| Pterodaustro | |
|---|---|
 | |
| Cast of a fossil specimen at theMuseo Argentino de Ciencias Naturales in Caballito, Buenos Aires, Argentina | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Order: | †Pterosauria |
| Suborder: | †Pterodactyloidea |
| Family: | †Ctenochasmatidae |
| Genus: | †Pterodaustro Bonaparte, 1970 |
| Species: | †P. guinazui |
| Binomial name | |
| †Pterodaustro guinazui Bonaparte, 1970 | |
| Synonyms | |
| |
Pterodaustro (fromGreekpteron,'wing' andLatinauster,'south'[2]) is agenus ofctenochasmatidpterodactyloidpterosaur fromSouth America. Itsfossil remains dated back to theEarly Cretaceous period, about 105 million years ago.
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The first fossils, among them theholotypePVL 2571, a thigh bone, were discovered during the late 1960s byJosé Bonaparte in theLagarcito Formation, situated in theSan Luis Province ofArgentina, and dating from theAlbian. The genus was subsequently reported inChile from the Quebrada La Carreta locality, in the Sierra da Candeleros, Segunda Región de Antofagsta, but this turned out to be erroneous; the fossils belong another pterosaur, the dsungaripteridDomeykodactylus ceciliae.[3] At the Argentine site, the just 50 square meters (540 sq ft) large "Loma delPterodaustro",[4] since then, during several expeditions, over 750Pterodaustro 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.[citation needed]
The genus was named in 1969 byJosé Bonaparte as an as yet undescribednomen nudum. The first description followed in 1970, making the name valid, thetype species beingPterodaustro guiñazui.[2] Thegeneric name is derived from Greekpteron, "wing" andLatinauster, "south (wind)". The elements are combined as a condensedpteron de austro, "wing from the south". Thespecific name honorspaleontologistRomán Guiñazú. It was amended in 1978 byPeter Wellnhofer intoguinazui, becausediacritical signs such as thetilde are not allowed in specific names.[citation needed]
Pterodaustro had a maximum adultwingspan of approximately 3 m (9.8 ft) and a maximum body mass of approximately 9.2 kg (20 lb).[5] 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.[6]
Pterodaustro has a very elongated skull, up to 29 centimeters (11 in) long. The portion in front of the eye sockets comprises 85 percent of skull length. The long snout and lower jaws curve strongly upwards; thetangent 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 straincrustaceans,plankton,algae, and other small creatures from the water.[7] These teeth stand for the most part not in separatealveoli but in two long grooves parallel to the edges of the jaw. They have a length of 3 centimeters (0.098 ft) and are oval in cross-section, with a width of just 0.2 to 0.3 millimeters (0.0079 to 0.0118 in).[8]
At first it was suspected these structures were not true teeth at all, but later research established they were built like normal teeth, includingenamel,dentine and apulp. 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.[8] The upper jaws also carried teeth, but these were very small with a flat conical base and a spatula-formed crown. These teethalso 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.[9] It appears that they were not replaced, unlike the teeth of most other reptiles.[10]
The back of the skull was also rather elongated and in a low position; there are some indications for a low parietal crest.[9]
Pterodaustro probably strained food with its tooth comb, a method called "filter feeding", also practised by modernflamingos.[11] Once it caught its food,Pterodaustro probably mashed it with the small, globular teeth present in its upper jaw.[12]
Like other ctenochasmatoids,Pterodaustro has a long torso and proportionally massive and splayed hindfeet, adaptations forswimming.[12] A recent study suggested that its ankle facilitated movements required for wading behavior.[13]
Robert Bakker suggested that, like flamingos, this pterosaur's diet may have resulted in apink hue.[14]
At least two specimens ofPterodaustro have been found, MIC V263 and MIC V243, withgizzard stones in the stomach cavity, the first ever reported for any pterosaur. These clusters of small stones with angled edges support the idea thatPterodaustro ate mainly small, hard-shelled aquaticcrustaceans using filter-feeding. Such invertebrates are abundant in the sediment of the fossil site.[15]
A study of the growth stages ofPterodaustro 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.[16]
In 2004 aPterodaustroembryo in an egg was reported, specimen MHIN-UNSL-GEO-V246. The egg was elongated, 6 centimeters (2.4 in) long and 22 millimeters (0.87 in) across, and its mainly flexible shell was covered with a thin layer ofcalcite, 0.3 millimeters thick.[17] Three-dimensionally preserved eggs were reported in 2014.[18]
In 2009, possible medullary bone tissue was reported from the largest known femur ofPterodaustro (V 382). Medullary bone tissues are previously only known from modern birds that are laying eggs in reproduction, and some non-avian dinosaurs such asTyrannosaurus rex, so this record would make it the first reported occurrence of a non-dinosaurian medullary bone.[19] In 2021, Padian and Woodward suggested that this tissue might instead represent a crushed endosteal tissue.[20]
Comparisons between thescleral rings ofPterodaustro and modern birds and reptiles suggest that it may have beennocturnal and similar in activity patterns to modernanseriform birds that feed at night,[21] although method of this research is questioned by some researchers.[22]
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 moderngeese andswans.[12]
Bonaparte in 1970 assignedPterodaustro to thePterodactylidae; in 1971 to aPterodaustriidae. However, from 1996cladistic studies byAlexander Kellner andDavid Unwin have shown a position within the familyCtenochasmatidae, together with other filter feeders.[12]
In 2018, a topology by Longrich, Martill and Andres recoveredPterodaustro within the familyCtenochasmatidae, more precisely within the tribe calledPterodaustrini, in a more basal position thanBeipiaopterus andGegepterus.[23]
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