Those holding out for altcoin season may have to wait a little longer.

Bitcoin now boasts a market dominance of 66 percent, the highest since April 2017. Market dominance is a figure that represents how much money is held in bitcoin, compared to other cryptocurrencies–and is a measuring tool for assessing the relative health of other coins in the cryptocurrency ecosystem.

Bitcoin hit its lowest market dominance at 33 percent, on January 8, 2018. At that time, one bitcoin was worth just shy of $16,000–a big valuation doesn't not always equal ecosystem dominance. Over the last year and a half, however, while it's price has been cut in half, its share of the market has doubled.

This was likely due to the altcoin rally in late 2017 and early 2018, when investors went looking for the next big thing and poured millions into alternative projects. The alt bull run sent the market for alternative coins from $76 billion in total market cap to $495 billion in just under two months. But the boom times didn't last long.

Many of the projects turned out to be duds, and some were just elaborate pump and dump schemes where a select few got rich by exploiting unwitting investors. Since then, the value of many altcoins has fallen dramatically—with price drops ranging between 90 and an eye-watering 99 percent for many coins.

In contrast, the price of bitcoin fell around 80 percent, before stablizing at $4,000. Recently it rallied above $13,000—but is struggling to keep that momentum.

In Facebook's hearings about Libra yesterday, the one thing missing was the word bitcoin. But by the look of things, it's the one thing that matters.