. & Schwarz-Wings D. (2012)
The Braincase of the Basal Sauropod Dinosaur Spinophorosaurus and 3D
Reconstructions of the Cranial Endocast and Inner Ear.
PLoS ONE 7(1): e30060
doi:10.1371/journal.pone.0030060
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0030060




Background

Sauropod dinosaurs were the largest animals ever to walk on land, and,
as a result, the evolution of their remarkable adaptations has been of
great interest. The braincase is of particular interest because it
houses the brain and inner ear. However, only a few studies of these
structures in sauropods are available to date. Because of the
phylogenetic position of Spinophorosaurus nigerensis as a basal
eusauropod, the braincase has the potential to provide key evidence on
the evolutionary transition relative to other dinosaurs.

Methodology/Principal Findings

The only known braincase of Spinophorosaurus (‘Argiles de l'Irhazer’,
Irhazer Group; Agadez region, Niger) differs significantly from those
of the Jurassic sauropods examined, except potentially for Atlasaurus
imelakei (Tilougguit Formation, Morocco). The basisphenoids of
Spinophorosaurus and Atlasaurus bear basipterygoid processes that are
comparable in being directed strongly caudally. The Spinophorosaurus
specimen was CT scanned, and 3D renderings of the cranial endocast and
inner-ear system were generated. The endocast resembles that of most
other sauropods in having well-marked pontine and cerebral flexures, a
large and oblong pituitary fossa, and in having the brain structure
obscured by the former existence of relatively thick meninges and
dural venous sinuses. The labyrinth is characterized by long and
proportionally slender semicircular canals. This condition recalls, in
particular, that of the basal non-sauropod sauropodomorph
Massospondylus and the basal titanosauriform Giraffatitan.

Conclusions/Significance

Spinophorosaurus has a moderately derived paleoneuroanatomical
pattern. In contrast to what might be expected early within a lineage
leading to plant-eating graviportal quadrupeds, Spinophorosaurus and
other (but not all) sauropodomorphs show no reduction of the
vestibular apparatus of the inner ear. This character-state is
possibly a primitive retention in Spinophorosaurus, but due the
scarcity of data it remains unclear whether it is also the case in the
various later sauropods in which it is present or whether it has
developed homoplastically in these taxa. Any interpretations remain
tentative pending the more comprehensive quantitative analysis
underway, but the size and morphology of the labyrinth of
sauropodomorphs may be related to neck length and mobility, among
other factors.