How heavy may have been Livyatan melvillei ?

[Grey]

Livyatan has been described as the biggest tetrapod bite known and one of the largest predators known to science.
The skull of the holotype topped 3 m long and 2 m wide, the TL estimates are either 13,5 m (based on Physeter), 16,2 m (based on Zygophyseter) and 17,5 m (based on liberal Zygophyseter estimate).

Whatever the exact figure (I suspect that neither are perfect models and the exact size to be in the middle of this, probably around 15 m, but that's my modest feeling only), what could be the approx. correct body mass for this animal ?

Given the size of the skull, it sounds clear that it outweighs the maximum weight predicted for the very largest pliosaurs of ~20 tons (McHenry 2009), and thus, with only Carcharocles, is the only known exception of marine macrophagous hypercarnivore to have exceeded the limits known in orcicines, pliosaurs, mosasaurs and others.

There's no peer reviewed prediction of Livyatan body mass.
The only mentions I know from the describers paleontologists are :
- several tens of tons, like a male sperm whale from Lambert (private com.)
- 30 tons from Rodolfo Salas (video interview during the Lima exhibit).

Certainly these are both educated guess. The one from Salas is probably a safe figure.
I question here the guess of each one.

I reject the 50 tons estimate as serious proposition, unless under liberal figure. I think this 50 tons figure has been made up by amateurs, enthusiasts bloggers, presumably based on the weights of large bull sperm whales and the traditional figure given to megalodon.

I don't argue this figure is totally unlikely, I argue it sounds a bit far-fetched and based on unadapted models (Large Physeter/meg).

Looking at the skulls, my actual guess (once again, nothing definitive here) is that the Melville whale was a shorter, more robust, a bit smaller, more fearsome macropredatory version of the actual sperm whale, and in the lack of more material, just looking at the scale and proportions with Physeter skull, I would accord a plausible body mass of at least 30 tons for Livyatan, around 35 tons, possibly approaching 40 tons. 50 tons is unlikely to me as such a body mass is reached only occasionally by massive bulls sperm whales today.

[theropod]

I'll repost a modified version of my comments in the intraspecific-conflics-section here, as this is relevant to the cetaceans overall size:

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

_{no copyright infridgement intended}

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?

May 18, 2013 22:35:34 GMT 5 theropod said:

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 obviously gives 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 when talking of animals in 15m+ territory. 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 that 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 depending on posture, 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, 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.

May 19, 2013 0:14:03 GMT 5 theropod said:

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:

_{no copyright infridgement intended}
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.

May 19, 2013 3:24:22 GMT 5 theropod said:

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 a stem physeteroid as well.

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 useless for size estimations anyway, should it be true. As there are no postcrania, using it to estimate Livyatan would be like using Oxalaia to estimate Spinosaurus.

May 19, 2013 15:00:02 GMT 5 theropod said:

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 have certainity 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, and extant analogues could be used as a point suggesting higher ranges like the one suggested by Z. varolai.
To me personally, the skull in the skeletal seems too massive in comparison with the body, eg. the skull is about as long as the whole ribcage. That's something we simply do not see in other relatively unspecialized raptorial cetaceans, only in highly adapted suction or filter feeders like Balaena or Physeter.

[creature386]

Mar 22, 2013 5:58:07 GMT 5 Grey said:

I think this 50 tons figure has been made up by amateurs

Probably. I got a similar weight (56 t) when scaling an orca to 17,5 t, so you can see that as the very maximum.

[theropod]

I think near the upper size range suggested for the L. melvillei holotype, 50t is not unrealistic, and 30 definitely too low. Near the lower end (that's what you see in the skeleton above), 30-40t sounds good.

Grey: How heavy was the C. megalodon in the skeletal you gave me supposed to be? That'd help to gauge the mass of the smallish Livyatan.

[Grey]

This is the Gottfried meg, so it depends the body length.

But the problem that Kent told me in that model is that the upper lobe of the tail is a bit too much strained at the back, which increases the actual length.

Anyway, if it is at 52 feet, it is roughly 48 tons.

[Fragillimus335]

I'd say ~35 tons, perhaps a bit more if it packed on the blubber!

[creature386]

May 21, 2013 0:52:03 GMT 5 theropod said:

I think near the upper size range suggested for the L. melvillei holotype, 50t is not unrealistic

The upper end however may be unrealistic. Grey wrote under my second blog entry, that Lambert (in a mail) believes a bit more than 15 m to be the most likely estimate.

[theropod]

Exactly, he believes that, which doesn't mean it must be true. That's a mere personal opinion.

I'd say ~30-35t are good for the Livyatan I made based on B. shigensis, when comparing it to the 48t meg next to it.

[Grey]

Reading at the supplementary information, I remarked that there is a difference between skeleton length and body length. Looking at the datas for similar-sized cetaceans, this 12,5 m skeleton should give an approx. 13,5 m animal in life, so similar to the one based on Physeter.

At the Lima exhibit about the discovery, Livyatan melvillei was listed at 25 tons for 15 m.
Whetever this is too light or not, this at least provides an idea of the range they guess their giant sperm whale.

[theropod]

Museums are unreliable, or we could start arguing about the weight for 50m Argentinosaurus lol (would be ~330t...)

Considering it would be bulkier than Physeter, 25t at 15m is too low.

[Grey]

That's not the Museum stuff, that's the whole team stuff.

That's probably a rough guess, it gives an idea of the scale and range, not an actual precise data.