''Pterodaustro'' is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

of ctenochasmatid

pterodactyloid Pterodactyloidea (derived from the Greek words ''πτερόν'' (''pterón'', for usual ''ptéryx'') "wing", and ''δάκτυλος'' (''dáktylos'') "finger" meaning "winged finger", "wing-finger" or "finger-wing") is one of the two traditional ...

pterosaur Pterosaurs (; from Greek ''pteron'' and ''sauros'', meaning "wing lizard") is an extinct clade of flying reptiles in the order, Pterosauria. They existed during most of the Mesozoic: from the Late Triassic to the end of the Cretaceous (228 ...

from

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the sou ...

. Its

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

remains dated back to the

Early Cretaceous The Early Cretaceous (geochronology, geochronological name) or the Lower Cretaceous (chronostratigraphy, chronostratigraphic name), is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 145& ...

period, about 105 million years ago. The most distinctive characteristic that separates ''Pterodaustro'' from other ctenochasmatids is its bristle-like teeth, a feature not seen in any other pterosaur.

Discovery and naming

The first fossils, among them the

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of seve ...

PVL 2571, a thigh bone, were in the late sixties discovered by Bonaparte in the

Lagarcito Formation The Lagarcito Formation is an Albian geologic formation in Argentina. Pterosaur fossils have been recovered from the formation. The formation overlies the La Cruz Formation and is overlain by the San Roque Formation. The sandstones and mudstone ...

, situated in the

San Luis Province San Luis () is a province of Argentina located near the geographical center of the country (on the 32° South parallel). Neighboring provinces are, from the north clockwise, La Rioja, Córdoba, La Pampa, Mendoza and San Juan. History The cit ...

Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the List of South American countries by area, second-largest ...

, and dating from the

Albian The Albian is both an age of the geologic timescale and a stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early/Lower Cretaceous Epoch/ Series. Its approximate time range is 113.0 ± 1.0 Ma to 100.5 ± 0 ...

. The genus has later also been found in

Chile Chile, officially the Republic of Chile, is a country in the western part of South America. It is the southernmost country in the world, and the closest to Antarctica, occupying a long and narrow strip of land between the Andes to the eas ...

in the Santa Ana Formation. At the Argentine site, the just large "Loma del ''Pterodaustro''", since then, during several expeditions, over 750 ''Pterodaustro'' specimens have been collected, 288 of them having been catalogued until 2008. This makes the species one of the best known pterosaurs, with examples from all growth stages, from egg to adult. The genus was named in 1969 by

José Bonaparte José Fernando Bonaparte (14 June 1928 – 18 February 2020) was an Argentine paleontologist who discovered a plethora of South American dinosaurs and mentored a new generation of Argentine paleontologists . One of the best-known Argentine paleo ...

as an as yet undescribed ''

nomen nudum In taxonomy, a ''nomen nudum'' ('naked name'; plural ''nomina nuda'') is a designation which looks exactly like a scientific name of an organism, and may have originally been intended to be one, but it has not been published with an adequate desc ...

''. The first description followed in 1970, making the name valid, the

type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specim ...

being ''Pterodaustro guiñazui''. The generic name is derived from Greek ''pteron'', "wing" and

Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through ...

''auster'', "south (wind)". The elements are combined as a condensed ''pteron de austro'', "wing from the south". The specific name honors

paleontologist Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (roughly 11,700 years before present). It includes the study of fossi ...

Román Guiñazú. It was amended in 1978 by

Peter Wellnhofer Peter Wellnhofer (born Munich, 1936) is a German paleontologist at the Bayerische Staatssammlung fur Paläontologie in Munich. He is best known for his work on the various fossil specimens of ''Archaeopteryx'' or "Urvogel", the first known bird. W ...

into ''guinazui'', because diacritical signs such as the

tilde The tilde () or , is a grapheme with several uses. The name of the character came into English from Spanish, which in turn came from the Latin '' titulus'', meaning "title" or "superscription". Its primary use is as a diacritic (accent) i ...

are not allowed in specific names.

Description

''Pterodaustro'' has a very elongated skull, up to long. The portion in front of the eye sockets comprises 85 percent of skull length. The long snout and lower jaws curve strongly upwards; the

tangent In geometry, the tangent line (or simply tangent) to a plane curve at a given point is the straight line that "just touches" the curve at that point. Leibniz defined it as the line through a pair of infinitely close points on the curve. Mo ...

at the point of the snout is perpendicular to that of the jaw joint. ''Pterodaustro'' has about a thousand bristle-like modified teeth in its lower jaws that might have been used to strain

crustaceans Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean g ...

plankton Plankton are the diverse collection of organisms found in water (or air) that are unable to propel themselves against a current (or wind). The individual organisms constituting plankton are called plankters. In the ocean, they provide a cruc ...

algae Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular micr ...

, and other small creatures from the water. These teeth stand for the most part not in separate

alveoli Alveolus (; pl. alveoli, adj. alveolar) is a general anatomical term for a concave cavity or pit. Uses in anatomy and zoology * Pulmonary alveolus, an air sac in the lungs ** Alveolar cell or pneumocyte ** Alveolar duct ** Alveolar macrophage * M ...

but in two long grooves parallel to the edges of the jaw. They have a length of and are oval in cross-section, with a width of just . At first it was suspected these structures were not true teeth at all, but later research established they were built like normal teeth, including enamel,

dentine Dentin () (American English) or dentine ( or ) (British English) ( la, substantia eburnea) is a calcified tissue of the body and, along with enamel, cementum, and pulp, is one of the four major components of teeth. It is usually covered by e ...

and a pulp. Despite being made of very hard material, they might still have been flexible to some extent due to their extreme length-width ratio, a bend of up to 45 degrees being possible. The upper jaws also carried teeth, but these were very small with a flat conical base and a spatula-formed crown. These teeth also do not have separate tooth sockets but were apparently held by ligaments in a special tooth pad, that was also covered with small ossicles, or bone plates. The back of the skull was also rather elongated and in a low position; there are some indications for a low parietal crest. ''Pterodaustro'' had an adult

wingspan The wingspan (or just span) of a bird or an airplane is the distance from one wingtip to the other wingtip. For example, the Boeing 777–200 has a wingspan of , and a wandering albatross (''Diomedea exulans'') caught in 1965 had a wingspan o ...

of approximately . Its hindlimbs are rather robust and its feet large. Its tail is uniquely elongated for a pterodactyloid, containing twenty-two caudal vertebrae, whereas other members of this group have at most, sixteen.

Paleobiology

''Pterodaustro'' probably strained food with its tooth comb, a method called "filter feeding", also practised by modern flamingos. Once it caught its food, ''Pterodaustro'' probably mashed it with the small, globular teeth present in its upper jaw. Like other ctenochasmatoids, ''Pterodaustro'' has a long torso and proportionally massive and splayed hindfeet, adaptations for

swimming Swimming is the self-propulsion of a person through water, or other liquid, usually for recreation, sport, exercise, or survival. Locomotion is achieved through coordinated movement of the limbs and the body to achieve hydrodynamic thrust that r ...

.Witton, Mark P. (2013). Pterosaurs: Natural History, Evolution, Anatomy. Princeton University Press. . Robert Bakker suggested that, like flamingos, this pterosaur's diet may have resulted in a

pink Pink is the color of a namesake flower that is a pale tint of red. It was first used as a color name in the late 17th century. According to surveys in Europe and the United States, pink is the color most often associated with charm, politeness, ...

hue. At least two specimens of ''Pterodaustro'' have been found, MIC V263 and MIC V243, with gizzard stones in the stomach cavity, the first ever reported for any pterosaur. These clusters of small stones with angled edges support the idea that ''Pterodaustro'' ate mainly small, hard-shelled aquatic

crustacean Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapoda, decapods, ostracoda, seed shrimp, branchiopoda, branchiopods, argulidae, fish lice, krill, remipedes, isopoda, isopods, barnacles, copepods, ...

s using filter-feeding. Such invertebrates are abundant in the sediment of the fossil site.Codorniú, L., Chiappe, L.M., Arcucci, A., and Ortiz-Suarez, A. (2009). "First occurrence of gastroliths in Pterosauria (Early Cretaceous, Argentina)". ''XXIV Jornadas Argentinas de Paleontología de Vertebrados'' A study of the growth stages of ''Pterodaustro'' concluded that juveniles grew relatively fast in their first two years, attaining about half of the adult size. Then they reached sexual maturity, growing at a slower rate for four to five years until there was a determinate growth stop. In 2004 a ''Pterodaustro''

embryo An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male spe ...

in an egg was reported, specimen MHIN-UNSL-GEO-V246. The egg was elongated, long and across, and its mainly flexible shell was covered with a thin layer of

calcite Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on the Mohs scale of mineral hardness, based on scratc ...

, 0.3 millimeters thick. Three-dimensionally preserved eggs were reported in 2014. Comparisons between the

scleral ring Sclerotic rings are rings of bone found in the eyes of many animals in several groups of vertebrates, except for mammals and crocodilians. They can be made up of single bones or multiple segments and take their name from the sclera. They are beli ...

s of ''Pterodaustro'' and modern birds and reptiles suggest that it may have been

nocturnal Nocturnality is an animal behavior characterized by being active during the night and sleeping during the day. The common adjective is "nocturnal", versus diurnal meaning the opposite. Nocturnal creatures generally have highly developed sens ...

and similar in activity patterns to modern anseriform birds that feed at night. Because of its long torso and neck and comparatively short legs, ''Pterodaustro'' was unique among pterosaurs in having difficulties to launch. Even with the pterosaurian quadrupedal launching mechanism, it would have required frantic and fairly-low angled take-offs possible only in open areas, much like modern

geese A goose ( : geese) is a bird of any of several waterfowl species in the family Anatidae. This group comprises the genera '' Anser'' (the grey geese and white geese) and ''Branta'' (the black geese). Some other birds, mostly related to the she ...

and

swan Swans are birds of the family Anatidae within the genus ''Cygnus''. The swans' closest relatives include the geese and ducks. Swans are grouped with the closely related geese in the subfamily Anserinae where they form the tribe Cygnini. Som ...

Phylogeny

Bonaparte in 1970 assigned ''Pterodaustro'' to the Pterodactylidae; in 1971 to a Pterodaustriidae. However, from 1996

cladistic Cladistics (; ) is an approach to biological classification in which organisms are categorized in groups ("clades") based on hypotheses of most recent common ancestry. The evidence for hypothesized relationships is typically shared derived char ...

studies by

Alexander Kellner Alexander Wilhelm Armin Kellner (born September 26, 1961) is a Brazilian geologist and paleontologist who is a leading expert in the field of studying pterosaurs. His research has focused mainly on fossil reptiles from the Cretaceous Period, i ...

and

David Unwin David (; , "beloved one") (traditional spelling), , ''Dāwūd''; grc-koi, Δαυΐδ, Dauíd; la, Davidus, David; gez , ዳዊት, ''Dawit''; xcl, Դաւիթ, ''Dawitʿ''; cu, Давíдъ, ''Davidŭ''; possibly meaning "beloved one". w ...

have shown a position within the family

Ctenochasmatidae Ctenochasmatidae is a group of pterosaurs within the suborder Pterodactyloidea. They are characterized by their distinctive teeth, which are thought to have been used for filter-feeding. Ctenochasmatids lived from the Late Jurassic to the Early C ...

, together with other filter feeders. Pterodaustro guinazaui

In 2018, a topology by Longrich, Martill and Andres recovered ''Pterodaustro'' within the family

, more precisely within the tribe called Pterodaustrini, in a more basal position than ''

Beipiaopterus ''Beipiaopterus'' is a genus of ctenochasmatid pterosaur from the Early Cretaceous period (Aptian stage) of what is now the Yixian Formation of the China. The genus was named in 2003 by Lü Junchang. The generic name is derived from Beipiao C ...

'' and ''

Gegepterus ''Gegepterus'' is a genus of ctenochasmatid pterosaur from the Early Cretaceous period of what is now the Yixian Formation of Liaoning, China. Only one species is known, ''G. changi''. History and etymology The genus was named in 2007 by Wang X ...

''.Longrich, N.R., Martill, D.M., and Andres, B. (2018)
Late Maastrichtian pterosaurs from North Africa and mass extinction of Pterosauria at the Cretaceous-Paleogene boundary.
''PLoS Biology'', 16(3): e2001663.

References

External links