Megalodon vs. Livyatan melvillei

[Grey]

Thanks Life.

Now I suggest it would be interesting to somhow place the skull of Livyatan on that skeleton, perhaps with a human shape for scale ? If someone can do it that would be great.

[theropod]

Thanks life, that helps! Looks in between an Orca's and a Sperm whale's skeletal-morphology for me.

[theropod]

This got really awkward-looking, and extremely short, even shorter than based on Physeter. I tought it should get to around 15m based on B. shigensis? based on the reported skull lenght and total lenght, it should be (7m Tl/1,4m Sl), but the skeleton is in disagreement with this. Could it be the holotype of Brygmophyseter is a juvenile?

[Grey]

You forget that the tail fluke is not counted in the skeletal structure. You can add perhaps 1,5-2 m of body length, even though I agree that's surprisingly conservative in length, but also quite a bulky looking animal. I suspected that. That fits with the figure "dinorider" had heard from the Lima exhibit, something smaller than Physeter but bulkier (Gimli/Legolas !). That's why again, overall, I suspect Livyatan (holotype) to have been quite not as large as some megatooth sharks specimens are reconstructed.

Good job theropod that being said.

[creature386]

May 18, 2013 16:24:46 GMT 5 theropod said:

Could it be the holotype of Brygmophyseter is a juvenile?

www.gmnh.pref.gunma.jp/research/no_10/bulletin10_1_1.pdf
They said it has a medium body size in adulthood, as we only have one specimen, it was very likely reffering to the holotype.

[Grey]

Thanks for the paper man, you're both good at use peer-reviewed stuff at now.

I'm thinking theropod, if you can you could also use this Carcharocles skeletal reproduction and compare it with that Livyatan speculative skeletal structure at the respective scales (16,8 m for megatooth).



I'm sorry, I'm a di*k at manipulating images.

[theropod]

Like this?

If I find time I'll search for some other animals to base Livyatan on.
One thing to note is that while the Megatooth is at a pretty good size estimate imo, this is a lenght well below even the most conservative lenghts ever proposed for the cetacean, so it might give a pretty one-sided image.

In such a short-bodied animal I doubt the fluke would add much, it mainly does due to slight perspective in almost every drawing of a cetacean there is and even then not more than 0,5-1m. This Livyatan is less than 13m long, while even the bizygomatic width of huge-skulled Physeter macrocephalus suggested ~14m. I find it strange the actual lenght of B. shigensis deviates so far from the one given for it. Could this also hold true for C. megalodon? In my scaling-experiments with Theropods I found out with very few exceptions all of them consistently ended up significantly shorter than the given axial lenghts, which is the reason I now only use anatomical measurements that don't change, like femoral or skull lenght. This Livyatan bases on skull lenght, the Carcharocles on total lenght.
Best would be to do more than one Livyatan restoration. However this one is indeed an extremely bulky animal, more like Orcinus than Physeter in this regard, even tough as large-skulled as the latter.

Sorry for the bad resolution, I relied on the images posted here and had to scale them even further down to make them fit each other. This is just an arbitrary scale anyway, but I think it is still possible to see it properly.

Grey: Gimp's really easy, you should try it if you have time! You'll see, it is not only useful but also fun.

@creature: Thanks for the paper, I'm gonna read it!

[Grey]

Excellent work.

The issues for estimating Carcharocles sizes are not the same than for the physeteroid here. But no, I think that the fluke shape actually adds a bit more of length if I remember right.

Would also the skeleton of Brygmophyseter lacks some vertebras ?

With all these uncertainties, I'm quite sure the dead end approaches 14 m, perhaps 15 if there are really missing vertebras.

[theropod]

Good idea, missing vertebrae are a possibility.

Regarding the fluke, have a look at early comparisons of mine. the Cetaceans were consistently much larger than this one, and affected by slight perspective, still, the fin did only add short of a metre.
lh3.googleusercontent.com/-dAo5l6y7oWU/UAwlgo02P8I/AAAAAAAAArk/tATuSpBT9Mg/w381-h702-no/plio_mio_sea_comp-NEW.jpg

However the fluke is not included in valid measurements of cetaceans as far as I know, whales are measured in one line from the tip of the rostrum along the midline to the medial indentation.

[theropod]

Here's the fluke of an Orca:
animalgalleries.org/albums/Ocean%20Mammals/Orcas/Orca%20Orcinus%20Killer%20Whale%20%20fluke%20tail_waving02.jpg

and this I think belongs to a humpback whale, but I didn't check:
www.mnh.si.edu/exhibits/whales/WhaleFluke.jpg

The humpback's fluke has a deeper notch and would add more to the total lenght. That being said, neither would add a lot, and enough to make the livyatan above much longer, tough enough to make consideration in visual comparisons necessary, and Sperms whales are closer to Orcas in terms of fluke morphology.

For comparisonal purposes, here's the skeleton of O. orca, this should give an idea of how much smaller the head of a raptorial cetacean can be:

This one's total lenght is about 6,3 times its total lenght, in the Brygmophyseter above it is roughly 4,25 times.
I think the real proportions of Livyatan ought to be somewhere in between.

[Grey]

Interesting posts, especially about the fluke question.

However, I don't see why Livyatan skull should be somewhere between the ratio of B. shigensis and O. orca. All three are raptorial but B. shigensis is definitely far more revelant to be compared with Livyatan. O. orca is a delphinid, all delphinids have different ration and body structures than the extant and extinct sperm whales. There is no reason to date to suggest Livyatan was somewhere between its physeteroid relative and the delphinid.

Or we could use Basilosaurus then and end up with a 30-40 m Livyatan...

Physeteroids and overall sperm whales are a very particular looking group and the only Livyatan has to be compared with.

Even though, Livyatan proportionned like an orca would be perhaps the most monstrous carnivore that ever lived, rivaling or surpassing Carcharocles, but there's just no reason to think this. The barrel chest body in orcas is itself very specific.

[theropod]

The chest of Brygmophyseter is kinda like an Orcas', not the same but it is clearly more barrel-chested than an extant sperm whale, like you supported yourself.
I am not suggesting to use O. orca, tough it might be at least as good as using Physeter, but apparently Z. varolei is in between these two, and it is too a stem physeteroid.

There are certain parallels leading to analogous morphology in animals with similar ecology, this is why Zygophyseter has a proportionally smaller head than Physeter. Unfortunately neither Zygophyseter not Brygmophyseter resembles Livyatan closely in terms of cranial morphology, both of them having much flatter skull roofs than the one of L. melvillei, O. orca or A. deinodon, and less curved jawlines the Livyatan or Acrophyseter. Such details can matter a lot.

There are no postcrania of Acrophyseter, and based on the really small size I have wondered whether it could be a juvenile specimen, which would make it pretty useless for size estimations anyway, should it be true.
It could potentially be quite useful if it had a postcranium tough!

[Grey]

Still, no reconstruction of all these physeteroids describe a barrel-chested animal, nor a ratio skull/head similar or approaching the one in orca. Being bulkier does not mean approaching the built of an orca. Zygophyseter does not exhibit an orca-like body, but a modified Physeter-like body shape.

The convergent evolution is too limited and not evidenced at this point, especially between two members of differents families, of different sizes (Livyatan is in clear superior size range/scale than the orca), of different eras and oceanic environments, and not necessary of an absolutely similar lifestyle.

I'm strictly opposed to establish O. orca as a better analogue than Physeter for Livyatan ! This has not been suggested at all since phylogenetic prevails on a speculative convergent evolution. All the raptorial cetaceans apex carnivores that ever evolved did not have a body like O. orca.

To me, use O. orca as a physical built model for Livyatan is barely more logical to use an archeocete of a suggested similar niche.

I could send a mail with such a question to Lambert, but frankly I already know the kind of response incoming...

[creature386]

By the way, does anyone know the skull length of Acrophyseter? It looks like ~80 cm (I added a bit, as I didn't measure it along the curve). in that image:

www.provincia.livorno.it/attivita/museo/pubblicazioni/23/lambert.pdf
If the length estimates are correct, it would yield over 15 m for Livyatan, but it isn't more complete than Livyatan, so this is pointless.

[theropod]

Yeah, it is pointless. A bit like using Oxalaia to estimate the size of Spinosaurus.
But I admire your skills to find PDF's, I had already searched for that paper without success.

Grey: I do not suggest O. orca as an analogue (but neither Physeter), I wanted to point out that brygmophyseter seems very large-skulled when compared to other raptorial cetaceans. And "Archaeocetes" with snakelike, elongate bodies, that haven't even fully developed their blowholes or fully lost their external hindlimbs are hardly a suitable comparison for an analogy between two Odontocetes with similar niches and morphologies.
Convergent evolution can lead to surprisingly similar morphologies. Cetaceans themselves or Birds are the best examples of this, but just have a look at the surprising amount of polyphyletic groupings that has happened over time! This of course applies to Brygmophyseter as well, but morphology and ecology can be at least as important as phylogeny when it is about proportions. Livyatan's skull shows marked morphological similarities to that of an Orca, and as proposed in its description and concluded from said morphology, probably had a simialr lifestyle.
Hence I do not really see a reason why Physeter macrocephalus should be a better base then O. orca, tough both are not really good.
It is important to be aware of the uncertainity and possible different proportions in this case, after all we have to do that with C. megalodon as well.

We will only be able to see which is right when new remains are found, but I would suggest Brygmophyseter-based estimates, which may barely reach 14m as some of the posterior caudals seem to be missing (the skeleton as it is is 12,5m!), should be taken as a lower bound.