The organisms have been named after former President Barack Obama and renowned British naturalist Sir David Attenborough.
Bloodthirsty rivalry may have driven the rapid evolution of these fearsome beasts.
This was from long before the dinosaurs.
These rocks formed at the bottom of ancient lake beds between three and four billion years ago, when the Martian surface was abundant in water and its climate was warmer.
Around 550 million to 540 million years ago, there was a remarkable explosion in the diversity and complexity of animal life on Earth.
Researchers say the fossil underscores how little we know about these mysterious ancient beasts.
Scientists now believe humans stalked and then confronted a giant ground sloth thousands of years ago in New Mexico.
The ancestors of modern humans once had a very pronounced ridge on their brow, however, over time, our foreheads gradually became smoother and the eyebrows more visible and versatile.
The fossil is 25,000 years older than traditional theories would expect.
Not all animals take the time to parent their young, especially if they have hundreds per clutch of eggs. But it looks like this invertebrate did.
The fossil is 127 million years old.
The creature fills the gap between ancient tailed arachnids and true spiders.
This is the first time Candelarhynchus padillai has ever been seen in tropical South America.
The human jawbone, which still has teeth, is between 175,000 and 200,000 years old.
The palace is constructed from oolitic limestone, a material that contains 200-million-year-old microbes.