Hot Fossil Mammals May Give a Glimpse of Nature’s Future

The present is the key to the past. Every geologist worth their sodium chloride knows this. The famous phrase, a distillation of the principle of uniformitarianism, can be seen emblazoned on mugs, bumper stickers, and more in college geology departments around the country. But while it’s true that phenomena currently in action can help us understand what transpired during prehistory, the flow of clues isn’t one way. The past may very well be the key to the future, especially when we want a preview of what can happen during periods of rapid climate change (like the human-caused one we’re in now). The latest study in this emerging area of research centers on the fate of ancient mammals that went through a period of warming similar to the one we’re starting to experience now.

During the dawn of the “Age of Mammals”, around 56 million years ago, the global temperature rapidly stabbed upwards. In about 100,000 years temperatures rose over 40 degrees Fahrenheit. Paleontologists know this as the Palaeocene/Eocene Thermal Maximum (PETM for short), and there’s hardly a better place to see its effects than the deserts of Wyoming. The fossil localities here are famous for producing a detailed sequence of species from this time, recording how life responded to rapid climate change.

Insects, for example, fared quite well. So much so that plant fossils from the PETM show a spike in holes and divots created by hungry, hungry arthropods. And then there are the mammals. The mammals that lived in the ancient Wyoming basins during the heat wave were smaller than those that came before or after. The fauna seem to have shrunk in the heat.

But what does this change really mean? Up until now, paleontologists have considered two hypotheses. It could be that the larger mammal species evolved to become smaller over time in a straight-line fashion called anagenesis. Then again, the smaller species could be closely-related immigrants that had lived in warmer habitats and were able to thrive as the larger species went extinct. Either way, the hypothesis is that smaller-bodied mammals were probably better able to shed heat and cope with altered nutritional values of plants that go along with high CO2 levels.

But the new study by Brian Rankin and colleagues looks at another possibility – species selection. The logic is the same as that of natural selection, but bumped up one level. Just like individuals, the argument goes, some species will vary in ways that make them more successful in splitting off descendant species than others. In this case, large-bodied mammal species would have suffered in the hothouse world, while the species that were already small would have spun off an increased number of new lineages. While the large species went extinct, the small species would have proliferated.

Fortunately the Bighorn and Clarks Fork Basin faunas have been so extensively studied that paleontologists have been able to reconstruct body sizes, ancestor-descendant relationships (which is a rare feat), and identify immigrant species. This is what decades of fieldwork leads up to – a dataset of over 2,000 localities, 5,000 specimens, and 50 species carefully arranged according to the times and places those mammals lived. Plugging all that into a modified version of what naturalists call the Price equation, Rankin and colleagues were able to parse why the ancient beasts became downsized.

There wasn’t a single reason why mammal body size changed during this narrow span of Cenozoic time. The primary cause, Rankin and colleagues conclude, is the immigration of small species into the Bighorn and Clarks Fork Basins as the large native species disappeared. These were mammals like the archaic hoofed herbivore Ectocion parvus and the primate Teilhardina brandti. The paleontologists also found evidence for some native species, such as the carnivore Viverravus politus, becoming smaller with time.

But here’s the strange part. The paleontologists found some influence of species selection in these basins, but it was in favor of larger mammals. This was a one-two punch of extinction and evolution. Some small animals, like the early primate Carpolestes simpsoni, went extinct at the same time that large ones, such as the superficially rodent-like Azygonyx, were leaving big descendant species.

Without species selection causing some large species to more successfully leave big-bodied descendants, the mammal fauna of the PETM would have been even smaller than what was left behind in the rock. And as the simmering heat decreased, species selection still favored larger species, with anagenetic change and immigration being less important. This might mean that species selection was a relative constant during the days of the Palaeocene and Eocene but became briefly suppressed when intense heat threw a brief advantage to smaller mammals.

Similar influences may soon come into play, if they haven’t already. During very short time frames, Rankin and coauthors write, the influence of climate change can be see within species. But in the long term – the extended effects that we can see coming down the line from anthropogenic climate change – species selection starts to come into play. Which species go extinct and which are able to keep spinning off descendants begins to shape the world in new ways. There’s no set path to evolution. No destiny. But by looking to the deep past, maybe we can begin to perceive the rough outlines of the new world we’re inadvertently creating.

For more, check out Shaena Montanari’s post on the same study, as well as this interview with study author Jessica Theodor I filmed at the Society of Vertebrate Paleontology meeting last fall:


Rankin, B., Fox, J., Barron-Ortiz, C., Chew, A., Holroyd, P., Ludtke, J., Yang, X., Theodor, J. 2015. The extended Price equation quantifies species selection on mammalian body size across the Palaeocene/Eocene Thermal Maximum. Proceedings of the Royal Society B. doi: 10.1098/rspb.2015.1097

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Noah (and his ark) Updated, Improved for Our Time

Instead of the Noah you know, the one who built the ark, sheltered all those animals, sailed for 40 days and 40 nights and got to see God’s rainbow, instead of him, I want you to meet a new one. An updated version.

This Noah shows up in a tough little essay written by Amy Leach, of Bozeman, Montana, who knows her science, knows there’s a flood coming—a flood of humans, seven billion and counting, already swamping the Earth, crowding the land, emptying the sea, and her more modern Noah—informed, practical, not inclined to miracles—has a different plan. He announces,

water color painting with text reading ''unfortunately, animals. we are not going to be able to bring all of you with us this time.''
Illustration by Robert Krulwich

The old Noah, you may remember, squeezed eight humans (wife, kids, their spouses) and at least two of every critter, big and small, onto his crowded ship. But the new Noah, being more practical, feels he can winnow a little. “Everybody” is a lot of animals, more than you know. Back in the day, Amy Leach writes,

pink watercolor background with two drawings of frogs peeking up over the text, which talks about what it would be like to bring two of every creature onto noah's ark
Illustration by Robert Krulwich

And, honestly, (I’m thinking to myself), if the world lost a scorpion or two, would anyone notice? Or want them back? And blotchy toads, biting little flies—some animals are hard to keep going on a tight, crowded ship. On the last voyage, dormitory assignments were beyond difficult.

And all those supplies? Amy Leach writes how the first Noah would have had …

a yellow watercolor background covered with text about collecting food for animals
Illustration by Robert Krulwich

This doesn’t mean we don’t care, new Noah says to the animals. We definitely, absolutely want to bring a bunch of you with us. But, we’ve got to be practical.

Even if our ark has grown to the size of a planet, carrying everybody through is not going to be logistically possible, which is why, he says,

blue watercolor background with black text on it about being in charge of a future noahs ark where not all animals are included
Illustration by Robert Krulwich

And anyway, that first Noah? He lived in a different age, a time they call the Holocene, before humans began to dominate and crowd out the other species. Back then, there weren’t as many people. And there were more kinds of animals, closer by, hiding in the woods, clucking in the yard, so the world was more various then, more intimate, more riotous, and thinking about it (a little wistfully, if only for a moment), the new Noah quietly recalls that on that first ark …

yellow watercolor background with text on top related to how noahs ark would be different today than it was in the Old Testament
Illustration by Robert Krulwich

And now, animals, it’s time for many of you to step away. You’ve had your unruly eons. They were wild, unplanned, noisy, great fun. Natural selection ran the world. Crazy things happened. Those were good times, Amy’s essay concludes …

blue watercoor with black text on top that reads''But the future belongs to us.''
Illustration by Robert Krulwich

Amy Leach is a writer living in Bozeman. Her collection of very short pieces—about jellyfish, beaver, salmon, plants that go topsy turvy and stand on their heads—are collected in a wonderful little book called “Things That Are.” In this column I do to Amy what the new Noah is doing to our planet: I edited her down, sliced, diced, slimmed (lovingly, I hope), trying to give you a taste for her fierce, crazy prose. But like the planet, she’s wilder in the original, so I hope you go there and sample the unedited version.

Temperature Key to Crocs in the Sea

Evolution is great at producing novelty. Every organism that has ever lived – from the first cell to the grass on your lawn and the blue whales in the sea – is a testament to that. But evolution can also repeat itself. From disparate starting points, evolution can spur some lineages to serendipitously converge on similar forms or behaviors. Among these replays – arguably among evolution’s greatest hits – are no less than five varieties of marine crocodile.

None of these seabound reptiles exist today. True, saltwater crocodiles and even American alligators can be seen at sea, but they are not as tied to the ocean as the prehistoric crocodylomorphs that spent most – if not all – of their lives in the marine realm. These salty archosaurs all lived between 199 and 34 million years ago, with each of the five groups representing independent oceanic invasions.

But why did seagoing crocodiles keep evolving and going extinct? What regulated their rise and fall? Part of the answer, University of Bristol paleontologist Jeremy Martin and colleagues suggest, may be the constantly-changing temperature of the ocean.

Metriorhynchoids may have spent their entire lives at sea. Art by Dmitry Bogdanov, CC BY 2.5.
Metriorhynchoids may have spent their entire lives at sea. Art by Dmitry Bogdanov, CC BY 2.5.

Paleontologists have floated a number of explanations for the recurring rise and crash of marine crocodiles. These range from a lack of complete fossil sampling to major sea changes wherein ocean chemistry drastically restructured marine life. But in their study, Martin and coauthors compared the varying diversity of marine crocs to a pair of possible explanations – shifting sea levels and changes in the sea surface temperature.

The reach of the ocean appears to have little to do with marine croc evolution. That’s probably because these carnivores were able to catch a broad variety of prey and even make forays into freshwater habitats, Martin and colleagues suspect. Changes in surface sea temperature offer a better fit.

Starting with an Early Jurassic group called thalattosuchians, almost every lineage of crocodylomorph to slip into the seas did so during a time of warm surface temperatures. The crocs crashed when sea temperature dipped. With the exception of one lineage, Martin and colleagues found, the marine crocs followed a pattern seen among their close relatives.

Fossil crocodylomorphs are often taken as a rough proxy for warm habitats. During a global heat spike 52 million years ago, for example, alligators lived in the Arctic, and paleontologists can track how gators followed warm temperatures down the latitudes as the global climate cooled. That’s because the prehistoric crocodylomorphs, like their living relatives, had a physiology in which their body temperature was regulated by the outside the environment. They were ectotherms. To survive, they had to follow the heat.

But one group didn’t behave like the rest. Metriorhynchoid crocs became intricately-adapted to ocean life, their limbs modified to flippers and their tails bearing large, vertical flukes. They may not have been able to return to land at all. And, Martin and coauthors found, they proliferated during a time when Jurassic sea temperatures were dropping.

Perhaps the metriorhynchoids were stuck. They were so quickly adapted to an exclusively marine life that the only evolutionary paths open to them laid in the seas. Then again, Martin and colleagues write, perhaps metriorhynchoids like the fearsome Dakosaurus had a way to cope with cooler marine temperatures. Maybe, like some other marine reptiles, the metriorhynchoids were able to keep their body temperatures several degrees above the ambient water temperature. Further study is needed to find out, but metriorhynchoids may have been hot-running crocs.

The marine croc Dyrosaurus - here at the Wyoming Dinosaur Center - lived about 50 million years ago. Photo by Brian Switek.
The marine croc Dyrosaurus – here at the Wyoming Dinosaur Center – lived about 50 million years ago. Photo by Brian Switek.

No one has ever found marine crocodiles from sites that sat near the poles, though. Whether ectothermic or warm-bodied, seagoing crocs were restricted in time and space by the warmth of the seas. Crocs slid into the sea during warm times, and they disappeared when the chill set in.

The last of the truly marine crocs died out over 34 million years ago. Among these holdouts were the dyrosaurids – crocs that survived the fifth mass extinction and enjoyed the global hothouse that came in the disaster’s aftermath, only to disappear as sea temperatures again fell. But thanks to our addiction to fossil fuels, we’re rapidly recreating the hothouse conditions under which the marine dyrosaurids thrived. As we warm the world’s seas, perhaps marine crocs will evolve anew.


Martin, J., Amiot, R., Lécuyer, C. Benton, M. 2014. Sea surface temperature contributes to marine crocodylomorph evolution. Nature Communications. doi: 10.1038/ncomms5658

Don’t Panic – How Humanity Might Survive the Next Million Years

Our species is going to go extinct. We may have descendants – a new species, or some sort of post-human meld that we construct ourselves – but the long roll of lost creatures preserved in the fossil record leaves no doubt that extinction is inevitable. But just as the survival of the human lineage is only a vague possibility at this point, our eventual downfall also remains in the realm of the unknown. Our destruction could transpire in a blink of geologic time, or be at some future point millions of years hence. What will make all the difference is our ability to learn from the past and how we use that knowledge to construct the foundation of our future. In Scatter, Adapt, and Remember, io9 editor in chief Annalee Newitz considers just that in an optimistic exploration of how the key to our long-term survival can be forged from prehistoric clues and technological possibilities.

scatter-adapt-rememberSo far, there have been five absolutely devastating mass extinctions in the history of life on Earth (with a smattering of lesser, but still calamitous, events scattered through time). And if we’re not actually in a sixth mass extinction right now, we’re not very far off from the tipping point. The blame for this state of affairs rests with us.

We’ve drastically altered the Earth’s climate and seas through greenhouse gas emissions, we are spreading invasive species around the world, and we’ve taken a horrifyingly active role in directly destroying a variety of species and ecosystems. And given all this change, we’re not guaranteed a persistent place on the planet. As adaptable as we are, we’re still the last human species in existence and can only claim a relatively short tenure on this planet – our species has only been around for about 200,000 years. Whether we’re snuffed out in the next few millenia or extend the track record far into the future relies on our abilities to understand the risks that face us and responsibly use the best scientific tools at our disposal to mitigate against our self-imposed threats.

Learning from prehistory is one way to outline possibilities of what the future might hold. Paleontologists with an ecological bent have already begun to investigate these potentials, looking to how organisms have reacted to climate change and other familiar phenomena in the past for a view to what makes the difference between persistence, evolution, and extinction. To that end, Annalee* briefly surveys four of the Big Five mass extinctions, reiterating the point that there have always been survivors. If there had not, we wouldn’t exist. Our ancestors, as well as the ancestors of every other species in existence today, persisted through extinction’s worst and continued to change through the ages. And while what makes the difference between death and survival during global disasters is still being debated for all of these extinctions, some trends – such as being a widespread generalist capable of wandering far to rare resources in extinction’s aftermath – give some organisms an advantage over specialists restricted close to home.

Threats to our existence don’t always come in the form of asteroid impacts or intense volcanic activity, as they were during some mass extinctions. Disease and famine have horrifically ended human lives much closer in time. From the fall of South American civilizations to the Great Irish Famine, Annalee also surveys dangers that we create for each other, from the spread of disease and war to the mismanagement of arable land. But after cataloging all the dangers, including the blip in prehistoric time when our species almost went extinct prior to a dramatic rebound, Annalee begins to lay out possibilities for survival in a conversational style that would feel just as at home on io9 as in a book.

Some of these examples in the middle section don’t entirely fire. While the long-range migration routes gray whales employ are certainly important for their survival (the “Remember” example of the title), Annalee recognizes that human conservation efforts and future attempts not to disturb the whales are why the cetaceans still exist in the Pacific today. Still, Annalee sets up the general strategies of being able to wander far, shift with changing conditions, and recall what survival tricks worked in the past as hopes that mold more specific ways in which we might allow humanity to avoid extinction for a long time yet to come.

Lessons of death and survival can be drawn from a variety of examples, from organisms that withstood mass extinctions to people who succumbed to pandemics in recent history. And the point of this reflection, Annalee writes, is to ask “How will we convert our guardedly hopeful stories of a human future into a real-life plan for survival that avoids some of the worst failure modes?”

An initial step involves altering cities, especially as our global population continues to climb. Aside from relatively abstract goals that depend on those living in a particular place – such as an openness to innovation and created areas of shared green space – Annalee also investigates the technologies that may allow us to survive in the near and long term. Carefully-designed subterranean cities might be essential in the aftermath of nuclear war or a terrible asteroid strike, while buildings partly made of biological materials might reduce energy costs while providing us with a space to grow food right where we live. Likewise, a better understanding of the way earthquakes and disease work, paired with models that better predict the damage such phenomena cause, could allow us to make ourselves more resistant to such persistent challenges and respond more effectively. Tragically, as Annalee recognizes, the benefits of such innovations will be spread unequally. Those in affluent, developed nations are more likely to see the kind of safe, green cities that Annalee describes, while people elsewhere will suffer.

The promise of geoengineering raises the same dilemma. Scientists and engineers are trying to come up with solutions to global climate change, ocean acidification, and other problems that are global in scale. Given the experimental nature of programs – such as creating more cloud cover to partly block the sun while also trying to lessen the amount of carbon dioxide in the atmosphere – no one really knows what such endeavors would do in this country or that as weather and climate patterns changed. We do not live on a homogenous planet, and alterations that benefit one part of the globe might devastate another. If we’re going to modify the planet to best suit our needs and survival, as Annalee argues we should if we want to celebrate the millionth birthday of our species, who will decide what changes to implement and how?

Many of the possible solutions Annalee discusses are still in the realm of science fiction, or, at least, speculative science beyond the reach of what we can presently achieve. That’s not to say that tweaking Earth to better ensure our survival or even setting up shop on a distant planet are out of the question. Technology, politics, and culture will constrain our long-term efforts at survival, but given how much the human experience has changed during the past century – not to mention our cultural evolution over the relatively scant 200,000 years since our species originated – how strange our future might be is a tantalizing  mystery. Will we live in a Star Trek like existence, strange yet still familiar? Or will “human” mean something entirely different – people genetically altered to cope with life elsewhere in the solar system, or perhaps digital copies of minds that have an almost immortal life inside machines? More likely, humanity one million years hence – if we ever get that far – will be something far stranger than we can imagine today.

We won’t ever live in the glow of another star unless we ensure our survival on Earth, though. The challenge that faces us, Annalee demonstrates, is how to pair new ideas and innovations with what already exists. We can’t simply start from scratch. The world of tomorrow is going to be built on top of and around the world we know. And even if we can predict the forces that might drive us extinct, there’s no guarantee that we’ll have the time or tools to react to such threats. But there’s hope that we can.

In the end, survival will mean stretching our perceptions of what is natural. The idea of “hacking the planet” or altering ourselves to better match our surroundings might sound anathema to some, but the truth is that we are already doing so. The history of Earth is one of dramatic and constant change, and trying to recapture some romantic notion of Nature would be ignoring the reality of persistent planetary permutation and the way we’ve already made use of the Earth (for good and ill). Even restoring damaged habitats requires human intervention and stewardship – places of we think of as wild still bear our distinctive fingerprints. Maintaining the dichotomy of “human-made, bad; natural, good” will help no one. Instead, we need to recognize and come to terms with our capacity for both destruction and preservation – to use the best of our scientific knowledge and imagination to predict what tomorrow might hold and make careful decisions of what the future of Earth is going to be like for our species and all the others that dwell here. Annalee’s new book is a hopeful overview of such a possibility. We’ll never have total control of the planet nor our ultimate fate, but we have the ability to explore what we want the future of our species to be like.

*Since I know Annalee personally and have worked with her for some io9 posts, I decided to call her by her first name in this review.

Further reading: Annalee wrote a guest post for this blog about her favorite icon of long-term survival, Lystrosaurus.

Reinventing the Mammoth

The first groaner of the TEDxDeExtinction conference cropped up less than an hour into the program.  Paleontologist Michael Archer was on stage, wrapping up his talk on possibly recreating the gastric brooding frog and the thylacine – two species totally lost from Australia in recent time. Archer laid out the technological particulars of the plans, as well as where the animals might live, but at the end he took a turn for the transcendentalist in justifying the difficult endeavor to resurrect these creatures. Since our species played a prominent role in wiping out both species, Archer argued, we have an obligation to “restore the balance of nature that we have upset.” If I had brought a flask with me, I might have taken a strengthening sip of whiskey right then.

There is no such thing as “the balance of nature.” If sifting through the fossil record has taught me anything, it’s that change is the rule. Balance is only a temporary illusion created by the difficulties of envisioning life on a geological scale. That, and quite a few conversations with practically-minded ecologists and biologists, means that I’ve become a bit allergic to snuggly phrases that are often trotted out to emphasize the inherent goodness of nature – whatever “nature” means – in a way that suggests we can simply restore the complexity of life to a stable state that the ghosts of Thoreau, Emerson, and Muir would honor us for. And the irritation of that line kept with me throughout the rest of the day. Perhaps the closing appeal to the balance of nature was a trifling throwaway, yet that one line underscored the problematic nature of the major proposal the assembled speakers and guests had been called to consider – that we can, and should, resurrect lost life to take some of the tarnish off our ecological souls. The concept falls under the banner of “de-extinction.”


Fossils of Future Past

Dinosaurs were prehistoric wonders, separated from us by an unfathomable amount of geologic time. But, albeit briefly, the Victorian geologist Charles Lyell thought that the ruling reptiles might someday return.

Years before his friend Charles Darwin would turn Lyell’s head toward evolutionary views, the Scottish champion of uniformitarianism tried to find a balancing point between the order and flux of life through time. In his scientific epic Principles of Geology, published in three volumes between 1830 and 1833, Lyell rightly recognized that different sets of organisms inhabited the world at different times. But, he cautioned, there was no evidence that evolution was behind the stately march of species.

What controlled the life and death of species? Lyell couldn’t say. Creatures simply popped into existence, ideally-suited to their surrounding conditions. Those conditions, Lyell believed, were symptoms of geologic change – the constant, consistent reconstitution of the planet. As lava poured out, mountains eroded away. Earth was always shifting, but in a completely balanced way. In Lyell’s mind, there could be no doubt that climate and habitats were affected as seas rose or receded, as hills were thrust up or ground down.

Henry De la Beche's 1830 watercolor 'Duria Antiquior - A more Ancient Dorset', inspired by the fossil finds of Mary Anning along England's Jurassic coast.
'Duria Antiquior - A more Ancient Dorset', drawn the same year as Lyell began to published Principles of Geology, envisions the life of England's Jurassic coast, based on the finds of Mary Anning.

If biology was at the mercy of geology, then accumulated geologic conditions might eventually return the continents and climate to a state not seen since what Lyell’s generation called the Secondary era – the time when reptiles ruled the Triassic, Jurassic, and Cretaceous. As Lyell explained in Principles of Geology:

We might expect, therefore, in the summer of the “great year,” which we are now considering, that there would be a great predominance of tree-ferns and plants allied to palms and arborescent grasses in the isles of the wide ocean, while the dicotyledonous plants and other forms now most common in temperate regions would almost disappear from the earth. Then might those genera of animals return, of which the memorials are preserved in the ancient rocks of our continents. The huge iguanodon might reappear in the woods, and the ichthyosaur in the sea, while the pterodactyle might flit again through umbrageous groves of tree-ferns.

Lyell’s artistically-talented colleague Henry De la Beche lampooned the notion of future ichthyosaurs in a cartoon titled “Awful Changes—Man Found Only In A Fossil State—Reappearance of Ichthyosauri”, and, a few decades later, Darwin and Alfred Russel Wallace tied the succession of prehistoric life to an evolutionary idea with a plausible mechanism. The idea that Earth will continually cycle through Primitive, Secondary, and Tertiary periods at the whim of geologic change never took hold. Natural selection ruled out such a possibility. The wonder of evolution is that the form of future life is contingent upon what has come before, yet organisms are not locked into predetermined pathways. What Nature will look like a million, ten million, or a hundred million years from now rests in the realm of speculation.

Yet, strange as it may seem, paleontologists, climate scientists, and conservationists have been plumbing the depths of the fossil record for clues about the kind of “awful changes” our own species is responsible for. Although we’re still supposed to be in the shuffle of Ice Age oscillations, our thirst for fossil fuels has dumped so many climate-altering compounds into the air that we may be creating an artificial greenhouse world. No one expects that Triceratops and Allosaurus will return – as in Mark Schultz’s fantastic Xenozoic Tales series – but the way species have reacted to past climates might give us a broad outline of what’s to come. Included in the swath of species paleontologists have been interrogating for clues are mollusks that thrived in a warm, shallow sea that once splitNorth America in two.


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For polar bears, the price of rapid evolution is a weaker skull


Polar bears have become a poster child for the impacts of climate change on wildlife. Their future may be bleak but their past is altogether more glorious. Polar bears are an evolutionary success story. They’re a recent addition to life’s repertoire, splitting off from their closest relatives – the brown bears – as recently as 150,000 years ago. Within just 20,000 years, they accumulated many adaptations that have made them the masters of their icy realm. But some of these same adaptations could now be their undoing.

The polar bear is the only bear that eats nothing but meat. It is wonderfully adapted to live off the flesh of seals. Graham Slater from the University of California Los Angeles has found that the shape of the polar bear’s skull has evolved at around twice the rate of the bear family as a whole. It’s flatter and more slender than those of other bears, all the better for thrusting into the dens and breathing holes of seals. Their eyes sit high up on their skulls, as is often the case for animals that spend a lot of time swimming.

But this rapid change has come at a cost for this specialist seal-killing skull turns out to be surprisingly weak. Slater used a technique called finite element analysis to put the skulls of a polar bear and a brown bear through a ‘digital crash-test’. He used a medical scanner to create virtual models of real skulls and then subjected them to different forces in his computer.


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A warmer ocean is a less green one


The Earth’s oceans are mysterious and largely unexplored. Many of their inhabitants are familiar to us but their whereabouts and numbers are far less clear. This is starting to change. In two new studies, Boris Worm from Dalhousie University has revealed an unprecedentedly detailed portrait of the planet’s marine life, from tiny plankton to mighty whales. And with that knowledge comes concern, for neither study paints an optimistic picture about the fate of tomorrow’s seas, as changing climate slowly raises their temperature.

Graduate student Daniel Boyce focused on some of oceans’ smallest but most important denizens – the phytoplankton. These tiny creatures are the basis of marine food webs, the foundations upon which these watery ecosystems are built. They produce around half of the Earth’s organic matter and much of its oxygen. And they are disappearing. With a set of data that stretches back 100 years, Boyce found that phytoplankton numbers have fallen by around 1% per year over the last century as the oceans have become warmer, and if anything, their decline is getting faster.  Our blue planet is becoming less green with every year.

Meanwhile, post-doc Derek Tittensor has taken a broader view, looking at the worldwide distributions of over 11,500 seagoing species in 13 groups, from mangroves and seagrasses, to sharks, squids, and corals. His super-census reveals three general trends – coastal species are concentrated around the western Pacific, while ocean-going ones are mostly found at temperate latitudes, in two wide bands on either side of the equator. And the only thing that affected the distribution of all of these groups was temperature.


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Pocket Science – belly-flopping frogs, and fattening marmots

Not Exactly Pocket Science is a set of shorter write-ups of new stories with links to more detailed takes by the world’s best journalists and bloggers. It is meant to complement the usual fare of detailed pieces that are typical for this blog.

Frogs evolved to jump before they perfected landings

Most frogs are can leap large distances in a single bound, jumping forward with a thrust of their powerful hind legs and landing gracefully on their front ones. But it wasn’t always like this. A study of one of the most primitive groups of frogs suggests that the first frogs landed in an awkward belly-flop. These animals evolved to jump before they perfected their landings.

Virtually all frogs jump and land in the same way. But Richard Essner Jr from Southern Illinous University discovered a unique leaping style in the Rocky Mountain tailed frog. This species belongs to a group called the leiopelmatids, more commonly (and accurately) known as the “primitive frogs”. Using high-speed video footage, Essner showed that the tailed frog’s landings are an awkward mix of belly-flops, face-plants and lengthy skids. Only when it grinds to a halt does it gather its outstretched limbs together. By contrast, two more advanced species – the fire-bellied toad and the northern leopard frog – rotate their limbs forward in mid-air to land gracefully. The tailed frog managed to jump a similar distance, but its recovery time was longer.

These results support the idea that frogs eventually evolved their prodigious jumping abilities to escape from danger by rapidly diving into water. Landings hardly matter when you’re submerged and the ability to pull them off elegantly only evolved later. Essner thinks that doing so was fairly simple – if the tailed frog starts pulling its legs in just slightly earlier, it would land with far more poise. This simple innovation was probably a critical one in frog evolution. The primitive frogs never got there, but they have other ways of coping with their clumsy crash-landings. They’ve stayed very small to limit the injuries they sustain, and they have large shield-shaped piece of cartilage on their undersides to protect their soft vital organs.

Reference: Naturwissenschaften; Video by Essner; soundtrack by me.

More on frogs: Tree frogs shake their bums to send threatening vibes, pesticide-stricken frogs, ‘Wolverine’ frogs, a lungless frog, and seven habits of highly successful toads


Changing climate fattens marmots

The media is rife with tales of animals from polar bears to corals suffering as a result of climate change. But some species stand to gain from the rising global temperatures. In Colorado’s Rocky Mountains, warmer climes allow the yellow-bellied marmot to awaken from its winter hibernation earlier. With more time available to eat, they become bigger and so do their populations. In just three decades, their numbers have tripled.

Arpat Ozgul from Imperial College London studied a 33-year census of Colorado’s marmots, where individuals have been tracked over their entire lifetimes. These rodents spend the winter hibernating in their burrows. But since 1976, they have been waking up earlier and earlier in the year, presumably because of a rise in warm days. That gives them more time to eat and grow before their next hibernation, and the adults have become around 10% heavier. Ozgul found that being fatter offers many advantages for a marmot – females are more likely to breed, youngsters grow more quickly, and adults are more likely to survive their next bout of hibernation.

It’s no surprise that their population has shot up dramatically, although surprisingly, this wasn’t a gradual process. Their numbers seemed to be fairly stable but they passed a tipping point in 2000 and have skyrocketed ever since. By modelling the changes in their bodies over time, Ozgul concluded that the marmots haven’t changed much genetically – their extra pounds are the result of their response to environmental changes. For example, the bluebells that they like to eat declined after 2000, which might have prompted them to seek other fattier foods.

But Ozgul worries that this boom period has a bust on the horizon – it’s a short-term response to warmer climate. These are animals that are adapted to chilly mountainous temperatures and they don’t fare well in heat. If temperatures continue to rise and summers get longer and drier, their health might suffer and their populations might crash.

More on this story from Jess McNally at Wired and Lucas Laursen at Nature

Reference: Nature; image by Ben Hulsey

More on climate change and animal populations: The rise of “weedy” mice, the mystery of the shrinking sheep, lost clownfish, marching emperor penguins, and declining amphibians and reptiles


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Losing Nemo 2 – clownfish swim towards predators as CO2 levels rise

If you think the stars of Pixar’s Finding Nemo had it rough, spare a thought for the plight of real clownfish. These popular fish may struggle to survive in oceans that are becoming enriched with carbon dioxide. High levels of CO2 dissolved in the water can muddle a clownfish’s sense of smell, preventing it from detecting both shelter and threats.

Philip Munday from James Cook University has shown that at levels of carbon dioxide within what’s predicted for the end of the century, a clownfish’s ability to sense predators is completely shot. Some larvae become literally attracted to the smell of danger and start showing risky behaviour. It’s not surprise that they die 5-9 times more frequently at the mouths of predators.


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Sperm whale poo offsets carbon by fertilising the oceans with iron


While the world wrangles over ways of reducing carbon emissions, some scientists are considering more radical approaches to mitigating the effects of climate change. Dumping iron dust into the world’s oceans is one such strategy. Theoretically, the iron should act as fertiliser, providing a key nutrient that will spur the growth of photosynthetic plankton. These creatures act as carbon dioxide pumps, removing the problematic gas from the air and storing the carbon within their own tissues. When the plankton die, they sink, trapping their carbon in the abyss for thousands of years.

It may seem like a fanciful idea, but as with much of our technology, nature beat us to it long ago. Trish Lavery from Flinders University has found that sperm whales fertilise the Southern Ocean in exactly this way, using their own faeces. Their dung is loaded with iron and it stimulates the growth of plankton just as well as iron dust does.

Sperm whales are prodigious divers, descending to great depths in search of prey like squid. When they’re deeply submerged, they shut down all their non-essential bodily functions. Excretion is one of these and the whales only ever defecate when they reach the surface. By happy coincidence, that’s where photosynthetic plankton (phytoplankton) make their home – in the shallow column of water where sunlight still penetrates. So by eating iron-rich prey at great depths and expelling the remains in the shallows, the whales act as giant farmers, unwittingly seeding the surface waters with fertiliser.

There are approximately 12,000 sperm whales left in the Southern Ocean. By modelling the amount of food they eat, the iron content of that food, and how much iron they expel in their faeces, Lavery calculated that these whales excrete around 50 tonnes of iron into the ocean every year.  And based on the results of our own iron fertilisation experiments, the duo calculated that every year, this amount of iron traps over 400,000 tonnes of carbon in the depths, within the bodies of sinking plankton.

Previously, scientists assumed that whales (and their carbon dioxide-rich exhalations) would actually weaken the Southern Ocean’s ability to act as a CO2 pump. But according to Lavery, this isn’t true. She worked out that the whales pump out just 160,000 tonnes of carbon through their various orifices. All of these figures are probably conservative underestimates but even so, they suggest that sperm whales remove around 240,000 more tonnes of carbon from the atmosphere than they add back in. They are giant, blubbery carbon sinks.

However, their true potential will go largely unfulfilled thanks to our harpoons. Many sperm whales have been killed by industrial whalers, and the population in the Southern Ocean has declined by some 90%. On the bright side, the Southern Ocean’s population represent just 3% of the global total, so this species may have an even greater role as a warden for carbon than Lavery has suggested. Other seagoing mammals probably have a part to play too, provided that they feed at depth and excrete near the surface. Several other toothed whales do this, and some filter-feeding ones may do too.

Reference: Proc Roy Soc B

Image by Cianc

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“Weedy” mice dominate a warming world while other small mammals suffer

Deer_mouseToday’s mammals are facing the twin threats of a rapidly warming planet and increasingly intrusive human activity. As usual, the big species hog the limelight. The world waits on bated breath to hear about the fates of polar bears, whales and elephants, while smaller and more unobtrusive species are ignored. But smaller mammals are still vital parts of their ecosystems and it’s important to know how they will fare in a warmer world. Now, thanks to Jessica Blois from Stanford University and a hoard of new fossils, we have an idea. As they say, all this has happened before


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Tree rings reveal two droughts that sealed the fate of Angkor

AngkorToday, the city of Angkor in Cambodia lies in ruins. But a thousand years ago, life there was very different. Then, Angkor was the heart of the Khmer empire and the largest preindustrial city of its day. It had a population of a million and an area that rivalled modern Los Angeles. And the key to this vast urban sprawl was water.

Radar images of the city by the Greater Angkor Project (GAP) revealed that Angkor was carefully designed to collect, store and distribute water. The “Hydraulic City” included miles of canals and dikes, irrigation channels for supplying crops, overflow channels to cope with a monsoon, massive storage areas (the largest of which was 16km2 in area), and even a river diverted into a reservoir. Water was the city’s most precious resource, allowing it to thrive in the most unlikely of locations – the middle of a tropical forest.

But water, or rather a lack of it, may have been part of Angkor’s downfall. Brendan Buckley from Columbia University has reconstructed the climate of Angkor over the last 750 years, encompassing the final centuries of the Khmer Empire. The records show that Angkor was hit by two ferocious droughts in the mid-14th and early-15th century, each lasting for a few decades. Without a reliable source of water, the Hydraulic City’s aquatic network dried up. It may have been the coup de grace for a civilisation that was already in severe decline.

Many theories have been put forward for the downfall of Angkor, from war with the Siamese to erosion of the state religion. All of these ideas have proved difficult to back up, despite a century of research. Partly, that’s because the area hasn’t yielded much in the way of historical texts after the 13th century. But texts aren’t the only way of studying Angkor’s history. Buckley’s reconstruction relies on a very different but more telling source of information – Fujian cypress trees.


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Climate change and the mystery of the shrinking sheep

Blogging on Peer-Reviewed ResearchThe island of Hirta, on the western coast of Scotland, is home to a special breed of sheep. Soay sheep, named after a neighbouring island, are the most primitive breed of domestic sheep and have lived on the isles of St Kilda for at least a millennium. They’re generally smaller than the average domesticated sheep, and that difference is getting larger and larger. Over the last 20 years, the Soay sheep have started to shrink.

SheepSoay.jpgThey are becoming gradually lighter at all ages such that today’s lambs and adults weigh around 3kg less than those from 1986. Their hind legs have also shortened to a similar degree, suggesting that they have indeed shrunk, rather than fallen increasingly ill.

The reasons behind this downward trend have now been revealed by a group of British scientists led by Arpat Ozgul from Imperial College. Using decades’ worth of data, the team showed that natural selection normally favours larger sheep, as the odds of survival increase with body size. But this evolutionary pressure has been overwhelmed by the effects of climate change. Warmer winters have led to easier conditions, and less need to pile on the pounds in the first years of life. The lambs can afford to grow more slowly and they become smaller adults, who are only physically capable of raising small young themselves.

Soay sheep live in a closed population that doesn’t have to deal with human interference, predators, migrants (either in or out), or significant competitors. That makes them an ideal population to study if you’re an evolutionary biologist interested in how animal populations change over time. One such group, including Ozgul and his colleague Tim Coulson, have been studying the Soay sheep since 1985 and have brilliantly called themselves SLAPPED (short for Studies in Longitudinal Analysis of Population Persistence and Evolutionary Demography).

The group wanted to work out the extent to which the sheep’s shrinking size is due to the influence of natural selection and to what extent it is just an ecological response to changing environments. To that end, they developed a mathematical job designed to analyse their 24 years of data and tease apart these contrasting effects.


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Bleached corals recover in the wake of hurricanes


Blogging on Peer-Reviewed ResearchIn 2005, corals in the large reef off the coast of Florida were saved by four hurricanes. Tropical storms seem to be unlikely heroes for any living thing. Indeed, coral reefs directly in the way of a hurricane, or even up to 90km from its centre, suffer serious physical damage. But Derek Manzello from the National Oceanic and Atmospheric Administation has found that corals just outside the storm’s path reap an unexpected benefit.

Hurricanes can reverse coral bleaching by cooling surrounding waterHurricanes can significantly cool large stretches of ocean as they pass overhead, by drawing up cooler water from the sea floor. And this cooling effect, sometimes as much as 5°C, provides corals with valuable respite from the effects of climate change.

As the globe warms, the temperature of its oceans rises and that causes serious problems for corals. Their wellbeing depends on a group of algae called zooxanthellae that live among their limestone homes and provide them with energy from photosynthesis. At high temperatures, the corals eject the majority of these algae, leaving them colourless and starving.

These ‘bleached’ corals are living on borrowed time. If conditions don’t improve, they fail to recover their algae and eventually die. But if the water starts to cool again, they bounce back, and Manzello found that hurricanes can help them to do this.