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Trackways of the Paluxy River

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Trackways are actually quite common.  They come from all periods of time and all sorts of animals.  How do we know which animal made the tracks?  Paleontologists study foot bones of fossils to determine size, shape, and stride.  They also study living animals.  Current footprints show how hooves, foot pads, and claws compress mud.  Then the best candidate fossil is chosen as a match to the footprint.

Take a walk at Dinosaur Valley State Park, in Glen Rose Texas, and you can literally walk in dinosaur footprints.  The Paluxy River still runs across the prints and will erode the limestone tracks until none are left.  To preserve the existence of this wonderful story, paleontologists have removed some of the tracks.  You can see a long series at the Texas Memorial Museum at Austin.


Pleurocoelus: (PLUR-o-SEE-lus) Sauropod, 50 ft long, 80,000 lbs.

Acrocanthosaurus: (AH-cro-CAN-tho-SAW-rus) Theropod, 35 feet long, 12,000 lbs.

Iguanodon: (e-GUAN-o-don) close cousin of the Hadrosaur, 30 ft long, 10,000 lbs.


The Tracks Tell a Story

Early Cretaceous 113 mya

Once upon a very long time ago, dinosaurs lived near a limey mudflat close to a shallow inland sea.  A Pleurocoelus strolled across unaware of danger; its feet sinking deep into the soft mud.  Stalking him, an Acrocanthosaurus, walked, crouched, and ran, hoping to catch a meal.  Nearby an Iguanodon watched both animals carefully, as it nibbled delicate ferns.

Soon afterwards another layer of mud gently filled the prints, preserving them. Many layers covered the first.  After millions of years, the calcium carbonate in the lime consolidated (cemented) forming limestone.  Each layer contained different amounts of minerals, making harder and softer layers of stone.  Millions of years passed again.  In 1908 a huge flood ripped through the Paluxy River removing several feet of stone layers, exposing the limestone prints. 

Mistaken Identification

In 1909, while wandering in a tributary of the Paluxy River, a teenager discovered giant turkey tracks.  A local teacher had heard of tracks from New England and correctly identified these as dinosaur.  The next year two more teenagers found tracks in the River itself.  Accompanying the three-toed tracks were oblong tracks 15 to 18 inches long.  The boys described them as “giant man tracks.” 

In the 1930’s, locals cut out and pried up slabs of tracks to sell as curiosities.  One resident sold oblong “man tracks”.  But carving loose slabs was much easier than raising actual prints from the riverbed.  He added details not found in the originals to make them look more human.  These people were not promoting a scientific or theological agenda.  They only wanted to feed their families during the Great Depression.

The first paleontologist to look at the tracks, R. T. Bird, arrived in 1938 after seeing a few carvings in New Mexico.  He found no human tracks but could not explain the oblong impressions.  He also discovered wash tub sized tracks.  While three-toed Theropod tracks had been seen before, this was the first report of Sauropod tracks.

The people supporting “man tracks” have misquoted Bird's writings and used photos of the carved footprints as proof of humans living at the same time as dinosaurs.  Ironically, one of the main groups to publicly dispute human tracks came from a team of Creationists.  They found dinosaurian digits and erosion oddities but no evidence of human trackways.  They noted that many of the “man tracks” had actually been highlighted with oil to make them more human-like.  No reputable researcher has ever found credible “man tracks” in the limestone of the Paluxy River.

So, What Are They?

The three-toed tracks are accredited to Acrocanthosaurus, a common Theropod of the Early Cretaceous.  In hunting, Acrocanthosaurus used different modes of locomotion.  Scientists can tell if the animal was walking or running by the stride of the three-toed footprints.

The oblong tracks belong to this animal also.  Like birds, Theropod dinosaurs walk and run on their toes with the ankle and smallest toe held off the ground.  In 1979, G. J. Kuban concluded that the oblong tracks show a new way of walking.  Here the weight of the animal rests on the ball and heal of the foot instead of the toes.  In the oblong impressions, shallow toe marks and the smallest toe can often be distinguished.  Why would a Theropod do this?  Was it for better traction in the mud? Or did the animal crouch low while it stalked its prey?


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