The discovery is the oldest known footprint ever found of hominins.
Julian Gagnon was out with his parents at Dinosaur Hill Nature Preserve in Rochester Hills, Michigan when he came across what he thought was a "dragon's tooth."
The fossils, which date to between 66 and 68 million years ago, could also represent a new species altogether, according to paleontologists.
Comparing the Ulughbegasaurus to the ancestor of the T. rex is like comparing a grizzly bear to a coyote, said a researcher who helped identify the huge reptile.
The approximately 2,200-pound dinosaur is believed to have been the apex predator of its ecosystem.
The animal, estimated to be 10 feet long and weighing around 1,320 lb, would likely have been a top predator like the killer whale of today.
The site contains the preserved remains of Jurassic-era echinoderms, including starfish, sea urchins and sea cucumbers.
"It was surprising, and I didn't really understand the impact of it in the beginning," said the woman who found the fossil while visiting her son on the dig.
The YouTuber, who has found hundreds of tiny shark teeth and several whale skulls, began posting videos on his channel Mamlambo Fossils two years ago.
Researchers estimate that the species could have reached 25-40 meters (82-131 feet) in length.
The boy and his family were vacationing on a South Carolina beach when the huge fossil was uncovered.
The paleontologists who made the find believe that it could take years to exhume the remains completely.
Hundreds of specimens have been recovered so far, including a practically intact set of mastodon tusks.
Because we also had sediment that the fossil was found in, we were able to use chemicals to date the sediment and determine that this dinosaur is from the later Crustacean Period and is roughly 70 million years old.
Megalodon was the largest shark ever to have lived, potentially growing up to around 60 feet in length.
Researchers have discovered the fossilized remains of at least 40 different species of ancient shark in Mammoth Cave in Kentucky, dating back to around 325 million years ago.
The predation event took place 99 million years ago in what is now Myanmar.
"Diagnosis of aggressive cancer like this in dinosaurs has been elusive," said researcher Mark Crowther.
The fossilized excrement could help to shed light on what the extinct animal once ate.
Researchers also found another news species of prehistoric shark in Georgia.
The reptile is an early member of the animal group Ornithodira to which both dinosaurs and pterosaurs belong.
Latest study supports the idea that the asteroid impact 66 million years ago was the main driver of dinosaur extinction, not intense volcanic activity as some have suggested.
Many giant dinosaur specimens are very incomplete, which makes it difficult to produce reliable body mass estimates.
The latest findings also help to shed new light on other sites in South Korea where scientists have previously found footprints that were originally thought to belong to giant flying reptiles.
"The finding of the actual preserved stomach contents from a dinosaur is extraordinarily rare," said researcher Jim Basinger.
The dinosaur is one of the largest and youngest megaraptors on the fossil record, say paleontologists.
Scientists describe the two-inch bone of a 110 million-year-old elaphrosaur found in Victoria, Australia, after it was misidentified as belonging to a pterosaur.
The shape of the structures resemble that of complex carbon molecules known as "fullerenes," which were one of the first nanoparticles discovered by scientists.
Bones from a fossil rich site at Tanque Loma in Ecuador offers clues to how a group of 22 plus giant sloths met their end 18,000 years ago.
A new Spinosaurus skeleton proves one of the largest dinosaur predators ever discovered lived a largely aquatic lifestyle, opening up a new understanding of dinosaur's place in the ancient world and overturning old dogmas.