What is your favorite extinction event, and why?

Discussion: you can have an "extinction event" in any ecosystem-- not just biological ones.

For example, the abandonment of steam locomotives in the mid-20th-century, or the Home Computer crash of the 1980s.

Similar to a biological mass extinction, you have:

• A discernable ecosystem change, either a sudden event (the introduction of reliable, mass-produced diesel locomotives), or a measurable decline of "habitability factors" (as hundreds of firms brought cheap 8-bit computers to market, retail space and overall consumer interest saturated)
• a rapid diversification of new and exotic types to fill the vacated niches (the cabless "B-unit" and flexible "road-switcher" locomotive types didn't exist in the steam era. The post-crash computer market brought in new entrants like cheap IBM clones, the C128 and Atari 130XE, all chasing a sub-$1000 market that was now free of Sinclair, Coleco, and Texas Instruments)
• followed by a shake out and consolidation of the survivors/winners as they select for fitness in the new world (ALCO was a strong #2 in the diesel locomotive market in 1950, but didn't make it to 1970. The C128 never became the world-beater its predecessor did.)
• a few niches largely untouched (China was still building steam locomotives into the 1990s. The Apple II series lasted about as long.)