The Skinniest Pterosaur

Pterosaurs are known as lightweights, with their extremely hollow bones and hollow skulls. In the Late Triassic there was a pterosaur that had little room within its bones because they were so gracile, so skinny. This pterosaur opted for a lightweight morphology by shrinking the diameter of its arms.

Raeticodactylus

Figure 2. Raeticodactylus in lateral view. Note the extremely slender humerus, radius and ulna. Not much room for hollowness here, although all three bones were still tubes. Here’s a skeleton that could be made of toothpicks!

Raeticodactylus filisurensis (Stecher 2008) Upper Norian, Late Triassic, ~203 mya, wingspan 135 cm was extremely primitive, yet quite distinct from MPUM 6009 hinting at a much broader and earlier radiation of pterosaurs in the Triassic. Derived from a sister to MPUM 6009, Raeticodactylus was a sister to the Austrian specimen of Austriadactylus and was basal to all subsequent pterosaurs.

Distinct from MPUM 6009, the skull of Raeticodactylus was more robust and topped by a rostral crest that likely supported larger soft tissues. The naris was smaller and further back on the skull, nearly completely over the antorbital fenestra. The back of the skull sloped downward and the quadrate was deeply inclined. The jugal was much deeper, especially so below the orbit. The teeth were robust and packed tightly against one another. The mandible was deep with a ventral keel beneath the crest. The retroarticular process was extremely well-developed.

The cervicals were longer and larger.

The wing was extremely gracile, narrower than in any other pterosaur. All the elements were elongated. Thus, this pterosaur could easily stand quadrupedally while also balanced on its hind legs.

The femoral head was bent at a right angle. The hind limbs were relatively much shorter.


A partial mandible named Caviramus schesaplanensis Fröbisch and Fröbisch 2006) may be related.


Nesbitt and Hone (2010) in their misguided attempt at force-fitting pterosaurs into the archosauriforms claimed that Raeticodactylus had an antorbital fossa, a structure otherwise unknown in the Pterosauria. They did not realize that what they identified as a fossa was simply the depth dimension of the fenestra along with the dorsal skull in ventral exposure, bent over due to crushing.

3. Raeticodactylus in dorsal view, skull in lateral view. This is as skinny as any pterosaur ever got. Note the right angle femur indicating a completely upright, narrow-gauge configuration – like a dinosaur by convergence.

With a femoral head bent at a right angle, this pterosaur would have had the most erect hind limbs among pterosaurs. This meant they were probably better runners, but probably could not elevate their hind limbs into the horizontal plane while flying.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
Fröbisch NB and Fröbisch J 2006. A new basal pterosaur genus from the upper Triassic of the Northern Calcareous Alps of Switzerland”. Palaeontology 49 (5): 1081–1090. doi:10.1111/j.1475-4983.2006.00581.x. Retrieved 2007-03-02.
Nesbitt SJ and Hone DWE 2010. An external mandibular fenestra and other archosauriform character states in basal pterosaurs. Palaeodiversity 3: 225–233
Stecher R 2008. A new Triassic pterosaur from Switzerland (Central Austroalpine, Grisons), Raeticodactylus filisurensis gen. et sp. nov. Swiss Journal of Geosciences 101: 185. doi:10.1007/s00015-008-1252-6. Online First

wiki/Raeticodactylus

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