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Dicraeosaurus species morphology

From: Ben Creisler

 A new online paper:

Daniela Schwarz-Wings and Nico Böhm (2012)
A morphometric approach to the specific separation of the humeri and
femora of Dicraeosaurus from the Late Jurassic of Tendaguru/Tanzania.
Acta Palaeontologica Polonica (in press)
doi: http://dx.doi.org/10.4202/app.2011.0095

The two species of Dicraeosaurus, D. hansemanni and D. sattleri, have
been distinguished mainly by their differences in size and geological
age, as they occur in different members of the Late Jurassic Tendaguru
Formation of Tanzania. Linear and geometric morphometric measurements
distinguish between the humeri and femora of both species. Linear
measurements and Principal Component Analyses of Thin-plate Splines
(TPS) reveal strong differences in size and shape between their humeri
and weak differences between their femora, also supported by a
Discriminant Factor Analysis. Generally, the humerus and femur of D.
hansemanni are slightly longer and more robust than those of D.
sattleri. Further, the humerus is shorter in relation to the femur in
D. sattleri, related to its more distally positioned deltopectoral
crest, resulting in differences in its arc of movement and mechanical
power. Thus, a morphological separation between the humeri and femora
of D. hansemanni from the Middle Dinosaur Member and D. sattleri from
the Upper Dinosaur Member of the Tendaguru Formation can be confirmed.
Morphometric comparisons of the humeri and femora of Dicraeosaurus
with the single known humerus and femur of Amargasaurus cazaui reveal
many shape differences between the two genera, which are especially
well marked in the TPS analysis and affect in particular the humerus.
These results suggest a closer relationship between D. hansemanni and
D. sattleri than between D. sattleri and A. cazaui, and a clear
separation between the two genera.