Following wagons, are family sedans going extinct?

For several decades, the station wagon was the default car choice for most U.S. families.

But now those families clamor for SUVs instead, and wagons are virtually nonexistent in the North American car market.

Will the SUV onslaught stop there, or will it claim another victim?

If the trend toward greater SUV sales continues, that next victim could be the mid-size four-door sedan, sales of which are in "free fall" according to Automotive News (subscription required).

While the industry as a whole is on track for another year of record sales, demand for mid-size sedans is at a five-year low, the industry trade journal reports.

The segment declined 27 percent in August alone.

In comparison, sales of compact and smaller cars declined by only 3.6 percent.

Mid-size sedans have been the cornerstone of the car industry for the past few decades, even during the previous SUV boom of the 1990s and early 2000s.

But this year, analysts predict that compact crossovers will outsell mid-size sedans.

In August, the Toyota Camry—the best-selling car in the U.S. for 14 consecutive years—was outsold by the brand's RAV4 compact crossover for the first time, as well as by the Honda CR-V and Nissan Rogue.

Low gas prices have only intensified consumer interest in SUVs, which waned during the economic turmoil surrounding the 2008 recession.

The current breed of car-based crossovers also demands fewer compromises in fuel efficiency and handling than traditional truck-based SUVs.

That's helping boost the popularity of SUVs not just in North America, but in other markets as well.

The global allure of utility vehicles has led Fiat Chrysler Automobiles (FCA), for instance, essentially to abandon mainstream cars, so it can focus on crossovers, minivans, and pickup trucks instead.

The Detroit carmaker has ended production of its Dodge Dart compact sedan, and will phase out the Chrysler 200 mid-size sedan, to free up production capacity for trucks.

FCA's decision indicates confidence that the SUV boom will continue for a long time, but will that really be the case?

In theory, a sudden spike in gas prices could force consumers to abandon SUVs for more fuel-efficient cars.

But because of continuous improvements in fuel economy owing to stricter emissions standards, the impact on consumers may be less severe than in previous gas-price spikes.

That may make consumers less likely to give up their SUVs—meaning the mid-size sedan segment could be in real trouble indeed.