marginocephalians

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I’ve seen this chart floating around on my dash, and it occurred to me that I never posted the original version. So here is my and Jon's Dinosaur Classification Chart, in a hopefully Tumblr-palatable format.

Click here to see the moderately large version at DA.

This is a much simpler examination of dinosaur relationships than most of my watchers would probably find useful. Most of you will know that theropods are broken up into tetanurans and ceratosaurs, and that birds are nested within coelurosaurs, and that there are many internal divisions within sauropods and ornithiscians as well. But this chart is intended to be more of a quick, concise reference for laypeople, teachers, children, or whoever might have a passing interest in dinosaurs. My hope is that anyone who wants to quickly figure out what major group any given dinosaur falls into can glance at this chart and know immediately. 

This was a collaboration between myself and Jon - I did the illustrations, and he did all of the layout and text. To see this chart in full resolution, please consider buying a poster in my Zazzle shop.

Pachycephalosaurus:The Sequel—The Fossil Presence of Keratin.

I was checking my deviantArt messages when I saw the piece of artwork you see above this text. http://malvit.deviantart.com/ is the illustrator, and here he has depicted a pair of jousting Pachycephalosaurus, a dinosaur that I have spoken of before. This is one of his most recent illustrations, inspired by the book All Yesterdays. I’m sure you’ll notice what’s different about it compared to other reconstructions of Pachycephalosaurus. Yes, you do. It’s got keratin horns atop its characteristic domed horns. Experts (such as Gregory Paul) have said that the presence of keratin horns on bosses and domes cannot be eliminated (In this case Paul was talking about Pachyrhinosaurus), because keratin doesn’t preserve. In All Yesterdays, C.M. Kosemen illustrated a magnificent “shrink-wrapped” rhinoceros, which had no horn or external ears, and the extended vertebrae on its back were interpreted (hypothetically, by hypothetical paleontologists of the future) as representing a sail, probably a way to poke a bit of fun at the fact that the majority of experts maintain that dinosaurs like Spinosaurus and Ouranosaurus possessed sails on their backs. But I’m getting off track here.

Anyway, there was a pretty good explanation for this keratin-adorned pachycephalosaur duo. Though the initial hypotheses about their domes suggested that these animals knocked skulls like bighorn sheep, but John Horner suggests that the skull of the animal couldn’t resist such a frontward collision with another animal’s head. As it still seems that the skull was specifically adapted to bear the weight of something heavy, MALvit suggests that the keratin horns, however strange-looking, may have served as the cranial adornments that pachycephalosaurs battled with. It doesn’t involve head-butting, but still involves head-jousting. In this way, it’s a bit more like the courtship battles of deer than those of bighorn sheep. It’s a plausible idea.

There are lots of competing hypotheses about what Pachycephalosaurus did with its skull dome, but this cool artist took it a step further and took the dome out of the picture, covering it in keratin pseudo-antlers. Kudos to him for this, and kudos to him for giving the creatures hair-like feathers.

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Texacephale langstoni: Authentic Head-Bangers?

Size: Roughly 6.6 feet (2 meters) long.

Time Period: The Campanian Stage of the Late Cretaceous.

Locale: The Aguja formation of the United States (namely, Texas).

Name: The generic name means “Texas head,” referring to the animal’s Texan locality and its thick-domed head. In fact, ‘cephale’ is a very common epithet for pachycephalosaurs due to this very reason. The specific name refers to Wann Langston, an American paleontologist.

The pachycephalosaurs are famously referred to as the ‘head-banging’ dinosaurs. The domed heads of many pachycephalosaurids are imagined to have been used by males that smashed dome against dome to win the attention of females during the courtship season. This, as we know now, may have been a myth.

Before I talk about that, I would like to talk about Texacephale. This animal most resembles Hansuessia and Sphaerotholus, animals that lived farther north than it. This further supplements the idea that there was a huge degree of endemism in North American fauna during the Campanian (during the Maastrichtian, this disappeared to some degree) stage. This endemism, combined with a high diversity of ceratopsids and hadrosaurs, meant that the Campanian Stage saw some of the most diverse North American faunal assemblages come into fruition.

Now, about the skull. Though some sources regarding Texacephale proclaim that its skull was surely built for head-butting because it possessed ‘gears’ that let it absorb impact, this probably wouldn’t outweigh how useless the skull structure was for knocking heads. In animals like bighorn sheep, who butt heads during the mating season, the skull is hardly domed and made of solid bone. The skull of Stegoceras, one of the most well-known of all dome-heads, shows that the dome is laced with the remains of blood vessels that made the skulls porous. The skulls of the aforementioned bighorn sheep have broad heads that possess spreading horns. The skull of a bighorn also has air-filled chambers in it, which are known to be good at absorbing impact. What would happen if a pair of Texacephale actually smashed their heads together? They would have probably killed each other.

Other methods of interspecies competition could be explored. Pachycephalosaurs could have attempted to hit each other’s flanks like some extant animals do on occasion. Pachycephalosaurs also had stiff tails with ossified tendons, which they could have hit each other with as well.

Aside from combat, what purpose did the domes serve? They may have been anchors for keratinous horns (as I’ve discussed in other posts), which could have indeed been used in courtship battles like the antlers of deer. It’s also possible that the domes were used for some kind of display. In Pachycephalosaurus, males were far more flamboyant than females, with elaborate scute arrangements and larger domes. It’s possible that this was a sexually selected trait, and that males with bigger domes got the ‘chicks.’

So we draw the curtain on this post with a myth dispelled. Those of us who grew up reading about the pachycephalosaurs will likely think of them as head-banging creatures that jousted for mating rights. It turns out that if they actually did that, they probably would have both suffered the consequences. As the field of paleontology evolves, natural selection wears away at the theories that we think are so grounded in fact.

First of all, I’m back. Second of all, you probably recognize this picture. It’s of Nasutoceratops titusi, a ceratopsid that wasn’t formally described the last time(s?) that I talked about it. Fans of ceratopsids will be pleasantly surprised to know that Nasutoceratops has been formally described, so I can talk about it with more certainty. Yay.

Nasutoceratops comes from the Campanian stage of the Late Cretaceous, and is from the Kaiparowits Formation of Utah. Looking at this dinosaur, one might assume that it’s related to Triceratops or Chasmosaurus, but it isn’t. Incidentally, its skeletal elements looked something like this:

From these skeletal elements, it’s been concluded that Nasutoceratops is a centrosaurine ceratopsid, and is most closely related to Avaceratops lammersi, another primitive centrosaurine with brow horns. However, Nasutoceratops is unique because its horns have an arrangement remarkably similar to that of modern bovines. These horns may have played a role in display or interspecies combat.

Near Nasutoceratops’s left shoulder, skin impressions were found. One of these impressions shows large hexagonal scales surrounded by small, triangular scales. This is reminiscent of the scale arrangement in other ceratopsians, which have similar geometric patterns.

The fact that Nasutoceratops exists is proof of the separation between the Northern and Southern fauna of Larimidia (what is now western North America). It retained long brow horns and a short (nearly unnoticeable in Nasutoceratops’s case) nose horn, contrary to the ornamentation of its northern kin. It may be a representative of a previously unknown clade of centrosaurines whose remains aren’t yet known.

Lastly, the origin of Nasutoceratops’s name is a bit convoluted. Devout fans of new dinosaur discoveries have probably heard the name Nasutuceratops, and are probably very confused thanks to my use of Nasutoceratops. The generic name of this dinosaur is derived from 'nasutus,' the Latin word for ‘big-nosed,’ as well as 'ceratops,' which is Ancient Greek for ‘horned face.’ The specific name, titusi, honors Alan Titus, the man who recovered fossils of Nasutoceratops.

Well, this was an interesting post. I do enjoy going back to old topics and revisiting them. This time, the post was tied in with the series I’ve been doing on new 2013 discoveries. 

Remember to send requests for posts.

All Yesterdays: A wider diet by ~Vitor-Silva:

One of my entries for the All Yesterdays Contest.
Here, an Avisaurus is enjoying the shadow of a Triceratops. Then, suddenly, the ceratopsian falls its body and crushes the bird, to eat it and enrich its diet with proteins. It is mainly based in new theories of ceratopsians be adapted and able to eat meat as well, and this “bird-crushing” behavior is observed in giant tortoises.

New 2013 Stuff: The Sequel

Besides Yunmenglong, which was discussed in my last post, a few more dinosaurs have turned up this year. They’re actually pretty interesting, and are listed as follows.

Jianchangosaurus yixianensis:This dinosaur, known from a juvenile specimen, is the latest feathered dinosaur to come out of China’s famous Yixian Formation. It is a basal therizinosaur that has a dental arrangement reminiscent of ornithopods and ceratopsians. Since Jianchangosaurus is the most complete therizinosaur known so far, it makes sense that it sheds light on the morphological gap observed between Falcarius and Beipaiosaurus, its two closest known relatives. As a Chinese therizinosaur that looks like the North American dinosaur Falcarius, Jianchangosaurus also proves the wide distribution of therizinosaurs during the Early Cretaceous period.

Aurornis xui:This creature, hailing from the Middle Jurassic of China, is described as an avialan dinosaur more primitive than even Archaeopteryx, the reputed ‘first bird,’ which it predates by 10 million years. It’s from the Tiaojishan Formation, a place also home to Tianyulong, Anchiornis, and other well-preserved dinosaurs. Aurornis’s bone structure is more primitive than that of Archaeopteryx, and the absence of larger feathers suggests that it was unable to fly or even glide. Based on about 15,000 anatomical characteristics, Aurornis is the most primitive confirmed avialan thus known.  However, exactly what we should call Aurornis in less technical terms is unclear, since it represents one phase of a great transition. The line between bird and dinosaur used to be clear, but new remains blur that line so significantly that the terms ‘bird’ and ‘dinosaur’ are really hard to define. Whatever the case, Aurornis is an important find and helps trace the evolution of birds.

Bravoceratops polyphemus: The only ornithischian in this edition of New 2013 Stuff is a chasmosaurine ceratopsian. Hailing from the Early Maastrichtian stage of Texas, this animal shares characteristics with the famous Torosaurus and Triceratops. It has a combination of primitive and derived characteristics, which not only suggests a relationship with Triceratops and co., but also with Coahuilaceratops, another transitional chasmosaurine (however, it lived in Mexico, not Texas). Like Coahuilaceratops, Bravoceratops follows a trend of some chasmosaurines in North America; a trend of changing into Triceratops-like forms. 

I hope you enjoyed this issue of New 2013 Stuff. Once more discoveries are unveiled, expect to see another update!

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Sinoceratops zhuchengensis: Asia’s Horned Face.

Size: 23 feet (7 meters).

Time Period: Unknown, but most likely the Maastrichtian Stage of the Late Cretaceous.
Locale: The Wangshi Group of China.

Name: 'Sinoceratops' means Chinese horned face, in reference to its place of discovery. 'Zhuchengensis' refers to the part of China that it was found in.

No dinosaur book is complete without Tyrannosaurus and Triceratops, usually in combat. I’d like to see a scene of these two doing absolutely nothing, or even interacting in a nonviolent fashion (a la All Yesterdays, a book which I keep referencing). We know a lot about these dinosaurs, and while tyrannosauroids were very widespread, our knowledge of ceratopsid distribution remains rudimentary.

You see, big ceratopsids like Triceratops and Styracosaurus seem to have been limited to Western North America, and their smaller contemporaries (such as Bagaceratops and Protoceratops) were limited to both this location and Eastern Asia. Only recently has Ajkaceratops, a close relative of Mongolia’s Bagaceratops, been found in Europe, increasing our knowledge of this group. But I’m not here to talk about little Ajkaceratops (that’s for another post, I suppose). I’m here to talk about the glamorous Sinoceratops.

You see, Sinoceratops is a representative of a group only previously known in North America, and it increases our information about the distribution of the mighty ceratopsids. It’s possible that they were more common than the fossil record suggests, but it’s also possible that these animals weren’t very common in Eastern Asia, as this place’s fauna is a bit different than Western America’s at the same time. Maybe big ceratopsids were rare animals that lived in the shadow of more successful herbivores like hadrosaurs and therizinosaurs. The sauropods were also fairly uncommon in this area, but again, it is possible that we just don’t have enough evidence of their commonality/uncommonality.

The anatomy of Sinoceratops is also an interesting talking point. This animal has a short, hooked nose horn typical of the centrosaurine ceratopsids. It doesn’t have any brow horns, and has a short frill with forward-curving hornlets that remind me of the very flamboyant Kosmoceratops. Not seen in any other horned dinosaur are the series of low knobs on top of the frill between the aforementioned hornlets. This animal is a member of the centrosaurines, like I said before, and resembles short-filled relatives such as Centrosaurus and Styracosaurus. These features are completely unseen in primitive members of this subfamily, and include the nose horn and reduced brow horns.The fact that Sinoceratops isn’t a primitive centrosaurine and shares characteristics with derived relatives from Montana and Alberta shows that no, ceratopsids did not evolve in Asia, nor did representatives of the group found in Asia resemble their primitive relatives such as Albertaceratops.

The implication that this animal has been found in Asia is that Sinoceratops is a representative of a movement of ceratopsids that invaded Asia from North America. Marginocephalians may have originated in Asia, as the earliest representatives of this clade have been found here, but the most famous among them were restricted to North America. Sinoceratops is an intriguing find because it implies that someday we may find even more Asian ceratopsids, and maybe one resembling the mighty Triceratops itself.