Dinosaur Valley State Park

Listen for the river first. The Paluxy runs shallow and clear here, sliding over pale grey rock with a soft, steady hiss. Cedar and oak lean over the banks. When the sun is high, the limestone in the riverbed turns almost white, and the water throws moving bands of light across it. Look down at that rock for a moment. Some of the dents and hollows under the water are not random. They are footprints.

You are standing in Dinosaur Valley State Park, just outside the small town of Glen Rose in Somervell County, Texas. This stretch of river holds some of the best-preserved dinosaur tracks in North America. They were made roughly 113 million years ago, in the Early Cretaceous period. That is the middle part of the age of dinosaurs, long before Tyrannosaurus walked the earth. The tracks stay in the open, in the place where they were made.

It helps to picture what this land looked like then. There were no hills, no cedar, and no river. Instead, this area sat near the edge of an ancient shallow sea. The shoreline moved back and forth over time. Animals walked across wide flats of soft, wet lime mud, close to the water. Their feet sank in. Then fine sediment covered the prints before waves or weather could smooth them away. Over millions of years, that mud hardened into the limestone under your feet.

Two main kinds of track makers left their mark here. The first are three-toed prints, with long, narrow toes. They come from a large meat-eating dinosaur that walked on two legs. Many researchers link these tracks to Acrocanthosaurus, a big predator known from this region and this period. The second kind is broad and round, almost like a dinner plate or a small tub. These belong to long-necked plant eaters called sauropods, which walked on all four legs.

Here is the first thing many visitors miss. The tracks are not simply scattered prints. In places they form trackways — a row of steps made by one animal as it moved. From a trackway, scientists can estimate how fast the animal walked, how long its legs were, and which way it was heading. A line of footprints is a record of behaviour, not just of body shape. You are reading a few seconds from one animal's day.

The story of how these tracks became famous has a surprising start. During the hard years of the 1930s, some local people carved fake footprints into loose blocks of limestone. They sold them to tourists and collectors. A few of these carvings looked like giant human feet. Those carved blocks travelled, and they caught the attention of a fossil hunter named Roland T. Bird, who worked for the American Museum of Natural History in New York.

Bird came to the Paluxy to find the source. He found real dinosaur tracks in the riverbed, many of them very clear. In the late 1930s and early 1940s, he led an excavation of a long sauropod trackway, with the tracks of a meat eater running alongside it. The crew had to divert the river to reach the rock. Sections of that trackway were cut out and shipped away. One section went to New York. Another went to the Texas Memorial Museum in Austin.

That side-by-side trackway led to a famous idea. Some people read it as a predator following a plant eater, perhaps even hunting it. Others are more cautious. The two animals may have passed at different times. Either way, the find helped prove that sauropods walked on land, carrying their own weight. Earlier, many scientists had pictured them living mostly in water.

Now for the second surprise, and it involves those carved human footprints. For decades, some visitors claimed that certain tracks along this river showed people walking beside dinosaurs. Scientists looked closely at these so-called man tracks. Most turned out to be eroded or partly filled dinosaur prints, where the toe marks had worn away or filled with sediment. The controversy is part of the river's story. It is also a good reminder to look carefully before believing what a shape seems to show.

The land became a state park in the early 1970s. Near the entrance area you may notice two large dinosaur models — a long-necked sauropod and a Tyrannosaurus. They are not scientific reconstructions of the animals that left these tracks. They were made for the 1964 New York World's Fair, for an exhibit sponsored by an oil company. Later they were donated to the park. Their style shows how people imagined dinosaurs in the 1960s, with upright, tail-dragging poses that science has since changed.

Whether you see tracks today depends on the river. When water levels are low and clear, the prints show up sharply, sometimes holding small pools of water. After heavy rain, the river can rise, turn cloudy, and cover them completely. Algae and silt can also hide the edges. So every visit is a little different. Rangers often sweep or clear some track sites, and the best viewing often comes in drier spells.

The park is more than a fossil site. Trails climb up from the river through juniper and oak onto limestone ledges with views across the valley. The rock layers in the bluffs are the same family of stone that holds the tracks, stacked like the pages of a closed book. Birds call from the cedar. In warm months the river draws families who wade in the shallows. It is worth walking a little away from the main crossing to find quieter stretches.

If you step into the riverbed, move slowly. The limestone can be slick, and the tracks are fragile. Try not to stand inside a print or scrape at its edges. Every small crack and every flake of loose rock adds to the slow wear of the river. These prints have lasted more than a hundred million years. Most of that time they were buried. Out here in the open, sun, floods and footsteps work on them every day.

Before you leave, kneel down near one clear print and look at it at eye level. Notice the curve of the toes, the slight ridge of mud pushed up at the sides, the way water sits in the hollow. An animal pressed its weight into soft ground here, at the edge of a sea that no longer exists. Then listen again to the Paluxy running over the stone. The river is wearing the tracks away, one season at a time, and you are here to see them.