Ornithischian Eyeshades

Ever wonder what that prong of bone in the orbits of ornithischian dinosaurs is called? I've often wondered that myself, and I accidentally came across the answer this morning while reading through Currie & Carpenter's Acrocanthosaurus description.

It's the palpebral bone! And it evolved independantly among many crocodilians and ornithischians. The feature seems primitive to the Ornithischia, although many groups subsequently lost it. Others enlarged it, among them "hypsilophodonts" (above) and basal ceratopsians. In his Predatory Dinosaurs of the World, Greg Paul suggests that the palpebral would have given ornithischians "eagle eyes." The bones would have certainly been covered with skin, and would have given the eyes of many ornithischians a certain "evil" glare. What purpose the palpebral bones served is not known (and I've never really seen it discussed in the literature). And why did some groups need it while others lost it completely?

Dino Diagnosis of the Day #2

You know? I have this great post in my head about pterosaur crest diversity. I've even got some of the sketches done. What sad is that I was slammed on my back this past weekend by the flu (or something like it) and this is the first significant time I've been out of bed. Very irritating symptoms: Snotting to no end (my...poor...nostrils), coughing so much my throat is raw, lack of energy, no appetite, mild joint pain, and ridiculous dehydration. And it seems to get worse as the day progresses. At any rate, I'm just too drained to write a real post, so I'm copping out and giving you kind people my second Dino Diagnosis of the Day!

This is a revised diagnosis:

Large theropod with elongate neural spines that are more than 2.5 times corresponding presacral, sacral and proximal caudal lengths of the centra. Lacrimal contracts postorbital; supraoccipital expands on either side of the midline to protrude as a double boss behind the nuchal crest; pleurocoelous fossae and foramina pronounced on all presacral and sacral vertebrae; cervical neural spines have triangular anterior processes that insert into depressions beneath overhanging processes on preceding neural spines; accessory transverse processes on mid-caudal vertebrae.

Go forth to your archives, dear readers, and come back with answers in tow!

Introducing Nyctosaurus

Well, here it is, ladies and germs: The first sketch I have accepted as "good" from the last two weeks of trying to knock out a Nyctosaurus for the art show. Previous efforts have been cave paintings by comparison. I will be painting Nyctosaurus on a large canvas for The Archosauria, and it will be accompanied by a rhamphorhynchoid of undetermined identity.

The original specimens of Nyctosaurus, described in 1958, lacked any kind of headcrest. Marsh allied Nyctosaurus with Pteranodon, but more complete skeletons, described and drawn by Williston in 1902, suggested that Nyctosaurus belonged in a family of its own. For one thing, the "naked lizard" is significantly smaller than Pteranodon, having a wingspan of less than ten feet. Additionally, Nyctosaurus has just three wing phalanges instead of the usual four. Stranger still, this Lower Cretaceous pterosaur has lost all of its non-wing digits (I-III). Because Nyctosaurus could not have spent its entire life on the wing, I have restored it with a fleshy pad capping the main joint of the wing finger.

The crestless Nyctosaurus existed until 2003, when two new specimens were discovered with giant reindeer antlers sticking out of their noggins. Marsh and Williston's crestless forms were probably sexually immature, and, like so many pterosaurs, the crest likely had a display function. Other possibilities exist, I suppose. Perhaps Nyctosaurus grew the crest annually, like modern deer do, but the lack of a rugose surface on the skullcap of the original Nyctosaurus material scratches that out. It's also possible that, like Pteranodon, Nyctosaurus was sexually dimorphic, and only one sex had the crest. This intruiging possibility cannot be adequately tested do to the scant remains of this "naked lizard."

Nyctosaurus has also been regaled to a more basal place on the pterodactyloid family tree. In their recent description of Nemicolopterus, Wang et al. (2008) placed Nyctosauridae as the basalmost clade within the Dsungaripteroidea.

Nyctosaurus is among my very favorite pterosaurs, and I'd like to do it proud. If there are any criticisms out there (Head too big? Legs too long? Crest too short?), I'd be happy to hear them!

Dino Diagnosis of the Day #1

Brian has Picture of the Day, and Darren has...well, Picture of the Day, too. I'm trying something different! Dinosaur Diagnosis of the Day! On occassion I will go into my closet full of paleo papers and pull out the description of some mesozoic dinosaur. I'd like to turn this into a game, as Darren originally did. We'll see how strong a response this maiden description gets.

Ready? Guess the beastie!

"Small to medium-sized theropods, lightly built and bipedal in posture. Fore limb not reduced. Manus long and slender with three functional digits, Digit III moderately divergent and carpus highly specialized with asymmetrical ginglymus on radiale. Hind limb long, pes of moderate length and functionally didactyl. Digit II modified as an offensive or predatory weapon with large, trenchant claw. Digits III and IV of subequal and normal, digits I and V reduced. Eight to 9 cervical vertebrae, 13 to 14 dorsals and 3 to 4 sacrals. Caudal series of ________ highly modified by extremely long prezygapophyseal and chevron processes which rendered the tail virtually inflexible throughout most of its length. Comparable caudal modifications are presumed, but not known, in other taxa referred to the family."

That's all quoted directly from the original description. Give it a shot, folks--who be it?

EDIT: Chris Taylor is our winner, correctly identifying the mystery taxon as Deinonychus antirrhopus. I should have picked somebody a little more derived! I wanted to do a dromaeosaur, but Chris was right in pointing out that, in 1969, these now ho-hum deinonychosaur features were diagnostic back then. Nowadays this description could apply to just about any deinonychosaur, including Troodon, Velociraptor, Sinornitholestes, Buitreraptor, etc. Our ideas of "small to medium-sized" have changed, too. Back in the day, Compsognathus was considered tiny. Deinonychus was 12 feet long and Ostrom considered it "small to medium-sized!"

Why do squamates molt?

Despite previous annoyances from a reader in doing so, I am once again thinking out loud, and I pose a question which I, at least, find interesting. Why do squamates shed their skin? Well, the first conclusion one draws is that perhaps skin-shedding is primitive for Reptilia. But if that were the case, then one would expect turtles and crocs to shed, but they don't. Turtles will slough off old or damaged sections of their shell, but it's not what one would call molting. Modern lizards and snakes go through the same ritual that arthropods do: They crawl out of their old skin.

Perhaps skin-shedding is primitive to Diapsida, which would make it a derived trait. But then crocs remembered how to grow larger without shedding? And what about dinosaurs and their kin? Certainly Diplodocus wasn't shedding its skin all the time. Birds lose feathers on occassion, but not to the same extent that squamates do. Birds shedding feathers is not homologous to my leopard gecko losing his skin.

Perhaps molting is specific to Squamata. Do Tuataras shed their skin?

And if it's a derived trait, what makes it more advantageous than just growing? There are plenty of risks that come from skin-shedding. A predator could grab you by your flaking skin and pull you towards it. If the humidity isn't right, my geckos have a difficult time shedding. The skin will flake off, or be sticky in places. Sometimes they won't get their "gloves" or "socks" off, and the dead skin will harden to the end of a toe, resulting in the loss of a terminal phalange. Occassionally, in my older gecko, sand will build up on the inside rim of his upper jaw, and when he sheds, his "lip" skin will become stuck beneath that sand rim, and I have to get the tweezers and pop that hardened sand out of his mouth before I can get his shed mouth skin off.

It's easy to see how, in the wild, lizards might have a difficult time shedding properly!

I have considered, however, that shedding might help heal wounds. My frog-eyed gecko, Big Boss, had a scratch on his throat when I bought him. The top layer of scales had been taken off by some unknown means (perhaps a fight with his pet store roommate), and a red patch remained. It wasn't an open sore, but it was clearly an injury. Big Boss shed soon after we got him home, and after that initial molt, the red spot had faded. He just shed a second time last night, and the wound is barely noticeable. He has regrown the scales over the red spot.

Another interesting tidbit. I have three leopard geckos, and they have all gotten on the same "shed schedule," in that they all shed around the same time. Not simultaneously, but when one starts shedding, you can be sure that the others will soon follow. And it's not like the leopards are getting any larger--my oldest, Mr. Fat, is twelve years old and hasn't grown a centimeter half a decade. He is getting darker, though. But the leopards are never injured, so I wonder why they still shed at all (they are all adult size and quite fat).

Anyway, just thinking out loud again. Feel free to chime in.

Pterosaur Wings--As I Understand Them

First of all, I have to thank David Hone, David Unwin, and Michael Skrepnick for helping me to understand this concept, as it was very difficult for me.

I am a pterosaur fan. I think the group is incredibly interesting, and I have devoted several posts to them in the last few years. I try to keep up on my pterosaur literature, but it's tough in Alaska. I try to nab any pterosaur books I become aware of, most recently David Unwin's spiritual sequel to Wellnhofer's Prehistoric Flying Reptiles, Pterosaurs from Deep Time. It is an excellent read, and it brought me up to date on many aspects of pterosaur anatomy that I was only vaguely aware of before reading it.

One of the areas I've constantly struggled with, however, is how the wing folds. More specifically, how the joint between the wing metacarpal and the first wing phalange operates. I've seen plenty of reconstructions, few of which agree with each other, of how the wing folds up while on the ground, and it's just confusing. Without a 3D model, imagining the process is strenuous, but I have put all the lessons together and tried to make an accurate diagram of how the finger joints operate (above).

If you want a human equivalent, here we go:

Put your arms out to your sides, slightly bent at the elbows, palms facing up. Now chop off your pinkie finger--you won't need that. Also, reorient your thumb so that it's no longer offset. Curl your now injured thumb, index finger, and middle finger. Notice how they all curl toward the palm. Great. Now here's the painful part: Dislocate your ring finger, spin it 180 degrees, and pop it back in place. Your ring finger will now curl toward the back of your hand. Ouch, right? Keep your palms up! When you curl that ring finger, notice that it starts pointing toward your elbow.

That's basically the situation in pterosaurs. While in flight, a pterosaur's palm faces forward, and its "ring" finger is bent slightly back. The manual digits--short 'n' scrawny by comparison--were kept in a relaxed position, probably slightly curled inward, toward the palm.

But now the pterosaur lands, and starts walking on all fours. What did the wing look like then?

Don't worry--things don't completely go to hell. You can still use your own arms as examples.

Get down on all fours (knees on the ground), and sprawl your forelimbs out to the sides, so that your elbows and fingers are pointing away from the body. Now rotate your wrists slightly so that your fingers are actually pointing slightly back. Remember that your pinkie finger has been severed (hope you've got some gauze on that wound!) and your ring finger is backwards.

Bend the base of your reversed ring finger "up," and notice how your ring finger now points toward your elbow again. In a pterosaur wing, the individual wing phalanges were virtually unable to move against each other, so aside from the metacarpal/phalange joint, your ring finger is a straight rod. Now imagine that your ring finger is just a bit longer than your entire arm. Whallah! Pterosaur wing!

Of course, if you want to go...you know...all out, you could try and keep your palm off the ground, because of course pterosaurs walked in a digigrade manner for their forelimbs, but plantigrade hindlimbs!

So, please tell me if I've gotten it right, folks! I apologize for using overly violent examples for a human analogue, but all the attempts I made to draw a human analogue ended up looking entirely too disturbing.

Another Trip to Sand Lake

Remember last week when I said I was walking on Little Campbell Lake? I was being scatterbrained. It's actually Sand Lake. And here's a better picture of that lake, with the sun doing down behind me.

Some Alaskans just can't stop fishing. This ice-fishing hole had been abandoned recently. See the dark blue dot at the top of the ice? It's begun freezing over again, but was probably drilled just a day before, if not less.

There was another Alces on the shore. A young'un was following it around. This mother-baby pair has been living in the neighborhood for weeks, and I will often see them wandering around people's yards in search of food.

I was unable to get a good picture, but a float plane like this one landed while Sable and I were out walking on the lake. Now I know what makes the big tracks in the snow--I thought somebody had plowed a path down the middle of the lake!

And here's one more look at the mountain range about a half-hour later, and from the opposite side of the lake. The pointy mountain is O'Malley, and the flat-topped mountain to its right is...well, Flattop Mountain. Both are popular hiking mountains, especially the latter, which is a great place to see H. sapians touristas in the warm summer months.

Dagon

Dagon, from the appropriately titled Lovecraftian short story Dagon (1917).

Dagon is a unique short story in Lovecraft's significant body of work. It is not considered Cthulhu Mythos canon, but it is an obvious forebearer. The story is told in flashback form by a madman, driven insane by nightmares of some unspeakable terror sighted in the distant past. Shipwrecked on a "slimy expanse of hellish black mire," our hero wonders the coast for days, hoping for rescue. Eventually he journeys inward, finding a stone relief with bizarre hieroglyphs depicting sea-dwelling humanoids and various normal sea creatures. While he looks on, a massive beast rises from the depths behind him and heads immediately for the stone tower, wrapping its arms around it and uttering strange noises in what appears to be a prayer.

The name "Dagon" is not the beast's name, but rather a Philistine fish-god. The story's protagonist wonders if "Dagon" might be real in some form, and perhaps he just saw it. "Dagon" appears in Lovecraft's more popular canonical Shadow Over Innsmouth, in which the Deep Ones are said to worship said deity. In that story, however, the name "Dagon" is applied to Cthulhu, most likely an attempt by the Innsmouth residents to apply an existing name to their undersea god. Thusly, the Dagon of Innsmouth is not the Dagon of Dagon.

I rather prefer to think of Dagon as kind of an outgroup to the Cthulhu Mythos, seeing as it shares so many commonalities with the latter body of work. Indeed, the fish-people of the stone tower may well represent the Deep Ones with whom the citizens of Innsmouth made their infernal pact.

My take on Dagon is still evolving, but the final draft will look similar to this. Keeping with my interpretation that Dagon has some connection to the Deep Ones (and Cthulhu), I tried to make it a tetrapod that would exist somewhere in the depths, but one corrupted by the Deep Ones. If humans turn into fish-people, what would a whale turn into? Or a crocodile? I don't know if I'll keep the arthropod legs, but I do like how they give the back half something to do. Let me know what you folks think! I am open to suggestions on how to improve this design.

Check out that Blogroll!

I finally got around to adding Carl Zimmer's excellent "The Loom" to my blogroll. Check it out--he discusses a new chiropteran version of Archaeopteryx today! Expect my first in a series of drafts of Lovecraftian beasties later today, too. I'd post it right now, but the scan-t0-email copiers are all broken at the moment. *sigh*

But do tune in later for one of the only earthan horrors in the Cthulhu Mythos!

Happy Birthday, Chuck D!

Were he still alive, Charles Darwin would be 199 years old today. The man is lauded (and demonized) for his "controversial" ideas about natural selection, but I prefer to think of him as a naturalist first and foremost. He lived in a time where natural history was a field, and generalist knowledge was actually prized. Darwin traveled the world, saw all sorts of awesome things (like the marine iguana above), and, as a result of all that exploration and observation, he proposed the theory of natural selection.

Speaking of pterosaurs...

Nemicolopterus crypticus was just announced at the National Geographic website. It's a smallest pterosaur ever found (check out the pictures, including the skeletal restoration) and will be published in the Proceedings of the National Academy of Sciences tomorrow. If the paper is not open-source, could one of you kind readers send me a copy? This is a pterosaur I need to restore!

UPDATE: Thanks to Nick Gardner for sending it to me. If you ever need a paleo-related picture, brother, let me know!

Are Rhamphorhynchoids Real?

I was musing this morning, as I often do, about pterosaurs, when a thought struck me. Is "Rhamphorhyncoidea" a natural group? Supposedly it forms a sister group to the Pterodactyloidea, but what if pterodactyloids are derived directly from rhamphorynchoids? Pterodactylus is still, as far as I know, the earliest known pterodactyloid, and it doesn't show up until the Late Jurassic, whereas rhamphorhynchoids are known since the Late Triassic, and in all likelihood, the group originated well before that. Were pterodactyloids an actual sister group, that would imply a very long ghost lineage leading back to the origins of the Pterosauria.

But then you look at anurognathid pterosaurs, who are "short-tailed rhamphorhynchoids," and wonder where that group perhaps shares a more direct relationship with pterodactyloids. Were that the case, then "Rhamphorhychoidea" would be paraphyletic. I'm not suggesting that some rhamphorhynchoids don't share some common ancestry. Rhamphorhynchus and Dorygnathus are certainly sister taxa. Dimorphodon and Peteinosaurus seem close enough. Certainly the scaphognathines form a monophyletic clade. But how do all these smaller groups relate to one another? What if rhamphorhynchoids form a stepwise progression leading to Pterodactyloidea, much like we know understand Prosauropoda to be a paraphyletic grade of animals leading to Sauropoda?

The name "Rhamphorhynchoidea" would have to be abandoned, unless we start calling Pteranodon a pterodontid ornithocheiroid pterodactyloid rhamphorhyncoid pterosaur. That wouldn't work.

Has any work been done on the interrelationships between the various families of the Rhamphoryhncoidea and that group's relationship to the Pterodactyloidea? And while we're on the subject of pterosaurs, does anybody have a good paper detailing Nyctosaurus' reindeer antler? I'm restoring that monster for the upcoming Archosauria art show.

Little Campbell Lake

I got home too late for the really good pictures--where the sun is just dipping below the mountains, but I don't think these are too bad.

Our house in the winter. The snow, in places, has risen above our meager front porch. There's a significant "hump" at the front of the driveway where the snow is more frozen. In the last week, the temperatures have dipped well below zero (it's -12 sometimes in the morning) and climb as high as...um...10 above. Walking the dog is a chore!

This is the main road past our house. There are streetlights, but they have an annoying habit of turning OFF as you approach them, so walking the dog after 6 o'clock requires a flashlight and lots of treats for when cars approach! The snowbirm I'm standing on is probably four feet high at this point. Somebody's been skiing on it.

This is Little Campbell Lake. Houses surround it, and most of the owners also have floatplanes, which sit at docks in the water. When the sun is right above the mountains, it's a beautiful sight! When I took these pictures it was probably 7 degrees. Sable doesn't seem to mind the temperatures at all--walks are her favorite thing in the whole wide world! Somebody was kind enough to plow a bit ski trail all around the lake, which I intend to make use of one of these days.

Big Boss, my frog-eyed gecko, would rather stay inside on his log. It's 80 degrees in HIS house. Must be nice!

Ridiculously Large Cretaceous Theropods

Different lineages of theropod dinosaurs independantly achieved gigantism several times throughout the Mesozoic. For the most part, these enormous theropods were not directly related. In a few cases, a single genus in a family of otherwise normal-sized theropods grew ridiculously large. Oddly, the groups represented here grew to their maximum sizes during the Cretaceous period. While theropods in the Jurassic (like Allosaurus and Saurophalanx) grew quite large, they could not complete with the behemoths of the Cretaceous.

Spinosaurus aegypticus may have been the largest terrestrial carnivore to ever walk the Earth. While its remains (sketched above by Stromer when he described the beast in 1915) were destroyed during WWII, a new snout specimen described by Dal Sasso et al. (2005) estimated the total body length may have been between 16 and 18 meters, making it significantly larger than Giganotosaurus, another monster theropod on this list. Other members of the Spinosauridae, like Baryonyx and Irritator, reached respectable lengths (30 feet, 36 feet) but they were dwarfed by their ultimate decendant.

Giganotosaurus was the largest member of the Carcharodontosauridae, an enormous Gondwanna branch of the Allosauroidea. Its body was built like a typical allosaur, but its head was long, tall, and built for killing sauropods. This 50-foot monster was the first dinosaur unearthed to beat out Tyrannosaurus rex for "biggest carnivorous dinosaur," and rightly deserves the title. While the tyrant lizard king is a more compact killing machine, Giganotosaurus was leaner and longer, focusing more on speed than strength. While this gigantic lizard couldn't crush bone, it would have delivered a fatal tearing bite to any prey item foolish enough to stand its ground.

Discovered by Barnum Brown in 1902, Tyrannosaurus rex was, for a very longn time, the largest carnivorous dinosaur known. While it no longer retains that title, it does get to keep another: strongest carnivorous dinosaur known. Tyrannosaurus rex could shatter bone with its bulldog grip, which left the arms with nothing to do, apparently. Although huge, Tyrannosaurus was compact for its size, with a short midsection, thick but short neck, and rounded muzzle. Compare Tyrannosaurus' skull to Giganotosaurus', and the differences are readily apparent. Tyrannosaurus seems to have gone through several growth phases, during which its diet and mode of prey capture may have changed. Thomas Holtz has wondered if this single species dominated the carnivore scene at the end of the Mesozoic. This would have made Tyrannosaurus rex the most powerful and most flexible carnivorous dinosaur known!

In a family of lightweight, midsized theropods, Deinocheirus really stuck out in a crowd. The Ornithomimidae is usually characterized by Struthimimus, Gallimimus, and Ornithomimus. The only known remains of their gigantic cousin--a pair of fearsome-looking arms, demonstrate that one of their ranks towered over the rest. If you scale the arms of Deinocheirus to one of its smaller brethren, you get an monsterous ostrich mimic that would have rivaled Tyrannosaurus in size. It could be that Deinocheirus' arms were out-of-proportion to the rest of its body, or that it wasn't an ornithomimosaur at all, but until more complete remains are found, Deinocheirus will remain the largest of the ostrich mimics.

Like Deinocheirus, this next dinosaur is a giant among much smaller cousins. Gigantoraptor, known from a fairly complete Mongolian skeleton, was about 30 feet long. While this doesn't seem very large in comparison to the other dinosaurs on this list, it's more than three times the size of Gigantoraptor's next-largest family member, Citipati. Aside from its strange size increase, Gigantoraptor is interesting for bucking a common trend among large carnivorous dinosaurs. In small theropods, like Coelophysis, Ornitholestes, and even Struthiomimus, the tibfib is longer than the femur. The metatarsals are also quite long. This usually means that the animal was a fast runner. The larger the theropod, however, the closer the ration becomes. In Tyrannosaurus, for example, the tibfib and femur are about the same length, and the metatarsals are quite short. Even in Albertosaurus, the bone length ratios are more similar to ornithomimids than big ol' T.rex. Larger theropods, then, were slower and did more walking than running. Gigantoraptor, however, despite its large size, retains its smaller cousin's leg proportions, implying that Gigantoraptor was the most able-legged runner of all the giant theropods.
While many theropods became very large in order to hunt larger game, one family increased in size due to a basic change in diet. The Therizinosauridae is a bizarre group of maniraptor theropods which switched from meat to vegetation during the Early Cretaceous. Very quickly, their anatomy changed to accomodate this change. In addition to an enlarged gut, retrovated pubis, hypertrophied pedal digit I, widened pelvis, and renovated pectoral girdle, therizinosaurs also began growing. By the end of the Cretaceous, Therizinosaurus was 40 feet long and may have converged to some degree with the lifestyle of sauropods, which had since disappeared from Laurasia. Not much of Therizinosaurus' skeleton is known, but it is most famous for its enormous, scythe-like manual claws. Whether it used the claws for defense, digging, or reaching tall branches, we may never know.

The smallest "giant" on our list may also be the deadliest. Utahraptor was a massive dromaeosaur, and may have reached between 18 and 25 feet long. While virtually none of its bones are known (a short caudal series, maxilla, and giant claws), scaling the beast to its close cousin Deinonychus results in a raptor that's almost twice as large! Utahraptor lived alongside Deinonychus during the Early Cretaceous, and neither animal had to compete with tyrannosaurs, which did not impede on their territory until the Late Cretaceous. It may have hunted resident ankylosaurs and ornithopods, as well as North America's remaining brachiosaur, Cedarosaurus.