|
|
Post by Grey on Apr 4, 2013 21:46:05 GMT 5
Carcharocles/Otodus megalodonThe megalodon is an extinct megatoothed shark that existed in prehistoric times, from the Oligocene to Pleistocene epochs, approximately 25 to 1.5 million years ago. Paleontological research indicates that C. megalodon is among the largest and most powerful macro-predatory fishes in vertebrate history. C. megalodon is principally known from partially preserved skeletal remains, which indicate a shark of gigantic proportions — approaching a length of around 20.3 metres (67 ft). C. megalodon is widely regarded as the largest shark to have ever lived. After scrutiny of its remains, scientists have assigned C. megalodon to the order Lamniformes but its phylogeny is disputed. Scientists suggest that C. megalodon looked like a stockier version of the great white shark, Carcharodon carcharias, in life. Fossil evidence confirms that C. megalodon had a cosmopolitan distribution. C. megalodon was a super-predator, and bite marks on fossil bones of its victims indicate that it preyed upon large marine animals.  ichef.bbci.co.uk/news/660/media/images/78483000/jpg/_78483514_c0043741-megalodon_shark_attacking_a_whale-spl.jpgLivyatan melvilleiLivyatan melvillei is an extinct species of physeteroid whale. Fossilised remains, comprising 75% of the animal's skull, and large fragments of both jaws and several teeth, were discovered in the Pisco-Ica desert in southern Peru in 2008, in Miocene rocks 12-13 million years old. The skull of Livyatan melvillei measured 3 metres long, its longest teeth were 36 cm long, and it is thought its overall length would have been in the region of 13.5-17.5 m. It was similar in size and appearance to the modern sperm whale. Unlike the sperm whale, however, which only has functional teeth in its lower jaw, Livyatan melvillei had teeth in both jaws, and is thought to have been an aggressive predator, possibly preying on baleen whales.  svpow.files.wordpress.com/2010/08/leviathan_melvillei_reconstructie.jpgCredit to Wikipedia
|
|
|
|
Post by Grey on Apr 4, 2013 21:59:37 GMT 5
I have no more access to carnivora but thanks to the archives datas boards, I've managed to have a look at the old thread and I quote here the last post by Theropod, which I may have missed at the time :   The one with real extant photos is still more indicative than the old drawing by Sam1, displaying a bias, an oversized mosasaur-like gape in the cetacean gape and a smallish, moderatly-sized meg jaws set. The pic with Chuck Ciampaglio clearly demonstrates a more gargantuan, more voluminous bite potency compared to the whale. Regarding the position of the young guy with Livyatan's skull you can still see that he's standing just aside of the tip of the snout thanks to his shadow. Even approximatively, there's no point, the photos give a pretty good idea of the proportions of both animals killing apparatus. This can be seen easily looking at other models.  It is quite evidential that where Livyatan could have engulfed one, perhaps two lying grown men at most, megalodon could have engulfed easily several adult men standing in the jaws. I have others pictures of the cetcean skull lateral view with a guy sanding with it, but I need some courtesy to use it. However, even laterally, the jaws in Livyatan are virtually a good deal smaller. And that's another point, we are comparing here the whole skull of the raptorial sperm whale with only the jawbones of the shark. The size of the predatory apparatus is decisive here. Until more material or news hints come to light, I don't see Livyatan prevailing with a basically quite a bit smaller jaw. The lateral model I've asked to coherentsheaf depicts the same conclusion.  I had sent this to Bretton Kent and he responded the comparison sounds pretty reasonnable, pointing on that both animals had likely distinctive feeding style and food sources. I mean, well, all of this sounds pretty clear to me. |
|
|
|
Post by creature386 on Apr 7, 2013 18:02:43 GMT 5
Is this just me, or is the head length in Sam's drawing more similar to a Sperm Whale's head length? (it is not just box headed, but also similar in length dimensions to a modern sperm whale)
Because in the comparision below, Livyatan's jaws look much shorter than in Sam's comparision.
|
|
|
|
Post by Grey on Apr 7, 2013 19:02:03 GMT 5
Not sure but truly I cannot trust Sam1 drawings, even if that one is pretty old. Real life photos are probably better, even if approximative. Here's Livyatan skull from lateral viewpoint. I guess the scale is pretty good. Rest my case, in terms of bite radius, I would even say they're not in the same league.  |
|
|
|
Post by Life on Apr 10, 2013 8:18:49 GMT 5
Is this just me, or is the head length in Sam's drawing more similar to a Sperm Whale's head length? (it is not just box headed, but also similar in length dimensions to a modern sperm whale) Because in the comparision below, Livyatan's jaws look much shorter than in Sam's comparision. You are correct to point this; That drawing is inaccurate. I had lengthy discussion with the guy in question about error in his drawing; I argued that the jaw structure in his drawing is detached. I eventually offered this evidence:  I predict a 6 feet gape from Livyatan holotype specimen; 7 feet maximum but this might be stretching it. Still a very formidable set of jaws. Hope this clarifies the situation.  GreyBro, when you cite an inaccurate work, you may highlight it as "questionable." This goes for all other members. |
|
|
|
Post by Grey on Apr 13, 2013 8:52:06 GMT 5
Yes, I've precised it was Sam1 bad homework in my response. Anyway, we'll admit there's no need to be a genius to remark this is completely flawed !  That being said, it seems his crap has been used since by some bloggers... I'm somehow surprised by how much megalodon jaws seem to outclass in many aspects of size the jaws of Livyatan. Of course, their respective predatory apparatus is very difficult to compare much more difficult than comparing the jaws of differents theropods dinosaurs. Livyatan obviously exceeds megalodon (and any other predator) in tooth size, and given their structure and the space for muscles attachments, I'm certains its bite force may have been of titanic proportions, rivaling the others estimated giants bites. That includes megalodon but as megalodon's bite itself is not so clear and excludes some considerations (lateral shaking), that's even more difficult to compare them. Now, regardless of megalodon actual bite force, we know it could actually slice through the body of multi-tons preys items with ease. We have no element for Livyatan attacking patterns. But at the end of the day, the reconstructed jaws in meg really seem to demonstrate a much higher potency in terms of volume per each bite during one attack. The jaws I have posted are actually not the largest (and somewhat debattable) models and still they could contain several guys. Regarding the size, there are margin of errors for both but the results of studies, big hints and educated opinions seem to place megalodon as most likely the larger predator of both (which does not reject any new possibility regarding Livyatan's dimensions). At now anything in 13,5 or 17,5 m has sense. From Lambert, I know that larger isolated teeth do not necessary indicate larger sizes, as among sperm whales, teeth continue to grow when the body has reached its full size and do not grow anymore. Kent, in his new paper, remarks that all the published or unpublished results of methods for estimate megalodon size are based on the largest teeth specimen available at the time for each author, and hence may not reflect the largest specimens. Looking at the elements we have of the marine environments and communities from Miocene and Pliocene, the fossil evidences or suggestions we have for both animals killing apparatus, morphology, size, abundance, existence, I still think that C. megalodon was the most dominant and largest predator of these epochs and that Livyatan was : - an "unsuccessfull" cetacean attempt to replace megalodons as ultimate apex predators for the ecological niche of mysticetes predators, as we strongly suspect killer sperm whales vanished from fossils records well before megalodon (like proposed by Mike Siversson). - or a perhaps smaller apex predator which did not compete directly with megalodon for food and could easily colived with it because they would not share the same lifestyle, added to the quantity of food sources available at the time (like proposed by Brett Kent). Another possible hint of the shark superiority comes from scientific litterature : Leonard Compagno argued that the various megalodon jaws reconstructions suggest a predatory apparatus able to inflict mortal injuries to even a fin whale or a blue whale. Christian De Muizon said in one interview that Livyatan could not have attacked something the size of a blue whale but the small to medium-sized Miocene cetotherids. The potential ability to subdue larger and more difficult preys items is quite revelant in my opinion. As ever, in science we can all the time be surprised, but to now and since a while this conclusion appears the most likely to me. |
|
|
|
Post by creature386 on Apr 14, 2013 15:01:48 GMT 5
I am not quite sure if Megalodon was more of a crusher, or a slicer. Because the teeth are wide from a frontal view, but not very thick from a lateral view, I now think it could have been more of a slicer.
Anyway, about the extinction:
I still think Megalodon may have survived, because sharks are less sensitive to food changes than cetaceans, as they can esier find food and don't need so much. I know, Great White Sharks eat more than previously tought, but probably still less than a similary sized mammal. Also, due to it's good sense of smell, Megalodon would have been faster at finding a carcass than Livyatan, what may have helped it to outcompeat it, but that won't help so much in an interspecific conflict, so I am not sure if this is relevant here.
P.S. What was Muzion's justification for that claim? Killer Whales have a similar skull and are able to attack large whales (I know, not so teribly larger than they are, but I mean proportionally, as Livyatan is also a lot larger than a Killer Whale). From my knowledge, Livyatan attacking medium sized whales was proposed, because they are energy rich, but that also would apply to a larger whale.
|
|
|
|
Post by Grey on Apr 14, 2013 21:24:59 GMT 5
Megalodon teeth are described incredibly thick and robust as far I can tell. Their thickness can be around 4 cm in the large teeth. Added to the width up to 14 cm, a compact shape and a massive root, they have no trouble at puncture bones.
I think there's no point to want classify it as a slicer or a crusher. That's not a tetrapod with dagger-like teeth and very long root.
Sharks teeth are not like this, even though in their structure and mechanism they have been compared to the teeth of Tyrannosaurus (Farlow). As far as sharks are concerned, it had no problem at puncture or crush bones, even though this was not technically a bone crusher, the description has been used for megalodon (Siversson). The teeth never evoved to get a large root as a part of the evolutionnary success in sharks is due to their ability to replace teeth very efficiently.
I'm not sure that sharks, especially as apex predators, are less sensitive than mammals of an equivalent niche but I would dig further in this.
There are an estimated 3 000 white sharks living on the planet, much less than orcas, and even before men's interferences, they were surely not more numerous than the large delphinid. White shark is gradually losing its position as an apex predator, whereas orcas are gaining since a few millions years. The various environmental issues in the oceans affect far more the white shark than the orcas.
Killer whales kill larger whales only in pods.
The skull of a blue whale is twice the length of the skull in Livyatan. I've never seen a killer whale killing alone a whale with a skull twice longer, and being probably overall twice longer and several times heavier.
I think De Muizon bases this simply because of the size and morphology of Livyatan jaws.
|
|
|
|
Post by creature386 on Apr 17, 2013 23:59:21 GMT 5
Well, as for the Great White Shark, it is more a systematic killing by the human that means the things what drive the Great White to extinction are only affecting the shark (I am talking of the finning).
I don't think it is because a food problem, or something like that, as Great Whites need less food (more than previously tought, but still not a lot, they are also smaller, so it's logical) and are not as "wasteful" as Killer Whales. They usually only eat the tounge, the lips, the genitals and the blubber of large whales (John E. Heyning, Marilyn E. Dahlheim; 1988).
Sources:
John E. Heyning, Marilyn E. Dahlheim (15.1.1988) Orcinus orca Mammalian Species, No. 304, pp. 1-9
|
|
|
|
Post by Grey on Apr 19, 2013 7:42:45 GMT 5
Not exactly, regardless of human activity, predatory lamniforms are in decline since the Pliocene era whereas orcas and carchariniforms are gaining. These sharks are just as sensitives than any rare top predator.
About human interferences, excluding the finning (which great white does not represent common catches) but all the others issues provoked by human activities.
That's why, I would not reject both of these suggestions to now.
Sure, killer sperm whales extinction or evolution into squid eaters can have been provoked by many others factors.
Still is the fact that there could have occurred an ecological battle for apex position in oceans, and virtually no impact on megatooth sharks populations are known because of the existence of the raptorial sperm whales which on the contrary, were extinct or had evolved in teutophagous specialists.
There's no conclusive answer there of course. But as we know, what happened during Late Cretaceous between mosasaurs and sharks did not happen during Miocene and Pliocene between odontocetes and lamniforms.
|
|
|
|
Post by Grey on Apr 19, 2013 21:07:02 GMT 5
Some meg teeth are extremely thick, these are not tools that can be compared to the teeth of some allosaurids theropods.   That specimen from South America approach the symbolic 7 inches mark and exceeds 7,7 cm in thickness. Courtesy Worthpoint. |
|
|
|
Post by elosha11 on Apr 24, 2013 22:45:34 GMT 5
^That tooth Grey posted appears to be 2430 grams, which is over 5.35 pounds. That's an incredibly heavy tooth. Very thoughtful posts on this conflict, which very likely actually occurred from time to time back in the Miocene! I will post more details of my opinion soon when I have more free time.
|
|
|
|
Post by coherentsheaf on Apr 25, 2013 0:32:16 GMT 5
Some meg teeth are extremely thick, these are not tools that can be compared to the teeth of some allosaurids theropods. That specimen from South America approach the symbolic 7 inches mark and exceeds 7,7 cm in thickness. Courtesy Worthpoint. Whoa, this tooth looks simply enormous!!! |
|
|
|
Post by Grey on Apr 25, 2013 20:16:16 GMT 5
Yes, I wonder if the thickness is not related to the age and body size in the animal either. Does anyone has data about the weight of a white shark tooth ? About comparing megalodon and Livyatan feeding apparatus, I try to use the most reliable reconstructions. The skulls of Livyatan are from the Lima and Rotterdam Museums, directly reconstructed by the describers. The two reconstructed jaws of meg I used have been supervised under scientifical viewpoint in TV shows and are likely among the most reliable we can use. I tend to avoid using Vito Bertucci and Cliff Jeremiah reconstructions because the jaws are stretched just like some jaws in modern sharks are when dried, and show small curvature, in an unatural way or in a carcharhinid style. I would tend to use the suggestion of Renz (2002) for the size in C. megalodon jaws :  |
|
stomatopod
Junior Member
Gluttonous Auchenipterid
Posts: 182
|
Post by stomatopod on Apr 26, 2013 23:13:27 GMT 5
I could weigth a tooth of "Cosmopolitodus xiphodon", (though this is only a transitional form, basically an unserrated Carcharodon).
|
|
