The Kiwi Pterosaur
Leptostomia begaaensis, a probe-feeding pterosaur. Art by Nick Longrich, 2020.
A few years back, I was looking at an assortment of scrappy little fossils from the Kem Kem beds of Morocco, and spotted an odd little bone. It was long and skinny, like a bit of stick, and didn’t look like much of anything. In terms of shape, it looked like some sort of spine, perhaps from the fin of a fish. But then I saw the texture, and knew it was something else- pterosaur- a new, strange, little pterosaur that my colleagues- Roy Smith, Dave Martill, Alexander Kao, Samir Zouhri- and myself have recently named Leptostomia begaaensis.
When trying to identify fossils, you have a lot of different clues to work with. One of them is texture- different species grow their bones differently, and have different textures as a result. The bone of a duckbill dinosaur is fibrous, like some kind of fine-grained wood. The bone of a mosasaur is fibrous, like a coarse-grained wood. The bone of a carnivorous theropod is dense and smooth, almost like porcelain. The bone of a plesiosaur is gnarly. And soforth. I learned this little trick prospecting in badlands and museum collections in Alberta, and it’s always come in handy when I don’t know what a bone is, which is often.
Part of the long, skinny upper beak of Leptostomia begaaensis. From Smith et al. (2021)
Now, pterosaur also has a distinct texture- it’s fairly smooth, but with very fine, parallel striations, where the blood vessel canals are carefully aligned- likely an adaptation that helps the bones retain strength even though they’re paper-thin to reduce weight, to help the animal get off the ground and stay aloft. I saw it was pterosaur- but it wasn’t shaped like any other pterosaur I’d ever seen.
Beak of Leptostomia begaaensis, showing the fine, parallel grain of pterosaur bone. From Smith et al. (2021)
It was a bit of beak- long and skinny, flattened top to bottom. It was shaped not like a pterosaur, but the beak of a kiwi bird- a bird that uses its long, skinny beak to probe in the dirt for worms and invertebrates. It would have come from a small pterosaur- with a wingspan of maybe 1-2 meters, and being toothless it would probably have been related to the Azhdarchoidea- a group that includes giants like Quetzalcoatlus, which weighed perhaps 250 kg and had a wingspan of 10 meters or more.
A curlew (Numenius) uses its long bill to pull this sand crab out of its burrow (Wikipedia).
Lots of birds have this sort of beak and this sort of feeding strategy. Kiwi birds, but also hoopoes, snipes, woodcocks, curlews, godwits, sandpipers, ibises. Some of them, like kiwi, hoopoe, and woodcock, feed mostly on earthworms in soils. Most, like ibises and most sandpipers, feed in the muds and sands of estuaries and tidal flats, hunting for bristle worms, fiddler crabs, and small clams, and so on. It’s a strategy that has evolved multiple times in modern birds- but here we had a small pterosaur doing it, 100 million years ago.
The Kem Kem beds are an aquatic habitat- a river system feeding into delta and estuary, it had a rich fauna of fish, sharks, turtles, and the aquatic Spinosaurus eating them. So it’s probable that Leptostomia was hunting in the mud of the riverbanks, estuaries, and mangroves. Prey could have included worms, little clams, or perhaps crabs- which are known from mangrove deposits of the same age in Egypt. That being said, if there were earthworms around in the Cretaceous, it would have been unsurprising if Leptostomia, or its relatives, hunted after them the way that kiwis and hoopoes do.
So what does this tell us? Well, more than a century after the pterosaurs were first described, they continue to surprise us. Here’s a pterosaur acting unlike any other pterosaur we’ve ever seen, and acting like a modern bird. What this suggests to me- the fact that we’re still finding pterosaurs occupying entirely new niches- is that we’re far from having a good sample of pterosaur diversity. There are lots of species, niches, even families that we’ve been overlooking.
Coloborhynchus fluviferox, a probable fish-eating pterosaur from the Kem Kem beds of Morocco.
A very high proportion of pterosaurs we’ve described are interpreted as fish-eaters, for example, Coloborhynchus fluviferox, a toothed pterosaur from Morocco, which lived alongside Leptostomia. The reason is that the pterosaur record is highly biased. Most pterosaurs come from a handful of environments- lagoons like the Solnhofen, lakes like in the Yixian Formation, seas like the Niobrara. These are watery habitats. Water-loving pterosaurs, those that hunt on the wing for fish, living like modern seagulls, frigatebirds, and albatrosses, are likely to fly over and drown in water. So we probably have a pretty good record of fish-eating pterosaurs. But other pterosaurs, the types feeding either along the water’s edge, or inland, would tend to avoid water- most modern birds prefer not to fly over water if they can avoid it. They will much more rarely end up in the fossil record. Leptostomia, hunting along shores, likely flew over water, but likely spent most of its time near land, and wouldn’t tend to occur with pterosaurs in more offshore environments.
Known pterosaur diversity in the Late Maastrichtian, blues = marine, browns = terrestrial. Many were probably fish-eaters, but they’re probably over-represented. As with living birds, most diversity was probably in terrestrial species.
If you look at the bird fossil record for an example of how this bias works, we have a very good record of aquatic birds- ducks, penguins, albatrosses, auks, tropicbirds, and soforth. Our record of terrestrial birds- falcons, owls, hummingbirds, woodpeckers- is far less complete, even though land birds outnumber aquatic birds. If you were to look at just the bird fossil record (imagine, for a moment, birds were extinct, and we had only their fossils ) a paleontologist might conclude that most birds ate fish and hung around near water, when in fact only a handful of species do. Overwhelmingly, modern bird diversity is in terrestrial ecosystems.
The same may be true of pterosaurs. As diverse as they were- and they were very diverse- the record is probably heavily biased towards fish-eating pterosaurs, things like the marine-soarer Pteranodon because fish-eating pterosaurs hang out near water, and water is where you get fossils buried by sediments.
Reconstruction of Leptostomia begaanesis. From Smith et al. (2021)
It’s likely that only a small fraction of pterosaurs ate fish- most probably ate anything and everything else- bugs, lizards, baby dinosaurs, fruit, plants, other pterosaurs. I strongly suspect that at least some pterosaurs were plant-based omnivores (that is, getting most calories from plants, protein from animals, like modern cranes) or even full-on plant-eaters (that is, vegan pterosaurs). For example, some tapejarids have beaks suggesting herbivory (deep, strongly decurved bills), and the sheer size of the pterosaur Hatzegopteryx suggests it needed a lot of food- which is just easier for an herbivore to find. It’s just inconcievable that a group that was so diverse and so long-lived would have failed to exploit plants.
To that list of probable food items, we can now add worms and burrowing invertebrates. And we will almost certainly find more weird pterosaurs, doing things we didn’t expect pterosaurs to do.
This specialization probably explains the huge diversity of pterosaurs seen in Morocco. They include toothed pterosaurs like Coloborhynchus, Anhanguera, and Ornithocheirus, beaked pterosaurs like Afrotapejara, Apatorhamphus, Xericeps, and the long-jawed Alanqa. Scraps hint at still more undescribed species. Specialized ecologies allowed diverse pterosaurs to coexist without competing, since each specialized on different things, a bit like the diversity of birds in the Galapagos.
References
Longrich, N.R., Martill, D.M., Andres, B., 2018. Late Maastrichtian pterosaurs from North Africa and mass extinction of Pterosauria at the Cretaceous-Paleogene boundary. PLoS Biology 16, e2001663.
Jacobs, M.L., Martill, D.M., Ibrahim, N., Longrich, N., 2018. A new species of Coloborhynchus (Pterosauria, Ornithocheiridae) from the mid-Cretaceous of North Africa. Cretaceous Research.
Jacobs, M.L., Martill, D.M., Unwin, D.M., Ibrahim, N., Zouhri, S., Longrich, N.R., 2020. New toothed pterosaurs (Pterosauria: Ornithocheiridae) from the middle Cretaceous Kem Kem beds of Morocco and implications for pterosaur palaeobiogeography and diversity. Cretaceous Research 110, 104413.
Martill, D.M., Ibrahim, N., 2015. An unusual modification of the jaws in cf. Alanqa, a mid-Cretaceous azhdarchid pterosaur from the Kem Kem beds of Morocco. Cretaceous Research 53, 59-67.
Martill, D.M., Smith, R.E., Longrich, N., Brown, J., 2021. Evidence for tactile foraging in pterosaurs: a sensitive tip to the beak of Lonchodraco giganteus (Pterosauria, Lonchodectidae) from the Upper Cretaceous of southern England. Cretaceous Research 117, 104637.
Martill, D.M., Smith, R., Unwin, D.M., Kao, A., McPhee, J., Ibrahim, N., 2020. A new tapejarid (Pterosauria, Azhdarchoidea) from the mid-Cretaceous Kem Kem beds of Takmout, southern Morocco. Cretaceous Research 112, 104424.
Martill, D.M., Unwin, D.M., Ibrahim, N., Longrich, N., 2018. A new edentulous pterosaur from the Cretaceous Kem Kem beds of south eastern Morocco. Cretaceous Research 84, 1-12.
McPhee, J., Ibrahim, N., Kao, A., Unwin, D.M., Smith, R., Martill, D.M., 2020. A new? chaoyangopterid (Pterosauria: Pterodactyloidea) from the Cretaceous Kem Kem beds of southern Morocco. Cretaceous Research 110, 104410.
Smith, R.E., Martill, D.M., Kao, A., Zouhri, S., Longrich, N., 2021. A long-billed, possible probe-feeding pterosaur (Pterodactyloidea:? Azhdarchoidea) from the mid-Cretaceous of Morocco, North Africa. Cretaceous Research 118, 104643.
Links
Leptostomia begaaensis wikipedia page