Horns & Spikes Part 2: Nasal Horns!

The ceratopsid nasal horn is comprised of towering, fused nasal bones. In chasmosaurines, a small epinasal bone sits atop the nasals until it is incorporated into the bony structure of the horn. The epinasal is most obvious in certain juvenile and subadult Triceratops specimens. Unlike the postorbitals, nasal horns may not be primitive for Ceratopsidae—Zuniceratops lacks any kind of nasal horn, and the plasticity of the nasal structure in both ceratopsid subgroups suggests that they formed independently in both groups. We’ll talk about chasmosaurine nasal horns first, as they are the most standardized and vanilla.

Chasmosaurine nasal horns are never all that tall, and while they appear early in life, the horn itself does not become truly noticeable until late in life. Certainly the suggestion of a horn is there in subadult animals—in fact, it forms a noticeable “step up” from the rostrum to the forehead (see growth series below). However, aside from the small epinasal, a true horn does not develop until the chasmosaurine reaches maturity. In almost all genera, the horn is angled anteriodorally, forming a “ski slope” toward the rostrum. Once chasmosaurines reach maturity, the nasal horn continues to thicken and elongate—in old adult Triceratops specimens, the horn points subhorizontally. Some chasmosaurines, such as Torosaurus, place less emphasis on the nasal horn, seemingly content with developing a narrow, almost rounded horn. Agujaceratops follows a similar pattern. Even as its postorbital horns rise ever higher, the nasal horn remains short and rounded, though definitely more distinct than in Torosaurus.

Nedoceratops (= Diceratops, Diceratus) apparently has no nasal horn, but a close inspection of the type (and only) skull reveals that in fact it has a very small one. Lacking an epinasal, the stepped structure of the horn may suggest that the individual is simply a subadult who has not developed its nasal horn yet. On the other hand, it may also be related to Torosaurus (as a recent phylogeny suggests), which itself has an abbreviated nasal horn. Much has been made of Arrhinoceratops’ alleged lack of nasal horn (thus its name), but rest assured that a nasal horn is present, just partially broken off. In fact, its nasal horn may have been quite impressive.

Centrosaurine nasal horns are divided basically into two types: horns and bosses. A small banana-shaped boss is present on Albertaceratops, and two veeery small horns are present on an undescribed taxon from Utah (seems they could easily be sections of a broken boss). Horns are generally more prevalent than bosses among centrosaurines, though they come in some weird shapes. Centrosaurus (= Monoclonius) has a large, singular horn which curves every which way in different individuals. As you can imagine, early American fossil hunters gave different genus/species names based on different horn shapes. The result is that Centrosaurus has perhaps the most complex taxonomic history of all ceratopsids (except maybe Triceratops). Most skulls assigned to Monoclonius have been sunk into Centrosaurus, or have been unassignable to specific genera given what we now know of ceratopsid ontogeny. Styracosaurus albertensis was once restored with a towering nasal horn, but a reappraisal of the genus by Michael Ryan showed that this is wrong—Styracosaurus actually had a mid-sized nasal horn that may not have been all that pointy.

A sampling of ceratopsid nasal horns. From top to bottom: Triceratops prorsus (YPM 1922); Torosaurus latus (MOR 981); Pachyrhinosaurus lakustai (TMP 1989.55.1234); and "Monoclonius flexus" (AMNH 5239).

Midway between horn and boss is Einiosaurus, a mid-sized taxon from the Two Medicine Formation whose horn goes through quite a transformation as it ages. In young animals, the horn is short and slightly recurved. Once adulthood is reached, though, the horn quickly dominates the face as it grows up and then dips forward. It ends up looking something like a hook. The horn is laterally narrow, but its anterior-posterior breadth is impressive, and the horn narrows to a blunt point. Further toward the bossy end of things is Achelousaurus, from the same formation, but quite distinct (for an interesting interpretation of their differences, see Sampson 1995). Achelousaurus is a basal member of the Pachyrhinosaurini. As it reaches adulthood, all horny growths on the nasal and postorbital are reabsorbed, leaving large, rough-textured bosses in their place. The living bony tissue was probably fairly brittle toward the surface, and it would have been protected by a large keratin or horny covering. I like the suggestion that pachyrhinosaurine bosses were covered with oxen-like horn—the texturing is consistent.

The king of nasal bosses, however, is Pachyrhinosaurus, the largest of the centrosaurines and the most northerly: the taxon is known from the North Slope of Alaska. There are currently two recognized species: P. candensis and P. lakustai, both from Canada, but occur in different stratigraphic layers. Both show remarkable facial reconstruction with age. P. lakustai is the better-known animal, and a monograph was recently published on it. An ontogenetic series demonstrates the bizarre nature of the boss: babies and juveniles have respectable nasal horns and short postorbital bumps. As they grow, the nasal horns do not grow upwards, but laterally, eventually spilling over the lateral edges of the nasal bones (see illustration below)! In P. canadensis, the nasal and postorbital bosses eventually grow together to form a gigantic bony mass, but in P. lakustai, they all remain separate structures. In some individuals, the ballooning nasal boss begins to reabsorb and becomes concave.

Last time, I lamented how postorbital horns are not good phylogenetic markers, but nasal horns may be. All members of the Chasmosaurinae have basically the same nasal horn structure with different sizes and shapes depending largely on ontogenesis. The horn is almost always ski-sloped, fairly short, and sometimes rounded or blunt. The nasal horn often “steps up” the skull from the rostrum. The most impressive nasal horn among chasmosaurines may belong to Triceratops itself. Even its closest relatives (Torosaurus and Nedoceratops) have pitiful nasal horns by comparison. Even so, chasmosaurine nasal horns seem to have common features, and nasal horn morphology could be useful in establishing at least whether a ceratopsid is a chasmosaurine or not. As for centrosaurines, nasal horn morphology is strikingly different from chasmosaurines. The nasal horn is expressed just as often as a boss! When a horn is present, it grows vertically rather than angling forward, and it often dominates the face. In pachyrhinosaurs, a short nasal horn is present in juvenile animals but quickly becomes a boss in subadults. However, these bosses are very distinct from the small, smooth banana-shaped boss in Albertaceratops.

Horn growth in chasmosaurines, as exemplified by Triceratops. Note the "stepped-up" look of the rostrum in everyone except MOR 004.

How did ceratopsids use their nasal horns? In addition to figuring out that Triceratops used its postorbital horns for intraspecific combat, Andrew Farke also discovered that Centrosaurus must not have fought the same way, as the frills he studied carried virtually no scars attributable to intraspecific battle. This is not so surprising—without large postorbital horns, it’s difficult to see who centrosaurines head-to-head in quite the same manner, but it would appear that even the elongate nasal horn did not inflict injury on conspecifics. Absent any pathological evidence, it becomes very difficult to figure out what the nasal horns were used for. In chasmosaurines, they may have simply served as age indicators—Horner & Goodwin demonstrated that nasal horn morphology changes significantly along with postorbital morphology during growth in Triceratops. Like the angle and curve of the postorbitals, chasmosaurines may have looked to the development of the nasal horn to assess age and fitness amongst themselves. But what of centrosaurines, who exhibit a far greater range in nasal horn morphology?

Sexual dimorphism is often invoked. In fact, it’s been suggested that Centrosaurus apertus is simply the female of Styracosaurus albertensis—an idea that has largely been ignored. Sampson discussed the possibility that Einiosaurus and Achelousaurus were sexual dimorphs of the same species, but decided that without a large, mono-specific sample size (like a river crossing bonebed), there was just no way to be sure. Indeed, sample size is the biggest roadblock to determining sexual dimorphism among any extinct organism. Sexual dimorphism has been shown in Protoceratops andrewski only because its bones are littered across the Mongolian desert, and sample size is not a problem. When you only have a few partial skulls or skeletons, though, demonstrating sexual dimorphism becomes much more difficult if not impossible. Even where monospecific bonebeds are known, as in Pachyrhinosaurus lakustai, sexual dimorphism could be confused with ontogenesis. Is this individual a female, or just a subadult male? Or a subadult female? There is often no way to know for sure.

Horned centrosaurines may have used their horns as part of the overall display, and perhaps they lacked any kind of practical purpose aside from perhaps defense. Like the giant postorbitals of Triceratops, I can’t see Styracosaurus turning its horn away from a charging tyrannosaur. One wonders, however, about the bone strength of such horns. Could a predator be impaled without risk of injury to the horn itself? A recently-described Triceratops horn shows evidence of having been bitten off by a tyrannosaur! Pachyrhinosaurs, with its broad, horn-covered boss, would have been better protected against attack, as head-ramming would be a more viable alternative to impaling from both an injury prevention and practical standpoint. The bosses may also have been used in intraspecific combat—shoving matches or aggressive charges are well within the realm of possibility. It would be really cool if some pachyrhinosaur skeletons showed broken and/or healed ribs, which you’d think would be caused by intraspecific combat. Unfortunately, there are no postcranial details in the P. lakustai monograph, but hopefully somebody can investigate that in the future!

Overall, nasal horn morphology is more variable than postorbital horn morphology and may hold more value phylogenetically.

The Overhype--It Burns!

Surely you've all heard of Ida the Adapid by now. She has, perhaps, been oversold. She is not the "Holy Grail" of paleontology, nor does she cure cancer, though you wouldn't know that based on the mainstream media, who is going apeshit insane over this relatively vanilla fossil (save for its awesome preservation). No time right now to comment further, but read all those links and this one too for a pretty complete picture of the animal's relevance.

Horns & Spikes, Part 1: Postorbital Horns

Ah, ceratopsian dinosaurs. They are quickly becoming my favorite terrible lizards, and in this series of posts (Horns & Spikes), I intend to discuss the various horns, spikes, and generally pointy structures that decorate the typical ceratopsid skull. For convenience's sake, I will here only cover the Ceratopsidae--with one or two invocations of most basal taxa where proper. The series will consist of four parts: Postorbital Horns, Nasal Horns & Bosses, Epoccipitals, and Jugal "Horns." Granted, that last section will be pretty short. I hope you enjoy the series! And here's part one:

Postorbital Horns

The postorbital horns are among the most obvious features of the ceratopsid skull: their great length in most chasmosaurines is impressive, and their absence in most centrosaurines is striking. Postorbital horns are basal for Ceratopsidae, occuring in the family's outgroup taxa, Zuniceratops and Turanoceratops, and having been inhereted by both the Chasmosaurinae and Centrosaurinae. Basal members of both groups have elongate postorbital horns. Surprisingly, the basalmost centrosaurines, Albertaceratops and an undescribed Utah taxon, have more exaggerated postorbital horns than basal chasmosaurines! The postorbital horns of Chasmosaurus (C. belli and C. kaiseni) are relatively short--but thick--while those of Albertaceratops are surprisingly long and erect.

As centrosaurines evolved, however, they seem to have lost interest in retaining their postorbital horns. Styracosaurus and Centrosaurus both retain short, rather stubby postorbitals early in life, but these are reabsorbed and shrink away to nothingness during adulthood. A similar process occurs in Einiosaurus. Pachyrhinosaurines, however, make use of their postorbitals differently: the postorbital horns of juvenile animals are small and laterally compressed. With growth, however, the postorbitals grow not upwards, but laterally, forming eventually forming wide bosses that nearly meet in the middle of the skull. Oddly, old adults still reabsorb postorbital tissue, and the surface becomes pitted or, in places, hollow. In some specimens of Pachyrhinosaurus lakustai, both the postorbital and nasal bosses are actually concave due to reabsorption!

A sampling of ceratopsid postorbital horncores. From top to bottom, left to right: "Monoclonius flexus" (AMNH 5239), Styracosaurus albertensis (CMN 344), Albertaceratops nesmoi (TMP 2001.26.1), Achelousaurus horneri (MOR 485), Chasmosaurus kaiseni (AMNH 5401), Pentaceratops sternbergi (OMNH 10165), Pachyrhinosaurus lakustai (TMP 1989.55.1234), Triceratops horridus (SDSM 2760), Anchiceratops ornatus (AMNH 5251), Avaceratops lammersi (MOR 692), Torosaurus latus (MOR 1122). Not to scale: the purpose is to show the diversity of postorbital shapes.

Chasmosaurines retained the ancestral condition and went to town with it. While Chasmosaurus lacks impressive postorbital horns, later chasmosaurines are anything but. Most chasmosaurine postorbital horns are tall, and curve gently forward along their length. A few expections exist, including Agujaceratops, whose horns are nearly erect (and if anything, slightly backswept); Avaceratops, whose horns are surprisingly short; and Arrhinoceratops, whose relatively short horns are curved strongly forward. The most impressive postorbital horncores must belong to a giant specimen of Pentaceratops (OMNH 10165), whose horns are measured at 106 cm along their curve. That's 41.7 inches, or just over three feet!

How did chasmosaurine postorbital horns grow? Centrosaurines reabsorbed their horns, but in Triceratops, at least, the postorbitals changed significantly as the animal matured!

Babies have stubs for horns, and these horns grow straight up before curving back in juvenile animals. This posterior curve is retained in subadults, but the horns then sweep forward strongly, more or less at the base, in adult animals. From this point on, the horns actually begin curving anteriorly until they appear subhorizontal in some individuals. Furthermore, as the animal matures, the interior portion of the postorbital horn is reabsorbed! Surprisingly, this complicated reorientation of the postorbitals may be primitive for Ceratopsidae--the same process can apparently be seen in Zuniceratops! Another important point here is that the great chasm in morphology between juvenile and old adult Triceratops provides evidence against Forster's two-species idea. According to Horner & Goodwin's analysis, T. prorsus is merely a subadult T. horridus.

Do the shape or orientation of the postorbital horns have any phylogenetic significance? Sadly, probably not. Because their shape changes so radically with growth (in all ceratopsids), their taxonomic significance is negligible. What appears to be a unique feature, like the strongly angled horns of Arrhinoceratops, is more likely age-related. Even the mere presence of postorbital horns, which at one point separated chasmosaurines from centrosaurines, is no longer a viable phylogenetic feature, since basal centrosaurines also have long postorbital horns, as did the common ancestor of both groups. Even the presence of a postorbital boss vs. horn may not be significant--juvenile centrosaurines, including pachyrhinosaurs, have small horns while the adults have bosses. This puzzle is perhaps best exemplified by "Brachyceratops," a small juvenile centrosaurine from Montana. Its child-like features include small, slightly recurved postorbital horns and an unfused nasal horn. The structure of its squamosal bone gives it away as a centrosaurine, but given what we now know about postorbital growth, its horns hold little value in determining its classification. Generally, the structure or presence of postorbital horns is helpful only after other factors are considered.

What did ceratopsids use their postorbital horns for? The obvious answer is "defense!" And indeed, I doubt Triceratops turned its horns away from an attacker. However, their primary purpose may have been signaling and/or intraspecific combat. The fact that different age classes in Triceratops look different means that individuals could tell how each other animals were at a glance, or how experienced they are. And look at African antelopes--subtle differences in horn morphology reflects differences in taxonomy. Although between you and me, the ceratopsian differentiator was probably parietal morphology (we'll look at that later). Still, within a group of animals, it would have been very useful to identify individuals' ages and ranks at a glance, which differing postorbital horn morphology can do.

Andrew Farke has argued convincingly that ceratopsids with long postorbital horns may have used them for intraspecific combat. He first played figured out how Triceratops was able to lock horns, as it were, and then went out to the fossils to look for signs of pathology that would validate (or tear down) his idea. Turns out Triceratops skulls show numerous injuries to the squamosal bones, just where the point of the postorbitals would be pressed in a fight. So aside from perhaps defense and intraspecific signaling, ceratopsians with long brow horns used their postorbitals for intraspecific combat, as well! Gotta love practical experiments!

So what have we learned today? Well, large postorbital horns are plesiomorphic for Ceratopsidae, but aside from that, the animals within the two groups (Chasmosaurinae and Centrosaurinae) differ wildly in their expression of those postorbital horn morphology. Not only that, but the postorbitals of all ceratopsids change radically throughout life. Postorbital horns would have had many uses, including defense, intraspecific signaling, and most interestingly, intraspecific combat.

Next up: Nasal horns!

P.S. I'm too tired to write the whole big reference list right now. I'll just copy and paste it from my electronic index later. For now, trust that I'm not making anything up.

Oh, the Burning!

Read this post and watch the videos. No, don't turn them off. Sit through that shit. Soak it in. Now, remember when I asked why people believe crap like this? Today I have a new question: Why does the media give quacks like this a voice? Why do they get ANY time in the spotlight? I'm all for freedom of speech, but when that freedom of speech actually misinforms the public and potentially causes harm, isn't it like screaming "FIRE" in a crowded theater?

Also: Sorry it's been slow lately. I'm working on three big ol' posts for The Boneyard. The art is taking awhile.

Ze Bonyard's Triumphant Return!

Remember the Boneyard? If not, click the corresponding tag. I will return to this humble blog on June 12th, so get those entries written and submitted to me either via comment or email (sillysaur at gmail dot com). I'm going to try and include important stories from the last few months, so anything you've written about Puijila, Tianyulong, Miragaia, etc., include it here. The Synapsid Art Show will be linked to, all that good stuff. Get those entries in, dear readers! This will be epic!

Rationality: 1, Kooks: 0

Yahoo! Our justice system steps up against idiocy. My faith in humanity has been (slightly) restored.

More Medical Quackery

I didn't have the energy to find these links before, when I was talking about idiots who treat their kids with homeopathy and/or prayer, but I've since run across them.

Prayer does not cure diabetes, Part the First.
Prayer does not cure diabetes, Part the Second.
Herbs and ionized water probably aren't going to help with cancer.
Here's the proof.

If you read some of those links, you'll notice that in many cases the parents are being strung up on criminal charges, which I support entirely. The child's rights are being quashed by the religious/nutjob beliefs of the parents, who are voluntarily sending their spawn to an early grave. On the one hand, this does get rid of idiots from the gene pool (parents die and they killed their offspring already), but on the other hand, I really hate these people. My desire to see justice done outweighs my apathy towards the death of morons.

So again I ask: what drives people to such incredible acts of cognative dissonance? When your daughter is days from death's door, what moves you to email your friends and ask for "emergency prayers?" Because prayer worked so well until that point! A few emergency prayers will do the trick! ACK!

*storms out of the room*

As a brief aside, here's a great Discover magazine story about those moronic anti-vaccine activists and why, even after all their claims have been discredited, they still parade their cause.

ANGRY POSTSCRIPT: Look, just because your fringe, nutcase belief is not supported by science or, perhaps, the public in general, does not mean that there's a gigantic conspiracy going on to subdue said belief. Life is not the The X-Files. Here's how science works: If you don't have a falsifiable theory to support your claim, you MUST defer to the theory that DOES have the evidence, at least until you can present actual evidence to your claim. This is a principle I really want to hit the BAND members over the head with (among other groups). If you can't show me a basal crurotarian or archosaur who shares multiple non-convergent synapamorphies with birds that are not plesiomorphies, shut the fuck up and move on. Merely trying to poke holes in established theories is NOT science. You have to come up with a falsifiable alternative yourself, too. If all available evidence shows that vaccines do NOT cause autism, get the fuck over it and move on with your life. Why is it so difficult for people to accept falsifiability? ARGH!

*storms out of room again*

Synapsid Show, and my EPIC FAIL

Another quick post. If you haven't already, check out the incredible Permian Synapsid art gallery over at the Art Evolved! blog. And while you're there, check out my self-loathing explaination of how I totally fucked this one up. I think you'll agree.

BG&E Fans: Pay Attention

Just click the link and soak it in.

Water: The Magical Cure-All

Homeopathy kills a child. Now, I'm not surprised that this happened (or happens). What I'm curious about is the motivation for such irrationality. What drives people to seek out bizarre, unproven, "mystical" treatments for maladies that are perfectly treatable with real medicine? Humans have a talent for cognitive dissonance. Even if all evidence points to the contrary, Jenny McCarthy still believes (and that's the proper term) that vaccinations cause autism. Holocaust deniers still believe that Hitler did not, in fact, kill a bunch of Jews. AIDS conspiracy theorists believe that AIDS is a government-created disease meant to thin the population and/or get rid of homosexuals.

But here's my question: why do people believe this nonesense? What is the draw? If I can explain something in perfectly reasonable terms in a way that's clearly observable, why does that not suffice? Why does mysticism have to play a part at all? Look, here's an example. Let's say that one of your friends believes that keeping a dryer sheet in your pocket will keep mosquitoes away. That's an attractive proposition, given that Alaska's mosquitoes are the size of songbirds and darken the skies with their numbers during the height of summer. So you try this. It does not work. You rub the dryer sheet all over your head and neck. Still nothing. You pack several dryer sheets in your pockets. Nada. The mosquitoes don't care. You know what does work? Mosquito repellant, easily purchased as the grocery store for like two dollars. It's a little like suntan lotion, although there's a spray-on kind, too. The point is, repellant works, but the dryer sheet does not.

But your friend still believes that dryer sheets work. Why? When all evidence to the contrary demolishes one's belief, what is the point in retaining that belief? This question applies to a great many subjects including conspiracy theorists, members of the BAND*, homeopaths, religion in general, this guy, and many more.

So I guess my question is this: why do people believe crazy things when they have absolutely no evidence to back those claims up? And why, when contrary evidence is introduced, do they hold on to those beliefs, often with a tightened grip?

*Birds Are Not Dinosaurs

A Teaser with Teeth

Just to let you all know, I'm prepping a big ol' post about saber-toothed mammalian carnivores. It's the next in my "taxonomy lessons" series. Remember the first one? A few posts down? About Puijila? Geeze, I'm focusing on mammals a lot lately. As I admitted to Scott earlier, the more I study mammals, the more interesting they become! I think it's the embolotheres that won me over. Freaky big-nosed brontotheres, man. Anyway, stay tuned for a new taxonomy lesson in the next day or so.

Engarde!

I recommend hopping on over to Coherent Lighthouse and having a look at Scott's new manifesto against Creationism and its ilk. One of the best rants I've read in a long time. Brings to mind our dear friend the Blue Collar Scientist (science rest his soul).

To the left is Tiktaalik rosea, a *gasp* transitional form. But I forget--there are no transitional forms.

Gorgonopsids and Dicynodonts and Pelycosaurs, OH MY!

The newest art show at the Art Evolved! goes up today. Its theme: Permian synapsids, a wondefully diverse but, alas, poorly-known group of critters that deserve a whole lot more time in the spotlight. My own submission is painfully horrible and difficult to look at now. Forgive my feeble attempts at coloring things with Photoshop. The sketch had so much promise! I shall blog about my failings at a later date, but I eagerly await seeing what my talented colleagues came up with! Perhaps I shall throw together one of my "signature" pen & ink pieces tonight for inclusion...