Pterodaustro is a member of Pterosauria, one of the flying reptiles of the Mesozoic.It lived in the Late Jurassic of South America, approximately 125 to 100 million years ago. It had a wingspan of around 1.2 m (4 ft). Pterodaustro has a very distinctive appearance due to its long and upward curving jaws. The skull is around 23 cm (9 in) long, and the bulk of the length is from the jaws. The lower jaw was densely packed with long, fine teeth, with smaller teeth in the upper jaw. These highly specialized teeth and jaws have led paleontologists to conclude that Pterodaustro was a filter feeder. It could have skimmed the surface of the water with an open mouth and caught small organisms, such as plankton, on its sievelike teeth. This is a similar feeding mechanism to that used by baleen whales today (1).
Due to their hollow and fragile bones, pterosaurs are rare fossils. Because of the scarcity of specimens, it can be difficult to draw conclusions about certain aspects of pterosaur biology. Pterodaustro is unique in that many specimens have been discovered, including juveniles. By looking at the internal bone structure of these fossils, paleontologists have been able to describe Pterodaustro growth patterns.
Pterodaustro hatchlings appear to grow at a high rate for approximately 2 years. At this point, they have achieved close to 50% of their adult size. In the bone, this change is reflected by a shift from the deposition of fibrolamellar bone tissue to parallel-fibered bone. Fibrolamellar bone is produced much quicker than parallel-fibered bone and indicates a faster growth speed. The slowing in growth after 2 years could indicate that Pterodaustro begins reserving its energy for reproduction rather than growth at this point (1). This is a pattern seen in many modern reptiles (2). Though Pterodaustro might have achieved sexual maturity at two years, it continued to grow for another four to five years until it reached full size. Growth appears to have ceased in the largest specimens examined, indicating that specimens had reached their maximum adult size (~1.2 m wingspan) (1).
Pterodaustro is part of the order Pterosauria, a group of extinct flying reptiles that lived during the Mesozoic (~228 to 66 million years ago). This is the first known vertebrate group to have achieved flight (1). Due to the scarcity of pterosaur fossils, researchers have previously only had access to incomplete data sets to perform phylogenetic analyses with. This has led to a high level of difficulty in identifying evolutionary relationships among this group. However, incorporation of new data has brought clarity.
Pterodaustro is classified within the group Ctenochasmatidae in recent studies. Ctenochasmatidae is split into two subgroups, Gnathosaurinae and Ctenochasmatinae. Pterodaustro, along with the other filter-feeding pterosaur called Ctenochasma, is part of Ctenochasmatinae. However, Pterodaustro is more closely related to Eosipterus, Beipiaopterus, and Gegepterus (2).
Ctenomastidae is fairly derived within Pterosauria. It is a part of Pterodactyloidea, the “pterodactyl” pterosaurs. Members of this group have short tails, and long hand bones in the wings. Some have crests and many lack teeth, but Pterodaustro retains its teeth and has no evidence of a crest (3).
Much like a modern flamingo, Pterodaustro was likely a filter feeder. It had upwards-curving jaws, which made most of the length of the skull. The lower jaw was packed with hundreds of long and thin teeth, densely packed. The upper jaw had smaller and sparser teeth (1). The teeth on the lower jaw were less than a millimeter in diameter, but around 40 mm long (2). These long teeth were capable of flexing without damage (3). The teeth are much thicker near the front of the lower jaw. Though these teeth are used in filter feeding and serve the same function as baleen in whales, they are not anatomically synonymous. Whale baleen originates from specialized tissue of the jaws, while Pterodaustro used highly derived teeth (4).
Pterodaustro likely used these modified teeth to filter microorganisms from the surface of the water, such as plankton, algae, or small crustaceans (1). The organisms would have become trapped between the closely packed fine teeth of the lower jaws, and then crushed by the more conical upper teeth, or simply swallowed (4).
Modern flamingos have a pink color due to their food supply. Some paleontologists have suggested that Pterodaustro may have been pink as well, since it fed off of similar food sources as a flamingo does (5). However, this assumption is probably incorrect. The use of carotenoids as a pink pigment is a relatively advanced trait in birds, and it is unlikely to have existed in the common ancestor between birds and pterosaurs (6).
To assist with digestion, Pterodaustro may have used gastroliths. Gastroliths are small stones swallowed by an animal that are used to grind food internally and aid in the digestion process. Birds, crocodiles, and seals are all known to use gastroliths among modern animals. Paleontologists think that Pterodaustro may have used gastroliths as well because of fossil evidence. Pterodaustro specimens have been found with gravel preserved inside the abdominal cavity. These have been interpreted as gastroliths due to their position and composition. The size range of these gastroliths is similar to those seen in modern birds. Pterodaustro could have used these gastroliths to internally grind and process any hard-shelled organisms which it ingested (7).
