to thousands. Many of these species breed in colonies with other waterbirds, which can include other species of storks, herons and egrets, pelicans, cormorants and ibises. White storks, Oriental storks and Maguari storks are all loosely colonial, and may breed in nests that are within visual range of others of the same species, but have little to do with one another. They also may nest solitarily, and the reasons why they choose to nest together or apart are not understood. Systematics A DNA study found that the families Ardeidae, Balaenicipitidae, Scopidae and the Threskiornithidae belong to the Pelecaniformes. This would make Ciconiidae the only group. Storks were distinct and possibly widespread by the Oligocene. Like most families of aquatic birds, storks seem to have arisen in the Palaeogene, maybe 40–50 million years ago (mya). For the fossil record of living genera, documented since the Middle Miocene (about 15 mya) at least in some cases, see the genus articles. Though some storks are highly threatened, no species or subspecies are known to have gone extinct in historic times. A Ciconia bone found in a rock shelter on the island of Réunion was probably of a bird taken there as food by early settlers; no known account mentions the presence of storks on the Mascarene Islands. Extant storks Fossil storks Genus Palaeoephippiorhynchus (fossil: Early Oligocene of Fayyum, Egypt) Genus Grallavis (fossil: Early Miocene of Saint-Gérand-le-Puy, France, and Djebel Zelten, Libya) – may be same as Prociconia Ciconiidae gen. et sp. indet. (Ituzaingó Late Miocene of Paraná, Argentina) Ciconiidae gen. et sp. indet. (Puerto Madryn Late Miocene of Punta Buenos Aires, Argentina) Genus Prociconia (fossil: Late Pleistocene of Brazil) – may belong to modern genus Jabiru or Ciconia Genus Pelargosteon (fossil: Early Pleistocene of Romania) Ciconiidae gen. et sp. indet. – formerly Aquilavus/Cygnus bilinicus (fossil: Early Miocene of Břešťany, Czech Republic) cf. Leptoptilos gen. et sp. indet. – formerly L. siwalicensis (fossil: Late Miocene? – Late Pliocene of Siwalik, India) Ciconiidae gen. et sp. indet. (fossil: Late Pleistocene of San Josecito Cavern, Mexico) The fossil genera Eociconia (Middle Eocene of China) and Ciconiopsis (Deseado Early Oligocene of Patagonia, Argentina) are often tentatively placed with this family. A "ciconiiform" fossil fragment from the Touro Passo Formation found at Arroio Touro Passo (Rio Grande do Sul, Brazil) might be of the living wood stork M. americana; it is at most of Late Pleistocene age, a