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Anhanguera (Pterosauria) stance and gait on land



From: Ben Creisler
bcreisler@gmail.com

A new online paper:

Fabiana Rodrigues Costa, Oscar Rocha-Barbosa & Alexander Wilhelm Armin
Kellner (2013)
A biomechanical approach on the optimal stance of Anhanguera piscator
(Pterodactyloidea) and its implications for pterosaur gait on land.
Historical Biology (advance online publication)
DOI:10.1080/08912963.2013.807253
http://www.tandfonline.com/doi/full/10.1080/08912963.2013.807253#.UdWKGfm1FcQ

The stance of pterosaurs on land is traditionally a controversial
question. Here, we show that pterosaurs like Anhanguera piscator were
quadrupeds. An osteological model of A. piscator was
three-dimensionally built in digital space. The reconstructed muscles
of its pelvic girdle were then placed on their points of origin and
insertion to allow the biomechanical calculations to find the most
efficient stance on land to be performed. The hindlimb readjustment
(i.e. the repositioning of the hindlimb according to the achieved
results) led to a pelvic counterclockwise displacement at 10°, which
means that the ilium previously placed at 0° regarding an axis
parallel to the ground was moved (and so the whole pelvis) 10° up from
the preacetabular process. This new position prevents A. piscator from
having a fully upright stance. A 10° displacement of the pelvic girdle
would compel the forelimbs to be highly sprawled. Therefore, this
study affords A. piscator having a quadrupedal gait and demonstrates
that a bipedal stance is not viable once the lever arm values decrease
abruptly both for extensor and flexor muscles during the femoral
extension. This is the first time this approach is used to shed light
on this question.