Aramus guarauna (Linneaus 1766) is the extant limpkin. It is often considerd transitional between rails and cranes. In the large reptile tree (1121 taxa) the limpkin nests basal to seagulls and hummingbirds, plovers and crowned cranes, common cranes and stilts, terns and loons, kingfishers and jabirus, murres and penguins.
Extant limpkins eat snails.
Primitive limpkins like Aramournis probably had a more diverse diet. It is known from a distal tarsus.
like the corn crake (Crex) and the coot (Fulica) are much more basal birds that give rise to chickens, sparrows and parrots. Adding Rallus, the Virginia rail, to the LRT nests it between Aramus and the rest of the clade, which, phylogenetically makes hummingbirds, terns and penguins variations on the rail theme and Rallus at least a Middle Cretaceous taxon radiation.
Congeneric specimens of Aramus
are found in the Miocene, but more derived penguins are found in the Paleocene, pointing to a mid-Cretaceous radiation of this clade.
Limpkins are derived from Cretaceous sisters to
hamerkops (Scopus) and stone curlews (Burhinus), both long-legged taxa. By the evidence shown in the crown bird subset of the LRT (Fig. 4), long legs, like those shown by Aramus, the limpkin, are basal traits. The retention of hatchling short legs occurred several times by convergence, sometimes during the Cretaceous. See the earlier post on post K-T non-arboreal birds.
Linneaus C von 1766. Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio duodecima, reformata. pp. 1–532. Holmiæ. (Salvius)