November 13, 2012
East coast dinosaurs are few and far between. Unlike the exposed formations in the western badlands, much of the dinosaur-bearing strata in the eastern states are hidden beneath forests, lawns and parking lots. But you can still find signs of dinosaurs if you know where to look.
Amateur ichnologist Ray Stanford has a knack for finding dinosaur tracks and traces in the Baltimore, Maryland and Washington, D.C. area. Among his recent finds are an impression of a baby ankylosaur–on display at the Smithsonian National Museum of Natural History–and a track made by an adult of a similar dinosaur on the grounds of NASA’s Goddard Space Flight Center. As our paleontology curator Matthew Carrano says in the video above, Stanford’s talent for tracking dinosaurs has helped fill out our understanding of east coast dinosaurs in deposits where bones are scarce.
September 24, 2012
Paleontologist R.T. Bird inspected many dinosaur trackways while combing Texas for the perfect set to bring back to the American Museum of Natural History. During several field seasons in the late 1930s, Bird poked around in the Early Cretaceous rock in the vicinity of the Paluxy River for a set of sauropod footprints that would fit nicely behind the museum’s famous “Brontosaurus” mount. Bird eventually got what he was after but not before poring over other intriguing dinosaur traces. One of the most spectacular seemed to be made by a swimming dinosaur.
Known as the Mayan Ranch Trackway, the roughly 113-million-year-old slab is almost entirely made up of front foot impressions. The semicircular imprints were undoubtedly left by one of the long-necked sauropod dinosaurs. But towards the end of the trail, where the dinosaur’s path makes an abrupt turn, there was a single, partial impression of a hind foot.
At the time Bird and his crew uncovered this trackway, sauropods were thought to be amphibious dinosaurs. Other than their immense bulk, what defense would they have had but to trundle into the water, where theropods feared to paddle? Under this framework, Bird thought he knew exactly how the Mayan Ranch Trackway was made. “The big fellow had been peacefully dog-paddling along, with his great body afloat, kicking himself forward by walking on the bottom here in the shallows with his front feet,” Bird wrote in his memoir. The great dinosaur then kicked off with one of its hind feet and turned.
With the exception of well-defended dinosaurs such as the ceratopsids and stegosaurs, many herbivorous dinosaurs were thought to be at least semi-aquatic. There seemed to be only two options for Mesozoic prey species–grow defenses or dive into the water. In time, though, paleontologists realized that the sauropods, hadrosaurs and other herbivores didn’t show any adaptations to swimming. Our understanding of the ecology of these dinosaurs was based on false premises and faulty evidence.
In the case of the Mayan Ranch Trackway, for example, there’s no indication that the sauropod that made the trackway was swimming. A more likely scenario has to do with evolutionary changes among sauropods. While the sauropods that dominated the Late Jurassic of North America–such as Diplodocus, Apatosaurus and Barosaurus–carried much of their weight at the hips and left deeper hindfoot impressions, the center of mass shifted among their successors–the titanosaurs–such that more of the weight was carried by the forelimbs. Hence, in some trackways, the deeper impressions made by the forefeet are more likely to stand out than those made by the hindfeet, especially if some of the top layers of the rock are eroded away to leave only “undertracks.” What seemed to be evidence of swimming sauropods instead owes to anatomy and the characteristics of the mucky substrate the dinosaur was walking on.
As far as I’m aware, no one has yet found definitive evidence of swimming sauropods or hadrosaurs–the two groups previously thought to rely on water for safety. Stranger still, paleontologists have recently uncovered good evidence that theropod dinosaurs weren’t as bothered by water as traditionally believed. In 2006, paleontologists Andrew Milner, Martin Lockley and Jim Kirkland described swim tracks made by Early Jurassic theropods at a site that now resides in St. George, Utah. Such traces weren’t the first of their kind ever discovered, but the tracksite was one of the richest ever found.
Small to medium-sized theropods made the St. George swim tracks–think of dinosaurs similar to Megapnosaurus and Dilophosaurus. Even better, the large number of smaller-size swim tracks hints that whatever dinosaurs made these tracks were moving as a group as they struggled against the current in the lake shallows. The larger dinosaurs, on the other hand, were a bit taller and able to wade where their smaller cousins splashed around.
A different team of researchers announced additional evidence for swimming theropods the following year. Paleontologist Rubén Ezquerra and co-authors described dinosaur swim traces from Early Cretaceous rock near La Rioja, Spain. Based on the details of the track and their direction, the theropod was swimming against a current that pushed the dinosaur diagonally. Along with other theropod swim tracks, the researchers noted, the discovery meant that paleontologists would have to revise their ideas about the kind of habitats theropods lived in and what carnivorous species would do. Theropod dinosaurs were not so hydrophobic, after all.
Does this mean that dinosaurs like Dilophosaurus were adapted to an amphibious lifestyle? Not at all. As Ezquerra and co-authors pointed out, the swimming strokes of these dinosaurs were exaggerated walking motions. The way the dinosaurs moved on land allowed them to be adequate swimmers while crossing rivers or lakes, but, compared with semi-aquatic animals such as crocodiles and otters, no known dinosaur shows traits indicative of a primarily waterlogged existence. (And dinosaurs found in marine sediments don’t count as evidence, as these were washed out to sea prior to burial. I can’t imagine ankylosaurs taking to life among the high seas, in any case.) Some dinosaurs could swim, but that doesn’t mean that they made the water their home. Still, thanks to special prehistoric traces, we can imagine packs of Megapnosaurus fighting to get ashore, and Dilophosaurus strutting into the shallows, aiming to snatch whatever fish were foolish enough to swim into the carnivore’s shadow.
Bird, R.T. (1985). Bones for Barnum Brown, edited by Schreiber, V. Forth Worth: Texas Christian University Press. pp. 160-161
Ezquerra, R., Doublet, S., Costeur, L., Galton, P., Pérez-Lorente, F. (2007). Were non-avian theropod dinosaurs able to swim? Supportive evidence from an Early Cretaceous trackway, Cameros Basin (La Rioja, Spain) Geology, 40 (10), 507-510 DOI: 10.1130/G23452A.1
Milner, A., Lockley, M., Kirkland, J. (2006). A large collection of well-preserved theropod dinosaur swim tracks from the Lower Jurassic Moenave Formation, St. George, Utah. New Mexico Museum of Natural History and Science Bulletin, 37, 315-328
January 4, 2012
Even before we knew what they really were, dinosaurs inspired our imagination. Unidentifiable bones and tracks formed the basis of legend–they were the evidence of great battles, fearsome monsters and times when the world was new and hostile to human existence. Indeed, contrary to what John Noble Wilford wrote in The Riddle of the Dinosaur, fossilized bones were not just ignored or ground up for “dragon-bone medicine” in the centuries prior to the scientific discovery of dinosaurs. People have puzzled over dinosaurian fossils for centuries. Some of that folklore still persists today.
In a paper recently published in Ichnos, researchers Lida Xing, Adrienne Mayor, Yu Chen, Jerald Harris and Michael Burns focus on one particular source of dinosaur-inspired myths–trackways found in China. Just as dinosaur tracks in New England generated tales about primeval monsters, huge turkeys and ostrich-like birds, the tracks in China motivated the creation of different stories to explain just what left such imposing footprints.
According to the new study, Chinese folklore about dinosaur tracks can be divided into four categories–mythical birds, mammals, plants, and gods or heroes. In the case of three-toed theropod tracks discovered in Chabu, Inner Mongolia, for example, the footprints had been known to local farmers since the 1950s and were believed to be footprints of a “divine bird.” As explained by Xing and co-authors, “The herders believed that the tracks represented beautiful wishes for human happiness left by the sacred bird Shen Niao.” This is a common theme across sites where theropod tracks are found. Three-toed dinosaur footprints have often been interpreted as the steps of birds, and other sites in Heibei, Yunnan, Guizhou and Liaoning provinces have been attributed to other mythical birds, such as the golden and heavenly chickens.
Not all the dinosaur tracks are associated with supernatural avians. The fossil footprints of a sauropod dinosaur near Zigong City have traditionally been cast as the footprints of a rhinoceros–”The tradition of counting the footprints to pray for good fortune is popular,” the authors note–and hadrosaur tracks at Qijang County may have been interpreted as impressions of lotus flowers on stone. The size of the impressions and the fact that they were made on stone were often taken to mean that some supernatural agency was involved. What else could leave such detailed markings on rock?
One such powerful figure, according to myths about footprints found in Changdu County, Tibet, was the Mountain Deity. During the construction of a highway through the area in 1999, construction crews found several large footprints. Local villagers believed that all the noise had disturbed a god who dwelt in the mountains, and when the deity fled, it left the footprints in stone. Though not everyone agrees. Others think that the footprints represent King Gesar, a warrior featured in an epic poem about Tibet’s history. In reality, the tracks are the fore- and hindfoot impressions of a sauropod dinosaur. The shape of the tracks and their arrangement roughly resemble a large human footprint, and so the legendary explanation was born. Indeed, not all myths about dinosaur remains are ancient. In places where people don’t know about dinosaurs or paleontology, fantastic stories are still employed to explain the origin of fossils.
The nature of tracksites themselves may explain why they often find their way into folklore. Fossilized bone is often fragile and visible on the surface for a short time before eroding away. Exposed tracks, on the other hand, often remain in place for generations before fully succumbing to the wear of wind and water. The persistence of the tracks may allow them to become more readily established in cultural tradition–the stone footprints are visible for years and act as evidence of the stories.
And these legends have practical applications for paleontologists. By using rumors of “dragon bones” and stories about stone footprints, researchers can use local folklore to locate previously-unknown fossil localities. Folklore may tell tales too fantastic to believe, but they may be based on very real traces of prehistoric life.
Xing, L., Mayor, A., Chen, Y., Harris, J., & Burns, M. (2011). The Folklore of Dinosaur Trackways in China: Impact on Paleontology Ichnos, 18 (4), 213-220 DOI: 10.1080/10420940.2011.634038
December 19, 2011
Edward Hitchcock was one of America’s first dedicated dinosaur paleontologists. He just didn’t know it. In fact, during the latter part of his career, he explicitly denied the fact. To Hitchcock, the tracks skittering over red sandstone in the Connecticut Valley were the marks of prehistoric birds from when the Creation was new. Hitchcock could not be dissuaded. As new visions of dinosaurs and the notion of evolution threatened to topple his life’s work, the Amherst natural theologian remained as immutable as the fossil footprints he studied.
Hitchcock was not the first to wonder about the prehistoric imprints. Members of the Lenape, a Native American group in Canada and the northeastern United States, had seen the bizarre, three-toed tracks and ascribed them to monsters and other beings. These were the footsteps of creatures that ruled the world before humans came to dominance. European settlers and their descendants had to stretch their mythology a little more to accommodate the tracks. Some thought such tracks might have been left by Noah’s raven after the biblical deluge, although many simply called them “turkey tracks” and apparently were little concerned with where they had come from.
It wasn’t until 1835 that James Deane, a doctor with a curiosity for natural history, found out about a sample of the peculiar tracks near Greenfield, Massachusetts. He knew that they represented prehistoric organisms, but he wasn’t sure which ones. He wrote to Hitchcock, then a geology professor at Amherst, to inquire about what could have left such markings in stone. At first Hitchcock didn’t believe Deane. There might be some quirk of geological formation that could have created track-like marks. But Deane was persistent. Not only did he change Hitchcock’s mind, but the geologist became so enthusiastic that he quickly became the most prominent expert on the tracks—a fact that frustrated Deane and led to tussles in academic journals over who really was the rightful discoverer of the Connecticut Valley’s lost world.
Hitchcock began publishing about the peculiar trace fossils in 1836. He was confident from the very start that they must have been created by prehistoric birds. (He was so enthused by the idea he even wrote poetry about the “sandstone birds.”) No variety of creature matched them better. The word “dinosaur” had not even been invented yet; the British anatomist Richard Owen would establish the term in 1842. The few dinosaurs that had been found, such as Iguanodon, Megalosaurus and Hylaeosaurus, were known only from paltry remains and all were believed to have been enormous variations of lizards and crocodiles. Dinosaurs were a poor fit for the tracks, and became even worse candidates when Owen gave them an anatomical overhaul. Owen not only named dinosaurs, he re-branded them as reptiles with mammal-like postures and proportions. The huge sculptures of the Crystal Palace exhibition, created with the help of artist Benjamin Waterhouse Hawkins, are a testament to Owen’s view of dinosaurs as reptiles that had taken on the anatomical attitudes of rhinoceros and elephants.
But Owen and other paleontologists did not agree with Hitchcock’s interpretation. They argued that the tracks could have been made by some unknown variety of amphibian or reptile. This was not so much because of the anatomy of the tracks—anyone could see that they were made by creatures with bird-like feet—but because no one thought that birds could have lived at so ancient a time or grown large enough to make the biggest, 18-inch tracks Hitchcock described. Even though early 19th century paleontologists recognized that life changed through the ages, they believed there was a comprehensible progression in which so-called “higher” types of creatures appeared later than others. (Mammals, for example, were thought to have only evolved after the “Secondary Era” when reptiles ruled since mammals were thought to be superior to mosasaurs, ichthyosaurs, and other creatures of that middle time.)
Hitchcock remained steadfast, and his persistence was eventually rewarded with the discovery of the moa. These huge, flightless birds recently lived on New Zealand—they were wiped out more than 500 years ago by humans—and in 1839 Richard Owen rediscovered the birds through a moa thigh bone. He hypothesized that the bone must have belonged to a large, ostrich-like bird, and this idea was soon confirmed by additional skeletal bits and pieces. Some of these ratites stood over nine feet tall. When the news reached Hitchcock in 1843, he was thrilled. If recent birds could grow to such sizes, then prehistoric ones could have been just as large. (And, though Hitchcock died before their discovery, preserved moa tracks have a general resemblance to some of the largest footprints from the Connecticut Valley.) Opinion about the New England tracks quickly changed. There was no longer any reason to doubt Hitchcock’s hypothesis, and paleontologists hoped that moa-like bones might eventually be found to conclusively identify the trackmakers.
Lacking any better hypotheses, Hitchcock prominently featured his avian interpretation of the three-toed tracks in his 1858 book The Ichnology of New England. It was a gorgeous fossil catalog, but it also came at almost precisely the wrong time. Gideon Mantell, the British doctor and paleontologist who discovered Iguanodon, was beginning to wonder if some dinosaurs primarily walked on their hind limbs in a bird-like fashion, and the Philadelphia polymath Joseph Leidy described Hadrosaurus, a dinosaur certainly capable of bipedal locomotion on account of having shorter forelimbs than hindlimbs, the same year that Hitchcock’s monograph came out. Dinosaurs were undergoing another major overhaul, and the few that were known at the time were being recast as relatively bird-like creatures. Even worse for Hitchcock, the following year another student of the Connecticut Valley tracks, Roswell Field, reinterpreted many of the footprints and associated traces as being made by prehistoric reptiles. Especially damning was the fact that deep tracks, left when the creatures sunk into the mud, were sometimes associated with drag marks created by a tail. Hitchcock’s tableau of ancient Massachusetts moas was becoming increasingly unrealistic.
If Hitchcock ever doubted his interpretation, he never let on. He reaffirmed his conclusions and modified his arguments in an attempt to quell dissent. In his last book, A Supplement of the Ichnology of New England, published in 1865, a year after his death, Hitchcock used the recently discovered Jurassic bird Archaeopteryx as a way to save his interpretation. Tail drags were no obstacle to the bird hypothesis, Hitchcock argued, because Archaeopteryx was generally regarded as being the primordial bird despite having a long, reptile-like tail. Perhaps such a bird could have been responsible for the trace fossils Hitchcock called Anomoepus, but the tail drags left by the animals that dwelled in Jurassic New England were also associated with tracks indicating that their maker walked on all fours. In response, Hitchcock cast Archaeopteryx as a quadrupedal bird—a representative of a new category different from the classic, bipedal bird tracks he had promoted for so long.
Other paleontologists took a different view. If Archaeopteryx looked so primitive and lived after the time when the red Connecticut sandstone was formed, then it was unreasonable to think that more specialized, moa-like birds created Hitchcock’s tracks. Furthermore, a few bones found in a Massachusetts quarry of roughly the same age in 1855 turned out to belong to a dinosaur—a sauropodomorph that Othniel Charles Marsh would later name Anchisaurus. The bird bones never turned up, and all the while dinosaur fossils were becoming more and more avian in nature. By the 1870s the general paleontological opinion had changed. New England’s early Jurassic was not filled with archaic birds, but was instead home to dinosaurs which were the forerunners of the bird archetype.
Our recent realization that birds are the direct descendants of one group of coelurosaurian dinosaurs has led some of Hitchcock’s modern day fans to suggest that he was really right all along. In an essay for the Feathered Dragons volume, paleontologist Robert Bakker extolled Hitchcock’s scientific virtues and cast the geologist’s avian vision for the tracks as essentially correct. Writer Nancy Pick, in her 2006 biography of the paleontologist, wondered, “What if Hitchcock clung to his bird theory because he was right?” But I think such connections are tenuous—it is a mistake to judge Hitchcock’s work by what we have come to understand a century and a half later.
While Bakker is right that Hitchcock stuck to his bird hypothesis early on because dinosaurs were not known in the 1830s to 1850s to be suitably avian, this does not explain why Hitchcock refused to entertain a dinosaurian origin for some of the tracks when evidence for such a connection began to accumulate. By sticking to the same point, Hitchcock went from being right to being so wrong that he tried to fit creatures like Archaeopteryx into the footprints to preserve his point. More importantly, though, Hitchcock promoted a variety of creationism that we would probably label as intelligent design today—he detested the idea of evolution by means of natural selection that Charles Darwin articulated in 1859. Hitchcock would not have accepted the idea that birds are the evolutionary descendants of dinosaurs. He likely would have rejected the idea of avian dinosaurs that some writers wish to attribute to him.
Hitchcock himself acknowledged that he was a stubborn man. Perhaps his obstinacy prevented him from accepting new ideas during a critical period of change within geology, paleontology and natural history. We may never know. Unless a letter or journal entry articulating his thoughts on the subject appear, his anti-dinosaur interpretation will remain a mystery. All we know for sure is that, regardless of whether he agreed with the label or not, Hitchcock was one of the first interpreters and promoters of North American dinosaurs.
Bakker, R. 2004. “Dinosaurs Acting Like Birds, and Vice Versa – An Homage to the Reverend Edward Hitchcock, First Director of the Massachusetts Geological Survey” in Feathered Dragons. Currie, P.; Koppelhus, E.; Shugar, M.; Wright J. eds. Bloomington: Indiana University Press. pp. 1-11
Pick, N. and Ward, F. 2006. Curious Footprints: Professor Hitchcock’s Dinosaur Tracks & Other Natural History Treasures at Amherst College. Amherst: Amherst College Press.
Switek, B. 2010. Written in Stone. New York: Bellevue Literary Press. pp. 91-104
October 6, 2010
From the emergence of the first of their kind about 228 million years ago to the modern abundance of birds (their living descendants), dinosaurs have been one of the most successful groups of organisms on the planet. Why they originated in the first place, however, has been a much trickier subject to tackle. A study published today in the Proceedings of the Royal Society B suggests that the rise of the dinosaurs may be related to the greatest evolutionary shake-up this planet has ever endured.
At the close of the Permian period, 252 million years ago, life on earth suffered the worst mass extinction of all time. More than 90 percent of known species in the seas disappeared, as did more than 70 percent of organisms known on land. In the wake of this catastrophe the surviving lineages proliferated and continued to evolve, and among them were the ancestors of the dinosaurs. We know this not from bones, but from tracks recently discovered in three approximately 251- to 249-million-year-old tracksites in Poland’s Holy Cross Mountains.
According to American Museum of Natural History paleontologist Stephen Brusatte and co-authors, the tracks were made by dinosauromorphs—forerunners of the dinosaurs which were more closely related to dinosaurs than to pterosaurs, crocodiles, or other archosaurs. Fossils of the bodies of these animals have been found dating back to about 243 million years ago—such as the recently described creature Asilisaurus from Tanzania—but the track fossils further close the gap between the emergence of the dinosauromorphs and the evolutionary recovery from the end-Permian mass extinction.
That the tracks were made by dinosauromorphs and not some other kind of creature was determined by comparing the limb skeletons with the footprints. “Footprints are notoriously difficult to identify,” Brusatte says, but the identity of the animals behind the Polish tracks can be narrowed down because of three factors: the two outer toes (the first and fifth) were reduced and the middle three were prominent; the middle toes were nearly parallel; and the back of the footprints are straight thanks to a simple, hinge-like arrangement of the ankle unique to dinosaurs and their closest relatives.
Small tracks made at one site, for example, closely matched the specific hand and foot anatomy of a dinosauromorph called Lagerpeton that walked on all fours, and a new larger type–given the designation Sphingopus–appeared to closely resemble the early predatory dinosaur Herrerasaurus. University of Utah paleontologist and expert on dinosaur origins Randall Irmis, who was not involved with the new study, generally agrees with this interpretation, saying “these do look like potential dinosauromorph tracks, and I think the authors make a good case for their identification.”
These tracks confirm what scientists have suspected on the basis of recently described body fossils: there was a “ghost lineage” of dinosauromorphs stretching back to the beginning of the Triassic. While Irmis stresses that the geologic timing of the Early Triassic is still being ironed out, the tracks are further evidence that the dinosaur stem lineage evolved shortly after the Permian mass extinction. “I don’t think anyone is surprised by Early Triassic dinosauromorph fossils that are 5 million years older than those previously known,” Irmis says, but adds that “it’s definitely good to have some confirmation of these ghost lineages, and the authors are certainly right that the track record is under-utilized.” Both Brusatte and Irmis are confident that body fossils of the earliest dinosauromorphs will eventually be found, although due to the shifting of the continents over the past 250 million years, the deposits in which these fossils might be found are scattered from central Europe to Brazil to Africa.
What the tracks and other recent dinosauromorph discoveries mean for the big picture of dinosaur evolution is that the origins of these creatures must now be viewed in the context of the end-Permian mass extinction. The tracks from Poland were very rare—only 2 to 3 percent of those found at the tracksites–meaning that dinosauromorphs were marginal components of the ecosystem. It took a few million years for their diversity to increase, and the first dinosaurs did not branch off from their dinosauromorph relatives until about 228 million years ago. “Really, for most of the Triassic dinosaurs and their close relatives were completely overshadowed by the more common and diverse crocodile-line archosaurs,” Brusatte says, “and it wasn’t until the Early Jurassic—some 50 million years after the first dinosauromorphs evolved—that dinosaurs were truly the pre-eminent terrestrial vertebrates in ecosystems across the globe.” These giants owed their origins to the earlier kinds of creatures that made the Polish tracks in the wake of the end-Permian extinction. While deadly for some, Brusatte casts the event as “a great opportunity for new groups to originate, diversify, and radiate in the barren and open landscapes of a post-apocalyptic world. Without the great contingency of the [Permian-Triassic] mass extinction, the Age of Dinosaurs probably never would have happened.”
Stephen L. Brusatte, Grzegorz Niedz´wiedzki, and, & Richard J. Butler (2010). Footprints pull origin and diversification of dinosaur stem-lineage deep into Early Triassic Proceedings of the Royal Society B : 10.1098/rspb.2010.1746