Did brontotheres headbutt?

[Infinity Blade]

I don't think the last thread I made was executed quite well, so I've decided to change the topic title (although, the fundamental question is still sort of the same, in a way). What I wonder is, did brontotheres actually headbutt other animals? It was initially assumed they could headbutt with solid bone(?) and certainly impressive looking horns, but Donald Prothero claimed that brontothere horns were anchored onto thin nasal bones of a skull that itself was lightly built and filled with spongy bone. Despite evidence of injury in brontotheres, presumably caused by conspecifics (a rib injury found in a Megacerops), Prothero believes head shoving and lateral head swinging would have been sufficient to cause such damage (link 1, link 2).

However, bighorn sheep horn cores contain trabeculae as well, and these have been found to actually be beneficial for headbutting (relative to hollow horns with the trabeculae removed, anyway; link). On the other hand, elephants and rhinos have pneumatic skulls as well, and yet I've seen no accounts or evidence of them headbutting like say, a bighorn sheep.

So what do you all think? Could at least some brontotheres headbutt or were their skulls simply not up to the job? Is there something I'm missing here or mixing up?

[Infinity Blade]

I'm going to bump this thread because I've changed the topic title and I think I have a more fleshed out question now.

[blaze]

The trabecular bone inside a bighorn sheep's horn core gives it sort of a honey comb interior, it makes sense that it helps to absorb impacts but its horns aren't, as you said is the case in brontheres, anchored to thin nasal bones, in this respect brontothere horns and overall skull build resembles that of a rhino.

Rhino and brontothere have their horns anchored to relatively weak parts of the skull, which could suggest that the spongy bone is more for weight saving, as is the case of elephants and their pneumatic skulls

[Infinity Blade]

I also realized how rhino horns are attached to skin that in turn attaches to the nasal bone, which seems to create a structural weak point. When it comes to ramming/butting something (especially something that itself is rhino-sized, if not bigger), that doesn't sound ideal. Brontothere horns might have fared better in this regard (since they're literally just bone extensions of the skull), but I guess they were still unable to headbutt or ram given their horn placement.

I guess what you said about the nasal bone being relatively thin is why that replica Triceratops skull in The Truth About Killer Dinosaurs' crash test shattered its nasal region (meanwhile, the brow horns were perfectly fine).

(Also, elephant tusk placement is incomparable to horn placement in rhinos, brontotheres, and ceratopsids, so, in terms of whether or not their weapons are placed in a structurally stable area, I'm not sure how they'd compare to these creatures. In any case, the fact that their tusk bases are hollow, thin-walled, and filled with pulp in life makes me think that they too are not built for charging and colliding their tusks into similarly large animals)

[blaze]

Yeah, in a way, elephant fights resemble more the way deer fight with their antlers

[Infinity Blade]

One thing I'm still confused about: when, if ever, can we say that pneumatized bones compromise the strength of the bone? Clearly it helps the horns of a bighorn sheep to withstand an impact, but what about in other animals? Like the crania of elephants and rhinos, or the bones of saurischians? I was under the impression that they at least wouldn't compromise any strength.

[theropod]

Pneumatization ALWAYS compromises the strength of the bone compared to a bone of equal diameter that is solid bone all the way through. But it INCREASES the strength relative to a non-pneumatic bone with the same amount of bone tissue, hence why it is so ubiquitous as a weight-saving adaption. That is because spreading out the same amount of bone tissue from the centroid axis of the bone increases its second moment of area, which is a measure of the resistance of the structure to deformation. That’s also why generally, metal pipes or I-beams are used in construction instead of solid rods.
The only exception to that is with a very thin-walled pneumatic bone whose walls might be more prone to fail locally, e.g. if something tried to bite through them or impacted them on a small area (like an Ankylosaur tail club, maybe).

[Infinity Blade]

And then considering that some bones aren't completely solid but have a marrow cavity, such bones are NOT stronger than pneumatized bones (with the same amount of bone tissue), yes?

One other pneumatization question: did theropod skull bones have that honeycomb-like interior or was it just the fenestrae in the skull and the air sinuses that made their heads pneumatic in life?

[theropod]

As for the first thing, exactly right. The marrow doesn't contribute to structural strength, you can pretty much ignore it when it comes to that. Pneumatic bones definitely have the better strength-to-mass ratio.
Of course bone marrow fulfills other important functions though, so at least theoretically animals that lack it need to compensate for that somehow (strangely I read that birds actuallly have proportionately ssmaller spleens than mammals...).

As for the second thing, that is an excellent question. I don't know. Off the top of my head I'd expect both compact and trabecular bone to be present in different regions of the skull and different species of theropod. I don't really have any concrete data though, although I'm sure something of the sort muust exist somewhere.

[jhg]

It depends on the brontothere. I thought Megacerops did.

[Infinity Blade]

I remember someone on Carnivora posting some information about brontotheres and their adaptations for headbutting. See this paper (hyperlinked); interestingly it compares brontotheres to rhinos (which they explicitly point out do NOT ram/butt; guess that ends that debate) and points to potential adaptations for headbutting the former seem to have. But then I found this:

HORN FUNCTION IN BRONTOTHERIIDS (PERISSODACTYLA; CERATOMORPHA) RECONSIDERED
BALES, Gerald, Western University of Health Sciences, Pomona, CA, USA

Morphological evolution in Brontotheriidae (Osborn’s “titanotheres”) included attainment of large body sizes and paired, frontonasal bony horns. Incipient horns (mere elevations) appeared in tapir-sized taxa then lengthened with positive allometry. Other horn features are the degrees of rostral migration, basal fusion, and angulation. A priori assumption of intraspecific combat led to proposed horn functions including lateral butting, vertical tossing, and forward ramming. Horn lengthening (post orthogenesis) required a strongly selectionist interpretation. Dramatic function was a focus to explain a greatly over-estimated positive allometry in selection terms. Battering ram proponents analyzed long horn features in terms of mechanical needs to validate the behavioral assumption. The attractive qualities of the battering ram horn change scenario combined with routine propagation of short-to-long horn diagrams give a lop-sided view of brontothere evolution. The “long” horned form was one of several lineages in a bushy phylogeny persisting near extinction. Terminal genera show a diversity of lengths and shapes including (1) long, basally fused and (sometimes) recurved, (2) long, narrowly divergent, and without basal fusion (3), short and conical (4), medium length, rounded, and widely divergent (5), short, irregular flanges (6), and doubly-bifurcate (branched) [in an as yet not officially named AMNH brontothere]. A universal battering ram function might argue for evolution more convergent than divergent. Size - shape diversity notwithstanding, problems with the battering ram hypothesis include (1) what biomaterials were impacting skin? (2) what forces would be generated and was surface area adequate to withstand them? (3) what damage would occur and is this seen in the fossils? Paleobehavior inference is aided by Rudwickian plausability where the morphology is shown to be mechanically sufficient for the performance. Preliminary calculation of ramming forces based on estimates of running speed, body mass, and impact area for opposing males of a large brontothere suggest that the forces exceed that of known compressive strengths of bone.

This was all the way back from SVP 2007, btw. Sadly, from what I can find it only seems to be an abstract even to this day.

[dinosauria101]

Just out of curiosity, was this thread revived because of the Megacerops vs Daspletosaurus thread?

[Infinity Blade]

I just found a very interesting study that found a strong correlation between head-butting behavior (which in this study refers to both wrestling and ramming species) and the orientation of the lateral semicircular canal.

For over a century, researchers have assumed that the plane of the lateral semicircular canal of the inner ear lies parallel to the horizon when the head is at rest, and used this assumption to reconstruct head posture in extinct species. Although this hypothesis has been repeatedly questioned, it has never been tested on a large sample size and at a broad taxonomic scale in mammals. This study presents a comprehensive test of this hypothesis in over one hundred “ungulate” species. Using CT scanning and manual segmentation, the orientation of the skull was reconstructed as if the lateral semicircular canal of the bony labyrinth was aligned horizontally. This reconstructed cranial orientation was statistically compared to the actual head posture of the corresponding species using a dataset of 10,000 photographs and phylogenetic regression analysis. A statistically significant correlation between the reconstructed cranial orientation and head posture is found, although the plane of the lateral semicircular canal departs significantly from horizontal. We thus caution against the use of the lateral semicircular canal as a proxy to infer precisely the horizontal plane on dry skulls and in extinct species. Diet (browsing or grazing) and head-butting behaviour are significantly correlated to the orientation of the lateral semicircular canal, but not to the actual head posture. Head posture and the orientation of the lateral semicircular canal are both strongly correlated with phylogenetic history.

Taxa that engage in head-to-head combat have almost the same average neutral orientation of their head as non-head-butting taxa (34° and 33° respectively) (Fig. 7). In sharp contrast, they show a significantly more anteriorly tilted reconstructed cranial orientation (average = 46°) compared to non-head-butting taxa (average = 33°). Unlike what is observed between browsers and grazers, the values here are markedly different (Fig. 7) and the difference is highly statistically significant (p-value = 0.002). It is unlikely that the reconstructed cranial orientation reflects the posture during head-butting, as animals keep their head extremely low during this activity, much lower than their corresponding reconstructed cranial orientation (Fig. 13b). A phenomenon of re-orientation of the braincase and basicranium in head-butting “ungulates” that would not affect head posture overall seems more probable. Such cranial flexure would result in a misalignment of the main axis of the braincase with that of the snout (Fig. 13), a condition termed cyptocephaly and commonly encountered in head-butting “ungulates”. This implies that natural selection on the alignment of the plane of the LSC to the horizontal was muted by another, likely more important adaptation to head-butting. This may be the necessity to re-orientate the braincase and basicranium in order to align the fighting surface of the skull, occipital condyles, and vertebral column to help dissipate the energy of the impact to the body and away from the brain. Another hypothesis would be that the re-organization of the braincase serves to accommodate the development of the large cranial apparatuses found in most head-butting species (e.g. horns and antlers). In our dataset, 56% of species without horns do not head-butt, and 83% of species with horns do head-butt (Supplementary Table S1), which would partly support this hypothesis. In contrast, intraspecific variations in the presence or absence of horns appear to have no impact on neutral head posture on average (Fig. 14; Supplementary Table S1). These two hypotheses will need further observations and biomechanical modeling to be addressed adequately.

www.nature.com/articles/s41598-020-76757-0

Interestingly, this study provides a useful dataset on who uses their head to wrestle or ram and who doesn't.

The second predictor is whether a species practices head-to-head combat. The head-butting category includes wrestling and ramming species (hereafter referred to simply as head-butting species) but excludes flank-butting species (e.g. giraffes).

See Table 1. Elephants and bison wrestle and/or ram, but rhinos don't.

www.nature.com/articles/s41598-020-76757-0/tables/1