Termites are very ancient organisms; they have even existed before ants. So, perhaps it can be regarded that ants “adapted” their complex social structure from the termites, and not the other way around. What I notice is that termites back then and today are not much different in terms of morphology, or how they look.
The first termites are estimated to have appeared during the Triassic (some believe they have existed during the Permian age), while ants came onto the scene during the Cretaceous period – millions of years later. While ants gone on to diversify into the over 12,000 species known today (and many more still unknown), termites seem to be more or less stuck on the evolutionary scale, with currently 2,600-3000 species estimated to exist. I believe they are limited in part to their dependency on plant matter as their diet.
That said, termites have coped very well throughout millions of years because of their ability to burrow and live in the soil, while other species evolved to become “farmers” cultivating fungus gardens in elaborate nests. This is actually a very high level of sophistication.
Different termite families evolved in different continents, although you need to remember all continents were joined together at one time as a super continent – Gwondanaland. For example, the Macrotermitinae and Apicotermitinae are believed to be Ethopian in origin, while the Rhinotermitidae are believed to be Oriental. However, most families are widely distributed in the world today.
There are probably many more species than the 2600 known today, since most termites live in tropical forests, and the species found in mountain forests are very poorly known. As many tropical forest tracts give way to clearance, there is a possibility many localized and specialized species of termites go extinct – forever.
The oldest “living fossil” termite is the Mastotermes darwiniensis, or the Giant Northern Termite of Australia. It seems to be the last of its kind, the Mastotermitidae, bears some resemblance to a cockroach and lays eggs in pods, like cockroaches do. This is not surprising to me, since termites are related to cockroaches but only Mastotermes bears the most resemblance to them.
A lot of amber and copal specimens have termites in them. This is likely due to the fact that termites being vegetarian, do a lot of foraging around plants, and those unfortunate ones who were foraging got caught in exuded plant resins which preserved them for thousands (in the case of copal) or millions of years (in the case of amber). I have a copal specimen which has many termites encased inside it, and what strikes me is there is no change in the basic morphology or appearance of termites despite the elapsed years.