What would a massive extinction event look like in the fossil record?

When I started getting into in paleontology, I was puzzled for a long time about how a mass extinction event, like the one that obliterated the dinosaurs, would manifest in the fossil sequence. I didn’t look it up, because I wanted to think logically about it for myself.

I did, however, come across a text that mentioned that extinctions occur at the point when a species or group is no longer found in younger rock layers. This makes complete sense, as we should not find traces of an animal later than the time it ceased to exist. An organism is extinct when it stops forming fossils, and thus disappears from the fossil record.

This answer was simple enough to silence my wonders about mass extinctions. I figured that mass extinction events must be points where there are lots of organisms disappearing at the same time – i.e. lots of extinctions at the same time. I didn’t think much more about it; the simple answer was satisfying.

Also, I was glad to note that it is not quite as straightforward. If we find traces of the organism from time a to time b, we are confident that that organisms existed between those times. However, because of the nature of the fossil record, i.e. because organisms are not necessarily preserved (and found!) throughout their existence, we cannot be sure that time a marks the precise emergence and time b represents the exact disappearance of the organism. Because a new species is always rare when it has just appeared, and similarly are typically rare when they are near extinction (although, extinction could probably happen suddenly to an abundant species during a truly catastrophic event – e.g. a rapid mass extinction event?), it is less likely that species are preserved as fossils at their dawn and demise. Therefore, paleontologists always have in mind that times a and b are not the definite boundaries of the organism, but rather the time interval when we can be certain that this organism did exist, representing its minimum life span.

As a well-known example of how the earliest time we find fossils might completely miss the time of true extinction, we have the coelacanth fish Latimeria. The coelacanths were thought to have gone extinct in the Late Cretaceous because there have been no fossil evidence of their presence since. However, since the late mid-1990s, live specimens of two species Latimeria have been fished out of the deep oceans – unambiguous evidence that this lineage did indeed survive for 80 million years longer than shown by the fossil record.

So, I was happy with that explanation: Extinctions are manifested as disappearance in the fossil record of younger rocks, but there is some uncertainty about the timing, due to the fossil record being incomplete by nature. I liked the simplicity, coupled with some inherent difficulties due to the nature of the subject.

However, this morning I was struck again with wonder. How would the mass extinction events look in the precise moment, rather than after the event? How could we recognise a mass extinction without looking at what went missing later?

Mass extinction certainly implies mass death, and mass death should also mean mass fossilisation. I understand that more deaths do not mean more fossilisation events, as the conditions for preservation depend primarily on physical and chemical factors. However, while the number of preservation events probably was unaffected, each of those events ought to have involved more organisms, since more organisms were dead. So, I expect that there would be a relative increase in the abundance of fossils in each locality – while not necessarily an increase in the number of fossil localities – during a mass extinction event.

As a counter argument, I guess one could claim that during such disastrous times, maybe there will be fewer occurences where the conditions are right for fossilisation. Maybe the sheer chaos prevents proper fossilisation?

However, considering that many mass assemblages of organisms, especially large ones, are interpreted as having occurred during storm floods and similar catastrophic events. Many others are thought to have been formed through long-term accumulation of organisms in a calm setting, such as a lagoon, or quicksand swamp, and these tend to give much better-preserved fossils. So, maybe we could extract a pattern from this?

I am tempted to predict that mass extinctions would, at the precise event, contain an increase in the number of fossils found, but a potential decrease in the number of localities and in the quality of preservation. Hopefully, I will find an opportunity in the future to see for real what a mass extinction sequence looks like.  

Eyes and the emergence of predators

I'm sure most of you are familiar with the idea that the first real animal predators – i.e. animals that actively seek out and eat other organisms for food – evolved pretty much in association with the appearance of eyes, in the shallow Cambrian seas, about 500 million years ago.

I just had a thought about that: if there was a strong link between the evolution of eyes and of predators, which suggests that the world's animals were sort of waiting to be able to see before they started hunting, why is it then that so many predators that have evolved since primarily use other senses, such as smell and hearing, to locate their prey? Why go back?

Don't get me wrong, I'm not suggesting something is odd or amiss here – just that it is a curious thought. Evolutionary reversals are not uncommon. Since vertebrates managed to crawl onto land and become adapted to terrestrial life, several groups have gone back to the sea, including plesiosaurs, placodonts, nodosaurs, ichthyosaurs, mosasaurs, cetaceans (whales, dolphins, and porpoises) and pinnipeds (basically seals); crocodiles evolved to become semi-aquatic. Since birds evolved flight, several groups have lost that ability: ratites (ostriches, emus, etc.), penguins and the ancient terror birds. One could probably write a dozen books on just the topic of reversals in evolution.

A simple answer to the question earlier could be that, while many predators today use their smell or hearing to locate prey at a distance, they still rely on eyesight when they are close enough. I recall reading that sharks, having exremely poor vision, use their insanely acute sense of smell to detect a wounded animal maybe miles away, and, when they come within a metre or so of the prey, they use their eyes, but when coming even closer, they cannot see (for their big snout being in the way, I guess) and then use their special sense that can feel electric impulses from the animal's muscles, to direct where they close their jaws.

This makes some sense (pun not intended, but I like it!), especially for land- and water-based predators, since vision is physically limited by trees, bushes, hills, or simply the natural murkiness of water. Scent particles and noise, on the other hand, won't be as restricted. But, sight is probably the most convenient way of homing in on prey when you have it within visible range, so I wouldn't be surprised if most predators shift to sight-dominated pursuit when they are close enough to their prey.

And, maybe that explains why the evolution of eyes sparked the emergence of predators...

T. rex – a scavenger?

Tonight I’m just going to write a short entry about the old idea of Tyrannosaurus rex being an obligate scavenger – i.e. incapable of feeding itself by other means than scavenging, or, in other words, incapable of killing prey. This hypothesis, proposed by John R. Horner, gained disproportional attention in the media (probably because T. rex is such a popular dinosaur, and such an iconic killer), and I think that is what spurred a (in my opinion) disproportional effort from the scientific community to respond with new evidence to counter this idea.

I think if I just go though the evidence for the scavenger hypothesis, you will understand my opinion that this should not have been taken seriously in the first place.

As a disclaimer, I must note that I have not done any research into this topic for two or three years, and what I am writing to you now is what I can remember from the sources I accessed ages ago. However, the focus of this post is on thinking and evaluating arguments. Therefore, if the facts seem a bit fishy, I urge you to do some research on your own, as my memory might not be as sharp as I hope it is. What I want with this entry is to inspire you to think about information that is presented to you, and to pay attention to how you can evaluate it critically.

For clarity, I will repeat the hypothesis: the idea is that T. rex would have been completely unable to kill its own prey, and therefore survived as a scavenger.

One line of evidence points to the short, atrophied arms of T. rex. (‘Atrophied’ basically mean greatly reduced, often due to neglect.) Horner argued that predators must use their arms to grab and hold prey in order to subdue and kill them. Think about this for a second. What does this imply? That all prey run away; none of them stand and fight. Considering that many dinosaur herbivores were rather heavy, and walking on all fours, with the front limbs shorter than their back legs, I doubt that would have been the case in the dinosaur era – especially not Triceratops, Ankylosaurus and the like. Think back to the old tv-shows with fight scenes between T. rex and some other dinosaur: how many of them involved chases? Seriously…

And what is worse, the idea that grasping forelimbs is a prerequisite for predation nothing more than a poor generalisation. Consider which types of land vertebrate animals use their forelimbs for grabbing prey. I can only think of mammals, a group with little connection to dinosaurs, being separated by 300 million years of evolution. In contrast, we have all the animal types that typically don’t use their forelimbs: birds, crocodiles (both being the closest relatives of dinosaurs), lizards, snakes, amphibians. Yes, as you can see, pretty much all animals except mammals are perfectly successful predators without really using their forelimbs for grabbing prey. How valid does Horner’s argument seem when you look at the spectrum of predators alive today?

A second argument is based on the shape of the teeth of T. rex: conical, designed to crush bones. In fairness, this is a rather useful adaptation for a scavenger, which cannot expect to be the first to feed from a carcass and might need to be able to crunch some clean bones to get to the nutritious bone marrow contained inside. However, since Horner is arguing that T. rex couldn’t have been a predator, this evidence misses the point by a mile. Crushing the bones of a prey with a powerful bite is a sure way of inflicting crippling pain and is almost guaranteed to stop the prey from either running or fighting back. I fail to see how a set of bone-crushing teeth could not be used to kill prey.

A third set of evidence reasons around what we guess about T. rex’s senses. Brain scans and other types of studies give clues that T. rex probably had poor eyesight, compensated by a really sharp sense of smell. This is indeed typical for a scavenger, in particular truly obligate scavengers – of which vultures are the only well-known, living examples. T. rex most certainly did not have binocular vision – i.e. the ability to judge distances – which is essential for many swift-striking predators, in particular those aiming for small prey. Now, I do not see T. rex as either a swift attacker or one that would go for prey so small it might miss them if it cannot judge distances effectively. While the lack of binocular vision definitely would have limited T. rex’s potential hunting prowess (if it was a hunter… let us keep an open mind), but doubtfully to the extent of complete incapacity. Similarly, a keen sense of smell is an excellent trait for a scavenger, since carcasses smell, and vultures have among the most acute sense of smell among land animals. But, there is nothing saying that a sense of smell is useless for a predator; there are in fact plenty of predators out there today that have smell as their primary sense.

I saved the best argument for last. I honestly mean that, though. This is the only piece of evidence I have seen presented for the scavenger hypothesis that I accept as a valid proposal of a serious difficulty T. rex might have faced when trying to kill prey. It points to the set of combined evidence suggesting that T. rex lacked speed and agility. Just looking at it, you can see it was a ponderous animal. Detailed studies of biomechanics and whatnot have shown, for example, that it could have taken T. rex as much as twenty seconds (I think it was, but I might not remember the figures accurately) to make a full turn. (When taking this into account, the problem of lack of depth perception might become a concern.) The speed at which T. rex could move has been debated about with such varied results I doubt there is any consensus even among the experts, but it is still challenging to imagine such a large animal chasing down a hadrosaur across a field. I doubt T. rex would have chased anything around in a tight forest either, again due to its size. Maybe it would have been better off as an ambush hunter? Again, I find difficulties imagining such a large dinosaur hiding effectively.

Still, this point is far from conclusive. Recall my argument that it is likely that many potential prey species would have tried to fight the predator off rather than try to outrun it? Now, these dinosaurs would have been well defended, with bone plates in their skin, bone shields, and offensive weapons such as facial horns, sharp beaks and bony tail clubs. Therefore, it would be ideal to get around them and attack any weak spot in these formidable defences. But without agility, that seems rather hopeless, so I can see another difficulty T. rex would have faced as a predator. However, some evidence points toward T. rex being potential team hunters, possibly working together in family groups. As a team, it would not be as difficult to surround the prey and strike at weak spots. It would mostly be a challenge if the prey live in tight herds as well. Triceratops probably did, but Ankylosaurus is thought to have been more solitary. Hadrosaurs, such as Edmontosaurus, on the other hand, were heard-living, but basically defenceless, and probably not particularly fast runners. It seems they might have been the preferred prey of T. rex, if it was a predator. When there is potential prey that is not impossible to subdue, it seems extreme to argue that T. rex would never have made a kill.

As a concluding remark, I want to add that while this evidence fails miserably to support the proposal of T. rex as and obligate scavenger, it does highlight some good reasons for why we should accept the possibility that T. rex may have been an occasional or opportunistic scavenger, while still perfectly capable of killing prey when an opportunity was presented. Indeed, this is where it seems the debate landed, and it further appears to have opened up our eyes to the potential benefits for predators of opportunistic scavenging, which has spread to many other predators, as you might see paleontolgists (proudly) talking about in tv-shows, etc.

I will finish by repeating my warning from earlier: please do not use this article as a source of information, but rather as a source of thoughts! If you are interested in this debate, check well-referenced sources for the details.  

Getting down... I mean up, to doing things

I was just watching an inspirational interview with Tony Robbins about what drives some people to pursue something so persitently that they finally reach it. Among many other insightful points, Tony Robbins emphasises that the way to break through is to take action, and do that every day. The idea is that if you make it something you purposefully do on a daily basis, you will gain such momentum that it helps you break through, and, eventually, it becomes a standard, a part of what you normally do, and then it won't be an effort any longer.


Now, I have been looking for a good enough reason to get back to blogging again, because I genuinely miss it, but keep finding excuses not to. This video literally moved me from the comfy place on my bed to my (less comfy) working chair with the clear and doubtless intention to start getting something written every day.

So, I thought for a second about what I could write about every day, and my idea is to pick a single concept, theory or idea related to paleontology and just write as much as I can about it in one sitting. I consider myself having been good at developing ideas, of extracting more out of them, usually by relating them to other things, by putting them into context.

However, I find the demand from university to learn at such broadth and arbitrary detail (that including a whole lot of crap I don't see how most of us would find use in knowing those things), that it comes at the expense of depth and insight. Those who have followed my blog should know by now how draining I find this, how it limits the students' potential to use their thinking abilities, rather than memory capacity.

The difference, now, is that I am sick of feeling pulled in that direction, and finally realised that I have to take the matter in my own hands. No more complaining about the education system (or, well... a little bit more complaining, maybe); I have no choice but to take the responsibility to, on my own, learn and develop the abilities I believe will be useful.

I feel I am already starting well. I had no plan to discuss what I have in the last two paragraphs, but it came as a logical extract of the core subject. Maybe I haven't lost the ability to expand thoughts, just forgotten about it!

I feel that this time I am driven to see this through, driven by the desire to rediscover and further develop my thinking ability – to repair the damage with added improvement! Rather than seeing it as a burden of time, seeing it as work, I now view this exercise as a way to evolve as a thinker!

Ages ago...

I know it has been ages ago since I wrote anything for either of my blogs. I didn't even get started with the promised weekly quick essay training posts.

I don't have any good enough excuse other than not having had the time to dedicate to the blogs. This unfortunately only means a lack of motivation, because if you want to do something real bad, you will find the time. I think my motivation has been largely drained by the course material being utterly uninspiring: the only thing I truly enjoy reading at the moment is statistics, and I'm not going to write blogs about that, for the love of god...

I have also had a major rethink about career choice, which has taken much of my attention from pretty much everything else work-related. I might write about my thoughts at some point, probably will, but won't disappoint you with another promise to be broken...

Part of me really wants to pick up blog writing again, though. And I do have some ideas... But I won't reveal them, because of a TED talk by Derek Sivers, who presented the idea that if you have a new goal or idea that you are excited about, you should resist the first impulse of telling everyone. The reason is that if you do tell someone, you will feel happy or even proud of the idea – without even having carried it out – and the contentment will make you less likely to actually do it!



I have indeed been watching a plethora of TED talks these last weeks, because (most of them) are simply amazing! Maybe that is another reason why I haven't felt inspired to write about paleontology? I have been filled with so many other inspirational thoughts!

Anyway, we will see what happens next!

Sorry

Last time I promised to start a weekly project of short essay-writing on specific topics related to my coursework. It has now been two weeks and I haven't done anything...

Part of the excuse is that I am keen to engage in the Bristol Public Speaking Society, and as I feel that my abilities to talk in public need more polishing than my writing, I want to priotise this for now.

Also, the only course I am doing at the moment is statistics... not much to write about; in fact, most of you would probably beg me not to try!

I am reading some sedimentology as well to prepare for next term, and I find few topics there worth discussing or describing there as well.


This leaves me with the only choice to pic a topic of choice and write about... but I'm low on creativity these days. Maybe if you could suggest a topic, I'd be happy to write it up!

Return of the Something...

Okay, I couldn’t come up with a catchy title… but the message still comes through: I have returned to the writing table (or laptop keyboard) after a considerable break. Not that I considered much during the break… but it was long. Two months.

I officially started the second academic year at the University of Bristol today (with a tutorial that never took place… haha), so now the serious stuff starts for real. This means I have a lot of work to do. However, curiously enough, my timetable is arranged so that I have only two courses in the first term, and eight in the second! I will try to avoid being completely overwhelmed in the second term by doing a lot of background reading for four or five of those courses in this first term, but this still means I have quite a bit of free time. Or, rather, I should say that I have available time, and uncommitted things that really ought to be done, and it is up to me to make sure I do them.

In this illusion of having a surplus of free time, I naturally want to resume blogging! However, I have been thinking about doing it in a slightly different fashion. I have a strong feeling that my main weakness in last year’s exams was my lack of practice in writing (ridiculously) short essays in little time. In my IB years, we did practice quick and precise essay writing, but no essay examination was shorter than one and a half hour (so about four pages long); last year, we were asked to write essays in about 35 minutes (roughly a page in length… including the introduction). This was not only an issue of adopting a different time management strategy, but also of somehow cramming in substantial amounts of detailed information and logical analysis of a rather broad question onto a single page.

Therefore, I want to allocate a few weekly hours to practice fast and effective writing on specific topics. These might just be perfect to publish in this blog!

I was thinking of either picking topics or questions directly from the course material, or just coming up with random ideas. Considering I have only statistics for the first five weeks, I might try the latter out at first!  The idea is to spend some time on focused research, then quickly design a coherent structure, and write it out efficiently. I will also aim to make the mini-essays thought-provoking, hoping to engage you (and hopefully impress examiners if I manage to apply this to the exams later).

This is one of the many things I want to do this term outside of the uni curriculum, but definitely the one I look forward to the most!