Proavis is ahypothetical extinct species or hypothetical extincttaxon. The term was coined in the early 20th century in an attempt to support and explain the hypothetical evolutionary steps and anatomical adaptations leading from non-aviantheropoddinosaurs tobirds. The term has also been used by defenders of thethecodontian origin of birds.
The term "Proavis" was first coined, although under the form "Pro-Aves", byEnglishosteologist andzoologistWilliam Plane Pycraft in "The Origin of Birds", a 1906 article published in the magazineKnowledge and Scientific News.[1] Pycraft added to his article his own drawn depiction of the hypothetical animal, a restoration entitled "One of the Pro-Aves". Pycraft's "Pro-Avis" (singular of "Pro-Aves") wasarboreal, as suggestedProfessor Osborn six years before, in 1900, in an article dealing with the hypothetical common ancestors of dinosaurs and birds.[2][3] Pycraft assumed that birds had developed as tree-dwelling dinosaurs, gliding on membranes between the limbs and the trunk. These membranes would gradually have been covered by increasingly more elongated scales, which eventually would have evolved into feathers.
A year after Pycraft's article, theHungarianaristocrat andpaleontologistFranz Nopcsa, who, while residing at London, had seen Pycraft's restoration, drew his own vision of the animal, a picture and article[4] published in a 1907 issue of theProceedings of the Zoological Society of London (an English science publication nowadays known asJournal of Zoology). But this time, for his own "Pro-Avis" restoration, Nopcsa suggested acursorial origin, not arboreal. The "Pro-Avis" would thus have been a running animal, accelerating and prolonging its jumps by flapping with feathered forelimbs. There is a model of Nopcsa's restoration, still preserved, and recently restored, in theGrant Museum of Zoology,[5] the only remaining university zoological museum in London.[6]
When Pycraft published his bookA History of Birds, in 1910, he reinserted his 1906 restorationOne of the Pro-Aves (in page 39).[7] In the following years, as of 1913,Danish artist and amateurzoologistGerhard Heilmann also used and popularised the termProavis, this time presenting the public with more accurate and anatomically probable drawings. Heilmann favoured a scientific model in which the assumedProavis was arboreal and of thecodontian descent, thus not a dinosaur.
In 1961,Czech paleontologistJosef Augusta included "Proavis" in his bookPrehistoric Birds and Reptiles. The animal illustration, as were all illustrations in the book, was painted byZdeněk Burian.[8]
During the 1970s the work ofJohn Ostrom, breathing new life into the hypothesis that birds were dinosaurs, revived the interest in the direct ancestors of birds. Ostrom assumed these were cursorial. An illustration of a running dinosaur explicitly indicated as a "Proavis" was in 1976 published byDieter Stefan Peters.[9]
In 1991 and 1996 "proavis" or "protoavis" models were proposed by respectivelySamuel Tarsitano[10] andAlan Feduccia,[11] both adherents of the "thecodont" hypothesis about the origins of birds. These "proaves" were supposed to be arboreal, with short necks, long trunks, sprawling legs, non-elongated hindlimbs, small hands and feet, small general size, and gliding on membranes. Feduccia's "protoavis" had membranes on the forelimbs only and was fashioned on the model ofMegalancosaurus.[11]
The termProavis was used again in 1999, when Joseph Garner, Graham Taylor, andAdrian Thomas proposed their "pouncing proavis model", an hypothesis entailing that the origin of avian flight rested in a predatory behaviour, the "proavis" jumping on its prey from trees (seepouncing proavis model inOrigin of avian flight).[12]
In his 2002 bookDinosaurs of the Air,Gregory S. Paul tried to conceptually model a "pro-avian". In his view the direct ancestors of birds cannot have been completely arboreal, because in that case they would probably have used membranes to fly. He thought they must have represented an intermediate ecological stage, in which the hindlimbs still had largely cursorial adaptations whereas the arms had been elongated in order to climb. Feathers, originally serving the insulation of an already warm-blooded animal, would by elongation have turned the arms into wings in order to fly. More generally, the proavians would, in view of their basal theropod forebears and bird descendants, have been typified by long necks, a short trunk, long fingers with opposable digits, a decoupling of thelocomotor functions of the forelimbs and hindlimbs, a lack of apropatagium, a shallow tail, and a weight of about one kilogramme. Paul illustrated his analysis with a skeletal diagram, accompanied by alife illustration of a "proavis".[13] When in 2013Aurornis was described, at the time the most basal known member of theAvialae, the group consisting of birds and their closest relatives, the Italian paleontologistAndrea Cau remarked it bore an uncanny resemblance to Paul's "proavis".[14]
