Thread by @JacquelynGill

For today’s #MakeAPlanet quiz, lets zoom in on what we now call North America. Only one of these mammals evolved here; the others dispersed over land bridges long ago. Which species actually got its start on this continent?

A) Porcupines
B) Bison 🦬
C) Opossums
D) Horses🐴

Deep time—a phrase coined by the writer John McPhee to refer to the vastness of geologic time—shakes up, challenges, and expands so many preconceived ideas about nature. That’s one reason I love it so much.

Answer time! I really love the conversation and thought processes that went into folks' answers. The goal of these quizzes is to get people thinking, wondering, and learning.

So first, let's talk about what DIDN'T originate, evolutionarily speaking, in North America.

First off, 🦬! This iconic ungulate is the most recent arrival of the list! North American 🦬 descended from Eurasian steppe 🦬 that came via Beringia some 200,00-135,000 years ago. Nearly wiped out by settlers, this keystone species is being restored to many parts of its range.

Opossums are marsupials, a group that originated in North America (!) ~110 million years ago when the continents were closer. But by the time opossums evolved ~20 million years ago, there were no marsupials in N. America. They came from South America when the continents rejoined!

Based on the fossil record, porcupines are thought to have evolved in Africa, and then rafted across to Brazil ~30 million years ago. Like opossums, they came north when the Isthmus of Panama connected the Americas, ~3 million years ago. Jug bands came much later.

The earliest horses showed up in the fossil record in North America ~55 million years ago. By 10 million years ago, there were as many as ten species! Horses later crossed Beringia into Eurasia, and then went in extinct in North America*, later to be reintroduced by the Spanish.

*Some Indigenous scholars have questioned whether American horses went extinct, and this is an active area of research. I should also note that the "last" horses in North America are effectively the same as today's horses; they're considered modern, genetically and anatomically.

Want to learn more about plate tectonics and how the movements of the continents shaped life on Earth? Enjoy spending your lunch break lost in ancient worlds? Back @MakeAPlanetPod so we can tell more mind-bending stories about our deep time friends!

kickstarter.com/projects/makea…

I know there are a ton of demands on everyone's wallets right now, from the recession to mutual aid and various crises. If you can't back the Kickstarter, but still want to see us succeed as an AD-FREE show for all, you can share us with your networks! That helps a bunch!