LONDON – For most of us, “pterodactyls” are large, vicious and ugly gargoyles with leathery wings and jaws lined with savage teeth, the sort of disreputable brutes we find in Arthur Conan Doyle’s “The Lost World,” the “Jurassic Park” franchise — even a recent episode of “Doctor Who.”
Such works suggest we should think ourselves lucky that these flying reptiles were confined to the Mesozoic era (250 million to 65 million years ago) and that they aren’t alive today to menace mankind.
Of course, the popular understanding of these fossil animals and their world is only a distant echo of reality, a construct of poor scientific communication, melodramatic media and romantic storytellers.
Pterodactyls have suffered more than most in popular depictions. We frequently don’t even employ the correct name for them. Strictly speaking, “pterodactyl” refers to a specific type of flying reptile found in Upper Jurassic rocks (145 million years old) of Germany. The correct name for the group is “pterosaurs,” which translates from the Greek as “winged lizards.” They are named after their flight apparatus which, like the wings of bats, is made of membranes supported by their limbs and digits. Unlike bats, however, pterosaurs supported their distal wing with a single, retractable finger instead of the entire hand.
The well developed shoulder anatomy of pterosaurs indicates that they possessed large muscles to flap their wings, meaning their flight was self-propelled instead of gravity assisted. Pterosaurs achieved this milestone in vertebrate animal evolution well before birds or bats appeared, taking off approximately 225 million years ago. Their dynasty lasted at least 160 million years and ended 65 million years ago, leaving only strangely proportioned fossil bones as evidence of their existence.
We’ve known about pterosaurs for a long time. The first remains were unearthed in Germany in the late 1700s. Many 19th-century pterosaur scholars considered them to be active, dynamic animals but, by the 20th century, their reputation was not so gleaming. In the eyes of many, pterosaurs were crude biological hang gliders, useless at everything but remaining airborne, and little more than ancient equivalents of modern seabirds.
They were constantly and unfavorably compared with bats and birds, animals that were thought to be anatomically superior and more adaptable. Pterosaurs may have had the bold first stab at powered flight but were only warming up the skies. If pterosaurs were considered little more than evolutionary curios by the scientists studying them, it’s hardly surprising that popular depictions have been far from complimentary.
This view of pterosaurs remains prevalent among many, but that may be about to change. The past three decades have seen a dramatic rise in pterosaur research, calling for the revision and overturning of many long-standing ideas and a greater degree of consensus among pterosaur researchers.
The result is what vertebrate paleontologist David Hone called a “golden age of pterosaur research” in a 2012 paper, a movement born from the rising popularity of paleontological science, the development of research equipment and the recent discovery of relatively abundant, high-quality pterosaur fossils in Brazil and China. Most fossils known prior to the 1980s were fragments, and only a few sites yielded complete specimens. Even fewer specimens recorded delicate soft tissue such as wing membranes and integument.
Good pterosaur fossils are rare because, in life, their bones were expanded by air sacs to enhance their size without adding mass. Like inflating a bony balloon, these air sacs pushed pterosaur bones to their mechanical limits, reducing their bone wall thicknesses to mere millimeters. Enormous but lightweight skeletons like this are excellent for flying animals but they make fossilization tough on pterosaur skeletons.
Accordingly, the relative bonanza of good pterosaur material gave pterosaur research a shot in the arm, providing scientists with considerable amounts of new data on pterosaur anatomy, paleobiology and diversity. When combined with increasingly detailed assessments of other pterosaur fossils, the new remains improved our understanding of pterosaur skeletal function, brain shape, and soft-tissue anatomy considerably.
They also revealed a swathe of new pterosaur groups, many of which had anatomy that must be seen to be believed. We now know of more than 130 pterosaur species sporting all manner of bizarre jaws and teeth, variable wing proportions and tail lengths, and many with ridiculous looking headcrests. It’s no exaggeration to say that some pterosaurs are among the most bizarre looking vertebrate species in the fossil record.
With this increased appreciation of pterosaur anatomy and diversity came a revised understanding of many aspects of pterosaur paleobiology. Pterosaurs are now seen as a successful, diverse group of animals with sophisticated anatomy and interesting lifestyles. Exactly where they plug into the reptile family tree remains uncertain, but it seems increasingly likely that pterosaurs were close relatives of dinosaurs, and they share many surprising characteristics with this group.
Like many dinosaurs, pterosaurs seem to have possessed an extremely effective, bird-like respiratory mechanism comprising a solid lung ventilated by air sacs lining the body cavity.
Their bodies, also like many dinosaurs, were covered in a layer of hair-like fuzz, the structure of which may even be homologous to the “proto-feathers” being discovered in many dinosaur lineages.
These features are probably indications that pterosaurs were warm blooded, insulating their bodies to store heat derived from burning calories, rather than deriving warmth from their local environment like modern lizards and crocodiles. They were probably as hyperactive and energetic as modern birds and mammals, and nothing like the slow, labored gliders they were once thought to be. Far from being scary, scaly beasts, pterosaurs would have been warm, soft to the touch and strokable. Pet stores would be lining up to sell smaller pterosaur species if they were still around today.
Another recent revelation concerns their proficiency when walking and running. While it has been long established that pterosaurs could fly, historically their capabilities on the ground have been controversial at every level, including whether they moved on two legs or four.
Reappraisals of pterosaur trackways and limb joints in the 1980s and ’90s finally laid parts of the controversy to rest, demonstrating that pterosaurs walked on four limbs held almost vertically beneath the body. This energy-efficient stance is reminiscent of the limb carriage in most birds and mammals, rather than the sprawled limbs of modern reptiles.
Experts have taken this as a sign that pterosaurs were adept terrestrial animals, as well as fliers, and it even seems that some pterosaurs, such as the gigantic, giraffe-sized azhdarchids, spent much of their time on the ground in search of food.
One researcher behind this idea, Darren Naish, thinks this foraging method was only one among many. “This hypothesis is a world away from the conventional view that all pterosaurs hung around bodies of water … we suspect that azhdarchids were only part of a very diverse group of animals that were far more ecologically dynamic than convention suggests.”
Far from only dining on fish, pterosaurs probably ate insects, fruiting bodies and even small animals, including dinosaurs, using a range of foraging strategies.
Pterosaur researchers are also realizing how powerful and capable pterosaurs were in flight, including answering a persistently difficult question: How did they take off? Scientists have struggled to marry the enormous size of giant pterosaurs with a bird-like takeoff strategy, in which only the hind limbs are used to generate thrust for getting airborne.
Multiple lines of evidence indicate that pterosaurs took off using all four limbs, where the tremendous power of their winged forelimbs helped propel them skyward. Michael Habib, the researcher who published the quadrupedal launch hypothesis in 2008, suggests that “using all four legs, it takes less than a second to get off of flat ground, no wind, no cliffs.”
Such launches, which are practiced nowadays in a few species of bat, are much more powerful than hind-limb launches because they utilise the largest muscles in the pterosaur body for takeoff, the flight muscles. This may explain, in part, how pterosaurs remained flightworthy at sizes well beyond those of any other flying animals. Habib notes parallels between this reimagined launch strategy and our own engineering principles. “We put V8 engines in our biggest, heaviest cars, not V4s.”
It seems, then, that scientists are getting a handle on many aspects of pterosaur paleobiology, and the results are casting pterosaurs in whole new lights. They were not evolutionary also-rans, but strong, adaptable animals that earned their 160 million years of evolutionary history.
But many questions remain for researchers to address. Many aspects of pterosaur relationships remain hotly debated, and the nature of their immediate ancestors remains mysterious. The lifestyles and flight mechanics of many species remain completely uninvestigated, and the causes of their extinction are poorly understood.
The classic explanation is that pterosaurs lost a long battle with birds for resources. This interpretation has recently been challenged, however, as bird and pterosaur evolutionary patterns show no obvious correlation, and were probably not directly linked in competition.
Cautious interpretations of the pterosaur fossil record suggest flying reptiles were nonetheless slowly losing diversity toward the end of the Mesozoic, making them vulnerable to the turbulent environmental changes, the intense volcanic activity and the famous meteorite impact that marked the close of this chapter in Earth’s history.
We await more fossils and data to assess how accurately this describes the final years of the pterosaur dynasty, and to answer the many remaining questions we have about these fabulous animals.
Mark P. Witton is the author of “Pterosaurs,” published by Princeton University Press