Branching Beaks


Rhampho Solnhofen small

What a strange animal, I think, is the Rhamphorhynchus muensteri.

The Solnhofen seems to refer to a lagoon, a sheltered cove of sorts, with a slow-moving, oxygen-deprived bottom that becomes excellent for preserving the skeletons of animals that die in its waters.

In those waters, in an archipelago that most of Europe was during the Late Jurassic, pterosaurs as we know them are so extraordinarily diverse as to defy our imagination. Many seem to have fed on fish. Rhamphorhynchus specimens are known to have remains of fish (or what seem like fish) in their guts, a clear indication as any that they, amongst all pterosaurs at Solnhofen, were piscivores.

This fuzzy animal seems quite suited to the task, with its short, triangular skull but long, anglerfish-like jaws. A real trap for fishy prey. We might imagine these pterosaurs as sleek hunters of prey, dashing about on the wing to sight a fish near the surface and then—SPLASH!–a dive to grab prey. Soaring up through the waves, prey in jaw, these pterosaurs’ sleek appearance and robust jaws would have helped them support this lifestyle.

Maybe. Unlike many piscivores, Rhamphorhynchus doesn’t have vertically interlocking teeth: they are pointed forward, slightly curved but not angled to the closing of the jaw. An animal like this trying to spear prey on its teeth might find its jaws caught in the fishy innards, and would have to pry the food off else it couldn’t close its mouth. Rather than a long, slender jaw, with a serrated margin that seems keen for catching wriggly, small prey, much like Pterodactylus antiquus (a soft-bodied specialist?) Rhamphorhynchus has the jaw that evokes the skimmer Rhynchops nigra, with a long-keel-like jaw that would help it “feel” prey below the water, to be quickly snatched up. But of course, skimmers don’t have teeth, and those teeth make for a strange bedfellow. Many other soaring, seafaring birds that catch fishy prey on the wing also don’t have teeth–or serrated jaw margins–but some do. Gulls and albatrosses are suited surface fishers, with narrow-gauge and high-aspect wings that help them soar with minimal energy output, and what beautiful soaring sights they make. Quite likely, the pseudodont birds, or pelagornithids, were very similar, yet those had such wicked serrated teeth we might easily imagine them as spearing food on their sharp “teeth.” But these birds also have hooked beaks, and in the gulls and albatrosses, and many pelacaniform birds like cormorants, the upper jaw features a very large hook, while the lower is shorter, down-curved. For these birds, the hooked bill is to help grab prey, quickly caught in the jaws and swallow, on the wing if need be.

I doubt Rhamphorhynchus had such help: It has no hooked upper jaw, and its teeth seem ill-suited for spearing. But they do seem useful for trapping prey, a comparison one might make for anglerfish, as alluded to. I sort of imagine a tidal forager, though of course this is an imperfect comparison. The long, toothless prow of the beak could be useful for pushing around through muck and water, to find juicy soft prey. The teeth, for grabbing jellyfish to be swallowed whole. It would help segregate the pterosaurs of Solnhofen, who each seem unique in some way, a helpful way to discriminate their diets when in competition with one another.

Piscivory is an odd type of feeding, and one of the things that I’ve noticed is that animals that specialize in fish tend to have different adaptations depending on their method of locomotion, their habitat, or even how they eat fishy prey. For the jaws, there aren’t really “one special set” of adaptations that say “Look, here’s a piscivore!” You make inferences based on similar animals, but those require close, in-group specializations. Broad, across-group features are mostly absent. Except for teeth. If the predator’s jaw anatomy is suited for catching fishy prey, lest it escape the teeth must impale the prey, and they work best when vertically oriented. Fish-eaters will also tend to have a bit of an overbite or upper jaw that curves downward: the front teeth of the jaw are angled into the mouth. This is seen in mostly aquatic predators, such as other fish, crocodilians that specialize on fish, etc. Rhamphorhynchus just seems to lack these features. Indeed, amongst all Solnhofen pterosaurs, only Scaphognathus seems to suggest it had this type of fishy-predator look, even though others have been treated as generalists or piscivore-generalists (like Pterodactylus). They can’t all have been swooping around the lagoon or out in the open ocean diving for or snatching fish from the surface.

But that’s a casual reading of the data on what it is to be a piscivore. Like I said, it depends on what kind of animal you are: birds have different adaptations from crocs, from lizards, from other fish. Turtles have no teeth, and those that have serrated margins of their jaws (many tortoises) tend to be vegetarians.

No matter. Pterosaurs are odd. And collections of them from primarily aquatic environments as odd. Deposits in the Yixian, Jiufotang, Solnhofen, Niobrara, Crato, and Romualdo formations suggest that our biases to seeing pterosaurs as piscivores is an entrenched one. Clearly, many were not. Azhdarchids were terrestrial stalkers, but some must have focused on more aerial (anurognathids) or terrestrial prey. It’s just a matter of being a lot more judicious and plenty analytical about the features we ascribe to these animals to assume their diet.

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18 Responses to Branching Beaks

  1. Nothing really to do with the subject of your article, but more to do with your general reconstruction (which is really, really nice). Presumably you don’t subscribe to the idea of an ankle attachment for the brachiopatagium?

    • Something in my head kinda breaks when I try to draw a sitting/standing pre-pterodactyloid with the ankle-attached cruropatagium. It makes me realize that the digit would become horribly twisted unless very slack. When we imagine these pterosaurs flying, we put the legs out in splayed position, which turns the side of the foot up, and that includes the fifth toe. Which patagium, then, does the toe attach without becoming twisted again? If the toe curls palmarly or up towards the hip when in flight, it only works well for the cruropatagium when the leg isn’t splayed, but just extended backwards. For Sordes pilosa, the cruropatagium seems to just extend towards the shank but no further, whilst the uropatagium attaches to the splayed ankle at the fifth toe. If this pattern is true for all long-fifth-toe-bearing pterosaurs, then the uropatagium should attach to the toe in Rhamphorhynchus. It would seem that a longer, ankle-based attachment occurs with the loss of the fifth toe in pterodactyloids — maybe, perhaps, equivocation making gestures.

  2. Duane says:

    OR… given the abundance of shelled, pelagic molluscs in Jurassic seas- belemnites, ammonites- maybe the strange jaws/teeth of Rhamphorhynchus made a great tool for probing into and extracting tasty tid bits from said prey items. Kind of like the small, pronged forks that we use for extracting crab meat from today when one enjoys a nice Dungeness…

    • That’s something I’d wondered too; a belemnite guard is quite a heavy, cumbersome object to have to pass/regurgitate – compared to the fleshy payoff.

      • If you’re gonna invest in such a specialized diet, I’d imagine the payoff is the whole point, however inconvenient the rest. Some snakes just deal with the cumbersome bones and shells of their prey, whilst others take the nonchalance and pass it. Owls just hack up the bits it don’t like. Cost / benefit.

    • I thought once this made great sense for the beak, as it’d make a great plover-like shell-opening tool. The teeth just have a sort of “scooping” — non-pelican-like, I should imagine — aspect to them, and it’s one that makes me question the “piscivore” generalization. I’m working on a survey of features amongst various feeding mechanisms in vertebrates, so this was a sort of preview of that for Piscivory.

  3. Duane says:

    Snail kites eat the flesh, leave the shell. Consuming the whole belemnite/ammonite is not such a great idea if you are scavenging washed up big ones. Consumption of ammonites/belemnites appears to be a specialist niche from our modern ecological perspective because modern oceans lack abundant, pelagic shelled prey comparable to the amount seen in the Mesozoic. But there is much to suggest, based on the ubiquity of such shelled prey in those days, that exploitation of such a prey base may have been the bread and butter for a number of marine tetrapod predators. But infaunal probing is another interpretation and I am admittedly ignorant about the record of infaunal prey at Solnhofen. I do know however that shelled pelagic molluscs were abundant at Solnhofen and we should expect to find predators that ate them. Possible nocturnal foraging based on sclerotic rings (coincident with the known nocturnal activities of modern squid/nightly vertical migration), probing/unusual dentition, and the abundance of shelled molluscs leads me to favor a lifestyle of shelled pelagic mollusc consumption.

    • I’m having to consider feeding behaviour for a current project (though for pterodactyloids). A seagoing pterosaur which, according to a recent study, is unlikely to happily sit at the surface for any length of time, presumably deals with its prey on the wing. Do they limit themselves to smaller cephalopods? Or do the somehow remove the shell/guard prior to swallowing? That’s what I was toying with, anyway. Perhaps some sort of soft-tissue structure with which they manipulate food – a strongly-prehensile tongue – or even just a damn good shake? Anyway… just thinking aloud (in a typey way).

      • A robust, “prehensile” tongue would be useful, but I suspect unlikely. Such tongues are usually related to large gular volume and robust hyoid bones. We have ceratohyals, but the key for a robust tongue would certainly have to be better-developed elements, such as an ossified basihyal, as in turtles and some birds which use the tongue to manipulate or aid in prey acquisition (parrots, flamingos, some ducks).

    • Great thoughts. I’d note that a fair number of mosasaurids seem to have been hard-cephalopod specialists, but rather than ferret the prey out of their shells they seem to have merely taken the shell and soft-bits whole, crushing along the way.

  4. Duane says:

    Sorry I should be saying cephalopod instead of mollusc to be more precise.

  5. Duane says:

    It is also possible that maybe some pterosaurs (Pteranodon, Nyctosaurus come to mind) may have ghosted mosasaurs/other marine predators the way that some albatross have been reported to do so with killer whales.
    http://www.dailymail.co.uk/sciencetech/article-1218702/Albatross-killer-whale-relationship-revealed-amazing-pictures.html
    If mosasaurs sounded for large cephalopods and then returned to surface to recuperate with the prey the smashed bits of cephalopods, bits of tentacle etc etc may have been a good feed. Possible the mosasaur had to recuperate a bit while re-oxygenating allowing pterosaurs access to choice bits.

    • Are you implying scavenging, second or third order of arrival at prey species? Basically, smallest vulture level?

      • Duane says:

        Yeah I guess I am suggesting a way scavenging could have occurred in some pterosaurs- the high aspect ratio oceanic soaring guys- that is similar to what albatross do. And ways to make a living outside of classic piscivory. I don’t know… is there a word for cephalopod consumers? I do find the word piscivory limiting in conceptual terms because who is to say that cephalopods were not more important than fish in the diet of some pterosaurs- scavenged or hunted? Even today squid biomass may in fact be more important than fish biomass in certain oceans
        http://www.hermonslade.org.au/projects/HSF_04_4/hsf_04_4.htm
        and I vaguely remember reading in Ellis’ book on giant squid that cephalopod biomass may in fact exceed fish biomass primarily because they dominant in abyssal/mesopelagic environments compared to fish. And these deep sea haunts constitute the largest environment on earth. Citation needed of course. If you want to take this fish vs cephalopod notion further on a cultural level, fish is a much more comfortable food in western society than squid is. And paleontologists/biologists are still, as much as they may insist they are not, somewhat beholden to the culture they are part of being cultural animals after all.

        Anyways all this discussion is very fun and I think I will do a blog post shortly on cephalopods vs fish on antediluvian salad soon.

        Cheers

  6. Interesting discussion. I would only add that the wingtips should be about twice as tall as the skull and that your uropatagium is pretty extensive. The dark wing specimen preserves a good pair. Reduced, like Pterodactylus.

    • This is art. It is very much not much more than that. I also assume the preserved specimen shows that whatever the shape of the patagia are they will be offset by taphonomy from the living condition, and the condition in various poses. It happens.

  7. Pingback: A Skull For Rhamphorhynchus, Part Two | The Bite Stuff

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