What you mentioned about the denomination is not exactly accurate. The st thomas christians or syrian christians or malankara nasranis in kerala or the malabar region, were part of church of east that follows east syriac liturgy. The Malankara Orthodox Syrian Church (or Indian Orthodox Church) that follows west syriac liturgy is a new church started out of a court case in the 19th century.
So, in short, it's like: was unified st thomas christians from st thomas arrival in the 1st century and under church of east since 4th century when it was organised as independent from church of rome till 15th century portuguese arrival and forced latinisations by them leading to coonan cross oath protest, splitting the community into two: one new catholic faction(84 church out of then 116 churches) using the modified east syriac liturgy and the other faction(32 church out of then 116 churches) under patriarch of antioch, adopting the west syriac liturgy locally called the jacobites. The catholic faction mentioned grew into the current syro malabar catholic church. The orthodox jacobite faction underwent another split when british came in the 18th-19th century and tried to create protestant influence, leading to the creation of the marthoma church, which is a protestant church using a protestantised west syriac. In the 18th-19th century times, if I am not wrong, a small faction from the syro malabar catholic church joined the chaldean syrian church, creating a small archdiocese of assyrian church of the east in kerala. Now in the 19th century, a small faction in this jacobite came into communion with vatican keeping the west syriac litury, forming the syro malankara catholic church. At this time in the 19th century the internal conflict regarding whether to be directly under patriarch of antioch came in the jacobites leading to Malankara Orthodox Syrian Church (or Indian Orthodox Church) faction that was mentioned in the comment above.