February 1, 2011
In 1999, construction workers creating a highway from Tibet’s Bangda Airport to Changdu County uncovered a set of enormous tracks. They had been left more than 160 million years ago by a large sauropod dinosaur, but the local Tibetan people had other interpretations. Some believed that the tracks had been left by the “Deity of the Mountains,” scared away by the noise of the construction, while others asserted that the tracks were left by King Gesar, the legendary star of one of the world’s longest epic poems.
This was not the first time that fossils have been mistaken for the signs of gods, monsters, and heroes. Thanks to the work of historians such as Adrienne Mayor, we now know that fossils have been inspiring myths and legends for centuries. It has only been very recently, since the 17th century, that we have recognized what they truly are. What makes the case of the Tibet tracks unusual, however, is that the myths surrounding their origin are entirely new and sprang up as soon as the tracks were discovered. Given the shape of at least two of the traces, it isn’t difficult to see how they were interpreted as the footsteps of a giant human.
The details of the tracks have just been reported by Xing Li-da, Jerald Harris and Philip Currie in the Geological Bulletin of China. Arrayed on part of a cliff face tilted almost perpendicular to the ground, the slab contains multiple footprints from at least three different trackways, all left by sauropod dinosaurs. Among them are two sets of front- and hind-foot impressions that were close enough together to make the shape of a large human-type foot. Close inspection shows that these particular traces were made by the hindfoot coming down close to where the front foot had lifted up, but it is easy to see how they could have been mistaken for something else. (Even naturalists have made this sort of mistake. In the 1880s, some naturalists mistook the footprints of a giant ground sloth found in Nevada for those of an immense, sandal-wearing human.)
Exactly what species of dinosaur left the track is unknown. Early and Middle Jurassic trackways are rare, and there are no corresponding body fossils to identify the dinosaur. Based on the width of the trackways, though, the paleontologists propose that the tracks were left by a titanosauriform dinosaur—a variety of sauropod known for leaving wide-gauge trackways. This identification of the tracks has not dissuaded the local people for leaving colorful scarves at the site as friendship offerings, though. In an article about the find in the People’s Daily, lead author Xing reported that some worshipers at the site are now paying homage to a dinosaur god. The modern mythology surrounding the tracks remains.
Xing, Li-da; Harris, Jerald; Currie, Philip. (2011). First record of dinosaur trackway from Tibet, China Geological Bulletin of China, 30 (1), 173-178
December 1, 2010
Fossilized dinosaur tracks can be exceptionally informative traces of prehistoric life, but figuring out what dinosaur made a particular set of footprints can be tricky. Unless an animal literally dies in its tracks, the best we can do is to match the skeletal anatomy of dinosaur feet with the anatomical clues left in the impressions they left behind. Even then, however, the relationship between a given track and the potential trackmaker is subject to change. Through a reinvestigation of tracks from Australia, a pair of paleontologists has just pulled off the impressive feat of turning a charging theropod into an iguanodont out for a stroll.
The new research, by Anthony Romilio and Steven Salisbury, will appear in Cretaceous Research. The objects of their attention were tracks preserved at the approximately 100-million-year-old Lark Quarry site in Queensland, Australia. Believed to have been left by a large theropod dinosaur, the tracks were referred to the footprint type Tyrannosauropus. (Tracks are given their own unique names since it is often impossible to tell the exact genus of dinosaur that made them, especially since there are so many dinosaurs yet to be discovered!) This identification is probably incorrect, but to explain why, Romilio and Salisbury first untangled some of the confusion about this particular track type.
The problems started with large, three-toed tracks illustrated in a 1924 Natural History article by William Peterson about dinosaur footprints found in the roofs of Utah coal mines. Some of these tracks were proposed to have been made by Tyrannosaurus rex and were given the name Tyrannosauripus (with an “i”) in 1955. Since this proposed name had not formally applied to any of Peterson’s tracks, though, the name Tyrannosauripus was still available and was re-applied to a more definitive track of a giant theropod from New Mexico described in 1994.
Here’s where things really got complicated. Peterson’s 1924 article also contained illustrations of a second track type, and this different track variety was used to establish the name Tyrannosauropus (with an “o”) in 1971. These, too, were thought to have been the footprints of a tyrannosaur, but all the Utah tracks later turned out to have been made by hadrosaurs. Given all this confusion, it seemed possible that the Australian Tyrannosauropus tracks had also been misidentified.
Using line drawings, photos, casts, and examinations of the original tracks, Romilio and Salisbury re-analyzed the dimensions of the Lark Quarry footprints. Altogether, the footprints were of the size and shape expected for an ornithopod dinosaur—the group containing hadrosaurs, iguanodonts, and their close relatives—and were inconsistent with the kind of tracks made by large theropods. In fact, only the recently described theropod Australovenator was in the right place at the right time to be the potential trackmaker, but it was far too small and did not match the Lark Quarry prints.
So what dinosaur actually left the three-toed tracks at Lark Quarry? It is difficult to say for sure, but Romilio and Salisbury note their close resemblance to other three-toed tracks from other localities given the name Amblydactylus. The features visible on these tracks—especially the slightly-pointed hoofs—would indicate that the animal was probably an iguanodont, and the overall best match in terms of anatomy, size and time period is Muttaburrasaurus. Through a bit of fossil sleuthing, Romilio and Salisbury turned a rampaging carnivore into an herbivore.
This change in identification drastically alters the story behind the Lark Quarry tracksite. It was originally thought that the big, three-toed tracks had been made by a predator that sparked a stampede of smaller dinosaurs in an attempt to ambush its prey. As presented on an Australian Broadcasting Corporation website about the tracks:
These footprints preserved in stone give us a glimpse of what happened in one moment millions of years ago when the large flesh-eating dinosaur approached the edge of a lake where about 150 small dinosaurs were drinking. All the small dinosaurs ran away from the lake’s edge toward the big predator in a desperate bid to escape. One might have been captured as it ran past, but there are no signs of struggle recorded at the site.
Now the story has to be revised. The trackways still record how a large group of small carnivorous and herbivorous dinosaurs scattered, but we can no longer envision a large predator bursting out of the trees to run after the tiny prey animals. What caused these small dinosaurs to run off remains a mystery, but the place can still rightly be called Dinosaur Stampede National Monument.
Romilio, A., & Salisbury, S. (2010). A reassessment of large theropod dinosaur tracks from the mid-Cretaceous (late Albian–Cenomanian) Winton Formation of Lark Quarry, central-western Queensland, Australia: A case for mistaken identity Cretaceous Research DOI: 10.1016/j.cretres.2010.11.003
November 2, 2010
When the term “sauropod” comes up in discussion, I most often think of the lumbering giants from the Late Jurassic of North America—Apatosaurus, Diplodocus, Barosaurus and Brachiosaurus. They were some of the largest terrestrial animals ever to have evolved, yet each individual dinosaur among these genera started off small. Despite their impressive adult size, sauropod dinosaurs began their lives as relatively puny little pipsqueaks, and the fossil evidence of the early life stages of these dinosaurs is quite rare (at least in part because predatory dinosaurs probably considered them to be tasty treats).
At this year’s annual Geological Society of America (GSA) meeting in Denver, however, paleontologists Matthew Mossbrucker and Robert Bakker have presented the preserved trackways of a very small—most likely juvenile—sauropod dinosaur. The tracks comes from the famous Quarry 5 locality in Morrison, Colorado where the 19th century paleontologist Arthur Lakes found the type specimen for the famous Late Jurassic dinosaur Stegosaurus armatus. Based on their spacing, the tiny trackway indicates that the small sauropod was running, but what has grabbed the attention of multiple news outlets is that only the hind feet prints were preserved. As interpreted by Mossbrucker, this young sauropod was running on its hind legs “like a Basilisk lizard,” possibly because something spooked it.
That this baby sauropod reared back on two legs to run is an astonishing claim, but, frustratingly, almost nothing is said about the sauropod tracks in the technical abstract related to this news. Most of what has been said about the find so far has only appeared in secondary sources, although the Discovery News coverage of the story includes a few photographs of the tracks. The photos show that these are not immaculately preserved footprints but rather mushy imprints made by tiny feet, and that may be a clue to why the forefeet tracks are missing.
Prehistoric trackways can be difficult to interpret, especially since there is more than one layer to any footprint. Depending on the type of surface a dinosaur is walking on, its footsteps can deform the sediment beneath the feet to create what paleontologists call undertracks, or lower-resolution traces of the original tracks created by the pressure of the dinosaur stepping down. (If you would like more detail about undertracks, see this recent paper on their formation by J. Milàn and R.G. Bromley in Palaeogeography, Palaeoclimatology, Palaeoecology.)
Without being able to look at the paper or the tracks in detail it is difficult to say for certain, but it is possible that the traces presented at GSA are undertracks. If the dinosaur was exerting more force on the ground with its hind limbs than its forelimbs as it ran, then the sediment beneath its hind feet would have deformed to a greater degree than that under its forefeet. Then, thanks to erosion, the top layers of the trackway may have been eroded away, leaving behind only the undertrack impressions.
Furthermore, the baby dinosaur could not have run just like a basilisk lizard does. The reason has to do with its posture. Whereas basilisks (sometimes called “Jesus Christ lizards” for their ability to run over the surface of water for short distances) have sprawled limb postures that require them to rotate their legs around with each step, the sauropod carried its legs in a pillar-like manner underneath its body and primarily moved them from front to back. Perhaps Mossbrucker’s comment was meant in the more general sense—that the dinosaur reared up on its hind limbs to run just as a basilisk lizard runs bipedally—but from a biomechanical perspective the two animals are very different when it comes to running.
For now, we just have to wait for the analysis of the paper. Mossbrucker and Bakker appear to have found a unique trace of a young sauropod dinosaur running, but just how it ran will require further scrutiny to determine.
July 8, 2010
Fossil dinosaur tracks don’t often get the same popular attention that skeletons do. The impressions within the rock seem to pale in comparison to the beautiful organic architecture of the bones, but, while they might not be as aesthetically interesting to some, tracks are bits of behavior preserved for millions of years. They were made by living creatures, and by studying them carefully paleontologists can reconstruct the details of how these animals moved.
There are many dinosaur track sites scattered all over the world, but in a paper published in Palaeogeography, Palaeoclimatology, Palaeoecology, scientists Bo Seong Kim and Min Huh focus on just one small set of Cretaceous-age footprints preserved in South Korea. Called “trackway B”, this set of impressions was made by a theropod dinosaur while running—the footprints clearly show that it was increasing its stride length between each step as a sprinting creature would do. In order to better appreciate how this dinosaur was moving, though, Kim and Huh made numerous measurements of the tracks to estimate the size of the dinosaur, its speed and how quickly it accelerated as it began to run.
Using the size of the footprints to calculate size, the scientists estimated that the dinosaur would have been about three feet high at the hips—this was a relatively small theropod. It would have been pretty fast, though. The speed estimates obtained for the tracks suggest that the dinosaur was moving at about seven miles per hour and then accelerated to between nine and twenty miles per hour. It appears that the dinosaur was already trotting at the beginning of the trackway, but the latter portion of it shows a quick uptick in speed to full running.
Just what spurred this dinosaur’s turn of speed, though, is unknown. The authors state that it was probably running about as fast as it could, so obviously it was moving with some urgency. Perhaps the dinosaur was after a potential meal, or was in danger of becoming a meal itself. We will probably never know for sure, but, regardless of what happened, the footprints represent a snapshot into a dinosaur’s life.
Kim, B., & Huh, M. (2010). Analysis of the acceleration phase of a theropod dinosaur based on a Cretaceous trackway from Korea Palaeogeography, Palaeoclimatology, Palaeoecology, 293 (1-2), 1-8 DOI: 10.1016/j.palaeo.2010.04.020
October 13, 2009
Even though some of the largest dinosaurs get the most attention, dinosaurs actually came in a variety of sizes. This past week paleontologists announced two discoveries that emphasize just how large, and how small, some dinosaurs were.
From Plagne, France came the announcement of the largest dinosaur footprints yet discovered. Naturalists Marie-Hélène Marcaud and Patrice Landry found the tracks back in April, at which point paleontologists Jean-Michel Mazin and Pierre Hantzpergue from the Université Claude Bernard Lyon went out to have a look. They discovered that the 150-million-year-old tracks were made by enormous sauropod dinosaurs, the largest probably stretching over 85 feet and weighing more than 40 tons.
Contrast that with a find announced yesterday in the Korea Herald. The newspaper reported that a resident of one of South Korea’s southern provinces discovered one of the smallest dinosaur footprints ever found: the track of a theropod dinosaur measuring only half an inch long. According to Kim Gyeong-su of Chinju National University of Education, the track is about 100 million years old and is consistent with a previously-known track type called Minisauripus.
I wonder how many of the tiny theropods could have fit into just one track made by the enormous sauropod!