Tag Archives: Paleo

Protect Gold Butte

Most of you have never heard of it, but northeast of Las Vegas, in one of the least-visited parts of the continental United States, a desert treasure in Nevada needs your support.

I visited Gold Butte for the first time in 1997. I was just passing through, heading for a tiny outpost in the Arizona Strip called Pakoon Springs, which later became part of the Grand Canyon Parashant National Monument. A fire there had damaged a Joshua tree forest some years before, and I wanted to take a look at the recovery so far. My old truck carried me up over the slopes of Virgin Peak and across the state line, where I took some photos that turned out to be abysmally fuzzy. Joshua tree near Pakoon Springs, AZ (The fire had burned patches of the landscape, but not all of it. Much of it looked intact. In this shot, taken facing eastward into the Arizona Strip, the long ridge in the background is the Grand Wash Cliffs escarpment. The notch in the Cliffs toward the right? That’s the downstream end of a rather famous natural landscape feature. )

My old truck was a four-cylinder 2WD, so my relief at not getting stuck in the Pakoon’s washes was considerable, and I headed back across the line into Gold Butte to explore the Whitney Pockets area for a little while. I’ve always meant to get back to Virgin Peak and do some hiking, like these folks did:

It’s one of the best places I’ve ever been. It’s wild, wide, open, and spacious. Gold Butte is a botanical, geological, and archaeological treasure. It’s priceless habitat for desert tortoise and bighorn sheep. It’s also within a couple hours’ drive from two fast-growing cities — the metastasopolis of Las Vegas, and the smaller but even more enthusiastically desert-defacing St. George, Utah — and the almost-city of Mesquite NV. As a result, those who use the desert as a blank slate across which to scratch their grubby fingernails pose a significant and increasing threat to the landscape:

And unlike the Pakoon and other adjacent lands across the Arizona line in the Parashant NM, Gold Butte is essentially unprotected.

Nevada environmentalists and land managers are working with local elected officials to change that. Last year Representative Shelley Berkley introduced HR 7132, a bill that would have given Gold Butte National Conservation Area status, like the Red Rock Canyon area on the other side of Las Vegas. The NCA would have covered 362,177 acres, with 200,000 more acres of BLM and Park Service lands in the area declared wilderness. The bill did not pass, and must be reintroduced in this theoretically more receptive Congress.

The Nevada Wilderness Project has an action site where you can find ways to help them protect Gold Butte, from writing letters to sharing your hard-earned cash.  The Friends of Gold Butte has a website and a companion blog where you can stay informed, and if you’re in the area, there are events listed in which you can take part.

And if you’re not a local, you can still let people know Gold Butte exists. It’s one of the last best places, a forgotten puzzle piece in the Grand Canyon biome, and it deserves protection.

Paleontology

[Time to haul this one out of the archives, what with all the targazing I’ve done the last couple days.]

Paleontology

“What is it that sets us apart,” she asked,
“from sunset or sierra?
What is the line between ourselves
and the terrain from which we come?”

He thought he knew, but something in her eyes
transfixed him in a way he knew too well.
Deep and dark and wet they stuck him fast.

In parts of California, long ago,
impressive monsters ambled in the hills:
placid armored sloths two people tall,
cats with teeth as long as boning knives,
dogs the size of bears. Now and again,
a glint of water tempted them, or else
a furry piece of meat held strangely still,
and only after the imprudent pounce
would the tar entomb them.
Now, the graduate students pick their bones.

When the land thus asserts your membership
in the vast assemblage of dust and bark,
of feather, fur and rock in which we live,
it’s best not to struggle overmuch.
The land is patient, yet insistent.
Fighting off the tar will muss your hair.
Paleontologists an era hence
will find your clothes awry. Embarrassing!
Far better just to let oneself be swallowed
in all-consuming pitch, placidly slurped
into the balm of Quaternary ages.

That’s what her eyes felt like, he thought;
a sudden lack of individual
identity: nothing sets us apart
one from the other, nor from the land around.

Breaking Pleistocene Update

I Am Zed's Mandible

I went over to the Page Museum this morning to get a look at some of the fossils they pulled out from underneath the May Company parking lot.

I got a handful of blurry, underexposed photos with my phone. They’re here.

On a side note, why is it the tourists always come up to me and ask me to explain things? I was just minding my own business reading the latest issue of Natural History near Pit 91, not bothering a soul or looking at all intelligent. Always, ALWAYS happens. Weird.

Major cache of fossils unearthed in Los Angeles

From the Los Angeles Times:

Workers excavating an underground garage on the site of an old May Co. parking structure in Los Angeles’ Hancock Park got more than just a couple hundred new parking spaces. They found the largest known cache of fossils from the last ice age, an assemblage that has flabbergasted paleontologists.

Researchers from the George C. Page Museum at the La Brea tar pits have barely begun extracting the fossils from the sandy, tarry matrix of soil, but they expect the find to double the size of the museum’s collection from the period, already the largest in the world.

Among their finds, to be formally announced today, is the nearly intact skeleton of a Columbian mammoth—named Zed by researchers—a prize discovery because only bits and pieces of mammoths had previously been found in the tar pits.

According to the story, “Zed” is being cleaned in the Page Museum’s “fishbowl,” which means I’m gonna go gawk at it tomorrow.

The paleocontractors doing the excavating have a blog. You can see photos of one of them woman-handling an intact American lion (Panthera atrox) skull here.

[Updated] In other Breaking La Brea Tar Pits News,* researchers have isolated new species of bacteria and archaea living in—and off—the asphaltum in the Rancho La Brea seeps. These extremophile organisms possess the ability to metabolize the tar, and biotech developers are eyeing the microbes for environmental cleanup potential. I’m hoping for a spray application that will dissolve big knobby tires.

* How many redundancies can you spot here? The answer may scare you.

Spermophilus

Here is a fine, very well-fed individual of the species Spermophilus variegatus, also known as the rock squirrel. This one happened to be working the crowd outside the El Tovar on the south rim of the Grand Canyon, but the species ranges throughout the Southwestern states and Mexico, edging just barely into that part of the state of California that fronts the Colorado River, for instance my neighborhood here.

The rock squirrel is one of 18 or so Spermophilus species in the western part of North America. There are currently 42 species worldwide.  Spermophilus itself — the name means “seed lover” — is one of three genera of true ground squirrels, along with Ammospermophilus, the antelope squirrels of the desert Southwest, and Cynomys, popularly known as prairie dogs. Close relatives of the three genera include marmots and chipmunks. Taxonomists group ground squirrels, chipmunks and marmots into a “tribe” within the squirrel family called Marmotini, which sounds like something you’d find on the menu in a spaghetti joint in Bozeman, or maybe a mixture of gin and wheatgrass juice.

Anyway, there are Spermophilus of various species living everywhere in Western North America from the beaches of the Arctic Ocean to southern Mexico. Their appearances vary widely, with some looking very much like your basic tree squirrels, some — the golden-mantled ground squirrel, S. lateralis, for instance — looking like glorified chipmunks, the flickertails (S. richardsonii) essentially trimmed-down prairie dogs, and the thirteen-lined and Mexican ground squirrels (S. tridecemlineatus and S. mexicanus, and I bet you can guess which is which) looking like nothing I’ve ever seen.

I found myself facing down a Spemophilus day before yesterday up at Cima Dome. I didn’t get a chance to ask it to display its tail. A tail with short hair would have made it a round-tailed ground squirrel, S. tereticaudus. Rock squirrels have bushy tails like tree squirrels. On reflection, though, I’ve decided it was probably a rock squirrel. Round-tails are low-elevation denizens, from what I can tell, preferring warmer, sandy wastes like the one I nearly got the Jeep stuck in about two hours before I saw the squirrel. The squirrel and I were up a bit, at around 5,500 feet. Also — another clue — it was hanging out in a big pile of rocks.

Still, I was a little hesitant to make the call because my squirrel field guide, Tamara Hartson’s Squirrels of the West, has a range map for the rock squirrel that implied it was unlikely I’d find any Spermophilus variegatus near Cima Dome. I decided, though, that the maps in Hartson were — how do I put this kindly? — drawn without reliance on primary sources. The range map provided for the one other Spermophilus living in the Mojave Desert, Spermophilus mohavensis, was, well, inaccurate. It shows the Mojave ground squirrel as ranging south and east of Joshua Tree National Park, almost to the Colorado River at Blythe. The actual southeastern limit of the Mojave ground squirrel is pretty much the Mojave River. That’s about a 130-mile error, about a two-fold increase in the actual range of the species.

The southeastern limit of the Mohave ground squirrel’s range is, and not by coincidence, the northwestern limit of its closest relative, the round-tailed ground squirrel. To a first approximation, each species lives on its own side of the Mojave River and nobody fishes in the middle. This becomes a little confusing when you remember that while there is water flowing in the Mojave River, it mainly does that flowing beneath several feet of gravel and sand. There’s nothing in that riverbed, 364.5 days out of your typical 365, that would provide the kind of barrier to migration — and thus gene exchange —  that usually causes one species to diverge into two sibling species. A squirrel spotting a likely mate on the other side wouldn’t even have to get its feet wet to exchange some genes.

And in fact, there is a little bit of interbreeding going on along the river, which is a pretty romantic spot when you get right down to it, and squirrelologists have found a few hybrids between the two species here and there, mainly in disturbed areas where the typical behavior of each species may have been disrupted. The breakdown of the natural order of things has likely resulted in interspecies mating, and yet the Mormon church is strangely silent on the matter.

If there’s no barrier to the populations of squirrels meeting, and they can still interbreed, what was it that split the original species in two in the first place?

The Mojave River is still a possibility despite its current lack of, well, current. Before 6,000 years ago there was water flowing in the river, lots of it, running down off the slopes of the Pluvial-era San Bernardino and San Gabriel mountains, filling what are now dry washes and alkaline playas with water too broad for a squirrel to ford. There was a vast network of lakes and streams in the Mojave then, with water off the east side of the Sierra Nevada joining in from the northwest, filling Owens and Searles lakes and spilling over into the Panamint Valley and Lake Manly on the floor of Death Valley. For its part, the Mojave River filled immense lakes where Harper Lake is now, near Hinkley, and Coyote Lake, north of Yermo. Its main flow continued past them and cut a gorge now called Afton Canyon, filled up Soda and Silver Lakes near Baker, and ended up in Lake Manly as well.

It may be that there were other factors beside swollen rivers keeping the squirrels apart. The heart of the Mohave ground squirrel’s habitat in the northwestern Mojave, smack dab in the rainshadow of the Sierra, is thought to have remained somewhat arid during the Pluvial, and may have been a refugium of sorts where desert-adapted critters were able to escape competition from less-droughty species taking advantage of the wetter Mojave elsewhere. But when you map out the boundary between the ranges of the Mohave and round-tailed ground squirrels, it’s never farther than about 30 kilometers from the Pluvial Mojave River System waterline. Things dried up 6,000 years ago, so that’s a migration rate of about five meters a year, not unlikely given ground squirrel behavior as we see it today.

I love this kind of story so much. Who but a complete geek would take note of seemingly arbitrary boundaries between the ranges of two very similar squirrel species? The Mohave is a little more pink-gray than the round-tailed, and the underside of its tail is white where the round-tailed’s is solid cinnamon-colored; the first likes gravel and the second sand. These are differences all but invisible to the vast majority of people, especially in a genus as diversely-appearanced as Spermophilus.

But when you start paying attention to why the ranges of animals and plants and other living things are the way they are, when you start paying attention to how the arrangement of life on today’s Earth came to be the way it is, epics unfurl themselves before you. Caruthers Canyon, a valley near here full of incongruous oaks and manzanitas and other usually-coastal chaparral plants, reveals itself to be a redoubt, a place where hundreds of generations of plants have held on as mountain ranges rose, blocked the rain, made two hundred miles of desert between them and their nearest kin. Uninspiring, ratty rings of creosote bush become impossibly ancient matriarchs, already 5,000 years old or more when the First Dynasty struggled to power in Egypt.

And a vague line between the ranges of two drab species of burrowing rodent becomes mythic, Noachic, the heavens opening up, a millennia-long flood separating brother from brother, sister from sister, two histories diverging from a common root, one nation cleft into two and the two meeting again as strangers.

The desert is woven of these stories, and I could spent the rest of my life reading them and be content.

By A Nail

Canis latrans, running, by Carl Dennis Buell
A running coyote, painting by Carl Dennis Buell

The ancestor of all dogs climbed trees like a cat.

Or so the experts hypothesize. The raccoon-sized, foxy omnivore Prohesperocyon is as likely a candidate for the ancestor of all dogs, wolves and foxes as any fossil species known. It lived in what is now the American Southwest. It probably had retractile claws. The later, closely related species, Hesperocyon almost certainly had retractile claws. It had only been about ten million years since caniforms and feliforms had diverged, and most feliforms can sheath those daggers.

If you had to sum up the history of the world since Prohesperocyon‘s time in two words, the phrase “grasses won” would be as accurate and all-encompassing as most phrases you might choose. Cold spread, and with the cold came dry. Moist temperate and subtropical forests receded. Dry open woodlands became more common. Grasslands spread out from their riparian Eocene habitats. By the Miocene savannas covered much of the Earth.

As grasslands expanded, animals ventured out into them. It’s harder to hide in the grass than it is in the forest. In the forest, you can hold still and hope the trees hide you from the animal trying to eat you, or from the animal you’re trying to eat. In the grassland, you’d better run for your life.

Prohesperocyon‘s successors ran. It was, to mix a metaphor, an arms race. Grazing animals died if they couldn’t outrun the predators. Predators starved if they couldn’t catch their prey. Natural selection favored the survival of the fastest.

Prohesperocyon‘s successors ran, and natural selection sculpted them for running. Strides grew longer. (As legs grew longer necks grew as well, to accommodate running with the nose near the ground — a boon to scent-hunting.) Dog’s ancestors began running on their toes, adding the length of their foot bones to their effective leg length. Toes became less about grasping surfaces for climbing and more about cushioning the shock of impact while running, with frequent sideline use as digging tools.

Eventually, dogs lost the ability to retract their claws.

image

The bones on the left are the phalanges — fingerbones — of a cat. On the right, a dog’s equivalent phalanges. The drawing is by Mauricio Anton, from the book Dogs: Their Fossil Relatives and Evolutionary History by Xiaoming Wang and Richard Tedford. I’ve cleaned up the scan a bit and darkened the arrow pointing to a concavity in one side of the cat’s second phalange. When a cat retracts its claws, the first phalange slides back into that concavity, more or less locking in place. (Imagine being able to retract your fingernails up behind the first joint.)

See the dog’s far more symmetrical second phalange? No concavity means no retractile claws. This is why dogs make this noise on hardwood floors:

…and cats don’t, usually.

Non-retractile claws take a beating, from hardwood floors or rocky soil. Retracting one’s claws allows them to stay protected from wear and thus sharper. Still, in the modern hardwood-based environment, they sometimes don’t seem to offer much in the way of strategic advantage:

Non-retractile claws would seem to offer an advantage in the cursorial lifestyle, offering a bit of extra traction like studded tires to help those sudden starts and stops and turns. It’s worth noting that the one cat with a truly cursorial hunting strategy, the cheetah, has claws that — while still technically retractable — are constantly exposed and probably noncoincidentally blunt. Other cats run, but rarely in more than short bursts.

There’s a lifestyle threshold for mammalian predators at around twenty kilograms — 45 pounds or so. Meat-eaters smaller than that threshold weight can sustain themselves on small prey: rodents, small lizards, invertebrates and such. Above 45 pounds, though, and moving fast enough to hunt requires more energy than small prey will provide. It’s not an entirely ironclad rule: smart carnivores will take easy pickings even if they’re the wrong size. But it’s not a bad rule of thumb: coyote-sized and smaller predators eat things smaller than themselves, while predators larger than coyotes eat things bigger than themselves.

That’s rather an abrupt change in strategy, and we see it now in Northern coyotes. Freed in most places from competition with larger wolves, and in some places hybridizing with those wolves, coyotes in the North have gotten their average weight up above that 45-pound threshold, and in places like Yellowstone those larger coyotes are now hunting in packs, taking down elk eleven times their size.

The pack thing is important. When cats evolved past the 45-pound mark, they had the tools to tackle larger prey on their own. Those sharp, protected claws let the cats get a secure hold on their intended meal, allowing the hunter to dispatch its prey with a precisely targeted bite. Tigers, for instance, will sever the spinal cord through the nape of the neck for prey of about human size, changing the angle of attack for buffalo-sized victims and crushing their tracheas. The old-school Smilodons, sabre-tooths, targeted a slashing bite at their prey’s abdomen, then stepped decorously back a bit to let it die of blood loss.

Dogs faced a serious disadvantage in taking down the larger grassland equids and camelids and gomphotheres and such. Those blunt claws were just fine for digging out rabbit warrens or slapping kittens off of coffee tables, but nearly useless for grabbing hold of a bison’s hide.

The solution, as expressed by those Yellowstone coyotes: cooperate in the hunt.

Large dog species, from wolves and coyotes and domestic dogs to African wild dogs, hunt cooperatively. They’ve done so for some time, as witness this rendering by Mark Hellet of a Miocene pack of Epicyon haydeni — members of the extinct Borophagine, or “bone-crushing dog” clade, at almost a meter tall at the shoulder the largest known dog in Earth’s history —  seriously ruining a Synthetoceras’ day near Red Rock Canyon State Park in Holocene Kern County. They work sophisticated and flexible strategies, acutely aware of the presence and activity of their packmates, and able to change plans as a group on a moment’s notice merely by communicating with one another.

Kind of like this one other blunt-clawed species of social hunting animals whose progenitors were thrown out of the forest and forced to make a living in the grasslands.

And this, this cascade of consequences of a minor modification of a toe bone, is why dogs were, despite being large, dangerous predators, the first species we humans domesticated, and the one most closely interwoven into the human lifestyle. Losing the ability to retract their claws set the stage for innovation of a social hunting strategy into which we humans could cleverly intrude.

Yes, we domesticated cats as well — one of the smallest species available, and they still haven’t quite made up their minds whether the arrangement is really working for them. Domesticated cats live with us in an arrested foster-maternal roleplay, having avoided the near-paranoiac isolation wild adult cats prefer.

Dogs, on the other hand, live with us without repressing much in the way of their basic nature. It’s as if it’s in their bones.

Desert Bones

Despite its dangerous reputation among non-physicists, the typical uranium atom is only weakly radioactive. More than 99 percent of the uranium found in nature consists of the isotope U-238, whose atomic nucleus contains 92 protons and 146 neutrons. The laws of physics make this a very stable configuration, with a half-life of 4.46 billion years. In other words, it takes four and a half billion years for half of the sample of U238 you hold in your hand to decay. U-235, with 143 neutrons, is far more radioactive: it has a half-life of just 704 million years. Anti-nuclear activists, among whose number I count myself, will often view these long half-life statistics with alarm, as they imply the material being discussed will be radioactive for a mind-bogglingly long time. And that’s true. For your handful of U-238 to become completely non-radioactive, you’d need to wait maybe eleven times longer than the universe has existed so far. But very long half-lives mean relatively low radioactivity. Stable isotopes have the longest half-lives of all, at infinity and change. It’s the stuff with the short half-lives you have to watch out for. Out in the desert, the naturally occurring uranium mixed in with minerals such as zircons and apatites and such is approximately as dangerous as lead. You wouldn’t want to refine it and pour it on your cornflakes, but if you did the heavy metal poisoning would get you long before the radiation would.

U-235 is a different matter: it’s what they make the bombs and nuclear power plants out of. U-235 spits out around seven times as much radiation as its heavier sibling, and is thus radioactive enough to support a self-sustaining chain reaction. U-238 isn’t. Of course, if you really want radioactive danger you turn to something like plutonium-239, which decays something like 200,000 times faster than U-238.

But U-238 does decay, and it does so at a known and predictable rate. Each decaying nucleus emits an alpha particle — a clump of two neutrons and two protons, a.k.a. a helium atom without its shell of electrons — to begin a cascade of decay, becoming one new unstable isotope after another as the nucleus tries to reach equilibrium. The first alpha emission transmutes the atom into thorium-234, which has a half-life of 24 days. The thorium-234 nucleus emits a beta particle, turning a neutron into a proton and raising its atomic number by one, and thus becomes protactinium-234. Protactinium-234 emits another beta particle to become the highly radioactive uranium-234, which emits an alpha particle to become thorium-230. Thorium begets radium; radium begets radon. Fourteen transmutations, in a cascade that can take a minute or millions of years, bring the decayed U-238 atom at long last to stable lead, 32 nucleons lighter. Eight alpha particles lighter.

When that decaying atom is part of a larger hunk of rock, each of those departing alpha particles tears through the surrounding rock. The particle ionizes many of the molecules it passes, slowing down with each encounter until it finally comes to rest a few micrometers from its parent nucleus. That parent nucleus recoils like a rifle, doing a bit of ionizing of its neighbors as well. The result is a tiny ionized tunnel, sometimes as long as a thousandth of an inch, through the surrounding rock. Each ionized molecule is repelled from its newly ionized, like-charged neighbors, and the tunnel widens a bit. If that tunnel, or fission track, is in a piece of rock of more or less uniform characteristics — a crystal, say, or a bit of volcanic glass, to provide a little bit of uniform background — you could see the tracks with a cheap microscope.

Zircon often has a significant amount of U-238 in it. So do obsidian and mica and titanite. Apatite, a class of phosphate minerals that together make up one of the most common substances in the earth’s crust, is another mineral that reliably contains uranium. Each of these minerals displays fission tracks rather nicely. Researchers will polish and etch a surface, train a microscope on it, and count the tracks.

Apatites are interesting for a number of reasons. Our bones, it turns out, are a sophisticated composite material consisting of organic fibers and apatite nanocrystals. Bone apatite less resistant to acid than fluoroapatites, which is why dentists encourage us all to substitute fluorine atoms for the hydroxyl or carbonate ions in the apatites in our teeth. (Fluoroapatites also have less tensile strength than do the apatites in our bones, which is why people with lots of fluorine in their groundwater have more hip fractures later in life.) Apatite is a source of phosphorus for industrial fertilizer, and those of you who are alive when we run short on available phosphorus, probably in about thirty years, will probably see the price of apatite skyrocket as lots of people starve. (Peak Phosphorus will mandate organic agriculture the way Peak Oil will mandate bicycling.)

Apatite also does something interesting when its temperature begins to approach the boiling point of water: its crystalline structure relaxes ever so slightly. It begins at around 70°C (158°F): small imperfections, scratches, and gaps in the mineral begin to smooth over. Tiny little flaws in the rock, fission tracks included, are annealed. Eventually, they vanish. The higher the temperature, the faster the annealing: at about 400°C, some apatites anneal their fission tracks in the time it might take you to eat a leisurely lunch. At 70-100°C, the time scales needed tend more toward the geological than culinary. But rocks do have time in abundance.

All this means that if you have a sample of apatite of which you know the uranium content, you can count the number of unannealed fission tracks and divide by the rate at which fission tracks would be produced by the sample’s uranium content. The result: a chronometer of time elapsed since that material was heated past 100°C or so. Usually, that means burial under a whole lot of rock. The rule of thumb is that each kilometer below the surface adds about 25°C to the ambient temperature, so if you determine that the apatite crystals in your sandstone show six million years worth of fission tracks, and you’ve determined by, say, the fossil content of the rock that the rock was first formed forty million years ago, then you know that the rock was more than a mile beneath the surface when it was 33 million years old or so. It’s one thing to simply know the age of the rock you’re hefting, another to gain some insight into the evolution of the landscape from which the rock came. The layers that were above your sample may have eroded away completely, no vestige of them remaining anywhere on the earth, but you have tangible proof that they existed, and evidence of their magnitude.

The few kilograms of apatite I hope to leave behind as a minor mineral deposit in the desert when I die are unlikely to be of much use to future researchers: the crystals are too nano-, and besides in my lifetime the desert has had its share of fission tracks significantly enhanced. But the phosphorus in my bones does have an infinite half-life. It isn’t going anywhere. The patience of rocks is also infinite, and I have been pleased these last few months to imagine, some few dozens of millions of years hence, some of that phosphorus deep-buried, refined and metamorphosed. That part of what was me becomes fine green crystals. The crystals await their chance to cool. Uncovered, they begin to count out the age of the earth again.