The Triassic is old. This book is new. That is a hard to beat combination.

Let’s see … The Triassic is about here:

(You can also look it up in this PDF file supplied by the USGS.

It is situated between two major extinction events, and is especially interesting because it is during this period that modern day ecological systems and major animal groups took a recognizable form. The preceding Permian, if contrasted with modern day, would form a very stark contrast while the Triassic would be at least somewhat more recognizable.

But of course the Triassic was in many ways distinct, different, and fascinating. Dinosaurs arose during the Triassic. The Triassic is also famous for its enormously large insects. It was also the time of Pangaea, where most of the Earth’s land was concentrated instead of being more or less spread out as it is now. Mammals, or at least the progenitors of what we now know of as mammals, arose then as well.

The Triassic was hot compared to today, and dry. Lots of sandy, arid-land deposits visible today date from this period. The poles were temperate, and the middle regions of the one giant continent was probably … very continental (mainly, dry).

So, all this adds up to the simple fact that the Triassic was a very interesting time period, and I assume that you would like to know a lot more about it. That would be where the new book, Triassic Life on Land: The Great Transition, comes in. This new volume in a series on “Critical Moments and Perspectives in Earth History and Paleobiology” (of which there are several other interesting must-have installments) comes in.

Sues and Fraser’s accessibly priced volume is neither a popularization of palaeontology nor a monotonous monograph of esoterica. It is a scholarly but readable detailed yet succinct description of this incredibly interesting time period. This is the kind of book that you will sit down to relax with, but do so with a pack of post-it notes handy just in case you need to mark something. Triassic Life .. is sufficiently detailed and well documented (excellent references and index) to be used as a textbook in a middle level palaeontology course, and sufficiently engaging for you to use as a source book for your next cocktail party.

The authors are widely recognized and respected experts in their field. The publisher did an excellent job with the book, which is very heavily illustrated and well laid out. Yet, most of the illustration are very nicely done line drawings and black and white photos, which keeps the price of this volume down despite the nice paper and excellent binding.

The book has eleven chapters, seven of which serve as mini-monographs of specific Triassic sub periods in specific geographical locations (such as “Late Middle and Late Triassic of Gondwana” and “Late Triassic of the Western United States”). Each of these chapters gives the basic information on where, when, and what for that particular subset of paleontological phenomena. Chapter 9, “Two Extraordinary Windows into Triassic Life” focus on two cases of Konzentrat-Lagerstätten (places of especially good preservation or richness): Solite Quarry in the eastern US and Madygen in Central Asia. Triassic insects. Very nice.

Chapter 10 is an overview of the large scale pattern of biological change during the period, and Chapter 11 examines the Triassic end-times, exploring the possibility of an end-Triassic impact, and other issues.

If you have an evolution-oriented relative or friend who’s birthday is coming up, now’s your chance: The book is new enough and specialized enough that there is no way they’d have it already. And, it looks enough like a coffee table book that others looking on will see it as a great gift even if it is a bit over the top in geek points.

I refer, of course to the realization that a giant object from outer space can land on the earth with catastrophic consequences, perhaps causing a mass extinction, and that this could for the first time nicely explain a strange pattern in the fossil record which, in turn, had only just then been discovered: that long periods of boring stasis were occasionally (maybe even periodically) punctuated by mass extinction events.

These realizations … this fundamental, holistic and richly explanatory rewrite of paleontology … happened more or less spontaneously from about 1970 to 1990. Oh, I should note: In geology, 20 years is less than an instant. (And I’m not talking about the fossil record here, but rather, the often glacial pace at which ideas set in stone are either buried or eroded into dust. Often at no great loess.)

It has been understood for a very long time that the history of life on earth can be divided into great ages during which time one or another fauna and flora dominated. The Devonian was the age of fish. We are at present in the age of mammals. The age of dinosaurs spans the Triassic, Jurassic and the (K)Cretaceous (ignore that “K” for now) which together make up the Mesozoic Era (225 to 65 million years ago). Of course, all these ages together are really the Age of Bacteria. But that is another discussion for another time.

What was not appreciated for all this geologist time (the past couple of centuries) is that very stark boundaries separated many — maybe all — of these time periods. The realization that this is so was famously made official by Niles Eldridge and Stephen Gould in a 1972 paper on what they called punctuated equilibira (not equilibrium). To make a long story short, during the 1970s and into the 1980s paleontologists and geologists, as well as evolutionary biologists, made an important transition; At the end of this period of intellectual history, most people accepted as very likely the idea that species evolution is rare and slow and unspectacular for long periods of time, and that these periods of relative stasis (equilibrium) are punctuated by very short periods … geological instants … during which there was lots of extinction. The extinction presumably caused open niches, and possibly the causes of extinction caused changes in conditions, so extinctions would be followed by lots and lots of speciation. Because something bad happened, and that bad thing may well have been a large object hitting the earth, nasty volcanism, dramatic sea level change causing the chemistry of the oceans to shift dangerously, or whatever.

In the late 1970s a large impact crater was discovered in the Yucatan. The crater became known as Chicxulub. Later on in time, a team of physicists and geologists, the core members being Luis and Walter Alvarez, made the startling observation that here and there around the earth one can find a layer different from whatever is below it, and different from whatever is above it, and that itself contains an anomalously high concentration of iridium, an element that usually shows up from outer space, and that is otherwise quite rare on earth.

So over several years, the pattern of the fossil record, based on data that had been built up over centuries, was reinterpreted to be based on a framework of sudden, major, occasional events, a giant impact crater that dated to the time of the dinosaur impact was discovered, and convincing geological evidence of a global event marking the Cretaceous-Tertiary transition … called the KT boundary (K for Cretaceous) was identified.

Theory, data, smoking gun. Case closed.

The exact order of discovery, realization, integration, and synthesis was actually somewhat complex. My personal recolleciton is that many geologists took a long time to get on board with each of these elements. I’m pretty sure that the Alvarez Hypothesis was extant, and being taken pretty seriously, before the argument that the Chicxulub crater in the Yucatan was the impact site for this event fully took hold, but that eventually did happen.

I remember well one moment in the history of this punctuation in thinking among geologists and paleontologists. It was at a meeting of the American Association for the Advancement of Science (probably in New York). It was something that Stephen Jay Gould Said:

“Get that thing closed or tell those people to shut up … I’m trying to give a lecture here….”

Oh, no wait, that’s not it. yes, he did say that, but I was thinking of something different. Let’s see (…. accessing memory banks ….) maybe this:

“No, Bernard, I do NOT give you permission to answer that question for me. I said I was not answering it and that’s the end of it! It was a stupid question when asked of me and asking if of you does not change that situation one iota!”

No, wait, that wasn’t it either. Let me think about this for a secon….. Oh, OK, I got it! He said:

“It is a remarkable observation of the history of science and intellectual discourse generally that what may well be the most important single fact to come to light relevant to the human endeavor, indeed to the survival of humanity itself, was gleaned from the close scrutiny and dedicated study of of the dull gray fossil record by earnest but mostly boring paleontologist working in the dusty attics and store houses of largely neglected natural history museums the world over.” … or words to that effect.

(I must say … I actually got a headache writing that last paragraph.)

But as you probably know by now, because a lot of people have been talking about it, the case is not as closed as was once thought. After two decades of transformation of geologists and paleontologists the world over, who tend to be very conservative about their ideas (the utterly obvious idea of plate tectonics took about a half a century to fully take hold … the first use of stable isotopes to document glacial change was in the late 1960s but the method did not become normal and accepted by everyone until the mid 1980s … and so on), there is now evidence that the Chicxulub impact occurred 300,000 years before the KT boundary indicated by the iridium.

The evidence is actually pretty straight foward. It consists of a layer of sediment that post dates the impact and that seems to have been laid down by normal processes, over a reasonably well estimated interval of 300,000 years. The KT layer sits atop this layer.

Here is a description of this finding by the discoverer of this evidence, Gerta Keller:

The newest research … uses evidence from Mexico to suggest that the Chicxulub impact predates the K-T boundary by as many as 300,000 years. “From El Penon and other localities in Mexico we know that between 4 and 9 metres of sediments were deposited at about 2-3 centimetres per thousand years after the impact. The mass extinction level can be seen in the sediments above this interval” says Keller.

Advocates of the Chicxulub impact theory suggest that the impact crater and the mass extinction event only appear far apart in the sedimentary record because of earthquake or tsunami disturbance that resulted from the impact of the asteroid.

‘The problem with the tsunami interpretation’ says Dr Keller, ‘is that this sandstone complex was not deposited over hours or days by a tsunami; deposition occurred over a very long time period’.

The study found that the sediments separating the two events were characteristic of normal sedimentation, with burrows formed by creatures colonising the ocean floor, erosion and transportation of sediments, and no evidence of structural disturbance.

As well as this, they found evidence that the Chicxulub impact had nothing like the dramatic impact on species diversity that has been suggested. At one site at El Peon, the researchers found 52 species present in sediments below the impact spherule layer, and counted all 52 still present in layers above the spherules. In contrast, at a site at La Sierrita which records the K-T boundary, 31 out of 44 species disappeared from the fossil record.

“We found that not a single species went extinct as a result of the Chicxulub impact…these are astonishing results that have been confirmed by more studies in Texas” says Keller.

There are two elements in this description: 1) The sepration of the Chicxulub impact and the KT event; and 2) the relative ho-hum nature of the KT boundary itself. A third element not mentioned is that Keller suggests that a major volcanic event in India may have been the actual cause of extinction that we associated with the end of the Cretaceous.

So is this correct? I shall explain.

The separation of the Chicxulub impact and the KT boundary needs to be very firmly established, and maybe it is so established at this point. This would rule out Chicxulub as the cause of the KT event. However, this does not rule out an impact. The iridium is still there.

It might be that the 300,000 year intervening time period is not really there. This hinges mainly on a small number of geological sections that are interpreted using techniqes that are a) well established but b) not necessarily tested under all the necessary circumstances to be truly bullet proof. I myself was involved in an excavation where such evidence was used to argue for a certain sedimentary process, but under careful examination we turned out to be (probably) wrong. Things are not always what they seem in the geological record. (See: The Greg Layer.) Having said all that, I’m currently liking the 300,000 year time interval, but that is subject to revision.

Again, separating a particular crater from the KT boundary does not eliminate the impact idea, it just complicates things (in important ways).

Regarding the lack of extinction across the boundary in some places: That is interesting. This has been noted before in other areas, and in some cases the seeming lack of extinction went way when it was realized that the fossils above the boundary were actually from below the boundary, but were washed into the upper sediment (from raised-up fossil beds). Also, we expect the boundary to be imperfect … there should be groups of organisms surviving past the boundary then going extinct later (and some, obviously, not going extinct at all). These particular cases, if verified, are not hypothesis killers, but rather, they are just reality complexifiers.

So, I conclude: The next couple of years studying this is going to be interesting. Don’t you think?

The research summary quoted above can be found here.

Kim Hannula gives her perspective here.
Ethan Siegal discusses this issue here.
Suvrat Kher provides his analysis here.

This is an open access paper published a while back that will give you an excellent orientation to this work:

Keller, G. (2004). From The Cover: Chicxulub impact predates the K-T boundary mass extinction Proceedings of the National Academy of Sciences, 101 (11), 3753-3758 DOI: 10.1073/pnas.0400396101

Gerta Keller, whose studies of rock formations at many sites in the United States, Mexico and India have led her to conclude that volcanoes, not a vast meteorite, were the more likely culprits in the demise of the Earth’s giant reptiles, is producing new data supporting her claim.

Keller, a Princeton professor of geosciences, and several co-authors lay out the case in a paper published April 27 in the Journal of the Geological Society of London. Examinations at several new sites have produced “biotic evidence” — the fossilized traces of plants and animals tied to the period in question — indicating that a massive die-off did not occur directly after the strike but much later.

In addition, Keller and other researchers have found “aftermath” sediments that remained undisturbed and showed signs of active life, with burrows formed by creatures colonizing the ocean floor. This would quash a theory advanced by some that a massive tsunami followed the impact, Keller said.

“Careful documentation of results that are reproducible and verifiable will uncover what really happened,” Keller said. “This study takes an important step in that direction.”

Much of the new data comes from a trench dug out of low-lying hills in northeastern Mexico at a site called El Peñon. A group of Princeton undergraduates accompanying Keller on a field trip to Mexico in 2004 excavated the area and uncovered the new evidence. Keller and her team have been analyzing that evidence for the last several years.

Understanding what caused the dinosaurs to disappear remains a great mystery. Theories attempting to explain it include asteroid or cometary impacts, volcanoes, global climate change, rising sea levels and supernova explosions. Scientists know that at a point about 65 million years ago, some phenomenon triggered mass extinctions on the land and oceans.

This event defines the boundary between the older Mesozoic Era, the “Age of Reptiles,” and the modern Cenozoic Era, the “Age of Mammals.” On a finer geological scale, the disappearances occurred between the Cretaceous (K) period and the Tertiary (T) period. As a result, scientists refer to this time as the K-T boundary.

At many locations, the K-T boundary is clearly visible in rock formations, which contain a thin layer of clay rich in the element iridium. Because iridium is more common in asteroids and comets than on Earth, scientists proposed in 1980 that an asteroid or comet must have struck Earth just at the boundary and caused the mass extinction of dinosaurs and many other animals. They thought they had found the culprit when they discovered the Chicxulub impact crater in Mexico’s northern Yucatan.

Keller began studying the K-T boundary in 1984 — the year she arrived at Princeton. She discovered that the evidence for the asteroid theory was not so clear. In field investigations, she and her team of students and collaborators found populations of Cretaceous age foraminifera, one-celled ocean organisms that evolved rapidly during select geological periods, living on top of the impact fallout from Chicxulub. The fallout from the asteroid that struck Chicxulub is visible as a layer of glassy beads of molten rock that rained down after the impact. If this impact caused the mass extinction, then the foraminifera above the impact glass beads should have been the newly evolved species of the Tertiary age.

Using these fossil remains to construct a timeline, she and her team were able to date the surrounding geologic features and begin to piece together proof that the impact occurred 300,000 years before the great extinction.

Over the years, Keller’s group has amassed evidence for as many as four major events widely separated in time in that area of Mexico as well as in Texas. The oldest of the four events is the Chicxulub impact, seen by the fallout of glass beads. The second is about 150,000 years later and seen in a layer of sandstone with Chicxulub impact glass beads that were transported from shallow shore areas into deep waters during a sea level fall and was commonly interpreted as a tsunami generated by the Chicxulub impact. About 100,000 to 150,000 years later, the third event struck at the time of the K-T boundary with its iridium layer and mass extinction. This event may represent a second large impact or massive volcanism. The fourth event is possibly a smaller impact as evidenced by another iridium layer about 100,000 years after the mass extinction.

Advocates of the Chicxulub impact theory suggest that the impact crater and the mass extinction event only appear far apart in the sedimentary record because an earthquake or tsunami caused slumps and mixing of sediments surrounding the Gulf of Mexico. To date no evidence of major disturbance has been found in the sediments.

Keller says her team’s newest research, however, confirms what she has found in earlier studies — that the sandstone complex that overlays the impact layer was not deposited over hours or days by a tsunami but over a long time period. From El Peñon in Mexico and other sites listed in the new study, the scientists were able to calculate that between 13 and 30 feet of sediments were deposited at a rate of about an inch per thousand years after the impact. These sediments separating the impact layer from the sandstone complex and the overlying mass extinction were formed by normal processes. There is evidence of erosion and transportation of sediments in the sandstone layers, but no evidence of structural disturbance, Keller said.

Also at El Peñon, the researchers found 52 species present in sediments below the impact layer and counted all 52 still present in the layer above it, indicating that the impact has not had the devasting biotic effect on species diversity as has been suggested. “Not a single species went extinct as a result of the Chicxulub impact,” Keller said.

In contrast, she noted, at a nearby site known as La Sierrita where the K-T boundary, iridium anomaly and mass extinction are recorded, 31 out of 44 species disappeared from the fossil record at the K-T boundary.

“Keller and colleagues continue to amass detailed stratigraphic information supporting new thinking about the Chicxulub impact and the mass extinction at the end of the Cretaceous,” said Richard Lane, program director in the National Science Foundation’s division of earth sciences, which funded the research. “The two may not be linked after all.”

Keller suggests that the massive volcanic eruptions at the Deccan Traps in India may be responsible for the extinction, releasing massive amounts of dust and gases that could have blocked sunlight, altered climate and caused acid rain. The fact that the Chicxulub impact seems to have had no effect on biota, she said, despite its 6-mile-in-diameter size, indicates that even large asteroid impacts may not be as deadly as imagined.

She regards the latest evidence as sufficiently convincing and compelling to allow her to move on and investigate further the evidence for Deccan volcanism as being at the root of dinosaur extinction. But she does not expect her teams’ present work will stop the raging debate at the heart of this controversy.

“The decades-old controversy over the cause of the K-T mass extinction will never achieve consensus,” Keller said. But consensus, she added, is not a precondition to advancing science and unraveling truth. “What is necessary is careful documentation of results that are reproducible and verifiable,” she said.

Co-authors of the paper are Thierry Adatte of the University of Lausanne in Switzerland; Alfonso Pardo Juez of the CES Fundación San Valero in Spain, who earned a Ph.D. from Princeton in 1995; and José Lopes-Oliva of the University of Nueva León in Mexico, who earned a Ph.D. from Princeton in 1996. The journal is published by the Geological Society of London. The research was funded by the National Science Foundation and the Swiss National Fund.

The latest science is beginning to suggest that it is all even more interesting and exciting (and scary) than previously thought.

The Younger Dryas is named after a cute little yellow flower called the Dryas. There were two periods during the last “Ice Age” Where Dryas pollen shows up as a kind of marker in ancient sediments (like in the muck on the bottom of a pond or lake, for instance). The younger layer is called the Younger Dryas, and it has been known for many decades.

Meanwhile, around the world in regions previously covered by the last glacier there was recognized a phenomenon called a “readvance.” When glaciers stop expanding, there is a lot of melting at the leading edge of the ice. Here form features called moraines, consisting of cobbles, gravel, silt, etc. … the dirty crap that the glacier has chewed up as it grew that is now being spewed out the edge like the icky sandy stuff you see all over parking lots in the spring when the winter snow melts (this will mean nothing to those of you living in warm environments, of course).

The moraines can be very large and impressive features. For example, Long Island. The whole freakin’ thing is a giant Moraine. Or Cape Cod.

These moraines can be dated using a variety of technique, and they are then understood to be the terminal feature of one particular glaciation. Often, because history tends to repeat itself under certain circumstances, we find moraines on top of moraines, with the deeper ones representing earlier glacial periods. The study of moraines was key to the initial understanding that there even was an Ice Age, and in working out the basic chronology of glaciations.

So, a “readvance” is when you have a moraine indicating that a glacial cycle is ending, and then somewhere stratigraphically above the moraine and in a somewhat (but usually not too much) different geographical location, you find another mini-moraine, indicating that the glacial ice temporarily expanded again. The glacier came back. Advanced again. Readvanced.

So there are a number of long-ago identified “readvances” in North America and Europe. It turns out that all of the latest “readvances” linked to the last ice age date to the same time period as each other, and to the same time periods at the Younger Dryas.

So the last glacial cycle happened, then abated, and by the way, the retreat of the glaciers that occurred then was linked to very very warm conditions. I once found a subtropical species of clam in the late glacial sediments near Boston, and that was pretty run of the mill evidence … one bit among many … indicating that the end of the last glacial cycle was accompanied by very warm conditions in the north Atlantic and elsewhere.

But then that retreat stopped and, apparently, full blown glacial conditions returned.

This is very interesting for many reasons, but mostly because it is a tiny, recent, and thus quite manageable and observable using good techniques, example of the onset of glacial conditions It is very hard to understand and study the onset of glacial conditions in the distant past, because subsequent glacial activity may damage much of the relevant evidence, and because it is a long time ago. But the Younger Dryas is smaller, less destructive of evidence of its own origin, and recent. So we can perhaps use it as an example of glacial onset and address the question: What causes an Ice Age to happen?

All I want to do here is to point you to a new article in Science that provides further evidence for a theory that originally was viewed with great skepticism but that has recently started to show some promise as it passes trough the gamut of professional obstinacy we know of as the Scientific Method. But first, a quick review of what we thought caused the Younger Dryas.

Back in the 1980s, we were all very excited to have a very cool theory for the start of the Younger Dryas based on then novel ways of looking at ocean currents together with extremely high resolution climate data from an increasingly large number of ocean and lake cores. This was the Atlantic Conveyor theory.

The Atlantic Conveyer is a current that starts as a poorly organized surface current (really a bunch of enormous blobs) of warm water exiting from the Indian Ocean into the southern Atlantic. This water then moved north to the North Atlantic where it cooled and evaporated. The evaporation exacerbated the cooling and made the water more saline. Thus, warm water became denser and colder, and thus sunk to the bottom of the ocean. What goes down must come up, etc., so this sunk cold water would the run in a deep water current …. a kind of giant sub-oceanic river greater in volume than all the world’s fresh water rivers combined times some not too small number …. back to the Indian Ocean where it was heated up again.

The loss of heat from this water in the North Atlantic kept the northern continetns relatively ice-age free. The idea is that every now and then the conveyor turns off and an ice age happens. In the case of the Younger Dryas, the thing that turned it off, according to this model, was the influx of great amounts of fresh water from an inland sea that flooded the North Atlantic.

There is no doubt that this great inland sea (and other like it) existed, and there is no doubt that there were great influxes of fresh water into the North Atlantic (and elsewhere, such as the Gulf of Mexico, etc.) at various times. The problem, as was discovered with even greater resolution of the climate data, that the 1,300 year long Younger Dryas began at a time centuries away from the most likely time of the flood.

A second idea that had been around for some time then came to prominence. This is the idea that the great Mountain Wave simply moves up and down. It works like this. There is a wave of air moving around the earth at any given latitude. As you go up and down the longitudes, the direction of the wave shifts back and forth and changes in it’s character. The junction between two of these waves is the jet stream, and there are several such features. The details are way more complicated than I can address here. The point of this idea is that there is a big wave of air movement over the North American continent, and it moves seasonally (winter vs. summer), but it also moves at a larger scale, such that for some centuries, or for thousands of years, or even longer periods, it has one pattern, and for other periods, it has a different pattern. One pattern gives you ice ages, a different pattern does not.

The third and most recent theory is that some kind of enormous extraterrestrial but near earth explosion happened … like a swarm of comets hitting the atmosphere all at once and exploding, maybe even running into the earth but not leaving much of a crater. This theory gets pretty zany. In one region of North America, researchers claim that there are little tiny bits of shrapnel in almost every large extinct mammal bones that they find. In other words, the North American megafauna got wiped out in a matter of seconds or minutes because they literally got fragged.

This event would have also involved climate change of the type we see with the Younger Dryas, and the timing of the event is quite possibly perfect for explaining the onset of the Younger Dryas glaciation.

The latest study is from Science, and is a follow up on criticism leveled at an earlier paper published in PNAS. From the Science paper:

We report abundant nanodiamonds in sediments dating to 12.9 … thousand calendar years before the present at multiple locations across North America. [there are two types of ] diamond … in this boundary layer but not above or below that interval. Cubic diamonds form under high temperature-pressure regimes, and n-diamonds also require extraordinary conditions, well outside the range of Earth’s typical surficial processes but common to cosmic impacts. …. These diamonds provide strong evidence for Earth’s collision with a rare swarm of carbonaceous chondrites or comets at the onset of the Younger Dryas cool interval, producing multiple airbursts and possible surface impacts, with severe repercussions for plants, animals, and humans in North America.

This study is reviewed in a recent blog post at Real Climate

I venture to guess that this impact theory will pan out and be demonstrated as very likely. All of this must be understood in the context of Milankovitch Cycles, of course. These are the orbital cycles that more or less (more more than less, as a matter of fact) map onto the comings and goings of ice ages over the last two million years. Within the context of these orbital geometric cycles, events such as running into a herd of comets or great fresh water inland seas catastrophically dumping into the ocean or sudden metastable changes in air currents could turn on, or off, a particular climate pattern.

We have not seen the end of this discussion, no doubt.

D. J. Kennett, J. P. Kennett, A. West, C. Mercer, S. S. Q. Hee, L. Bement, T. E. Bunch, M. Sellers, W. S. Wolbach (2009). Nanodiamonds in the Younger Dryas Boundary Sediment Layer Science, 323 (5910), 94-94 DOI: 10.1126/science.1162819

Today it is common knowledge that the dinosaurs were wiped out by a meteorite impact sixty-five million years ago, which killed half of all species then living.Far less well-known is a much bigger catastrophe – the greatest mass extinction of all time – which occurred 251 million years ago, at the end of the Permian period. In this cataclysm, at least ninety per cent of life was destroyed, both on land, including sabre-toothed reptiles and their rhinoceros-sized prey, and in the sea.After the event the Earth was a cold, airless place, with only one or two species eking out a poor existence. What caused destruction on such an unimaginable scale, and how did life recover?Michael Benton’s book about this catastrophe – When Life Nearly Died: the greatest mass extinction of all time – has been published in paperback this week. Michael Benton is Professor of Vertebrate Palaeontology at the University of Bristol.James Lovelock said of the book: “Michael Benton’s book brings back to Earth Science a sense of adventure … it is both a wonderfully good read and a valued reference”.When Life Nearly Died documents not only what happened 251 million years ago, but also the recent rekindling of the idea of catastrophism, after it was seemingly extinguished in a great battle of ideas in the early nineteenth century. Scientists have at last come to accept that the world has been subject to huge cataclysms in the past. For the end-Permian event the killing models are controversial – was the agent the impact of a huge meteorite or comet over ten kilometres in diameter, or prolonged volcanic eruption in Siberia? The evidence has been accumulating through the 1990s and into the new millennium, and Michael Benton gives his verdict at the very end of this book.

…In this study, we combined paleo-climate simulations, climate envelope models (which describe the climate associated with the known distribution of a species–its envelope–and estimate that envelope’s position under different climate change scenarios), and a population model that includes an explicit treatment of woolly mammoth-human interactions to measure the extent to which climate changes, increased human pressures, or a combination of both factors might have been responsible. Results show a dramatic decline in suitable climate conditions for the mammoth between the Late Pleistocene and the Holocene, with hospitable areas in the mid-Holocene being restricted mainly to Arctic Siberia, where the latest records of woolly mammoths in continental Asia have been found. The population model results also support the view that the collapse of the climatically suitable area caused a significant drop in mammoth population size, making the animals more vulnerable to increasing hunting pressure from expanding human populations. The coincidence of the collapse of climatically suitable areas and the increase in anthropogenic impacts in the Holocene are most likely to have been the coup de grace, which set the place and time for the extinction of the woolly mammoth.

The map of diminishing envelope looks like this:View larger imageWe are left still not knowing what happened to the Woolly Mammoth. It is tempting to assume that once their range was restricted, humans would have easily finished them off, but the area to which their range was restricted probably never had that many humans living in it. Simple range restriction followed by any one of a number of bits of bad luck would have done it.The technology to bring the Woolly Mammoth back is almost within reach. We should start thinking about that as an option. Just for fun.

Related posts:Did Humans or Climate Change Cause the Extinctions of Pleistocene Eurasian Megafauna?Darwin and the Voyage: 11 ~ Elephants and HorsesThe Evolution of the Modern Climate: New Evidence from Plant RemainsAre We In The Anthropocene? No.Mammals and the KT EventAfter the End Permian Mass ExtinctionRelated posts from other blogs:Not Exactly Rocket Science: Climate change knocked mammoths down, humans finished them offA Blog Around the Clock: So, why did the mammoths REALLY go extinct?Source:(Sorry for the odd formatting … this is an automatically generated reference that allows important inter-tube magic to happen so I don’t want to mess with it…)NoguÃ?©s-Bravo, D., RodrÃ?­guez, J., Hortal, J., Batra, P., AraÃ?ºjo, M.B., Barnosky, A. (2008). Climate Change, Humans, and the Extinction of the Woolly Mammoth. PLoS Biology, 6(4), e79. DOI: 10.1371/journal.pbio.0060079>Please note our new “share this” feature (below). If you were wondering where the “email this post” button went, you will find it there.

1. The diversification of the major groups of mammals occurred millions of years prior to the KT boundary event; and
2. The further diversification of these groups into the modern pattern of mammalian diversity occurred millions of years later than the KT boundary event.

The KT boundary event is the moment in time when a ca. 10 km. diameter object going very fast hit the earth in the vicinity of the modern Yucatan, causing the extinction of the dinosaurs (and almost everything else larger than a microwave). It has been suggested that this event resulted in (allowed for) the subsequent diversification of the mammals, presumably because the earlier extinction event opened up previously filled niches, into which the mammals evolved, and possibly because of dramatic climate change that occurred with this event.One of the reasons that this study is important is that it seems to falsify this long-standing hypothesis.This paper is thoughtfully discussed on Pharyngula and Sandwalk, and I recommend that you have a look at those sites.I have a number of comments on this paper. Before I make them I want to say that I have absolutely no strong feeling on which of these ideas is either likely or important. I’m not coming at this with a particular agenda regarding this evolutionary pattern of mammal evolution. The KT boundary question is not directly in my area of research (I’m post middle Miocene). I do have one agenda-like perspective, however, that I want to lay out in the beginning: Larry Moran points out that the evidence for close connections between climate change and evolution seems to weaken with every new study, and that we have to simply start believing that the connection is a falsehood. I disagree with this conclusion, but in a way that is not meant to preserve the old “climate change – evolution” link. I agree with Larry that the link as I’ve ever seen it described and tested has failed to find support in the data. However, I do not believe it is correct to say that there is no relationship between climate change and speciation. I think that the way the link has usually been postulated is incorrect, and that when it comes to understanding the environmental change-speciation link we are dumb little babies (so far). I’ll discuss this in more detail below.The following figure is from the Nature paper, and shows the new mammal phylogeny. The dotted circle is the KT boundary. Notice that the major taxa are shown to have emerged before the event, and the rise of numerous subsequent species after it. The lineages shown on this graph represent nearly every single living mammal, but no fossil species are used since this is a molecular phylogeny. Click on the figure to get a larger copy.The (Possibly) Real Importance of this PaperNever mind the KT event or the test of the hypothesis that mammalian radiations are linked to it. This paper provides what appears to be the best current phylogeny of the living mammals at the higher taxonomic level, significantly better than anything we have had before. One could argue about some of the details (one has to pick “a” tree for this kind of study, and there are alternative possibilities) and the resolution of the given tree is poor for the more recent radiations (I’m personally looking for the best current rodent tree and I’m afraid this one won’t do). However, attempts to put the major groups together have been difficult and often unsatisfying, so it is great to have a new, most up to date version.However, the reader should not assume that this tree is the final accepted phylogeny of the mammals. Other research teams will come out with critiques and there will be revisions, I’m guessing sooner rather than later. Watch for it. What will be interesting is to see if the critiques involve the overall pattern described here in relation to the KT boundary.I am not certain that we are ready to believe calibration of molecular phylogenies.The timing of events on this tree are estimated by using molecular clocks calibrated by various bits of the fossil record. The authors were fairly careful in doing this, not using a single clock, but adjusting for suspected rate variations among different clades. The fossils give minimal dates for divergences …. so if you have a fossil that has an undoubted featured of a certain clade, and the fossil is dated, then you know that the split between that lineage and it’s nearest molecular relative predated that fossil date.I have not done a thorough analysis of the supplemental data supplied with the paper, so please understand that I do not have a specific criticism of the way in which the molecular data are calibrated. My gut feeling is that the authors did a great job. However, I do have an overall problem with molecular calibration and I want to preach caution.The initial diversification of the living superorders and orders is set in this study at 93 million years ago. An acceleration of diversification is set startling at the “Early Eocene” (the paper does not give a date for this, so I’ll set it at 54 million years ago).Taking 65 million years ago (the KT event) as a benchmark, the earlier date would have to be moved towards the present by 43 percent in order to “fit” the data with the KT boundary. I other words, if you KNEW that the initial diversification happened at the KT boundary, then you would have to adjust all of your molecular data by 43 percent, or putting it yet another way, if all you had was the molecular phylogeny and the date of the KT event, you would have to have confidence in your molecular calibration sufficient to believe that you could not be wrong by 43 percent. Forty-three percent sounds like a lot.I guarantee you that most molecular biologists will say that 43 percent is a very large number. I also guarantee you that a LOT of fossil people will say that 43 percent is NOT a large number, and that there have been many cases where the molecular calibration is off by a factor of two.For example, over the period of several years, the molecular data for the split of humans and the other apes had the following pattern: In the 1970s, there was one group saying 5 million, other groups saying much more, like 6-7. Over time, the “long view” groups revised and revised until finally they were also saying something close to 5 million, or even a little less. Then a fossil was found in Ethiopia that dated to just under 5 million and it looked like a good candidate for an australopith at the boundary between a last common ancestor and early hominids. So everybody was pretty darn happy with 5 million years.Then, suddenly, more fossils started to show up and now we are looking at likely hominids closer to 6.5 or even 7 million years. The hominid-ness of the earliest fossil is somewhat in dispute, but frankly, the nay-sayers are probably wrong … the hominid-ape split probably dates to between 6 and 7 million, closer to 7.So, the calibration of the DNA systems used to date the human-nonhuman ape split, a topic that has received considerable attention, has a fudge factor of 30 or 40 percent, depending on how you look at it.Now, some of you are already thinking: Right, sure, but the early date in this study (93 million years) must be based on dated fossils! You can’t move the molecular estimate of the timing of a split between lineages to a point in time AFTER the existence of fossils demonstrating the split! Yes, you would be correct about that. So now the question is, are the early diversifications (the ones around 93 million years) linked to fossils that demonstrate the split? Again, I have not looked at the specific cases used for this calibration, but I believe that there are fossils of early mammals, indicating these splits, dated to well before the KT event. However, the first appearances in the fossil record of terrestrial mammals is hard to estimate, and the earlier in time one looks the more likely one underestimates the age of these events. If anything, I would guess that the 93 million year date is an underestimate, and that these splits really happened a bit earlier.Is the Eocene (and Later) Estimate for Diversification Wrong?Let’s say that the 93 million year date is an underestimate by 15 percent. If we recalibrate the entire tree based on this guesstimate, then the later diversification (said in this paper to be Early Eocene) would move from 55 million years to 63.5 million years ago.Eocene and later diversification is not about the KT boundaryIf it is true that there is a post-Paleocene (Eocene and later) diversification of living mammals, then this does not mean that mammals did not diversify in the early Paleocene, just after the KT event.Studies looking at just the fossils did not disappear on the publication of this paper. I’ll give you one very handy and excellent example: John Alroy of the Smithsonian has a paper looking at early appearances of mammalian taxa in North America in relation to time. The following figures are from his paper: http://www.nceas.ucsb.edu/~alroy/Paleocene.htmlFigure 1. North American mammalian diversity, origination (new appearance) rates, and extinction rates through the late Cretaceous and Cenozoic. Data are based on multivariate ordination and standardized sampling of faunal lists. (a) Standing diversity. Y-axis is logged to show the lack of either a log-linear (exponential) or asymptotic (simple logistic) pattern; instead, an offset between two logistic curves at about 65 MYA is indicated. (b) Origination rates. (c) Extinction rates.Figure 2. Trends through time in North American mammalian body mass distributions. All species falling into each 1.0 MY-long bin are considered. (a) Mean body mass. (b) Standard deviation of body mass.These fossil dates do not require calibration in relation to the geological column … they ARE the geological column. There is no ambiguity about the relationship between a spike in mammal species novelty and the KT event, at least in North America (where the direct events of the KT event may have been the most severe, by the way). The conclusion from the molecular data appears to be incorrect from this perspective.Is the Later Diversification a Later “Event” or an Artifact of the Pattern?It is possible that for any molecular record of sufficient diversity (a record of several higher taxa) and time depth, there will emerge “waves” of diversification that are partly determined by actual splits between species and partly determined by the patterns of extinction such that the apparent timing of the diversification a) has little do to with the actual events and b) follows along behind the “present” in fits and starts. Let’s look at an example, at least of “a”.Now, I’m not going to do the actual work on this, I’m just going to mentally walk you through it. Imagine we wanted to estimate the time of diversification of the dinosaurs from the molecular data. We determine the clade of living forms that includes all possible dinosaurs. This would be the Archosauria, which includes the dinosaurs, the birds, and the crocodiles. Unfortunately, since we are basing this on living forms (using DNA) we can only sample the crocodiles and the birds, no dinosaurs.The resulting analysis would show an initial diversification (the bird/croc split) way earlier than the presumed dinosaur radiations (I’m assuming there were multiple!) and another, much later radiation (the birds). We would be like the three statisticians hunting rabbits … we might be able to convince ourselves that we hit the rabbit, but the rabbit would be laughing at us.It seems to me that the fossil record shows a diversification of mammals hard on the heels of the KT boundary, and the living mammal molecular reconstruction either has some calibration issues or is tracking a different phenomenon. Or both.Even if the later radiation is “the” radiation… was KT unimportant? (Is environmental change really unrelated to speciation?)This is a bit of a philosophical question, but it gets to the issue I mention above about the relationship between climate change and speciation. Larry is not going to like this, and I heartily look forward to his comments if he has chance to make some.Free oxygen in the atmosphere is essential to much life on this planet. But it did not always exist. Had the biological processes that resulted in atmospheric oxygen not happened, all of the organisms that depend on it today would not exist. So, that ancient event – a clear example of environmental change — has a lot to do with all later evolution.That is a very indirect link, making it trivial to the question of a connection between environmental change and speciation.In terms of numbers of species as well as biomass, living ungulates mainly depend on widespread grasslands. Widespread grasslands emerged as a feature of the environment during the Miocene. The radiations we see of ungulates could not have happened were it not for the appearance of these grasslands (an environmental change). That is a less trivial link. It is not likely (as has been attempted) to find specific events … a particular dessication event, the closure of the Panama land bridge, etc. etc. to a particular radiation of the ungulates. And there is more than one radiation, likely. But the grass-ungulate link is less trivial than the oxygen-nearly everything link.The rise of a particular evolutionary novelty and a particular climate event or environmental change is perhaps unlikely to have happened, and if it did, it would be hard to see. The history of speciation is not clearly linked to specific environmental changes to the extent that would be necessary for this to be our main explanation. This is complicated by the fact that many of the major “events” we see are rare, but we know that at least in the last few million years (and probably at various other longish periods of time in the past) orbital geometry running on cycles of tens of thousands of years has to be accounted for. But there is a very large scale link, and sometimes that link is closer and better fit historically and functionally than other times.It is wrong to say that “environmental change causes speciation” and leave it at that. But it is also wrong to say that “environmental change is unrelated to speciation,” because there is a range of “trivial” to more direct connections between environments and adaptive patterns. I believe that we are not in a position to describe a pattern or to develop a strong theory in this regard at this time. Persistent belief in a simple environmental change-speciation link has probably, in retrospect, wasted a lot of our time and energy, but that is how science works. We need to move on towards a more nuanced and meaningful set of models.It was the Birds Fault!OK, so let’s say the fossil record is wrong, and we must simply believe the molecular record. Mammal radiation did not occur right after the KT boundary. Why?Well, I want to re-emphasize that it probably did, so “why” may not be a valid question. However, there is one thing I’d like to throw into the works. I am about to make a number of enormous logical leaps, so hang on to the safety rope.Some clades experience increase in body size over time. This does not necessarily mean that small forms disappear, but rather, the range of body sizes across species in a clade increases. In a way, you can think of this as diversification of potential niches, because (at least for terrestrial mammal) there is a link between body size and several important aspects of “niche” running from diet to predator-related issues to nesting, etc. So one thing you might expect is for there to be a link between increase in range of body size and increase in species diversity.One system that may drive body size increase is the predator-prey relationship, whereby prey “outgrow” various predators, but predators also increase in size, over evolutionary time. It seems that dinosaurs at various time and places experienced predator-prey “arms races” in body size. It seems that this also happened with mammals.Now, in the Paleocene, after the KT boundary, it is my understanding that few large (like, mammoths and such) critters were to be found, and that terrestrial ecosystems were dominated by largish avian predators. These Killer Big Birds (much like the Big Bird from Sesame Street but with a larger beak and a much coarser attitude) were probably the main predator on early post KT terrestrial mammals. But it seems (and I may be totally wrong here) that there was not an arms race for body size. Maybe a little one, but the mammals did not grow enormous during this period. That was to occur later, starting in the Eocene.Why? Well, my hypothesis is this: Growing large has costs and benefits, but other adaptations do as well. The costs of growing large include slower reproductive rate and greater vulnerability in relation to the food supply, for instance. What if mammals that were being preyed on by Big Bird were able to adapt to this predation in a different way than getting larger? There are of course many ways to adapt to predators other than to outgrow them, and even when we do see large body size emerging we also see other things happening at the same time (like being fast, being cryptic, or being hard like a walnut).Specifically, I hypothesis that the benefits of large size after subtracting the costs of large size were less than the benefits of some other strategy, and that strategy is one that would only work for a mammal being eaten by a bird. Perhaps the slightly different thermodynamics of mammals and birds was exploited, different diurnal patterns of energetics, or locomotory patterns. Fill in the blank: Mammals, with the special mammal feature of X reduced predation by birds, who were limited by Y by using strategy Z, such that Z is NOT increase in body size.When Big Bird was replaced by mammalian predators, then we have mammal preying on mammal, and this discordance between X and Y (allowing for adaptation Z) did not apply. Large body size still has it’s benefits, and that becomes a major mode of adaptation, so we see the Eocene beginnings of a mammalian radiation involving body size increase and diversification of species. (This could also explain why rodents have not all grown to be larger than snakes and hawks.)ADDED LATER: There is an excellent discussion of this research on Panda’s Thumb.______________________________________________________________________________Sources:Alroy, John. nd. The Fossil Record of North American Mammals: Evidence for a Paleocene Evolutionary Radiation. http://www.nceas.ucsb.edu/~alroy/Paleocene.htmlBininda-Emonds, O.R.P., Cardillo, M., Jones, K.E., MacPhee, R.D.E., Beck, R.M.D., Grenyer, R., Price, S.A., Vos, R.A., Gittleman, J.L., and Purvis, A. 2007. The delayed rise of present-day mammals. Nature 446: 507-512.

Hearing … of the remains of one of the old giants, which a man told me he had seen on the banks of the Parana, I procured a canoe, and proceeded to the place. Two groups of immense bones projected in bold relief from the perpendicular cliff [but] I could only bring away small fragments of one of the great molar-teeth … sufficient to show that the remains belonged to a species of Mastodon. The men who took me in the canoe, said they had long known of them, and had often wondered how they had got there: the necessity of a theory being felt, they came to the conclusion, that … the mastodon formerly was a burrowing animal!

In remote St. Fe …

A tooth which I discovered … interested me much, for I at once perceived that it had belonged to a horse. Feeling much surprise at this, I carefully examined its geological position, and was compelled to come to the conclusion, that a horse, which cannot … be distinguished from the existing species, lived as a contemporary with the various great monsters that formerly inhabited South America. Mr. Owen and myself, at the College of Surgeons, compared this tooth with a fragment of another, probably belonging to the Toxodon, which was embedded at the distance only of a few yards in the same earthy mass. No sensible difference in their state of decay could be perceived; they were both tender, and partially stained red. … Certainly it is a marvellous event in the history of animals, that a native kind should have disappeared to be succeeded in after ages by the countless herds introduced with the Spanish colonist! But our surprise should be modified when it is already known, that the remains of the Mastodon angustidens (the tooth formerly alluded to as embedded near that of the horse, probably belonged to this species) have been found both in South America, and in the southern parts of Europe.

Weighty considerations of the distribution of extinct and extant fauna lead Darwin to the neighborhood of modern geological concepts.

Very few species of living quadrupeds, which are altogether terrestrial in their habits, are common to the two continents, and these few are chiefly confined to the extreme frozen regions of the north. The separation, therefore, of the Asiatic and American zoological provinces appears formerly to have been less perfect than at present. The remains of the elephant and of the ox have been found on the banks of the Anadir (long. 175° E.), on the extreme part of Siberia, nearest the American coast: and the former remains, according to Chamisso, are common in the peninsula of Kamtschatka. On the opposite shores, likewise, of the narrow strait which divides these two great continents, we know, from the discoveries of Kotzebue and Beechey, that the remains of both animals occur abundantly: and as Dr. Buckland has shown they are associated with the bones of the horse, the teeth of which animal in Europe, according to Cuvier, accompany by thousands the remains of the pachydermata of the later periods. With these facts, we may safely look at this quarter, as the line of communication (now interrupted by the steady progress of geological change) by which the elephant, the ox, and the horse, entered America, and peopled its wide extent.

Now, here we have Darwin on the verge of understanding the rise of the Panama Land bridge (or something like that) based on the biogeography. The above passage, the following passage, and other material is very frustrating. If Darwin was not such a geological gradualist he could have advanced geology to the 1950s with a single fell swoop of reasoning!!!!

The occurrence of the fossil horse and of Mastodon angustidens in South America, is a much more remarkable circumstance than that of the animals mentioned above in the northern half of the continent; for if we divide America, not by the Isthmus of Panama, but by the southern part of Mexico, .. where the great table-land presents an obstacle to the migration of species, … we shall then have two zoological provinces strongly contrasted with each other. Some few species alone have passed the barrier, and may be considered as wanderers, such as the puma, opossum, kinkajou, and peccari. The mammalogy of South America is characterized by possessing several species of the genera of llama, …, tapir, peccari, opossum, anteater, sloth, and armadillo. If North America had possessed species of these genera proper to it, the distinction of the two provinces could not have been drawn; but the presence of a few wanderers scarcely affects the case. North America, on the other hand, is characterized by its numerous rodents, and by four genera of solid horned ruminants, of which section the southern half does not possess a single species.

Just so you know, South and North America were separated, and had largely independent mammalian evolution (and migration), until very recently, about five million years ago, when the isthmus of Panama was raised.Darwin is seeing the very time-deep echo of this event, masked by subsequent migration of North American mammals in to South America, and clouded by the more pressing (to him) question of Old World and New World relationships.It is interesting that the monkey’s (appearing in both the old world and new world tropics) don’t freak him out. They freak me out.

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A case can be made for its consideration [of the Anthropocene] as a formal epoch in that, since the start of the Industrial Revolution, Earth has endured changes sufficient to leave a global stratigraphic signature distinct from that of the Holocene or of previous Pleistocene interglacial phases, encompassing novel biotic, sedimentary, and geochemical change. These changes, although likely only in their initial phases, are sufficiently distinct and robustly established for suggestions of a Holocene-Anthropocene boundary in the recent historical past to be geologically reasonable.

Why is this scientifically invalid? There are several reasons. The Anthropocene is minimally as scientifically valid as the Holocene, the bit of geological time that would be trimmed to make room for the Anthropocene. and the Holocene is not scientifically valid. The Holocene is a non-glacial period distinct from the previous Pleistocene because the Pleistocene is a glacial period. Or at least, that is more or less (I’m oversimplifying a bit) how things were conceived when these periods were defined. It turns out, however, that the Holocene is almost certainly just another interglacial during a longer epoch of periodically repeating and increasingly severe glacials.This means that we are not in the Holocene, but rather, in the Pleistocene. Therefore, the proposal to call the present (and going back a short period of time) something different would rest on he argument that the defining factors of the Anthropocene are more determinative of geological epochal identity than the defining factors of the Pleistocene. And they are not. Glacial cycles are big powerful things that change every aspect of the biota, carve up huge areas of the earth, deposit enormous loads of sediment globally that would not otherwise (in the absence of glacial action) be deposited, change sea levels dramatically, and so on. The geological and biotic markings of the present century and the last … all the mucking around that humans are doing … is not demonstrably greater than, or even nearly equivalent to, the great changes wrought by glaciation.Then, there is the scale problem. Geological periods are defined by changes that can not only be viewed from a great distance in time, but can’t be missed from so far away. It should be as reasonable to define a geological epoch as it is to note the existence of a mountain chain from many kilometers away. It might be that anthropogenic changes to the biota and the landscape are sufficiently blatant and long lasting to create a such a distinct distance, or they may not. The Holocene itself is invalid because it is too near-sighted (in time) of a concept, considering a mere several thousand years and calling it a distinct period. And we (well, they, I wan’t even born yet) got that totally wrong. How does a few centuries of observation translate into a valid geological periodization? It does not. It is possible that we can define a new period that begins about now (plus or minus in geological time). But those proposing the Anthropocene are several million years premature. They need to be more patient.Finally, while anthropogenic effects cannot be used to define a new geological period, they have already, in my view, met or exceeded the minimal requirements to be considered a geological “event.” In particular, an extinction event, and in addition, a major biogeographical event. Never before has there been such a massive transfer of species … in all the Kingdoms of life … across otherwise separated continents. This massive, multi directional invasion, as well as the widespread harvesting of the plant life of certain major biomes (such as forests), have caused a mass extinction. Some of the prior mass extinction events have been much more severe than the present one, but perhaps not all. There is evidence that the present mass extinction event is only getting started. But unlike geological periodizaiton, which requires the perspective of millions of years to really evaluate, the reality and validity of a mass extinction event can be observed and verified in much less time.Mass extinction by invasion and steady habitat loss, as opposed to mass extinction by massive volcanic eruption or extraterrestrial object impacts, will be very slow as mass extinction events go, but the relevant comparison here is between days or months on one hand to centuries on the other. We see that more vulnerable, or more targeted, biomes are well into the range of the highest levels of extinction rates. In Polynesia, about 90% of endemic bird species have gone extinct (varying greatly across the region) in the last 400 years. Birds are going extinct at an alarmingly high rate globally. I believe that there are entire biomes that have been wiped out long enough ago that the numerical contribution of these losses to the overall event are uncountable (this includes European temperate forests and seasonally dry African tropical forest).I don’t think it is reasonable to define a new era called the Anthropocene. But I do think it is entirely scientifically valid to define an event that could be called the Anthropogenic Extinction.I started out saying that the proposal of the Anthropocene is both scientifically invalid but also obnoxious. Well, it could be obnoxious simply because it is scientifically invalid. But there are other reasons. The main reason is that it is anthropocentric. “But wait,” you say, “It might not be a valid period, but the stuff the authors of that paper are talking about are human-caused, so why not call it ‘anthro-whatever whatever.'” But that, dear reader, would be yet another anthropocentric misconception.To the extent that the events of the modern era, including over harvesting major biomes and global warming, are cause by human activities, it also has to be recognized, from a strictly evolutionary and biological point of view (as opposed to a human-centric point of view) that this is not a human event, but a multi-species event. Viewed from the perspective of a sentient being from another planet that has absolutely no human-like preconceptions and no way to directly relate to the point of view of any Earthling species … say a sentient being evolved from silica dust particles that that exist as dust-sized individuals organized in eusocial metabeings that are several Jupiters in size and that do not perceive light … humans are certainly not the only thing, or even the most common thing, in this picture. The authors of this paper argue, for instance, that human population size has skyrocketed in the last several thousands of years. But how? Why? Our little/big silica-beings would view this very differently. They would see the emergence, some 10,000 years ago, of fewer than a half dozen different forms of grass as dominant species, spreading across the planet at the expense of many other life forms. The spread of these grasses (rice, corn, wheat, etc.) is associated with, possibly facilitated by (but wait, these silica beings might not be adaptationists, so we should not put ideas in their dusty little brains) four and two legged, mobile warm-blooded things that tend the grasses, and in return, are fed by the grasses.This may sound funny, but I’m not joking. Not even a little. Modern human societies do not exist outside of biology, and some of the most important aspects of our energetics as a species derive from very tight knit co evolutionary relationships with a variety of grasses, microbes, and a few other plants, and some animals. All this talk about recent, and possibly accelerated, human evolution all about this co-evolutionary relationship.But I suppose I would not expect geologists to be keyed into that way of thinking.But, obviously, while we may agree that there is an extinction event going on now, the same reasoning that tells us to avoid the anthropocentric terminology should caution us to not call this event the “anthropogenic extinction event.” So we need another name.Most of the plants involved in this extinction event are either grasses or other Monocots (such as plantains). So this could be the Monocot Event. But since the rise of grasslands per se is actually a Miocene event, perhaps this could be the Monocot-Anthropoid Event. Clearly, more work is needed on coming up with a suitable term. Suggestions are welcome!

Zalasiewicz, J., Williams, M., Smith, A., Barry, T.L., Coe, A.L., Bown, P.R., Brenchley, P., Cantrill, D., Gale, A., Gibbard, P., Gregory, F.J., Hounslow, M.W., Kerr, A.C., Pearson, P., Knox, R., Powell, J., Waters, C., Marshall, J., Oates, M., Rawson, P., Stone, P. (2008). Are we now living in the Anthropocene. GSA Today, 18(2), 4. DOI: 10.1130/GSAT01802A.1See also:Pimm, S. (2006). From the Cover: Human impacts on the rates of recent, present, and future bird extinctions. Proceedings of the National Academy of Sciences, 103(29), 10941-10946. DOI: 10.1073/pnas.0604181103This paper is also being discussed here:Do we need a new geological epoch?Just a blip of the geologic radar