Repost – Unique Fossils Record the Dining Habits of Ancient Sharks

A photograph and line drawing (left side) of the fossil dolphin Astadelphis gastaldii. The crescent-shaped line in the drawing represents the bite of a large shark, with the red portions representing damage done directly to the bone. From Bianucci et al, 2010.

Blogging on Peer-Reviewed ResearchMoving to a new area can be a daunting experience, especially if you don't know anyone. At first, you might cling to any friends who do live nearby but eventually, you meet new people and start to integrate. As it is with humans, so it is with elephants.

Noa Pinter-Wollman and colleagues from the University of California, Davis wanted to study how African elephants behave when they move to new environments. This happens quite naturally as elephants live in dynamic societies where small family groups continuously merge with, and separate from, each other. But they also face new territories with increasing regularity as human activity encroaches on their home ranges and forces them further afield, and as increasing conservation efforts lead to individuals being deliberately moved, or exchanged between zoos and wildlife parks.

Pinter-Wollman took advantage of just one such forced relocation to see how the animals would react. In September 2005, in an effort to reduce conflicts between humans and elephants, Kenya's Wildlife Service moved 150 individuals from the Shimba Hills National Reserve to the Tsavo East National Park, some 160km away. They consisted of 20 groups of around 7 individuals each - mainly adult females and calves - and 20 independent males. Their new home was very different to their old one and Pinter-Wollman wanted to see how they reacted to it.

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By identifying the immigrants through ties on their tails and numbers on their backs, she found that, at first, they elephants spent a lot of time with others. But they became socially segregated and would mostly interact with other migrants, largely to the exclusion of the local Tsavo elephants. Their amity wasn't solely due to family, just familiarity - the newcomers would happily mix with other unrelated groups from their same home region. And the more the immigrants stuck together, the less likely they were to mingle with the locals.

Over time, things changed. A year later and the displaced elephants had become much less segregated, moving from a closed enclave into an integrated part of the social structure within their new home. But on the whole, they also became less sociable as time went by, with both new acquaintances and comrades from home.

Elephantcrate.jpg This is the first study to look at how an animal's desire for companionship changes depending on how well they know their environment. Pinter-Wollman says that the elephants' behaviour suggests that in the face of unfamiliar ground, it pays them to associate with others so that they can learn from one another. Indeed, among the migrants, the most sociable ones were also in better health (although this could be because sick elephants are shunned). Over time, they become more familiar with their new stomping grounds and the need to socialise lessens.

The initial social segregation probably reflects the strong social ties that elephants have. While it would benefit the newcomers to learn about their new environment from the natives, that may not have been possible. On two anecdotal occasions, she saw the locals behaving aggressively towards the unfamiliar elephants in their midst. It's behaviour that really seems all-too-human. 

Reference: doi:10.1098/rspb.2008.1538

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Shark attacks are events of speed and violence. When they have locked-on to a prey item, sharks seem to come out of nowhere, and though they can be quite gentle with their jaws (as on occasions when they are unsure about whether something is food or not) their ranks of serrated teeth can inflict a devastating amount of damage. They are not the cruel, vicious, or bloodthirsty villains they have often been portrayed as, but instead are exquisitely-adapted predators which rely on their ability to catch and consume a variety of prey. And, just as it is among present day sharks, so it was among their prehistoric relatives.

Between 19 and 8 million years ago Maryland’s Calvert Cliffs were covered by the ocean. Those shallow waters were inhabited by at least fifteen different genera of sharks, and their teeth (typically all that is left of them today) are scattered everywhere along the beaches. Indeed, they are abundant enough that paleontologists Christy Visaggi and Stephen Godfrey recently cataloged of 26,000 of them to determine what kinds of sharks lived off the shores of ancient Maryland and in what numbers.

Their findings, printed in the Journal of Vertebrate Paleontology, reveal that this place was home to a mix of both living and extinct shark genera. There were fossils from Hemipristis (snaggletooth sharks), Galeocerdo (tiger sharks), Carcharias (sand tiger sharks), Carcharhinus (a subset of requiem sharks), and Isurus (mako sharks) in addition to the famous superpredator Carcharocles megalodon, most of which came from the time interval between 19 and 14 million years ago. (Teeth from many other genera, such as those related to whale sharks and great white sharks, were also found, but were so rare that they did not constitute a significantly significant sample.) While not exactly the same as their living relatives, these Miocene sharks would have looked very familiar to us, and clearly the area that would become the Calvert Cliffs was a very productive marine ecosystem which could support such a wide array of predators. Not surprisingly, there was plenty of prey in the water, too. Although not explicitly considered in their study, Visaggi and Godfrey noted that fish, sea turtles, crocodiles, birds, seals, sea cows, and numerous whale species all lived in the same place, and every now and then a specimen of one of these animals is found showing evidence of shark attack.

In a second new paper published by Godfrey and Joshua Smith in Naturwissenschaften, the paleontologists report on one such trace. In this case the evidence is two coprolites (fossil feces) that had been washed out of the Miocene fossil deposits and found on the beach. Exactly what species produced the coprolites is unknown, but after analyzing a third specimen of the same composition found nearby the scientists determined that it had been produced by a carnivorous vertebrate other than a shark. A crocodile seemed to be a likely candidate, but the thing that made the paleontologists undertake this analysis in the first place was that the fossil feces showed characteristic tooth marks; one of the coprolites had been bitten into and the other had been severed. (You don’t often see lines like “This tooth penetrated the feces to a depth of about 3 mm.” in the literature.) A shark had bitten into these feces, but what kind of shark, and why?

Photographs of the coprolites CMM-V-2244 (left, lower surface) and CMM-V-3245. The specimen on the left preserves the tooth impressions of the attacking shark while the specimen on the right was severed (the numbers denote where the teeth cut through the feces). From Godfrey and Smith, 2010.

Elephants always count as star attractions in any zoo or wildlife park lucky enough to have them. But while many visitors may thrill to see such majestic creatures in the flesh, some scientists have raised concerns about how well animals so sociable and intelligent would fare in even the best of zoo environments.

Now, a new study suggests that some of these concerns might be warranted. Ros Clubb from the RSPCA, together with colleagues from various universities and the Zoological Society of London, studied the health of zoo elephants with a census of mammoth proportions.

Concentrating on females, she surveyed 786  captive elephants, representing about half the total zoo population. She compared them to about 3,000 individuals who either live wild in protected Amboseli National Park in Kenya or who are employed by the Burmese logging industry.

The survey revealed incredible differences in the life spans between the captive and wild creatures. On average, African elephants in Amboseli live for about 56 years, while those born in zoos lasted a mere 17 years. Even wild elephants that were killed by humans managed a good 36 years of life. These grim statistics were due to adult females dying much earlier - the death rates among Infant and juvenile individuals were the same in both wild and captive populations.

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For Asian elephants, the picture was similar. Those that worked in natural environments for the Burmese logging industry lived longer, averaging a lifespan of 42 years, compared to a figure of just 19 of their zoo-born peers. In their case, infant deaths accounted for much of the difference made a massive difference and the death rate was twice as high among newborns at the zoo than in those in Burma. 

Clubb thinks that the low infant survival among zoo-born Asian elephants is due to very early events in their lives, possibly even before they leave their mothers' wombs. Indeed, even elephants that are captured from the wild (usually at the age of 3-4 years) have higher life expectancies than those born to captivity.

Things have certainly improved. Clubb found that in recent years, the lifespan of zoo elephants had increased, but their odds of dying early were still about 3 times higher than those of their wild cousins. And the poor infant death rates for Asian elephants hadn't improved. Asian elephants are also sensitive to being shuttled around between zoos, particularly if calves are separated from mothers, and such transfers can affect their health up to four years later.

Devielephant.gifClubb points the finger at stress and obesity as the main factors behind the earlier demise of zoo elephants. The problems highlighted in this survey back up a large amount of anecdotal evidence. In 2002, the RSPCA conducted a review of European zoo elephants, which found worrying rates of herpes, tuberculosis, lameness and infertility and of adults killing calves. And zookeepers are well aware that, unlike many other animals, elephants cannot be kept in captivity with enough success to create self-sustaining populations - new individuals need to be brought in from elsewhere.

If this new study is to be believed (and it will undoubtedly provoke strong responses from zoos), the biggest remaining question is whether the benefits to keeping elephants in zoos, in terms of both education and conservation, are large enough to justify the costs that such homes could exert on their health? It would also be interesting to see a deeper study looking at the extent to which the quality of a zoo affect an elephant's lifespan. Put simply, there are zoos and then there are zoos.

Reference: Science 10.1126/science.1164298

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The coprolite that had been severed, given the label CMM-V-3245, was not especially helpful in identifying the biter, but the other coprolite (CMM-V-2244) preserved a row of tooth marks. The scientists made a silicone cast of the impressions to see if the punctures held any clues as to the identity of the biter. What they found was that the animal that had made them had a single row of asymmetrical teeth, and while there were as many as eight shark genera with this characteristic, most of these were deemed “innocent” on the basis of anatomical peculiarities. The best fits for the tooth marks were the genera Physogaleus and Galeocerdo (which, in fact, might be synonymous), sharks that, like their living relative the tiger shark (Galeocerdo cuvier) possessesed asymmetrical teeth in the shape of a bent A.

With the list of potential culprits successfully narrowed down Godfrey and Smith were left with the question of how the bite marks had been made. Even though coprolites are relatively common at the Calvert Cliffs site, no one had ever found a shark-bitten piece of shit before, so they had no other reference to go by. They ultimately settled on several possible scenarios.

The simplest explanation was that the shark (or sharks) which left the marks had been intentionally trying to eat the feces. “From the curvature of the toothmarks and their positions on the specimens,” Godfrey and Smith write, “we reason that the majority of the fecal masses were in the sharks’ mouths.” Yet, strangely, the coprolites were not ingested. Even though tiger sharks have often been cast as indiscriminate when it comes to food there has been no indication that they have ever deliberately eaten feces, and so the authors looked for a different explanation.

A restoration of a "tiger shark" (either Galeocerdo or Physogaleus) attacking a crocodile. The shark could have left impressions of the feces inside the crocodile during this stage of the attack or after the viscera of the crocodile had become exposed. The restoration was created by Tim Scheirer, the premier artist when it comes to restorations of the fossil animals of the Calvert Cliffs. From Godfrey and Smith, 2010.

Blogging on Peer-Reviewed ResearchWhen normal bacteria are exposed to a drug, those that become resistant gain a huge and obvious advantage. Bacteria are notoriously quick to seize upon such evolutionary advantages and resistant strains rapidly outgrow the normal ones. Drug-resistant bacteria pose an enormous potential threat to public health and their numbers are increasing. MRSA for example, has become a bit of a media darling in Britain's scare-mongering tabloids. More worryingly, researchers have recently discovered a strain of tuberculosis resistant to all the drugs used to treat the disease.

New antibiotics are difficult to develop and bacteria are quick to evolve, so there is a very real danger of losing the medical arms race against these 'super-bugs'. Even combinations of drugs won't do the trick, as resistant strains would still flourish at the expense of non-resistant ones. Antibiotic combos could even speed up the rise of super-bugs by providing a larger incentive for evolving resistance.

Clearly, fighting the rapidly evolving nature of bacteria is a dead end. So Remy Chait, Allison Craney and Roy Kishoni from Harvard Medical School used a different strategy - they changed the battle-ground so that non-resistant bacteria have the advantage. And they have done so using the seemingly daft strategy of using combinations of drugs that work poorly together, and even those that block each other's effects.

The trio looked at two strains of the common bacteria Escherichia coli - one that was normal, and another that was resistant to doxycycline. Doxycycline is widely used to fight off a variety of bacterial invaders, but resistant E.coli use a specialised molecular pump to remove the drug. It can withstand 100 times more doxycycline than its normal counterparts.

First, the team hit the two strains with doxycycline and erythromycin, a combination of drugs that work particularly well together and enhance each other's effects. The resistant strain was certainly more vulnerable to this double-whammy, but as expected, it always outperformed the normal bugs. With that advantage and enough time, it would inevitably evolve resistance to both drugs.

But Chait managed to remove this evolutionary impetus by combining doxycycline with a third drug, ciprofloxacin, a combination that would normally be useless. Doxycycline actually blocks the effects of ciprofloxacin, and the two drugs together are weaker than either alone. Predictably, the resistant bug did what it had evolved to do - it pumped out doxycycline. But in doing so, it also unwittingly removed the block on ciprofloxacin, restoring this second drug to its full killing power.

To fight bacteria like MRSA, we need new strategiesThe normal strain encountered no such problem. By leaving the drugs alone, it never faced the full effects of either, and out-competed their more heavily-pummelled resistant cousins.

Chait cautions that it's too early to transfer his findings across to hospital beds. The experiment used non-lethal antibiotic concentrations in a very controlled environment. But they have certainly pointed other researchers down a new and interesting path.

Combinations of drugs that block each other have previously been dismissed by doctors because they would require higher doses. But Chait's study suggests that they could be the key to controlling bacterial drug resistance. We clearly can't stop bacteria from evolving, but we can certainly steer the course of that evolution in our favour.

Reference: Chait, Craney & Kishony. 2007. Antibiotic interactions that select against resistance. Nature 446: 668-671.

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Another possibility was that the shark bit the coprolites to see if they were palatable. Sharks have been known to tentatively bite objects for this reason, yet if the shark in question did so, the authors noted, the bite marks would have been deeper on both sides of the coprolites (particularly CMM-V-2244). Hence the authors favored a different scenario. The pattern of the bite marks and the fact that the feces were not ingested is consistent with a reconstruction in which, during an attack on another animal, the shark either bit through the body wall and guts to leave the tooth impressions or bit the intestines after disemboweling its prey. Such an attack would have left tooth marks on the feces, which probably fell out of the intestine shortly afterward, hence “In this scenario, the shark chose not to eat the feces, which drifted away, settled out of sight, or otherwise avoided attention.”

Unfortunately there is not enough information to know for certain how the coprolites from the Calvert Cliffs came to be bitten, but another discovery made on another continent is a little more straightforward. As reported in the latest issue of Palaeontology, scientists Giovanni Bianucci, Barbara Sorce, Tiziano Storai, and Walter Landini took another look at the exceptionally-preserved remains of a 3.8-3.1 million year old dolphin Astadelphis gastaldii which had been discovered in Italy during the late 19th century. Though long-forgotten, this particular specimen was significant as its bones were lacerated by the teeth of a large shark (thought to be a great white by the naturalists who originally examined it), and the team of researchers went back to these bones to see if they could reconstruct what had happened to the dolphin.

Signs of a shark attack; bite marks on the 6th-11th ribs on the left side of the Astadelphis gastaldii skeleton. This damage would have been done by the shark's lower jaw. From Bianucci et al, 2010.

Blogging on Peer-Reviewed Research In Shark Bay, off the Western coast of Australia, a unique population of bottlenose dolphins have a unusual trick up their flippers. Some of the females have learned to use sponges in their search for food, holding them on the ends of their snouts as they rummage through the ocean floor.

To Janet Mann at Georgetown University, the sponging dolphins provided an excellent opportunity to study how wild animals use tools. Sponging is a very special case of tool use - it is unique to Shark Bay's dolphins and even there, only about one in nine individuals do it. The vast majority of them are female. A genetic analysis revealed that the technique passes down almost exclusively from mother to daughter, and was invented relatively recently by a single female dolphin, playfully named "Sponging Eve".

Dolphins tend to sponge only in deep water, which is why little has been done to study this behaviour since its discovery a decade ago. Now, Mann has published the first detailed analysis of dolphin sponging. She watched every dolphin who knows the technique and analysed how much time they spent on it and what it meant for their success at raising calves. This incredibly thorough analysis revealed that sponging dolphins are the most intense tool-users of any animal, except for humans.

Mann confirmed that the dolphins were using the sponges to root out potential meals. On days when the sea was exceptionally clear, she could see the animals swimming slowly along the sandy bottom while wearing their spongy muzzles and disturbing the sand. When they spotted something, they dropped the sponge and probed about with their beaks, often surfacing with small fish that they quickly swallowed. Meal in throat, they retrieved their unusual hunting aid and started again.

The technique worked for humans too. Mann's team tried it themselves for four hours with sponges over their hands, and consistently ferreted out the same species of fish - the spothead grubfish. Before the sponges were used, the fish were completely invisible to the divers but once revealed, they were easily spotted, tracked and found again when they reburied themselves. A single photo of a sponging dolphin with a fish in her mouth, while blurry, suggests that they too could be after grubfish.

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Mann thinks that sponging has allowed dolphins to effectively hunt for elusive prey in a difficult environment - deep water channels. There, female dolphins are relatively rare and about half of those who are present are spongers, suggesting that it's not the best habitat for a dolphin unless it devises some cunning tricks.

The sponges are clearly important to dolphins, for they will carry them around for later use. Indeed, Mann found that these specialists did little else in the way of hunting, using their sponges for 96% of their foraging time. The quest for food also consumed almost half of their time, while most other dolphins typically spend about a third of their time foraging.

Even if you just consider the time that they spent actively using sponges, Mann estimates that the spongers spend 17% of their waking hours on this one activity, which makes them the most intense tool-user of any animal, save us humans. The runner-up - the Galapagos woodpecker finch - spends just 10% of its active life using tools and chimps and orang-utans spend a measly 3% of their time. Mann suggests that these other species have more diverse diets that they can acquire through a range of means, while the sponging dolphins have learned to become specialist grubfish-hunters.

Bottlenosedolphinas.jpgSpongers are also more solitary than the average bottlenose, spending more time alone and having fewer associates than other adult females. But this extra investment in foraging didn't cost them anything in the long run though, for their success at raising calves was the equal of their peers.

Female dolphins were far more likely to pick up sponging than males and they did so at a much younger age, even before they had been weaned from their mothers. Mann used her knowledge of the dolphins' family trees to show that the behaviour is mainly passed down from mother to daughter. In over 2,000 hours of observation, Mann never saw the child of a non-sponger use the technique. In contrast, at least half of the children of sponger females learned how to do it.

Mann thinks that this bias exists because females are more likely to stick within the same areas as they grow up, and benefit from picking up the tactics of their mothers. Male dolphins roam more widely as they mature and need to focus on setting up long-term alliances - they cannot afford to learn a specialised procedure that could limit both their range and their social time. There's actually a similar pattern in chimps, where females are more likely to learn foraging techniques such as "fishing" for termites using sticks.

But why then is the technique limited to family lines? Why don't other females learn it from their peers? Mann thinks that it's because daughter dolphins have a stronger tendency to copy their mothers than other dolphins do. And since the spongers tend to be more solitary anyway, their children may be the only ones to see enough of the behaviour to be able to copy it successfully.

The statistics back that up - in 83% of the sponger sightings, the animal was either alone or accompanied by a daughter or mother, while in just 6% were they accompanied by a non-sponger. Sponging, then, is an all-or-nothing behaviour - learning it is too complicated and restrictive for any individual that lacks the time and impetus to do so.

There are probably many other undiscovered dolphin behaviours that fit the same pattern. These animals are highly intelligent, adaptable, and can survive in a broad range of ocean environments. They also have a prolonged infancy when they spend a lot of time with their mother and are extensively exposed to her own peculiar quirks. Together, these traits conspire to shape an animal that is very likely to evolve a myriad of different cultural traditions.

Reference: Janet Mann, Brooke L. Sargeant, Jana J. Watson-Capps, Quincy A. Gibson, Michael R. Heithaus, Richard C. Connor, Eric Patterson (2008). Why Do Dolphins Carry Sponges? PLoS ONE, 3 (12) DOI: 10.1371/journal.pone.0003868

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Like the scientists working with the geologically older Calvert Cliffs material, one of the first steps in reconstructing the events was determining what kind of shark had bitten the skeleton. There was a diversity of large genera, both living and extinct, to choose from, but the marks seemed most consistent with those of a large shark with pointy, unserrated teeth, with the top contenders being Cosmopolitodus hastalis and its still-living relative Isurus oxyrinchus (the shortfin mako). To test this idea the researchers used teeth from both these sharks to make cutmarks on plasticine, but while the marks seemed to be consistent with the damage seen to the dolphin skeleton it was difficult to distinguish between the damage caused by each type of tooth. Likewise, even though the maximum height of Cosmopolitodus hastalis teeth was three millimeters higher than the tallest shortfin mako teeth, this alone was not enough to distinguish between the marks the two species might have left on the bone. The apparent size of the shark involved makes Cosmopolitodus hastalis a seemingly better candidate, but there was no way to tell for sure.

Nevertheless, the numerous toothmarks on the jaw, vertebrae, and ribs of the Astadelphis specimen confirm that it had been bitten by a large shark with smooth-sided, sharp teeth. Now the question was whether the bones recorded an actual hunting event or were the result of a shark scavenging an already dead dolphin. As the scientists discovered, there were traces of both types of feeding.

Sequence of a shark attack. The shark approaches from behind (A), bites the dolphin on the right side (B), and bites it again behind its dorsal fin (C). From Bianucci et al, 2010.

Blogging on Peer-Reviewed ResearchThe Humboldt squid is not an animal to mess with. It's two metres of bad-tempered top predator, wielding a large brain, a razor-sharp beak and ten tentacles bearing 2,000 sharp, toothed suckers. It cannibalises wounded squid, and it beats up Special Ops veterans. But over the next few years, the Humboldt faces a threat that even it may struggle against, one that threatens to deprive it of the very oxygen it needs to breathe - climate change. 

Humboldtsquid.jpgThe Humboldt squid (also known as the jumbo squid) lives "chronically on the edge of oxygen limitation". Through an unfortunate combination of physiology, behaviour and environment, it has an unusually high demand for oxygen and a short supply of it. Its survival is precariously balanced and changes to local oxygen levels brought on by climate change could be the thing that tips them over the edge. 

For a start, the Humboldt needs a lot of oxygen compared to a fish of equal size. It is incredibly active but it relies on jet propulsion to get around, a relatively inefficient method compared to fins or flippers. Worse still, a fluke of physiology means that the squid's blood has a surprisingly low capacity for oxygen compared to equally active fish. And every time it circulates round the body, whatever oxygen there is gets completely used up with nothing left in reserve.

Unfortunately, supply doesn't always meet demand. Their home in the Eastern Tropical Pacific already has some of the highest temperatures  and lowest oxygen levels in the oceans. The middle depths are particularly low in oxygen and every day, the squid migrate through these "hypoxic zones", rising vertically from the ocean's depths to the oxygen-rich waters of the surface.

But these zones are expanding. As global warming takes hold, the seas will warm, dissolved carbon dioxide will render them more acidic and their oxygen levels will fall. It has already begun - climate scientists have found that over the past 50 years, the low-oxygen zones of the eastern tropical Atlantic Ocean have expanded vertically, to cover a taller column of water. In doing so, the squid's range is being squeezed into an ever-narrower area.

Humboldtsquid.jpgRui Rosa and Brad Seibel from the University of Rhode Island tested the Humboldt's ability to cope with predicted climate change, by capturing 86 live squid and putting them through their paces in special tanks aboard their research vessel.

Rosa and Seibel found that the squids use up more oxygen than almost any other marine animal. Even their lowest metabolic rates are higher than those of sharks and tuna. However, they are also capable of slowing their metabolism down by about 80% in order to cope with a dearth of oxygen.

It's a very useful ability - without it, the squid would need to take more "breaths" and because they do that by contracting their large muscular bodies, their oxygen demands would rapidly escalate to unfeasible levels. Tuning down their metabolism also allows them to cope with conditions that put off other fishy predators and allows them to dive into far deeper and colder waters. But they can't keep it up forever. After a while, anaerobic respiration depletes their reserves and builds up toxic chemicals (like the lactic acid that accumulates in our muscles). They eventually need oxygen and they rise to the surface to get it.

To see how the changing ocean environment would affect these animals, Rosa and Seibel exposed their captive squid to and range of different temperatures, oxygen levels and carbon dioxide levels, including the most pessimistic predictions of the Intergovernmental Panel for Climate Change for 2100.

They found that the squid struggle to cope with a combination of less oxygen, more carbon dioxide and higher temperatures. Being cold-blooded, a squid's internal temperature is very tied to its environment and warmer waters cause its metabolism and need for oxygen to rise to unsustainable levels. If its home waters warm by 2 to 3C, as predicted by the end of the century, it risks incurring an "oxygen debt" that is can't repay.

Unfortunately, the increasingly acid oceans will also hit its ability to carry oxygen in its blood, and that in turn will limit how fast and active it can be. Its changing environment risks making the Humboldt a poorer hunter and an easier catch.  The expanding oxygen-poor zone in the ocean's middle layers will also squeeze them into ever tighter ranges and could even create an invisible ceiling that prevents them from accessing the shallow waters at night.

Rosa and Seibel fear for the Humboldt's ability to cope with these changes, and for what that could mean for other animals. The Humboldt is an important species - it has recently expanded its range to areas where overfishing have removed other top predators such as sharks, and it provides food for many bird and mammal species, including humans. Similar animals, whose lives are a fine balancing act, may soon number among the many casualties of our changing climate.

Reference: R. Rosa, B. A. Seibel (2008). Synergistic effects of climate-related variables suggest future physiological impairment in a top oceanic predator Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.0806886105

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Based upon observations of damage done to large prey by living sharks, the authors of the study propose that a large shark killed the dolphin. As indicated by the deep cuts on the dolphin’s rib bones it appears that the shark attacked the dolphin from behind and to the right. The dolphin struggled to get away, causing further trauma to the flesh and bone, and there is little doubt that after the initial bite the dolphin would be suffering catastrophic blood loss. As it died it appears that it may have rolled over onto its back, and at this point the shark bit again just behind its dorsal fin (leaving a second set of bite marks along the vertebrae). Then the shark probably began to feed on the dolphin’s soft tissues, and the array of other small scrapes and marks on the ribs and jaws of the dolphin would have been inflicted by smaller scavengers who picked at the remains after the attacking shark had finished. In the ocean, bodies do not go to waste.

(Alternatively, the bite marks could represent the scavenging of a large shark which was consuming an already-dead dolphin. Distinguishing between predation and scavenging in the fossil record can be extremely difficult, and while the attack scenario is more dramatic, a scavenging event cannot be ruled out.)

Together the discoveries from Maryland and Italy provide scientists with narrow, but very informative, windows into the distant past. They remind us that fossils are not just inert remains. They are the last vestiges of living creatures and every single fossil, from the most common shell to rare treasures like shark-bitten croc poop, tell us about what ancient life was like. We cannot answer all the questions we have, but discoveries such as these allow us to reconstruct the past in way usually only possible in our imaginations.

CHRISTY C. VISAGGI and STEPHEN J. GODFREY (2010). VARIATION IN COMPOSITION AND ABUNDANCE OF MIOCENE SHARK TEETH FROM
CALVERT CLIFFS, MARYLAND Journal of Verterbrate Paleontology, 30 (1), 26-35

Godfrey, S., & Smith, J. (2010). Shark-bitten vertebrate coprolites from the Miocene of Maryland Naturwissenschaften DOI: 10.1007/s00114-010-0659-x

BIANUCCI, G., SORCE, B., STORAI, T., & LANDINI, W. (2010). Killing in the Pliocene: shark attack on a dolphin from Italy Palaeontology, 53 (2), 457-470 DOI: 10.1111/j.1475-4983.2010.00945.x

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