Gannets and Germanodactylus, Convergent Diving Lifestyle?

Gannets
The northern gannet (Morusis bassanus) is a living seabird that hunts fish by diving into the sea and pursuing prey underwater. Here is a YouTube video of gannets fishing. As the headline suggests, it is amazing. And fun! Click on the image to see it on YouTube.

Gannet diving video.

Figure 1. Gannet diving video. Click to see it on YouTube.

Gannets have sharp beaks and pointed wings. They remind me of a series of varied pterosaurs, collected under the genus, GermanodactylusOne wonders if they had similar diving abilities.

Gannet on the left. Germanodactylus on the right.

Figure 1. Gannet on the left. Germanodactylus on the right. Did a sharp beak and similar robust build mean Germanodactylus might have dived for fish prey like the living gannet? Perhaps G. cristatus is not the perfect analog, but there is another candidate below.

Germanodactylus
With its sharp beak and similar size and shape, Germanodactylus appears to be a good gannet analog for the Late Jurassic. Those big wings could have tucked themselves in close to the body, the claws would have faced their palmar surfaces medially. A deep chord wing membrane extending to the ankle, the traditional model, probably would not have worked. Here the wing membrane essentially disappears when folded, as several Pterodactylus fossils show.

Diving Germanodactylus.

Figure 3. Another species of Germanodactylus, this time in a dive. There aren’t that many aquatic lizards, but if this counts as one, add another to the list. And don’t forget to close that mouth before hitting the surf.

Then, of course, there’s the crest question…
Does a soft skull crest put a kabbash on the diving hypothesis? Perhaps. But then think about the super fast fish with crests (sailfish, marlins, swordfish) and let’s start the arguments! Your thoughts, please!

References
youtube-gannet video

11 thoughts on “Gannets and Germanodactylus, Convergent Diving Lifestyle?

  1. I would include Nyctosaurus here as a possible example of coevolution with boobies. it foraged apparently way offshore. The “beak” is also similar to a gannet beak. Of course there is the problem of the antlers.

    • Perhaps so! Basal nyctosaurs did not have the crest. Only derived ones. Super sharp beak, that’s for sure. With Nyctosaurus you get a slightly different configuration with the metacarpals extending as far as the beak tip when all folded up. Not quite the same for diving. Relatively larger wings compared to the body suggest Nyctosaurus could have hovered over a select spot with sea breezes sustaining its gliding wings. Often the lower beak was longer than the upper, perhaps for skimming.

      • These are interesting ideas. But the wings do not have to be completely folded up in plunge divers. For example the Brown Pelican folds the wings sort of half way during the plunge, so do terns of the genus Sterna.
        And what is also interesting: Would you ever expect from the morphology that Pelecanus occidentalis is mainly a plunge diver. The American White Pelican (Pelecanus erythrorhynchus) for example is not known to plunge dive and has a very similar anatomy. So sometimes it is difficult to make conclusion from the anatomy about behavior.
        And how about Tapejara? Did it fish (if they fished at all) puffin-like?

  2. Regardless of the toothless tip of the rostrum, the pterosaur in question (you appear to be using Germanodactylus cristatus, but do not indicate) is toothed and adapted (it appears) to orthal biting and some moderate level of non-prehension oral processing, as the teeth are labiolingually compressed and somewhat bladelike, rather than just ordinarily conical. They are also short, which defies typical fish-capture dentition (various fishes, whales, crocodilians, or other pterosaurs). This implies instead that Germanodactylus cristatus was feeding on non-aquatic prey. Germanodactylus rhamphastinus is likely a tad better for aquatic prey, as the teeth are more numerous and have a lower aspect (crowns higher relative to fore-aft basal length), but in both the dentition remains low-crowned, there is a general lack of differentiation along the tooth row (no rostral “rosette” or enlarged array of teeth), and no specialization of the posterior mandible for the jaw adductor musculature, which should be robust for the sake of closing the jaw under pressure (such as when diving). Compare to the mandible of a gannet: mandibular length versus depth is greater in the bird than the pterosaur, an effect of both relative leverage of the crosswise oblique-acting pterygoideus ventralis and pseudotemporalis/mAM groups of muscles; the pterosaur has these muscles at nearly right angles, with the latter group acting almost to merely pull the jaw BACK, rather than up, suggesting a weaker bit overall. These indicate both higher leverage and strength during closing in the bird, but more a quick, snatching bit in the pterosaur. We see the latter in small-prey, terrestrial or aerial specialists, not aquatic predators.

  3. I think teeth are irrelevant in that the gannet has none. In any case, it was just a guess over something we will never know. Likely prey capture would have been by spearing with the single-tooth tip, so jaw muscles and their angles would have been irrelevant, IMHO. The diving specimen, JME Moe12 (plate) BSP 1977 XIX 1 (counterplate), has been known for awhile, probably a unique species. It matches none of the others.

    • Teeth are relevant in respect to direct prey interaction: One uses their shape to preject how the animal would acquire, and maintan hold, on it’s food. When you consider toothless animals, beak shape takes on a role with respect to how the animal interacts with its food, but it isn’t as significant as the relative position and directionality of the jaw muscles. Gannet jaws function very similarly to penguin jaws, and are shaped similarly, but not to heron jaws, despite their similarity, due to relative orientation and leverage of muscle action and moments (respectively). Simply having teeth makes this job easier than gross jaw morphology, because it allows us to make additional inferences to prey capture than a toothless jaw does; it does not making the presence of teeth irrelevant.

  4. You mentioned in a previous post that pterosaurs (or at least some subset of them) were isometrically scaled. I had intended to mention that isometry usually means the animals are marine or aquatic (e.g. modern cetaceans) because buoyancy supports the animal’s mass under gravity and there are no extreme stresses associated with locomotion. In contrast, terrestrial animals (modern mammals) are typically hyperallometric (skeletal mass increases faster than body mass), and this is esp. true in avians, which is contrary to conventional wisdom about the “lightness” of avian skeletons, probably because of the extreme stresses associated with flight (esp. landing). On this basis, the pterosaurs (or at least the larger ones) may indeed have been primarily aquatic, which would be a very significant discovery.

  5. What about Rhamphorhynchus? I remember reading (in a Nat Geo magazine I think?) that it could have been a diver as well. Any evidence for this as of now?

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