Although generally similar, it subtly differs in the curvature of the bill and the size of the ventral keel of the maxilla, both signs that Harrisonavis was not yet as adapted towards filter feeding as modern species are.

Harrisonavis was first reported in 1852 by paleontologist Paul Gervais on the basis of a nearly complete skull which showed a similar morphology to modern flamingos of the genus Phoenicopterus.

Due to this superficial similarity, it was assumed that the fossils belonged to an extinct species of said genus, then named Phoenicopterus croizeti.

Like in modern flamingos, the region before the nares leading up to the tip is lined with foramina, however uniquely the bone itself is mostly solid and not reticulated like in extant taxa.

The maxillary keel, located on the underside of the upper bill, is more similar to Phoenicopterus, if even shallower than seen in either the modern species or the extinct genus Leakeyornis.

[3] † Juncitarsus Podicipediformes † Palaelodidae †Harrisonavis Phoenicopterus Phoenicoparrus The close resemblance to modern flamingo species indicates that Harrisonavis was already a filter feeding animal.

Specifically, the curvature of the bill may have meant that Harrisonavis held its head more vertically while filtering, as opposed to the upside-down position assumed by modern flamingos.

Although the articulation of the lower bill was also found to differ, with the reduction of certain muscles impacting the way the head could be held during feeding and display, it is not yet clear how great the effect would have been exactly.