Proavis

Proavis refers to a hypothetical extinct species or hypothetical extinct taxon and was coined in the early 20th century in an attempt to support and explain the hypothetical evolutionary steps and anatomical adaptations leading from non-avian theropod dinosaurs to birds. The term has also been used by defenders of the thecodontian origin of birds.

History

The term "Proavis" was first coined, although under the form "Pro-Aves", by English osteologist and zoologist William Plane Pycraft in "The Origin of Birds", a 1906 article published in the magazine ''Knowledge and Scientific News''. 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") was arboreal, as suggested Professor Osborn six years before, in 1900, in an article dealing with the hypothetical common ancestors of dinosaurs and birds. 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, the Hungarian aristocrat and paleontologist Franz Nopcsa, who, while residing at London, had seen Pycraft's restoration, drew his own vision of the animal, a picture and article published in a 1907 issue of the ''Proceedings of the Zoological Society of London'' (an English science publication nowadays known as ''Journal of Zoology''). But this time, for his own "Pro-Avis" restoration, Nopcsa suggested a cursorial 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 the Grant Museum of Zoology, the only remaining university zoological museum in London.

When Pycraft published his book ''A History of Birds'', in 1910, he reinserted his 1906 restoration ''One of the Pro-Aves'' (in page 39). In the following years, as of 1913, Danish artist and amateur zoologist Gerhard Heilmann also used and popularised the term ''Proavis'', this time presenting the public with more accurate and anatomically probable drawings. Heilmann favoured a scientific model in which the assumed ''Proavis'' was arboreal and of thecodontian descent, thus not a dinosaur.

In 1961, Czech paleontologist Josef Augusta included "Proavis" in his book ''Prehistoric Birds and Reptiles''. The animal illustration, as were all illustrations in the book, was painted by Zdeněk Burian.

During the 1970s the work of John 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 by Dieter Stefan Peters