For all the dust and bug bites involved, paleontology comes off as a romantic science. In pop culture, at least, it’s a discipline suited for Cary Grant, Sam Neill, and, to a lesser extent, David Schwimmer. But, as with almost any line of work, the image is often more glamorous than the reality. Paleontology isn’t just about searching for bones in the desert or reconstructing enormous skeletons. Sometimes it requires that you look closely at some ancient upchuck.
Back in 1989 paleontologist Fabio Marco Dalla Vecchia and colleagues described an unusual fossil from the 228-208 million year old rock of Italy. It seemed to be a gastric pellet—the sort of mass of hard-to-digest materials that birds of prey regurgitate—containing the bones of an early pterosaur. While the researchers could have hoped for a specimen that hadn’t been partially-digested first, Triassic pterosaurs are so rare that it was a notable find in the history of the flying reptiles.
But now Dalla Vecchia, Borja Holgado, and colleagues have determined that the Triassic throwup doesn’t contain a pterosaur, after all. Analysis of microCT scans made of the fossil have revealed that the animal inside the pellet was one of the protorosaurs – strange reptiles that came in a bizarre variety of shapes. Specifically, Holgado and colleagues write, the bones are similar to the superficially lizard-like species Langobardisaurus pandolfii found in the same formation.
So let this be a lesson to any aspiring paleontologists who happen to be reading. There is fun in fieldwork and joy in reconstructing the ancient dead, but that’s only a part of what the science requires. You may find yourself picking bone by bone through someone’s prehistoric puke.
I’m going to teach you how to do a pterosaur impression.
Stick your arms out to your sides with your palms facing forward. Now, while keeping the rest of your fingers curled in a loose fist, stick out your fourth finger. It’s like you’re giving a New Jersey hello, but with your ring finger instead of your middle one. That’s really all there is to it. Flap and squawk a bit and the illusion will be complete.
Or maybe not. We have many of the same bones as pterosaurs – skull bones, vertebrae, ribs, limbs, and so on – but the thin-walled bones of the flying reptiles evolved into very different shapes from our own. Not to mention that they had a bone that we don’t – the pteroid.
The bone is easy to spot. It’s a curved splint on the pterosaur wrist, in between the body and the fingers. It acted as a skeletal support for the leading edge of the pterosaur flight membrane called the propatagium. The question paleontologists have struggled with, however, is how this important little bone was oriented in life.
Paleontologists have discovered dozens and dozens of pterosaurs, some of which are beautifully-preserved with wing membranes intact, but the proper position of the pteroid bone has remained controversial. Pterosaurs did not think to die in splayed-out, proper anatomical position to make it easy on us. So while some researchers have proposed that the splint of bone pointed straight forward, others have reconstructed the pteroid pointing towards the body at a low angle.
Which is correct? Perhaps a future find will clear up the matter once and for all. But, using what’s known about the requirements of flight, mechanical engineer Colin Palmer and paleontologist Gareth Dyke investigated how the two competing arrangements would affect the aerial abilities of the Coloborhynchus – a pterosaur with a 19-foot-wide wingspan that flew over Cretaceous England about 98 million years ago.
The forward-pointing pteroid didn’t work so well. In their calculations, Palmer and Dyke found that the straight-ahead position increased strain on the little bone. Not only that, but this pteroid position would have required a very flexible membrane that could stretch 40% between furled and extended positions. This would have made the leading edge of the wing relatively weak and made it more difficult for Coloborhynchus to fly.
Coloborhynchus didn’t seem to have these problems with the inward-pointing pteroid, though. The bone would have kept the membrane as a relatively rigid, stable edge during flight. It’s indirect evidence, true, but we can assume that these animals evolved for optimal flight ability within the constraints of their anatomy, and other pterosaurs likely shared what Palmer and Dyke reconstructed for Coloborhynchus. So if you’re going to build a pterosaur suit to bring your Pteranodon impersonation to the next level, it’s wise to keep that pteroid medial.
Pterosaurs were into fuzz before dinosaurs. That’s true in a historical sense, at least.
In 1831, over a decade before the word “dinosaur” had even been coined, the German paleontologist August Goldfuss mentioned that a small pterosaur he had studied seemed to have a coat of mammal like “fur”. This was strange. Even though some naturalists had proposed that pterosaurs were weird proto-bats, the consensus was that they were reptiles. Why should reptiles have a fluffy coat? Perhaps it was another indication, as some paleontologists suspected, that pterosaurs were highly-active animals with mammal-like metabolisms and a need to stay warm.
The fossil Goldfuss described wasn’t an anomaly. As the decades flew by, other researchers found weird fibers on the bodies of pterosaurs. One species, Sordes pilosus, was nicknamed the “hairy devil” because it was so damn fluffy, and now it seems that all pterosaurs wore such structures on their bodes. Even though the prospect of enfluffled Velociraptor or Tyrannosaurus can still send comment threads into chaos, everyone seems cool with the idea that pterosaurs had fine coats of simple fuzz.
In 2009, Alexander Kellner and colleagues finally gave a formal name to the fossilized wisps. What had been referred to as “hair”, “fur”, and “integument” would henceforth be known as pycnofibers. But what was this fluff?
Pycnofibers were short, simple structures. The only internal landmark in these filaments was a canal running up the middle, and, unlike mammalian fur, pycnofibers were not deep-set in the skin. These differences set pterosaur pelts apart from those of other prehistoric creatures, including protofeather-covered dinosaurs. And yet, the relationship between pterosaurs and their dinosaurian cousins may have major implications for when prehistory started to get fuzzy.
Pterosaurs were not dinosaurs. They were a separate lineage of flying creatures. Exactly where they fit in the tree of life is a contentious issue, but pterosaurs are often placed as the closest lineage to the dinosaurs. In this arrangement, both shared a common ancestry and form a group called the Ornithodira. And if this truly was the case, the relationship between pterosaurs and dinosaurs raises the possibility that fluff – or the propensity to evolve it – is a very ancient trait.
At the moment, the pycnofibers of pterosaurs and the simple protofeathers of dinosaurs are treated as structures that evolved independently of each other. Yet paleontologists are still learning more about the occurrence and early evolution of these body coverings. Pycnofibers were a universal pterosaur trait, likely present in the earliest members of the lineage, and there’s a mounting body of evidence that protofeathers may have been present in the earliest dinosaurs. If the establishing members of both closely-related lineages were fuzzy, might it be possible that they inherited this trait from an even earlier ancestor? We need more fossils – particularly from the days of Triassic pterosaurs and dinosaurs – to find out.
There’s another possibility, of course. Pterosaurs and dinosaurs may have evolved their pelage independently of each other. (In dinosaurs, it’s possible that feather- and bristle-like structures evolved multiple times.) Even so, this may be a hint that pterosaurs and dinosaurs inherited some sort of developmental pathway to produce simple, fluffy body coverings – perhaps having to do with the mechanisms that link structures as disparate as bird feathers and alligator scales. Whether pycnofibers turn out to be the same as dinosaur protofeathers or not, they’re a sign that prehistory was fluffier than previously imagined.
Imagine a balloon inside a cask. There’s an opening at the top to blow air into, but here’s the problem – the balloon hugs the wooden walls of the chamber. There’s nowhere for the balloon to expand into and no way for old air to be pressed out. The sides of the barrel won’t move. But there is another way to move air in and out of that balloon. If you partitioned the balloon in the front half of that barrel with a disc of wood, you could make a piston to pump forward and backward, expanding and contracting that bag of air. And if you can envision that, you can wrap your head around how pterosaurs breathed.
Commonly called “flying reptiles”, pterosaurs were close cousins of dinosaurs and the first vertebrates to take to the air. They did so on wings of skin stretched between their bodies and extraordinarily-elongated fourth fingers. The first of their kind were relatively small, but, over time, their ranks swelled to include giants such as Quetzalcoatlus with wingspans over 33 feet across. And as with many outstanding extinct organisms, paleontologists are trying to puzzle together the biological basics of these animals. Among the major mysteries – how did big pterosaurs fill their lungs with air?
Answering the question is impeded by the fact that no one knows what pterosaur lungs looked like. Such soft tissues have not been found just yet, and may never be. But, as Sonoma State University paleontologist Nicholas Geist and colleagues point out in a new Anatomical Record paper, skeletal anatomy offers a few clues as to the bony constraints pterosaurs faced as they inhaled and exhaled.
Geist and colleagues focused on large pterosaurs – species with wingspans over 9 feet across. That’s because large pterosaurs had relatively rigid torsos. Some of their vertebrae fused into a stiffened rod of bone that was reinforced by “a dense latticework of mineralized tendons”, and the large ribs at the front of large pterosaur chests fused to their supporting vertebrae to create a stiff structure the researchers call a synthorax. This strengthened the skeleton and reduced the need for heavy muscles, coming with the cost of highly-reduced torso flexibility. No wonder Geist and colleagues titled their paper “Breathing in a Box.”
All that skeletal fusion limited the ways in which pterosaurs could have filled their lungs. The ribs around their lungs couldn’t flex inward and outward to help pump air. And despite the fact that pterosaurs had a system of air sacs invading their bones – much like birds and other dinosaurs on the saurischian line – large pterosaurs wouldn’t have been able to breathe the way modern birds do. Birds rely more on up-and-down motions of the sternum to expand and contract their complex system of lungs and air sacs, but the corresponding bones in large pterosaurs were too rigid to allow this.
The answer to the problem might rest among different living relatives of pterosaurs – the crocodylians. Alligators and crocodiles expand and contract their lungs by way of what’s called a hepatic piston. The liver acts as a barrier between the lungs and the viscera – like the disk of wood in the barrel analogy – and can be retracted to squish the innards down to make room for an alligator’s lungs to expand. Muscles on the animal’s side can then act on the gastralia – belly ribs – to bring the liver back into position and compress the lungs for exhalation. Geist and colleagues suggest that this method could have worked for large pterosaurs, too, moving the guts instead of the bones.
This way of breathing may not have been a specialization of the largest pterosaurs. While they had more mobile chest bones, Geist and coauthors point out, some articulated skeletons of small pterosaurs like Rhamphorynchus hint that these little fliers kept their torsos relatively rigid. They may have established the piston-pump method early, and, if this was the case, then the trait may have been part of what allowed pterosaurs to reach truly gigantic sizes. What started off as an evolutionary option ended up as an essential feature of the largest animals ever to soar over the planet.
Earlier this year, in the journal Gondwana Research, paleontologists Gerald Grellet-Tinner and Vlad Codrea announced an unexpected pterosaur. Consisting solely of a triangular hunk of bone found in the 70 million year old rock of Romania, the fossil was presented as a snout piece of Thalassodromeus sebesensis, a new species of a previously-named genus. This was very strange.
The original Thalassodromeus species – T. sethi – lived 42 million years earlier in Early Cretaceous Brazil. If this new animal really belonged to the same genus, as Grellet-Tinner and Codrea proposed, then paleontologists were missing an extended period of this pterosaur’s history. Grellet-Tinner and Codrea tentatively filled in the gap with hypotheses about dispersal routes, the co-evolution of Thalassodromeus with flowering plants, and the odd “island effect” that alters species bound to geographic dots in the ocean, but there is a much simpler explanation for the out-of-place pterosaur. This “pterosaur” was really a turtle.
In a comment to the same journal, Gareth Dyke and 19 other paleontologists affirm that the peculiar Thalassodromeus bone from Romania is actually a piece of a turtle’s belly shell. The single piece of bone lacks any characteristic that conclusively identifies it as belonging to a pterosaur. “[I]t is not a pterosaur head crest, or a pterosaur bone of any kind,” the researchers write. Rather, the bone is a perfect fit for part of the bottom shell of a Cretaceous turtle named Kallokibotion that has been known from the same area for about 90 years. Sadly, Dyke and co-critics write, “the misidentification of one fragmentary fossil [led] to a cascade of elaborate ideas with increasingly far-reaching implications.”
Grellet-Tinner and Codrea had entertained the turtle possibility in the supplementary information of their study, but rejected it in favor of a pterosaur interpretation. And they still uphold their original conclusion.
In their own reply, Codrea and Grellet-Tinner say their critics’ comments are “most welcome” but then pile on personal jabs and conclude with a cryptic line that the “conspicuous persistence, hastiness, and zeal of [the critical comment], may indeed reflect of deeper, perhaps irritating, issues in Transylvania.” Just as strange, Codrea and Grellet-Tinner complain that their critics have not studied the fossil in person, yet principally defend their own position by citing figures from other studies.
Codrea and Grellet-Tinner promise that planned 3D scans of the fossil “will concomitantly eliminate any doubt regarding [the specimen], if there were any.” I’m betting the results come up turtle. The shape and anatomy of the bone are a much better fit for a familiar chelonian than a pterosaur unstuck in time. Such is the nature of paleontology. The true identity of puzzle pieces isn’t always what we first expect them to be.
The pterosaur-turtle mix-up isn’t the only case of mistaken identity, though. A different team of researchers has just revised the identity of another European pterosaur.
In 1990 paleontologists found a pair of weird bones in England’s Cromhall Quarry. They seemed to be hand bones – metacarpals – from a pterosaur, and this was especially interesting because the site was Late Triassic in age. If the identification was correct, then the bones would be from the early days of these leathery-winged reptiles and the only evidence of pterosaurs in Triassic England.
But upon re-examination, paleontologists Fabio Marco Dalla Vecchia and Andrea Cau found that the bones more closely match the fingers of weird “monkey lizards” called drepanosaurs. Other bones from these weird, clasp-footed reptiles have been found in the same quarry, but were not known in 1990, and so it was easy to mistake the unusual fossils for pterosaur hand bones. The upshot, Dalla Vecchia and Cau write, is “there is no unequivocal evidence of pterosaurs in the Triassic of the UK.” Sometimes that’s the way the pterosaur crumbles.
[For more on the Thalassodromeus debacle, read Mark Witton’s post breaking down the details.]