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