Tag Archives: Paleontology

Go Carl!

Mr. Buell makes the big time, talking (albeit briefly) about Manhattan mastodons to NPR’s science writer Robert Krulwich. A four-minute piece of audio is available at the top of the page.

That’s the second time in a couple weeks NPR has covered coevolution of plants and Pleistocene megafauna. I smell a fad. By summer, I expect an all-Osage-orange channel on basic cable.

When Carl Buell is credited as a co-author of a new book,

the thing to do is to go to the Amazon page of the book in question, find the Publisher’s Weekly review and read it:

[Donald R.] Prothero, a geologist at Occidental College (After the Dinosaurs), explains how rich the fossil record has become. His goal is two-fold. First, he wants to demonstrate the wide variety of transitional forms that have been found, many within the past 20 years. Second, he aims to discredit the creationist movement. I have tried to document how they routinely distort or deny the evidence, quote out of context, and do many other dishonest and unethical things—all in the name of pushing their crusade. He accomplishes both of his goals (though he can be repetitious regarding the creationists), and his descriptions of recent research, much of it his own, are compelling. Prothero explains that the Cambrian explosion of life forms was anything but an explosion, and presents the impressive transitional fossils between reptiles and birds, along with striking evidence for mammalian evolution, including the relationship among hominid groups. With good science and some specific rebuttals to creationist arguments, this book demonstrates the importance of paleontology to the study of evolution. 208 illus. (Nov.)

Emphasis added. 208 illustrations. Carl Buell. 29.95. That’s 14 cents per Buell. We’d be stupid not to buy it. [Carl corrects the struck-out material in comments. It actually works out to a dollar per Buell. And though I of course did not mean to slight Dr. Prothero by emphasizing Carl’s work, Carl — in typically generous fashion — corrects my slight anyway.]

There is no balance of nature

I go to the desert hoping the desert will wreak changes in me, which is more than one should ever ask of a landscape. I want the wind to peel me slowly, layer by layer and imperceptibly, until my unnecessary armor is stripped clean.

It never happens. Not that way.

I sit and wait for the change to come. I long for it. I imagine the change coming as slight and as easy as a snakeskin shed well, and anticipate the clearing of vision that comes from losing the old, used-up lenses. And I am disappointed, and restless, and then when the change comes it is less like the abrasion of thin layers and more like the cracking of a walnut. I blink hard at the new, intimidating glare.

The desert has been working on me the whole time. It is a matter of thresholds. At some point the pressure becomes too great. Running this morning, the fence lizards that lined my path saw me coming from some yards away, and yet they did not retreat stealthily, methodically. Instead they froze in place until the terror I instilled in them became too great. A trigger reached when the clomping of my clumsy feet became too much to bear, they exploded one by one into noisy flight.

This is the geometry of change in the natural world. Continuous change is uncommon, and where found it is usually part of a cycle, the increase by small increments of morning air temperature, the upward march of tides. The sun will set and the air cool, and the tides will recede, and even with those familiar examples the continuity of the change vanishes if you change the scale in which you examine them. Each tide cycle is thousands of crashing waves, each wave a torrent of turbulent collisions never to be exactly duplicated. Each degree of warming is a chaos of unpredictable breezes, air temperature rising not at all for minutes and then by jumps as a warm wind flutters over the landscape, and temperature itself a measure of the speed of random collisions of air molecules.

The San Andreas Fault slips at about an inch and a third each year across California, but some decades it moves hardly at all and then it jumps 30 feet in a second.

I am tempted sometimes to parochialize, to claim that living in the arid West with its lower biomass tonnage per acre promotes a more visceral awareness of the true nature of change. Humid environments seem more insulated against change. Growing up back East one is more tempted to believe in things such as the “Balance of Nature.” Even the ugliest scar on the land is soon cloaked by ailanthus trees. The non-botanist is tempted to take that as healing. The western landscape suffers visible change from cattle, from tire tracks, from campfires and rainstorms. Those agents of change work in the humid world as well, but their immediate effects are subtler and thus harder to discern.

The sheer fecundity of the world conceals its vulnerability to change.

Creationists seeking to argue against evolution often liken the evolution of complex organisms by natural selection to the building of a DC-10 by a hurricane blowing through a junkyard. Their conclusion? Since such an event is staggeringly unlikely, a special sentient hurricane must have built the plane deliberately. But grant a few quintillion junkyards and continuous hurricanes, and further grant the nuts and bolts and sheet metal the ability to make copies of themselves if they find themselves blown into configurations that cannot be easily blown apart by the next hurricane, and give this whole process a couple of billion years to ferment, and the evolution of machinery as complex as airplanes is almost certain. Though you might not get a DC-10, exactly.

(Come to think of it, that is how DC-10s made their appearance. Two monkeys, given 25 million years, produced not just the Shakespeare folios but every other word ever written in any language. They didn’t need typewriters to do so, but they invented them anyway. Of course they didn’t set out with that in mind.)

With a wet rock bathed in light and hospitable to the rise of complex, mutable life, it was near inevitable that complex networks of such organisms would arise, each organism trying to survive, new properties of the system emerging with each new level of complexity.

But we mistake this complexity for law.

A farmer razes a forest, plants a crop, plants another, grows old and dies. Ragweed grows up in the furrowed earth, and sumac, and silver maple. In a generation the land is forest again. We once watched that process and ascribed it to an imperative we thought the land possessed. The forest was called a climax community, as though the land had a sexual urge to grow wood. But with each razing and re-growth the character of that forest changes. It is a matter of chance what manner of tree grows in the new-bare earth, a stochastic result of which seeds first lay successful claim to the vacant territory. Sometimes no forest at all grows when the plowing ends.

Climax communities were so described because they appeared stable. The living world tends toward stability, it was thought. When there is a long enough gap between catastrophes, the land cycles through a number of unstable states and reaches a stable one. It is a stable state because it lasts longer than the unstable states. On Cima Dome this week I expect to kick a number of rocks down talus slopes, most of them unintentionally. Dislodged from its place, where it might have been content to rest for centuries, each kicked stone will touch the earth in a dozen spots, none of them sufficient to hold it, until it finds a ledge or an obstructing rock or shrub to halt its downward progress, and there it will stop, at least for a time. Would we then say that tumbling rocks seek out stable states on the hillside?

Stable states last longer. This is not an insight into the fractal geometry of the world: it is a tautology.

There is no balance of nature. Or if there is, it is the balance of a teetering rock on a pedestal stable enough to hold it for the moment.

The living earth renews itself after each disaster only in the sense that what survives the disaster may, with luck, bear progeny better suited to disastrous times. Odds are those progeny will not be to our liking. It is the weeds and plagues and pests, the irruptive big-litter breeders, that repopulate the disaster areas.

North America was once trampled by huge herds of huge animals. Mammoths and mastodons, bears the size of Ford Excursions, ground sloths and camels and horses, vultures with 17-foot wingspans. There are paleontologists who hold that most of these went extinct due to hunting pressure from humans, the ancestors of present-day Native Americans. (This is not a popular notion among some, including some present day Native Americans, who feel it smacks of blame. As for me, when considering that some people armed only with sharpened stones may have killed off the short-faced bears, I can summon no emotion other than reverent awe.)

Population biologists have calculated that human hunters need have killed only a very small percentage of the North American megafaunal population each year, a few baby mammoths here and a pesky short-faced bear there, to cause a devastating ecosystem collapse in short order. When the large animals died out, everything that depended on them for food, for seed dispersal or for habitat, to compete with their enemies and rivals… all those were pushed to the brink. And change almost certainly happened abruptly, with all seeming more or less well until it suddenly all fell apart.

There are a lot more of us now, with technology far more destructive than Clovis points. We plow much of the land and trawl most of the shallow sea. We change the atmosphere, the temperature, the color of sunlight. More and more of the produce of the earth is diverted to our mouths. The balancing rock may be large, its pedestal broad, we seeming but flies alighting on it, but there will be a time when that rock reaches a threshold and falls, and we may not see it coming.

And all of our environmentalist culture is predicated on the notion that change is continuous. The sustainability ethic that environmentalists endorse is based on the assumption that that rock, seeing itself growing too light on one side, will smile indulgently at us flies and shift its weight so that we might carry on in comfort.

River of fire, river of stone

Did they look up, fox-wolves drinking the sudden
warm water? Did they even have the time
to look up at the odd glow to the east,
a second hellish sunrise, red as fire
incinerating forests? Broadleaved oaks
and ash, the lurid-leaved persimmon trees
whose fruit fattened the horses, fed the short
faced bears, leaf litter of magnolia trees
ablaze at once? The sky would have been dark
for days, the eddied stratosphere pregnant
with dust, and thin plumes of it blowing west
against the usual ocean wind, the storm
of fire stoked by a scouring blast
across the plains. Did the Eucyons flee,
or drawn by terror-stricken, injured prey
would they have chased the fire along its edge
coyote-like? (The opportunist dog
as old as Hesperocyon, 40 million
years ago.) Guile doomed Eucyon’s whelps
to leg-hold traps, to tar pits, to the leash,
so as the peccaries, pronghorn, the sloths
and rabbits ran wild-eyed and westerly,
the fox-wolves might have headed toward the fire.
No matter. They were drinking. Did the banks
glow ruddy? Did the wretched stream run dry?
The earth had opened up, and lava bled
into the Miocene Sierran streams,
ran toward the Fresno Sea. Did they look up?
That old, steep-sided river canyon might
have taken a few moments to escape.
Fish would have been turning belly up
as river water warmed, the main stem blocked
and shrinking pools filled gills with caustic ash.
They may have been distracted. When the wall
of seething rock, molten and fast, came down
the river canyon, sandbar pools in steam
subliming at its front, air crackling and the screams
of animals unable to escape
to herald it, they may have stood, eyes wide
reflecting fatal red, transfixed, and then
even the water in their veins would burn.
Who knows? The red brim-filled the rill,
burned every tree, each fish, each sprig of moss
and raptor’s nest, melted the top few feet
of gold-flaked cobble, scoured the soft rock walls
the river had incised, flowed swift until
the earth’s anger subsided, cooled, a strange
traumatic calm descended slow after
burn-out, and other fox-wolves came to eat
what meat there was, charred by the pallid fire
of trees, cool by comparison, and the new rock’s
red glow subsided over days. Rain came
and then the river, ousted from its bed
worked on the softer rock. Eucyon whelped
the wolves. The sloths died off. The salmon lost
its fangs. The land grew cold and mountainous,
ice shrouded the peaks, and fed the streams
to quarry out the rock. That river now
a long mountain, the lava all that still
remains of those old days, the canyon walls
long gone, the sea the river fed now plowed
for cotton, its flow frozen fine-grained rock,
wild oat awns nodding from its crevices,
and travelers intent on granite domes
pass by the mountain, never seeing it.

Xeric Conifer Woodland, then and now

Caution: do not anthropomorphize

MB said something about Joshua trees and junipers in the same field of view a few days back, and I promised a post. It’s not actually all that uncommon to see the two species growing together, as the lower altitudinal limit for junipers in the Mojave is just about where the upper elevational limit of Joshua trees lies, with some overlap due to local microclimates and such. Sometimes a fault will run through the bedrock and provide a path for groundwater to approach the surface, and junipers — which in the Mojave are generally kept from growing lower than around 6,000 feet due to drought stress — will thrive a bit lower, their roots stuck in the water table. If you climb the Sierra Club trail up Teutonia Peak on Cima Dome and look back to the east from which you came, you’ll see a straight line of old junipers stretching a mile back to Sunrise Rock. They grow at just above 5,000 feet, and though they set abundant seed each year there are no other junipers nearby. You have to climb a few hundred feet up Teutonia to find junipers growing off the fault line. On the plain between Teutonia and Kessler peaks, the junipers form a line of perforation running through the thick Joshua trees, the only real source of shade in the forest.

Go to one of the junipers, look around for a while — mind the cholla stems — and you will likely find nearby a low mound of twigs and Joshua tree leaves and cactus skeletons, sometimes two feet high by five wide. This is the home of the desert woodrat, a.k.a the desert packrat, a.k.a. Neotoma lepida. Packrats are ubiquitous in the Joshua tree forest, and the wealth of berries a juniper provides each year prove a powerful inducement to settle nearby. The rats, which are the smallest of their genus at about eight inches from nose to tail tip, are mainly nocturnal: they come out of their nests — “middens” — at night and forage for plants to eat. On Cima Dome they seem especially fond of Joshua tree leaves. Or maybe that’s just what’s there. As you walk you’ll see trees where each leaf on one side of a particular branch has been sheared off evenly — nay, meticulously and methodically, as if the branch were a cob of corn being eaten by an ex-Navy man at a Fourth of July barbecue. This is the work of Neotoma lepida, and if you look around you will find a packrat midden within 50 feet: if not a pile of debris out in the open, then a comfy sheltered midden wedged between rocks or under overhangs, which is the setup the rats actually prefer.

Thus, two important facts about Neotoma lepida: they collect plant material and their range is about a hundred feet in diameter. Add to those two facts a third: a midden, once built, may house many generations of packrats. Many generations. Hundreds. Thousands. There’s a Pleistocene-era midden in the Colorado Rockies that was used more or less continuously from 950,000 years ago to 800,000 years ago: 150,000 years of habitation, a pile of sticks and leaves with a history compared to which the cathedral at Chartres is essentially a Quonset hut, Stonehenge a tilt-up strip mall. That, my friends, is tenancy.

Middens that are out in the open suffer the depredations of rain and snow, gales and determined badgers. The rock-fortified middens are more secure. Over the years the rats will bring in leaves and twigs, fruits and shiny stones and car keys, and then new layers of material will be brought in to put atop the old, and as the woodrats carry out their daily affairs in the midden they will urinate over it all over a period of years. Woodrat kidneys are desert kidneys, rather efficient at excreting salts without too much water to carry them, and the salty mess congeals into a hard, ochrous resin.

That resin — charmingly called “amberrat” by packratmiddenographers — preserves the plant material. In a cave, or under a nice big sheltering rock, away from the elements, the amberrat can preserve the material for thousands of years.

Thus an old packrat midden is a record of the vegetation of the immediate area over the span of time in which the midden has been used. And where you have thousands of years’ worth of well-preserved plant material collected from a precise location, there you have paleontologists. (Where the material is preserved by stanky rat piss, there you also have graduate students whose job it is to clean the stuff.) The plant material is identified and dated, and then we have a bit of a picture of how the vegetation in the area changed, if at all, over thousands of years. (Given the rats’ proclivity for collecting small pieces of bone, the middens occasionally provide a glimpse into animal life as well.)

And since packrats are thick on the ground in the southwest deserts, our recapture of information contaned in packrat middens is limited primarily by the supply of graduate students. There are lots and lots of data out there. And in the Mojave, one of the things those data tell us is this: the altitudinal ranges of both Joshua trees and junipers were once very different than they are today.

17,000 years ago the desert didn’t just smell like rain, it often felt like rain. Where there are now playas and salinas at the bottoms of Mojave valleys, there were broad freshwater lakes rich in wildlife. It was a wetter time, and though the countryside was not particularly lush, there was enough water in the soil that junipers could grow far down-slope. So could Joshua trees, for that matter, and even single-needle pines. In a number of places throughout the desert, the valley floors — when not flooded — were covered in what is sometimes called a Xeric Conifer Woodland, what modern-day desert rats of the two-legged variety call “P-J,” or Piñon-Juniper Woodland. Joshua trees were a minor component of that forest.

And then the dry came. Around 16,000 years ago the drought started, and it really got underway about 10-12,000 years ago. The lakes dried up, even the deepest one in the Mojave, Lake Manly, leaving its bed in Death Valley dry and crackling in the heat except for sometimes. The valley floors got too dry and hot for PJ with scattered Joshua trees. The first creosote bushes started to sprout on valley floors, and some of those plants are still alive. With their fruit dispersed by any number of birds and mammals, piñon and juniper gained a foothold in the (relatively) wetter mountains. Joshua tree didn’t rise quite as far. But deprived of competition with their former conifer neighbors, the Joshuas now dominate their part of the Mojave — at least visually.

In the Antelope Valley, 60 miles from the ocean, downstream from the well-watered San Gabriels and Tehachapis, the valley floor still hosts mixed forests of Joshua trees and junipers. Or at least it does in those few square miles, like in the photo above, not cleared for development. Flickers still cut their arcing paths between the trees, and woodrats collect sardine can keys and pull tabs to perplex the graduate students of 14007 AD.

Understanding

Thanks, all, for answering the poll below. I wanted to double-check my assumptions before weighing in on the latest discussion making the rounds of science blogs, to wit: whether scientists should think about framing in discussing science with the public. For those of you not up to speed on the discussion, I’ll just say that there is disagreement over whether framing is lying or spin, or whether it’s just something people do anyway and one might as well be conscious of it. Bora has, I think, the best summary of people’s positions on the topic that I’ve seen, and some cogent thoughts of his own as well, some of which I think I agree with.

I do think framing science in mass writing is important, and on alternate days I think framing science is inevitable even when writing for an audience of scientists. When my writing here really works, I think, it’s because I’ve stumbled upon (what I will here call once and never again) a frame that compels attention, that brings the reader a new perspective on a topic. My success rate is subjectively determined, but I think I’ve hit the mark once or twice. I’m sympathetic to those who’d rather simply present their results in flat, straightforward form, but I have never once seen a scientific paper that did not in some way use metaphor or simile — frames — to get the point of the paper across to readers. Take a recent abstract of a notable article in Nature, which article we will revisit later in the post:

Did the end-Cretaceous mass extinction event, by eliminating non-avian dinosaurs and most of the existing fauna, trigger the evolutionary radiation of present-day mammals?

Where are the metaphors? There’s the “radiation of mammals,” an explicit reference to the way a phylogenetic schematic of a diversely branching clade looks. There’s an extinction that may have “triggered” that radiation. There’s the peculiar inversion of causality implied in the notion that the end-Cretaceous mass extinction event “eliminated” dinosaurs et al, when in actuality the extinction event and the dying out of the dinosaurs and ammonites and such are one and the same. There’s no escaping portrayal by metaphor, really.

But despite my I suppose postmodernist take on objectivity and its inaccessibility to the likes of us humans, I must confess to an extreme impatience with an undercurrent I see running through the defenses of conscious framing of science. There is an assumption regarding the inherent nature of that exchange that I find troubling, if not downright insulting. I metaframe that offensive frame below in graphic form:

framing science

The best, most neutral, least inflammatory, and yet still wholly disheartening summation of that undercurrent is this explicit statement by Matt Nisbet in a list of social uses of frames:

Average citizens use frames as schematic short cuts. Frames allow citizens to make up their minds about a topic with little or no other information, and to talk about their opinions with others.

I will say I don’t have an issue with that as a description of what is. But as a prescription for what ought, rightly, to be? Elitism, pure and simple.

Carl Zimmer had the best response to that sentiment, it seems to me:

[F]raming doesn’t seem like quite the right response to the fact that over two-thirds of people in this country don’t know enough about science to understand a newspaper story on a scientific subject. It seems more like surrender to me. Fixing high school science education seems a better plan. Don’t let kids come out of high school without knowing that a laser emits light, not sound; without knowing about standard deviations; without knowing what a stem cell is. Fixing high school science would be a lot harder than staying on message, but it would be a lot more important.

According to my statistically non-significant poll, a quarter of CRN readers claim to read science blogs occasionally despite science not being a main life interest. More than half read at least a few science blogs regularly. It’s a mistake to read too much, or maybe even anything, into that poll, especially given the venue, which if anything has spent the last four years collecting people tolerant of the author’s diverse and shifting attention. But a divide between a lethargic, ignorant public and an elite corps of pure scientists, it seems to me, would likely be expressed in fatter tails on that bell curve. I think this topic is worthy of further study and the NAS and NEA are thus each cordially invited to fund my important cross-disciplinary research, checks to be made out to the Consortium for the Advancement of Science Heuristics, which is a pretty long name so just put the acronym in the payable to line. Thanks in advance.

It’s a bit ironic. I decided today I’d better write something about this once I meet my paid writing deadline on Wednesday, then went off to get this week’s hay fever shots. They make me wait after, as I have mentioned, and I used the opportunity to catch up on the reading that had piled up while I spent February and March hiding under my blanket. I had missed, for instance, the fact that Jennifer had snagged a spot in the Valentine’s Day edition of Nature, which is cause for unbridled admiration and a little envy. And I read that piece, and then I turned to the above-mentioned Mammals in the Cretaceous article, the gist of which is that mammals seem to have diversified abundantly tens of millions of years before dinos went missing. There was a graphic in the article which I’d seen on people’s blogs:

Mammal phylogeny

I took a good look at the graphic in print, with reading glasses, sitting there in the allergy clinic waiting room, and suddenly the floor fell out from under me and I was doing my best to stifle sobs, and failing.

It’s a phylogeny chart, a graphic representation of the relationships among existing families of mammals, drawn roughly to scale in the time dimension to give an indication when different groups of mammals diverged from one another. The time line begins at the center of the circle, and along any path the closer you get to the perimeter the closer you get to the present day. The meat of the article is expressed in that dotted black circle, the end-Cretaceous mass extinction. Most of the branching that represents the evolved diversity among mammal families took place after that event, but a surprising amount of that diversification took place in the shadow of the dinosaurs, a cool enough conclusion in any event. The chart is color coded to represent the five major mammalian clades as described in the article: monotremes, marsupials, Afrotherians, Xenarthrans, Laurasiatherians, and Euarchontoglires. Primates are Euarchontoglires, as are rodents and rabbits, and a couple small families closely related to but not primates: the tree shrews and flying lemurs. Marsupials seem to have diversified after primates, an interesting blow to an old preconception of marsupials as somehow far more primitive than placental mammals, let alone our own vaunted order. Tarsiers and monkeys split before possums and kangaroos did.

There are lots of little tidbits like that in the chart, and I was finding them and enjoying myself, and then I noticed that Euarchontoglires and Laurasiatherians diverged about 100 million years ago. About 100 million years ago there was a population of weird little mammals, and some of them went off to become the ancestors of the Euarchontoglires, and others to become the ancestors of the Laurasiatherians.

I am, as implied above, a Euarchontoglire.

Zeke was a Laurasiatherian.

I looked at the point on that chart where the green Laurasiatherian branches and the red Euarchontoglire branches shared a common root, a hundred million years ago, and tears welled up. A hundred million years ago we diverged, our family riven, and an impossible length of time afterward we met, our lines scourged by a half-dozen mass extinctions and the good times between them none too pleasant at that. It is ridiculous to think of it as a reunion: I may as well weep to be reunited with my distant cousin the grass pollen making my eyes water, lost lo these billions of years. It’s a stretch, in fact, to think in terms of families. The chart describes populations, not individuals. The two clades may have diverged a million years after my common ancestor with Zeke perished.

I am but an untutored yokel and the complexities, the obligatory qualifiers are no doubt lost on one like me, without a Learn’d Scientist there to explain to me how I am wrong.

But a frame is a frame, and I wept in the fucking allergy clinic waiting room looking at lines on a phylogenetic map for a beloved cousin found and then lost again.