Traditionally, the order

Order (biology)

In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...

 Ciconiiformes has included a variety of large, long-legged wading birds with large bills: stork

Stork

Storks are large, long-legged, long-necked wading birds with long, stout bills. They belong to the family Ciconiidae. They are the only family in the biological order Ciconiiformes, which was once much larger and held a number of families....

s, heron

Heron

The herons are long-legged freshwater and coastal birds in the family Ardeidae. There are 64 recognised species in this family. Some are called "egrets" or "bitterns" instead of "heron"....

s, egret

Egret

An egret is any of several herons, most of which are white or buff, and several of which develop fine plumes during the breeding season. Many egrets are members of the genera Egretta or Ardea which contain other species named as herons rather than egrets...

s, ibis

Ibis

The ibises are a group of long-legged wading birds in the family Threskiornithidae....

es, spoonbill

Spoonbill

Spoonbills are a group of large, long-legged wading birds in the family Threskiornithidae, which also includes the Ibises.All have large, flat, spatulate bills and feed by wading through shallow water, sweeping the partly opened bill from side to side...

s, and several others. Ciconiiformes are known from the Late Eocene

Eocene

The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...

. At present the only family retained in the order is the storks, Ciconiidae.
Following the development of research techniques in molecular biology

Molecular biology

Molecular biology is the branch of biology that deals with the molecular basis of biological activity. This field overlaps with other areas of biology and chemistry, particularly genetics and biochemistry...

 in the late 20th century, in particular methods for studying DNA-DNA hybridisation

DNA-DNA hybridisation

DNA-DNA hybridization generally refers to a molecular biology technique that measures the degree of genetic similarity between pools of DNA sequences. It is usually used to determine the genetic distance between two species...

, a great deal of new information has surfaced, much of it suggesting that many birds, although looking very different from one another, are in fact more closely related than was previously thought.