When pterosaurs were still mammals: evolving views of the flying dragons

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Love in the Time of Chasmosaurs

In the history of palaeontology there is the recurring attempt to compare the past with the present, even to force the past in our present schemata - an extreme example was (and in part is) the tentative to classify and compare fossil vertebrates among the animals we know best: the mammals.
Both dinosaurs and birds in the past have been attributed to this order, but also the perhaps most mysterious vertebrates ever known: the pterodactyls.

Cosimo Alessandro Collini, the director of the Cabinet of Curiosities of the principality of Pfalz (southwest part of modern Germany) was the first to speculate about pterodactyls in 1784.

Fig.1. Pterodactylus antiquus (Upper Jurassic, Eichstätt, Bavaria), the first by Cosimo Collini in 1784 scientific described pterosaur.

Fig.2. Copper engraving of the holotype fossil of Pterodactylus antiquus (SOEMMERRING, 1812) by Italian naturalist Cosimo A. Collini in 1784.

Based on a fossil found in a limestone quarry near the town of Eichstätt and associated with remains of fishes and crustaceans, he proposed that the strange animal lived in the sea and was an aquatic creature.
It was the French-German naturalist Johann Hermann (1738-1800), observing the drawings of Collini the first to guess correctly that the creature possessed a membrane supported by the elongated fourth finger and was able to fly. In March 1800 he contacted the French palaeontologist Cuvier with a letter in which he presented a reconstruction of the animal resembling a mammal: with a body covered by fur (which, even if Hermann had studied the original specimen, is not preserved), large wings that resemble those of a bat - especially the part between the neck and the limbs of the animal - and what look like's external genitalia.

Fig.3. First life restorations of Pterodactylus antiquus by Jean Hermann of Strasbourg, sent in a letter to George Cuvier in 1800.

Studying the description and drawings in 1801, but not the fossil, Cuvier confirmed the membrane and the fly capacity of the animal and classified it as reptile. Perhaps Cuvier realized that his classification of pterodactyls between reptiles would not be universally accepted, so he added to his statement the notion that the animal was the strangest of all prehistoric creatures.
In fact, even after Cuvier, some authors returned to the idea that the pterodactyl was a sea creature, whose wings were used as fins.
But this reluctance is not to surprising, in the classic models of physiology reptiles were assumed far to inferior compared to birds and mammals to be able to fly.
The English palaeontologist Owen accepted the classification as a reptile, but noted that the metabolism of these reptiles only enabled them to an unsafe flight and their possible maximum size would not exceed those of modern vertebrates. In 1847 this theory was refused by the discovery of "Pterodactylus giganteus", an animal with a wingspan of over 4.7 m, much larger than every modern flying bird or mammal.
The naturalist and entomologist Edward Newman (1801-1876), founder of the magazine "The Zoologist", published in 1843 his opinion on the pterodactyls-matter, where he dared to contradict the mighty Cuvier. Given the similarity of the skeleton with today's bats (See also the historical reconstruction of Pterodactylus antiquus by Th. von Soemmerring in 1817) and the need for an endothermic metabolism, pterodactyls ranks among mammals, he concluded. So the famous reconstruction by Newman shows an creature resembling a flying marsupial, a mammalian group that at these times was known to be of ancient origin.

Fig.4. Reconstruction according to Newman´s hypothesis of "Pterodactylus crassirostris" and below "Pterodactylus brevirostris", from NEWMAN 1843.

Despite these attempts, in the following decades the classic reptilian reconstruction will prevail, with animals resembling large winged, scaly lizards. Only in Germany, where Goldfuss interprets minute pits found on the wing membranes as hair follicles, flying reptiles can be reconstructions as more dynamic and "evolved" creatures.

Fig.5. "Group of small flying dragons, or Pterodactyls" from HUTCHINSON 1897.

Fig.6. Rhamphorhynchus by Heinrich Harder (1858-1935), from the collector cards series "Tiere der Urwelt" (Animals of the Prehistoric World), 1916.

Modern research has finally established that pterosaurs are closely related to the archosaurs, and some species were definitely covered by a kind of fur, but the onset of these "hairs", or better "bristles", in the outer epidermis makes these structures only superficial resembling the true hairs of mammals, it's an example of convergent evolution, where feature for thermoregulation were evolved independent in both animal groups.

Fig.7. Specimen of Rhamphorhynchus muensteri (Upper Jurassic, Eichstätt Bavaria).

Fig.8. Anterior, left arm with membrane of Rhamphorhynchus muensteri (Upper Jurassic, Eichstätt Bavaria). On this specimen, nicknamed "Zittel-wing", the palaeontologist Karl Alfred von Zittel in 1882 described the form and the structure of the wings of pterosaurs.

Bibliography:

HUTCHINSON, H.N. (1897): Extinct monsters: A popular account of some of the larger forms of ancient animal life. Chapman & Hall, ld. London
NEWMAN, E. (1843): Note on the Pterodactyle Tribe considered as Marsupial Bats. The Zoologist 1: 129
SEELEY, H.G. (1901): Dragons of the air, an account of extinct flying reptiles. Appleton. New York

P.S. By the way I´m still searching for this paper:
TAQUET & PADIAN (2004): The earliest known restoration of a pterosaur and the philosophical origins of Cuvier’s Ossemens Fossiles. Comptes Rendus Palevol, 3(2): 157-175