Pterodactylus

''Pterodactylus'' (from Greek () meaning 'winged finger') is an extinct genus of pterosaurs. It is thought to contain only a single species, ''Pterodactylus antiquus'', which was the first pterosaur to be named and identified as a flying reptile.

Fossil remains of ''Pterodactylus'' have primarily been found in the Solnhofen limestone of Bavaria, Germany, which dates from the Late Jurassic period (early Tithonian stage), about 150.8 to 148.5 million years ago. More fragmentary remains of ''Pterodactylus'' have tentatively been identified from elsewhere in Europe and in Africa.

''Pterodactylus'' was a generalist carnivore that probably fed on a variety of invertebrates and vertebrates. Like all pterosaurs, ''Pterodactylus'' had wings formed by a skin and muscle membrane stretching from its elongated fourth finger to its hind limbs. It was supported internally by collagen fibres and externally by keratinous ridges. ''Pterodactylus'' was a small pterosaur compared to other famous genera such as ''Pteranodon'' and ''Quetzalcoatlus'', and it also lived earlier, during the Late Jurassic period, while both ''Pteranodon'' and ''Quetzalcoatlus'' lived during the Late Cretaceous. ''Pterodactylus'' lived alongside other small pterosaurs such as the well-known '' Rhamphorhynchus'', as well as other genera such as '' Scaphognathus'', '' Anurognathus'' and '' Ctenochasma''. ''Pterodactylus'' is classified as an early-branching member of the ctenochasmatid lineage, within the pterosaur clade Pterodactyloidea.

Discovery and history

The type specimen of the animal now known as ''Pterodactylus antiquus'' was the first pterosaur fossil ever to be identified. The first ''Pterodactylus'' specimen was described by the Italian scientist in 1784, based on a fossil skeleton that had been unearthed from the Solnhofen limestone of Bavaria. Collini was the curator of the , or nature cabinet of curiosities (a precursor to the modern concept of the natural history museum), in the palace of Charles Theodore, Elector of Bavaria at Mannheim. The specimen had been given to the collection by Count around 1780, having been recovered from a lithographic limestone quarry in . The actual date of the specimen's discovery and entry into the collection is unknown however, and it was not mentioned in a catalogue of the collection taken in 1767, so it must have been acquired at some point between that date and its 1784 description by Collini. This makes it potentially the earliest documented pterosaur find; the "Pester Exemplar" of the genus '' Aurorazhdarcho'' was described in 1779 and possibly discovered earlier than the Mannheim specimen, but it was at first considered to be a fossilized crustacean, and it was not until 1856 that this species was properly described as a pterosaur by German paleontologist .

In his first description of the Mannheim specimen, Collini did not conclude that it was a flying animal. In fact, Collini could not fathom what kind of animal it might have been, rejecting affinities with the birds or the bats. He speculated that it may have been a sea creature, not for any anatomical reason, but because he thought the ocean depths were more likely to have housed unknown types of animals. The idea that pterosaurs were aquatic animals persisted among a minority of scientists as late as 1830, when the German zoologist Johann Georg Wagler published a text on "amphibians" which included an illustration of ''Pterodactylus'' using its wings as flippers. Wagler went so far as to classify ''Pterodactylus'', along with other aquatic vertebrates (namely plesiosaurs, ichthyosaurs, and monotremes), in the class Gryphi, between birds and mammals.

The German/French scientist Johann Hermann was the one who first stated that ''Pterodactylus'' used its long fourth finger to support a wing membrane. Back in March 1800, Hermann alerted the prominent French scientist Georges Cuvier to the existence of Collini's fossil, believing that it had been captured by the occupying armies of Napoleon and sent to the French collections in Paris (and perhaps to Cuvier himself) as war booty; at the time special French political commissars systematically seized art treasures and objects of scientific interest. Hermann sent Cuvier a letter containing his own interpretation of the specimen (though he had not examined it personally), which he believed to be a mammal, including the first known life restoration of a pterosaur. Hermann restored the animal with wing membranes extending from the long fourth finger to the ankle and a covering of fur (neither wing membranes nor fur had been preserved in the specimen). Hermann also added a membrane between the neck and wrist, as is the condition in bats. Cuvier agreed with this interpretation, and at Hermann's suggestion, Cuvier became the first to publish these ideas in December 1800 in a very short description. However, contrary to Hermann, Cuvier was convinced the animal was a reptile. The specimen had not in fact been seized by the French. Rather, in 1802, following the death of Charles Theodore, it was brought to Munich, where Baron Johann Paul Carl von Moll had obtained a general exemption of confiscation for the Bavarian collections. Cuvier asked von Moll to study the fossil but was informed it could not be found. In 1809 Cuvier published a somewhat longer description, in which he named the animal ''Petro-Dactyle'', this was a typographical error however, and was later corrected by him to ''Ptéro-Dactyle''. He also refuted a hypothesis by Johann Friedrich Blumenbach that it would have been a shore bird. Cuvier remarked: "It is not possible to doubt that the long finger served to support a membrane that, by lengthening the anterior extremity of this animal, formed a good wing."

Contrary to von Moll's report, the fossil was not missing; it was being studied by Samuel Thomas von Sömmerring, who gave a public lecture about it on December 27, 1810. In January 1811, von Sömmerring wrote a letter to Cuvier deploring the fact that he had only recently been informed of Cuvier's request for information. His lecture was published in 1812, and in it von Sömmerring named the species ''Ornithocephalus antiquus''. The animal was described as being both a bat, and a form in between mammals and birds, i.e. not intermediate in descent but in "affinity" or archetype. Cuvier disagreed, and the same year in his ''Ossemens fossiles'' provided a lengthy description in which he restated that the animal was a reptile. It was not until 1817 that a second specimen of ''Pterodactylus'' came to light, again from Solnhofen. This tiny specimen was that year described by von Sömmerring as '' Ornithocephalus brevirostris'', named for its short snout, now understood to be a juvenile character (this specimen is now thought to represent a juvenile specimen of a different genus, probably '' Ctenochasma''). He provided a restoration of the skeleton, the first one published for any pterosaur. This restoration was very inaccurate, von Sömmerring mistaking the long metacarpals for the bones of the lower arm, the lower arm for the humerus, this upper arm for the breast bone and this sternum again for the shoulder blades. Sömmerring did not change his opinion that these forms were bats and this "bat model" for interpreting pterosaurs would remain influential long after a consensus had been reached around 1860 that they were reptiles. The standard assumptions were that pterosaurs were quadrupedal, clumsy on the ground, furred, warmblooded and had a wing membrane reaching the ankle. Some of these elements have been confirmed, some refuted by modern research, while others remain disputed.

In 1815, the generic name ''Ptéro-Dactyle'' was latinized to ''Pterodactylus'' by Constantine Samuel Rafinesque. Unaware of Rafinesque's publication however, Cuvier himself in 1819 latinized the name ''Ptéro-Dactyle'' again to ''Pterodactylus'', but the specific name he then gave, ''longirostris'', has to give precedence to von Sömmerring's ''antiquus''. In 1888, English naturalist Richard Lydekker designated ''Pterodactylus antiquus'' as the type species of ''Pterodactylus'', and considered ''Ornithocephalus antiquus'' a synonym. He also designated specimen BSP AS.I.739 as the holotype of the genus.

Description

''Pterodactylus'' is known from over 30 fossil specimens, and though most belong to juveniles, many preserve complete skeletons. ''Pterodactylus antiquus'' was a relatively small pterosaur, with an estimated adult wingspan of about , based on the only known adult specimen, which is represented by an isolated skull. Other "species" were once thought to have been smaller. However, these smaller specimens have been shown to represent juveniles of ''Pterodactylus'', as well as its contemporary relatives including ''Ctenochasma'', ''Germanodactylus'', '' Aurorazhdarcho'', '' Gnathosaurus'', and hypothetically '' Aerodactylus'' if this genus is truly valid.

The skulls of adult ''Pterodactylus'' were long and thin, with about 90 narrow and conical teeth. The teeth extended back from the tips of both jaws, and became smaller farther away from the jaw tips, this was unlike the ones seen in most relatives, where teeth were absent in the upper jaw tip, and were relatively uniform in size. The teeth of ''Pterodactylus'' also extended farther back into the jaw compared to close relatives, and some were present below the front of the ''nasoantorbital fenestra'', which is the largest opening in the skull. Another autapomorphy that ''Pterodactylus'' has is that the skull and jaws were straight, which are unlike the upwardly curved jaws seen in the related ctenochasmatids.

''Pterodactylus'', like related pterosaurs, had a crest on its skull composed mainly of soft tissues. In adult ''Pterodactylus'', this crest extended between the back edge of the antorbital fenestra and the back of the skull. In at least one specimen, the crest had a short bony base, also seen in related pterosaurs like ''Germanodactylus''. Solid crests have only been found on large, fully adult specimens of ''Pterodactylus'', indicating that this was a display structure that became larger and more well developed as individuals reached maturity. In 2013, pterosaur researcher S. Christopher Bennett noted that other authors claimed that the soft tissue crest of ''Pterodactylus'' extended backward behind the skull; Bennett himself, however, didn't find any evidence for the crest extending past the back of the skull. Two specimens of ''P. antiquus'' (the holotype specimen BSP AS I 739 and the incomplete skull BMMS 7, the largest known skull of ''P. antiquus'') have a low bony crest on their skulls; in BMMS 7 it is 47.5 mm long (1.87 inches, more or less 24% of the estimated total length of its skull) and has a maximum height of 0.9 mm (0.035 inches) above the orbit. Several specimens previously referred to ''P. antiquus'' preserved evidence of the soft tissue extensions of these crests, including an "occipital lappet", a flexible, tab-like structure extending from the back of the skull. Most of these specimens have been reclassified in the related species ''Aerodactylus scolopaciceps'', which may however be nothing more than a junior synonym. Even if ''Aerodactylus'' were valid, at least one specimen with these features is still considered to belong to ''Pterodactylus'', BSP 1929 I 18, which has an occipital lappet similar to the proposed ''Aerodactylus'' definition, and also possesses a small triangular soft tissue crest with the peak of the crest positioned above the eyes.

Paleobiology

Life history

Like other pterosaurs (most notably '' Rhamphorhynchus''), ''Pterodactylus'' specimens can vary considerably based on age or level of maturity. Both the proportions of the limb bones, size and shape of the skull, and size and number of teeth changed as the animals grew. Historically, this has led to various growth stages (including growth stages of related pterosaurs) being mistaken for new species of ''Pterodactylus''. Several detailed studies using various methods to measure growth curves among known specimens have suggested that there is actually only one valid species of ''Pterodactylus'', ''P. antiquus''.

The youngest immature specimens of ''Pterodactylus antiquus'' (alternately interpreted as young specimens of the distinct species ''P. kochi'') have a small number of teeth, as few as 15 in some, and the teeth have a relatively broad base. The teeth of other ''P. antiquus'' specimens are both narrower and more numerous (up to 90 teeth are present in several specimens).

''Pterodactylus'' specimens can be divided into two distinct year classes. In the first year class, the skulls are only in length. The second year class is characterized by skulls of around long, but are still immature however. These first two size groups were once classified as juveniles and adults of the species ''P. kochi'', until further study showed that even the supposed "adults" were immature, and possibly belong to a distinct genus. A third year class is represented by specimens of the "traditional" ''P. antiquus'', as well as a few isolated, large specimens once assigned to ''P. kochi'' that overlap ''P. antiquus'' in size. However, all specimens in this third year class also show sign of immaturity. Fully mature ''Pterodactylus'' specimens remain unknown, or may have been mistakenly classified as a different genus.

Growth and breeding seasons

The distinct year classes of ''Pterodactylus antiquus'' specimens show that this species, like the contemporary ''Rhamphorhynchus muensteri'', likely bred seasonally and grew consistently during its lifetime. A new generation of 1st year class ''P. antiquus'' would have been produced seasonally, and reached 2nd-year size by the time the next generation hatched, creating distinct 'clumps' of similarly-sized and aged individuals in the fossil record. The smallest size class probably consisted of individuals that had just begun to fly and were less than one year old. The second year class represents individuals one to two years old, and the rare third year class is composed of specimens over two years old. This growth pattern is similar to modern crocodilians, rather than the rapid growth of modern birds.

Daily activity patterns

Comparisons between the scleral rings of ''Pterodactylus antiquus'' and modern birds and reptiles suggest that it may have been diurnal. This may also indicate niche partitioning with contemporary pterosaurs inferred to be nocturnal, such as ''Ctenochasma'' and ''Rhamphorhynchus''.

Diet

Based on the shape, size, and arrangement of its teeth, ''Pterodactylus'' has long been recognized as a carnivore specializing in small animals. A 2020 study of pterosaur tooth wear supported the hypothesis that ''Pterodactylus'' preyed mainly on invertebrates and had a generalist feeding strategy, indicated by a relatively high bite force.Bestwick, J., Unwin, D.M., Butler, R.J. et al. Dietary diversity and evolution of the earliest flying vertebrates revealed by dental microwear texture analysis. Nat Commun 11, 5293 (2020). https://doi.org/10.1038/s41467-020-19022-2

Paleoecology

Specimens of ''Pterodactylus'' have been found mainly in the Solnhofen limestone (geologically known as the Altmühltal Formation) of Bavaria, Germany. The main composition of this formation is fine-grained limestone that originated mainly from the nearby towns Solnhofen and Eichstätt, which is formed by mud silt deposits. The Solnhofen Limestone is a diverse Lagerstätte that contains a wide range of different creatures, including highly detailed fossilized imprints of soft bodied organisms such as jellyfishes. Abundant specimens of pterosaurs similar to ''Pterodactylus'' were also found within the formation, these include the rhamphorhynchids ''Rhamphorhynchus'' and '' Scaphognathus'', several gallodactylids such as ''Aerodactylus'', '' Ardeadactylus'', ''Aurorazhdarcho'' and '' Cycnorhamphus'', the ctenochasmatids ''Ctenochasma'' and ''Gnathosaurus'', the anurognathid '' Anurognathus'', the germanodactylid ''Germanodactylus'', as well as the basal euctenochasmatian '' Diopecephalus''. Fossil remains of the dinosaurs ''Archaeopteryx'' and '' Compsognathus'' were also found within the limestone, these specimens were related to early evolution of feathers, since they were some of the only ones that had them during the Jurassic period. Various lizard remains were also found alongside those of ''Pterodactylus'', with several specimens assigned to ''Ardeosaurus'', ''Bavarisaurus

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