The fossil record is poor, but the Early Miocene fossil species " Plegadis paganus " has some intermediate features.
The glossy ibis is easily the most widespread of the three species . " Plegadis " contains the following three species:
The genus " Eudocimus " appears to be most closely related to ( but more primitive than ) " Plegadis ", the latter distinguished anatomically by the conformation of the tarsometatarsus.
Richard Sharpe classified it in the genus " Eudocimus ", but Storrs L . Olson placed it in the genus " Plegadis " due to anatomical similarities closer to that genus.
It has two foramina in the intertrochlear groove of its distal tarsometatarsus, as do " Plegadis " in contrast to the single foramen of " Eudocimus " and many other bird species.
The American white ibis is found in mixed-species foraging flocks with the glossy ibis ( " Plegadis falcinellus " ) in flooded fields, and the two species select different food items with little overlap; the former foraging for crabs and aquatic insects and the latter feeding mainly on grain.
The ibises of the genus " Plegadis " have two natural foramina ( holes ) in the intertrochlear groove in the distal section of the tarsometatarus, where as ibises of " Eudocimus " ( and many other species of bird ) have one small foramen . " P . paganus " has two small holes akin to living species of " Plegadis ".
The ibises of the genus " Plegadis " have two natural foramina ( holes ) in the intertrochlear groove in the distal section of the tarsometatarus, where as ibises of " Eudocimus " ( and many other species of bird ) have one small foramen . " P . paganus " has two small holes akin to living species of " Plegadis ".