Crows, hamerkops, pelicans and shoebills: related.

Today
the large reptile tree (LRT, 1110 taxa) grew by one taxon, the pelican (Pelecanus, Fig. 1). It nested between the hamerkop (Scopus, Figs. 3, 4) and the shoebill (Balaeniceps, Fig. 5, 6) and all were derived from a taxon close the American crow, Corvus (Fig. 2).

Cornvus brachyrhynchos (Linneaus 1758) is the extant American crow. Derived from herons and cuckoos, Corvus is generalized bird basal to a long list of sea and land birds all with a long maxilla.

Scopus umbretta (Brisson 1760, 56 cm tall) is the extant hamerkop, a mid-sized wading bird. It nests with the shoebill and pelican (below) in the large reptile tree. This clade nests between storks, like Threskiornis and petrels, like Macronectes all derived from a sister to Corvus the crow.

So essentially,
the hamerkop is a long-legged wading crow with a long beak.

Balaeniceps rex (Gould 1850, up to 140 cm tall) is the extant shoebill stork. It has a broad beak, a flat head and robust cheek bones. Here it nests with the hamerkop and pelican.

So essentially
the shoebill is a longer-legged, broader-billed hamerkop.

Pelecanus onocrotalus (Linneaus 1758) is the extant great white pelican. It has a large skull, longer wings and shorter legs than its relatives, the hamerkop and shoebill.

So essentially
the pelican is a short-legged, long rostrum hamerkop.

Key point of today’s blog:
Just think of all the transitional taxa between these terminal extant specimens, now extinct. Pelicans (genus Pelecanus) go back at least 30 million years. Of course, that means the above list of taxa goes back much, much further. Someday we’ll find Late Cretaceous crows and maybe hamerkops, IMHO.

References
Brisson MJ 1760. Ornithologie, ou, Méthode contenant la division des oiseaux en ordres, sections, genres, especes & leurs variétés : a laquelle on a joint une description exacte de chaque espece, avec les citations des auteurs qui en ont traité, les noms quils leur ont donnés, ceux que leur ont donnés les différentes nations, & les noms vulgaires
Gould J 1850. The birds of Asia. Part I. London.
Linnaeus C 1758. Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata.

wiki/Corvus
wiki/Scopus
wiki/Shoebill
wiki/Great_white_pelican