Januari 04, 2017
today 'd like to welcome the very first of our speakers in the harry butler lecture series dr mikael siversson, dr dr mikael siversson is a palaeotologist with the earth and planetary sciences department down at the western australian museum he gained his phd in geology in 1993 from the lund university in sweden he's regarded by most of his peers as the world's leading authority on cretaceous lamniform sharks and during his scientific career mikael has described one new family, 8 new genera 17 new species of cretaceous and palaeoscene sharks and rays. apart from working on fossil sharks and rays, he's also published on dinosaurs mammals from the age of dinosaurs and mesosaurs
which is an extinct group of giant marine lizards. he organises annual field excursions and expeditions to remote parts of western australia and one of his long term goals is to to improve western australia's stature in the palaeotologist community in regards to its fossil record on dinosaurs, which currently doesn't have particularly good record, so to tell you more and to welcome hm to geraldton dr mikael siversson (applause). i can just briefly mention regarding dinosaurs that western australia, we've had in total 3 dinosaur bones and 2 of them are from gerladton
so although it's still a pathetic record, geraldton is the mecca of dinosaurs in western australia yes, welcome to 2010 international year of biodiversity series talks occurring here at the museum the talk i'm going to give today has 3 components. one is obviously looking at the biodiversity, and since we are looking at extinct animals we going to look at one particular group of sharks and we're going to see how they're diversity has change over 130-140 million years. the other aspect is to look at this particular group of sharks, the lamniform sharks and see how they have fought epic battles against various groups of extinct marine reptiles for supremacy in the oceans because for a long period of time these sharks were the apex predators in the oceans.
and the third aspect is to look at more detail what we do at the museum in this regard of fossil sharks i'm going to give examples of where we go and what we find. but if we start by very briefly looking at a jaw of a modern lamniform shark, but what is a laminform shark? there are 8 or 9 orders of modern sharks, and lamniform sharks happen to be one of those, and examples of modern lamniform sharks include the great white shark, the grey nurse shark, the megamouth shark and since sharks, their skeleton is made up of cartilage which usually does not preserve very well, compared toand since sharks, their skeleton is made up of cartilage
which usually does not preserve very well, compared to for example, an ancient marine reptile, which has a skeleton made up of bone but sharks, they have a lot of teeth and they continue to produce teeth throughout their lives, any given shark will produce 1000s of teeth and they are shed on a more or less regular basis and incorporated into the sediment and have a high preservation potential, so sharks teeth are common in sediments, so the most common fossils we do find of sharks, are their teeth in some groups of sharks, their vertebrate are
calcified by calcium phosphates so they tend to preserve quite well in some of these sharks and by the way this is the long-finned mackle shark, which is one of the lamniform shark and one character in lamniform sharks, that sets them apart from other sharks is they have this so-called lamniform tooth patterns, which means in the upper jawis they have this so-called lamniform tooth patterns, which means in the upper jawis they have this so-called lamniform tooth patterns, which means in the upper jaw the teeth are formed in two troughs (?) and many of the lamnites, the third tooth is reduced. is just one of many characters in this group and when you do, you go out into the field as a paleontologist primarily, you look at say, when you find say, isolated teeth
you try to collect as many of you can, then you try to reconstruct the dentition in rare cases you may find an association of teeth and other remains, vertebrate, of a shark that actually died on the spot. and this is an example of a, don't pass this on confidential... i've got permission... because that's my name and look... haha... yes, this is a shark that was found in kansas it's a species that also occurs in some deposits in western australia, in kalbarri for example in the derailia (?) range, and this specimen was found
as an association of teeth from one single individual by using modern lamniform sharks as templates, we've tried to reconstruct the dentition it's also interesting, this particular specimen, it shows a general trend, and i will get back to that, of tooth reduction. the early lamniform sharks they had lots of teeth, whereas many of the modern ones have rather lower number of teeth, the white shark, the maker shark for example they had around 12 tooth files and that's one of the main reasons for the reduction is for these to develop larger teeth, if you develop larger teeth you have to get rid of tooth files and you can see here the initial stages of tooth reduction, you see this is the first tooth in the
lateral patch, and it's quite reduced, where as if you had gone back 10 million years this tooth would be much larger. but if we leave the sharks for a moment and look at the interaction we look at the apex predators in the ocean, lets travel back 150 million years to the jurassic period, where the giants ruled the earth. this is a monsterous pliosaur he was found in savlbard, which is an island north of norway and it hasn't been formally described, it's been called predator x but these were the apex predators in the oceans for a long time, the giant pliosaurs
aand another group of extinct marine reptiles called the ichthysosaurs and we know from skeletal remains of another type of long-necked plesiosaurs in england, that they were often attacked by the pliosaurs. and these pliosaurs were formidable animals, typically they would grow to about 10 metres, maybe weighing up to about 5 tonnes. has anyone of you seen the bbc series 'walking with dinosaurs'? some of you might have seen that. there is one episode devoted to these pliosaurs, giant pliosaurs. one interesting thing about that specific episode is that it's portrayed as an absolutely eronmous animal, 25 metres long with a weight of a 150 tonnes.
people in general would probably believe that's based on a good skeleton are at least a partial skeleton but it's an interesting story surrounding that particular individual. a number of decades ago in a museum in england there was a large, marine, reptile bone... a vertebrate about that size. lying on a shelf, and during a time that there was probably not a lot of funding going into the museum i mean funding, it goes up and down, sometimes museums have more money, sometimes they have less. and presumably during a time that they didn't have a curator of palaeontology at some stage, someone decided they were going to do something about this giant vertebrate they found, they were thinking what do we do, i know what we do "we'll paint it blue"
so they painted it blue, so now they had this blue, large, precious giant vertebrate of giant extinct marine reptile, and the next idea they had was we need a door stop, let's use it as a door stop. so they had this absolutely precious giant vertebrate, now painted blue, now used a door stop. and many decades later, a guy that was working pliosaurs he came across this big thing, that at least at times, had been used as a door stop. and he saw similarities between that vertebrate and neck vertebrate of some of the pliosuars, the only thing was it was much, much bigger. and somehow bbc picked up on that these giant pliosaurs and his estimate would have been it must have been 25 metres long and they came up with a
weight of a 150 tonnes, which is fair enough, based on the matching specimen. but other people starting looking at this vertebrate and they concluded that it probably was the tail vertebrate, not a neck vertebrate of a sauropod dinosaur, which is something totally different. so, eventually, the 25 metre liopleurodon is back to 10 metres instead of 150 tonees, it was just 3,4 maybe 5 tonnes but regardless they were fearsome predators and they ruled the oceans. and there were sharks around at this time, but they quite small, maybe up to 2 or 3 metres. in australia, our pliosaur was kronosaurus it's been found primarily in queensland.
our last field trip up to kalbarri was in october 2008, we did find a vertrebate of kronosaurus. kronosaurus grew to about 10 metres and would have weighed again, 3, 4 maybe 5 tonnes. and for a long time, it was regarded as, and still is, by the people working on pliosaurs no doubt, as the apex predators in the inland sea that covered australia, during this time the sea level is much higher kronosaurus is from the early part of the cretaceous period, 110-120 million years ago the other type of large reptile that was also basically among the apex predators were the ichthyosaurs, and the common ichthyosaurs we had in australia was the platypterygius and we have a set of vertebrate on display in the gallery here and we found quite a few reamins of these in western australia in kalbarri
and the gerailia (?) range. some of the early ichthyosaurs they were absolutely enormous, there's one shonisaurus from the later part of the triassic that could grow to about 20 metres. but it seems that it switched to a plankton diet, because the adults you can see a reduction in teeth as they reached adulthood. and this is an image of the skeleton of the ichthyosaurus. you can see lots of vertebrate and they are the most common fossils that we do find. there's one site in kalbarri, every time we go there we will find bones of ichthyosaurs
110-120 million years old. and here we are, one of our volunteers he's very good at finding fossils. and he's holding a vertebrate of a ichthyosaur's front (?). the ichthyosaurs however, they... once you get into the cenomanian period which is one period within the cretaceous period, the cretaceous is between 140-145 million years ago to 65 million years ago, and the cenomanian is basically right in the middle. and this is a section in up near kalbarri and the sediment we see here all of this was layed in the oceans, on the shelf, see the sediment here is a green sand and then here you get a laminations preserved of this boundary.
when you have laminations formed in marine sediment they that indicates that there's very low levels of oxygen. because normally if you have a well oxygenated bottom condition you have a lot of worms and other animals digging in the sediment and basically destroying an primary lamination form by the sediment as it's deposited. and it turns out at this boundary between the cenomanian period and the turonian period, anywhere you look worldwide you get the same story you get laminations, black shales are laid down. and the prevailing theory is at this time we had a very rapid
and large global sea level rise. so the water are flooding the oceans and there's a lot of organic material being flushed out from land and as this organic material is oxidised in the oceans it consumes all the oxygen so basically anyhwere you look in world at this particular interval where the sediment was layed down below 140 metres there's no oxygen so it's a major extinction event at this level. and the ichthyosaurs they went extinct, but they had already been in decline for 10 or 15 million years. and why is that? one could ask
the pliosuars, the really large pliosaurs, they died out a few million years later and that was a bit strange, one would think. when when i first came over here in 1994 i started looking at shark's teeth, that was my speciality i went out into some of the sites in the geraillia range (?) and kalbarri and found all these beautiful shark's teeth. here's one that's perfectly preserved from the geraillia (?) range from the cenomanian period, would be about 95 million years old. when you look at the teeth of a shark, you use the modern ones as a template, you get a rough idea about the length of the sharks, or so we thought. very rough estimate, if you look at the largest teeth in the jaw there are 3cm, that would indicate a shark that's roughly 3 metres.
very roughly, in that group of sharks. and the largest ones i found were about 3.5 cm, indicating we had sharks that were about 3.5 metres long and there were no other large apex predators around in this particular area so it was unusual to have an apex predator that was that small in the modern... the true apex predator today would be the orca, i'd say... as the sperm whale is very large, but it's very specialised in its feeding habits. one day in 1996, when i was talking along the outcrops in the geraillia (?) range that was just a few days before there was a tropical cyclone, olivia i believe, struck that area of came very close. iwas walking along the outcrops with my wife
and we spotted all these shark's teeth lying on the ground, and that particular species i found the odd isolated tooth elsewhere, and i tried to figure what where it belonged among the lamniform sharks. finding an association among teeth and vertebrate is very rare, usually you only find isolated teeth so we started excavating and we find all these beautifully preserved teeth adn these are teeth from the lower jaw i'm not sure if you are very good at looking at stereoscopic images, but if you can cross your eyes this is a stereo image, so you can get a 3d image as well. these are teeth from the lower jaw. these are from lower jaw of the other side, and in general they get smaller towards the corner of the mouth, they'll be the more distally curved.
there are upper jaw teeth, and this turned out to be undescribed shark and he was found on the cardabia station, so i named it cardabiodon, which mean the tooth from cardabia it also established a new family the cardabiodontidae, because of the quite unique dental formula, obviously that's to some extent open to interpretation because once you get all this teeth you then have to figure out how they were positioned in the jaw. so you try again, you look at the modern sharks
using that as template and you try to figure out the dentition the interesting bit there was apart from the, well part from obviously finding all the teeth, but we found more things and that just blew my mind, because we found this big whooping vertebrate now the vertebral centra in a shark gives a better indication of the size of the shark if you look at the modern lamnid shark such as the maker shark and the porbeagle shark for example there's a strong correlation between the maximum vertebral diametre and the total length
of the shark. and there were huge. much bigger than i would expect of a shark that would teeth up to about 3.5cm they were in fact of the same size as those of the white shark between. 5.5 and 6 metres. and i also found initially when i tried to reconstruct the dentition that i... there's seems to be a lot more tooth files than in the modern ones, and i thought, well, that makes sense when i found all this big vertebrate and it turns out that as we found more undescribed species that
back in the middle part of the cretaceous, about 95 million years ago many of these early lamniform sharks they had not yet started the process of tooth reduction. so they had a lot more tooth files. so we had under-estimated their size so it turns out that this particular shark cardibidon could probably grow to about 8 metres. and if it was built like a white shark at that length it would 3-4 tons.
which puts it right up at the size of pliosaurs so it seems that by... and already the early really large sharks we find again are from australia, so australia is very important when it comes to the study of these early giant lamniform sharks the single most important place in the world in fact. and we have remains from the undescribed species from the genus cardibidon from queensland that indicate that already by 110 million years ago we had sharks about 6,7,8 metres
so it seems that they for the first time pose a serious threat to the reptiles as apex predators and eventually won that battle. so the last pliosaurs they died out they died out around 92 million years, roughly, and now the lamniform sharks, they rules the oceans, they were the apex predators. and one interesting thing with this cardibidon is the project that i recently started with some canadian people they found remains of the cardibidon shark in canada as well
so what we did is we took a vertebrate from the cardibidon shark and we sectioned it and we looked at these growth bands. when you look at modern lamniform sharks they deposit a darker band on what is believed to be an annual basis so based on that, it seems that the cardibidon shark was around 12 years old at the time it died and it was probably not an adult, because in modern sharks
as sharks reach maturity their growth tend to slow down. and you can only possible see a slow down at the very last.. maybe it was sick so it also gives an idication about the size when he was born. it gives an idication of the diametre of the vertebrate and my using lamniforms as templates these were were problaby born at a large size, about two metres. which is similar to the white shark, relatively speaking because this is a larger shark, probably growing to about 8 metres. this is another individual of cardibidon
and you can see here a marked crowding of the growth rings after about five indicating that this one was a more mature shark. maybe the first one was a female female lamniform sharks, they tend to mature at a later age maybe this was a male, or they could be just variation within that species.
here we can see the growth curves of the sharks plotted... these are some of the other extinct sharks, cretoxyrhina and you can see it's increasing in size quite rapidly. i mentioned that this particular species has been found in other places, well canada this is a beautifully preserved tooth from the lower jaw found in the chalk of england.
so it was a widespread shark but it occurs mainly in the higher paleolatitudes, i mean the latitudes that applied back then the continent as you may know shift around continuously. so we had a situation where the laminform sharks they ruled the oceans, they were the apex predators. this is western kansas and look at this beautiful image.
no vegetation here. beautiful, as a paleontology you don't want vegetation to cover the outcrops. you want what they call a 'badland' area with no plants. and all these beautiful outcrops, and this a very well known formation called the niobrara chalk and it's a renowned for its perfectly preserved vertebrate fossils. this was a
much of the north america, the western part of north america was covered by an inland sea about 100 to 65 million years ago and there was something on the rise, the reptiles, marine reptiles had briefly given up the struggle for supremacy when the ichthyosaurs had died out about 92. 93 million years ago at the pliosaurs, the really large pliosuars died out soon afterwards.
but something was on the rise, but look at this, this is a beautifully preserved skull of a new breed of marine reptiles, the mosasaurs. at this measure, i think this is one metre, so it's really large mesosaur. the first mosasaurs that evolved were quite small, 2-3 metres and they are particularly common in the niobrara chalk.
so what did the sharks, what was the sharks response to this new breed of fericious marine reptiles? well, they responded in grand style. look at that image, this image is based on an actual fossil found in niobrara chalk, it is a cretoxyrhina shark which at that time could grow of a size of up to 7 metres
that's grabbed hold of a mosasaur and you can see the mosasaurs they they are probably most closely related to the monitor lizards but some researchers believe they are more closely related to the snakes but they were equiped with a large head they had an extra hinge here so they could really open up their gape tremendously the bones in the skull were
loosely attached by ligaments like a snake, so they could really expand their mouth. that ability ws reduced later on, as the skull grew more solid so the later forms of mosasaur they had a more solid construction of the skull. this is a beautifully
preserved skull of the cretoxyrhina shark partly mummified found in kansas, you can see lying upside down. this is the outline of the lower jaw, this is the upper jaw, you can see all these fearsome teeth. and this is the fossil that the illustrations are actually based on and the mid section of the back of
the six metre long mosasaur it's been attacked by a cretoxyrhina shark that basically took a big bite basically it's severed the mosasaur into two pieces, well it kept the third piece in it's mouth and swallowed it. so they were absolutely brutal these sharks, and you can see there's a tooth broken tooth of cretoxyrhina still stuck in the verebrate of the mosasaur
a few days, a few weeks later these remains were regurgitated and the mosasaurs often or the sharks often did that, whereas reptiles, they have better ability to actually dsolve the bones, but the sharks you see, as you walk the outcrops there in kansas every now and then you come across a little pile ex-mosasaur bones
which is, they've now been regurgitated by the sharks. ... there's another illustration illustration showing the probably outline fo the mouth with that section of the jawbone. here, other examples from the niobrara chalk there is bones of mosasaurs
they all show signs of being corroded by the gastric fluids of the sharks, and then regurgitated so it was a not a, easy environment for these reptiles to gain any dominance over the shark so what do they do, the reptiles in order to counter this very obvious
threat from these giant cretoxyrhina sharks? well we actually been looking at a growth rates in the largest of the mosasaurs, tylosaurus, and it shows that they changed tactics, they accelerated the growth rate of juveniles, so they tried to reach maturity faster. sort of outgrow the sharks.
and eventually, they won that battle and cretoxyrhina went extinct 80 million years ago and by the time it went extinct the largest tylosaur was absolutely enormous 13 metres long. you can see here and compare the skeleton of tylosaurus with that a t-rex. so the mosasaurs now ruled the ocean, not the sharks and they did so for the remaining 15 million years of the cretaceous period.
until a meteorite struck the earth and wiped out the dinosaurs they wiped out the tylosuars, the other mosasaurs, plesiosaurs pterosaurs, as well as extinct marine reptiles about half of all shark species went extinct, but during these 15 millions years of time you don't find any sharks basically larger than 3, maybe 4 metres, so they were kept in check by the mosasaurs
but once the mosasaurs went extinct, so we have these the largest lamniform sharks being around 3 or 4 metres and then we have the extinction, and then they just go sky-high, they just explode in size. clearly showing that they were unable to compete for that niche with the mosasaurs because once the mosasaurs were gone, they immediately took over that niche.
here's just to show you that we do have some remains of mosasaurs, this is a tail vertebrate from a tylosaur mosasaur found in the gerallia range (?) and it's 66, maybe 67 millions years ago, the extinction of all the dinosaurs and all the other animal life took place about 65 million years ago. so you have basically 2 or 3 lineages of lamniform shark that quickly move into that niche as apex predator
and this was one of them palaeocarcharodon so palaeocarcharodon presumably had a long evolutionary history as a shark with fairly narrow teeth, probably specialising on fish once the mosasaurs is gone it starts developing serations you can see a gradual aquisition of seration that process took about 2 million years and once it evolves serations, its better
adapted to attack larger prey because it can cut out pieces of flesh from a larger prey but as you switch to a larger prey it also makes you more vunerable to extinction and sure enough about 2 millions after it had evolved these beautiful serations it went extinct. another lineage of lamniform shark, the otodus-carcharocles lineage evolves serations during the eocene period
roughly, 50-55 million years ago. and again this is from a sequence in kazakhstan where we have nice, continuous record over this period, and you can see here how they gradually evolved serations. around that time, eocene, you get the first whales develop and that is a particularly important event in the history of the giant lamniform sharks, because that provides these sharks with a food source, i mean nature will only allow
you to grow gigantic if there is a suitable food source to go with it so this lamniform shark carcharocles now had a perfect food source that was increasing in size, so it started increasing in size, and it grew and it grew and it eventually produced the absolutely the absolutely colossal carcharolces megalodon. this is the largest predator excluding filter feeders, the largest predator this planet has ever seen. and the latest estimates is that they could grow, the largest ones could grow to 18, 19 metres.
weigh up to 50 metric tonnes. by compraison, white sharks an exceptionally large female white shark may reach possibly 2 tonnes if its well feed, i think the largest reliably measured was just 6 metres. there are numerous reports of bigger ones but once you scrutinise the data they all fall apart, so 6 metres about the maximum length for a white shark, so they were absolutely eronmous and they died out as recently as 2 million years ago, 2-2.5 million years ago. and they feed on baleen whales
on giant baleen whales, our ancestors, our hominid ancestors probably witnessed these absolutely epic battle, when you had these poor baleen whales being attacked by these sharks and megalodon is unique in that it was very thick teeth as well a white shark has broad teeth, but they are quite flat white shark, when it attacks something boney like, a marine mammal, it often goes for the softer parts not megalodon, it had a bone crushing dentition, it would crush the rib cages it would bit through the huge vertebrate of these baleen whales
so i've seen baleen whales about this big looks like someone's gone through it with a chainsaw so that were absolutely spectacular. but when you are 18,19 metres and weigh 50 tons you are putting yourself on a precarious situation, because you depend on availability of baleen whales and there was a very important change in environment that was taking place about 2 million years ago when head into the first ice age.
and... what happens, as far as the shark perspective, their food source disappeared because every summer the baleen whales would migrate to higher latitudes to feed on crustaceans, in these cold waters and carcharocles couldn't follow, it could not adapt quick enough so it was basically left without a food source for a large part of the year, at least several months. so they disappear, they go extinct, and that's best shot at explaining why they went extinct.
and so basically, as a lamniform shark once you develop serations and start develop big teeth you are setting yourself up for extinction. this is a carcharocles megalodon tooth it's the remains from the largest known predator from western australia based on its size and comparing it whole dentitions that we have found of carcharocles megalodon it probably grew to about 13,14 metres give or take a metre of so, and a weight of probably 20 tons,
that's about tons the weight of the heaviest white shark we are going to go back to this site on cape range in probably august, of course after secured all the necessary permits from dec and but i'm sure we will get that, surely... i'm going to prepare this out of the rock, but it's a nice display showing it how it was found and we have a couple more of these megalodon teeth from cape range in the rocks of the miocene period. then returning to the white shark itself, the white shark has a different origin, for a long time people thought that megalodon and the white shark were closely related, there's a few
there's a few scientists that still believe so, but the majority of us we see the white shark evolving from the maker sharks. and this is an early white shark, about 79 million years old, you can see no serations and then about 6 million years ago, they start developing weak serations, a bit stronger here, about 4.5 million years this one is about 2 million years, and they have fully developed serations like the modern ones what does that mean for the white sharks prospect for survival? well, based on its relatives
it might have set itself up for extinction curiously, it hasn't really increased in size, which is the normal pattern once they evolve seration they increase in size but that could be possibly due to the ice age, so once we get out of the ice age they might start increasing in size but the odds are that the white shark will eventually go extinct even without human intervention because that certainly has been the pattern in the past and here's the comparison of the early white shark
and its traditional form, and the modern white shark compared to megalodon, the one difference here is the lamniform sharks they had a reduced 3rd upper anterior tooth which means they can put it more power basically into the remaining cusps, instead of having to distribute the power of the jaws, the front teeth of three points and now it's just two points. whereas megalodon has immense bone crushing dentition so it wouldn't need that adaptation. and just finally going back to look at biodiversity
basically what this talk is partly about. this is images taken from compagno sharks of the world and it shows the comparison between lamniform sharks and whaler sharks which are in the order carcharhiniformes. if we look at the lamniform sharks they reached a main the peak in diversity around 100 million years ago. when we had about, very roughly about 100 species. and ever since the middle part of the cretaceous they have lost ground, their diversity has been steadily going down
so today we have about 15 species. and the trend is that they will go extinct, and if we look at the lamniform sharks that has gone through about 130, 140 million years of evolution, they are all extremes, look at the thresher sharks. "hey look at me, i've developed a humongous tail, i'm the king of the tails". now, if the thresher shark's environment suddenly collasped, it couldn't go up river and start feeding in rivers with that whooping big tail the same with the megamouth shark, really highly specialised filter feeder, same with the basking shark and the white shark, super predator needs an abundance of certainly large prey as adults
whereas the whaler sharks, which evolved about 50 million years ago they look at the same, if you put whaler sharks about 20 metres away it would be very hard even for an expert to tell them apart, they are very similar they are radiating very rapidly and increasing in diversity at the expense of the laminform sharks. if you look at an assemblage of sharks 30-40 million years ago, they might be half laminform sharks in the shallow water, half would be whaler sharks but today they would be predominantly whaler sharks, there's a black-tip shark, a bull shark bronzed whaler, silver-tipped shark. so they are highly successfully the lamniform sharks, whereas the lamnids
or the whaler sharks... whereas the lamniform sharks, if you imagine a tree branching off and producing all these branches producing extreme forms, but most of these branches are now gone through extinction, you have these few specialists remaining that's why it's especially important on the conservation of these lamniform sharks, including the white sharks because they are threatened, their survival is threatened even without human intervention. and i think that basically concludes my talk. i thank you for, listening to my talk and i hope you learnt something about lamniform sharks thank you.
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