Most of you might have noticed that Lord Vishnu bears Mahalakshmi in his chest. In many temples today, they keep a metallic icon of mahalakshmi over the main statue of Vishnu. Be it anantasayin (sleeping form) or standing form - Vishnu will always have lakshmi in his heart.
If you look at the ancient sculptures, you will find that this is not depicted as a full human form of mahalakshmi. It is shown in a very peculiar form. This can be clearly seen in Pallava vishnus. In Thanjavore art gallery near the entrance - next to the gajasamhara and vakeesa moorthy, there is a standing vishnu (i'll try to put the photo in files). In this, this iconic representation is clearly seen. This vishnu is bronze but the lakshmi representaton is quoted with gold and later somebody has tried to remove the gold
This is called "Thiru maru" in vaishnavite literature. It is depicted just as a projection on lord's chest. Sri is the name given to Lakshmi. So Sri nivasan means somebody in whom sri resides or mahalakshmi resides. Mahalakshmi means "thiru" in tamil and "sri" in sanskrit
Thus the thirumaru is also called "sri"
Some of you might remember a controversy that came up during the samprokshanam of sri ranganatha temple of srirangam. The kerala namboodhiri who renovated main deitie's body removed sri representation and did a triangular representation which was against the original. Lot of protests came and triangle was made back to sri.
This ancient sri is not human form but a peculiar icongraphic representation
Uttaramerur has 2 unique sri sculptural representations that shows this icon was independently worshipped. Both are not shown in vishnu's chest but as independent icons.
And neither of them are in the famous sundara varadha perumal temple !