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Showing posts from 2007

Allosaurus fragilis 2

Continuing on from where I left off last time, I've been painstakingly coloring in my Allosaurus line drawing using Adobe Illustrator. This is my first attempt at a dinosaur drawing with Illustrator. First of all, I just colored in the basic colors and added 'scutes' (?) and scales and what not.

Then, I started adding in shades using black and light areas using white. I used black and white hoping that by making them transparent would have the effects of shading and hi-lighting. And it seemed to work. The beauty of this is that I now have a generic shade/lighting pattern that is consistent regardless of the undertone colors. But getting it right took a lot of time and loads of trial and errors...


But then, I realised my Allosaurus looks too glossy and looks more like an amphibian or one of those old 1950's- 1960's reconstructions. So I added in a whole load of scaley patterns again with black and made them transparent. For simplicity, I just made a handful of little …

Allosaurus fragilis

Okee dokey - continuing on with the theme, I've started tracing out this hand-drawn Allosaurus. The original was drawn ages ago - I can't really remember when. But it's up on my website (http://www.geocities.jp/raptors_nest_theropoda/).

Anyway, since I already have a digital version, all I need to do now is to import it into Illustrator and trace it out.

The next step is to use the Pen Tool and just manually trace out the outline of the drawing. This is actually quite time consuming and it's taking as long or longer than it'd take me to draw a dinosaur from scratch...

Now this is what it looks like with the tracing and the coloured-in eyeball superimposed (right).

And without the original (left). Unfortunately, this is as far as I got today, and my neck and back is starting to hurt since I've been crouching in front of my laptop for over 2 hours now....I'll resume some time later and start on colouring - I am not looking forward to that process. Actually, the …

Fighter jet

Umm....so, this has nothing, absolutely nothing to do with dinosaurs, palaeontology or science at all, but I just drew an imaginary fighter jet. Here's the rough sketch to the left.

I scanned this into my computer and used Illustrator to trace half the outline and coloured it all in and flipped a duplicate to make it all symmetrical. Then exported it as a gif and used Photoshop to add in the details like shades, scorches, and oil stains.

The result is below.

It's still rough but I was just having a bit of fun. I guess I could brush up on this technique and apply it to dinosaur drawings...that'd be pretty cool.

Cranial skeleton vs postcranial skeleton

Having said what I said in my last post (about a few minutes ago...) I find it rather annoying that there is a huge abundance of literature on the detailed anatomy of the cranial skeleton but less so on the postcranial skeleton. If the dinosaur is known only from postcranial materials then there is a relatively good account of it - of course what else can you write about? Howver, if there is a perfect skeleton preserved, chances are, the description would be skull-heavy. The authors may even state that "the postcranial skeleton would be described elsewhere" but it probably won't be for another decade or so until this publication actually comes out.

I mean, I like cranial skeletons. Skulls are cool! That's what I work on.

But having collected measurements of postcrania from the literature, this popularity of cranial skeleton is really inconvenient...and I don't have the money or time (well for now) to go all over the world and measure these myself. And a lot of the …

Spinosaurus aegyptiacus

This is an old picture of Spinosaurus aegyptiacus. I drew this about four years ago using Windows Paint. These were the days before I discovered PhotoShop or Illustrator.

The anatomy may not be exactly correct as I'd only started palaeontology back then - I didn't do any anatomy for my undergrad...

Anyway, this was also about the time I started to get obsessed with spinosaurs. There was something about the skull morphology that really hooked me into them. In more poetic terms, you could say that I fell in love with the beauty of the slender and curvy silhouette of the snout. This was just purely an obsession of mine with no scientific context whatsoever.

Still, I find it quite intriguing that we find rather derived or highly specialised forms such as spinosaurs but no transitional forms. We don't have good fossils that show the evolution of such unique skull morphology...then again, basal tetanuran fossil record is pretty scrappy anyway - for instance Chilantaisaurus tashuiko…

Albertaceratops nesmoi

This is my attempt at Albertaceratops nesmoi. This is pretty my first attempt at a ceratopsian as well...

The plate-like epidermal structure on the face is purely speculation on my part.

Albertaceratops is yet another one of those interesting centrosaurine with a blade-like nasal 'horn' or ridge, but with postorbital horns that are very large for a centrosaurine.

If ceratopsians locked their horns in intraspecific combat, then Albertaceratops must have had a fairly similar style of combat with Triceratops and other long-horned chasmosaurines - perhaps???

Ontogeny and taxonomy of pachycephalosaurs

There were two interesting talks on pachycephalosaurs at the SVP annual meeting in Austin, Texas. I don’t know if they were coincidental but both talks dealt with the possible synonymy of Dracorex, Stygimoloch and Pachycephalosaurus.

The first talk was by John Horner. Horner (2007) used comparative cranial morphology, computer tomography and osteohistology to hypothesize that Dracorex, Stygimoloch and Pachycephalosaurus all represent different stages in an ontogenetic series of a single taxon Pachycephalosaurus.

Aside from having a flat head, Dracorex differs from Stygimoloch and Pachycephalosaurus in having large supratemporal fenestrae. Dracorex also has extensive ornamentation along the squamosals. Stygimoloch has closed off its supratemporal fenestrae and have a well-developed frontoparietal dome incorporating the rostral part of the frontal and postorbital but not the lateral and caudal elements of the skull. Stygimoloch also has extensive cranial ornamentations along the squamosal…

Deinonychus antirrhopus

I painted an older sketch of Deinonychus antirrhopus using Photoshop. I must admit, I'm no where near a computer artist but I had quite a bit of fun with Photoshop. I didn't know you can do so much with it...

Anyway, the all-too-famous Deinonychus antirrhopus. One of my favourite dinosaurs thus far. I didn't draw flight feathers on this guy mostly because of the simpler integuments of Sinornithosaurus but its quite obviously outdated now that we know one of its closest relative Velociraptor was found to have quill knobs on its ulna. These are little bumps on the surface of the bone and are typically associated with flight feathers in modern birds.

Wood-eating behaviour in hadrosaurs

I came across a really interesting article yesterday about some hadrosaur coprolites from the Upper Cretaceous Two Medicine Formation that contained woody materials (Chin 2007). This is direct evidence that at least some hadrosaurs ate wood. Coprolites at this locality regularly contain wood indicating that conifer wood was regularly ingested. Wood contains lignin which cannot be digested by vertebrate herbivores so there is no nutritional value on its own. Thus, in order for any animal to intentionally ingest wood it must have a very good reason of doing so as processing wood is such an effort, both in mechanical digestion (chewing) and chemical digestion. The absence of little twigs from the coprolites pretty much rules out accidental ingestion while foraging leaves.

On the other hand, the author found signs of fungal decomposition in the wood material. So apparently, the hadrosaur was eating fungus-infected, or in other words, rotting wood. Fungus de-lignifies wood and makes cellulo…

Eustreptospondylus oxoniensis

This is one of my favorite dinosaurs - Eustreptospondylus oxoniensis. It's also perhaps one of the most complete theropod fossils from Britain. Eustreptospondylus is a Middle Jurassic 'megalosaur' from the Oxford Clay of Oxfordshire. Now, I'm not much of a historian so I won't claim to know all the details, but it was known for a long time as 'Streptospondylus' but was subsequently renamed by Walker in 1964 in his paper 'Triassic reptiles from the Elgin area: Ornithosuchus and the origin of carnosaurs'.

Ornithosuchus is nowadays regarded as an archosaur so for some time, I was baffled as to why Walker addressed the question of carnosaur origins by redescribing a Triassic archosaur. However, it appeared I was just being lazy (as usual) as I had not even read the abstract. It is made quite clear that Walker considered Ornithosuchus to be a theropod dinosaur, a primitive carnosaur close to the ancestry of Megalosauridae and Tyrannosauridae. Thus, Walker…

Jaw biomechanics of Smilodon fatalis 2

I attended the 8th International Congress of Vertebrate Morphology (ICVM8) in Paris last week. There were a lot of interesting talks and I personally felt like I had information over-load!

One talk in particular that I found extremely interesting was that by Adam Hartstone-Rose, a PhD student at Duke University, who had painstakingly collected data of the physiological cross-sectional areas (PCSA) of extant felids, something I've always thought was in dire need. I'm particularly interested in this because this allows us to estimate bite forces in felids to a fair amount of accuracy. The most common source for bite force estimates in mammalian carnivores come from dry skulls which have been shown to underestimate (Thomason 1991). Bite forces estimated from calculations based on PCSA on the other hand seem to be in more congruence with actual in vivo bite forces (Thomason 1991). As there are currently no studies except for Binder and van Valkenburgh (2000) on in vivo bite forces …

Felid skulls

I've been looking at and taking measurements from felid skulls now for a few weeks. I've been up in Edinburgh at the National Museum of Scotland for three days and I've also been at the osteological collections at the Bristol City Museum and Art Galleries for the last week now. I've covered 30 species of the 41 recognised extant felid species.

The funny thing is that some of the older specimens in the Bristol Museum are either mislabeled or not labeled at all and we sat there for some time comparing specimens trying to ID the damned things. I'm starting to pick up some subtle morphological distinctions but it's all kind of useless unless I can link them to the right species. All I need is a list of diagnostic characters...

Jaw biomechanics of Smilodon fatalis

Biomechanically, Smilodon fatalis is an interesting animal. Where most extant felids have big strong canines, S. fatalis had long flat ones.

This implies that Smilodon would not have been capable of the same kind of precision biting that modern cats employ. Struggling with prey to deliver a fatal bite to the nape of the neck and dislocating the cervical vertebrae would result in the canines contacting with bone. The long flattened canines of Smilodon probably would not have withstood that kind of load.

The canines of Smilodon don't look like stabbing teeth like in modern cats, instead they look more like slicing teeth - like in Komodo dragons.
To the left is a tiger skull for comparison. The tiger has a lower longer face, larger eyes, and above all has pronounced zygomatic arches. Smilodon on the other hand had smaller zygomatic arches. This reduced the amount of available space for the temporalis muscle thus reducing the overall muscle force.

The tiger also has huge coronoid process…

Megalosaur

This is some kind of a megalosaur I drew some time ago. I think it's supposed to be a Dubreuillosaurus, but I didn't really bother with any anatomical accuracy so I just call it a megalosaur.

Anyway, megalosaurs are interesting. They're usually agreed to be basal tetanuran theropods and sister-taxon to spinosaurs, together forming the Spinosauroidea. But the intrarelationship among the Megalosauridae is a mess. In short no one really knows which dinosaur is more closely related to the other. This is inevitable to a certain extent due to the fragmentary nature of many megalosaur specimens but also because of the historical treatment of 'megalosaurs' being kind of a wast basket for theropod fossils of uncertain affinities.

Unilateral vs bilateral biting

Well, I haven't really had anything to post for awhile but I came up with an idea today.

Another one of my introductions into bite force analyses. This time, it's a relatively old but very well cited study by Jeff Thomason et al. (1990). This study is usually cited for the isometric stress values in jaw adductor muscles. What this means, is that when muscles contract, the individual fibres exert a certain amount of stress (force over a unit area). Thomason et al. (1990) showed that the mean muscle stress was 317 kPa which was well within the range of 147 - 392 kPa obtained for other vertebrates in a previous study (Carlson and Wilkie 1974).

The significance of these results is that they allow us to calculate muscular contractile forces from the physiological cross-sectional areas (PCSA) of muslces. Since stress is force over unit area, if the total area is known, then force can be calculated. Now, since stress value seems to be within a known range, we can multiply the stress va…

Maximum bite force in Tyrannosaurus rex

I'm on a roll today. Might as well post another.

So obviously, this is a Tyrannosaurus rex. It's so famous I'm afraid I don't really know what else to write about. Oh well, I'll just ramble on about bite forces then.

T. rex has been the focus of many biomechanical studies. Bite force is no exception. However, as much of a celebrity T. rex is, as far as I'm aware, there have only been two studies so far that have attempted to estimate the bite force of T. rex: Erickson et al. (1996) and Meers (2002).

Erickson et al. (1996) had an interesting approach of reproducing bite marks using cast replicas of a T. rex tooth and ramming it into a cow bone. They recorded the forces needed in order to penetrate the bone to different depths. The depths of T. rex bite marks found on a Triceratops ilium was compared to this relationship of puncture depth and forces needed. As a result they found out that a bite force of 6.4 kN were needed in order to to make that bite mark. From th…

Coelophysis bauri

I'm going to start using this blog not only for my technical comments but also to introduce my attempts at life-restorations of theropod dinosaurs. Left is the famous Coelophysis bauri. Coelophysis is one of the best preserved theropods with numerous complete specimens.

One interesting thing about this animals is the supposed evidence of cannibalism. Two specimens have been long considered to have
remains of members of its own species in their thoracic cavities. This view has been recently challenged by Sterling Nesbitt et al. A closer reinspection of the specimens revealed that in one specimen (AMNH FR 7223) the gut contents were actually not even inside the ribcage but underneath it. The second specimen (AMNH FR 7224) on the other hand was shown to actually have bone materials within its thoracic cavity. However, detailed histological study has shown that none of these bones had any diagnostic characters to suggest they were Coelophysis but were more likely to be from a small croc…

Terrestrial-style feeding in Acanthostega

Although the very early tetrapod Acanthostega possesses many adaptations for an aquatic lifestyle, recent work by Molly Markey and Charles Marshall of Harvard University suggests it had a more terrestrial-style feeding. This is a pretty cool piece of work as suture morphologies on the skull roof of a modern fish Polypterus was correlated with suture functions during feeding. Stain gauge measurements in the skull of Polypterus show tension in the anterior and compression in the posterior parts of the skull. The cross-sectional morphology of these sutures seem to be correlated well with the strain patterns. (image left taken from here)

The authors then went on to quantify suture morphology in fossil forms, a sarcopterygian Eusthenopteron, an early tetrapod Acanthostega, and a fully terrestrial Phonerpeton. The cross-sections revealed that while Eusthenopteron showed similar suture morphology to Polypterus, Acanthostega and Phonerpeton did not. Extrapolating the relationship between sutu…

DinoBase Launch

So I am managing an online resource called DinoBase. DinoBase was set up by Mike Benton of University of Bristol about 7 years ago, but had recently undergone a complete make-over. While the old DinoBase used to be literaly tens and hundreds of html pages, the new DinoBase features a dynamic system. It's pretty much a relational database, where all the different categories of information (e.g. genus, location, reference, etc.) are stored in separate tables but link to other tables. This enables data entry to become very quick and easy.

As far as the user is concerned, the information on these individual tables are pulled out and compiled onto a single page, just like any webpage, only that that particular page doesn't exist online as an individual page. So type in a dinosaur genus, species, year of description or author, click on the one you want to view and all the relevant information about that dinosaur will be presented in a single page. This, I think is a very cool system.

Robotic salamander

I know this isn't about dinosaurs but it's more to do with scientific methods in palaeontology. Recently, in the journal Science, there was a paper about a robotic salamander where its gaits are controlled by a spinal cord model. The spinal cord model gives out signals that oscillates the trunk. The team confirmed that the more intense the signal, the higher the frequency of the oscillation gets. This higher frequency oscillation produces a swimming gait similar to that of real salamanders. On top of that, they found that limb oscillation saturates at a lower frequency and the robot switches from walking to swimming.

According to the authors, the main significance of this study is 'to show how a tetrapod locomotion controller can be built on top of a primitive swimming circuit and explain the mechanisms of gait transition, the switch between traveling and standing waves of body undulations, and the coordination between body and limbs'.

This work has been taken up pretty …

Ultrasaurus and Ultrasauros

This is an ancient topic, but I was just thinking about it the other day.

Do you remember that whole thing about Ultrasaurus?

In 1979, James Jensen of Brigham Young University found what he believed to be the largest sauropod ever. The press went mad and widely publicised the dinosaur under the name Ultrasaurus. I remember as a kid that Ultrasaurus (along with Supersaurus) was always depicted as a huge brachiosaur dwarfing even Brachiosaurus.

However, it took another 6 years before Jensen finally published his findings. By then, a Korean palaeontologist, Haang Mook Kim, had already named a sauropod with the name Ultrasaurus because he thought it belonged to the same genus that Jensen had found. But it turned out that Kim's Ultrasaurus was something different, and when Jensen wanted to use Ultrasaurus, his first preference, he couldn't because it was 'preoccupied'. So he instead named his dinosaur Ultrasauros with an 'o'.

Funnily enough, Kim's Ultrasaurus later …

Rough reconstruction of jaw muscles in T. rex

So this is yet another one of my reconstructions, but this time, it's on jaw muscles, yeah!
The skull is redrawn from a photo I took of Stan the T. rex displayed at the Oxford Univesity Museum of Natural History. It's just a cast replica, but the quality is amazing. You can actually determine muscle scars on the surface!
So I've simply reconstructed four major groups of jaw adductor muscles; the Musculus adductor mandibulae externus (MAME), the M. adductor posterior (MAMP), M. pterygoideus anterior (MPTA), and M. pterygoideus posterior (MPTP). I included the M. pseudotemporalis as part of the MAME just for simplicity.
Muscle attachement areas were determined (pretty roughly) from visible muscle scarrings on the casts, cross-referenced with muscle attachments of modern birds and alligator (through dissections).
It's pretty interesting how, even though details differ, that all reptiles possess the same five major adductor groups. The homology is confirmed, so I'm happy t…

Testing: Deinonychus skull

This is a reconstruction of a Deinonychus skull I've attempted some time ago. All I did was scan in Ostrom's figures of the individual skull elements, scaled them to an arbitrary size (which I thought may be reasonable) and reassembled and coloured on Photoshop.

The main reason I did this was because I was not really happy with the reconstructions that are out there now. Most are based on Ostrom's initial reconstruction in his monograph which I think doesn't really look right. On the other hand, many museum displays will have reconstructions with a very pointy snout which frankly I don't really know how that came to be either. These reconstructions don't resemble close relatives such as Velociraptor or Dromaeosaurus at all. The best one I've seen so far is by Greg Paul.

And on top of that, I thought that these previous reconstructions (excluding Paul's) didn't really look like the actual fossils themselves figured in Ostrom's monograph. So, I wa…