Pterodactylus

Pterodactylus is a genus of pterosaur (the first to be named and identified as a flying reptile) that lived during the late Jurassic Period. It was a carnivore and probably preyed upon fish and other small animals. Like all pterosaurs, the wings of Pterodactylus were formed by a skin and muscle membrane stretching from its elongated fourth finger to its hind limbs. It was supported internally by collagen fibers and externally by keratinous ridges. Fossils have been discovered in Europe and Africa.

The name derives from the Greek words pteron (πτερόn, meaning 'wing') and daktylos (δάκτυλος, meaning 'finger') and refers to the way in which the wing is supported by one large finger.

Description[]

Pterodactylus is known from over 27 fossil specimens, and though most of those are juveniles, many preserve complete skeletons. The discovery of several specimens with well-preserved soft tissue traces has allowed scientists to faithfully reconstruct the life appearance of Pterodactylus. Pterodactylus was a relatively small pterosaur, with an estimated adult wingspan of about 1.5 meters (4 feet 11 inches) P. antiquus. 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 Ctenochasma, Germanodactylus, and Gnathosaurus.

The skulls of adult Pterodactylus were long and narrow with about 90 large, 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. Unlike related species, the skull and jaws were straight, not curved upwards. A small, hooked beak was present in the very tips of the jaws, with both upper and lower hook no larger than the teeth that surrounded them.

The neck was long, and covered in long, bristle-like pycnofibres. A throat pouch extended from about the middle of the lower jaw to the upper part of the neck.

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. The back of the crest extended upward into a backward-curving cone-shaped structure. The crest was composed mainly of long, hardened fibres (twisted together in a spiral pattern inside the conical part of the crest), and covered in scales. 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. MCZ 1505, a specimen of Pterodactylus antiquus, had a roughly triangular soft tissue crest extending upward above the posterior half of the naso-antorbital fenestra and the orbit; the crest was 44 to 51 mm long (around 38 to 45% of the total length of the skull) and reached a maximum height of 9,5 mm. 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.[4] 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.

The wings were long, and the wing membranes appear to have lacked the furry covering of pycnofibres present in some other pterosaurs (such as Pterorhynchus and Jeholopterus). The wing membrane extended between the fingers and toes as webbing, and a uropatagium (secondary membrane between the feet and tail) was present, as well as a propatagium (membrane between the wrist and shoulder). Both the finger and toe claws were covered in keratin sheaths that extended and curved into sharp hooks well beyond their bony cores.

Paleobiology[]

Year classes[]

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 demonstrated that there is actually only one valid Pterodactylus species, P. antiquus.

The youngest immature Pterodactylus specimens have a small number of teeth (as few as 15), and the teeth have a relatively broad base. The teeth of older specimens are both narrower and more numerous (up to 90 teeth are present in some specimens).

Pterodactylus antiquus 1888 Lydekker R — Diagram of the original *P. antiquus* specimen by Richard Lydekker, 1888.

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. 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.