Get the latest market trends in your inbox

Stay on top of the latest market trends and economic insights with the Axios Markets newsletter. Sign up for free.

Please enter a valid email.

Please enter a valid email.

Subscription failed
Thank you for subscribing!

Catch up on coronavirus stories and special reports, curated by Mike Allen everyday

Catch up on coronavirus stories and special reports, curated by Mike Allen everyday

Please enter a valid email.

Please enter a valid email.

Subscription failed
Thank you for subscribing!

Denver news in your inbox

Catch up on the most important stories affecting your hometown with Axios Denver

Please enter a valid email.

Please enter a valid email.

Subscription failed
Thank you for subscribing!

Des Moines news in your inbox

Catch up on the most important stories affecting your hometown with Axios Des Moines

Please enter a valid email.

Please enter a valid email.

Subscription failed
Thank you for subscribing!

Minneapolis-St. Paul news in your inbox

Catch up on the most important stories affecting your hometown with Axios Minneapolis-St. Paul

Please enter a valid email.

Please enter a valid email.

Subscription failed
Thank you for subscribing!

Tampa-St. Petersburg news in your inbox

Catch up on the most important stories affecting your hometown with Axios Tampa-St. Petersburg

Please enter a valid email.

Please enter a valid email.

Subscription failed
Thank you for subscribing!

Please enter a valid email.

Please enter a valid email.

Subscription failed
Thank you for subscribing!

A boy looks on at the skull of a dinosaur fossil in Taipei, Taiwan. Photo: Chiang Ying-ying / AP

Mammals were primarily nocturnal until about 66 million years ago — about the time when dinosaurs were wiped out. Then, they became diurnal creatures active during the daytime. The two events may be linked, according to a new study published in Nature Ecology & Evolution.

The big picture: Scientists have a long-held hypothesis that ancient mammals were nocturnal so they could avoid dinosaurs — predators who were active in the daytime. This study's analysis of 2,415 different mammal species showed that the switch from being active in the nighttime to the daytime occurred after dinosaurs were killed off. "Though scientists can't say that one caused the other, the study provides fresh circumstantial evidence," Amina Khan wrote in the LA Times.

But, but, but: Scientists found some species that are cathemeral — meaning they are out and about both during the day and the night — held those patterns of living about 9 million years before dinosaurs became extinct. This could be because dinosaurs may have been dying out before an asteroid hit Earth, allowing opportunities for mammals to come out during the day.

Go deeper

Broncos and 49ers the latest NFL teams impacted by coronavirus crisis

From left, Denver Broncos quarterbacks Drew Lock, Brett Rypien and Jeff Driskel during an August training session at UCHealth Training Center in Englewood, Colorado. Photo: Justin Edmonds/Getty Images

The COVID-19 pandemic has thrown the NFL season into chaos, with the Denver Broncos' quarterbacks sidelined, the San Francisco 49ers left without a home or practice ground and much of the Baltimore Ravens team unavailable, per AP.

Driving the news: The Broncos confirmed in a statement Saturday night that quarterbacks Drew Lock, Brett Rypien and Blake Bortles were identified as "high-risk COVID-19 close contacts" and will follow the NFL's mandatory five-day quarantine, making them ineligible for Sunday's game against New Orleans.

Updated 5 hours ago - Politics & Policy

Coronavirus dashboard

Illustration: Sarah Grillo/Axios

  1. Health: WHO: AstraZeneca vaccine must be evaluated on "more than a press release."
  2. Politics: McConnell temporarily halts in-person lunches for GOP caucus.
  3. Economy: Safety nets to disappear in DecemberAmazon hires 1,400 workers a day throughout pandemic.
  4. Education: U.S. public school enrollment drops as pandemic persists.
  5. Cities: Surge in cases forces San Francisco to impose curfew — Los Angeles County issues stay-at-home order, limits gatherings.
  6. Sports: NFL bans in-person team activities Monday, Tuesday due to COVID-19 surge — NBA announces new coronavirus protocols.
  7. World: London police arrest more than 150 during anti-lockdown protests — Thailand, Philippines sign deal with AstraZeneca for vaccine.

Tony Hsieh, longtime Zappos CEO, dies at 46

Tony Hsieh. Photo: FilmMagic/FilmMagic

Tony Hsieh, the longtime ex-chief executive of Zappos, died on Friday after being injured in a house fire, his lawyer told the Las Vegas Review-Journal. He was 46.

The big picture: Hsieh was known for his unique approach to management, and following the 2008 recession his ongoing investment and efforts to revitalize the downtown Las Vegas area.