Pterodactylus

Pterodactylus
Sub-adult type specimen of P. antiquus, Navarian State Collection for Palaeontology and Geology
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Order:	†Pterosauria
Suborder:	†Pterodactyloidea
Family:	†Pterodactyldae
Genus:	†Pterodactylus Cuvier, 1809
Type species
†Pterodactylus antiquus Sömmerring, 1812
Species
†Pterodactylus antiquus (Sömmerring, 1812) †Pterodactylus kochi? (Wagner, 1837)
Synonyms
Genus synonymy Ornithocephalus Sömmering, 1812 Pterotherium Fischer, 1813[1] Macrotrachelus Giebel, 1852 Diopecephalus? Seeley, 1871 Species synonymy Pterodactylus longirostris Cuvier, 1819 Pterodactylus crocodilocephaloides Ritgen, 1826 Ornithocephalus kochi? Wagner, 1837 Pterodactylus mayeri Muenster, 1842 Pterodactylus spectabilis Meyer, 1861 Pterodactylus westmani Wiman, 1925 Pterodactylus cormoranus Döderlein, 1929

Pterodactylus (/ˌtɛrəˈdæktᵻləs/ TERR-ə-DAK-til-əs, from the Greek πτεροδάκτυλος, pterodaktulos, meaning "winged finger") is a genus of pterosaurs, whose members are popularly known as pterodactyls ( /ˌtɛrəˈdæktᵻlz/). It is currently thought to contain only a single species, Pterodactylus antiquus, the first pterosaur species to be named and identified as a flying reptile.

The fossil remains of this species have been found primarily in the Solnhofen limestone of Bavaria, Germany, dated to the late Jurassic Period (early Tithonian), about 150.8–148.5 million years ago,^[2] though more fragmentary remains have been tentatively identified from elsewhere in Europe and in Africa.

It was a carnivore and probably preyed upon fish and other small animals. 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.

Description

Size of the sub-adult holotype (blue) and adult (green) specimens in both flying and standing postures, compared with a human

Pterodactylus is known from over 30 fossil specimens, and though most of those are juveniles, many preserve complete skeletons.^[3][4] Pterodactylus antiquus was a relatively small pterosaur, with an estimated adult wingspan of about 1.04 meters (3 feet 5 inches) (the only known adult specimen is represented by an isolated skull).^[3] Other "species" were once thought to be smaller. However, these smaller specimens have been shown to represent juveniles of Pterodactylus, as well as its contemporary relatives including Ctenochasma, Germanodactylus, Aerodactylus, Aurorazhdarcho, and Gnathosaurus.^[5]

The skulls of adult Pterodactylus were long and thin with about 90 narrow, conical teeth. The teeth extended back from the tips of both jaws, and became smaller farther away from the jaw tips (unlike some relatives, where teeth were absent in the upper jaw tip and were relatively uniform in size). The teeth extended farther back into the jaw than in close relatives, as some were present below the front of the nasoantorbital fenestra, the largest opening in the skull.^[3] Unlike related species, the skull and jaws were straight, not curved upwards.^[6]

Reconstructed life appearance

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 (the largest opening in the skull) 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.^[3][7] Bennett (2013) 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.^[3] 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 (more or less 24% of the estimated total length of its skull) and has a maximum height of 0.9 mm above the orbit.^[3]

Paleobiology

Year classes

Juvenile specimen of P. antiquus

Like other pterosaurs (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 Pterodactylus species, P. antiquus.^[6]

The youngest immature Pterodactylus antiquus specimens (alternately interpreted as young specimens of the distinct species P. kochi) have a small number of teeth (as few as 15), and the teeth have a relatively broad base.^[4] The teeth of other P. antiquus specimens are both narrower and more numerous (up to 90 teeth are present in some specimens).^[6]

Pterodactylus specimens can be divided into two distinct year classes. In the first year class, the skulls are only 15-45mm in length. The second year class is characterized by skulls 55-95mm long, but still immature. 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.^[4]

Growth and breeding seasons

Fossil pelvis of a large specimen, referred to the dubious species P. grandipelvis

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.^[4][8] 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.^[4]

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.^[9]

History

Original copper engraving of the P. antiquus holotype by Egid Verhelst II and published by Cosimo Collini, 1784

The type specimen of the animal now known as Pterodactylus antiquus was one of the first pterosaur fossils ever to be identified. The first Pterodactylus specimen was described by the Italian scientist Cosimo Alessandro Collini in 1784, based on a fossil skeleton that had been unearthed from the Solnhofen limestone of Bavaria. Collini was the curator of the "Naturalienkabinett", or nature cabinet (a precursor to the modern concept of the natural history museum), in the palace of Charles Theodore, Elector of Bavaria at Mannheim.^[10] The specimen had been given to the collection by Count Friedrich Ferdinand zu Pappenheim, probably around 1780, having been recovered from a lithographic limestone quarry in Eichstätt.^[11] The actual date of the specimen's discovery and entry into the collection is unknown. It was not mentioned in a catalogue of the collection taken in 1767 and so 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 Pterodactylus micronyx was described in 1779 and possibly discovered earlier than the Mannheim specimen, but it was at first considered to be a fossil crustacean.^[12]

Wagler's 1830 restoration of an aquatic Pterodactylus

Collini, in his first description of the Mannheim specimen, 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.^[13][14] 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.^[15]

Hermann's original life restoration, the first of any pterosaur, 1800

It was the German/French scientist Johann Hermann who first stated that Pterodactylus used its long fourth finger to support a wing membrane. In March 1800, Hermann alerted the French scientist George 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.^[14] 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.]"^[16] 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 a "ptero-dactyle" and refuted a hypothesis by Johann Friedrich Blumenbach that it would have been a shore bird.

Von Soemmerring's incorrect 1817 restoration of P. brevirostris

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 27 December 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.^[17] The animal was described as being both a mammal, 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.^[18] 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 Soemmerring 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^[3]). He provided a restoration of the skeleton, the first one published for any pterosaur.^[14] This restoration was very inaccurate, von Soemmerring 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.^[19] Soemmerring 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.^[20] Some of these elements have been confirmed, some refuted by modern research, while others remain disputed.

Classification

A P. antiquus specimen (AMNH 1942) showing muscle impressions

The genus now known as Pterodactylus was originally named Petro-Dactyle by Cuvier in 1809,^[21] though this was a typographical error, later corrected by him to Ptéro-Dactyle.^[14] In 1812, Samuel Thomas von Sömmerring named the same specimen Ornithocephalus antiquus. The genus name was emended to the current Pterodactylus by Constantine Samuel Rafinesque in 1815. Unaware of Rafinesque's publication, Cuvier himself in 1819 again emended the genus name,^[22] but the specific name he then gave, longirostris, has to give precedence to von Soemmerring's antiquus. In 1888 Richard Lydekker designated Pterodactylus antiquus the type species. The original specimen is the holotype of the genus, BSP No. AS.I.739.

Hermann von Meyer, in 1830, used the name Pterodactyli to contain Pterodactylus and other pterosaurs known at the time. This was emended to the family Pterodactylidae by Prince Charles Lucien Bonaparte in 1838. This family has more recently been used to refer to many similar species from Germany and elsewhere, though recent studies suggest it may be a paraphyletic or polyphyletic unnatural grouping with respect to more advanced members of the Ctenochasmatoidea (or Archaeopterodactyloidea).^[23][24]

Below is a cladogram showing the results of a phylogenetic analysis presented by Andres, Clark & Xu, 2014.^[25]

Species

Specimen of P. kochi, Bürgermeister Müller Museum

Pterodactylus kochi

Numerous species have been assigned to Pterodactylus in the years since its discovery. In the first half of the nineteenth century any new pterosaur species would be named Pterodactylus, which thus became a typical "waste-basket taxon". Even after clearly different forms had later been given their own generic name, new species would be created from the very productive late Jurassic German sites, often based on only slightly different material.

Around 1980, subsequent revisions by Peter Wellnhofer had reduced the number of recognized species to about half a dozen. Many species assigned to Pterodactylus had been based on juvenile specimens, and subsequently been recognized as immature individuals of other species or genera. By the 1990s it was understood that this was even true for part of the remaining species. P. elegans, for example, was found by numerous studies to be an immature Ctenochasma.^[6] Another species of Pterodactylus originally based on small, immature specimens was P. micronyx. However, it has been difficult to determine exactly of what genus and species P. micronyx might be the juvenile form. Stéphane Jouve, Christopher Bennett and others had once suggested that it probably belonged either to Gnathosaurus subulatus or one of the Ctenochasma species,^[5][6] though after additional research Bennett assigned it to the genus Aurorazhdarcho.^[3] Another species with a complex history is P. longicollum, named by von Meyer in 1854, based on a large specimen with a long neck and fewer teeth. Many researchers, including David Unwin, have found P. longicollum to be distinct from P. kochi and P. antiquus. Unwin found P. longicollum to be closer to Germanodactylus and therefore requiring a new genus name.^[23] It has sometimes been placed in the genus Diopecephalus because Harry Govier Seeley based this genus partly on the P. longicollum material. However, it was shown by Bennett that the type specimen later designated for Diopecephalus was a fossil belonging to P. kochi, and no longer thought to be separate from Pterodactylus. Diopecephalus is therefore a synonym of Pterodactylus, and as such is unavailable for use as a new genus for "P." longicollum.^[26] "P." longicollum was eventually made the type species of a separate genus Ardeadactylus.^[3] In 2014, P. scolopaciceps, formerly regarded as a junior synonym, was moved to its own genus, Aerodactylus.^[27]

Juvenile type specimen of P. kochi

The only well-known and well-supported species left by the first decades of the 21st century were P. antiquus and P. kochi. However, most studies between 1995 and 2010 found little reason to separate even these two species, and treated them as synonymous.^[23][26] In 1996, Bennett suggested that the differences between specimens of P. kochi and P. antiquus could be explained by differences in age. In a 2004 paper, Jouve used a different method of analysis and recovered the same result, showing that the "distinctive" features of P. kochi were age-related, and using mathematical comparison to show that the two forms are different growth stages of the same species.^[6] An additional review of the specimens published in 2013 demonstrated that some of the supposed differences between P. kochi and P. antiquus were due to measurement errors, further supporting their synonymy.^[3] However, in 2014 Steven Vidovic and David Martill concluded that the differences between P. kochi and P. antiquus, including the shorter neck vertebrae of P. kochi, were significant enough to separate them. Vidovic and Martill also performed a phylogenetic analysis which treated all relevant specimens as distinct units, and found the P. kochi type specimen did not form a clade with that of P. antiquus. They concluded that the genus Diopecephalus could be returned to use to distinguish "P". kochi from P. antiquus, and further suggested that Germanodactylus rhamphastinus was probably the adult form of "P." kochi, due in part to its short neck vertebrae and much larger size.^[27]

List of species and synonyms

During its over-200-year history, the various species of Pterodactylus have gone through a number of changes in classification, and thus have acquired a large number of synonyms. Additionally, a number of species assigned to Pterodactylus are based on poor remains that have proven difficult to assign to one species or another, and are therefore considered nomina dubia ("doubtful names"). The following list includes names that are based on German material presently, or until recently, thought to be pertaining to Pterodactylus proper and names based on other material that has as yet not been assigned to other genera.

References

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