prof_pangaea | Entries tagged with paleontology rocks

Here is a poem I wrote about the recent discovery of soft tissue in a Tyrannosaurus rex fossil:

soft science/
hunk sandstone forced break solid fossilized bone rock lab chemically hard cold lab bone dead minerals bone fossilization fossils fossil fossils sandstone excavated fossil cracked cracking bones cut bone cut
hard science/
yielded soft tissue blood vessels cells blood vessels bone cells blood cells transparent flexible vessels flexible squeezed cells flexibility transparency soft tissue soft tissues warm living blood vessels blood vessels yielded flexible fibers cells soft tissue wrapping soft tissue soft tissue

And here is a link to the article:
http://www.msnbc.msn.com/id/7285683

Excerpt from:

Wonderful Life: The Burgess Shale and the Nature of History
by Stephen Jay Gould

VII. The Origin of Homo sapiens

I will not carry out this argument to ridiculous extremes. Even I will admit that t some point in the story of human evolution, circumstances conspired to encourage mentality at our modern level. The usual scenario holds that attainment of upright posture freed the hands for using tools and weapons, and feedback from the bahavioral possibilities thus provided spurred the evolution of a larger brain.

But I believe that most of us labor under a false impression about the pattern of human evolution. We view our rise as a kind of global process encompassing all members of the human lineage, wherever they may have lived. We recognize that Homo erectus, our immediate ancestor, was the first to emigrate from Africa and to settle in Europe and Asia as well ("Java Man" and "Peking Man" of the old texts). But we then revert to the hypothesis of global impetus and imagine that all Homo erectus populations on all three continents moved together up the ladder of mentality on a wave of predictable and necessary advance, given the adaptive value of intelligence. I call this scenario the "tendency theory" of human evolution. Homo sapiens becomes the anticipated result of an evolutionary tendency pervading all human populations.

In an alternative view, recently given powerful support by reconstructions of our evolutionary tree based on genetic difference among modern groups (Cann, Stoneking, and Wilson, 1987; Gould, 1987b), Homo sapiens arose as an evolutionary item, a definite entity, a small and coherent population that split off from a lineage of ancestors in Africa. I call this view the "entity theory" of human evolution. It carries a cascade of arresting implications: Asian Homo erectus died without issue and does not enter our immediate ancestry (for we evolved from the African populations); Neanderthal people were collateral cousins, perhaps already living in Europe while we emerged in Africa, and also contributing nothing to our immediate genetic heritage. In other words, we are an improbably and fragile entity, fortunately successful after precarious beginnings as a small population in Africa, not the predictable end result of a global tendency. We are a thing, an item of history, not an embodiment of general principles.

The claim would not carry startling implications if we were a repeatable thing -- if, had Homo sapiens failed and succumbed to early extinction as most species do, another population with higher intelligence in the same form was bound to originate. Wouldn't the Neanderthals have taken up the torch if we failed, or wouldn't some other embodiment of mentality at our level have originated without much delay? I don't see why. Our closest ancestors and cousins, Homo erectus, the Neanderthals, and others, possessed mental abilities of a high order, as indicated by their range of tools and other artifacts. But only Homo sapiens shows direct evidence for the kind of abstract reasoning, including numerical and aesthetic modes, that we identify as distinctly human. All indications of ice-age reckoning -- the calendar sticks and counting blades -- belong to Homo sapiens. And all of the ice-age art -- the cave paintings, the Venus figures, the horse-head carvings, the reindeer bas-reliefs -- was done by our species. By evidence now available, Neanderthal knew nothing of representational art.

Run the tape again, and let the tiny twig of Homo sapiens expire in Africa. Other hominids may have stood on the threshold of what we know as human possibilities, but many sensible scenarios would never generate out level of mentality. Run the tape again, and this time Neanderthal perishes in Europe and Homo erectus in Asia (as they did in out world). The sole surviving human stock, Homo erectus in Africa, stumbles along for a while, even prospers, but does not speciate and therefore remains stable. A mutated virus then wipes Homo erectus out, or a change in climate reconverts Africa into an inhospitable forest. One little twig on the mammalian branch, a lineage with interesting possibilities that were never realized, joins the vast majority of species in extinction. So what? Most possibilities are never realized, and who will ever know the difference.

Arguments of this form lead me to the conclusion that biology's most profound insight into human nature, status, and potential lies in the simple phrase, the embodiment of contingency: Homo sapiens is an entity, not a tendency.

By taking this form of argument across all scales of time and extent, and right to the heart of our own evolution, I hope I have convinced you that contingency matters where it counts most. Otherwise, you may view this projected replaying of life's tape as merely a game about alien creatures. You may ask if all my reveries really make any difference. Who cares, in the old spirit of America at its pragmatic best? It is fun to imagine oneself as a sort of divine disc jockey, sitting before the tape machine of time with a library of cassettes labeled "priapulids", "polychaetes", and "primates." But would it really matter if all the replays of the Burgess Shale produced their unrealized opposites -- asn we inhabited a world of wiwaxiids, a sea floor littered with little penis worms, and forests full of phororhacids? We might be shucking sclerites instead of opening shells for our clambakes. Our trophy rooms might vie for the longest Diatryma beak, not the richest lion mane. But what would be fundamentally different?

Everything, I suggest. The divine tape player holds a million scenarios, each perfectly sensible. Little quirks at the outset, occurring for no particular reason, unleash cascades of consequences that make a particular future seem inevitable in retrospect. But the slightest early nudge contacts a different groove, and the history veers into another plausible channel, diverging continually from its original pathway. The end results are so different, the initial perturbation so apparently trivial. If little penis worms ruled the sea, I have no confidence that Austrolopithecus would ever have walked erect on the savannas of Africa. And so, for ourselves, I think we can only exclaim, O brave -- and improbable -- new world, that has such people in it!

Excerpt from:

Wonderful Life: The Burgess Shale and the Nature of History
by Stephen Jay Gould

VI. Passing the Torch to Mammals

Can we not grant the traditionalist some solace? et contingency rule right to the origin of mammals. Can we not survey the world as mammals emerged into the realm of the dinosaurs, and know that the meek and hairy would soon inherit the earth? What defense could large, lumbering, stupid, cold-blooded behemoths provide against smarts, sleekness, live birth, and constant body temperature? Don't we all know that mammals arose late in the reign of dinosaurs; and did they not hasten the inevitable transition by eating their rivals' eggs?

This common scenario is fiction rooted in traditionalist hopes for progress and predictability. Mammals evolved at the end of the Triassic, at the same time as dinosaurs, or just a tad later. Mammals spent their first hundred million years -- two thirds of their total history -- as small creatures living in the noks and crannies of a dinosaur's world. Their sixty million years of success following the demise of dinosaurs has been something of an afterthought.

We have no indication of any trend toward mammalian hegemony during this initial hundred million years. Quite the reverse -- dinosaurs remained in unchallenged possession of all environments for large-bodied terrestrial creatures. Mammals made no substantial moves toward domination, larger brains, or even greater size.

If mammals had arisen late and helped to drive dinosaurs to their doom, then we could legitimately propose a scenario of expected progress. But dinosaurs remained dominant and probably became extinct only as a quirky result of the most unpredictable of all events -- a mass dying triggered by an extraterrestrial impact. If dinosaurs had not died in this event, they would probably still dominate the domain of large-bodied vertebrates, as they had for so long with such conspicuous success, and mammals would still be small creatures in the interstices of their world. This situation prevailed for a hundred million years; why no for sixty million more? Since dinosaurs were not moving toward markedly larger brains, and since a prospect may lie outside the capabilities of reptilian design (Jerison, 1973; Hopson, 1977), we must assume that consciousness would not have evolved on our planet if a cosmic catastrophe had not claimed the dinosaurs as victims. In an entirely literal sense, we owe our existence, as large and reasoning mammals, to our lucky stars.

Excerpt from:

Wonderful Life: The Burgess Shale and the Nature of History
by Stephen Jay Gould

V. The Origin of Terrestrial Vertebrates

Our traditionalist is now reeling. He is ready to abandon virtually all of life to contingency, but he will make his last stand with vertebrates. The game, after all, centers on human consciousness as the unpredictable product of an incidental twig, or the combination of an ineluctable, or at the very least, a probable, trend. To hell with the rest of life; they aren't on the lineage leading to consciousness in any case. Surely, once vertebrates arose, however improbable their origin, we could then mount confidently from ponds to dry land to hind legs to big brains.

I might grant the probability of the most crucial environmental transition -- from water to land -- if the characteristic anatomy of fishes implied, even for incidental reasons, an easy transformation of fins into sturdy limbs needed for support in the gravity of terrestrial environments. But the fins of most fishes are entirely unsuited for such a transition. A stout basal bar follows the line of the body axis, and numerous thin fin rays run parallel to each other and perpendicular to the bar. These thin, unconnected rays could not support the weight of the body on land. The few modern fishes that scurry across mud flats, including Periophthalmus, the "walking fish," pull their bodies along and do not stride with their fins.

Terrestrial vertebrates could arise because a relatively small group of fishes, only distantly related to the "standard issue," happened, for their own immediate reasons, to evolve a radically different type of limb skeleton, with a strong central axis perpendicular to the body, and numerous lateral branches radiating from the common focus. A structure of this design could evolve into a weight-bearing terrestrial limb, with the central axis converted to the major bones of our arms and legs, and the lateral branches forming digits. Such a fin design did not evolve for its future flexibility in permitting later mammalian life; (this limb may have provided advantages, in superior rotation, for bottom-dwelling fishes that used the substrate to aid in propulsion). But whatever its unknown advantages, this necessary prerequisite to terrestrial life evolved in a restricted group of fishes off the main line -- the lungfish-coelacanth-rhipidistian complex. Wind the tape of life back to the Devonian, the so-called age of fishes. Would an observer have singled out these uncommon an uncharacteristic fishes as precursors to such conspicuous success in such a different environment? Replay the tape, expunge the rhipisdistians by extinction, and our lands become the unchallenged domain of insects and flowers.

Excerpt from:

Wonderful Life: The Burgess Shale and the Nature of History
by Stephen Jay Gould

IV. The Subsequent Cambrian Origin of the Modern Fauna*

Our traditionalist is not beginning to worry, but he will grant this one last point pour mieux sauter. OK, the very first Cambrian fauna included a plethora of alternative possibilities, all equally sensible and none leading to us. But, surely, once the modern fauna arose in the next phase of the Cambrian, called Atdabanian after another Russian locality, then the boundaries were finally set. The arrival of trilobites, those familiar symbols of the Cambrian, must mark the end of craziness and the inception of predictability. Let the good times roll.

This book is quite long enough already, and you do not want a "second verse, same as the first." I merely point out that the Burgess Shale represents the early and maximal extent of the Atdabanian radiation. The story of the Burgess Shale is the tale of life itself, not a unique and peculiar episode of possibilities gone wild.

Excerpt from:

Wonderful Life: The Burgess Shale and the Nature of History
by Stephen Jay Gould

III. The First Fauna of the Cambrian Explosion

Our hypothetical advocate of the cone and the ladder might be willing to give ground on the these first two incidents from the dim mists of time, but he might then be tempted to dig his entrenchment across the Cambrian boundary. Surely, once the great explosion occurs, and traditional fossils with hard parts enter the record, then the outlines must be set, and life must move upward and outward in predictable channels.

Not so. As noted in chapter II, the initial shelly fauna, called the Tommotian to honor a famous Russian locality, contains far more mysteries than precursors. Some modern groups make an undoubted first appearance in the Tommotian, but more of these fossils may represent anatomies beyond the current range. The story is becoming familiar -- a maximum of potential pathways at the beginning, followed by decimation to set the modern pattern.

The most characteristic and abundant of all Tommotian creatures, the archaeocyathids, represent a long-standing problem in classification. The familiar litany plays again. These first reef-forming creatures of the fossil record are simple in form, usually cone-shaped, with double walls -- cup within cup. In the traditional spirit of the shoehorn, they have been shunted from one modern group to another during more than a century of paleontological speculation. Corals and sponges have been their usual putative homes. But the more we learn about archaeocyathids, the stranger they appear, and most paleontologists now place them in a separate phylum destined to disappear before the Cambrian had run its course.

Even more impressive is the extensive disparity just now being recognized among organisms of the "small shelly fauna." Tommotian rocks house an enormous variety of tiny fossils (usually one to five millimeters in length) that cannot be allied with an modern group (Bengston, 1977; Bengston and Fletcher, 1983). We can arrange these fossils by outward appearance, as tubes, spines, cones, and plates, but we do not know their zoological affinities. Perhaps they are merely bits and pieces of an era of early, still imperfect skeletonization; perhaps the covered familiar organisms that later developed the more elaborate shells of their conventional fossils signatures. But perhaps -- and this interpretation has recently been gaining favor among aficionados of the small shelly fauna -- most of the Tommotian oddballs represent unique anatomies that arose early and disappeared quickly, For example, Rozanov, the leading Russian expert on this fauna, concludes his recent review by writing:

Early Cambrian rocks contain numerous remains of very peculiar organisms, both animals and plants, most of which are unknown after the Cambrian. I tend to think that numerous high-level taxa developed in the early Cambrian and rapidly became extinct (1986, p. 95).

Once again, we have a Christmas tree rather than a cone. Once again, the unpredictability of evolutionary pathways asserts itself against our hope for the inevitability of consciousness. The Tommotian contained many modern groups, but also a large range of alternative possibilities. Rewind the tape into the early Cambrian, and perhaps this time our modern reefs are built by archaeocyathids, not corals. Perhaps no Bikini, no Waikiki; perhaps, also, no people to sip rum swizzles and snorkle amidst great undersea gardens.

Excerpt from:

Wonderful Life: The Burgess Shale and the Nature of History
by Stephen Jay Gould

II. The First Fauna of Multicellular Animals

You might accept this last sobering scenario, but then claim, fine, I'll grant the unpredictability of getting beyond prokaryotic cells, but once you finally do get multicellular animals, then the basic pathways are surely set and further advance to consciousness must occur. But let's take a closer look.

The first multicellular animals, as discussed in chapter II, are members of a world-wide fauna named for the most famous outcrop at Ediacara, in Australia. Martin Glaessner, the paleontologist most responsible for describing the Ediacara animals, has always interpreted the, under traditional concepts of the cone, as primitive representatives of modern groups -- mostly members of the coelenterate phylum (soft corals and medusoids), but including annelid worms and arthropods (Glaessner, 1984). Glaessner's traditional reading evoked very little opposition (but see Pflug, 1972 and 1974), and the Ediacara fauna settled comfortably into textbooks as fitting ancestors for modern groups -- for their combination of maximal age with minimal complexity neatly matches expectations.

The Ediacara fauna has special importance as the only evidence for multicellular life before the great divide separating the Precambrian and Cambrian, a boundary marked by the celebrated Cambrian explosion of modern groups with hard parts. True, the Ediacara creatures are only barely Precambrian; they occur in strata just predating Cambrian and probably do not extend more than 100 million years into the uppermost Precambrian. In keeping with their position immediately below the boundary, the Ediacara animals are entirely soft-bodied. If taxonomic identity could be maintained right through this greatest of geological transitions, and without major disruption in design to accompany the evolution of hard parts, then the smooth continuity of the cone would be confirmed. This version of Ediacara begins to sound suspiciously like Walcott's shoehorn.

In the early 1980's, my friend Dolf Seilacher, professor of paleontology at Tubingen, Germany, and in my opinion the finest paleontological observer now active, proposed a radically different interpretation of the Edicara fauna (Seilacher, 1984). His twofold defense rests upon a negative and a positive argument. For his negative claim, he argues on functional grounds that the Ediacara creatures could not have operated as their supposed modern counterparts, and therefore may not be allied with any modern group, despite some superficial similarity of outward form. For example, most Ediacara animals have been allied with the soft corals, a group including modern sea fans. Coral skeletons represent colonies housing thousands of tiny individuals. In soft corals, the individual polyps line the branches of a tree or network structure, and the branches must be separated, so that water can bring food particles to polyps and sweep away waste products. But the apparent branches of the Ediacara forms are joined together, forming a flattened quiltlike mat with no spaces between the sections.

For his positive claim, Seilacher argues that most Ediacara animals may taxonomically united as variations on a single anatomical plan -- a flattened form divided into sections that are matted or quilted together, perhaps constituting a hydraulic skeleton much like an air mattress. Sine this design matches no modern anatomical plan, Seilacher concludes that the Ediacara creatures represent a entirely separate experiment in multicellular life -- one that ultimately failed in a previously unrecognized latest Precambrian extinction, for no Ediacara elements survived into the Cambrian.

For the Burgess fauna, the case against Walcott's shoehorn has been proven, I think, with as much confidence as science can muster. For the Ediacara fauna, Seilacher's hypothesis is a plausible and exciting, but as yet unproven, alternative to the traditional reading, which will one day be called either Glaessner's shoehorn or Glaessner's insight, as the case may be.

But consider the implications for unpredictability if Seilacher's view prevails, even partly. Under Glaessner's ranking in modern groups, the first animals share the anatomical designs of later organisms, but in a simpler form -- and evolution must be channelled upward and outward in the traditional cone of increasing diversity. Replay the tape, starting with simple coelenterates, worms, and arthropods, a hundred times, and I suppose that you will usually end up with more and better of the same.

But if Seilacher is right, other possibilities and other directions were once available. Seilacher does not believe that all late Cambrian animals fall within the taxonomic boundaries of this alternative and independent experiment in multicellular life. By studying the abundant and varied trace fossils (tracks, trails, and burrows) of the same strata, he is convinced that metazoan animals of modern design -- probably genuine worms in one form or another -- shared the earth with the Ediacara fauna. Thus, as with the Burgess, several different anatomical possibilities were present right at the beginning. Life might have taken either the Ediacara or the modern pathway, but the Ediacara lost entirely, and we don't know why.

Suppose that we could replay life's tape from the late Precambrian times, and that the fla quilts of Ediacara won on the second attempt, while metazoans were eliminated. Could life have ever moved to consciousness along this alternative pathway of Ediacara anatomy? Probably not. Ediacara design looks like an alternative solution to the problem of gaining enough surface area as size increases. Since surfaces (length2) increase so much more slowly than volumes (length3), and since animals perform most functions through surfaces, some way must be found to elaborate surface area in large creatures. Modern life followed the path of evolving internal organs (lungs, villi of the small intestine) to provide the requisite surfaces.. In a second solution -- proposed by Seilacher as the key to understanding Ediacara design -- organisms may not be able to evolve internal complexity and must rely instead on changes in overall form, taking the shape of threads, ribbons, sheets, or pancakes so that no internal space lies very far from the outer surface. (The complex quilting of Ediacara animals could then be viewed as a device for strengthening such a precarious form. A sheet one foot long and a fraction of an inch thick needs some extra support in a world of woe, tides, and storms.)

If Ediacara represents this second solution, and if Ediacara had won the replay, then I doubt that animal life would ever have gained much complexity, or attained anything close to self-consciousness. The developmental program or Ediacara creatures might have forclosed the evolution of internal organs, and animal life would then have remained permanently in the rut of sheets and pancakes -- a most unpropitous shape for self-consciousness as we know it. If, on the other hand, Ediacara survivors had been able to evolve internal complexity later on, then the pathways fro the radically different starting point would have produced a world worthy of science fiction at its best.

Excerpt from:

Wonderful Life: The Burgess Shale and the Nature of History
by Stephen Jay Gould

Seven Possible Worlds

The collapse of the cone* and the ladder** open the floodgates to alternative worlds that didn't emerge, but might have arisen with slight and sensible changes in early events. The unrealised universes would have been every bit as ordered and explainable as the world we know, but ever so different in ways that we can never specify in detail. The enumeration of unrealised worlds is a parlor game without end, for who can count the possibilities? The universe is not so tightly interconnected that the fall of a petal disrupts a distant star, whatever our poets sing. But most quirky changes of topograpy and environment, most appearances and disappearances of groups (if not of single species), can irrevocably alter the pathways of life in substantial ways. The playground of contingency is immeasurable. Let us consider just seven alternate scenarios, arranged in chronological order to home in on the biological object that most excites our parochial fancy -- Homo sapiens.

I. Evolution of the Eukaryotic Cell

Life arose at least 3.5 billion years ago, about as soon as the earth became cool enough for stability of the chief chemical components. (I do not, by the way, view the origin of life itself as a chancy or unpredictable event. I suspect that given the composition of early atmospheres and oceans, life's origin was a chemical necessity. Contingency arises later, when historical complexity enters the picture of evolution.)

With respect to the old belief in steady progress, nothing could be stranger than the evolution of life -- for nothing much happened for ever so long. The oldest fossils are prokaryotic cells some 3.5 billion years old. The fossil record of this time also includes the highest form of macroscopic complexity evolved by these prokaryotes -- stromatolites. These are layers of sediment trapped and bound by prokaryotic cells. The layers may pile up one atop the other, as tides bury and re-form the mats -- and the whole structure may come to resemble a cabbage in cross section (also in size).

Stromatolites and their prokaryotic builders dominated the fossil record throughout the world for more than 2 billion years. The first eukaryotic cells (the complex textbook variety, complete with nucleus and numerous structures of the cytoplasm) appeared some 1.4 billion years ago. The conventional argument holds that eukaryotic cells are a prerequisite for multicellular complexity, if only because sexual reproduction required paired chromosomes, and only sex can supply the variation that natural selection needs as raw material for further complexity.

But multicellular animals did not rise soon after the origin of eukaryotic cells; they first appeared just before the Cambrian explosion some 570 million years ago. Hence, a good deal more than half the histor of life is a tale of prokaryotic cells alone, and only the last one-sixth of life's time on earth has included multicellular animals.

Such delays and long lead times strongly suggest contingency and a vast realm of unrealized possibilities. If prokaryotes had to advance toward eukaryotic complexity, they certainly took their time about it. Moreover, when we consider the favored hypotheses for the origin of the eukaryotic cell, we enter the realm of the quirky and incidental side consequences as unpredictable sources of change. Our best best theory identifies at least some major organelles -- the mitochondria and cytoplasts almost surely, and others with less confidence -- as descendants of entire prokaryotic cells that evolved to live symbiotically within other cells (Margulis, 1981). In this view, each eukaryotic cell is, by descent, a colony that later achieved tighter integration. Surely, the mitochondrion that first entered another cell was not thinking about the future benefits of cooperation and integration; it was merely trying to make its own living in a tough Darwinian world. Accordingly, this fundamental step in the evolution of multicellular life arose for an immediate reason quite unrelated to its eventual effect upon organic complexity. This scenario seems to imply fortunate contingency rather than cause and effect. And if you wish nevertheless to view the organelles and the transition from symbiosis to integration as predictable in some orderly fashion, then tell me why more that half the history of life passed before the process got started.

One final point that I find chilling with respect to the possibility of something like human evolution in an alternative world: Even though this first event took more than half the known history of life, I might be prepared to accept the probability of an eventual origin of higher intelligence if the earth were slated to endure for hundreds of billions of years -- so that this initial step took but a tiny fraction of the potential time. But cosmologists tell us that the sun is just about at the halfway point of existence in its current state; and that some five billion years from now, it will explode, expanding in diameter beyond the orbit of Jupiter and engulfing the earth. Life will end unless it can move elsewhere; and life on earth will terminate in any case.

Since human intelligence arose just a geological second ago, we face the stunning fact that the evolution of self-consciousness required about half the earth's potential time. Given the errors and uncertainties, the variations of rates and pathways in the other runs of tape, what possible confidence can we have in the eventual origin of out distinctive mental abilities? Run the tape again, and even if the same general pathways emerge, it might take twenty billion years to reach self-consciousness this time -- except that the earth would be incinerated billions of years before. Run the tape again, and the first step from prokaryotic to eukaryotic might take twelve billion instead of two billion years -- and stromatolites, never awarded the time needed to move on, might be the highest mute witnesses to Armageddon.

*The term "cone" refers to the idea of "the cone of increasing diversity" of life. Many illustrations of life and evolution are based on such an idea -- for example, diagrams of an evolutionary tree. The idea implies low is primitive and few, high is better and more.
http://www.ries.com/images/2ndLevel/Books/cs_origin/chap-1.gif

** The term "ladder" refers to the idea of the "ladder of upward progress of life", also known, incorrectly, as the "evolutionary ladder". Gould disproves both the idea of the cone and ladder elsewhere in the book -- life is not "improving" or "progressing". It simply is.
http://www.islamonline.net/English/Science/2002/08/images/pic02-b.jpg

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The Holocene Mass Exinction Event

From Cambrian Explosion to Nuclear Winter

Entries tagged with paleontology rocks

soft tissue

Wonderful Life (Part VII, FINAL)

Wonderful Life (Part VI)

Wondeful Life (Part V)

Wonderful Life (Part IV)

Wonderful Life (Part III)

Wonderful Life (Part II)

Wonderful Life (Part I)