Back in 1996, Massachusetts resident Gary Gaulin was digging a hole for a backyard fishpond when he discovered something totally unexpected: dinosaur footprints. Landscaping plans foiled, Gaulin decided to keep excavating on what would turn out to be one of the world's best sources of prehistoric trackways, a site that attracts amateur and professional palaeontologists to this day, and now bears the name of its owner – the Gary Gaulin Dinosaur Tracksite. 

These are Anomoepus, small dinosaur tracks each no larger than 3cm (1 inch) long. The preservation here is so good that the sediment preserved the hand and footprints of this dinosaur as it walked on all fours, and even the grooves where its tail and toes dragged across the ground. Image: Sebastian Dalman

True to its name, the most common footprints at the site belong to meat-eating theropod dinosaurs that walked across this part of the world in the Early Jurassic, more than 175 million years ago. The largest of these, a type of footprint named Eubrontes (yes, footprints get their own genus and species names!), are as big as 40 centimetres (16 inches) long.

On the other end of the spectrum are diminutive tracks called Anomoepus, less than three centimetres (one inch) long, belonging to very small dinosaurs. Whether these came from a pint-sized species or younglings is uncertain, but the fact that many of these trackways occur together suggests these little dinos may have been gathering in groups.

This Eubrontes footprint, one of the best of its kind from this site, was left by a large predatory dinosaur. Image: Patrick Getty

"The Gary Gaulin site appears, at first glance, to be completely unimpressive," says Patrick Getty of the University of Connecticut, referring to the site's small area. "What makes it impressive is the types and quality of fossils that are being collected there."

Getty spoke about his own work on the site, and that of his colleagues, during the Triassic-Jurassic Research Symposium last week at the Bruce Museum in Connecticut.

The Gary Gaulin Tracksite is not large, but it contains layer upon layer of beautifully preserved fossil footprints. Image: Patrick Getty

The site, located in what is the city of Holyoke today, was once an ancient playa lake – a shallow, dry-climate body of water that fills in and dries out as the seasons pass.

The preserved ripple marks in the rocks are evidence of the lake's shallow waters, and a series of petrified mudcracks reveal a history of successive wetting and drying. Dinosaurs likely visited this body of water each year, leaving the footprints that are now entombed in multiple stacked layers of mudstone and sandstone.

Once you look past the eye-catching dinosaur prints, traces of much smaller prehistoric track-makers come into view. Tiny grooves running across the rock reveal the presence of long-gone arthropods that walked (or swam) by. The site is also pockmarked with the burrows of worms and insects that made their homes just beneath the lakebed. There's even the body imprint of a creepy-crawly that stopped for a moment to rest in the mud. 

Cheliceratichnus is a trace fossil unique to this site. It marks the spot where a prehistoric bug sat to rest. Exactly what animal made this impression is still under discussion – candidates so far include mayfly larva, whip scorpion and camel spider. Image: Sebastian Dalman

But perhaps the most surprising "footprints" at the site weren't left by feet at all, but by fins! S-shaped trails called Undichnus represent the sweeping tails of fish as they swam though the shallow waters during the wet seasons.

"The fish trails ... are important because they support the idea that the carnivorous dinosaurs in the valley ate fish," Getty explains.

Tracks of meat-eating dinosaurs are extremely common at the site, but herbivores are much rarer, which left researchers wondering what sort of creatures were once at bottom of the food chain here. "This helps to makes sense of what is a very weird ecological conundrum."

These tiny grooves called Bifurculapes are the footprints of a little arthropod that crawled (or swam) across the ground. Image: Patrick Getty

The northeast United States is actually famous for its many fantastic tracksites, formed at a time when the supercontinent Pangaea was breaking apart.

"As the landmass fragmented, huge valleys opened up [and] filled with lakes that had muddy and sandy margins that were conducive for footprint production and preservation," Getty explains. "A similar process is occurring today in the horn of Africa, which is pulling away from the rest of the African continent."

The Gaulin tracksite first appeared on Getty's radar during his university days, but even years later, he suspects the site has not yet run out of surprises. "I think it's got a potential for quite a bit more very exciting discoveries over the next couple of years."

Thousands of these three-dimensional burrows cut through the mud layers of the site. Known as Treptichnus, they were left by burrowing insect larvae. Similar burrows are made by such critters today. Image: Patrick Getty