There is only one species, Longisquama insignis, known from a poorly preserved skeleton and several incomplete fossil impressions from the Middle to Late Triassic Madygen Formation in Kyrgyzstan.

Unwin and Benton interpreted them as a single, unpaired row of modified scales that run along the dorsal midline.

[3] Feather-development expert Richard Prum (and also Reisz and Sues) see the structures as anatomically very different from feathers, and thinks they are elongate, ribbonlike scales.

[4][5] Still other observers (e.g. Fraser in 2006) believe that the structures are not part of Longisquama at all, that they are simply plant fronds that were preserved along with the reptile and were misinterpreted.

These structures are long and narrow throughout most of their lengths, and angle backward near the tip to give the appearance of a hockey stick.

The middle ridged lobe is made up of raised "rugae" and deep "interstices", which Sharov compared to rosary beads.

Moreover, the proximity of each structure to its corresponding vertebra suggests that a thick layer of soft tissue, possibly including a follicle, surrounded each base.

[9] Unwin & Benton did not think it was possible to diagnose the crucial fenestrae; the holes could simply be damage to the fossil.

According to a cladistic study by Phil Senter in 2004, Longisquama would be an even more basal diapsid and a member of Avicephala, more closely related to Coelurosauravus.

The authors of the study tentatively placed Longisquama among the Archosauromorpha as a result of their hypothesis of developmental "deep homology" between its plumes, bird feathers, crocodile scales and pterosaur pycnofibres.

Ample evidence for this hypothesis has been found in the fossil record, specifically for such dinosaurs as Kulindadromeus, Sinosauropteryx, Caudipteryx, Microraptor and many others.

Longisquama is thus regarded as a diapsid with strange scales, ambiguous skeletal features and no real significance to bird evolution.