Flugsaurier 2018: Web-footed little pterosaur MB.R.3531

Flugsaurier 2018 part 4
Since the purpose of the symposium is increase understanding of pterosaurs, I hope this small contribution helps.

Figure 1. Aurorazhdarcho primordial and the smaller Aurorazhdarcho micronyx to scale.

Figure 1. Aurorazhdarcho primordial and the smaller Aurorazhdarcho micronyx to scale.

Habib and Pittman 2018
bring us a rarely studied Berlin pterosaur, MB.R.3531 (Fig. 1) originally named Pterodactylus micronyx, then Aurorazhdarcho micronyx. This specimen nests with other wading pterosaurs, Aurorazhdarcho, Eopteranodon and Eoazhdarcho forming  a clade overlooked by other workers, at the transition between germanodactylids and pteranodontids, not related to azhdarchids.

FIgure 1. Reconstruction of MB.R.3531, nesting with Eoazhdarcho, Eopteranodon and Aurorazhdarcho.

FIgure 1. Reconstruction of MB.R.3531, nesting with Eoazhdarcho, Eopteranodon and Aurorazhdarcho.

But phylogeny is not what interests Habib and Pittman.
They report, “We provide the description of an exceptionally well-preserved specimen of a juvenile aurorazhdarchid from the Jurassic of Germany which preserves details of the wing membrane and pedal webbing and use it to address mechanical questions regarding launch from water in small pterosaurs.” We can’t be sure it’s a juvenile because pterosaur juveniles are isometric copies of their parents and phylogenetic miniaturization often attends the genesis of new pterosaur clades.

This is a wading pterosaur, part of a clade of long-legged wading pterosaurs. It has webbed feet for wading, not for swimming. Wading birds don’t go in water deeper than they can wade in and they take to the air by flapping their wings and leaping. The MB.R. specimen was originally mistaken for Pterodactylus because it greatly resembled Pterodactylus, another clade of small to medium-sized waders leaving numerous webbed tracks. Also back then they had fewer pterosaurs to compare, other than Pterodactylus.

Habib and Pittman don’t buy into the lepidosaur origin of pterosaurs.
They report, “The latest range of motion estimates for the pterosaur hind limb (Manafzadeh and Padian, 2018) suggest that the hind limbs in pterosaurs had more limited abduction than previously modeled and that the hindlimbs operated primarily in a vertical plane.” We invalidated that claim earlier using phylogeny (pterosaurs are more closely related to squamates than to birds). Dozens of pterosaur fossils show the hind limbs spread and form horizontal stabilizers during flight (Fig. 3). That’s when the webbed feet become useful, as twin vertical stabilizers. Webbed feet are primitive for pterosaurs and are found in pterosaur outgroups, like Sharovipteryx.

Figure 3. Click to animate. The Vienna specimen of Pterodactylus (wings folded). Animation opens the wings and legs to reveal the true shape of pterosaur wings, stretched between the elbow and wingtip with a short fuselage fillet extending from elbow to mid femur. The feet act like vertical stabilizers.

Habib and Pittman insist
“We estimate that MB.R.3531 was capable of taking off from the water surface with a single escape push (under the most liberal model values) or with 1-2 follow-up bounding phases (under the most conservative model values), with the majority of the takeoff energy expended on the initial escape phase. The added propulsive area of the pedal webbing had a notable effect on the overall launch performance, increasing estimated propulsive accelerations by over 20% and reducing the number of required propulsive bounding phases.” There’s no need for bounding for floating pterosaurs. They can simply stretch out and flap their wings like pelicans do (Fig. 4) while they frantically kick their feet. In any case, the MB.R. specimen is a wader, so the problem is moot. We looked at water-launch problems in pterosaurs earlier here, here and here.

Pelican take-off sequence from water.

Figure 4. Pelican take-off sequence from water. Click to enlarge.

Habib and Pittman conclude:
“The exact values and kinematic results should be taken with caution, given the large number of values that had to be broadly estimated or assumed.” One wonders why these authors don’t just let their hypothesis drop in favor of one that employs the more than adequate thrust generating power of pterosaur wings together with frantically paddling feet.

References
Bennett C 2013. New information on body size and cranial display structures of Pterodactylus antiquus, with a revision of the genus. Paläontologische Zeitschrift, 87, 269–289.
Habib M. and Cunningham J 2010. Capacity for Water Launch in Anhanguera and Quetzalcoatlus. Acta Geoscientica Sinica, 31, Supp.1, 24–25.
Habib M and Pittman M 2018. An “old” specimen of Aurorazhdarcho micronyx with exceptional preservation and implications for the mechanical function of webbed
feet in pterosaurs. Flugsaurier 2018: The 6th International Symposium on Pterosaurs. Los Angeles, USA. Abstracts: 41–43.
Manafzadeh AR and Padian K 2018. ROM mapping of ligamentous constraints on avian hip mobility: implications for extinct ornithodirans. Proceedings of the Royal Society B, 285(1879).

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