JOHN YANG: Paleontology, the study of fossils is one of the few fields where discoveries can come from experts and amateurs alike.
Ali Rogin is back with a story of some recent astonishing fossil finds.
ALI ROGIN: From the rugged coastline of northeast England.
MARIE WOODS, ARCHAEOLOGIST: I didn't know if what I was looking at was actually what I was thinking I was looking at.
ALI ROGIN: To the sandy beaches of the Chesapeake Bay in Maryland , fossil hunting is a hobby for young and old.
MOLLY SAMPSON, Fossil Hunter: At first, it was farther away, and I thought it was like a big rock.
And I went closer, and I saw that it was a big tooth.
ALI ROGIN: On Christmas morning, nine-year-old Molly Sampson put one of her new presents to good use, a pair of waders perfect to help in the hunt for ancient shark tooth.
MOLLY SAMPSON: I tried to scoop it up with my scooper, but the tooth was too big, and I just reached in and pulled it out of the water.
BRUCE SAMPSON: I think the windshield was 10 degrees, and yeah, she just overhands right in the water and scooped it out.
MOLLY SAMPSON: My hand was freezing after that for, like, oh at least for the time.
ALI ROGIN: I bet.
Fossil hunting runs in this family.
Bruce Sampson got his kids hooked from a young age.
BRUCE SAMPSON: It's so cool to see the enthusiasm and to see them get so excited about something that they find.
And one of the things I always tell the kids when they find something is that if you think about it's pretty cool to think about something that's 15 million years old, that's been sitting out there for all that time, and you're the first person to ever pick it up and hold it.
ALI ROGIN: The Sampsons took their fine to Stephen Godfrey, the curator of paleontology at the Calvert Marine Museum.
BRUCE SAMPSON: He said it was a very good specimen in good condition.
And ... MOLLY SAMPSON: Oh he said that it's about 15 million years old.
ALI ROGIN: Whoa.
MOLLY SAMPSON: Every inch of tooth equals 10 feet of, like, a shark, and it's five inches, so it would have been a 50-foot shark.
She said it was a five-foot lifetime.
STEPHEN GODFREY, CURATOR, CALVERT MARINE MUSEUM: I've told her, and I tell people repeatedly, look, you shouldn't expect to come to Calvert Cliffs and find a fossil like that, because there are people who have spent a lifetime and have not found a large tooth like that.
So, she just happened to be in the right place at the right time.
ALI ROGIN: Millions of years ago, in the Miocene era, this area was underwater.
Time and erosion have left fossils behind for paleontologists and amateur fossil hunters like the Sampsons to discover.
STEPHEN GODFREY: You would think that after 200 years of kind of Western culture collecting fossils from long cover cliffs, that we would know everything that there is to know about both the geology and the diversity of organisms that lived here during the Miocene Epoch.
But in fact, we don't.
And every year, we continue to make new discoveries.
ALI ROGIN: Across the Atlantic Ocean, Marie Woods made one of those new discoveries when she found a fossilized dinosaur footprint along the Yorkshire coast.
MARIE WOODS: Once I got up close and personal with it to kind of realize what it was, I wasn't necessarily aware of what type of dinosaur it was or indeed, the importance of it, the scientific importance of it.
But I knew enough to kind of start the next stages of processing it.
ALI ROGIN: Woods is an archaeologist who studies the medieval period downright modernity when compared to the age of the dinosaurs.
MARIE WOODS: I find it hilarious that I look at things from about 800 years ago.
And here's his footprint from 165 million years ago.
ALI ROGIN: Woods is one of the co-authors of a recently published study that confirmed the footprint was from a giant theropod, a dinosaur group that includes the T. rex.
Even better, the print revealed a new dinosaur behavior squatting.
MARIE WOODS: What they've said is quite significant about this particular print is the fact that it's the only one of its kind in the world that shows the behavior of a dinosaur of this kind actually taking a rest.
ALI ROGIN: I love that idea of it helping tell the story of the fact that these theropods could take rests and just maybe sit and admire the coast.
MARIE WOODS: Exactly.
Sit and relax on a sunny Scarborough day.
ALI ROGIN: To protect the footprint from the elements, fossil collectors carefully removed it from the rocky cliff.
That's when they realized another fossil hunter, Rob Taylor, had spotted the same print, just not fully exposed a few months earlier.
Woods and Taylor share in the historic find.
And though paleontology has been a field dominated by men, woods hopes her discovery will help change that.
MARIE WOODS: It's fantastic, especially for myself, to encourage more young women and, of course, school children to get involved in a science-based subject.
ALI ROGIN: And Molly Sampson's find is proof that neither gender nor age matters when it comes to contributing to science.
STEPHEN GODFREY: Paleontology is one of the disciplines of science where the avocational community, with whom we collaborate regularly, can make a significant contribution.
And so, just like Molly getting out and looking for fossils, there is a large, relatively large population of collectors who are very passionate and know a lot about the geology and paleontology who collect fossils and bring them to our attention.
ALI ROGIN: So tell me about what it takes to be a good fossil hunter?
BRUCE SAMPSON: It's not always easy to find stuff, right?
Sometimes you got to be patient and give out a lot and keep exploring and investigating different things, right?
MOLLY SAMPSON: Yeah like if you see the rocks, like you might not see them on top, but before start digging, you up on top, and then you can scrape the rocks and see if there's anything under them.
ALI ROGIN: Patience, a good eye, and a lot of curiosity.
For "PBS News Weekend," I'm Ali Rogin.