Will Watts meets me at the Watermark cafe on Scarborough’s North Bay seafront. We get in his car and set off up the coast. We are heading for Saltwick Bay near Whitby, where we will go for a walk.

“Will,” I say after a minute, “I can’t help but notice you have a Tyrannosaurus rex on the back seat.”

“Actually, it’s an allosaurus,” he says.

It’s just a skull, of course: the real live animal would not fit in a small hatchback, and would probably refuse to wear a seatbelt.

“Was that found here?”

“No, it’s an American specimen. But I keep it because we have similar-sized creatures here: megalosaurus – as tall as a double-decker bus, meat eater. I can show you footprints later.”

Will is a fossil expert and my guide in hunting out some specimens on the North Yorkshire coast. Not that I’m expecting large skulls, just some decent ammonites. My ambition is to find a nodule and split it open to reveal a perfect specimen.

Saltwick Bay is a small, sandy cove a mile east of Whitby, and at low tide you can wander on the scars – long flats of fissured intertidal rock, loved by wading birds, crabs and tiny sea creatures. The fossils, however, tend to be around the high-tide mark. But how do you recognise the rocks where the fossils are hiding? Will tries to explain. “They are often a bit misshapen. There’s a lump or a mark, or a line.” He bends down and picks one up. How did he spot that? It’s a nondescript rounded grey stone about five centimetres across, lying in a bed of similarly rounded stones of many shades and colours. He taps at its equator with a geological hammer and it splits to reveal a sharp, dark, little ammonite.

“Dactylioceras. Nice first find of the day.”

I was prepared to treat this fossil as a family heirloom, but Will seems confident of bigger, better finds, so we leave it on a rock for others to discover. We shuffle along the shoreline and I pounce on a rock.

“I don’t think so,” says Will.

To humour me, he splits it open. Nothing. He bends down. “Ah, here we go.” It is a lump of black Whitby jet as long as his index finger. It had been sitting right next to my rock.

“Now, that is unusual to find such a big piece.”

Jet is a semi-precious material and also a fossil, the resin of monkey puzzle trees from the Jurassic. “It’s very light, so it floats,” says Will. “You find it along the high-tide mark.”

Whitby jet was a jewellery favourite for Victorian funeral goers, and has been revived by goths.

Our next find is something considerably larger: a ship. We have walked out on the wrinkled winkle-crusted rocks around Black Nab, an evil thumb of rock that has snared many unfortunate ships. One was the trawler Admiral von Tromp (no, I’m not making it up – headline: “Tromp founders on Yorkshire coast”?). The remains lie in a hollow, like the fossilised skeleton of an iron creature, but in fact they’re only 40 years old. No one knows why the vessel hit the rocks, as the man on watch tragically drowned, along with one other.

Along the edge of the scars at low tide it’s easy to appreciate what gives this coast such a monstrous appetite for sailors’ lives: vast rollers slamming in, and a bitter easterly wind ripping watery veils from waves, twinned with cliffs up to almost 200 metres high. No wonder sailors who survived the wrecks in pre-lifeboat days often died trying to climb out of the sea.

Will and I move south by car to Ravenscar, where we have another foray along the beach, giving the seals as wide a berth as possible. And, at last, I spot a nodule.

“Looks hopeful,” says Will, handing me the hammer. I give it a few taps, then a hefty whack. It divides neatly and perfectly. And there, moulded by 180 million years, is a lovely ammonite.

“I never tire of that moment,” says Will, and I know what he means – it’s the magic of revealing something from so deep in the past, from a very different world.

Will is particularly good at conjuring that world. When we walk to our third and final site, Burniston, he gets his chance. The rocky shore here is littered with rocks of various colours, but it is a slim shelf of tawny and grey sandstone that interests Will: it runs along the cliff a little above head height. “That is an old muddy river bed through which dinosaurs walked 160 million years ago,” he says.

He spends several minutes scouring the fallen rocks until he finds what he wants. He settles down and begins to reveal a vivid picture of this area, pointing to the rocks around him. “See these ripples on this rock? They are the fossilised ripples in the sand. And this is fossilised wood – ginkgo and cycad. And here’s evidence of a forest fire – fossilised charcoal. These are worm burrows and traces of small creatures. And look…” His fingers trace out three toes. I stare. It takes a moment to comprehend what I’m looking at: the perfect stone cast of a dinosaur’s foot.

“This is a small predator, walking this way, hunting.”

I’m entranced. I never had that boyhood dinosaur obsession thing, but this stirs something. The Jurassic has come to life.

“We’ve found the footprints of around 30 different types of dinosaur.”

But now the light is fading. It is time to retreat to the Watermark cafe again. In the car, in the twilight, the allosaurus appears to be grinning at me.

• The trip was provided by North York Moors national park. Will Watts and Hidden Horizons run coastal fossil hunts and dinosaur walks (three-hour walk £25, 01723 817017). The Plough at Scalby (doubles from £100 B&B, singles from £65) is a handy base to see the Burniston dinosaur footprints. YHA Boggle Hole has beds from £15, private rooms from £30. The Watermark Café does excellent fish and chips, among other things.