Ralph Bagnold, the man who figured out how deserts work, was a brilliant scientist and engineer, but his writing could also be lyrical, his passion for the dramas of desert sand and dynamics of its performances showing through. He compared dunes to living organisms, and, in the midst of a sandstorm, made the following observation:
... above, the great fine-grained crests of the dunes were on the move. Cornices dissolved as we looked, swaying along the curving surfaces in heavy dark folds, as if the mane of some huge animal was being ruffled and reset in a new direction by the gale.
Historical stories of dunes swallowing individuals, caravans, and armies are common, the very word “swallowing” carrying anthropomorphic associations, the dunes alive and voracious. This theme forms a dramatic part of the Navajo creation legend, but, before we get to that, stories of life demonstrably engulfed and extinguished by sand – and how I came to find about this particular creation story (sand is a kind of primeval material in many such stories in different cultures around the world). Over the last few days there has been much justifiable excitement about the discovery and documentation of an extraordinary dinosaur skeleton disinterred from the base of a cliff near Bluff, Utah. The description of the fossil has been published in the online peer-reviewed journal, PloS ONE, and summarised by a multitude of online sources, for example, The Smithsonian and Physorg.com as well as being widely reported on the geoblogosphere; the original press release from the University of Utah can be found here. There are several reasons for the excitement about this particular dinosaur fossil – among them the completeness of the preservation and thus the knowledge provided about this herbivorous sauropodomorph in North America, where, unlike elsewhere in the world, only bits and pieces had been found before. As the Smithsonian reports:
What is most significant about this fossil, however, is that it is the best-preserved sauropodomorph yet found from the western United States. Paleontologists have been finding fragments of them for years, but this is the first time that enough has been found to compare the dinosaur to its relatives from elsewhere in the world. When Sertich and Loewen did so they found that Seitaad was most closely related to either Plateosaurus from Europe and its close relatives or Adeopapposaurus from South America and its kin. The trouble was that most of the comparisons made for these dinosaurs so far have relied upon characteristics of bones not preserved in this particular specimen (such as the skull). But it is most certainly a variety of sauropodomorph that probably spent much of its time walking on two legs (like its distant cousin Aardonyx).
So, the remarkably well-preserved remains of a 190 million year old dinosaur, discovered in the dune sands of the classic Navajo Sandstone, seemingly not a classic environment for preserving fossils (they are extremely rare in the Navajo). And then what on earth were dinosaurs doing in the desert? Perhaps surprisingly, there are other examples of such events, foremost amongst them being the stunning array of dinosaur remains found in what is today the Gobi Desert of Mongolia. It’s a fascinating story, and one that sheds light on the demise of our sauropodomorph. I wrote up this story for the book:
Even allowing for what awaited them sixty-five million years ago, the dinosaurs had a good run, and they live on dramatically in the popular imagination. But for a long time, they were known only from fragments of skeletons, bits and pieces, often imaginatively put back together. Then, in the 1920s, expeditions from the American Museum of Natural History discovered a treasure trove in the Gobi Desert, a beautifully preserved abundance of what the ancient Chinese called “dragon bones”; even nests with eggs were buried, essentially intact, in the sand. Today, the museum and the Mongolian Academy of Sciences, together with other research organizations, cooperate to reveal this treasure. In particular, the site at Ukhaa Tolgod, the Brown Hills, is a gold mine of paleontological riches. Ten million years before the catastrophe on the other side of the world, dozens of species of mammals and reptiles enjoyed a good place to live, and, from a paleontologist’s point of view, it was also a good place for them to die, for their remains are exquisitely preserved. Tiny mammals and dinosaurs sitting on their eggs have been painstakingly removed from the sand. But what kind of sand, and how could it achieve this extraordinary preservation? The creatures must have been rapidly buried, allowing no time for predators to dismember the bodies. On the face of it, the rich red sandstones in which the fossils are entombed bear all the hallmarks of desert dunes, ancestors of the Gobi sand seas of today. But today creatures are not suddenly buried by sand dunes—the dunes move too slowly and predictably, and even dinosaurs couldn’t have been stupid enough to simply stand around, waiting to be buried by a dune. Besides, how could dinosaurs have thrived if the place was like the depths of the Sahara today?
A clue came from the type of sand in which all the fossils were found. Associated with the fossil-rich layers were great thicknesses of sand that showed the characteristic cross-bedding of dunes (and, occasionally, dinosaur footprints), but the sand that entombed the dinosaurs had no such features—it was, in fact, featureless, a simple, structureless mass. Layers of mud between the dunes attested to the very different climate of the time, warmer and wetter, not unlike the Sand Hills of Nebraska today, where periodic torrential rains saturate the dunes and cause massive flows of waterlogged sand, which have been known to fill up buildings located in the shelter of a dune. In Mongolia, sandstones of the same age as at Ukhaa Tolgod show the remains of burrows made by creatures, like today, escaping the heat of the day, but there are signs that they had to excavate new burrows as the old ones were plugged up with mud from the rains. At Ukhaa Tolgod, layers of sand were found that were cemented by a kind of calcium carbonate found in arid environments and known as caliche. This would have effectively blocked water from draining away, out of the dunes. Combine these pieces of evidence and perhaps the mystery is solved. Cloudbursts were probably more frequent at Ukhaa Tolgod then than they are in Nebraska today, and the dunes were significantly bigger. Saturate a towering dune face with water, prevent the water from draining away, destabilize the sand through the effects of dilatancy, and the slightest tremor, perhaps the wind, perhaps an irritated dinosaur, would cause an instantaneous slide of huge volumes of sand slurry—burying the irritated dinosaur. Here are desert processes, diagenesis, the physics of granular materials seventy-five million years ago, and forensics at work.
Now, our sauropodomorph was found in the very first deposits of the great pile of desert dunes that would become the Navajo Sandstone, and these mark a dramatic change from the earlier sediments that were deposited in a much wetter environment, rivers and rain. Desert conditions began to take over, but there was a period during which the transition was occurring in which the dunes would undoubtedly be inundated by the occasional rainstorm – very much like conditions in Mongolia. As the press release states
Research suggests that the animal was buried in a suddenly collapsing sand dune that engulfed the remains and stood them on their head…this ancient desert must have included wetter areas with enough plants to support these smaller dinosaurs and other animals
So, having figured out how our friend met its end, let’s move on to its name and the Navajo legend. Again from the press release:
The new dinosaur species is named Seitaad ruessi (SAY-eet-AWD ROO-ess-EYE), which is derived from the Navajo word, "Seit'aad," a sand-desert monster from the Navajo (Diné) creation legend that swallowed its victims in sand dunes (the skeleton of Seitaad had been "swallowed" in a fossilized sand dune when it was discovered); and Ruess, after the artist, poet, naturalist and explorer Everett Ruess who mysteriously disappeared in the red rock country of southern Utah in 1934 at age 20.
“Swallowed in a fossilized sand dune,” “a sand-desert monster,” “ the Navajo creation legend.” It is hardly surprising that your humble correspondent became somewhat excited. The reference to a sand-desert monster was enticing, but it took me a while to discover the details. The Navajo creation legend is an epic story, a saga to be told and sung and incorporated into rituals, along, perhaps with sand painting. It’s a complex tale, with many different strands and characters, and, like many other mythologies, includes a pair of sacred twins (think Romulus and Remus). The twins inevitably must embark on a journey and along the way they encounter a desert – but not just a normal desert. It was one in which “hot, whirling piles of sand encroached upon anyone passing through. These were the Seit’aad, the Boiling Dunes that they were forewarned they would eventually meet.”
This description comes from “Dine Bahane': The Navajo Creation Story,” written by Paul Zolbrod, and included in Google Books. The story continues:
It was at this place where, boiling like water in a heated pot, these dunes burned the wayfarer to a shrivel, and covered up the remains. In reality they had been put there by the Naayee who had devoured so many people. Sure enough, they assumed the shape of sand dunes. But they had the will of monsters and the unrelenting appetite for the flesh and blood of people that monsters had.
Spotting the desert of rising sands, the twins kept right on walking as though they knew of no reason to do otherwise. Meanwhile, the dunes subsided and flattened out for them, appearing to permit them to come ahead. But barely a step or two shy of the desert’s edge, they stopped short! And the dunes, which at once began to swirl and boil, merely converged upon one another instead of submerging their victims.
Thus did the two youths trick the heaps of sand four times…..
“We must know who you are and where you come from,” insisted the dunes at last, roaring and filling the air with their furious heat as they spoke.
The boys explained who they were and where they were going, and then used the sacred object they were carrying, along with a magic formula, to overwhelm the hostility of the dunes, which slowly collapsed so that the desert floor could be easily crossed. “Continue on your journey,” responded the dunes quietly; “Long life is ahead. Happiness is ahead.”
And that’s the story behind the name of our friend, the sauropodomorph, Seitaad ruessi - and echoes of Ralph Bagnold's desert beasts.
[Illustration from the Plos ONE paper:
Sertich JJW, Loewen MA (2010) A New Basal Sauropodomorph Dinosaur from the Lower Jurassic Navajo Sandstone of Southern Utah. PLoS ONE 5(3): e9789. doi:10.1371/journal.pone.0009789]
Fascinating and imaginative scenario of the distant past. Thanks Michael!
Posted by: Jules | March 27, 2010 at 12:03 PM