Two faces on one head
Where twinning of the head itself is only partial, it can result in the condition known as diprosopus—one head with two faces. Earliest known occurrence
The February 22, 2007, issue of the journal Biology Letters detailed the discovery of a 122 million-year-old fossil of a two-headed Hyphalosaurus lingyuanensis, marking the earliest known occurrence of axial bifurcation. List of notable occurrences
Humans
Dicephalic conjoined twins (dicephalus parapagus dipus)
Lycosthenes described a pair of adult female twins who had separate necks but one body. Both heads ate, drank, slept, and spoke. They had to beg from door to door, "everie one giveing (sic) to her freely". They were banished to Bavaria due to fears pregnant women who saw them would give birth to similar children; nothing else is known of them. In 1990 Abigail and Brittany Hensel were born in Minnesota, United States. In 2000 Ayse and Sema Tanrikulu were born in Kahramanmaraş, Turkey
In June 2000 Carmen and Lupita Andrade were born in Veracruz, Mexico. They later moved to the United States for healthcare with their parents. In 2003 Sohna and Mohna were born in India
On June 13, 2003, twin girls named Huda and Manal Abdel Nasser Mohammed Mahmoud, were born in Asyut, Egypt
In 2006 Syafitri was born in Indonesia
In 2007 Mary Grace and Mary Divine Asis were born in the Philippines with only one heart. They died on April 30, 2008. On August 25, 2008, a baby boy named Kiron was born with two heads in south-western Bangladesh.
The baby was described by the gynaecologist present at the birth as having "one stomach and he is eating normally with his two mouths. He has one genital organ and a full set of limbs". He died on August 28, 2009. In July 2009, dicephalic twins were born in Indonesia with two hearts but  sharing all other internal organs. In 2011 Sueli Ferreira gave birth to a child with two heads in Campina Grande, in Paraíba state, Brazil, but the baby died a few hours later because of lack of oxygen to one of the heads. On December 19, 2011, a pair of male twins, Emanoel and Jesus Nazare, were born in Marajó Island, Brazil. The children had two heads, two legs and two arms, sharing all the body below the neck. Each child had a separate spine, but shared a heart, liver, lungs and pelvis, and both brains functioned. The boys appeared on the Channel 4 programme Bodyshock on December 19, 2012, where it was reported they had died at six months. In March 2014 dicephalic twin girls were delivered via caesarian section at Cygnus JK Hindu Hospital in Sonipat, Haryana, in northern India. The babies reportedly have two heads, two necks and two spinal columns but share all major organs. Craniopagus parasiticus
Craniopagus parasiticus is a condition in which a parasitic twin head with an undeveloped or underdeveloped body is attached to the head of a developed twin.