A creation hymn about the birth of the gods ends with two verses on Aditi. Eight sons were born from her body. She went to the gods with seven and cast Martanda away. Then she brought him back 'to spring to life and die again'. No reason is given, the sons are not named, and nothing is said about an egg or a shape.
Hymns of the Rigveda, tr. R. T. H. Griffith (1896), hymns read for the Vedic layer § 10.72.8-9
The Brahmana quotes the Rigveda verse and explains it. Seven of Aditi's sons are 'the gods'. The eighth, Martanda, is born unformed, a lump as broad as it is high (some say man-sized). The seven brothers say that what was born after them must not be lost and fashion him in the shape of a man. The flesh they cut off becomes the elephant, so an elephant is not to be accepted as a gift. The shaped son is Vivasvat the Aditya, and creatures come from him. He declares that whoever among his offspring offers a rice-pap to the Adityas will succeed.
Gives the reason (shapelessness), makes the brothers the rescuers, adds the elephant and names the son Vivasvat, ancestor of creatures.
The Satapatha-Brahmana, tr. Julius Eggeling (Sacred Books of the East 12, 41) § 3.1.3.2-5
Aditi, wanting offspring, cooks a rice mess for the Sadhya gods, eats the remains and bears four Adityas. She cooks a second, eats first hoping for stronger sons, and bears an egg that miscarries. She cooks a third for the Adityas; they choose as a boon that the one born shall be one of them and that the prosperous among his offspring shall be theirs. Vivasvant is born; men are his offspring. Hence the Aditya cup at the Soma pressing is drawn from the remnant.
Told from the mother's side with three pots of rice; the fault is eating before the gods; four sons (not seven) come first; an egg appears; the text does not say outright that the egg and Vivasvant are the same child; no elephant, no carving.
The Veda of the Black Yajus School (Taittiriya Sanhita), tr. A. B. Keith (1914) § 6.5.6
The Daityas and Danavas have taken the three worlds and the sacrificial shares from Aditi's sons. She praises the Sun with austerities; he appears like glowing copper and grants that he will be born from her with his thousand rays. A ray enters her womb and she keeps severe fasts. Kashyapa angrily asks why she is destroying the egg in her womb by fasting; she answers that it is not destroyed and will be the death of their enemies, and gives birth at once. A bodiless voice says that because Kashyapa spoke of the egg as destroyed the son shall be called Martanda. Martanda burns the Asuras to ashes with a glance and the gods regain their places.
No casting away at all: the 'dead egg' is only Kashyapa's angry word, which explains the name. The child is the Sun himself, born on purpose as a rescuer, not a mortal ancestor.
The Markandeya Purana, tr. F. E. Pargiter (Bibliotheca Indica, 1904) § 105.1-27
Sources: Hymns of the Rigveda, tr. R. T. H. Griffith (1896), hymns read for the Vedic layer; The Satapatha-Brahmana, tr. Julius Eggeling (Sacred Books of the East 12, 41); The Veda of the Black Yajus School (Taittiriya Sanhita), tr. A. B. Keith (1914); The Markandeya Purana, tr. F. E. Pargiter (Bibliotheca Indica, 1904)
Naraka of Pragjyotisha steals Aditi's earrings; Krishna kills him and returns them, and Aditi blesses Krishna and Satyabhama.
Why the Soma sacrifice opens and closes with a pot of rice for Aditi: the earth, left out of the rite, confounds it until she is given a share.
The Rigveda's six, seven or eight Adityas become the twelve months in the Brahmanas and twelve named sun-gods in the Puranas.
Aditi, grieving for her sons who have lost heaven to Bali, keeps the payovrata and Vishnu is born as her son Vamana.
In the Rigveda Vishnu's one deed is to take three steps that measure out the world and make room for people; the third step is a honeyed place out of sight. The Brahmanas turn the steps into earth, air and sky, the Ramayana gives them a dwarf and a king named Bali, and festivals in Kerala and the Deccan welcome that king home.
The Asuras have won the earth and are dividing it. They grant the gods only as much as Vishnu, a dwarf who is the sacrifice, can lie on; the gods enclose him with the metres and win the whole earth by worship. The Bhagavata Purana tells the bargain as Vamana and King Bali.
The Adityas outwit the Angirases with a same-day Soma sacrifice, make them their priests, and pay them with the sun as a white horse.
Agni is born in the highest heaven and lies hidden, far away.