March 2010

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
Smithsonianand 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
Seitaadwas  most closely related to either Plateosaurus from
Europe and its close relatives or Adeopapposaurusfrom 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] SIGNATURE

Originally published at: https://throughthesandglass.typepad.com/through_the_sandglass/2010/03/index.html