[Ptarmigan]

That would support that civilization existed before Sumeria. It likely stretched from India, Southeast Asia, Indonesia, Philippines, and Taiwan.

[SunkenCiv]

Samuel Noah Cramer pointed out that the names for the big rivers and towns of the Sumerians were not Sumerian names, but were borrowed by them from the original inhabitants. The only written traces (the only known ones at least) of those vanished folks' language(s?) are in Sumerian (and later Akkadian) cuneiform. Who they were, and what language they spoke, is unknown and probably unknowable. The Sumerians themselves also spoke of their own arrival from the sea. But yeah, I don't doubt that civilization (and even literate civilization) is far older than we know, and perhaps will ever know. Quick reprise:

In her Plato Prehistorian: 10,000 to 5000 B.C. Myth, Religion, Archaeology, Mary Settegast reproduces a table which shows four runic character sets; a is Upper Paleolithic (found among the cave paintings), b is Indus Valley script, c is Greek (western branch), and d is the Scandinavian runic alphabet.

[Cronos]

Possibly Sumeria was part of this civilisation and the survivor. This would trace Dravidians as Sumerians