Andrewsarchus mongoliensis vs. Sarkastodon mongoliensis

[theropod]

Looks like a very decisive victory for the Andrewsarcus. Also, looks as if Daeodon and Andrewsarcus actually were the biggest predatory land mammals we have.

here’s what I replied to Spinodontosaurus’ comparison between Andrewsarcus and Spinosaurus (note it obviously isn’t to scale):

theropod said:

Quite debatable whether one should call them similar at all, based on this comparison. Andrewsarcus has a wider and much deeper skull, a much steeper expansion of the posterior part, a far less uniform width throughout the rostrum, and heterodont dentition with caniniform and carnassialomorph parts. The posterior ones appear to be powerful shearing teeth with edges, actually, they are massive and very close to the jaw muscles, indicating large bite forces there, and although the skull is somewhat elongate, it is still fairly robust and not too far from canids (at least much closer than to Spinosaurines).

Their only similarity is that the anterior part shows a constriction and a gap between teeth (though that is far more marked in Spinosaurus). Actually, That isn’t even a superficial similarity. There are a few paralells, but I wouldn’t call them similar.

Actually, I think the skull is much more similar to a T. rex than to a Spinosaurus.

[creature386]

Looks like it could crush Sarkastodon's head with one bite.

[theropod]

Yes, probably. That’s one huge skull, giant zygomatic arches and temporal fossa, and massive teeth. I actually do not see it having a weak bite at all, even though its sagittal crest is small.

I find the thought intriguing that both of these may have been amphibious. The flat skull and the otter-like body in Sarkastodon are consistent with this. The elongate cranium of Andrewsarcus, not too different from that of Basilosaurus-grade cetaceans, is too. It could have belonged to an entelodont-like body-type as well though.

[theropod]

Spinosaurus and Andrewsarcus are to scale, T. rex is fitted to be the same skull lenght. You can see despite being only about half the total skull lenght, Andrewsarcus’ rostrum slightly wider and deeper than that of Spinosaurus. One can clearly observe an overlap with T. rex in terms of shape and robusticity, features that are adaptions for powerful biting such as the steep posterior expansion compared to the just moderately deep and wide rostrum, the large temporal cavity and the thick teeth.

[Infinity Blade]

Yet according to Darren Naish, there are also things to suggest a not-so powerful bite.

While it may well be that Andrewsarchus was an entelodont-like predator and/or omnivore (for more on entelodonts see Tet Zoo picture of the day # 23 and Giant killer pigs from hell), there are, however, indications that Andrewsarchus was freakishly weird, and doing something very special. In fact, the weirdness of its skull is routinely not depicted correctly in life restorations. Its snout is strikingly long and narrow, and ‘pinched in’ about half-way along its length. The result is that the distal end of the rostrum forms a sub-circular rosette that almost resembles that of a spinosaurid theropod. Its orbits are located way down on the sides of its skull and were widely separated by the broad base of the snout, and its entire occipital region looks narrower, and smaller, than expected in an animal of this size. The glenoid fossa is flattened compared to that of ‘proper’ mesonychians, and the associated pre- and post-glenoid structures on the zygomatic arch are small. The sagittal crest is small as well. These features all suggest that the jaws were relatively weak. And while the upper canines were said by Osborn (1924) to be enormous, they aren’t: ‘The canines are very reduced in size and in proportion to the whole dentition and to the whole skull’ (Szalay & Gould 1966, p. 154). Clearly, Andrewsarchus is just crying out for some neat functional study on cranial kinematics and function. Come on: surely someone, by now, must have thought of doing FEA or something on its skull?

scienceblogs.com/tetrapodzoology/2009/08/11/mesonychians-part-ii/

One of the commenters also stated large zygomatic arches (at least alone which admittedly doesn't seem to be the case here) don't equate to a powerful bite (despite holding more muscles and force), even calling the shape of them gracile.

I'm sort of in between this right now, adaptations suggesting a rather strong bite, and adaptations suggesting otherwise.

But it seems either way, Andrewsarchus should win easily.

[theropod]

I cannot see how they are gracile, they are actually tremendously robust. But yes, it is right that large zygomatics alone do not mean a powerful bite. They are just commonly associated with it in mammals, because the arch is where the jaw muscles go through, and it being large suggests the muscles to be large.

That "strikingly long" and gracile snout is still almost as robust as that of a T. rex, not that of Spinosaurus.

[Infinity Blade]

The snout also looks like Spinosaurus too (the pinch).

[theropod]

Yes, I have noticed that too. But this is the only similarity I can see, and it is still far less marked in Andrewsarcus than in Spinosaurus.

[creature386]

And that pinch still appears to be proportionally a lot wider than in Spinosaurus. While it is true that the pinch is hindering, due to the sheer size advantage of it's skull compared to Sarkastodon, it would still be superior in bite force, although I maybe have to retract my crushing statement.

[theropod]

Canine bite force may have been greater in the more brevirostrine creodont, but I think due to the sheer skull size, the bite force at the molars would be greater in Andrewsarcus, forming an effective "bone-scissor".

[blaze]

I think comparison with other mammals, specially those thought to be related to it puts the comments about small teeth, long snout and weakly developed sagittal crest and flattened glenoid fossa in perspective.

Szalay & Gould (1966) is the source of the small canines comment, noting that both Mongolonyx dolichognathus and Mongolestes hadrodens, with skulls half as long as that of Andrewsarchus, had canines just as big. You can see that in the comparison above that proportionally speaking, the canines of Harpagolestes were also massive compared to those of Andrewsarchus (compare the width of the alveolus not the outline of the size that Osborn estimated it at).

Measuring the distance from the tip of the premaxilla to the orbits and that from the tip of the premaxilla to the occipital condyles we get that the type of Harpagolestes uintensis has a snout that's 45% the length of its skull, in Andrewsarchus and "dinohyus" this distance is 56-57%, Osborn (1924) gives a similar measurement, length from first incisor to the last molar and last molar to basion (anteriormost point of the foramen magnum) giving us the snout of the same specimen of Harpagolestes uintensis at 48% and that of Andrewsarchus at 60%.

The gracile zygomathic arches, I think is more noticeable in photographs than in the illustration. Like this one

[theropod]

True.

But look at Harpagolestes, its sagittal creast is enourmous, also compared to the entelodont! Andrewsarcus’ teeth for the most part are really big. The canines aren’t though. Overall, I’d still say it’s similar to the Daeodon skull.

another thing is that not all mammalian jaw muscles attach at the sagittal crest, just the temporalis:



The "layout" of those muscles can vary, in animals with strong bites. And if the crest is atrophied, that might simply mean the temporalis’ role in jaw adduction was reduced compared to the masseter, not that the bite was weak overall. In this case, I’d definitely consider this, since that very process of the zygomatics that the masseter attaches on is hypertrophied immensely in entelodonts, and since the posterior part of the arch is very broad in Andrewsarcus.

[Infinity Blade]

Yep, by virtue of size alone, the artiodactyl will have a stronger bite. Mismatch.

[blaze]

Yes, even if it had a comparatively weak bite, the sheer size of the skull will make up for it.

theropod
It might have a strong bite or it might not, we can only hypothesize given the lack of remains. sadface

btw surprise surprise, Andrewsarchus is from China not Mongolia, how many of you already knew?

[Deleted]

It looks like the Andrewsarchus can just rip the head off of Sarkastodon.