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[theropod]

Sci-Hub can access the paper, but I have sent it to you

Yes, an empirical explanation would spring to mind, the problem is that I’m getting totally absurd results from the formula (which wouldn’t seem to fit any actual alligators over the size range they studied and the original data aren’t available to check against either. The only thing they seem to have used the equation for was for analyzing the residuals (which they state to be normally distributed), but they don’t report any of the actual figures.

[Infinity Blade]

Some people make a strict distinction between whales, dolphins, and porpoises. I've been reminded of this before and again recently. But can't/don't we just consider all cetaceans to be whales? For a while I've just thought of dolphins and porpoises as subsets of whales. All the more so since they're odontocetes and we consider other odontocetes (e.g. sperm whales) to just be whales. Isn't it a bit arbitrary to consider the common ancestor of all modern odontocetes to be whales, physeteroids and beaked whales to be whales, but this one family (Delphinidae; oceanic dolphins) and these three superfamilies (Inioidea, Platanistoidea, and Lipotoidea; river dolphins) to be dolphins but not whales, and this one family (Phocoenidae) to be porpoises but not whales?

I know this just concerns the usage of colloquial terms, not actual phylogenetic ones, but still.

[creature386]

I'm fairly used to this, let's call it "colloquial paraphyly". Humans are routinely excluded from apes and so are birds from reptiles/dinosaurs. However, in these cases, there are strong superficial phenotypical differences that justify this distinction. Dolphins on the other hand are just whales with funny noses, so I'm as confused as you are.

[theropod]

Sept 25, 2019 23:11:58 GMT 5 Infinity Blade said:

Some people make a strict distinction between whales, dolphins, and porpoises. I've been reminded of this before and again recently. But can't/don't we just consider all cetaceans to be whales? For a while I've just thought of dolphins and porpoises as subsets of whales. All the more so since they're odontocetes and we consider other odontocetes (e.g. sperm whales) to just be whales. Isn't it a bit arbitrary to consider the common ancestor of all modern odontocetes to be whales, physeteroids and beaked whales to be whales, but this one family (Delphinidae; oceanic dolphins) and these three superfamilies (Inioidea, Platanistoidea, and Lipotoidea; river dolphins) to be dolphins but not whales, and this one family (Phocoenidae) to be porpoises but not whales?

I know this just concerns the usage of colloquial terms, not actual phylogenetic ones, but still.

You are absolutely correct.
I have occasionally read this kind of statement on this forum before, and it always makes me cringe:
"X is not a whale, it’s a dolphin"
This is both wrong, and irrelevant.

It would be correct, and might be relevant, to note that a taxon is not a physeteroid, or balaenopterid, or ziphiid, but a delphinid, but then say it like that, don’t say that they are not whales, because they are just as much whales as any of those families. The term 'cetus' literally means 'whale'. Correct common names for odontocetes and mysticetes are 'toothed whales' and 'baleen whales'. It is clear that the term 'whale' applies to all cetaceans, popular usage of something like "whales, dolphins and porpoises" is a wrong and misleading terminology seemingly born out of an improper understanding of systematics.

[Verdugo]

Anyone knows the difference between 2D and 3D Bite Force methodologies? Have these concepts ever been officially described in any studies? Yes i usually talk about these concepts a lot, but to be honest, i do not understand it quite clearly myself i sometimes got quite confused with it. Most studies usually stated the methodologies they're using are 3D or 2D but sometimes they don't. For what i know, 2D methods are called 2D because it usually evolves only the measurement the temporal area and the actual muscle reconstruction is not necessary (hence the name 2D). For example, see Christiansen 2007:

As you can see, in this study, they only measured the area of the temporal region (in order to estimate the cross sectional area of the jaw muscles) but no reconstructions of actual muscles. In-level arms are usually assumed to be the distance between the centroid of the cross section and the mandibular joint instead of actual in level arms of such muscles.

On the other hand, 3D methods usually evolve more rigorous muscle reconstructions where researchers try to determine the muscle origin and insertion points based on the scars in the bones. For example, see Gignac 2017

As you can see, muscles are reconstructed rigorously. In-level arms will also be more specific to each muscle groups.

McHenry 2009 pointed out that main difference between 2D and 3D methods is that 3D usually provide more accurate in-level arms (thanks to more rigorous muscle reconstruction instead of just assuming the in-level arms based on the temporal openings):

However, dry skull derived estimates are potentially useful if the discrepancy is consistent. There is reason to think that the discrepancy between dry skull estimates and in vivo measurements is a result of two factors; (1) the 2D dry skull method underestimates the effective inlever of the jaw muscles, and (2) the measurement of cross-sectional area (CSA) of jaw muscles used in the dry skull method does not account for muscle pennation and therefore underestimates physiological cross-sectional area (PCSA). Evidence for the first comes from the 3D FE models constructed by McHenry et al. (2007) and Wroe et al. (2007); for the lion Panthera leo, the dingo Canis lupus dingo, and the thylacine Thylacinus cynocephalus6, the bite force from the 3D models was considerably greater than that derived from the same specimens using the 2D approach. Since the principal difference between the 2D and 3D models is the estimation of the jaw muscle inlevers – the 3D models approximate the actual geometry of the jaw muscle fibre bundles – it is tempting to conclude that this factor may be an important component of the difference between the 2D dry skull and the in vivo results.

The results highlight several technical issues relating to the methodology used to model skull biomechanics. Consistent with previous studies using these methods (McHenry et al. 2007, Wroe 2007)9, the estimate of bite force using the 3D finite element models was higher than the corresponding estimate using the 2D dry-skull approach: given that the estimates of muscle force and outlever distance are consistent between the 2D and 3D methods, this is likely to be a result of the geometry used to model the jaw muscles in the FE models increasing the lengths of the effective inlevers for the jaw muscles, as noted in Section 7.2 above.

Here is my problem, i came across this study on Carnotaurus's BF but i can't quite determine if the methodologies are more akin to 3D or 2D. Based on my understand, it seems more akin to 3D but i'm not sure...

[Infinity Blade]

Regarding the Carnotaurus study, I put the doi of it in sci-hub. This is what it says.

In this study, we constructed three-dimensional FE models of the cranium of Carnotaurus to evaluate how it performed mechanically under loads associated with biting and frontal butting.

Fig. 2 of the study is also a 3-D computerized model of the skull of Carnotaurus.

But with regards to bite force, they also say that they made clay restorations of the jaw musculature. So, uh...I don't know.

[Verdugo]

Sept 28, 2019 6:29:00 GMT 5 Infinity Blade said:

Regarding the Carnotaurus study, I put the doi of it in sci-hub. This is what it says.

In this study, we constructed three-dimensional FE models of the cranium of Carnotaurus to evaluate how it performed mechanically under loads associated with biting and frontal butting.

Fig. 2 of the study is also a 3-D computerized model of the skull of Carnotaurus.

But with regards to bite force, they also say that they made clay restorations of the jaw musculature. So, uh...I don't know.

They used the 3D FEA to test the skull performance, however, FEA was not used for calculating the BF. I have done quite a bit reading on various BF methodologies and i think i can conclude that the methodology in that Carnotaurus study is 2D level arm dry skull (of course, if you disagree, feel free to discuss). For example, you can look at Fig 3 which shows 2D level arms of different muscle groups. In fact, the methodology that they used is sort of an Archosaur version of Thomason 1991 (which is for Mammals). Sakamoto et al 2018 also used a somewhat similar 2D level arm methods too.

If you're interested in reading more about 2D and 3D level arm methods (not all 3D methods are FEA or MDA), i suggest you could read:
Lautenschlager (2012)
Sellers et al (2017)
Cost et al (2019)

[Infinity Blade]

I don't disagree.

If it's a two-dimensional bite force estimate, then I guess the absolute figures for bite force shouldn't be taken at face value. Therrien & Henderson (2005) also don't support the idea that Carnotaurus was a fast but weak biter either, although I'm skeptical of their bite force estimates too.

[Verdugo]

Sept 28, 2019 18:25:51 GMT 5 Infinity Blade said:

I don't disagree.

If it's a two-dimensional bite force estimate, then I guess the absolute figures for bite force shouldn't be taken at face value. Therrien & Henderson (2005) also don't support the idea that Carnotaurus was a fast but weak biter either, although I'm skeptical of their bite force estimates too.

To be fair, modelled BF hardly ever measure up to in vivo. I think this is an issue that we have talked quite a lot about in the past. To summary it, there two main issues of why modelled and in vivo BF usually do not match: pterygoid muscles in reptiles are difficult to estimate; they represent different concepts of BF (Snapping/Impact vs Sustained/Static). So yes, i agree we should not take it at face value.

However, i don't think we should just discredit modelled BF, especially 2D ones. Refer to McHenry 2009 in which he pointed out the principle difference in 2D and 3D is merely just the in-level arm. There are quite a few factors that could affect the BF estimate other than just in-level arms. For instance, BF could be estimated as:

BF = (Physiological cross sectional area) * (Specific muscle force/tension) * (In-level) / (Out-level)

Obviously, i'm probably oversimplifying it here for the sake of our discussion (other stuffs just too complicated for me to comprehend anyway). PCSA depends on pennation as you probably already knew. When taking into account of pennation, PCSA increases, leads to an increase in BF even though all else stay equal. Pennation is irrelevant of whether the methods are 2D and 3D. 2D methods can sometimes take into account of pennation (Sakamoto 2018) while 3D methods sometimes did not take into account of pennation (Gignac & Erickson 2017). For example, Stan BF in Sakamoto 2018 is 2D with pennations and it's higher than that of Gignac & Erickson 2017 which is 3D without pennation. What i'm trying to say here is that, just because it's 2D, does not mean that it always underestimate BF and that we should discredit it. 2D BF with pennation are still quite appropriate and the estimates are usually not that low. Regardless, 2D are still meaningful for comparison purpose (compare 2D to 2D, just don't compare it in vivo)

Regarding the Carnotaurus's BF, there are two BF figures for Carnotaurus in the study (Mazzetta 2009):
2D no pennation = 3300 N
2D with pennation = 5300 N

Let just see if those figures are too low,
Gator's BF from Sellers 2017:
3D with pennation = 3500 N
3D with pennation + pterygoid adjusted = 4500 N

Gator's BF from Bates (2012):
3D with pennation MIN = 3600 N
3D with pennation MAX = 5800 N

As you can see, only the MAX model in Bates 2012 is comparable to the 2D pennation BF of Carnotaurus. On the other hand, Carnotaurus's 2D no pennation is comparable to Gator's 3D pennation in Sellers 2017. Maybe it's not too impressive for a Carnivore of its size but certainly not too weak by any means, not in absolute terms. The Gator of the size in Bates and Sellers probably has an in vivo BF of 8000 - 9000 N so you could expect the Carnotaurus in vivo to be in that range, if not even higher.

Regarding Therien 2005 though, it's quite problematic tbh. I'm not suggesting that we should discredit it entirely but i'm not sure how much faith i want to put on it though. You can read Porro 2011 in which they pointed out that the methodology in Therrien is not accurate when compared to FEA:

Lever arm calculations and beam models have
been used extensively to evaluate the mechanical
behavior and morphology of archosaur crania and
mandibles (Sinclair and Alexander, 1987; Busbey,
1995; Cleuren et al., 1995; Mazzetta et al., 1998;
Henderson, 2002; Therrien, 2005; Desojo and Vizcaı
´no, 2009; Tanoue et al., 2009). The results presented
here suggest that these calculations provide
approximate estimates of the general orientation
of bite or joint reaction forces, and the general distribution
of dorsoventral bending stresses, and
sagittal and transverse shear stresses in the mandible.
However, they perform poorly in predicting
absolute or relative reaction force magnitudes, precise
reaction force orientation, and mediolateral
bending and torsional stress distribution within
the mandible. Although the beam models experienced
dorsoventral bending and sagittal and transverse
shear stress patterns similar to the Alligator
FEMs, stress magnitudes were substantially different.
One of the most notable differences between
the beam models and the Alligator FEMs was the
behavior of the balancing side, which varied with
changes in bite position in the Alligator FEMs,
suggesting that the behavior of the balancing side
is poorly represented in simple beam models in
which the working side and balancing side are
modeled separately. Overall, beam models do not
accurately represent the mechanical behavior of
the archosaur mandible, despite its superficial resemblance
to a beam.

Or you can see Therrien (2005) in which the BF of many Sabertooth Carnivores (such as Smilodon or Thylacosmilus) are overestimated when compared to 3D FEA BF in Wroe 2013. You could argue the Sabertooth are specialised feeders but that still makes the universal applicability of this method questionable. For instance, in Therrien 2005, he used the method on both Ora and Gator who have very different mandible morphology. One has kinetic mandible for swallowing large preys and the other had akinetic mandible for withstanding force.

Or in D'Amore 2011 in which they pointed out that the result in Therrien 2005 overestimated the BF of Ora when compared to in vivo:

2D models have been less accurate in predicting V. komodoensis bite force. Using the Sinclair and Alexander beam approach [8], the individual modeled by Moreno et al. above would have an anterior bite force of 11 N (taken from Moreno et al. [27]). This greatly underestimates our in vivo results. Therrien et al. [9] also proposed that a V. komodoensis individual with a 16.96 cm mandible should have a bite force 0.086 times that of an Alligator mississippiensis individual with a mandible length of 50.08 cm. Using the regression derived from experimentally acquired A. mississippiensis bite forces from Erickson et al. [18], the V. komodoensis individual modeled by Moreno et al. (HL = 14.20) [27] would have a maximum bite force of 695.97 N, greatly overestimating its capability.

Too many convoluted issues with Therrien 2005 imo

EDIT: If you think this is too off topic, feel free to move it to a more appropriate thread

[Infinity Blade]

creature386

How did you get the opportunity to go to SVPCA?

[creature386]

They give such an opportunity to pretty much anyone who can pay, regardless if they present or not. You can check out their website if you are looking for opportunities to apply to the next meeting.

I'm not sure if I'll be coming again any time soon, as my current trajectories (should I succeed in research at all) go more in the direction of palynology than vertebrate paleontology.

[Infinity Blade]

How do the two Edmontosaurus species really compare in size? I know (or think) there are a couple E. annectens specimens that were quite large (12-15m?), but weren't typical individuals much smaller than this? E. regalis is thought of as being, if anything, larger than the later species by Greg Paul (as recently as his 2016 edition of the Princeton Field Guide to Dinosaurs).

[Infinity Blade]

Oct 10, 2019 3:41:40 GMT 5 Infinity Blade said:

How do the two Edmontosaurus species really compare in size? I know (or think) there are a couple E. annectens specimens that were quite large (12-15m?), but weren't typical individuals much smaller than this? E. regalis is thought of as being, if anything, larger than the later species by Greg Paul (as recently as his 2016 edition of the Princeton Field Guide to Dinosaurs).

I've gotten this question answered for me.

randomdinos estimated a specimen of E. regalis at ~6.7t in one of his size charts.



These are a few E. annectens individuals.



They average at 7.72t, which would suggest E. annectens might be somewhat larger. So this would suggest that the claim that E. regalis was, if anything (which to be fair Paul does say exactly this), larger is incorrect, but it still seems to remain that Edmontosaurus did not get a whole lot bigger from the Campanian to the Maastrichtian.

Any other thoughts?

[Infinity Blade]

So, I've been trying to figure out the strength of an animal's horn composed of a horny sheath over a bony core composed of cortical bone walling with trabeculae inside (I figured that they should be similar across all animals with such a structure, whether we're talking about a bovid, a ceratopsid, etc.).

I found a study that found that, under 8% water content (where it has the highest work of fracture versus 19% and 0% water content), a domestic cattle horn has a tensile strength of 104.53 MPa (see table 2->). Because the keratin sheath and bone core complement each other in strength, would we then simply add on the tensile strength of the bone core (I posted earlier that this seems to be ~130 MPa) to the tensile strength of the sheath to find the whole horn's strength?

[Verdugo]

Nov 25, 2019 4:29:02 GMT 5 Infinity Blade said:

So, I've been trying to figure out the strength of an animal's horn composed of a horny sheath over a bony core composed of cortical bone walling with trabeculae inside (I figured that they should be similar across all animals with such a structure, whether we're talking about a bovid, a ceratopsid, etc.).

I found a study that found that, under 8% water content (where it has the highest work of fracture versus 19% and 0% water content), a domestic cattle horn has a tensile strength of 104.53 MPa (see table 2->). Because the keratin sheath and bone core complement each other in strength, would we then simply add on the tensile strength of the bone core (I posted earlier that this seems to be ~130 MPa) to the tensile strength of the sheath to find the whole horn's strength?

What did you mean by 'add on'? I hope you did not mean that we would just simply take a sum of the two figures and call it a day because i don't think that is mathematically appropriate (if my understanding of this stuff is correct).

What you could do instead, imo, is looking at the cross sectional area the horn to see how much of it is Bone and how much of it is Keratin, then you can work out the average of the entire structure (assuming the keratin and bone complement each other like you said and it does not just break at the weakest point, which would be the keratin).

For instance, if you found out that the structure is 60% keratin and 40% bone, then the Strength would be:
0.6*105 + 0.4*130 = 115 MPa

Or if it's 50/50 for each:
0.5*105 + 0.5*130 = 117.5 MPa