The creatures are invisible to the naked eye, measuring around 100 micrometers long—about as thick as a human hair.
The latest find is surprising because shark skeletons are made of cartilage—a rubbery tissue that doesn't preserve as well as bone.
The latest discovery comes four years after a similar find in the same region of Argentina.
The dinosaur could bite with about three times the force of large crocodiles or great white sharks.
The findings suggest that these early large, complex lifeforms were more like modern animals than previously thought.
The fossils are 15 million years older than any others belonging to the tyrannosauroid family that have been found in North America.
The clutch of babies were likely still inside their eggs.
Scientists named them Xenomorphia, after the bloodthirsty, chest-splitting creatures from the Alien movies.
These sharks are now the most popular in the ocean.
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.
The asteroid and its after-effects ushered in a great extinction event that wiped out some three quarters of all plant and animal life, including dinosaurs and most birds.
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.