Neuroanatomy of flying reptiles and implications for flight, posture and behaviour

Lawrence M. Witmer, Sankar Chatterjee, Jonathan Franzosa & Timothy Rowe

Click thumbnail to see a 4 mb virtual endocast animation.

ABSTRACT: Comparison of birds and pterosaurs, the two archosaurian flyers, sheds light on adaptation to an aerial lifestyle. The neurological basis of control holds particular interest in that flight demands on sensory integration, equilibrium, and muscular coordination are acute. Here we compare the brain and vestibular apparatus in two pterosaurs [Rhamphorhynchus muensteri and Anhanguera santanae] based on high-resolution computed tomographic (CT) scans from which we constructed digital endocasts. Although general neural organization resembles birds, pterosaurs had smaller brains relative to body mass than do birds. This difference probably has more to do with phylogeny than flight, in that birds evolved from nonavian theropods that had already established trends for greater encephalization. Orientation of the osseous labyrinth relative to the long axis of the skull was also different in these two species, suggesting very different head postures and reflecting differing behaviours. Their enlarged semicircular canals reflect a highly refined organ of equilibrium, which is concordant with pterosaurs being visually based, aerial predators. Their enormous cerebellar floccular lobes may suggest neural integration of extensive sensory information from the wing, further enhancing eye- and neck-based reflex mechanisms for stabilizing gaze.

see "Additional Imagery" for animations of the cranial endocast

This specimen was collected from the Upper Jurassic Solnhofen Lithographic Limestone in the Altmuhl River Valley, Germany. It was made available to the University of Texas High-Resolution X-ray CT Facility for scanning by Dr. Sankar Chatterjee of Texas Tech University. Funding for scanning was provided by Dr. Chatterjee. Funding for image processing was provided by a National Science Foundation Digital Libraries Initiative grant to Dr. Timothy Rowe of The University of Texas at Austin.

The specimen was scanned by Richard Ketcham and Cambria Denison on 15-16 December 1997 on the high-resolution (II) subsystem along the coronal axis for a total of 476 slices. Scanning parameters were as follows: 150 kV, 0.159 mA, no filter, air wedge, 190% offset, slice thickness = 0.25 mm, S.O.D. = 60 mm, 1800 views, 2 samples per view, interslice spacing = 0.2 mm, field of reconstruction = 35.5 mm, reconstruction offset 0, reconstruction scale 20, scanned in 2 passes using 3-slice mode.

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	Click on the thumbnail for a 1 mb animation of the cranial endocast around the yaw axis.
	Click on the thumbnail for a 2 mb animation of the cranial endocast around the roll axis.
	Click on the thumbnail for a 1 mb animation of the cranial endocast around the pitch axis.