The cheekbone case: Briefly about Ceratopsia

A quick background of the horned dinosaurs, the ceratopsians might be in order. In order to understand the cheekbone case in its broader context, I mean. What I am trying to say is: if you have a clear picture of these animals, many of the conclusions drawn in the investigation will probably make more sense.

I will try to keep it simple and broad, though I find many details incredibly fascinating and there is the risk of slipping into details about tooth shape and wear patterns… I hope to avoid this!

Ceratopsia includes the famous Triceratops and many other dinosaurs with impressive horns on their skulls, and, more characteristically, a large neck frill or neck shield that extends from the rear of their head toward their backs.

A fleshed-out drawing of a Triceratops, probably the most famous of the ceratopsian dinosaurs. 

Image from http://www.guardian.co.uk/science/2009/feb/07/dinosaurs-evolution-bipeds-quadrupeds

Like most land vertebrates, the ceratopsians walked on four legs – they were quadrupedal. Interestingly, however, their ancestor as well as many primitive ceratopsians were probably able to walk comfortably on two legs (bipedal), so there must have been a reason for the ceratopsians to evolve toward walking on all fours. A simple explanation is that the ceratopsians needed huge guts to process their food: plant material is much more difficult to extract energy from than flesh. Being big and heavy, they were probably sluggish most of the day – until something bothered or threatened them!

Since the ceratospians walked on four legs, both their legs grew sturdy and strong rather than slim and flexible, their hands and feed got broad, and their claws became blunt and hoof-like. Having perfect balance, they did not need a particularly long or stiff tail.

(In other words, their body was not very unique or interesting. That does not mean it is not important! Just that there is little to say about it unless you dig into a deeper level of anatomy. I do not think that is necessary at the moment; if any aspect of their bulk anatomy becomes relevant to the investigation, I think it will be more appropriate to mention it when it comes to that.)

I feel I should at least mention that there has been quite some debate about how these animals moved, in particular regarding whether they were cursorial – could run, to charge at an enemy like a rhino – or if they defended themselves by standing firm in place like a phalanx army. Though some studies favour the cursorial idea, I personally find it difficult to accept simply because the ceratopsians had considerably shorter forelimbs compared to their back legs. If they tried to run, their longer hind legs would eventually ‘catch up’ with the front limbs and they would topple over. (I also have a hard time accepting the computer models they create to calculate the optimal way of moving for the animal and assume that that would be how it moved. However, my dispute with this type of investigation is more philosophical than anything, and I realise that going on about that now would be stepping way out of line. Maybe another time!)

Let us move on to the heads of the Ceratopsia. Facial horns and a neck frill are their most distinguishing features, but there is an immense variety in their design, and probably also in their function.

Drawings of the skulls of some of the centrosaurines, a group of advanced ceratopsians, giving a taste of the tantalising diversity of horn and frill shapes and sizes in the Ceratopsia. Image from http://ceratopsiansrevealed.blogspot.se/2011/07/centrosaurine-or-chasmosaurine.html

PalQuiz 5

It was months ago since the last PalQuiz, which is a shame in hindsight, as I realise it could have been useful revision for my end-of-term exams. Now, however, I think it is about time I sit down and contemplate once again how to make evil, tricky questions for my beloved readers.

I will try to give good answers to the previous quiz, although I may not quite remember the purposes of many of the incorrect alternatives. I usually have a plan with each one of the four options; they are meant to fool you in different ways, make you think twice, and again, and one more time before you feel sure of the answer. That is always my aim.

1. Toothless (edentulous) beaks were actually very common among dinosaurs, mostly so among the ornithischians (bird-hipped dinosaurs) – that is why I chose most of the options from the saurischian (lizard-hipped) group. (If this confuses you, ignore it… this is not important for understanding the answer.) Gallimimus and Therizinosaurus are both theropods – members of the clade containing all carnivorous dinosaurs, plus a few herbivorous and/or omnivorous exceptions – and these evolved toothless beaks designed to process plant food rather than meat. (Actually, Gallimimus’ diet has been debated for long, and it might be safer to theorise that it was actually an omnivore… but it had a toothless beak nevertheless). Edmontosaurus is the typical duck-billed hadrosaur ornithopod, with beautifully advanced tooth batteries in the cheek region, but the front of the mouth had no teeth and formed a beak for raking in leaves and fruits from bushes and other low-growing plants. Diplodocus was also a herbivore, with the front region of the mouth serving the same function: taking in plant material. However, it had a completely opposite design: in the front of the mouth, all its long, pen-like teeth were concentrated, arranged so they interlock much like the fingers of your hand (they were interdigitating, in fancy words). These teeth would close around branches of shrubs or tree crowns, so that when the mouth was pulled back, they would scrape off leaves and seeds, which they then swallowed.

2. Well, I kind of gave you the answer for that one already… Therizinosaurus is one of those theropods that was assumed to be a carnivore when it was first found, simply because it belonged to the carnivore group. However, subsequent information about its diet pointed more and more toward it being a strict herbivore instead. It’s toothless beak and bulky belly hint toward a plant diet. It’s fossilised faeces have been showed to consist of plant material. Therizinosaurus had huge hand claws, but that is no evidence that it killed and then consumed other animals: the claws may very well be weapons solely for the purpose of defence.

3. I admit this was a quite evil one. If I was asked that question, I might not know where to look even! A good rule of thumb, however, is to always start looking at the head – that is where most of the unique features usually are. However, recall that I enjoy tricking you? I do not expect anyone to know the detailed skull characteristics of these dinosaurs. There is an easier way. If you study the options, you will realise that only one of them is an ornithischian. There is then a very simple way of testing whether this dinosaur is an ornithischian and therefore surely a heterodontosaurid: look at the hip bone arrangement! But… the problem is that on this picture you cannot really tell for sure whether it is a saurischian or ornithischian hip. So it does not work! You have been side-tracked! (Mwuahahaha I’m evil!) So… we have to look at the skull anyway. If you zoom in on it, you notice no extravagant head ornaments that can give you a clue. The next best thing is the teeth. In this dinosaur, the cheek teeth look blunt and packed tightly together, just like a typical advanced ornithischian, but there are also two large fang-like teeth in the front, more typical of a carnivore. However, recall from the previous answer that a weapon (such as fangs) is not necessarily evidence that it is a carnivore, as the definition of a carnivore is that it consumes meat. So, the teeth point (haha, what a pointless pun) toward this being a herbivore, but this is not precise enough as there are two herbivorous dinosaur groups as options: B and D. It then really comes down to knowing your stuff – i.e. being aware of the characteristic teeth of these dinosaurs. Ooops, it seems like you did need to know details of the skull to puzzle this one out. I wonder if I should top the evilness of this question by just not giving the answer? Yes, yes… I’ll do that. *rubbing hands maliciously*

4. The encephalisation quotient, commonly shortened EQ because it is such a mouthful, is an indirect estimate of the intelligence of any craniate animal. However, the EQ is actually measured as the brain size relative to and ‘expected’ brain size for the size of its body, which is determined by using a typical mammal for reference. So, basically, you take the brain size of an animal and divide it by the brain size of that standard mammal, and this gives you the EQ. I noticed now that I had written “head size” instead of brain size, so C may not strictly speaking be correct, so I would not judge you to be wrong if you chose D. D was meant to be the incorrect alternative that fools those who have a faint idea of what EQ is but are unaware of what it actually measures… but my silly mistake means that those who opted for D instead know better than me!

5. All the statements except for the first one are true (to the best of my knowledge)! That first statement was really the only one that was meant to be tricky – Othniel was called Charles Marsh, not Carl Marx, which was the Russian economist that founded the communist ideology.

Now on to the fifth PalQuiz!

1. The phylum name Brachiopoda means…?

A. Branching foot

B. Arm foot

C. Long foot

D. Tall foot

2. Which of these echinoderm groups is extinct?

A. Ophiuroidea (‘brittlestars’)

B. Crinoidea (‘sea lillies’)

C. Cystoidea (‘crystal apples’)

D. Echinoidea (‘sea urchins’)

3. The ‘egg thief’ dinosaur Oviraptor is actually poorly known. Paleontologists have only found a single, fragmented skeleton. On which other close relative is the bulk of our knowledge on the oviraptorid group based on?

A. Citipati

B. Ingenia

C. Gigantoraptor

D. Yulong

4. Mammals evolved from a group known as the ‘mammal-like reptiles’ (synapsids), which can be thought of as intermediates between ‘reptiles’ and mammals. Which is the main feature that marked the emergence of the first true mammal? (i.e. what made it a mammal rather than a mammal-like reptile?)

A. Fur

B. Hair

C. Middle-ear bones

D. Milk (lactation)

5. Which of the below is currently one of the leading paleontologists involved in the discoveries and research of the vast wealth of bird-like dinosaurs in China?

A. Robert T. Bakker

B. Xu Xin

C. Paul C. Sereno

D. Zhao Xijin

Back home in Sweden

After a smooth but tiering journey, I am once again back home with my family in Sweden! Wonderful, and weird! I will indulge in a few days of enjoyment and complete laziness before I pick up the hard blogging work again.

The cheekbone case: Entelodont relationships

While skimming Wikipedia for information about the precise name of the group that includes both entelodonts and pigs (suids), I discovered that entelodonts are not considered to be as closely related to pigs as I originally thought.

Since the entelodonts look pretty much like over-sized warthogs, I assumed they would all be part of the family Suidae. But, it turns out they are at different ends of the cetartiodactyl clade.

Cetartiodactyla is a group containing the artiodactyls, or even-toed ungulates, and cetaceans, such as whales, sea cows and relatives. (The story of how they came to be classified together is a fascinating one, but that will have to be for another time.) I made a very simple cladogram (a type of evolutionary tree diagram) over Cetartiodactyla based on what I could find on Wikipedia:

So, according to this, the entelodonts would be more closely related to cetaceans and hippos than to pigs and boars (Suina is a more inclusive group than the family Suidae that I mentioned before: Suina includes Suidae, which are Old World pigs, and the small family Tayassuidae, which are New World pigs).

Still, entelodonts look so similar to warthogs; they even have fairly similar jugal (cheekbone) processes, which is the topic of this investigation.

  A warthog skull, showing the pronounced outgrowths of the cheekbone 

(just under the eye socket), similar to those of the entelodonts (and ceratopsians), albeit broader. 

Picture from http://www.africahunting.com/before-after-hunt/7615-warthog-dipped-skull-opinions-wanted.html

Perhaps this is yet another case of convergent evolution, although maybe more intimate, as the warthogs are at least closer to the entelodonts than either are to the ceratopsian dinosaurs. Also, this makes me think I ought to check if there may be more cases of similar cheekbone anatomy within the cetartiodactyl clade. The more animal groups we compare with, the more accurate the picture will be – more complicated, surely, but more accurate.

Charmouth

On Saturday, my host family for next year invited me on a trip to Charmouth, one of the beaches along the Jurassic Coast – a stretch of the southern coast where there are plenty of Jurassic marine fossils. Charmouth is next to Lyme Regis, the famous site where Mary Anning found a vast wealth of ichthyosaur fossils, which we also visited later.

The weather was spectacular, the scenery mesmerising, and we had great fun. However, we hardly found any fossils at all! Only the eldest daughter found one finger-sized piece that definitely was a fossil (maybe a bit of a coral), and also I saw this gastropod impression in a large rock on the shore.

So, this post might turn out quite strange: the story of various things I hope are some sort of fossils, and if (or if not), I have no clue of what…

But first, some of the fun we had:

The beach was full of ‘egg fossils’, many of which were ready to ‘hatch’.

There was plenty of marl (a very fine-grained calcium carbonate sedimentary rock, much like limestone but muddier, i.e. smaller grains) that was so soft that one could easily make markings with a harder rock. We seized this excellent opportunity to prank other fossil hunters by carving in things like (my artistic interpretation of) the Transformers emblem, and this:

At Lyme Regis, on the dock wall, there was a large mat of a fossil bryozoan colony:

(well, not really, but I like to think it was…)

Now to the ‘fossils’ I brought back home. (I apologise for the strange structure of this post, but I found no sensible way of organising this… the fossils were, after all, secondary – the most important thing was to have a good time with the people I am living with next year!)

The cheekbone case: Introduction

Over a year ago, while watching a tv-show about extinct mammals, an idea struck me about a possible link between the odd cheekbones of the suids – boars and their relatives – and the similarly peculiar and peculiarly similar cheekbones of the ceratopsians, or horned dinosaurs. 

The skulls of an entelodont (extinct relative of boars; top) and a Protoceratops (a well-known early ceratopsian; bottom). Not to scale. Images from: (top) http://www.flickr.com/photos/velocibadgergirl/2072208547/; (bottom) http://www.flickr.com/photos/stevelewalready/3505166117/

I have thought about it from time to time, as a potential topic if we ever got tasked in school to investigate anything of our own choosing. However, I was thinking that it might be more fun to present it here to you.

I have not yet fleshed out the idea with any scientific sources, but I want to do the background reading after having presented the original idea. In that way, I hope to update you with findings from the scientific literature perhaps once a week, and so we may see how that argument develops, from an embryonic stage idea to hopefully a full-fledged hypothesis that may attract the attention of professionals (that is my goal!).

The curious similarity between these two animal groups, which never co-existed (the ceratopsians were extinct 65 million years ago; the suids evolved 30-20 million years ago) and whose ancestors were separated in the evolutionary line more than 300 million years ago, is that they evolved very similar-looking jugals or cheekbones (in mammals, the jugal may also be referred to as the zygomatic). Strictly speaking, it is the processes (outgrowths) of the jugals that I am referring to, not the entire bone, but the similarities are still striking: the processes are very large, lobed and point outward and downward (ventrolaterally, in fancy terms).

This connection ought to be related to some similarity in the diet of the animals, would you agree? However, while the suids are mostly omnivorous generalists (eat more or less any food they can get), ceratopsians are interpreted as strict herbivores, probably specialising on particular types of plants. These are rather different. Maybe, then, it has to do with something else they use their mouths for.

What about attack/defence? It is known that at least Protoceratops (the ceratopsians in the figure above) used its sharp, powerful beak in the best recorded instance of a dinosaur predator attacking a dinosaur herbivore: the famous ‘fighting dinosaurs’ fossil from the Mongolian desert of the Cretaceous shows a Protoceratops attacked by a Velociraptor. 

The ‘fighting dinosaurs’ fossil: the Protoceratops (top left) has its (missing) beak in a firm bite around the arm of the attacking Velociraptor, suggesting that at least this ceratopsians used its jaws in defence against predators. Image from http://www.sciencedaily.com/releases/2007/11/071107074326.htm

The suids naturally used their powerful jaws to subdue prey. In addition, it is known that at least the entelodonts frequently bit one another in fighting among themselves: bite marks, on the skull in particular, from teeth that match the same species, are common, and may have been caused during fights for territory or mating rights. It may further be possible that also ceratopsians used their beaks in territorial or courtship fights – at least in the early, hornless forms.

How could the cheekbone play a role in such use of the jaws? If it has been enlarged to that extent, it probably was important. What was the point of that shape?

In the tv-show I was watching when I got the idea, they argued that the entelodont jugals worked as jaw stabilisers. Entelodonts could open their jaws very widely, but when doing so, they could easily be dislocated by struggling prey. The large jugal processes served as attachment sites for powerful cheek muscles that would keep the jaws in place. Could this have been the same case for ceratopsians?

This is one of the questions where I would need to consult the scientific literature in detail. Were the ceratopsians able to open their jaws so widely? Would that have been advantageous? How?

Earlier, I did some broad thinking about what other animals have long jaws or big beaks, that might provide further insight to this mystery. I have only gotten as far as making a few bullet-point lists:

Big beaks (that open wide?)

• parrots
• toucans
• pelicans
• those big-beaked finches
• terror birds (extinct)
• hesperorniforms (extinct)
• turtles

Long jaws (that open wide?)

• crocodiles
• mosasaurs (extinct)
• pliosaurs (extinct)
• spinosaurids (extinct)
• pterodactyloid pterosaurs (extinct)

I want to add to these lists as this investigation goes along, as well as taking time to look through each of these in detail.

I hope you found this as curious as I do, and that you feel keen to come with your own thoughts and comments. I will warmly welcome and appreciate any feedback you may have, so please, do not hesitate to make your ideas heard. Together, we could make this into something big.