It walked slowly along the tidal flat, looking for something to eat that might have washed up on the shoreline. To its right were the sounds of the surf and the ancestral Gulf of Mexico. To its left was a dense forest.

Acrocanthosaurus, a fearsome meat-eating dinosaur 40 feet long and 16 feet tall, was on the move.

“It's the size of Tyrannosaurus rex — not as bulky, but as big. And here it is, walking across the beach 110 million years ago in what is now San Antonio,” said Thomas L. Adams, Ph.D., curator of paleontology and geology at the Witte Museum.

It's a striking discovery: the only publicly known dinosaur tracks in Bexar County. Officials have known about the tracks at Government Canyon State Natural Area for about 10 years, but it wasn't until this summer that scientists and students began work to catalog and protect them.

Dinosaur tracks might not seem to be as interesting as fossilized bones, but scientists beg to differ.

More Information Ancient life The new Dinosaur Gallery will feature numerous prehistoric beasts: Dinosaurs: Acrocanthosaurus Tyrannosaurus rex Agujaceratops Gryposaurus Alamosaurus Pterosaur: Quetzalcoatlus Crocodilyform: Deinosuchus Mosasaur: Tylosaurus Sea turtles: Protostega Toxochelys Prehistoric fish: Pachyrhizodus

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“The hard parts of the animals that are preserved are remains of dead animals,” Adams said. “They tell you something about a dead animal.

“This was made by a living animal. He was moving. He was interacting with his environment. It tells you many, many things. It tells you what the shape of its foot was like because in a skeleton we can't see that. These are the remains of living animals. They tell you a story.”

The Witte is working with the Texas Parks and Wildlife Department, which manages Government Canyon. on a joint project to bring the tracks to the public. Adams and John Koepke, natural area interpreter/volunteer coordinator at Government Canyon, are heading the research.

They and a team of volunteers primarily from UTSA and San Antonio College have been painstakingly cleaning, measuring and cataloging as many as 200 tracks exposed in Government Canyon Creek, now dry but occasionally filled with water after a heavy rain.

There are two main trackways at the site, lying on either side of the Joe Johnston Trail about 2.5 miles from its start near the visitor center. They are accessible by foot, though the trail is rough in places and may prove difficult for some to navigate.

The lower trackway, believed to have been created by Acrocanthosaurus, is at the base of a 50-foot cliff created by limestone sediments deposited in the millions of years since the tracks were made.

A second trackway, about 18 inches higher, likely was created by Sauroposeidon, a plant-eating dinosaur some 60 feet long and 25 feet tall. It's in another layer, made as many as several thousands years later.

“You can never tell 100 percent who the track maker was,” Adams said. “You can just make a scientific guess based off the fossils we have that occur at the same time in the same geographic area.”

In addition to the Acrocanthosaurus and the Sauroposeidon, the tracks indicate there were many other prehistoric animals traveling in the same area.

“To give you an idea where we are in time,” Adams said standing on the lower trackway, “We're in the Glen Rose formation, 80 feet below the Edwards — Glen Rose contact.”

Adams added, “We're about 110 million years ago in the Early Cretaceous and we're on a tidal flat. Sea levels have been rising but now they've fallen slightly, exposing these large, shallow water carbonate shelves where all this carbonate is being put down, all this limestone is being deposited.

“There are periodic low tides coming in every so often and these dinosaurs are taking advantage of that low sea level to walk upon this pretty much unhindered highway.”

The surface dried and hardened, preserving the Acrocanthosaurus tracks at the site, Adams continued, and then the sea level rose again bringing carbonate back in and depositing new layers of limestone.

“Then we have the sea level fall again, same condition for the first tracks and how we have a sauropod walk through here,” Adams said. “It's pretty much the exact same environment, the same situation, the same events occurring in the same order.”

The Witte Museum plans to display the casts made of the Acrocanthosaurus trackway underneath a life-sized skeleton of the animal in its new 3,000-square-foot Dinosaur Gallery, a part of the $60 million second phase of renovations in the “New Witte” expected to be completed in late 2017. Work on that project is expected to start this fall.

The casts, as well as other interpretive material, also will be on display at Government Canyon. As will the original tracks themselves.

The Witte and the state parks agency are committed to devising methods of “conservation and protection from potential vandalism or other loss” for the tracks.

“Every visitor that comes here is faced with a decision and it's an important one,” Koepke said. “Do I leave these alone or not? You know the expression 'pay it forward?' We're asking every visitor to pay it forward so that their grandkids, their grandkids' grandkids can each come here and have the thrill that they're going to have when they see these.”

Adams agreed.

“They've been there for 110 million years,” said Adams. “They've been exposed probably for the last several thousand years. But just within the last 10 years they're starting to disappear.”

“A lot of that has to do with human interaction,” he said. “People have a tendency to speed things up. We know this is going to happen, we can't avoid it. We have to prepare for it. “These need to be here for generations, so we need to make sure the public understands that here's this wonderful natural resource in San Antonio that we have,” Adams said. “They'll be here as long as people respect that.”

mpfeiffer@express-news.net