By Eduardo Flores

Sunset on Mars by NASA’s Curiosity Rover

The Sun from the Internation Space Station

Dunkleosteus

Dunkleosteus, a placoderm, or armoured, fish. It lived around 370 million years ago, during the Devonian period and is arguably the biggest predator of its time. This was a truly impressive fish, literally hard as nails, its head was encased in a solid armour plating and like a shark, it had a streamlike body to swiftly move through the water. Its heavy armour means it would’ve been a relatively slow swimmer, yet capable of short spurts of speed, sort of like some sharks today.

This formidable beast had a major evolutionary strength, a moveable jaw. Fish began to dominate the oceans when they evolved the ability to move their jaw, yet Dunkleosteus had no teeth, what it had was much more menacing. It had  razor like blades to slice its prey apart, like a pair of scissors to paper, with a bite more powerful than a great white. It would’ve been able to slice its prey in half so it was able to consume huge animals, yet on the downside the Dunkleosteus was unable to chew and on occasion its stomach found the huge chunks of meat hard to handle, evidence of this is in fossilised sick of the Dunkleosteus that has been found…

(Dunkleosteus armour means its head is often very well preserved. You can see how its teeth would’ve been more than capable of shearing through flesh.)

Relatives of the dunkleosteus, other armoured fish, were mostly dog sized, but Dunkleosteus was an exception. At 6 metres long on average, twice the length of human, this was a seriously big fish, yet it could reach up to 10 metres long, the length of a bus. 

Dunkleosteus seems like the perfect predator. However, in its bony plates, indents of other animal teeth have been found suggesting that despite its strength, it was itself hunted. Dunkloesteus teeth marks have been found in its own fossils, they would eat whatever they could get their teeth into, including each other. The success of this gigantic beast was short lived, it was outcompeted by the more nimble sharks. Placoderm fish themselves would be extinct by the end of the devonian, taking the Dunkleosteus with it.

(by lorenz.weisse)

The Himalayan plateau, as seen from the ISS by europeanspaceagency

Sea of Stars, Vaadhoo Island, Maldives by Doug Perrine

Dear @thought-cafe team, we need more Crash Course Astronomy episodes! Can you please do a Season 2? Dr. Phil Plait is awesome, and we miss him!

If you’re excited about the juno news today, sink your teeth into a Crash Course episode that’s all about Jupiter! 🔭  https://youtu.be/Xwn8fQSW7-8

Ctenophore

Plesiosaurus skeleton from the Houston Natural History Museum!

Daphnis and the Rings of Saturn : What’s happening to the rings of Saturn? A little moon making big waves. The moon is 8-kilometer Daphnis and it is making waves in the Keeler Gap of Saturn’s rings using just its gravity – as it bobs up and down, in and out. The featured image is a colored and more detailed version of a previously released images taken in 2017 by the robotic Cassini spacecraft during one of its Grand Finale orbits. Daphnis can be seen on the far right, sporting ridges likely accumulated from ring particles. Daphnis was discovered in Cassini images in 2005 and raised mounds of ring particles so high in 2009 – during Saturn’s equinox when the ring plane pointed directly at the Sun – that they cast notable shadows. via NASA