A brief flight with Pterosaurs

Planet Earth was a busy place 225mya. The super-continent, Pangaea, in the Northern Hemisphere started rifting, creating the beginnings of the North Atlantic Ocean. Dinosaurs began their campaign for global dominance of Mesozoic terrestrial ecosystems and drove many older reptile lineages into extinction. In the seas, enormous marine reptiles began to challenge fish for the role of top predators. Hidden in the shadows of this reptile-dominated world, the first mammals quietly appeared. Even plants were undergoing a revolution, as archaic seed ferns were replaced with sleek new conifers. Yes, the Late Triassic was a busy time indeed. However, away from all this bustle, in the treetops and skies, another branch of reptiles were quietly carving their own place in history, as the first vertebrates to evolve powered flight. These extraordinary animals were pterosaurs – the ‘flying reptiles’.

Fig. 01Fig. 1. Pterodactylus, the first pterosaur fossil to be described and named. This discovery marked the beginning of pterosaur research, a discipline now in its third century.

Most people are not terribly familiar with pterosaurs. Sure, they might have come across Pteranodon or ‘pterodactyls’ in books, films or television documentaries. However, pterosaurs are mostly cast as secondary components of prehistoric landscapes, playing bit parts in productions dominated by their dinosaur contemporaries. At most, pterosaurs have brief cameos in which they carry off scantily clad women or harass explorers on their entry to forgotten, lost worlds. However, these bit parts do little to tell the real pterosaur story. It is one of humble beginnings and eventual domination of Mesozoic skies for 160 million years, of global distribution and tremendous ecological diversity and, in the final days before their extinction 65mya, the evolution of the largest animals ever to grace the skies.

Of course, all that is left of pterosaurs today is their fossil remains. The first of these fossils (fig. 1) made known to science was found in the Solnhofen Limestones of Germany in 1784, 38 years before dinosaur studies really kicked off. Its describer, Cosimo Collini, thought it represented an extinct aquatic reptile. However, this notion was overturned in 1809 when the renowned comparative anatomist, Georges Cuvier, recognised the flight adaptations of the skeleton. Subsequently, he named the animal Ptero-dactyle, which translates as ‘wing-finger’, a name later modified to Pterodactylus (fig. 2). As more pterosaur discoveries came to light, it was realised that a whole group of these bizarre creatures once existed and, in 1834, the group was christened “pterosauria”, meaning “winged lizards”. Over the last 220 years, approximately 100 different species of pterosaur have been recognised and the continual discovery of new pterosaur fossils, on all seven continents, means this number is set to rise.

Fig. 02Fig. 2. Life restoration of Pterodactylus. Note the headcrest, shaggy mane of fur along the neck and large, recurved claws.

Pterosaur origins

Despite centuries of research, the beginning of the pterosaur story remains mysterious. Taxonomically speaking, just what are pterosaurs? They certainly aren’t ‘flying dinosaurs’. This title applies to birds, not pterosaurs. Nor are they lizards, despite their Greek name suggesting the contrary. In fact, establishing exactly where pterosaurs fit into a broader evolutionary picture has proved rather difficult as the earliest most ‘primitive’ pterosaurs already possess highly modified anatomy distinct from all other fossil forms, thereby shadowing their ancestry.

Fig. 03Fig. 3. Pterosaur wing anatomy, demonstrated by the Jurassic form Sordes (top). Bottom left, bat wing anatomy; bottom right, bird wing anatomy. Note that the bird uses elongate feathers to form a flight surface rather than the finger-supported membranes of bats and pterosaurs.

It seems likely that their origins lie in a taxonomic group known as “archosauromorpha” that is a collection of animals represented in modern times by crocodiles and birds. Opinions on where pterosaurs lie in this group differ: some folk include them right at the base with some unusual reptiles known as protorosaurs. Others place them close to crocodiles, whilst several studies present pterosaurs as close relatives of dinosaurs. Answering this rather elementary question is so difficult because the pterosaur fossil record is rather patchy, particularly at the very start of their evolutionary history. It is quite likely that pterosaurs evolved quickly in environments unsuited for fossil preservation (such as dense woodlands or forests) and, consequently, the fossil record misses the opening act of the pterosaur show. Clearly, new discoveries are required to shed light on this murky area of the pterosaur tree.

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Mark Witton works at the Palaeobiology Research Group at the University of Portsmouth, Burnaby Building, Burnaby Road, Portsmouth, PO1 5DF.  He can be contacted at Mark.Witton@port.ac.uk.

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