Dinosaur dance floor

Nicole Miller

'Dinosaur dance floor' unearthed in Arizona
Multitude of beastly tracks likely belonged to at least four different species

1. This Eubrontes dinosaur footprint, including three toes and a heel, measures roughly 16 inches long and is thought to have been made by an upright-walking meat-eater. Inset outlines the footprint shape.

2. More than 1,000 dinosaur footprints along with tail-drag marks have been discovered along the Arizona-Utah border. The incredibly rare concentration of beastly tracks likely belonged to at least four different species of dinosaurs, ranging from youngsters to adults.

3. The tracks range in length from 1 to 20 inches (2.5 to 51 centimeters).
"The different size tracks may tell us that we are seeing mothers walking around with babies," said researcher Winston Seiler, a geologist at the University of Utah.

4. The tracks were laid about 190 million years ago in what is now the Vermilion Cliffs National Monument.

5. "There must have been more than one kind of dinosaur there," said researcher Marjorie Chan, professor and chair of geology and geophysics at the University of Utah. "It was a place that attracted a crowd, kind of like a dance floor."

6. While the site is covered in sand dunes now, the researchers say the tracks are within what was a network of wet, low watering holes between the dunes. In fact, the tracks provide more evidence of wet intervals during the Early Jurassic Period, when the U.S. Southwest was covered with a field of sand dunes larger than the Sahara Desert.

7. Chan and her colleagues, including Seiler, described the dinosaur track site in the October issue of the international paleontology journal Palaios.
By studying the shapes and sizes of the tracks, Seiler suggests four dinosaur species gathered at the watering hole, though the researchers have yet to match the prints with specific species. Currently, the tracks are named for their particular shapes and include:

8. Eubrontes footprints measure 10 to 16 inches (25 to 41 cm) long and have three toes and a heel. These tracks likely were made by upright-walking dinosaurs with a body length of 16 to 20 feet (5 to 6 m), or smaller than Tyrannosaurus rex. Grallator tracks are about 4 to 7 inches (10 to 18 cm) long, are three-toed and were left by small dinosaurs only a few feet tall.

9. Sauropodomorph tracks, more circular than the other types, were left by creatures that walked on four legs and were the largest dinosaurs at the site. Their tracks range from 6 to 11 inches (15 to 28 cm) long. Seiler said the tail-drag marks are associated with these circular footprints, so they likely were made by sauropods.

10. Geologist Winston Seiler with some of the dinosaur tracks in northern Arizona, which are so abundant that the researchers refer to the site as a "dinosaur dance floor."

11. Anchisauripus tracks measure 7 to 10 inches (18 to 25 cm) long and were made by dinosaurs that ranged from 6 to 13 feet (2 to 4 m) in length. Numerous dinosaur track sites have been found in the western United States and elsewhere around the world. For instance, tracks from a herd of 11 giant sauropod dinosaurs were discovered in the ancient coastal mudflats of Yemen. But the new discovery is rare in the density of tracks.

12. "Unlike other trackways that may have several to dozens of footprint impressions, this particular surface has more than 1,000," Seiler and Chan write.

13. Chan first visited the site of the dinosaur tracks in 2005 with a U.S. Bureau of Land Management ranger who was puzzled by them. Chan initially called them potholes, which are erosion features common in desert sandstone. "But I knew that wasn't the whole story because of the high concentration and because they weren't anywhere else nearby but along that one surface."

rb

Dinosaurs

Dinosaurs

1. In the early 1800s people in England were fascinated with fossils. Fossils are the remains of living things that have been preserved in rock. Dinosaurs' fossils were found on nearly every continent. Mostly found in China and the United States.People found giant bones and wondered what animals they belonged to. They had never heard of dinosaurs.

2. In 1842, Richard Owen was the first person to use the word dinosaur, which means "fearfully great lizard."Fossils are buried deep in the ground. They come to the surface when the ground wears away or is dug up. A dead dinosaur sank in the mud or was covered by sand blown by the wind.Over a long period of time, the layer of mud or sand thickened and became hard rock. The animal remains hardened and turned into stone. This is called fossilization.

3. Movement of the earth's crust and erosion caused the fossils to rise back up to the surface.Scientists who study fossils are called paleontologists. The first thing a paleontologist does when fossils have been found is to make a detailed map of the bones.

4. They take measurements, make drawings, and take photographs.Fossil bones are wrapped in strips of plaster. Then they are transported to a laboratory, where they are identified. Once scientists put together a skeleton, they can figure out where the muscles went by marks they leave on bones.

5. Fossils are fragile. They have to be removed very carefully. Paleontologists use brushes, chisels, hammers, and picks. Scientists have learned more about dinosaurs by studying the footprints they left in the ground.Earth is about 4.5 billion years old.

6. Many kinds of animals or species have lived on Earth. Then the species died, or evolved into other species. The species called dinosaurs once lived all over the Earth.Many animals and plants already lived on Earth at the time. But not humans. We didn't appear until around 100,000 years ago. Around 65 million years ago, dinosaurs disappeared--- they became extinct.

7. Dinosaurs lived over a period of 170 million years. Some were enormous. Others were as small as chickens! But they all had certain characteristics in common. They had scaly skin. They laid eggs.They walked upright on their feet instead of crawling like other reptiles.

8. Dinosaurs are classified into two main groups according to their hips. Saurischians were "lizard-hipped" dinosaurs. Ornithischians were "bird-hipped" dinosaurs.All ornithischians, and some saurischians, were plant eaters, or herbivores. Other saurischians were meat eaters, or carnivores.

9. Plant-eating dinosaurs were the first animals able to reach treetops and eat the leaves. Carnivores gathered together in groups to hunt and feed off other animals.Scientists still don't know why dinosaurs completely disappeared 65 million years ago, while other animals survived. A meteorite may have crashed into Earth. There may have been gigantic volcanic eruptions.

10. Dinosaurs may have lost in competition with other species.After the Dinosaurs, other reptiles, however, survived. Fish and amphibans continued evolving. Mammals appeared at the same time as dinosaurs, 235 million years ago. They spread all over the earth. Mammals are warm-blooded. Their babies develop inside their mother before being born. At birth, they are nourished by their mother's milk.

rb