Pterosaur brain cavities vs. posture (Unwin 2003, Witmer et al. 2003)

Unwin 2003
reviewed views on pterosaur posture (Fig.1 ) from the Witmer et al. 2003 paper on pterosaur brains and ‘smart’ wings. Unfortunately, Unwin illustrated his Nature review with freehand illustrations from Wellnhofer 1991 (Fig. 1) that bear little resemblance to traced bone sizes and proportions.

And no one raised a finger in protest.

Figure 1. Images from Unwin 2003 compared to fossil tracings and reconstructions from ReptileEvolution.com. Dashed line above toes in Rhamphorhynchus indicates center of balance, below the wing root, as in birds. Note the imaginative illustrations Unwin uses with little to no basis in reality. The skulls display the appropriate rostral tilt.

Figure 1. Images from Unwin 2003 compared to fossil tracings and reconstructions from ReptileEvolution.com. Dashed line above toes in Rhamphorhynchus indicates center of balance, below the wing root, as in birds. Note the imaginative illustrations Unwin uses with little to no basis in reality. The skulls display the appropriate rostral tilt.

Inaccuracies are permitted for some workers. 
Some have license to misrepresent, to advance bogus concepts, and to omit taxa. Then again, mistakes do happen. If so when were these mistakes (Fig. 1) noted and corrected by pterosaur workers over the past 15 years? After all… this is science and accuracy should be paramount. Fact should not be confused with fantasy.

Pterosaur workers
have advanced competing hypotheses and reconstructions, but I rarely if ever, have seen them specifically criticizing competing hypotheses and reconstructions. (Send examples or citations of this if you have them.) Instead, pterosaur workers seem to avoid criticizing the work of colleagues, leaving that to bloggers.

Ironically
Unwin is of the mind set that pterosaurs were dinosaur relatives — but gave Rhamphorhynchus a sprawling, lizard-like posture (Fig. 1), with fingers pointing anteriorly. I gave Rhamphorhynchus an erect posture in the knowledge that some lepidosaurs were occasional bipeds while others, like Sharovipteryx (Fig. 2), Longisquama and Bergamodactylusdid not employ their forelimbs at all during terrestrial locomotion.

Figure 2. Cosesaurus was experimenting with a bipedal configuration according to matching Rotodactylus tracks and a coracoid shape similar to those of flapping tetrapods. Long-legged Sharovipteryx was fully committed to a bipedal configuration.

Figure 2. Cosesaurus was experimenting with a bipedal configuration according to matching Rotodactylus tracks and a coracoid shape similar to those of flapping tetrapods. Long-legged Sharovipteryx was fully committed to a bipedal configuration.

Caption to Unwin’s 2003 figures:
“The horizontal alignment of the lateral semi-circular canal, indicated by the red line, is consistent with a crouching posture and forward-directed head in basal pterosaurs, represented by Rhamphorhynchus. b, In derived forms such as Anhanguera, the reorientation of the canal can be interpreted in terms of an upright position and a downward-pointing head. (Pterosaurs redrawn from Wellnhofer 1991 and not to scale.)”

Back to the abstract of Witmer et al. 2003.
“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 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 different in these two pterosaur 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.”

References
Unwin DM 2003. Smart-wing pterosaurs. https://www.nature.com/articles/425910b.pdf
Witmer LM, Chatterjee S, Franzosa J. and Rowe T 2003. Neuroanatomy of flying reptiles and implications for flight, posture and behavior. Nature 425, 950–953.

 

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