Pick from the Past
Natural History, February 1941

A Dinosaur Walks into the Museum

Scientific detective work sheds new light on the habits and appearance
of the most gigantic animals that ever roamed the earth, when the
biggest footprints ever found are placed on display.

To read about the discovery of the Paluxy River site, see Roland T. Bird’s
earlier story, “Thunder in His Footsteps,” published in May 1939.

IECING together the story of prehistoric animal life is, in its entirety, a gigantic scientific detective problem. Rarely, however, does the process suggest so closely the classic methods of Sherlock Holmes as in the case of the footprints of the “Thunder Lizard,” for important new information on the appearance and mode of life of this titanic dinosaur has been deduced from the trail which he left in mud some 120 million years ago.

The general appearance of the “Thunder Lizard” has been known from abundant skeletal remains, fossilized in the rock pages of the earth’s history. But whether he walked on his four feet and trod the dry earth or lumbered about in shallow water, remained unknown, along with other important facts, until the eye of science fell upon these tracks.

Of all creatures that ever walked on earth, the “Thunder Lizard,” Brontosaurus, and other dinosaurs of his group, the sauropods, hold the world’s record for size. Indeed, they seem to have reached the possible limit that an animal with feet could attain. A few other sauropods were larger, but Brontosaurus is typical of the group.

One day late in November, 1938, while prospecting 80 miles southwest of Ft. Worth, Texas, I noted three or four huge depressions in the bed of the Paluxy River, —footprints of these gigantic monsters. On a rock ledge leading underwater was undoubtedly a trail left by a 60- or 70-foot sauropod weighing 20 or 30 tons, probably the “Thunder Lizard” himself. Specimens of this sort were hitherto unrecorded, and I faced the problem of removing a suitable selection for the American Museum.

The task promised to be in keeping with the magnitude of the tracks involved. How would one cope with the whims of a temperamental river while tracing 38-inch footprints underwater? By what method could a suitable section be removed from the solid rock? At each stride the animal moved ten or twelve feet. Where, indeed, could such a large exhibit find room in the Museum’s halls?

Almost two years later to a day, after five months of intensive work, the largest single display of dinosaur tracks ever uncovered was boxed up. With so great a wealth of material available, two other institutions shared in the collection. In all, 40 tons of track-bearing rock were removed from the river bed.

Visitors to the new Jurassic Hall in the American Museum will in time see the original footprints mounted in the base of the gigantic skeleton of the “Thunder Lizard.” As if this 120-million-year-old monster had just strolled into his present position in the hall, you will see the tracks as he would have left them, six front and six hind footprints, under glass resembling the water in which he waded. This solution of the exhibition problem had already occurred to curator-chief Barnum Brown’s fertile imagination before the venture was assured.

What the tracks revealed and how they were removed with the aid of the Texas State-Wide Paleontological Survey, a Works Progress Administration Project, is told in these pages, To Dr. E. H. Sellards of the Bureau of Economic Geology of Texas goes credit for having made possible this valued assistance. To all my other Texas friends, far too numerous to mention singly, who helped in this quest, both at Glen Rose and Bandera, where one other known locality for this type of track was found by us, I extend my heartfelt thanks.

ORIGINAL DISCOVERY: the footprints of one of the most gigantic animals ever to walk on earth, a sauropod dinosaur. Originally made on a soft mud flat, the trail was later covered by silt laid down in comparatively quiet water. On top of this, inland seas which invaded parts of Texas approximately 100 million years ago deposited sediments. These ancient, consolidated deposits have long since been elevated high above sea level, and the tracks have been exposed by the cutting action of the Paluxy River, which flows across them today. Only right hind and forefoot impressions were at first visible, but the trail continues underwater toward the rocky point beyond. Examination of the many additional prints was to settle the argument of whether these dinosaurs walked on all fours or crawled. Hind footprints were 38 inches long and 26 inches wide, and showed four claw impressions. Forefeet were smaller, more rounded, and the toes terminated in fleshy pads lacking the single claw known to have been carried by other sauropods whose skeletons have been found.

FIRST MOVE in following the trail was to construct a cofferdam of sandbags so that the area could be drained and the tracks examined. The dam rapidly nears completion as men drag sandbags across the mud-filled potholes that mark the course once followed by the dinosaurs. Fossil-hunting, entirely a new experience to the crew, all local men, excited mild curiosity in some, in others, keen interest. When told that the name Brontosaurus means “thunder lizard,” Monroe Eaton declared, “One certainly went here that shook the ground.”

TRACKS begin to appear as water is drained from the area. Lacking a gasoline pump, the men used buckets to remove the water, and could bail about twelve barrels a minute by this method. Keen to see what the tracks were like, they completed the task in less than two hours. But recurrent floods were to refill the dam many times.

THE BIG TRAIL led toward a shelving ledge and disappeared beneath it. One local man, inclined to scoff at the notion of finding additional tracks beneath the undisturbed overburden beyond, laughingly said, “Why, that animal didn’t walk under all that rock!” Actually, of course, the dinosaur walked before the overlying rock was deposited as soft sediment. From a study of the rocks the scientist can reconstruct the landscape and climate at the time.

A VIEW looking upstream along the tracks which had been underwater discloses positive proof that this great animal walked on all fours, for the hind and front footprints are clearly discernible in regular order. Only in one trail, at Bandera, were there eight or nine forefoot impressions and only one hind one, where a sauropod, buoyed up enough to go on fore legs, had put down a hind foot to turn. The absence of any mark of a dragging tail except in one instance was the next clue to the dinosaur’s habits. Fully 25 feet long and very heavy, the tail could not have been carried in the air. Therefore, the animal must have waded in the water, where the tail, tending to float, could have been held off the bottom.

AN EXCAVATION revealed much more of the path of the dinosaur, which swung gradually to the right. Was the dinosaur alone when he waded across the mud flat 120 million years ago?

ANOTHER TRAIL is found. While widening the excavation, a new series of even more promising tracks was located, coming in from the north on the bank side. Again beckoned by the unknown, the diggers began a new excavation to trace this second trail. Further surprises were in store.

A JUTTING LIMESTONE LEDGE is in the way, so it must go: broken sections being moved away with the aid of bars and rollers. It contained many fossil oyster shells and other marine invertebrates left there when the sea advanced over the area. Why have no sauropod tracks been discovered farther north in the United States, where skeletons of the animals have been found in large numbers? Dr. Brown deduces that only in seaside mud flats, as distinct from lake marshes, would the putty-like earth of decomposed marine organisms be firm enough to receive and hold the impression of the feet while underwater. Preliminary examination of the rock bears out the conclusion that the dinosaurs here were wading in a shallow, brackish arm of the sea, though the spot is now almost 300 miles from the coast. Farther north, where sauropods frequented the lakes, they died in great numbers in diminishing pools when the drying up robbed them of the water necessary to their existence.

WITH the limestone ledge blasted and cleared away, Trail Two stands out clearly on the right. Other trail disclosures indicate that no less than a dozen sauropods had crossed this section. All were progressing in the same direction as a herd moving across a shallow mud fiat.

MOST INTERESTING FEATURE uncovered during the season’s work was the trail of a flesh-eating dinosaur following that of a sauropod. This is seen at the left of Trail Two as a row of three-toed footprints. Made at a time when the mud was of the same consistency, these prints suggest that a fourteen-foot flesh-eater was actually stalking the big quadruped. At any rate, when the sauropod swung to the left, the carnivorous dinosaur did likewise. Along this ancient waterfront, the territory of these two distinctively different types of dinosaurs overlapped.

PREPARATIONS are made to remove the first slab of tracks, 29 feet long by eight feet wide, to be placed under the tail in the base of the Brontosaurus skeleton in the American Museum. Most fortunate circumstance of the entire season was the comparative thinness of the track-bearing layer, which was less than eighteen inches thick. The rock rested on a four-foot bed of soft clay and was not difficult to cut with chisels. The sequence and association of fore and hind foot impressions are typical of the trail made by any slow-moving, very heavy four-footed animal. Later a suitable section of the flesh-eating dinosaur trail was taken.

HOW REMOVAL of this 30,000-pound track slab was possible. In addition to the fortunate bed of clay underneath, the block also had convenient cross-fractures which allowed easy blocking off into sections. The edges were then covered with plaster jackets to preserve clean contacts, sections were given numbers, and their relationship recorded on a chart, so that re-assembly would present no problem.

PHOTOGRAPH OF THE PHOTOGRAPHER: the high scaffold "tripod" from which most of the trail pictures were made. In the background below, men are reducing the weight of several sections of slab by chiseling off surplus stone from the underside, preparatory to moving them up a 30-foot river bank where they were to be picked up by truck.

AFTER the American Museum specimens were removed, other track slabs were taken for the University of Texas and the U. S. National Museum in Washington. This photograph is not a picture of the world’s biggest jigsaw puzzle but just a fraction of the 1200-piece, 40-ton collection of tracks being crated for shipment. Materials used on the job included 1500 burlap sacks, 2000 pounds of plaster of Paris, and 8000 Kleenex tissues (to prevent plaster from adhering to track surfaces).

ONE of the major vicissitudes associated with collecting fossils from a river bed. When the river rose, dikes broke, and the quarry filled with mud. Most exasperating were repeat performances, just after the quarry had been cleaned. This shows the river receding from a typical five-foot rise, of which there were half a dozen during the summer.

HOW BIG is a big sauropod track? The young man examining this one, even to the point of taking a bath in the crazy thing, is young Tommy Pendley, who just wanted to find out. The footprint held eighteen gallons of water. Hailing from Cleburne, Texas, Tommy was the three-year-old son of one of the men engaged on the project. Beside it is shown the footprint of a large modern elephant reproduced in the same scale for comparison with the dinosaur footprint.

THE SKELETON of a sauropod, approximately the one which left his footprints in Texas mud: Brontosaurus, under whose tail the footprints will be mounted in the American Museum’s new Jurassic Dinosaur Hall. Once living in fresh and brackish water of lakes and lagoons, these creatures floated their huge bulks around in quest of the plants on which they lived, occasionally wading close to shore. That they were sometimes preyed upon by the fierce flesh-eating dinosaurs of the times is known from tooth-scarred bones, as well as from the tracks of a flesh-eater apparently following the trail of one of these huge creatures the whole length of the quarry in the foregoing photo- graphs. The skeleton is over 66 feet long and stands 15 feet high at hips.

AMNH Photo by Coles

To read about the discovery of the Paluxy River site, see Roland T. Bird’s
earlier story, “Thunder in His Footsteps,” published in May 1939.

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