Triceratops’ horns

[Minmiminime]

Something that's been long overlooked in palaeoart, the actual probable shape of Triceratops' horns! Mark Witton has written this insightful post on the subject taking into account ontogeny and likely biological constraints, and whilst it's all about Triceratops, the implications for any elaborately ornamented dinosaur are rather interesting:

http://markwitton-com.blogspot.com/2017/11/can-we-predict-horn-shapes-of-fossil.html

[stargatedalek]

I actually find his reconstructions of horns to be very dull and conservative. Just look at the amazing variety of colours and patterns birds can achieve with their beaks, no reason to assume ceratopsians should be as dull as mammalian horns. Especially given their origins as display structures where as most mammalian horns were always utilitarian.

[Minmiminime]

That is true, but at this stage they're about the most exciting ones out there..! Hopefully, it'll invigorate something in palaeoart

[Patrx]

Great read, and fascinating reconstruction. I particularly like the way the animal's cheek tissue (or lack thereof) has been left ambiguous. Some Triceratops figures could probably be augmented to match up with this line of thinking using epoxy putty or similar.

I actually find his reconstructions of horns to be very dull and conservative. Just look at the amazing variety of colours and patterns birds can achieve with their beaks, no reason to assume ceratopsians should be as dull as mammalian horns. Especially given their origins as display structures where as most mammalian horns were always utilitarian.

As this particular article seems like more of an introduction and explanation of the process involved in the reconstruction, it seems reasonable to keep the colour and specific geometry of the keratin sheaths pretty simple. Mark did recently publish a reconstruction of Stegosaurus (an updated version of an older painting) which is a little more speculative in that regard:

[ZoPteryx]

Really interesting!  The logic behind this theory makes a lot of sense, I really like it.

I do have one minor quibble with the new reconstruction, though.  Witton seems to be implying that the whole face was also covered in keratin (admittedly this is left ambiguous) which sounds rather implausible when you take into consideration the same sort of growth he's arguing for in the horns.  What I'm getting at is, how does the keratin face covering grow in the same way as the horns when there's no way the "shell" of a juvenile's skull could fit within the margins of an adult skull?  Would the frill essentially have a "pyramid" of old frill keratin stacked at its base?  Even if there was a break between the keratin of the face and the keratin of the horns to allow the horns to grow freely, the facial keratin would still have to expand in some way to accommodate the growth, despite it being dead tissue.

The only solutions I can envision are:
a) The juveniles' heads are keratonized, but the adults' are not.  The juvenile keratin is either shed or breaks up and is retained as armor in patches on the face of the adults.
b) The keratin only grows from a central point, probably the base of the horns.  Each new layer pushes each older layer further toward the margins of the skull, which means it's probably going to end up bunching up somewhere.  In this scenario, the skull/frill bones directly beneath the keratin are not actually producing anything, only the region around the horns is.  This could result in some really weird morphologies!
c) The keratin on the face is broken up into multiple segments that grow and slide past each other in different ways to accommodate for skull growth.  Again, this could result in some really weird morphologies!  However, as Witton pointed out with the horns, normally we some osteological indication in the form of contact-ridges when this is the case.
d) The face was not covered in keratin, only the horns were.

[Minmiminime]

It makes me wonder if a better analogy might exist among extant birds with casques like hornbills and cassowaries, but it's certainly food for thought

The whole "cheek" thing I'm a bit more cautious about, because what constitutes a "cheek" can be quite ambiguous; there seems to be this persistent notion that it must be a muscular structure, and that dinosaurs could not have had them, because no reptile does. But, and the commisure of the mouth could quite easily have been anterior and just behind the beak, rather than posterior and behind the teeth, thereby leaving non-muscular but nonetheless functional flesh pockets that helped to retain heat, food and moisture. This may explain the hollowed-out and smooth appearance of ornithischians skulls in the "cheek" region.

It's peculiar that now we're giving theropods lips again, we're taking "cheeks" away from ornithischians..!

[stargatedalek]

I still maintain that structures like what macaw have could be described as cheeks, and are by far the most likely sort of structure for ceratopsians. The way ceratopsian jaws move they need to open the mouth in order to grind food, so they should need something to keep food from falling out. Actually, the jaws move in a way eerily reminiscent of macaws.

[ImADinosaurRARR]

This is so cool! Reading this made me wonder about how other ceretopsians looked. If this hypothesis is correct, then it looks like all ceretopsians had an up-would pointing "hook" on the tip of each horn, since all known babies have back pointing horns.



Also, looks like DA user DiNoDrAwEr beat Mark to it ;P

[Minmiminime]

I still maintain that structures like what macaw have could be described as cheeks, and are by far the most likely sort of structure for ceratopsians. The way ceratopsian jaws move they need to open the mouth in order to grind food, so they should need something to keep food from falling out. Actually, the jaws move in a way eerily reminiscent of macaws.

I agree! I'm sure it applies to derived ornithischians in general. In birds, the gape of the mouth never seems to extend beyond the posterior border of the beak, so maybe this was the case in dinosaurs, too. And I cared for a little tortoise for a while, and he didn't have cheeks as such, but there was elastic skin at the corners of his beak which enclosed his small (but very powerful) mouth to a large degree.

Anyway, I digress!

As for the horns, and keratinous structures in general, I maintain hope that some evidence will be found to verify the validity of the hypothesis either way  I've often pondered just how much the plates of Stegosaurus resembled their bony cores in life. Many possibilities abound!