Mystery Skull #1

New game, kiddies. While I put the finishing touches on my Horns 'n' Spikes wrap-up post, I thought I might start something. I'll post a skull I've restored, and you get to guess what (or who) it is. Couldn't be easier, right? We'll start with an obvious one to start things off. Not all skulls will be reconstructed. Sometimes, you'll only get bits and pieces.

Hint: it is neither cute nor cuddly. Largely simplified from Paul (2002).

Wednesday Musings

It's a slow work day, so I've got plenty of time to think about thinking about things. Stumbled over a question in my head that I've never really considered before. What came first, the fruit or the flower? Both contribute equally well to the success of angiosperm plants: fruit disseminates the seeds while flowers advertise pollen and basically help the plants have sex. What do ya'll think? Talk amongst yourselves in the comments.

Open Lab!

Hey, kids! Have you seen any blog posts on this blog recently that've tickled your fancy? Why not nominate that post for Open Lab '09? How? Click this handy picture! I think. Also, keep an eye out for a rebuilt jugal horn post and a summary of the "Horns and Spikes" series coming soon.

Pet Peeve of Mine

I would like to read one book about modern birds...just one...where conservation is not a looming, overzealous theme. I own three books about modern birds, mostly for the sake of having reference photos, and all three of them beat the reader over the head with musings on how endangered, threatened, or otherwise in trouble these birds are. And what if the book discusses birds that are not threatened? Then it talks about potential threats to its habitat. You know, things to watch out for. It reads something like this:

"The Bohemian Waxwing is stupidly common and successful. However, in the future, human development might someday destroy its habitat. SAVE THE BIRDS."

Goddamnit, I know that countless animal species are threatened, endangered, etc., but when I'm reading a book for information, I don't need that fact hammered into my brain. It's not that I don't support bird conservation, because I do. But if I'm reading what's supposed to be an informative book about a particular animal, it's because I'm reading the book for information about that particular animal. I don't need to read two paragraphs about how threatened it is.

That is all.

Horns & Spikes, Part 4: The Frill

I've read--I forget exactly where--that the ceratopsian parietal is the most diagnostic bone in the entire head or body. Indeed, after researching and restoring parietals and squamosals for this post, I would tend to agree. While we've seen that postorbital horns are of little phylogenetic significance, nasal horns are little better, and jugal horns are virtually worthless, the structure and decoration of the parietal bone tells us not only whether the animal is a chasmosaurine or centrosaurine (every time), it is also an excellent genus or species specifier. The ceratopsian neck frill is an incredibly useful, diagnostic feature.

To avoid an overly-lengthy discussion, this post will focus only on the Ceratopsidae proper, though the frill structures of protoceratopsids and Zuniceratops are fascinating in their own rights. The former group in particular seems to have developed its own unique frill shape and design that's worthy of a separate post entirely. At any rate, all ceratopsid frills are built the same way: a hypertrophied, fused parietal bone connects to two large, plate or strap-like squamosals on either side. The shape of these bones determines the subfamily identity of the ceratopsid in question. In chasmosaurines, the parietal is long and hatchet-shaped--narrow at its proximal end, wider and curved at its distal end. The squamosals are elongate and knife-shaped, making up a large portion of the frill's outline. In centrosaurines, however, the parietal is much more circular, and the squamosals are shaped rather like a short machette, comprising little of the frill's total outline.

A sampling of chasmosaurine neck-frills, showing the structure of the parietal and squamosal bones. From left to right and top to bottom, Chasmosaurus belli, Triceratops "serratus," Anchiceratops ornatus, and Pentaceratops sternbergii. Note that even in Triceratops, the structure of the squamosals confers to the normal chasmosaurine form.

Chasmosaurines and centrosaurines appear to have approached frill decoration in subtley different ways. Centrosaurine frill development is better understood. Their parietals have seven points of spike growth, marked P1-P7, and these points of growth are called "loci" ("locus" singular). P1 is most often absent, but expresses as a ventrally-oriented spike that often overhangs the parietal fenestrae (it is most obvious in Centrosaurus). P2 expresses itself as a pair of small spikes which face each-other where the paired parietals would meet. In Centrosaurus brinkmani, P2 expresses as a cluster of small spikes that appear to cover P1. P3 is often the most obvious parietal spike in centrosaurines, almost always dominating the frill. In Styracosaurus albertensis, P3 is the first of three enormously elongate parietal spikes that give the genus such an impressive look. In Albertaceratops nemoi, P1 and P2 are completely absent while P3 has overtaken the frill, developing into enormously wide, flaring spikes which curve downward along their length. In Achelousaurus horneri, P3 forms a long, backswept and blunted spike that gives the frill a sort of "rabbit-eared" look.

A sampling of centrosaurine frills. The two on the left are Centrosaurus apertus (top) and C. brinkmani. On the right is Achelousaurus horneri. Note the absence in A. horneri of P1 and the wildly different forms taken by P2 and P3 in the two species of Centrosaurus.

In most centrosaurine taxa, P4-P7 are either extremely reduced. In Styracosaurus, however, P4 and P5 develop into elongate parietal spikes just as in P3, though P4 is shorter than P3, and P5 is shorter still. P6 forms a small hook-like spine. P7 is small and inconsequential compared to the other parietal spikes. In Centrosaurus, Achelousaurus, Einiosaurus, and Pachyrhinosaurus, P4-P7 are barely worth mentioning. In Albertaceratops, P4-P7 are, oddly enough, fairly uniform in size and shape as pointed finger-like projections. A few centrosaurines further modified their parietals to support bumps and spikes on the parietal bar itself. This is most obvious in Pachyrhinosaurus lakustai, where at least one specimen (TMP 1988.55.187) preserves a trio of parietal spikes, though the most impressive truly massive central prominance. Albertaceratops has five small bumps running down the length of the parietal bar, as does Centrosaurus brinkmani. In the latter species, the bumps become larger proximally. In Achelousaurus, the proximal portion of the parietal bar is decorated by three small spikes, perhaps predicting the condition in Pachyrhinosaurus.

The frills of Styracosaurus albertensis (left) and Albertaceratops nesmoi. Note the differing structures of P3-P7 in both animals.

Basal chasmosaurines may have initially followed a similar developmental path for the spikes of the parietal. However, given the different structure of the parietal itself, there was not as much room for spike loci. In Anchiceratops ornatus, spikes in locations analogous to P1-P5 are present. All are broad and roughly triangular, but there is no room for P6 or P7. "P5" is just above the contact between the parietal and squamosal. The situation is more dire for Pentaceratops, whose parietal is similar to that of Anchiceratops but even narrower--there is only room for "P1-P4." In Chasmosaurus belli, the dorsal edge of the parietal is almost totally devoid of spikes except for a two laterally-directed, triangular spikes acting as the "corners" of this ceratopsid's unusually triangular frill. In the most derived chasmosaurines (Torosaurus, Nedoceratops, and Triceratops, any sort of locus-like developmental process seems to have been completely lost, replaced by a smooth frill margin that is decorated by separate ossifications (epioccipitals). Most obviously apparent at an early age, the epioccipitals are quickly incorporated into the frill itself and tend to disappear in older animals.

Given that every ceratopsid seems to have a different parietal outline, one would think (quite rightly) that such a structure would have important consequences for intraspecific signalling. I am reminded of the many species of deer and antelope that are, aside from their antlers and horns, amazingly similar in body form. It would also be interesting to see if sexual dimorphism plays a role in parietal development, though an enormous sample size would be necessary to investigate such a possibility. Of all the spikes and horns on a ceratopsian's head, those of the parietal frill are the most relevant from a phylogenetic perspective. I am impressed by the diversity in frill shape and form within this group of animals.

Selected parietal elements from Pachyrhinosaurus lakustai, including the dorsal section of the parietal (bottom two) and two examples of spikes on the parietal bar. Note that in terms of spikes on the parietal margin, Pachyrhinosaurus was fairly conservative, having retained only P2 and P3 with any kind of prominance.

A note on parietal fenestrae. They refer to the holes in the frill that are common to almost all neoceratopsians. The exceptions seem to be Avaceratops (who is likely a chasmosaurine) and Triceratops. While the former has a truly solid frill (one wonders where the jaw muscles attached), Triceratops actually does not, despite claims to the contrary. While it does lack of parietal fenestrae, it still has small holes in the frill. What? It's a parietal fenestra if it is restricted to the parietal. Look at all of those pictures above: in almost all cases, the parietal fenestrae are totally within the parietal bone and are not formed by the border of the squamosal and parietal bones.

Here's an analogy: tetanurine theropods have antoribital fenestrae and maxillary fenestrae. The former is formed by the borders of several bones including the maxilla, nasals, jugal, and frontals. The latter, however, is restricted entirely to the maxilla. It's like a hole in the maxilla bone. So parietal fenestrae are like holes in the parietal bone. But look at Triceratops: it has small holes in the skull formed by the border of the parietal (which flares outward proximally) and the squamosals. It has holes in its skull, but they are not parietal fenestrae!

...at least, that's how I understand it.

Xenosuchus prognathus is an Archosaur

A note to the readers: this post deals with the "Alt-Permian" project that Will Baird and I have been working on for a few years. Perhaps you'll recall the Barbouronopsid and Neo-Dicynodonts from not too long ago. As a result, Xenosuchus prognathus is, sadly, not a real animal. But Will and I are having some fun with it.

Xenosuchus prognathus is a medium-sized crocodile-like archosaur from the Late Xenopermian of Ural region of Russia. It is thought to have occupied a freshwater niche that has not been filled by the giant marine hovasaurs. While its postcranial remains--what few there are--are largely uninformative, the excellent preservation of the skull bones allow much insight into the lifestyle and phylogenetic affinities of Xenosuchus. Its most remarkable feature is the fan-shaped expansion of the premaxilla in dorsal view.

The rostrums of Proterosuchus (left) and Xenosuchus (right). Not the fan-shaped expanion of the premaxilla, as well as the elongation of those bones toward greatly retracted external nares, in the latter.

The premaxilla is equiped with long spear-like teeth that lack serrations. The maxilla has small, subconical teeth running down its entire length. The fan-like shape of premaxilla, coupled with the specialized dentition, has been interpreted indicitive of a picsivorous diet. While very little of the mandible has been preserved, the anteriormost tip of the dentary is. Interestingly, the dentary is downturned, and the structure of the teeth match those of the premaxilla. However, the dentary is not laterally expanded, instead retaining a weak U-shaped symphesis. The tip of the dentary fits entirely within the premaxilla.

The smooth dorsal and ventral borders of a small antorbital fenestrae, probably triangular in shape, are preserved on the partial lacrimal and jugal bones. More interesting is the very small maxillary fenestrae which appears just caudoventrally to the external nares. Its smooth margins suggest that the fenestra is not an artifact of preservation, but whether it is the result of bone reabsorbtion or pathology is unknown at this time.

The orbit is small and divided into two parts by the intrusion of the postorbital, bringing to mind such an occurance in many rauisuchian-grade crurotarsians. The upper half is roughly D-shaped while the lower half is triangular. Bits and pieces of the sclerotic ring are preserved in the upper half of the orbit. The frontals are small but form a significant portion of the orbit's dorsal border. The postorbital is a large, plate-like bone that is one of the largest bones of the skull. It is matched in size by the jugal, which has a large ascending process that forms a significant portion of the temporal fenestra's cranial margin.

Most interestingly, the parietal bar is strongly reduced to a nub-like process while the squamosal bones are elongate and curve gently outward in dorsal view. The parietal does not articulate distally with the squamosals, and the skull's back half resembles a "W" in dorsal aspect. The temporal fenestrae are vertically elongate, bordered by the jugal, postorbital, squamosal, and quadrate. The posterior half of the articular is poorly preserved, but reveals a short postarticular process, indicating weak jaw-closing power.


A reconstruction of the skull of Xenosuchus prognathus. Rugose nasals restored on the basis of small rugose bone fragments found near the dorsal margin of the skull.

Though a basal member of the group, Xenosuchus is most assuredly an archosaur based on its socketed teeth and antorbital fenestrae. It most closely resembles Proterosuchus fergusi, another semi-aquatic form with a unique "hooked" premaxilla. The two genera are of comparible sizes as well: both are between two and three meters long.

Eye Boogers

Those who've been following my Facebook updates know that my youngest* leopard gecko, Liquid, has been battling a pretty horrible eye infection. The area directly behind his eye is swollen, mostly likely as a result of the gunk that's building up behind his eyelid. He generally keeps his eye closed, though not voluntarily. This gunk hardens quickly upon touching air, so his lid is closed because it's glued closed. Removing the obstruction (with my tweezers) immediately allows him to open his eye. But he can't actually see because of the greenish-white gunk that's in front of the eye itself. This last weekend, I set about construction a crude gunk-sucking contraption: basically a bulb attached to the glass part of a small eyedropper, with the intention of sticking the eyedropper end into his eye and sucking out as much gunk as possible.

You'd be surprised how difficult this task is on a fidgity leopard gecko. He was not amused, but I did manage to remove a little bit of junk from his eye. He still can't see, though. There's a lot of gunk.

Anyway, something really strange happened last night. I checked on him, and greenish gunk was sticking out of his eyelid. I grabbed the tweezers and pulled out a glob of sticky green stuff that was easily the size of his eye. In fact, I worry that the green glob was the remains of his eye, it having been ravanged by an infection for a month now. Since pulling out that nasty gunk (it just slid right out), he hasn't opened that eye. I hope his eye is still in there. My hope is that he starts eating, because he's lost his appetite and he's losing weight.

As squirmy as he is, though, I know that Liquid is happy to get anything out of his eye, even if it's uncomfortable at the time. Considering how Solid would react to me poking around his head, Liquid is ridiculously relaxed, so he must know it's benefitial. My biggest worry is that I'm doing more harm than good, but getting that giant glob out is definately a step in the right direction.

He has eye antibiotics, but I can't very well give them to him until his eye is cleared out.

*Saying he's the "youngest" isn't really correct because Solid is the same age. Liquid, though, is the smallest of the three leopards, so he's the baby of the trio.

Horns & Spikes Part 3: Jugal "Horns"

The ceratopsian jugal horn is unique in that it comes in two distinct forms: a non-capped form, where the jugal itself flares outward to a point without the assistance of an epijugal ossification; and a capped form, where the jugal flares outward to (usually) a point and is also capped by a separate epijugal ossification, sort of like the nasal horn. What's especially interesting is that the most impressive jugal horns--non-capped forms--are found in the most basal ceratopsians. The crowded genus Psiattacosaurus includes three species with particularly impressive jugal horns: P. sibiricus, P. major, and P. gobiensis.


In P. sibiricus, the jugal horn width (from tip to tip) is greater than the length of the skull. This Russian genus also has the distinction of being the horniest (snicker) psttacosaur. In addition to its impressive jugal horns, P. sibiricus also has small postorbital horns and amazingly large palpebral horns. I would not want to mess with P. sibiricus!


P. major is the largest species in the genus and features a large, triangular jugal horn which, unlike P. sibiricus but like most other ceratopsians, points lateroventrally. While not as wide as the skull is long, the jugal horn width is substantial, and a good swing of P. major's head could cause some serious damage.


Finally, P. gobiensis, the most recently-described species of Psittacosaurus, has large, laterally-pointing jugal horns that are textured in such a way as to suggest a large keratinous covering. Interestingly, P. gobiensis' jugal horns curve gently downward along their length, unlike the straight jugal horns of P. sibiricus and P. major. Among ceratopsians, these species have (so far) the most impressive jugal horns!


Epijugals didn't pop up until later in coronosaur evolution. Protoceratopsids (like Protoceratops, above) have large, flaring jugals with rounded ends and similarly rounded, blade-shaped epijugals. They give the skull a unique look in anterior view.


Ceratopsidae never developed the jugal "spikes" of psittacosaurs or the flaring jugal blades of protoceratopsids. Focusing instead on postoribtal and/or nasal horn development, most ceratopsids simply forgot about their jugal horns. In almost all specimens, the epijugal quickly fuses to the underlying jugal bone, and the two grow outward together. The separation is barely apparant in older animals. Just one chasmosaurine, Pentaceratops, has managed to somewhat revisit the glory days of jugal horns. Pentaceratops has a jugal horn length of about 144 mm. That may seem huge, but keep in mind that that's 14.4 cm, or about six inches--nothing to brag about when your postorbital horns are 56 cm long (about two feet).

Jugal horns are not phylogenetically relevant unless you're talking about the separation between capped and non-capped forms, which seems to be a consequence of higher taxonomy (coronosaur or non-coronosaur). Among ceratopsids, the jugal horns are almost always short and unimpressive, and all those illustrations you see of Triceratops with whopping jugal horns are almost certainly inaccurate, unless the epijugal was, itself, capped by a massive keratinous cover, which I find unlikely. The large jugal horns of protoceratopsids may have had some role in sexual display or species recognition (or sexual dimorphism), and the retention of epijugals was probably inhereted by ceratopsids, but that group never really did anything with them. They may be vestigal structures, overshadowed by the other horns and spikes of the head.