Monday, July 16, 2018

No, these pterosaurs were not Jurassic puffins

New research into pterosaur diets is overturning assumptions based on qualitative assertions made decades ago
Gharials like this Asian gharial are among the animals pterosaurs are often compared to. Photograph: -/AFP/Getty Images
Dimorphodon macronyx, a pterosaur from the Jurassic, once thought to be puffin-like. Researchers now know it was a poor flier more likely to forage on the ground. Photograph: Mark Witton/

What did it eat? This is one of the first questions the general public – and especially kids – ask about extinct animals. It may surprise you to know that palaeontologists sometimes struggle to work out the answer. They may look at living relatives for clues, but for long-gone animals with no living descendants, like pterosaurs, the job is much trickier. What can you sensibly compare them to? Even if you make a hypothesis on their diet, how can you test it?

Pterosaurs are a group of extinct flying reptiles that include the famous Pteranodon  and Pterodactylus. They are not dinosaurs, but a separate branch of reptiles that lived alongside them in the Mesozoic. They were the first group of backboned animals to evolve true flight, beating the avian dinosaurs to aerial domination by at least 60 million years. They came in many shapes and sizes, from kitty-sized cuties to giant stalkers that would have stood eye-to-eye with a giraffe – had giraffes been available in the Cretaceous. In their 140m-year span of existence, pterosaurs were a vital component of the many rich ecosystems of the Mesozoic. And yet we know almost nothing definitive about what they ate.
Gharials like this Asian gharial are among the animals pterosaurs are often compared to. Photograph: -/AFP/Getty Images
“The spectacular variety of shapes and sizes exhibited by jaws and teeth tells us that pterosaurs had a wide range of diets,” said Dr David Unwin, reader in palaeobiology at the University of Leicester and an expert on pterosaurs. “The problem is that so far it has been quite difficult to establish exactly what it is an individual species ate. With only one or two exceptions, there is little agreement on diet across Pterosauria.”

To start tackling this problem, University of Leicester PhD student Jordan Bestwick set to work reviewing the scientific literature, and his results were published earlier this month. Bestwick compiled conclusions about the diet of different species of pterosaur: “I also paid particular attention as to whether or not these dietary statements were supported by any kind of evidence, and if so, the type of evidence.” This review is one of the most comprehensive of its kind, and has yielded results that will help direct future research.

The main lines of support for diet in extinct animals come from qualitative analyses of the bones: namely, comparative anatomy or the fossilised remains of food items inside the stomach or throat. Although comparative anatomy has been the backbone of palaeontology for centuries, modern researchers ideally aim to support these observations with more quantitative techniques. For example, they can apply engineering principles to test the properties of skeletal structures, or use aeronautical mathematics and modelling to test flight capability. These data can tell us what extinct animal bodies were capable of, and support or cast doubt upon dietary hypotheses. Analysing isotopes in fossil bone can also provide rigorous data on the type of food an animal ate, as their bones carry the signature of chemicals in the food.
Gharials like this Asian gharial are among the animals pterosaurs are often compared to. Photograph: -/AFP/Getty Images
After meticulously combing through 124 published studies on pterosaurs, Bestwick found that a whopping 87% of the food preferences assigned to pterosaurs were based only on qualitative analyses. More than half of these were reached through comparative anatomy alone. “I was also not expecting so many interpretations to be based on untestable ideas,” said Bestwick. The result underlines the need for more rigorous analyses into the ecology of pterosaurs.

A good example of a dubious conclusion reached through comparison is found in Dimorphodon. This pterosaur, from the Jurassic of the UK, had a 1.5-metre wingspan, and an unusual skull. At the turn of the 20th century, researchers observed that the skull resembled that of the Atlantic puffin. As a result of this purported puffin-resemblance, “Dimorphodon was hypothesised as a piscivore [fish-eater],” said Bestwick. But the resemblance was superficial: they were comparing the skull bones in Dimorphodon to the keratinous beak of the puffin, a quite different structure made of different biological material. “With no way of reliably testing it, this idea it became perceived wisdom for the rest of the century,” Bestwick said.
Gharials like this Asian gharial are among the animals pterosaurs are often compared to. Photograph: -/AFP/Getty Images
Thankfully, palaeontologists are now revisiting some of these classic ideas and applying new techniques. “In the last few years flight models have shown that Dimorphodon was a poor flier,” said Bestwick, explaining the changing understanding of this reptile. “[It] would probably have been more at home foraging for terrestrial food items on the ground.”

So there were no Jurassic puffins after all – or to be more accurate, if there were, Dimorphodon was not one of them. Unwin, who co-authored the review of pterosaur diets, expanded on the team’s results: “What it tells us is that most of our current ideas are poorly founded, and largely depend on qualitative assertions often made decades, or even centuries ago. Once embedded in the literature these ideas tend to be adopted by successive generations of researchers and can be very difficult to overturn, not because they are well founded, but because ‘everybody knows that’.”
Gharials like this Asian gharial are among the animals pterosaurs are often compared to. Photograph: -/AFP/Getty Images
Such problems don’t only affect pterosaur palaeontologists, of course. All scientific research builds on the work of previous generations, but it is vital that researchers reassess the accepted wisdom of their disciplines to ensure it stands up to the latest analytical methods. The widespread use of micro CT scanning, for example, has led to multiple new studies of old fossil material. The computing power available for creating mathematically based models, and testing inference-based phylogenetic hypotheses, has transformed palaeontology from a drawer-shuffling hobby to a rigorous and modern scientific discipline. These updated understandings often take time to filter into popular consciousness. Unfortunately Hollywood continues to rehash past mistakes and reinforce them.

Having recognised this gap in pterosaur studies, what can be done to address it? “I am continuing with my research using quantitative microtextural analysis of their tooth microwear,” said Bestwick. Microwear analysis involves examining the microscopic scratches and pits on the surface of teeth. These patterns are caused in the process of eating, and can be quantified to categorise the food types that were processed by the animal. The method has already been used in studies of fossil mammal teeth to assess diet preference, but Bestwick will be the first to use it on flying reptiles. “This technique has never before been applied to pterosaurs, or reptiles in general for that matter,” he said, “so hopefully it will reveal new insights into the diets of some pterosaurs.”

Despite being a much-loved part of the pantheon of extinct reptiles, it is clear there is still much to learn about these incredibly successful creatures. “We still have a fair way to go before we can conclusively say what pterosaurs were eating,” said Bestwick.

Unwin added: “With this knowledge we would have a much better understanding of the nature and ecological roles of both pterosaurs and, more widely, Mesozoic terrestrial ecosystems in general.”


Bestwick J, Unwin DM, Butler RJ, Henderson DM, Purnell MA. 2018. Pterosaur dietary hypotheses: a review of ideas and approaches. Biological Reviews.

Gill PG, Purnell MA, Crumpton N, Brown KR, Gostling NJ, Stampanoni M, Rayfield EJ. 2014, Dietary specialisations and diversity in feeding ecology of the earliest stem mammals. Nature.

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