A few days ago I posited that humans are affecting ecosystems globally on a scale that rivals extinction events in the distant past.
Subsequent to that I unsealed an old copy of New Scientist that I'd been saving for a rainy day. The 12 November 2011 issue mentioned a disease that is "decimating frogs around the planet."
The cause is a fungus lethal to frogs called Batrachochytrium dentdrobatidis. Sixteen of the 20 samples collected globally were a genetically identical strain (called BdGPL), ie they were of the same origin. And they are "extremely virulent."
That strain was clearly a hybrid, formed in the past 100 years, most likely due to the "20th-century pet and food trade", which enabled the strains to meet.
Madagascar and south-east Asia are the regions most at risk right now, being "hotspots of amphibian diversity" and free of this fungus right now.
Globalisation is an inevitable process in the development of human society. Such collateral damage need not be inevitable, but it takes political will which in turn, at the very least, would entail using one's vote wisely.
Showing posts with label extinction. Show all posts
Showing posts with label extinction. Show all posts
Friday, January 13, 2012
Wednesday, August 19, 2009
Earth as Gaia - or Medusa?
The Gaia hypothesis keeps cropping up in fiction and popular science, doubtless to make a comeback in the context of climate change.
There are various articulations of Gaia, which proposes the Earth constitutes a complex regenerative system that always returns the environment to a life-sustaining equilibrium. One version maintains that Earth and its atmosphere and environments supports life and constantly brings it back into balance; another draws into the equation the Earth's biomass (the totality of life on the planet), to say that the full system constitutes a self-balancing (homeostatic) system.
Gaia was proposed in the 1960s by James Lovelock, with Dian Hitchcock. Working for NASA, they were charged with researching the atmosphere on Mars, for signs of life. Finding the Martian atmosphere to be in a deadly state of equilibrium, they contrasted this with Earth's atmosphere, in a relative state of flux (between oxygen and carbon dioxide in particular). Their Gaia proposal grew out of that.
Yet Lovelock's background was in chemistry and medical research rather than environmental science, and he was employed by NASA to develop equipment to analyse Mars' atmosphere. Hitchcock's background was philosophy, and she was to test his logic.
After the initial formulation, Lovelock's main collaborator has been Lynn Margulis, a biologist who couched the theory in more careful terms: of trends rather definitive equilibrium. (Margulis' reputation, however, is built on much more significant work, on the origin of organelles in eukaryotic cells: that is, that the organs of cells with nuclei emerged through symbiosis of separate entities). Her contribution to Gaia allows that no species has guaranteed passage through the bottlenecks of time.
But a major criticism of Gaia is its teleological nature: that is, that it implies some intention or purpose behind the planet's formation.
Recently, Peter Ward, an American biology professor, wrote a book that proposes the opposite: the Medea hypothesis, which says that life is constantly trying to kill itself and its own environment (The Medea Hypothesis: Is life on Earth ultimately self-destructive?). His overview in New Scientist is worth reading: it contains much background information about Earth's environmental changes.
My concern is that none of this is saying anything in particular. There is no guarantee that life in any form will survive a major disaster such as global nuclear war or a sufficiently large meteor impact. In fact, current projections are that the Earth will become totally lifeless within 500 to 1,000 million years, purely through the expansion of the sun - and that compares to the 3.8 billion years it has taken to develop to this point.
Behind both Lovelock's and Ward's articulation is the fact that Earth's environment and atmosphere has changed quite drastically over its history, causing mass extinction - several times, and life itself is the frequent culprit, due to cumulative changes in chemical composition of atmosphere and oceans. One such event was the evolution of photosynthesis 2.3 billion years ago. This entailed the absorption of carbon dioxide, and the emission of oxygen: a double whammy. On the one hand, oxygen was pure poison to most life at the time. On the other hand, over the course of 200 million years, the sucking out of carbon dioxide froze the oceans: this (first) snowball earth lasted 100 million years.
(although we credit the most well-known extinction event with an external cause - the meteor 65 million years ago that wiped out non-avian dinosaurs - most were due to events of local origin, pointing to imbalances that build up over time, usually from biological causes.)
There is no guarantee that the planet would return to a life-sustaining balance. Nor is there viable evidence that life deliberately tries to kill itself, or will ever succeed. Yet what it does say is that the variety of life is such that it has survived a number of cataclysmic changes. Pretty much all environmental niches that we can identify have corresponding life forms that could survive it (albeit most of the extreme cases are microbial).
On an immediate level, if we make the planet inhospitable for ourselves, other life forms will surely survive. For what it's worth. But human intervention has been nothing like any previous climate change bar the meteor: all others have been far more gradual. In terms of our lifetime, it's slow, but on a less anthropocentric scale, we are inducing a real shock to the planet. Yes, climate change is natural, but not in the framework in which we live. And the ride will be somewhere between bumpy and catastrophic, depending on our capacity to move forward together on the issue quickly enough.
There are various articulations of Gaia, which proposes the Earth constitutes a complex regenerative system that always returns the environment to a life-sustaining equilibrium. One version maintains that Earth and its atmosphere and environments supports life and constantly brings it back into balance; another draws into the equation the Earth's biomass (the totality of life on the planet), to say that the full system constitutes a self-balancing (homeostatic) system.
Gaia was proposed in the 1960s by James Lovelock, with Dian Hitchcock. Working for NASA, they were charged with researching the atmosphere on Mars, for signs of life. Finding the Martian atmosphere to be in a deadly state of equilibrium, they contrasted this with Earth's atmosphere, in a relative state of flux (between oxygen and carbon dioxide in particular). Their Gaia proposal grew out of that.
Yet Lovelock's background was in chemistry and medical research rather than environmental science, and he was employed by NASA to develop equipment to analyse Mars' atmosphere. Hitchcock's background was philosophy, and she was to test his logic.
After the initial formulation, Lovelock's main collaborator has been Lynn Margulis, a biologist who couched the theory in more careful terms: of trends rather definitive equilibrium. (Margulis' reputation, however, is built on much more significant work, on the origin of organelles in eukaryotic cells: that is, that the organs of cells with nuclei emerged through symbiosis of separate entities). Her contribution to Gaia allows that no species has guaranteed passage through the bottlenecks of time.
But a major criticism of Gaia is its teleological nature: that is, that it implies some intention or purpose behind the planet's formation.
Recently, Peter Ward, an American biology professor, wrote a book that proposes the opposite: the Medea hypothesis, which says that life is constantly trying to kill itself and its own environment (The Medea Hypothesis: Is life on Earth ultimately self-destructive?). His overview in New Scientist is worth reading: it contains much background information about Earth's environmental changes.
My concern is that none of this is saying anything in particular. There is no guarantee that life in any form will survive a major disaster such as global nuclear war or a sufficiently large meteor impact. In fact, current projections are that the Earth will become totally lifeless within 500 to 1,000 million years, purely through the expansion of the sun - and that compares to the 3.8 billion years it has taken to develop to this point.
Behind both Lovelock's and Ward's articulation is the fact that Earth's environment and atmosphere has changed quite drastically over its history, causing mass extinction - several times, and life itself is the frequent culprit, due to cumulative changes in chemical composition of atmosphere and oceans. One such event was the evolution of photosynthesis 2.3 billion years ago. This entailed the absorption of carbon dioxide, and the emission of oxygen: a double whammy. On the one hand, oxygen was pure poison to most life at the time. On the other hand, over the course of 200 million years, the sucking out of carbon dioxide froze the oceans: this (first) snowball earth lasted 100 million years.
(although we credit the most well-known extinction event with an external cause - the meteor 65 million years ago that wiped out non-avian dinosaurs - most were due to events of local origin, pointing to imbalances that build up over time, usually from biological causes.)
There is no guarantee that the planet would return to a life-sustaining balance. Nor is there viable evidence that life deliberately tries to kill itself, or will ever succeed. Yet what it does say is that the variety of life is such that it has survived a number of cataclysmic changes. Pretty much all environmental niches that we can identify have corresponding life forms that could survive it (albeit most of the extreme cases are microbial).
On an immediate level, if we make the planet inhospitable for ourselves, other life forms will surely survive. For what it's worth. But human intervention has been nothing like any previous climate change bar the meteor: all others have been far more gradual. In terms of our lifetime, it's slow, but on a less anthropocentric scale, we are inducing a real shock to the planet. Yes, climate change is natural, but not in the framework in which we live. And the ride will be somewhere between bumpy and catastrophic, depending on our capacity to move forward together on the issue quickly enough.
Tuesday, August 18, 2009
Peter Garrett: politics is hard on principles
Politics is hard. Rough and hard. Peter Garrett knows this better than most.
He's onto his third or fourth career now. From international success in the band Midnight Oil, he has had various roles in environmental activism, from president of the Australian Conservation Foundation to the board of Greenpeace international.
So what do you do if it's hard to make enough impact from the outside? Get on the inside, and know what real frustration is like. That must be life for Garrett as Australia's Environment Minister.
Last Saturday, an article in the Herald's Good Weekend (colour supplement) attempted to get to the core of Garrett's move. The results are predictable and disheartening: Garrett has learnt what it's like to be a politician.
His long-time associates do not doubt his sincerity and commitment to environment. However, the article stresses that in Garrett's position he is obliged to be a "team player". He's not rambunctious: he doesn't denigrate his colleagues either inside or out of cabinet, and he doesn't break ranks. All his politicking now takes place within cabinet, and he toes the line most strictly with whatever outcomes he has to swallow.
Case in point: in one of the "strongest speeches of his political career", Garrett has warned an international conference that some Australian animal species would have to face extinction. With 1750 threatened species, the government was moving from project-based ecology to preserving ecosystems - which would inevitably mean the death knell for some species.
That is understandable - quite rational, even, if cold-blooded. In fact, I cannot see the world changing course quickly enough to preserve all remaining species, let alone habitats. Human rapacity for land makes it inevitable that any ecosystem that is not explicitly preserved will be strongly threatened. Islands of wilderness are the only viable outcome of our present course.
But imagine being Peter Garrett, and having to announce the impending extinction of a random handful of species. And to keep that stony silence in the face of other environmental injustices that cabinet solidarity had demanded. At what point is one's voice sufficient on its own to sway outcomes? And by that point, are you then accustomed to compromising away your favoured outcomes for other factors?
My kids recognise Garrett more than other politicians - simply because he's our local MP, and he's been to their school. I'd hate them to come to understand him on the basis of what he can't achieve, rather than what he can. It's not his ideals that corrode - it's the political system that's corrosive. I still have hope he can sufficiently influence outcomes.
Update 06-Sep-09: A letter in today's Good Weekend in response to the above article vociferously sums up the attitudes of many:
It is worth pointing out that that writer fully misunderstand Garrett's situation. Despite being environment minister, he is bound by cabinet decisions - and so effectively has no say in many of his "decisions". The only options here available to him are to resign from cabinet - and so be able to speak out without any real effect - or to attempt to influence outcomes from within. I cannot comment on the actual machinations, but this process shows how politics can apparently corrupt (and actually corrupt the reputation of) even those with integrity.
He's onto his third or fourth career now. From international success in the band Midnight Oil, he has had various roles in environmental activism, from president of the Australian Conservation Foundation to the board of Greenpeace international.
So what do you do if it's hard to make enough impact from the outside? Get on the inside, and know what real frustration is like. That must be life for Garrett as Australia's Environment Minister.
Last Saturday, an article in the Herald's Good Weekend (colour supplement) attempted to get to the core of Garrett's move. The results are predictable and disheartening: Garrett has learnt what it's like to be a politician.
His long-time associates do not doubt his sincerity and commitment to environment. However, the article stresses that in Garrett's position he is obliged to be a "team player". He's not rambunctious: he doesn't denigrate his colleagues either inside or out of cabinet, and he doesn't break ranks. All his politicking now takes place within cabinet, and he toes the line most strictly with whatever outcomes he has to swallow.
Case in point: in one of the "strongest speeches of his political career", Garrett has warned an international conference that some Australian animal species would have to face extinction. With 1750 threatened species, the government was moving from project-based ecology to preserving ecosystems - which would inevitably mean the death knell for some species.
That is understandable - quite rational, even, if cold-blooded. In fact, I cannot see the world changing course quickly enough to preserve all remaining species, let alone habitats. Human rapacity for land makes it inevitable that any ecosystem that is not explicitly preserved will be strongly threatened. Islands of wilderness are the only viable outcome of our present course.
But imagine being Peter Garrett, and having to announce the impending extinction of a random handful of species. And to keep that stony silence in the face of other environmental injustices that cabinet solidarity had demanded. At what point is one's voice sufficient on its own to sway outcomes? And by that point, are you then accustomed to compromising away your favoured outcomes for other factors?
My kids recognise Garrett more than other politicians - simply because he's our local MP, and he's been to their school. I'd hate them to come to understand him on the basis of what he can't achieve, rather than what he can. It's not his ideals that corrode - it's the political system that's corrosive. I still have hope he can sufficiently influence outcomes.
Update 06-Sep-09: A letter in today's Good Weekend in response to the above article vociferously sums up the attitudes of many:
"Peter Garrett's plea that he was just following the party's orders is possibly the most famous dud defence known. Far from being the Faust or King Lear suggested, he appears to be the most common of political animals: the chameleon opportunist."
It is worth pointing out that that writer fully misunderstand Garrett's situation. Despite being environment minister, he is bound by cabinet decisions - and so effectively has no say in many of his "decisions". The only options here available to him are to resign from cabinet - and so be able to speak out without any real effect - or to attempt to influence outcomes from within. I cannot comment on the actual machinations, but this process shows how politics can apparently corrupt (and actually corrupt the reputation of) even those with integrity.
Tuesday, January 20, 2009
Early extinctions in New Zealand
New Zealand had a special environment. From the time it split from Antarctica about 80 million years ago, it was one of the larger, more isolated land masses in the world*. The fact that it was mostly free of terrestrian mammalian predators** eems to have, of itself, fostered a unique panoply of ground-based wildlife.
A recent article in American Scientist (The Rat's Tale) paints a picture of ecological destruction that followed the first wave of predatory mammals - although the second wave (Europeans) would ultimately have been more destructive.
The article details the laborious scientific process - and debate - in establishing the date for that first wave, which last year was settled with a period range of 1290 to 1380AD for the arrival of the Maori and the Polynesian rat, kiore or Rattus exulans.
The rats ate "plants, fruits, seeds, insects, lizards, snails, eggs, and the nestlings of ground-breeding birds".
Maoris were apparently responsible for the extinction of the largely predator-free [ostrich-like] moa, and the reduction in forestation of New Zealand from about 85-90% to 25-27% (according to the article). Good evidence suggests this latter was due to significant burn-offs - for various reasons, including living space, ease of travel, and fostering food sources, specifically the bracken root, a starchy staple.
From that first wave, human and rat between them precipitated a 50% decline in bird species and the extinction of bat, frog, and numerous lizard species.
The oldest verified archeological site in NZ is Wairau Bar in the South Island, dating to 1285 to 1300. Amongst many artifacts are the bones of 8000-odd moas and 2000 moa eggs - suggestive of the ease with which they were killed.
The Polynesian rats apparently took less than 80 years to spread throughout the North and South Islands - about the same time as it took the European rat, Rattus norvegicus, once introduced.
This is not a tale of Maori destruction - rather, it's the familiar one of human destruction: "The first duty of colonisers is to survive. That requires rapid population growth sustained by consuming the richest resources" (Atholl Anderson, Australian National University).
The main reference for the article is: Wilmshurst, J. M., A. J. Anderson, T. F. G. Higham and T. H. Worthy. 2008. Dating the late prehistoric dispersal of Polynesians to New Zealand using the commensal Pacific rat. Proceedings of the National Academy of Sciences 105:7676–7680.
*Albeit some theories (discussed earlier, here) posit complete submergence of the land mass for a period of time. I'm not convinced of this, particularly given the continued existence of the flightless ratite moa, discussed here.
**The recently discovered 'waddling mouse'/'sb mammal' -see here and here - notwithstanding. There doesn't seem to be any evidence that it impacted the significant and burgeoning terrestrial habiting bird population.
A recent article in American Scientist (The Rat's Tale) paints a picture of ecological destruction that followed the first wave of predatory mammals - although the second wave (Europeans) would ultimately have been more destructive.
The article details the laborious scientific process - and debate - in establishing the date for that first wave, which last year was settled with a period range of 1290 to 1380AD for the arrival of the Maori and the Polynesian rat, kiore or Rattus exulans.
The rats ate "plants, fruits, seeds, insects, lizards, snails, eggs, and the nestlings of ground-breeding birds".
Maoris were apparently responsible for the extinction of the largely predator-free [ostrich-like] moa, and the reduction in forestation of New Zealand from about 85-90% to 25-27% (according to the article). Good evidence suggests this latter was due to significant burn-offs - for various reasons, including living space, ease of travel, and fostering food sources, specifically the bracken root, a starchy staple.
From that first wave, human and rat between them precipitated a 50% decline in bird species and the extinction of bat, frog, and numerous lizard species.
The oldest verified archeological site in NZ is Wairau Bar in the South Island, dating to 1285 to 1300. Amongst many artifacts are the bones of 8000-odd moas and 2000 moa eggs - suggestive of the ease with which they were killed.
The Polynesian rats apparently took less than 80 years to spread throughout the North and South Islands - about the same time as it took the European rat, Rattus norvegicus, once introduced.
This is not a tale of Maori destruction - rather, it's the familiar one of human destruction: "The first duty of colonisers is to survive. That requires rapid population growth sustained by consuming the richest resources" (Atholl Anderson, Australian National University).
The main reference for the article is: Wilmshurst, J. M., A. J. Anderson, T. F. G. Higham and T. H. Worthy. 2008. Dating the late prehistoric dispersal of Polynesians to New Zealand using the commensal Pacific rat. Proceedings of the National Academy of Sciences 105:7676–7680.
*Albeit some theories (discussed earlier, here) posit complete submergence of the land mass for a period of time. I'm not convinced of this, particularly given the continued existence of the flightless ratite moa, discussed here.
**The recently discovered 'waddling mouse'/'sb mammal' -see here and here - notwithstanding. There doesn't seem to be any evidence that it impacted the significant and burgeoning terrestrial habiting bird population.
Tuesday, November 04, 2008
Reversing extinction via DNA
A recent study published in PNAS reported that mice had been cloned from frozen DNA (journal abstract here; press report here). This had been thought impossible: that cellular ice crystals would destroy the DNA.
This does not constitute a universal panacea for recovering extinct species, but it has implications for DNA recovered from unfossilised remains recovered from permanently frozen locations, especially Antarctica, Canada, and Russia.
There would remain a number of scientific hurdles, including incubation, but the puzzle pieces are starting to fall into place. Yet there are a couple of ominous tones in this news.
First, we may be running out of time. Permafrost regions have begun thawing already. (And this is a double-edged sword: on the one hand, it will make scientific discovery easier for a period of time, but on the other hand, it will likely hasten the warming process as masses of organic matter will also thaw, rot, and release more atmospheric carbon to hasten the warming process.)
Second, it would be tragic if scientific progress bred complacency towards looming extinctions. Prevention - preserving whole ecosystems - would be so much easier and less fraught than attempting to recreate the systems. But our form of democracy is traditionally geared to the dissonance of desiring an outcome but not making the hard decisions. A recipe for complacency.
This does not constitute a universal panacea for recovering extinct species, but it has implications for DNA recovered from unfossilised remains recovered from permanently frozen locations, especially Antarctica, Canada, and Russia.
There would remain a number of scientific hurdles, including incubation, but the puzzle pieces are starting to fall into place. Yet there are a couple of ominous tones in this news.
First, we may be running out of time. Permafrost regions have begun thawing already. (And this is a double-edged sword: on the one hand, it will make scientific discovery easier for a period of time, but on the other hand, it will likely hasten the warming process as masses of organic matter will also thaw, rot, and release more atmospheric carbon to hasten the warming process.)
Second, it would be tragic if scientific progress bred complacency towards looming extinctions. Prevention - preserving whole ecosystems - would be so much easier and less fraught than attempting to recreate the systems. But our form of democracy is traditionally geared to the dissonance of desiring an outcome but not making the hard decisions. A recipe for complacency.
Friday, April 04, 2008
Multituberculates - early successful mammals
Multituberculates are an early order of mammals that was very successful - as mammals go - during the Mesozoic era (in the shadow of the dinosaurs), but became extinct in the Paleozoic, at a time when mammalian species were radiating to fill the gaps in environmental niches left vacant when the dinosaur-killing meteor hit at 65 million years ago.
Their molars each have rows of tubercles - cusps - hence the origin of the name. Teeth are frequently an important determinant of how and what any given species eats, and thus their longer-term survivability. Much analysis has been given over to this aspect of mammalian evolution. (Yet toothed names are sometimes given simply because teeth are all that are found of a given species).
Multituberculates (covering a variety of species and environmental niches) survived to the end of the Eocene (according to Kielan-Jarowowska), perhaps up to 34 milion years ago. Their niches were roughly those filled today by rodents, who are perhaps the most successful - and definitely the most species-numerous - modern mammals.
That might suggest that the Rodentia order actually crowded out the Multituberculata order, and was more fit in evolutionary terms. In fact, Kielan-Jarowowska reports a 1966 review (Van Valen and Sloan) that concluded their demise was due, successively, to condylarths (early placentals, now extinct), primates, then rodents.
As an older lineage, they were close to the monotremes (which are the most basal surviving lineage of mammals), but were slightly more derived ("modern"). Are Multituberculates egg-laying (oviparous) or live birth (viviparous)? Kielan-Jarowowska (from an older study) refers to them as viviparous with an "extremely small neonate". It lists this as a competitive inferiority, along with an abducted (or sprawled) limb angle. This latter would have made prolonged running more difficult than for its competitors.
Note that the New Zealand fossil, the SB mammal or "waddling mouse" had a 'somewhat abducted' posture. Yet that creature survived until 19 mya - isolated on an island chain that had no other mammalian competitors.
References
Kielan-Jaworowska Z, Cifelli R L, and Luo Z-X (2004): Mammals from the age of dinosaurs : origins, evolution, and structure. New York, Columbia University Press.
Worthy T, Tennyson A, Archer M et al (2006): Miocene mammal reveals a Mesozoic ghost lineage on insular New Zealand, southwest Pacific in PNAS vol 103 no 51.
Their molars each have rows of tubercles - cusps - hence the origin of the name. Teeth are frequently an important determinant of how and what any given species eats, and thus their longer-term survivability. Much analysis has been given over to this aspect of mammalian evolution. (Yet toothed names are sometimes given simply because teeth are all that are found of a given species).Multituberculates (covering a variety of species and environmental niches) survived to the end of the Eocene (according to Kielan-Jarowowska), perhaps up to 34 milion years ago. Their niches were roughly those filled today by rodents, who are perhaps the most successful - and definitely the most species-numerous - modern mammals.
That might suggest that the Rodentia order actually crowded out the Multituberculata order, and was more fit in evolutionary terms. In fact, Kielan-Jarowowska reports a 1966 review (Van Valen and Sloan) that concluded their demise was due, successively, to condylarths (early placentals, now extinct), primates, then rodents.
As an older lineage, they were close to the monotremes (which are the most basal surviving lineage of mammals), but were slightly more derived ("modern"). Are Multituberculates egg-laying (oviparous) or live birth (viviparous)? Kielan-Jarowowska (from an older study) refers to them as viviparous with an "extremely small neonate". It lists this as a competitive inferiority, along with an abducted (or sprawled) limb angle. This latter would have made prolonged running more difficult than for its competitors.
Note that the New Zealand fossil, the SB mammal or "waddling mouse" had a 'somewhat abducted' posture. Yet that creature survived until 19 mya - isolated on an island chain that had no other mammalian competitors.
References
Kielan-Jaworowska Z, Cifelli R L, and Luo Z-X (2004): Mammals from the age of dinosaurs : origins, evolution, and structure. New York, Columbia University Press.
Worthy T, Tennyson A, Archer M et al (2006): Miocene mammal reveals a Mesozoic ghost lineage on insular New Zealand, southwest Pacific in PNAS vol 103 no 51.
Wednesday, March 26, 2008
Surviving early mammal lineages
Researching mammals seems to be a particularly popular occupation. Most of that research relates to extant species and their evolutionary history. So it's mostly eutherians (placentals), metatherians (marsupials), and monotremes. It's hard to find much detail about extinct lineages such as New Zealand's mysterious SB mammal fossil.
I'm currently browsing with curiosity a hefty tome called Mammals From The Age Of Dinosaurs. It's about as comprehensive as one can get, and is destined to be the reference book for early mammals. Written by three of the leading experts (and most widely quoted) in the field of mammal paleontology: Zofia Kielan-Jaworowska, Richard Cifelli, and Zhe-Xi Luo. It's dated 2004; to get anything more current, you'd have to be constantly scouring the journals (which is not a bad thing, as these are times of rapid change in knowledge and understanding in this field.)
The book contains many seminal reference points, including a full survey of distribution by location and period (to just past the Mesozoic boundary), and a fully detailed survey of each major lineage of the Mesozoic.The diagrams I find particularly useful are - two (alternative) cladograms of all major mammal taxa up to eutheria (pp521 & 522); - an overview of the changed view of the evolution of the major lineages (p5); - most importantly, a diagram of the temporal distribution (through the Mesozoic) and relationships of the main lineages (p3); - a clade table (listing) of all lineages down to family level (pp 14-15).
Of major interest is the comment (p13) that only four major lineages have a significant presence after the KT boundary (end of the Mesozoic, and the dinosaurs).
Four? To the extant lineages mentioned above, the book adds multituberculates (p15). In a footnote, they elaborate the list with the multituberculate suborder Cimolodonta (lasting to the Eocene), and one dryolestoid from the Paleocene of South America. However, that note is not complete, as there are scatterings of other multituberculate taxa that are mentioned as passing through to the Paleocene. These include Ptilodontidae, and Gondwanatheria. The latter are admitted as uncertain placement (Incertae sedis) - somewhere between monotremes and (metatherians plus eutherians) - but discussed with multituberculates.
Ptilodus, a Ptilodontid
[Update 27-Mar: Dryolestes is Trechnotherian - a clade (a superset of both eutherians and metatherians) which covers all mammals that give birth to live young. I'll now exclude these from the discussion, since I'm focusing on egg-laying mammals, which it looks like the SB mammal is.]
So far, then, we have three non-therian - egg-laying - groupings surviving into the Paleocene (which ended 55 million years ago): Monotremes, multituberculates and, arguably, Gondwanatherians. To this, we now add the even more enigmatic SB mammal, surviving all the way to the Miocene, 19mya.
So what does this say about the SB mammal?
On the one hand, Worthy et al place this mammal in an unresolved trichotomy with multituberculates (which it says are more basal) and the more derived clades that include (Tinodon + the viviparous therians). In effect, pretty close to multituberculates, but no match. On the basis of the femur fragment (specifically, the greater trochanter), it's more primitive than the latter - but that's predicated on the femur and jaw fragments matching. Parsimony suggested so, but it's not a guarantee.
On the other hand, the paucity - and piecemeal nature - of the book's references to non-therian KT survivors is a good reminder that we are dealing with a matching scarcity of pertinent fossils. What has been reported so far should not be taken as a complete and reliable guide to what did survive. New Zealand has, after all, sheltered such oddities as the lizard-like Tuatara and the Leopelmatid frog, no less surprising in their uniqueness.
Next up: more on multituberculates.
References
Kielan-Jaworowska Z, Cifelli R L, and Luo Z-X (2004): Mammals from the age of dinosaurs : origins, evolution, and structure. New York, Columbia University Press.
Worthy T, Tennyson A, Archer M et al (2006): Miocene mammal reveals a Mesozoic ghost lineage on insular New Zealand, southwest Pacific in PNAS vol 103 no 51.
I'm currently browsing with curiosity a hefty tome called Mammals From The Age Of Dinosaurs. It's about as comprehensive as one can get, and is destined to be the reference book for early mammals. Written by three of the leading experts (and most widely quoted) in the field of mammal paleontology: Zofia Kielan-Jaworowska, Richard Cifelli, and Zhe-Xi Luo. It's dated 2004; to get anything more current, you'd have to be constantly scouring the journals (which is not a bad thing, as these are times of rapid change in knowledge and understanding in this field.)
The book contains many seminal reference points, including a full survey of distribution by location and period (to just past the Mesozoic boundary), and a fully detailed survey of each major lineage of the Mesozoic.The diagrams I find particularly useful are - two (alternative) cladograms of all major mammal taxa up to eutheria (pp521 & 522); - an overview of the changed view of the evolution of the major lineages (p5); - most importantly, a diagram of the temporal distribution (through the Mesozoic) and relationships of the main lineages (p3); - a clade table (listing) of all lineages down to family level (pp 14-15).
Of major interest is the comment (p13) that only four major lineages have a significant presence after the KT boundary (end of the Mesozoic, and the dinosaurs).
Four? To the extant lineages mentioned above, the book adds multituberculates (p15). In a footnote, they elaborate the list with the multituberculate suborder Cimolodonta (lasting to the Eocene), and one dryolestoid from the Paleocene of South America. However, that note is not complete, as there are scatterings of other multituberculate taxa that are mentioned as passing through to the Paleocene. These include Ptilodontidae, and Gondwanatheria. The latter are admitted as uncertain placement (Incertae sedis) - somewhere between monotremes and (metatherians plus eutherians) - but discussed with multituberculates.
Ptilodus, a Ptilodontid[Update 27-Mar: Dryolestes is Trechnotherian - a clade (a superset of both eutherians and metatherians) which covers all mammals that give birth to live young. I'll now exclude these from the discussion, since I'm focusing on egg-laying mammals, which it looks like the SB mammal is.]
So far, then, we have three non-therian - egg-laying - groupings surviving into the Paleocene (which ended 55 million years ago): Monotremes, multituberculates and, arguably, Gondwanatherians. To this, we now add the even more enigmatic SB mammal, surviving all the way to the Miocene, 19mya.
So what does this say about the SB mammal?
On the one hand, Worthy et al place this mammal in an unresolved trichotomy with multituberculates (which it says are more basal) and the more derived clades that include (Tinodon + the viviparous therians). In effect, pretty close to multituberculates, but no match. On the basis of the femur fragment (specifically, the greater trochanter), it's more primitive than the latter - but that's predicated on the femur and jaw fragments matching. Parsimony suggested so, but it's not a guarantee.
On the other hand, the paucity - and piecemeal nature - of the book's references to non-therian KT survivors is a good reminder that we are dealing with a matching scarcity of pertinent fossils. What has been reported so far should not be taken as a complete and reliable guide to what did survive. New Zealand has, after all, sheltered such oddities as the lizard-like Tuatara and the Leopelmatid frog, no less surprising in their uniqueness.
Next up: more on multituberculates.
References
Kielan-Jaworowska Z, Cifelli R L, and Luo Z-X (2004): Mammals from the age of dinosaurs : origins, evolution, and structure. New York, Columbia University Press.
Worthy T, Tennyson A, Archer M et al (2006): Miocene mammal reveals a Mesozoic ghost lineage on insular New Zealand, southwest Pacific in PNAS vol 103 no 51.
Wednesday, February 27, 2008
Garnaut on emission changes: too late?
In commenting on the Garnaut report, the Herald's Ross Gittens points to the obvious elephants in the room: the economic growth of India and China.
Yes, we knew this. But he also provides an breakdown of carbon emissions increase.
Garnaut notes that global carbon emissions grew at an average rate of 1.1% per year through the 1990s. This would have been what was taken into the 1997 Kyoto talks.
However, from 2000 to 2006, the rate of increase surged to 3.1% per year.
This change has been attributed to the following:
Yes, we knew this. But he also provides an breakdown of carbon emissions increase.
Garnaut notes that global carbon emissions grew at an average rate of 1.1% per year through the 1990s. This would have been what was taken into the 1997 Kyoto talks.
However, from 2000 to 2006, the rate of increase surged to 3.1% per year.
This change has been attributed to the following:
- Global economic growth was 5% per year rather than the anticipated 3.3%
- Growth became more energy intensive. In the 1990s, the "energy intensity" of global gross domestic product fell (improved) by 1.4% per year; however this decade, the energy intensity has been falling by only 0.2%
- Energy use became more emission-intensive. Through the 1990s, cleaner fuels were used and the emission-intensity of energy use dropped 0.2% per year; however this emission-intensity increased by 0.4% per year this decade.
And all of this is said to be due to India and China coming on-stream in the economic world.
It remains difficult to begrudge those countries their due, although it makes the job that much harder.
Simulations run for Garnauts team require global emissions to peak by 2010 if atmospheric carbon is to stabilise at 450ppm.
Unlikely? It needs leadership from the developed world: to cut emissions by example, and to forge partnerships with those emerging nations to tip the balance in the right direction.
Two years is too short. Ten years might have done it. And that's what we lost with George Bush being declared winner in the 2000 presidential election. And officially, that's 537 Florida votes.
You couldn't write fiction like this.
Mass extinctions in earth's past, when due to climate change, have taken much longer than we're taking.
Sunday, February 24, 2008
Mass Extinctions explained: prokaryotes vs eukaryotes
An article in the New Scientist points to an important way to trace evolution through the sedimentary rock record.
In the development of life into multicellular organisms, there is some difference of opinion on the most significant step: whether it's from simple single-cellular organisms (prokaryotes) to complex ones with nuclei (eukaryotes), or the evolution of single-cellular life to multicellular. Most seem to favour the former.
Whereas stromatolites give a record of when the earliest lifeforms first emerged 3.5 billion years ago (according to Stephen Jay Gould this was just about as early as it could) there has been no way to trace back first emergence of eukaryotes - until now.
Peter Ward reports on chemical biomarkers in rock. Certain biological molecules break down under heating, cooling and pressure into highly stable organic compounds that could not be made by any known inorganic process. That last phrase is the kicker, which indicates that any such occurrence of the relevant compound would be an indicator of life. Moreover, some of the compounds are unique to particular groups of organisms. For example, C28 to c32 polyenoic fatty acids have been found to be unique biomarkers of sponges.
In the late 1990s, two Australians found steranes - biomarkers for eukaryotes - in Australian rock dating back to 2.7 billion years (but no older). This gives a good indication of the first emergence of lifeforms with cell nuclei.
By 800 mya, the biomarkers indicated multicellularity.
By 542 mya, the biomarkers indicated animal life - but we know this already as the Cambrian explosion.
In 2005, a Japanese team investigating the K-T extinction event (65 mya) they found, as expected, biomarker indicating a deluge of dead plant material. One study then found a decreased abundance of land plants for the next 7000 years.
Then to the Permian mass extinction event, the biggest of the lot. In 2005 a biomarker called isorenieratene was found at this point. These indicate green and purple sulpher bacteria, which cannot tolerate oxygen in water, in turn suggesting the oceans were [largely] devoid of oxygen and "saturated with hydrogen sulphide". A poisonous balance. A suggestion since (by Lee Kump) has been that hydrogen sulphide as the primary cause of the Permian extinction: so much in the ocean that it escaped into the atmosphere, poisoning land-based life and depleting the ozone layer.
The cause of this was in turn traced to global warming triggered by greenhouse gases from the Siberian Traps - the biggest ever volcanic eruption episode. The coinciding of the Permian extinction with the Siberian Traps has long been identified. although not all the mechanisms had been strung together: the global warming lessened the temperature differential between polar and tropic regions, in turn slowing ocean currents, causing stagnation (deoxygenation) then a buildup of anaerobic (oxygen-shunning) bacteria.
Via that biomarker isorenieratene, the same mechanism is seen to have happened - on a smaller scale, obviously - with the Devonian and Triassic extinctions. Ward comments that "it is beginning to look as if the K/T mass extinction was unique in having been caused by an impact [meteor]".
Ward's ultimate comment is that the planet is effectively a battleground between the early-emerging prokaryote life and the later-emergent eukaryotes (including us).
These periodic patterns seem only to serve to delay the emergence of tail-end complex life. And, as Gould would say, we just happened to get our chance due to that preceding history. Otherwise, it would have been down to the descendants of more advanced creatures than were our ancestors of the time.
In the development of life into multicellular organisms, there is some difference of opinion on the most significant step: whether it's from simple single-cellular organisms (prokaryotes) to complex ones with nuclei (eukaryotes), or the evolution of single-cellular life to multicellular. Most seem to favour the former.
Whereas stromatolites give a record of when the earliest lifeforms first emerged 3.5 billion years ago (according to Stephen Jay Gould this was just about as early as it could) there has been no way to trace back first emergence of eukaryotes - until now.
Peter Ward reports on chemical biomarkers in rock. Certain biological molecules break down under heating, cooling and pressure into highly stable organic compounds that could not be made by any known inorganic process. That last phrase is the kicker, which indicates that any such occurrence of the relevant compound would be an indicator of life. Moreover, some of the compounds are unique to particular groups of organisms. For example, C28 to c32 polyenoic fatty acids have been found to be unique biomarkers of sponges.
In the late 1990s, two Australians found steranes - biomarkers for eukaryotes - in Australian rock dating back to 2.7 billion years (but no older). This gives a good indication of the first emergence of lifeforms with cell nuclei.
By 800 mya, the biomarkers indicated multicellularity.
By 542 mya, the biomarkers indicated animal life - but we know this already as the Cambrian explosion.
In 2005, a Japanese team investigating the K-T extinction event (65 mya) they found, as expected, biomarker indicating a deluge of dead plant material. One study then found a decreased abundance of land plants for the next 7000 years.
Then to the Permian mass extinction event, the biggest of the lot. In 2005 a biomarker called isorenieratene was found at this point. These indicate green and purple sulpher bacteria, which cannot tolerate oxygen in water, in turn suggesting the oceans were [largely] devoid of oxygen and "saturated with hydrogen sulphide". A poisonous balance. A suggestion since (by Lee Kump) has been that hydrogen sulphide as the primary cause of the Permian extinction: so much in the ocean that it escaped into the atmosphere, poisoning land-based life and depleting the ozone layer.
The cause of this was in turn traced to global warming triggered by greenhouse gases from the Siberian Traps - the biggest ever volcanic eruption episode. The coinciding of the Permian extinction with the Siberian Traps has long been identified. although not all the mechanisms had been strung together: the global warming lessened the temperature differential between polar and tropic regions, in turn slowing ocean currents, causing stagnation (deoxygenation) then a buildup of anaerobic (oxygen-shunning) bacteria.
Via that biomarker isorenieratene, the same mechanism is seen to have happened - on a smaller scale, obviously - with the Devonian and Triassic extinctions. Ward comments that "it is beginning to look as if the K/T mass extinction was unique in having been caused by an impact [meteor]".
Ward's ultimate comment is that the planet is effectively a battleground between the early-emerging prokaryote life and the later-emergent eukaryotes (including us).
These periodic patterns seem only to serve to delay the emergence of tail-end complex life. And, as Gould would say, we just happened to get our chance due to that preceding history. Otherwise, it would have been down to the descendants of more advanced creatures than were our ancestors of the time.
Tuesday, February 05, 2008
Evolution: Mammals 2: Monotremes
Odd fact of the day: echidnas derived from platypus-like creatures.
Monotremes are the only group of extant mammals that are non-therian, i.e. non-placental. (The name refers to their peculiar single opening for intestinal/urinary/reproductory functions.)
There are five identified species: four are echidna, and one is a platypus.
I happen to be reading Richard Dawkins' Ancestor's Tale. Dawkins mentions platypus fossils (Obdurodon) older than the point at which echidna and platypus diverged, along with molecular analysis that strongly implies the echidna is derived from a platypus! - effectively, over time its ancestors gradually abandoned water, changed the form of their feeding appendage (duckbill to tubular) and acquired protective quills.
Monotremes are non-therian mammals, which would mean they lay eggs. I am casting aside the oft-used term Prototherian ('first animals') as not being truly cladistic, since it excludes descendant Eutherians ('placentals') and Metatherians (marsupials).
So to other non-therians: early mammals and their non-placental descendants.
Research is hard. The situation is not as simple as Tudge's statement (dated 2000) that there are eight types of non-therian mammals - that takes a judgment call, and a lot has happened since then.
Non-therians are typically taken to include at the least: monotremes, multituberculates, Morganucodonts, Triconondonts, Doconondonts... and a few others.
How they're grouped is a matter of current debate. It would take several posts, so I intend to lay this aside for the moment.
Most of the names above are based on characteristics of their teeth - I imagine for several reasons:
- teeth are often all that remains
- they're a useful differentiating characteristic
- they give some indication of diet, and thus niche, adaption, selectivity.
Another debate also seem to revolve around the time frames that they each occupy. Of particular interest are those mammal-like creatures (mammaliformes) that existed before the K-T boundary - the 65mya dinosaur extinction event that enabled mammals to proliferate. True mammals were all shrew-sized before then, barely eking an existence in the dominant shadow of the dinosaurs.
All this is relevant because it traces the evolution of mammals, how they developed their features over time (and how fast), and how successful they were in their environmental niches against competition from non-mammals and from later developments.
More to come on non-therians. I might take a break, however, to discuss the formation of New Zealand.
Monotremes are the only group of extant mammals that are non-therian, i.e. non-placental. (The name refers to their peculiar single opening for intestinal/urinary/reproductory functions.)
There are five identified species: four are echidna, and one is a platypus.
I happen to be reading Richard Dawkins' Ancestor's Tale. Dawkins mentions platypus fossils (Obdurodon) older than the point at which echidna and platypus diverged, along with molecular analysis that strongly implies the echidna is derived from a platypus! - effectively, over time its ancestors gradually abandoned water, changed the form of their feeding appendage (duckbill to tubular) and acquired protective quills.
Monotremes are non-therian mammals, which would mean they lay eggs. I am casting aside the oft-used term Prototherian ('first animals') as not being truly cladistic, since it excludes descendant Eutherians ('placentals') and Metatherians (marsupials).
So to other non-therians: early mammals and their non-placental descendants.
Research is hard. The situation is not as simple as Tudge's statement (dated 2000) that there are eight types of non-therian mammals - that takes a judgment call, and a lot has happened since then.
Non-therians are typically taken to include at the least: monotremes, multituberculates, Morganucodonts, Triconondonts, Doconondonts... and a few others.
How they're grouped is a matter of current debate. It would take several posts, so I intend to lay this aside for the moment.
Most of the names above are based on characteristics of their teeth - I imagine for several reasons:
- teeth are often all that remains
- they're a useful differentiating characteristic
- they give some indication of diet, and thus niche, adaption, selectivity.
Another debate also seem to revolve around the time frames that they each occupy. Of particular interest are those mammal-like creatures (mammaliformes) that existed before the K-T boundary - the 65mya dinosaur extinction event that enabled mammals to proliferate. True mammals were all shrew-sized before then, barely eking an existence in the dominant shadow of the dinosaurs.
All this is relevant because it traces the evolution of mammals, how they developed their features over time (and how fast), and how successful they were in their environmental niches against competition from non-mammals and from later developments.
More to come on non-therians. I might take a break, however, to discuss the formation of New Zealand.
Monday, January 14, 2008
Evolution: Wonderful Life 2: the pattern of early diversification
Recapping on the Cambrian explosion: this was pretty much the beginning of modern multicellular animal life about 530 million years ago. In The Lying Stones Of Marrakesh, Stephen Jay Gould characterised this as constituting the greatest of all mysteries: "the causes of both the anatomical explosion itself and the 'turning off'of evolutionary fecundity for generating new phyla thereafter."
This has troubled biologists since before Darwin, and is less likely to be due to a simple gap in the exposed fossil record than to other phenomena, such as an extinction event covering the preceding Ediacaran fauna (sessile - non-mobile sponge-like marine animals). That's just a guess, but it parallels what happened 65 million years ago (the KT event, the end of the dinosaurs), when a meteor caused mass extinctions and specifically allowed mammals to proliferate.
The Cambrian Explosion saw the emergence of most major animal body types (phyla), bar the relatively insignificant marine bryzoa.
I'll restate a key passage of Gould's book Wonderful Life:
"The major argument of this book holds that contingency is immesurably advanced by the primary insight won from the Burgess Shale - that current patterns were not slowly evolved by continuous proliferation and advance, but set by a pronounced decimation (after a rapid initial diversification of anatomical designs), probably accomplished with a strong, perhaps controlling, component of lottery." (p301)
(Here, decimation doesn't refer to the literal reduction by one-tenth, but more the common understanding of much more dramatic paring to a relatively small fraction.)
If you can picture this as a spindle diagram, as Gould suggests, the direction of time would be bottom to top, and the spindle's width at various levels would represent diversity. And the appearance of animal body types would be like a christmas tree - the bottom would depict a small diversity of type, followed by a rapid (relatively instantaneous) expansion, followed by a gradual reduction. This is probably contrary to popular understandings of evolution of animal variety, as being either like an inverted cone - a constant increase in variety - or perhaps like a diamond, where a constant increase is followed by a constant decrease.
example of a spindle diagram
Gould depicted the Cambrian phenomenon as one of sudden explosion of so-called disparity - that is, sudden appearance of a variety of fundamental animal body types, or phyla.
This is where it gets interesting: he notes that in recent studies, he "concluded that the pattern of maximal early breadth is a characteristic of lineages at several scales and times, not only of major groups at the Cambrian explosion". In effect, the bottom-heavy christmas tree shape happens often. He "surveyed the entire history of marine invertebrate life - 708 spindle diagrams at the level of genera within families". With only one exception, he found lineages that arose early in the history of multicellular life - Cambrian or Ordovician periods - had spindles with 'centre of gravity' less than 0.5 - ie more like a christmas tree than a diamond.
This is certainly food for thought. Why such a regular pattern?
The KT experience does suggest that mass extinction permits remaining life to proliferate into the ecological vacuums, but there is no immediate suggestion that this happened in the Cambrian explosion. Yet the disappearance of the Ediacarans shortly beforehand (in geological terms) must have left a gap.
In The Lying Stones Of Marrakesh, Gould details evidence of phosphorised embryos in precambrian rock [the phosphorisation process can preserve soft tissue that would otherwise decay, but it works only on very small entities], with some suggestion that modern animal phyla had emerged before the Ediacarans disappeared. Then there is the SSF (small shelly fauna) of early Cambrian times to account for.
The story continues, and there are obviously more discoveries to come, more theorising. The mystery is too big to remain unaccounted for too much longer.
References
Gould, SJ (1989): Wonderful Life. Penguin, London
Gould, SJ (2002): The Lying Stones Of Marrakesh. Vintage, London.
Wednesday, October 10, 2007
Recovery from mass extinction
Douglas H Erwin (Dept Paleobiology, Smithsonian Institute) - Lessons from the past: Biotic recoveries from mass extinctions
This paper, for a 2000 colloquium, "The Future of Evolution", is essentially a literature review in the area of recovery from mass extinction.
Although it's the extinctions that capture the imagination, environmental and species recovery can be seen as more pertinent, since this defines the pathway to the present.
Erwin characterises two types of extinction event: pulse extinction, which is too rapid to see adaptive organic response, and press extinctions, where the environment gradually turns sour (so to speak) for a large number of existing species, but for which steady adaption to environmental change is possible.
For pulse extinctions in particular, recovery is characterised as gradual expansion from more sheltered environments, best exemplified by deep water (below continental shelf) niches, which would be most resilient to changes in temperature or atmospheric oxygen.
Initial post-extinction fauna typically consists of a limited variety of widespread species. It's not obvious to me whether this is due to opportunistic expansion or good suvival of prevalent species, but the paper suggests the former. However, there's a cautionary note that that shouldn't be taken as global spread.
There is some support for the intuitive notion that more ["morphologically"] complex species suffer more in mass extinctions - ie the evolutionary clock is reset or wound back somewhat. That in itself should give pause for thought.
The paper makes several mentions of "Lazarus taxa" - species which apparently disappear at the event's boundary, only to subsequently reappear. These are often simply an illustration of the gappiness in the fossil record, but Erwin suggests this can often be due to biogeographic differentiation, ie local geography. For example, he says that extinction is less apparent in the southern hemisphere after the K/T event - the meteor in the shallow waters of Yucatan, Mexico.
A couple of minor extinction events are mentioned: the early Jurassic Toarcian event and the Late Cretaceous Cenomanian-Turonian event. In the descriptions given, I see both as bearing putative symmetry with current conditions: both are press extinctions involving marine anoxia (oxygen depletion) during relatively high sea levels and a greenhouse climate. Adaption (by anoxic-adapted species such as bivalves) is suggested rather than opportunistic expansion [by a few remaining species].
Lest this breed complacency, it's worth noting that recovery of the terrestrial (and thus atmospheric) carbon cycle took a mere 130,000 years!
From peak of extinction rates to peak of speciation (diverse and specialised fauna) is at one point set to about 3 million years - but I would find it hard to accept generalisations on this. Some interesting phenomena in the interval include:
- clades on the wane as others gradually take over, which is reversed by the extinction event, simply because of the greater resilience to the specific event. Erwin mentions cheilostome bryzoans taking over from cyclostomes, only to have the latter triumph over the conditions of the event;
- other lineages that survive the event, only to disappear as (re)speciation hits its peak.
Overall, the suggestion is that there is no clear relationship between the magnitude of an extinction and its evolutionary impact. Modelling has shown 80% of phylogenetic structure to survive a 90% overall species loss. That is, most body types survive, and subsequent speciation is only a matter of variants.
Which would bring us back to the question of the Cambrian Explosion: why a short period of evolutionary activity resulted in pretty much all the body types in existence today.
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