The Mystery (or not) of the Megafauna

Between 50,000 - 10,000 years ago over 90 genera and many hundreds of species of megafauna went extinct in what have become known as the Late Quaternary Megafaunal extinctions. Megafauna, or for our purposes large mammals weighing over 44 kg, lived around the globe on all continents except Antarctica but today they persist only in Africa. The causes for this dramatic decline in species over a relatively short window of time is a contentious topic which has two polar ends: humans and climate. Some papers argue that humans were the overriding factor through a variety of impacts such as hunting and habitat destruction, whilst others maintain that climate change was the real killer.

Some of the Quaternary Megafauna; Source.

The megafauna were more vulnerable to extinction than other animals, which is in part why they suffered such extreme losses, whether they be from humans or climate. In general, animals of a large size are more vulnerable to extinctions due to larger ranges and lower population densities. Johnson argued, however, that is was not size but a slow life history (slow reproductive rates and few young) that made the megafauna more susceptible to extinctions. Due to the fact that they have long lives (and therefore later sexual maturity) and relatively few young, they are more vulnerable to sudden changes in climate and habitat because it takes longer for generations to pass and therefore longer for the species to adapt to these changes. This supports climate causes over human, as hunting hypotheses focus on body-size. Johnson also found that those alpine, arboreal and nocturnal species with lower reproductive rates experienced less extinctions, likely due to their reduced exposure to humans but there is no clear link to climate.

Barnosky et al. conducted a review of the evidence from a variety of fields. They found that in some areas, such as Eurasia and North America there was strong evidence that humans contributed to the extinctions but also that pronounced climate change had a significant role. In Australia, humans were almost exclusively responsible for the loss of 21 genera whilst there was scarce evidence for the influence of climate. In other areas of the world, South America and Africa, there was not sufficient evidence to make a judgement on the causes of the extinctions, despite the fact that South America experienced the greatest species loss of any continent. In Africa, there is a very low number of genera lost in comparison to other continents. Why? This is yet another unanswered question but we think it is due to coevolution of humans alongside the megafauna.

Assessment of causes of extinction on each continent; Source.

There are various hypotheses for human caused extinctions, but I will briefly discuss the most common ideas. 

1. Blitzkrieg

Whilst this is now considered somewhat outdated by most scientists, one of the first ideas about the loss of megafauna was that humans had hunted them to extinction at such a rapid rate that their populations did not have a chance to recover. First proposed by Martin, the hypothesis assumes that as the animals had not encountered humans before, they would naively not be afraid of them and therefore easily hunted. Martin sought to provide explanation for the fact that there were so few archaeological sites containing extinct megafaunal remains, as the hypothesis put the extinctions within the space of 500-1000 years so interactions between humans and extinct species would have been brief. There are, however, a number of issues with this hypothesis. There is a severe lack of archaeological sites where large mammals are associated with stone tools and Barnosky et al state that when the entire breadth of climatic and archaeological evidence is considered, that blitzkrieg scenarios can be firmly rejected in western Europe, Siberia, Alaska, and probably Australia and central North America. Additionally, Wroe et al. among others argued that prey naivete would not have been sufficient for blitzkreig, as this is really not how animals work - prey quickly learn to flee from new predators. Whilst we know that hunting and predation by humans did have an impact on populations, and of certain species in particular, we know fairly certainly that it was not a blitzkrieg.

2.Sitzkrieg 

The wittily named Sitzkrieg hypothesis refers to the slower, sometimes indirect impacts humans would have had on megafaunal populations other than directly hunting them. This includes habitat loss and fragmentation, use of fire, and the introduction of foreign species and diseases. This has proven difficult to quantify as, for example, we cannot pinpoint whether charcoal comes from human or natural fire events and it is also difficult to know the extent of habitat loss. We have seen in island communities that 'sitzkrieg' style events have caused extinctions through multiple effects and synergy with hunting. For example, black rats as a human introduced species have caused extirpations in island communities, but this has not been replicated on mainland. Some suggest a hyper-disease hypothesis in which extinction is a result of hyper-virulent diseases to which the native species have no resistance. Again, there is a lack of evidence to support this - we do not actually know of any such extremely lethal cross species pathogens, for example. In their review, Koch and Barnosky find that none of the indirect sitzkrieg models make strong predictions regarding the megafaunal extinctions. Of all, the factors, habitat alteration seems the most likely culprit but it is unlikely any sitzkrieg parameters were dominant causes of the extinctions.

Hyper-disease, plausible or silly?; Source.

As for environmental hypotheses, climate change is the prevailing theory but there are also some other weird ideas out there.

1. Climate change

Throughout the last 50kyrs, there has been a lot of fluctuation between warm and cold events in the climate, known as Dansgaard–Oeschger (D-O) events (rapid warming events) and Heinrich events (cold events).  These events are likely to have caused abrupt shifts in temperature and precipitation which would destabilise habitats and species ranges. In a recent paper, Cooper et al identified that many extinctions seem to coincide with D-O events, shown in the graph below. Additionally, Gill et al found that Sporormiella (a dung fungus associated with large herbivores) declines in correlation with D-O events and overall gradually throughout the period, contrary to the aforementioned blitzkrieg ideas. The other trend we see is a gradual warming from the last glacial maximum (26.5kya) to the Holocene (11 kya), after which temperatures remain relatively stable. This warming would have caused major ecological changes, in particular the reduction of tundra biome and taiga forests reaching further north. Some species, such as mammoths, were not adapted to these warmer, wetter forests and would have suffered from a decreased range and were likely unable to keep up with a shifting habitat due to their large size and slow reproductive cycles.

Light grey bars represent interstadial warming events and have a marked association with extinctions; Source

2. A comet?

The Younger Dryas impact hypothesis suggests that a barrage of meteorites hit the ice sheet in North America and created instability and caused the onset of the Younger Dryas. However, this is widely discredited as we have evidence (such as Gill's sporormiella) that tells us the megafaunal extinctions were not clustered around or after 12.9kya when the impact occurred. The event itself is disputed due to lack of typical bolide indicators found in sediments from that time. So, not really anything to write home about, but just letting you know what's out there. ;)

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In summary, as shown in the original graph by Barnosky et al, the evidence points towards a mix of human impacts with a background of climatic events as the drivers of megafaunal extinctions across the Northern Hemisphere Whilst the jury is still out for most of the Southern Hemisphere, Australian extinctions appear to be very closely related to human impacts, with little climatic correlation. We have a good understanding of what happened to many of these genera, as shown by the number of green circles representing 'robust evidence' in Barnosky's graph, but there is still room for improvement, particularly for understanding what happened in South America and Africa. It would be interesting to hear your opinions on all this, particularly if you disagree with anything I've said! As always, questions and debate and welcomed in the comments section.

Worrying Predictions for the Amazon

Earlier in the week, a massive review paper was published by 170 authors from 102 affiliated institutions. The paper estimates and assesses the extinction risk of over 15,000 Amazonian tree species and produced the fairly alarming figure that 57% of them qualify as globally threatened under IUCN Red List criteria. Furthermore, they predict that the trends observed in Amazonia apply to tree throughout all tropical biomes and that likely over 40,000 tropical tree species worldwide would  qualify as globally threatened on the same criteria. The study has gained quite a bit of media attention for its 'shocking' claims that over half of Amazon tree species are going extinct, including coverage in mainstream news outlets such as the BBC and The Guardian. As we discussed in Part 3 of the 6th Mass Extinction, this can be an important way of communicating the severity of anthropogenic extinctions to the public.

Closer examination of the paper, however, reveals that some of its claims are not quite as dramatic or eye-catching as the media would make out. The 57% figure comes from Business as Usual (BAU) scenario which estimates that by 2050 40% of the original Amazon forest will be destroyed. BAU is commonly considered "worst-case-scenario" in environmental models, so we cannot take this as what will happen. An improved governance scenario (IGS), which estimates forest loss by 2050 at 21%, suggests that only 36% of species will be threatened. This is perhaps a more realistic (hopefully) estimation, as we know that governments and international bodies are working towards improving management and conservation of tropical ecosystems.

Results of the new study, showing the severity of a BAU scenario; Source.

Importantly, the paper highlights the urgency with which we need to address these projected losses in order for them to be prevented. It shows that protected areas in the Amazon are likely to be a successful way to protect populations if these areas to do not suffer further degradation. Clearly, improved governance has the potential to reduce species loss dramatically within the next 35 years, and this paper and the message it carries has come just in time to help highlight this at the COP21 later this week.

Are We Mass Murderers? Earth's 6th Mass Extinction - Part 3: Implications

The third and final entry in my discussion on whether or not we are entering a 6th mass extinction event. In this post, having got all the complicated stuff out the way, I will be discussing the societal implications of the 6th Mass Extinction as a concept and also the message we need to be taking away from this research, regardless of a definitive 'yes' or 'no' answer to the question. I hope you've enjoyed the journey and I would be really interested to know if your opinion on the 6th MEE has changed throughout it, let me know in the comments :)

If you missed them, check out Part 1 and Part 2!

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The results of the poll that you, my lovely readers, have been partaking in over the last few weeks show that really, we're all a bit confused about what's going on but we know it's something significant. To be fair, I think that quite adequately sums up how the academic community feel as well. There are a lot of big unknowns and uncertainties in the data, as discussed in the previous post, which have led to a lack of definite answers about extinction rates and extinction magnitude. Some of this can be improved by collecting more data on currently understudied groups, especially invertebrates - reminder that only 1% of bivalves have been assessed by the IUCN! However, there are many, many unsolvable issues with fossil data as every good palaeontologist knows, we can extrapolate and model and adjust for bias to our hearts content, but there are some species we will never know about and we will never know exactly what happened to them and their relatives. There are inherent problems with comparing data gathered in completely different ways and from animals in different states of existence, so perhaps the question is simply one we cannot easily answer. I pose a new question to you - does this actually matter? Does it matter that current extinction rates don't quite fit with the technical definitions of a mass extinction? We are well aware from the data of the abnormality of current extinction rates in comparison to natural variability through time, and well aware that we hold the majority of the blame for this. Do we need a dramatic title for it?

Your votes! Homegrown data.

In some ways, the answer is yes. It's a kind of depressing yes. If you Google "6th Mass Extinction", you will be greeted by a plethora of sensationalist news articles claiming that the 6th MEE has begun , and more importantly, will humans survive it?! Humans tend to care more about things when humans are involved, as we have demonstrated time and time again throughout history. If we look in the comments on some of these articles, readers actually don't seem to be getting the message that we need to change our collective behaviours. See the enlightened comment below from a Daily Mail reader, sporting the 2nd highest amount of up votes on the article:

"Whatever changes the climate may experience, the consequences will pale into insignificance compared to the catastrophe resulting from massive unrestrained population growth in the developing world. Open borders will make this our problem too"

Bringing it back to humans, with a hint of UKIP. Daily Mail readers aside, if you ask anyone in the street, they would probably say that of course they are aware of humans causing extinctions, but do they understand the extent of the problem? Probably not. Education, if you can call it that, through sensationalism is one way to get the message to the wider public. However, as the above shows, we need to be doing this in a more effective way. If scientists did agree on a technically defined or supported 6th MEE, then perhaps it could be something that got more serious journalistic attention and much needed political attention. Social scientists have suggested that "inadvertant envrionmentalism" is the way forward, as often there is a gap between our values, however sincere, and our actions. They advocate that government policies, such as limiting deforestation in this instance, as they have the power to change behaviours without the need for values. This is one way in which mainstream attention to a dramatically definite 6th MEE has the power to help. If we want to be more optimistic and think about changing values via awareness, Racing Extinction and the #StartWith1Thing campaign is great example that again relies on the sensationalism associated with the 6th MME (The working title of the film was 6!).

Sensationalist and melodramatic representation of the 6th MEE, could it be useful?; Source.

In others, the answer is no. In light of the sheer numbers of species lost, and the potential there is for that to increase in coming years, what we need to be thinking about are urgent conservation measures. As multiple papers have highlighted, the extinction rates and magnitude is likely to increase as years, and harmful anthropogenic practices, continue. In particular, Barnosky et al. highlight the destructive potential  for synergy between co-occurring environmental factors such as atmospheric composition and unusual climate dynamics, similar to how co-occurrences of bolide impacts and flood basalt volcanism have interacted dangerously in the past. Without mitigation of these unnatural factors, particuarly pollution and CO2 levels, extreme ecological stresses will be placed upon most living species, especially given the feedback of individual stressors. Ceballos et al. point out that, in human timescales, the loss of these species and the ecosystems services they provide would be effectively permanent. They argue, as do Barnosky et al, that avoiding a biodiversity crisis (regardless of what it may be called) requires rapid and greatly intensified efforts to alleviate pressures on endangered species and protect them from exploitation. Many of the pressures are intrinsicly related to population growth and economic inequalities, and have the potential to threaten humans alongside other species.

Are we going to run ourselves into the ground? Let me know your thoughts in the comments!; Source.

In summary, it is debatable whether or not the 6th Mass Extinction being confirmed matters, but there is one thing that isn't debatable, and I will leave this as a closing thought for you:

The window of opportunity to act is rapidly closing and with the COP21 talks starting in under a week, it is imperative that we are mindful of the extent to which we have affected global biodiversity and will continue do whilst CO2 levels continue to rise and corporate greed is placed above moral concerns.

Racing Extinction

Exciting news and a date for your calenders - On the 2nd of a documentary called Racing Extinction will première on the Discovery Channel, which had a première in New York on Friday. The documentary is focused on the anthropogenic impacts to biodiversity and the potential of a man-made extinction event, (6th Mass Extinction, anyone?). It takes a hard look at the international wildlife trade and shows covert footage of illegal trade in endangered species. The documentary aims to educate and inspire people to act and help prevent further species loss by embracing the solutions that will ensure a thriving planet for future generations - and the trailer will get you pretty excited for it!

Their website is a great interactive resource to educate yourself about your impact and what you can to do "Challenge Yourself" and lead a more environmentally friendly lifestyle. I highly encourage you to check it out and sign up for some of their challenges. Their tag - #StartWith1Thing - is "a call-to-action to each and every one of us across the globe to make small changes in our lives that will have a huge impact on the world". They want people to make a start with 1 thing, no matter how small, to make a difference to species loss and use the hashtag on social media to encourage their family and friends to do the same. I think it's a great idea and I will be 'blasting' it out, as recommended, on the 2nd December when the documentary airs - I hope to see some of you doing the same!

Are we Mass Murderers?: Earth's 6th Mass Extinction - Part 2: The Debate

Apologies for the delay between posts, but welcome to the highly anticipated Part 2 of the 6th Mass Extinction debate. In this post I will be discussing whether the current rates of extinction warrant being promoted to an Anthropogenic 6th MEE. Hopefully I will be able to give you a flavour of both sides of the debate and would be really interested to hear your thoughts and opinions in the comments! Don't forget to vote in the poll (right hand side), especially if your opinion has changed.

If you missed Part 1, catch it here.

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The question of whether this is the Anthropogenic 6th Mass extinction event is a contentious topic. If scientists decide that we are indeed in a 6th mass extinction, it would be a profound social statement and thus requires careful consideration before a decision is reached. As you will see, there is not quite a clear answer yet. Humans have been responsible for extinctions though activity such as habitat destruction, pollution, hunting and simple carelessness for many centuries, and some scientists argue that the 6th Mass Extinction encompasses the last 10,000 years and even as far back the Late Quaternary megafaunal extinctions (but whether or not those are anthropogenic is a debate for another post).

As we saw previously, a mass extinction is typically characterized as a relatively short period of time (geologically speaking) when the Earth loses a significant percentage of species, some suggest the threshold as 75%. This was certainly the case for the 'Big Five' extinctions that were discussed in the previous post, with the End-Permian event, as the biggest MEE in known history, reaching 96% loss of species. In a review paper published in Nature, Barnosky et al. compiled the below graph assessing modern extinctions in relation to the proposed 75% benchmark. It is clear that for most orders, modern extinctions do not reach anywhere near the required 75%. That does not, however, mean that the answer to our question is a 'no'. There are a plethora of data issues associated with fossil species estimates (Sampling bias, preservation bias, etc.), notably that most assessments of fossil diversity are done from genus level and calculated using species-to-genus ratios, extrapolating in potentially dodgy territory. There are also many modern taxa that are highly understudied, leaving modern assessments far from adequate for many groups (remember the snails?) - Barnosky et al. point out that only 1% of today's bivalves have been assessed, despite these making up a significant part of most of the 'Big Five' species counts. There also also other issues, such as the use of different species concepts inflating numbers of modern species. Due to this, magnitude estimates rely on theoretical predictions as opposed to empirical data for many species. Equations such as species-area relationships (SARs - have linked for Wikipedia for anyone feeling curious and mathematical) and other ecological models suggest extinctions could be between 21-52% at current. SARs have a whole host of problems associated with them in terms of validity and overestimation (Seriously, I'm not even going to go there), so this is still not terribly useful.

Percentage species loss recorded (white) and threatened (black) for modern orders in comparison to other MEEs; Source.

So really, we cannot reliably use percentage species loss to definitively validate or reject an Anthropogenic mass extinction. The other defining character of a MEE is that extinction rate reaches in excess of 1000x the natural background rate. This is typically expressed as E/MSY or Extinctions per Million Species-years, and the agreed background rate varies between groups of species and through time but on average tends to be 1 E/MSY. Recent and presumably anthropogenicly caused extinction rates have been estimated in various studies but are roughly between 100-1000 pre-human levels or background levels, and has the potential to increase tenfold if we lost all currently threatened species. These studies, in comparison to those only considering magnitude, tend to point towards a 6th Mass extinction event, or at least that we are approaching one. However, just as with the magnitude studies, this does not mean the answer to our question is a simple 'yes'. The major problem with the E/MSY metric is that fossil background rates are calculated on geological time scales, of a million year plus, whereas modern rates are calculated on centennial scales. Extinction rates have the potential, and do, vary immensely dependent on the length of time over which they are measured. We are extrapolating, again, to compare the rates from short timescales to rates from geological timescales and, as Barnosky et al. highlight, the rate is likely either much faster or much slower. Whilst we can definitely say that current rates are definitely higher than average fossil rates, and even above those from the late Quaternary megafaunal extinctions, there is considerable uncertainty within calculated rates. Some argue that they are likely serious underestimates of current E/MSY, but the elevated extinction rates have been unable to solve the debate.

Barnosky et al. were able to look at both of these variables together in a combined rate-magnitude comparison, shown below. The two, they argue, are intimately linked and therefore should be considered together in order to answer the question of whether the the 6th Mass Extinction is comparable to the Big Five. They were able to estimate the extinction rate of each Big Five event if it had hypothetically happened over 500 years, as is time scale of the current data (coloured dots below), which all sit roughly at 1000 E/MSY as expected. They found that the current extinction rates over the last 500 years for all vertebrate groups are at least as fast as and in some cases faster than rates that would have produced the Big Five over millions of years (Vertical lines below). From these results they were able to estimate that current rates may be sever enough to carry extinction magnitude to the 75% threshold within a few centuries. Again there are major unknowns within this data, as to whether the critically endangered and threatened species will go extinct and within calculation of the rates themselves. There could be a significantly different picture shown if invertebrate groups were included, but as previously mentioned, they are heavily understudied so any estimates for them have little meaning.

Complicated diagram but the message is extinction rates are high and on par with estimated precursors rates to the Big Five; Source.

Whilst there is not yet a stratigraphic signal for it, the 6th Mass Extinction or at least an elevated extinction rate is a clear part of the recent history of life on Earth. Numerically speaking, the evidence we have, when considered in the correct way, seems to suggest that although we are not quite at the charateristic 75% and 1000 E/MSY we are far from what should be though of as normal, and possibly not that far from reaching these thresholds. It is up to you to decide whether we have entered the 6th Mass Extinction or not, but it is for all of us to consider the message we need to take away from this: the world's biodiversity faces escalating threats and there is an urgent need for effective conservation measures. This will be expanded upon in part 3, but for now, I'll let you have a breather!

Are we Mass Murderers?: Earth's 6th Mass Extinction - Part 1: The Big Five

This will be the first in a series of posts about the 6th Mass Extinction debate, and will serve as an introduction to Mass extinctions in general and discuss the past 5 Mass Extinction events (MEEs). As someone with a fair knowledge and definite passion for palaeobiology and the history of life on Earth, I hope that I can share some of my interest with you all in this post! In my opinion, understanding the past can be the key to understanding the present (Uniformitarianism and all that jazz), but as Geographers we never really consider what Geologists call 'Deep Time' - aka stuff way, way, way before humans were even close to existing. So, if you're new to all this, I hope you enjoy a brief introduction.

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Whilst the fact that humans have had dramatic impacts to biodiversity and caused many extinctions (local and global) is relatively undisputable, the question of whether this is the Anthropogenic 6th Mass extinction event is a contentious topic, as we are to discover. However, this post, as I said, will serve to provide some background information on past MEEs so that we have something to compare a potential 6th Mass Extinction  to, in order to make an informed decision.

Officially, there are 5 MEEs that have taken place throughout the 4.5 billion year history of the Earth, as originally identified in the somewhat legendary paper by Sepkoski and Raup in 1982. Known as the "Big Five" informally,  these events were times when the extinction rate was massively higher than the background levels and a significant percentage of all species go extinct (Usually at least 70%, though some estimates for the Ordovician-Silurian event go as low as 60%). There are many other extinction events, such as the late Pleistocene Megafauna extinctions, that have taken place in the last 550 million years since the Cambrian explosion (the beginning of complex life), but they do not stand out from background levels significantly enough to be considered 'mass' extinction events. The Big Five, when they were defined, were identified as outliers from a general decline in extinction rates throughout the Phanerozoic (550-0Ma) and this is part of what made them so sensational. However, more recent statistical analysis by Alroy in 2008 has suggested that they are likely just large peaks within a "relatively smooth continuum of extinction events", but nevertheless, I think they're still pretty cool.

The Big Five shown as sudden dips in number of genera through time, Source.

1. Ordovician-Silurian (O-S) or Late Ordovician Mass Extinction
Occuring between 450-440Ma, the O-S event sits at the boundary between the Ordovician and Silurian periods, and is the combination of two events which resulted in the loss of 60-70% of all species which equates to 57% of all genera and 27% of all families. Some scientists rank this as the second largest of the Big Five, in terms of % genera lost. From what we understand, there were two pulses of extinction with a 4 million year gap between them that culminate in the overall extinction event.  The suggested cause for the event is the movement of Gondwana into the southern polar region which led to global cooling and sea level fall, which caused massive shallow water habitat loss along continental shelves. The very waters in which the first complex life had begun to diversity in 100 million year prior. The Trilobites and primitive Brachiopods (clams et al) were among those animals most heavily affected.

A typical Ordovician sea, prior to the MEE; Source.

2. Late Devonian Mass Extinction
The second of the Big Five occurred towards the end of the Devonian period, between 375-360Ma. There is evidence for a prolonged series of extinction pulses causing this event, which wiped out 70% of all species (50% of genera and 19% of families). There is considerable debate over the timespan of this extinction, with estimates ranging between 500Kyr and 20Myr - the jury is still out of this one. The causes of the extinction event or events are equally open to debate between researchers, but some of the strongest evidence points towards rapid sea level fluctuations associated with glaciation. Again, it was marine species that were hardest hit by the event, but the corals disproportionately so, to the point where they were almost entirely wiped out worldwide. The ancestors of the tetrapods (the first vertebrates to reach land) were also impacted, with 44% of high level vertebrate clades becoming extinct, and entire groups such as the Placoderms disappearing (the big fish in the picture below).

There's always a bigger fish...; Source.

3.  Permian-Triassic (P-T) or End Permian Extinction Event
This one is like the slam dunk of the Big Five, claiming the title of THE largest mass extinction of all time, ever. A whopping 90-96% of all species were wiped out by this event, that's 83% of genera and 57% of families. This thing is even called the "Great Dying", literally, everyone died. Although this really sucked for marine animals (RIP Trilobites) and it took the survivors about 10 million years to recover, it left huge vacant niches which allowed the ancestors of Dinosaurs, the archosaurs, to take to the stage and blossom. This event ended the Palaeozoic era and marked the start of the Mesozoic, the Age of Dinosaurs. The causes are still under a lot of debate, but it is likely that there was a catastrophic event involved, such as huge volcanicity in Siberia. Another likely factor is the formation of Pangaea, which had huge implications for climate and ocean circulations.

Trilobites looking pretty, from Haeckel's 'Art Forms in Nature'; Source.

4.  Triassic-Jurassic (T-J) or End Triassic) Extinction Event
One of the smallest of the Big Five, occurred 201.3Ma at the end of the Triassic period, resulting in the loss of 70-75% of all species, 48% of genera and 23% of families. This spelled the end of most non-Dinosaur archosaurs and large amphibians, leaving the way free of terrestrial competition for the Jurassic giants we're all familiar with to radiate. We have very little idea as to what actually caused this event, though it is likely linked, in my opinion, with the start of the fragmentation of Pangaea. Other suggested explanations include the usual culprits: meteors and volcanism.

Prestosuchus, a Pseudosuchid ("false crocodiles") lost at the T-J MEE; Source.

5. The One You've All Been Waiting For
That's right. The End Cretaceous or Cretaceous-Palaeogene (K-Pg) mass extinction event, 65.5 Ma and the infamous end of the Dinosaurs. 75% of all species went extinct (50% of genera and 17% of families), making it relatively small by Permian standards, but yet this is the one we all know and love (or not, depending on how strongly you feel about dinosaurs). All non-avian dinosaurs became extinct as a result of this event, leaving the way for mammals to radiate and become the dominant terrestrial group in the Cenozoic. Birds are the only dinosaurs that survived this event, whilst other reptiles such as crocodiles and turtles managed to pull through as well. This event, possibly due to a large amount of research bias, is probably the only mass extinction event that we can confidently say the cause of. A massive (10-15km wide) meteor smashed into the Earth in the Gulf of Mexico with the force of 100 teratonnes of TNT or over a billion times the energy of the atomic bombs at Hiroshima and Nagasaki combined . The impact triggered a variety of catastrophic events across the globe: radiation pulses, acid rain, massive fires, megatsunamis - the list goes on. The amount of evidence for this (such as the Iridium band) and the causes themselves are really interesting and encourage you to have a look into them further if you have the time! If you prefer the dinosaurs whilst they were alive, BBC's Walking With Dinosaurs never gets old.

"NOOOOOOOOOOOOOOOOOOOOOO"; Source.

So there you have it - the Big Five. We still have a lot to learn about many of these events, a paper published last month suggested that 3 of them were related to mineral depletion, which is a new one. We may never know the whole story, due to the nature of the fossil record and the difficulties associated with inferring things from half a billion year old rock. I hope that you've enjoyed this post and that it's been a nice warm up for the 6th Mass Extinction debate. If you have any questions, please feel free to ask in the comments and if you have any interest in materials/documentaries related to the End-Cretaceous event let me know - I have plenty!

Blog News!

To everyone reading, and who has been reading so far, thank you :)

I'm just making a quick post to announce that I've added a poll regarding your opinions on the contentious 6th Mass Extinction. I have a post in the works about the debate over this, and would like to get your opinions on whether you agree or disagree with it. It will also be interesting if you change your mind after my post, but who knows ;) So please, it only takes a second just to pick and answer! I have left one option as "Other- please comment" if you want to add another answer or just add to the discussion, then please direct the comments to this post, as I don't think there is a comment feature on the poll itself.

Thanks guys! In other news, I have also added a turtle virtual pet after yesterday's turtle themed post. The default name is 'Turby', which is rubbish. Taking name suggestions in the comments on this post - please feel free to feed 'Turby' - but no litter!

As a thank you for completing the poll, here are some cute pictures of some lesser known endangered animals and links to their IUCN pages for anyone who wants to know more <3

Spectacled Bear (Tremarctos ornatus), Vulnerable, Source.

Kleinmann's tortoise (Testudo kleinmanni), Critically Endangered, Source.

Sand Cat (Felis margartia), Near Threatened, Source.

A sad loss and a straw in a nose

Earlier this week, an 813-pound sea turtle was found dead off the coast of Massachusetts, which likely died from injuries caused by marine fishing gear, despite the use of turtle exclusion devices in many commercial fisheries.  The turtle was a leatherback sea turtle (Dermochelys coriacea), which is both the largest living turtle and a spectacular animal that we have reduced the population of, to the point where it is classified as Vulnerable by the IUCN. There is, however, a definite potential for the decline of this and other turtles if we do not step up to the mark in terms of conservation practices and multi-disciplinary approaches.

Aforementioned turtle :(, Source

The leatherback sea turtle provides a perfect platform to discuss a variety of human impacts on marine ecosystems.  One of the biggest threats is the commercial fishing industry, many turtles are caught as bycatch, approximately 1500 mature females alone in the eastern Pacific in the 1990s. Turtle excluder devices are ineffective with mature adults, as they are actually too big to get through the holes intended for their escape. Their pelagic lifestyle makes them common bycatch for vessels fishing for tuna swordfish and sharks, as the congregate in the same areas of upwelling that the leatherbacks use to feed. The turtles, being marine reptiles and not true fish (But seriously, let's not go there about what type of reptile they are - I had to write a paper on that last year. If you're interested, see a variety of papers with awful, awful names), need to return to the surface to breathe and often drown as a result of being caught up in the nets.

Second on the list is habitat loss. Sea turtles are hugely dependent on beaches for nesting, and although not as often as other turtles, tend to return to their own hatching beach. A variety of typical anthropogenic crimes on the environment: sea level rise, mass tourism and unconstrained coastal development, litter and pollution and others have disturbed and even completely destroyed some crucial turtle nesting beaches around the world. It is unfortunate that many of the areas where the turtles nest (Malaysia, Brazil, Costa Rica, Carrbiean Islands, etc) are all popular tourist destinations for the very beaches the turtles need. The coral reefs as well,  which are important feeding grounds, are suffering extensively as a result of bad tourism practices in many Caribbean countries. Many of the beaches also experience widespread illegal egg take, which seriously hampers leatherback numbers and distorts the natural sex ratio. A recent study  by Ohiana et al. discuss the viability of conservation options in regards to protecting the the nests of leatherbacks in the Dominican Republic. In the Dominican Republic there have been protection measures in place since 1974, but there is still an on going battle to protect the turtles. At one beach, clutch relocation has been in place since 1974 and is still assessed as the only viable option for the area, due to the sheer scale of the illegal poaching. Other beaches have had to implement less drastic measures, such as artificial incubation, but as the paper summises, community engagement and enforcement is needed in order to improve conservation measures. If we want to move towards more sustainable intervention tactics, the locals need to work with the scientists.

The final threat I will mention (but trust me, there are plenty more) is the often fatal impacts of pollution, both chemical and physical. Many turtles die from internal injuries and blockages caused by the ingestion of non-digestable material, such as a plastic bag which the turtle mistook for a jelly fish. Chemical pollution as well, impacts the viability of leatherback eggs, with high levels of the plastic compounds being measured in the yolks of their eggs. 83% of all sea turtles sampled in a recent study had ingested anthropogenic debris, of which plastic was the most prominent component, accounting for 95% of the dry weight of the total ingested material. This study highlighted out lack of understanding about the mechanisms which affect the dispersal of anthropogenic debris around the oceans and how these turtles end up ingesting it. To really ram the point home, and make you feel a bit bad for every McDonalds straw you've ever discarded carelessly, please take a look at the video below - a very real example of what can happen as a result of our carelessness.

EDIT: Here is a link to the GoFundMe page of the PhD Researcher who narrates in the above video, if you're interested in her work, take a look!

Setting new world records - a lot faster than a Snail's pace!

Apologies for my lack of blogging over the last week, I've been caught up with other projects - historical biogeography of the Felidae, anyone? For now, a short post to share a news article that caught my eye!

A paper published this week named 48 new species of snail from Borneo. Some of these are extremely rare, whilst others have been known for decades colloquially but never been formally described by academics. One snail in particular, Acmella nana, has set a new world record for the smallest land snail. It's size ranges between 0.6 and 0.79 millimeters and likely lives on a diet of bacteria and fungi growing on the walls of caves in which it lives. It snatched the title from Angustopila dominikae, a Chinese snail which was only discovered and crowned a month ago!

Other than this being fairly trivial and exciting, it serves as a reminder of the astonishing diversity of lesser studied organisms that we are only just discovering, or are yet to discover. Throughout the fossil record, conservation policy and the catalogue of species we have described lie the same biases. Vertebrates are bigger, more exciting, and most of time more relevant to us than the invertebrates  which are often neglected. Our understanding of invertebrate phylogeny, for example, is much more limited than most vertebrate groups. Mammals are one of the best studied groups in the world, we know the vast majority if not all species, we have sequenced most of their genomes and conducted hundreds of molecular phylogenetic analyses, using mitochondrial DNA to estimate divergence times and pinpoint relationships. We are a long way from this level of understanding for snails, for example, and I would like to hope that in future more work is done to better appreciate the diversity of invertebrates and other less studied organisms.

Angustopila dominikae, flaunting it's tininess. Source.