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Post by dinosauria101 on Sept 12, 2019 7:03:49 GMT 5
I couldn't find where the paper claims that. I also was wondering about the sharpness part. For that matter, sharpness of the edges or the point of the tooth? All macropredatory sharks have teeth with sharp edges and points (Captain Obvious strikes again), and some have serrated teeth to help with that. I may have misread the paper; it's not claiming what I first thought. And yes that is true but makos have the sharpness mostly on the tip. This is contrast to serrated teeth |
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Post by Infinity Blade on Sept 12, 2019 7:07:04 GMT 5
Any evidence for that?
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Post by dinosauria101 on Sept 12, 2019 7:12:28 GMT 5
As posted by arethousleepy in the bull shark vs shortfin mako shark thread:  Lacks in serrations quite a lot. Also I may be wrong but this may be helpful with bite force: www.fao.org/3/x9293e/X9293E07.pdf |
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Post by Infinity Blade on Sept 12, 2019 8:01:39 GMT 5
As posted by arethousleepy in the bull shark vs shortfin mako shark thread: Lacks in serrations quite a lot. Also I may be wrong but this may be helpful with bite force: www.fao.org/3/x9293e/X9293E07.pdfNo, I'm asking for evidence that they are comparatively sharper at the tip than serrated teeth. What in particular in that species catalogue description is helpful for bite force to you? |
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Post by dinosauria101 on Sept 12, 2019 13:08:04 GMT 5
As posted by arethousleepy in the bull shark vs shortfin mako shark thread: Lacks in serrations quite a lot. Also I may be wrong but this may be helpful with bite force: www.fao.org/3/x9293e/X9293E07.pdfNo, I'm asking for evidence that they are comparatively sharper at the tip than serrated teeth. What in particular in that species catalogue description is helpful for bite force to you? This source states the teeth lack serrations. Also I may have misread, but I think it states a higher bite force for makos than other sharks |
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Post by Infinity Blade on Sept 12, 2019 16:54:41 GMT 5
No, I'm asking for evidence that they are comparatively sharper at the tip than serrated teeth. What in particular in that species catalogue description is helpful for bite force to you? This source states the teeth lack serrations. Also I may have misread, but I think it states a higher bite force for makos than other sharks Again, that's not what I'm asking you about. I already know that mako sharks lack serrations on their teeth. I'm talking about this part: What I can gather from this is that you are implying that mako teeth have more pointed tips than serrated shark teeth, yes or no? If so, I need quantification for this claim. Again, where does it state that makos bite (comparatively or whatever) harder than other sharks? I actually used the search function on my laptop typing in both 'bite' and 'force', and nothing about bite force seems to pop up. I don't necessarily doubt the claim, but I still want evidence for it. Your source doesn't even seem to specifically discuss anything about the claim you made r.e. bite force. |
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Post by theropod on Sept 12, 2019 17:04:28 GMT 5
dinosauria101: Yes I believe we all know Mako shark teeth aren’t serrated. That’s also clearly figured in the FAO species catalogue you cited. But neither Compagno 1984 (general species descriptions) nor Lowry et al. 2009 (scaling of interdental distance and bite circumference in various sharks) have anything to do with Mako shark bite force. A positive correlation of pointier teeth and higher bite forces has been noted by Huber et al. 2009, however their sample of shark species didn’t include Makos, and at any rate this likely isn’t an important contributing factor to cutting ability, neither is the pointedness of tooth tips (because cutting is done by edges, not points). BTW what does exist in that paper is a bite force estimate for a 300 cm PCL, 581 kg Sphyrna mokarran, ~2432 N anterior bite force based on jaw geometry. This compares favourably to Wroe et al.’s estimate of 2341 N for a 423 kg great white. Scaled up to maximum weight, a Hammerhead might have an anterior bite force of ~4034 N based on that. So this is not that much lower compared to a great white of similar size (~4798 N). Compagno, L.J. 1984. Sharks of the world: an annotated and illustrated catalogue of shark species known to date. FAO Fisheries Synopsis Volume 4 (No. 125).
Huber, D.R., Claes, J.M., Mallefet, J. and Herrel, A. 2008. Is extreme bite performance associated with extreme morphologies in sharks? Physiological and Biochemical Zoology 82 (1): 20–28.
Lowry, D., de Castro, A.L.F., Mara, K., Whitenack, L.B., Delius, B., Burgess, G.H. and Motta, P. 2009. Determining shark size from forensic analysis of bite damage. Marine Biology 156 (12): 2483–2492.
Wroe, S., Huber, D.R., Lowry, M., McHenry, C., Moreno, K., Clausen, P., Ferrara, T.L., Cunningham, E., Dean, M.N. and Summers, A.P. 2008. Three-dimensional computer analysis of white shark jaw mechanics: how hard can a great white bite? Journal of Zoology 276 (4): 336–342.
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Post by dinosauria101 on Sept 12, 2019 17:10:34 GMT 5
Again, that's not what I'm asking you about. I already know that mako sharks lack serrations on their teeth. I'm talking about this part: 1: What I can gather from this is that you are implying that mako teeth have more pointed tips than serrated shark teeth, yes or no? If so, I need quantification for this claim. 2: Again, where does it state that makos bite (comparatively or whatever) harder than other sharks? I actually used the search function on my laptop typing in both 'bite' and 'force', and nothing about bite force seems to pop up. I don't necessarily doubt the claim, but I still want evidence for it. Your source doesn't even seem to specifically discuss anything about the claim you made r.e. bite force. 1: Maybe I didn't word it correctly. What I actually meant by that wasn't that the top was sharper than sharks with serrated teeth, but that most of the sharp area on the tooth was at the tip. 2: Admittedly. I had gotten that from an obscure post on here, which I can't find. Maybe it's the HITTING force that causes the breakage EDIT: theropod you ninja'd me. My post should cover it |
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Post by Infinity Blade on Sept 12, 2019 17:58:06 GMT 5
If most of what's sharp about a tooth is its pointedness as opposed to its edges, and yet it has no actual advantage in pointedness, what results is a tooth inferior in cutting ability.
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Post by dinosauria101 on Sept 12, 2019 19:15:23 GMT 5
If most of what's sharp about a tooth is its pointedness as opposed to its edges, and yet it has no actual advantage in pointedness, what results is a tooth inferior in cutting ability. And that's where the striking speed and striking force come in - they seem to help it. |
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Post by theropod on Sept 12, 2019 19:50:25 GMT 5
Well, you wrote the slicing ability came from sharpness and attack speed (and high bite force).
The speed part is presumably correct, although it should be noted that there are obvious limits on how much speed it can slam into something with without injuring itself (just like an eagle cannot slam into its prey item at 100 km/h no matter what some people on the internet will claim).
The sharpness claim isn’t. Ignoring serrations (which of course significantly improve cutting ability in most cases), the major factors for "sharpness" are the edge angle and the minimum thickness of the edge. Edge thickness can be low (it sometimes is in thick-toothed species, such as megalodon), but the shape of the tooth directly determines the edge angle, which determines how quickly the thickness increases as soon as the edge enters tissue. With a tooth crown with a rounded cross-section (like Mako or T. rex teeth), an acute edge angle simply isn’t possible. That’s why teeth adapted for slicing have broad, labiolingually compressed crowns.
The Mako’s tooth shape is an adaptation for gripping. This fits in well with the diet and pelagic lifestyle of makos. With most of the makos’ diet consisting of fish, it’s unsurprising its teeth are primarily evolved to hold, not cut.
However, as Compagno noted, very large Makos appear to develop more blade-like teeth that may be better suited for cutting larger prey, and those are the individuals that occasionally prey on dolphins.
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Post by dinosauria101 on Sept 12, 2019 20:37:41 GMT 5
Ah, yes, that makes more sense.
Now, I think the force lies within the impact
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Post by theropod on Sept 12, 2019 21:54:49 GMT 5
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Post by Infinity Blade on Sept 12, 2019 21:58:01 GMT 5
Interesting.
So what makes the mako the more adept macropredator? Its speed/levels of activity? Relative size of the mouth (great hammerheads don't seem to have the biggest mouths for their size, nor the proportionately largest teeth)?
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Post by theropod on Sept 12, 2019 23:13:11 GMT 5
Ah…mouth size for their body size…one thing Lowry et al. actually does provide us the answer for.
For I. oxyrinchus upper bite circumference=10^-0.778*TL[mm]^1.009
For S. mokarran Upper bite circumference=10^-1.780*TL[mm]^1.244
For a 3m individuals, the mako would have a bite circumference of 538 mm and the Hammerhead 351 mm. So on the surface, that does look like a small mouth for a given size. However, that’s a bit misleading, because a 3m Mako would mass an estimated 246 kg a 3m Hammerhead just 139 kg.
Scaling the Mako to the same weight as the Hammerhead would actually make it just 251 cm long, at that length the estimated bite circumference goes down to 448 mm. That’s still a 28% larger mouth, but that’s not considering that the Hammerhead seems to be typically larger than the Mako.
A 610 cm Hammerhead would have an estimated bite circumference of 849 mm, a 445cm Mako one of 800 mm (extrapolated beyond data range for both!).
Or for simplicity, for the respective longest individuals actually measured in Lowry et al.’s dataset, the Hammerhead had almost the exact same bite circumference (582 mm) as the Mako (580 mm), the Hammerhead being almost 1 m longer, but probably only around 25% heavier). Predicted mean values for both sizes would still suggest a Mako at those sizes should have a slightly larger mouth, but not much (574 vs 524 mm).
So yes, Hammerheads do seem to have relatively small mouths for a given total length, and to a lesser extent for a given body mass, but they probably don’t have smaller mouths than Makos in absolute terms.
So honestly I’ve got no clue why Hammerheads so overwhelmingly take small prey (in absolute terms). Their size, tooth morphology, mouth size and bite force wouldn’t seem to preclude them from taking similarly large prey as Mako sharks (though relatively smaller considering their own larger body size).
I do sometimes wonder if perhaps their weird head shape is some sort of obstacle when dealing with large prey, either as an obstacle to locomotion (Makos clearly are a lot more athletic, a Hammerhead might have a much more difficult time catching a dolphin than a Mako) or a vulnerability. They reportedly seem to use it for manipulating smaller animals, like stingrays, so that feature itself might be an adaptation for their prey. But that alone doesn’t seem like a satisfactory explanation for why there are so few records of them preying on anything bigger than a stingray or small reef shark.
That being said, there is in fact one record of a fatal attack by a hammerhead shark on a bottlenose dolphin according to Heithaus 2001, which, if legit, is pretty impressive. There are definitely a larger number of accounts of Mako sharks killing dolphins, but still the frequency of such events might be a bit overestimated here, if we follow Heithaus’ numbers Mako predation on cetaceans is very rare. It seems the vast majority of the Mako’s prey base is also fish, even though it (tuna, billfish etc.) is probably bigger than what the Hammerhead usually takes. There is likely a large amount of overlap in the prey size ranges of both species.
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