Nair Pillai and Shaiva Vellala Pillai: same surname, different castes

A few days ago, I saw an answer on a question-and-answer website, in which it was written that "In Kerala, Shaiva Vellala belong to Nair community." The Shaiva Vellala Pillai is a caste mostly found in Travancore. Though a caste of Vellalar community, they are mistaken as the Nair due to some misconceptions. According to the census report of 1901, the castes that use the surname Pillai are Nair, Agamudaiyan, Ambalakaran, Golla, Idaiyan, Nokkan, Panisavan, Panikkan(Kaniyar), Paraya, Saiyakkaranan, Sembadavan and Senaikkudaiyans. Pillai was also the title of male offsprings of Devadāsis. According to Edgar Thurston, many Paraya butlers serving Europeans assumed the title Pillai as a suffix to their names. If more than caste use same surname that doesn't mean that they have common ancestry. Surnames or titles were given according to profession, not according to castes. 

The Thondai Mandalam Shaiva Vellala are also known as Shaiva Vellala, Nayanar, Pillaimar, Vellala or Shaiva Vellalar. They use the titles Pillaimar, Nayanar, Mudaliyar, Udayar. They speak Tamil and are distributed in all districts of Tamil Nadu and Travancore region of Kerala. The Nāgas are mentioned in Tamil scriptures as Nāka and because of that there is a misconception that Nāgas were Tamils. In Manimekkalai, it is stated that the "speech of Nāgas was not Tamil but it was possible for a Tamil man to master it." The Vellalar were also called Gangakula or Gangavamsa, because they derived their descent from the great and powerful tribe named Gangavida, which inhabited in the valley of Ganges. 

Shaiva Vellalas are strictly vegetarians whereas Kiriyathil and Illathu Nairs are non-vegetarians. There is another misconception that all forward castes are vegetarians and vegetarians are seen as superior than non-vegetarians. This is purely a stupid belief. In forward castes, there are non-vegetarians too. For example, the Rajputs are non-vegetarians. In the Navaratri Pujas, they offer mutton to Goddess Durga. Similarly Bengali Brahmins, Assamese Brahmins and Kashmiri Pandits non-vegetarians. But at the same time, in Gujarat, 90% of Hindus irrespective of caste are vegetarians. 

Thondai Mandala Mudaliyar

In 'People of India - Tamil Nadu' I found a caste that is very similar to Shaiva Vellala. They are Thondaimandala Mudaliyar. They are also known as Thondaimandala Vellalar. They are a sub-caste of Vellalar community. They are originally from Thondaimandalam or the Pallava country, the present Chengai-MGR and North Arcot Ambedkar Districts. 
Territorially, Thondaimandalam is subdivided into Thuluva, who are believed to have come from Tulu country, the Poonamalee (or Pundamalli) Vellalar, so called from the town of that name near Madras, and the Kondakattis (those who do not cut their hair and tie it in a knot). All sections of Thondaimandalam Vellalar are subdivided into 24 Kottams and 79 Nadus. 
According to a legend a king once came to hunt in these wilds and in a place in the vicinity of the town of Kanchipuram in the kingdom of Arcot, he met a Nāgakanya. He fell in love with her. He promised her if she bore him a son, that son would succeed him as king. Years went by. The king returned to the kingdom and abdicated his throne in favour of his eldest son. When the son of the Nāgakanya was 14, he set out to meet his father, wearing a fruit of the Adhonda tree around his neck. Although his father recognised him at first, when the son recalled his promise to his mother and cited the Adhonda tree fruit as the witness, the king identified him and accepted him as son, the younger requested the king to give him an army with which he would conquer the kingdom for himself. This the king did, and the young prince subdued the Kurubavar who lived in Krishna and Kaveri. As the shepherds knew nothing of cultivation, the young king, now called Adhonda Chakra, returned to his father's kingdom and brought back from there as many Vellalar as who chose to migrate with him. The young Raja held out great encouragement, and a number of adventurers of that caste accompained him back. He gave them large grants of waste land and they established 1024 forts, 81 districts, and 1900 villages. This country was formerly called Dandaka Aranya. Adhonda chakra renamed it to Dhanda Mandalam or country of tree Dhonda, which bore testimony of his descent. The emigrants of the Vellalavaru are now called the Thondaimandalam Vellalar. 
The Thondaimandalam Mudaliars are pure vegetarians. Their staple food is rice. They use groundnut oil and gingelly oil for cooking. Whereas Nairs mostly use coconut oil for cooking. In the previously mentioned book, People of India -Tamil Nadu, it is stated that "both men and women of the Thondaimandal Mudaliar caste chew tobacco, betel and use snuff." Women of Kiriyathil and Illathu Nair castes don't use snuff. 
Gothrams like Tamilang and Kanimar are found among them. The function of the Gothrams is to regulate marriage alliances. Consanguineous marriages are permitted among the Thondai Mandala Mudaliar. They marry their father's sister's daughter, mother's brother's daughter or eldest sister's daughter. Sororate is permitted, but levirate is prohibited. Very few people know that in Nair community, sororate, levirate and avunculate marriages are prohibited. In cousin marriages, only cross-cousin marriages are allowed and the Tharavadu names husband and wife's maternal grandmothers, maternal grandfathers, paternal grandmothers and paternal grandfathers should not be same. 
At the time of first pregnancy, the Thondaimandala Mudaliyar observe pre-delivery rituals such as Valaikappu. Valaikappu is not one of the rituals of Nair community. Like all other Hindus, the Thondai Mandala Mudaliar cremate their dead. After the cremation, the sons of the deceased shave their head at the cremation ground. This ritual, that is, shaving the head after funeral rituals, is also not there in Nair community. 

Thondai Mandala Mudaliyar Christian

Those Thondai Mandala Mudaliyar who converted to Christianity are referred to as Thondai Mandala Mudaliyar Christian. Most of them are Roman Catholics and are said to have embraced Christianity during the period of St.Francis Xavier's evangelism in the southern part of Tamil Nadu. In those days, they were employed as custodians of Churches and some of them continue in the same employment at present. Their caste title is Mudaliyar.   

I hope it is clear that Shaiva Vellalas actually belong Vellalar community and are not at all related to Nairs. The Kiriyathil and Illathu Nairs are strictly religious. In the Report of Malabar Marriage commission, written in 1891, it is clearly given how strict these communities were especially in the case of marriage. There is nothing wrong in marrying from one's own caste, it is actually done to protect one's traditions. 

Reference: Historical Dictionary of the Tamils by Shri.Vijaya Ramaswamy, Jawaharlal Nehru University, History of Kerala: Written in the form of notes on Visscher's letters from Malabar by Shri.K. P. Padmanabha Menon, People of India - Tamil Nadu by Shri.K. S. Singh, Shri.R. Thirumalai and Shri.S. Manoharan.