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Is there a doctor in the house?

Well, yes, I just happen to be a doctor...

I passed my viva last Wednesday (it's been a whole week already). Despite my fears that my examiners were going to shred up my thesis, my examination went extremely pleasantly. It was almost like an extended discussion than what I'd imagined a thesis defense would be like. Both my examiners were very pleased and I passed with minor corrections, mostly typos, and clarification.

I was gonna post a bit on the content, but one chapter is almost ready to submit so I think I'll hold on to that until things are a bit more definite...

Updates and Pachyrhinosaurus

Having submitted my thesis on the 29th of September, a day before the absolute deadline (the University of Bristol permits exactly 48 months to submit a PhD thesis), I thought I could kick back and relax...maybe spend more time on drawing or blogging - but I was wrong.

Not having secured a postdoc position, I spend most days stressing, searching, working closely with academic staff on postdoc proposals, and working on converting my thesis chapters into manuscripts. At the same time, I'm trying to catch up on the reading that I'd put on hold while I was manically typing away on my thesis. I have quite a large 'to read' pile. There are some rather interesting papers out there that I only recently stumbled across and so I must blog about them sometime, when I get my head arround all the head-ouch evolutionary theories and models.

...I have this thing about not posting anything until I have something either interesting or useful to post, so not having devoted much time or ef…

My PhD thesis

With 42 days to go until I have to submit my PhD thesis, I haven't really had much time to blog...let alone draw dinosaurs! All I have time for is to get stressed out.

Anyway, in the midst of all this, I've finally decided on a thesis title:

Bite force, and the evolution of feeding function in birds, dinosaurs and cats.

The perfect title to show just how much unfocused my thesis is when it comes to a taxonomic group of interest, but extremely obsessed with bite force...ha! Of course it may be subject to change.

The actual thesis consists of five chapters:

Chapter 1: Introduction
Chapter 2: Myology and functional morphology of extant archosaurs
Chapter 3: Reconstruction of the jaw adductor muscles and jaw biomechanics in dinosaurs
Chapter 4: Dry skull bite force estimation in felids
Chapter 5: Tracing the evolution of bite force in Darwin’s finches and felids

Chapter 1 introduces biomechanical concepts regarding bite force and also introduces bite force as a useful single-value indicator…

The difference between Lion and Tiger skulls

A quick divergence from my usual dinosaurs, and I shall talk about big cats today. This is because to my greatest delight, I had discovered today a wonderful book. It is called The Felidæ of Rancho La Brea (Merriam and Stock 1932, Carnegie Institution of Washington publication, no. 422). As the title suggests it goes into details of felids from the Rancho La Brea, in particular Smilodon californicus (probably synonymous with S. fatalis), but also the American Cave Lion, Panthera atrox. The book is full of detailed descriptions, numerous measurements and beautiful figures. However, what really got me excited was, in their description and comparative anatomy of P. atrox, Merriam and Stock (1932) provide identification criteria for the Lion and Tiger, a translation of the one devised by the French palaeontologist Marcelin Boule in 1906. I have forever been looking for a set of rules for identifying lions and tigers and ultimately had to come up with a set of my own with a lot of help fro…

Albertaceratops nesmoi MK II

Albertaceratops nesmoi MK II! It looks a lot better than my previous one, which is way too embarassing to link to now... You may have noticed but I am having fun with all these ceratopsians. It seems like I'm stuck in a ceratopsian phase right now...

I can't really comment much on Albertaceratops other than what's already been covered elsewhere. I don't think there's really anything done with this dinosaur other than the original description. But then again, what is there to do with a dinosaur known from a single skull and some fragments? Ah - someone should do functional morphology, like FEA - provided they have access to a huge scanner, that is... Not just in Albertaceratops but someone should look into stress distribution patterns in ceratopsian crania using FEA. Better yet, someone should look at pachycephalosaurs...

Anyway, I think it's the new paper but the pencil just came out too dark...and it started getting smudged so I couldn't really add any more …

Triceratops vs tyrannosaur

This is my newest addition to the practice series. This time, it's not just a single dinosaur, but two dinosaurs interacting! Wow! It's incomplete as you can tell immediately...I might flesh them out and make them look nicer if I get around to it...

Anyway, its supposed to be a Triceratops flicking away a young tyrannosaur. In doing so, the Triceratops is almost rearing up...I initially wanted to draw the Triceratops standing firmly with both its forelimbs contacting the ground but ended up with this construct. So I guess the Triceratops locked its horns onto the tyrannosaur then reared upwards and flicked its head sideways, essentially pushing the tyrannosaur up off its feet then tossing it aside.

I doubt this would have happened between adult individuals. This tyrannosaur is probably inexperienced and got too close the Triceratops. Or perhaps it was starving and was willing to take the risk...who knows, perhaps we'll never know....

Centrosaurus apertus - initially Monoclonius crassus

My attempt at another ceratopsian; this time, Monoclonius crassus - but I realised after reading up on this genus that my drawing is probably more like Centrosaurus. Damn! I really wanted to draw Monoclonius but I guess the picture I found on the Wikipedia that was labeled "Monoclonius" is probably a Centrosaurus...

According to Sampson et al. (1997), "Monoclonius specimens are generally defined on the presence of a thin, scalloped parietal and on the absence of hooks, spikes and horns seen on the posterior transverse ramus of other genera". The only complete skull specimen of Monoclonius, a specimen previously attributed to M. lowei, has a short nasal horn core and a pair of low rounded supraorbital horns (Sampson et al. 1997).

The absence of elaborate cranial ornamentations in Monoclonius and its occurrences in slightly older strata can be indicative of a primitive condition in Monoclonius. On the other hand, these features are also commonly associated with juven…

Monolophosaurus jiangi

Monolophosaurus jiangi is a theropod from the Middle Jurassic of Xinjiang, China. It's phylogenetic position is rather uncertain - though there will be a monograph coming out soon but I can't remember if there was a phylogenetic analysis associated with this redescription.

Of course the most distinctive feature of Monolophosaurus is the large sagittal crest on the skull. The crest is quite thin and has several openings so is probably not a functional structure.

There was some speculation that the basal tyrannosauroid Guanlong wucaii, also from Xinjiang, represents a juvenile morphology of Monolophosaurus. However intriguing this claim may seem, at least one Guanlong specimen shows signs of arrested growth histologically so is quite likely to be an adult.

Here, you see a fine specimen of Monolophosaurus scoping out a carcass.

Thecodontosaurus antiquus

This is my attempt at a reconstruction of Thecodontosaurus antiquus. No one really knows what the skull looked like except for a juvenile of a closely-related southern Welsh species Pantydraco caducus (formerly known as Thecodontosaurus caducus) so I pretty much made it up - loosely basing it on Benton et al. (2000). The interesting thing about Theco is that there are so many postcranial jumbled together that no one has any idea what the forelimb to hindlimb ratio is. I attempted a lower fore-hind limb ratio - so as to make it look like Theco is actually not obligatory bipedally nor quadrupedally, basically facultative.

Thecodontosaurus was discovered in 1834 at the Durdham Down in Clifton, Bristol, UK and is the fourth dinosaur to be named. It is also the oldest dinosaur from Britain at 203-215 million years old. The original Clifton materials were destroyed in the second world war when a bomb hit the Bristol City Museum. However, some elements, including a braincase, had fortunately …

Allosaurus fragilis 3

So it has been a while...and for my rehabilitation, I give you, tah-dah... Allosaurus again! Well, it could be any non-descript tetanuran theropod...from this angle anyway. Again, this is one of my series(?) of practice drawings, and for that, who else but Allosaurus? I have attempted this angle before but never as "good" as this one turned out to be - at least I think it looks good enough.


Anyway, I had a bit of a problem with my scanner when trying to upload this - it always came up with some weird faint line across the middle. I tested all sorts of different papers and book covers to see what the cause was. It came out fine on really strong colours and backgrounds with multiple colours so I determined it was something to do with white so I thought it might need some adjustments or something. And I found the callibration button! Woohoo! Such a simple thing and it takes a postgrad student nearly half an hour to figure out...

Pelvic muscles for aquatic locomotion in crocs

It is widely known that crocodilians use a unique form of diaphragmatic breathing (Gans and Clark 1976; Farmer and Carrier 2000). Diaphragmatic breathing in crocodilians employs a hepatic piston or the movement of the liver driven by the diaphragmatic muscle. The diaphragmatic muscle attaches to the pelvis and to the liver. Contraction of the diaphragmatic muscle pulls the liver caudally increasing the volume of the pleural cavity. Farmer and Carrier (2000) further showed that the kinetic pelvis also contributes to breathing in crocodilians. Pelvic muscle activities were correlated with both inspiration (with M. ischiopubis and M. ischiotruncus rotating the pubes ventrally increasing abdominal volume) and expiration (with the M. rectus abdominis and M. transversus abdominis rotating the pubes dorsally). Activation of these four pelvic muscles are independent of locomotion and were presumed to be primarily for breathing function. This allows for a strong breathing capability independen…

Carnotaurus sastrei

I got a request from Zach to draw Carnotaurus so here is my attempted reconstruction of C. sastrei. Funnily enough I have never drawn or even attempted to draw Carnotaurus previous to this - that is except for the unsatisfactory precursor to this picture...It took me forever to finish but for a first attempt I kinda think it turned out pretty good.

There are some really strange things with Carnotaurus, the first obvious being the skull. Staring at Bonaparte et al.'s (1990) skull reconstruction and photos for a prolonged time and reading their description, I noticed that the postorbital region of the skull in Carnotaurus is really strongly deflected ventrally while the sagittal crest is extremely high. This results in the supratemporal fenestrae having their lateral borders ventrally displaced compared to the medial borders. The sagittal crest in reptiles generally serves as the attachment sites for jaw adductor muscles, namely the M. pseudotemporalis superficialis (MPsTs), M. adduc…

Allosaurus fragilis 3: Allosaurus yet again...

Yes it is, it's Allosaurus fragilis yet again! The point is, Allosaurus is by far the easiest theropod to draw...I don't know why, but perhaps it's because you see images of Allosaurus skulls everywhere, being depicted as the "generic" theropod. Of course it is one of the most abundant theropods ever so we do have a good idea of its morphology and to a certain extent its ontogeny - the vast majority of fossils are of adults or subadults while juveniles and hatchlings are very rare.

I use Allosaurus when I am testing out new ideas, whether it be biomechanics or just new angles to draw...certainly this is the case of the latter. It's not entirely a ground-breakingly new angle at all but one that I have attempted in numerous previous accounts and have never really gotten right. Though, I think I've got it almost right this time. I find angled shots really difficult - as you may have noticed, most of my drawings have got the skulls captured in a lateral aspect…

Ceratosaurus nasicornis

One of my all-time favourite theropod is for some reason Ceratosaurus nasicornis. You might think its the horns but I'm actually more drawn to the overall skull morphology. I can't remember now why but Ceratosaurus was one of the first theropods that I attempted to draw the skull of. So I guess it was the first theropod that I actually paid attention to the skull morphology in some detail...

In any case, Ceratosaurus is still a taxon of significance. It represents the diverse group of basal theropods otherwise known as Ceratosauria, though what constitutes the group has never been stable. Aside from Ceratosaurus, Ceratosauria has traditionally included such taxa as Elaphrosaurus, Dilophosaurus, Coelophysis, Syntarsus, abelisaurids and other "ceratosaurs". Recent work however seem to show Ceratosauria in this traditional sense to be unsupported. Most recent phylogenies would separate coelophysoids (Coelophysis, Syntarsus, possibly Dilophosaurus, etc.) from Ceratosauri…

More on jaw muscle reconstructions

I have some more old images of mine, this one is of the jaw muscle reconstructions in Deinonychus. The skull is reconstructed from Ostrom's (1969) original figures. And jaw muscles are based on personal observations in numerous modern bird species. Off the bat it's obvious I've only referred to birds and not crocodilians or other diapsids because of the way I've reconstructed the MAMES attaching with a tendonous attachment onto the coronoid process. The muscle attached to the dorsal and medial surfaces of the surangular just medial and posterior to the MAMES is the MAMEM. In contrast, the MAMES in crocodilians attach along the dorsal surface of the surangular with the MAMEM attaching just medial to that. I suspect given the arrangement of cranial bones that the muscles arrangements in theropods would be more similar to crocs (and other diapsids) than to birds. The MPT is reconstructed as wrapping around the ventral side to attach to the lateral surface of the angular a…

Centrosaurus

I've broken my routine and drew a Centrosaurus instead of a theropod. I couldn't decide what theropod I wanted to draw but I was getting a bit bored of theropods.

Anyway, I guess this would be Centrosaurus apertus Lambe, 1904 because of the cranial ornamentation. C. apertus and C. brinkmani Ryan et Russell, 2005 differ in their cranial ornamentations with C. apertus having larger parietal ornamentations. C. brinkmani is also restricted to the Oldman Formation of southern Alberta.

I don't really know enough about ceratopsians to write anything interesting (I just think they look great!) but I might as well comment on the forelimb posture...for the longest time, there has been a debate regarding the forelimb posture of ceratopsians. Some argued for an erect parasaggital posture while others argued for a sprawling posture with the humerus averted laterally. Anatomically, the sprawling posture seems to make sense. However, this left a discrepancy with ceratopsian trace fossils t…

Dromaeosaur head dissection

I was going through my older drawings and came across this. It's quite comical but its a dromaeosaur head midway through dissection. The skin has been peeled off to reveal the jaw adductor muscles, jaw depressor muscle, parts of the neck muscles, and trachea. I got this idea from my own numerous dissections of bird heads. Minus the fact that this looks like a dinosaur, the initial phases of dissections in bird heads also look something like this...

Even in birds there really isn't much of a subdermal layer of muscles, except some really thin sheets that presumably control the feathers. But other than that, archosaurs don't have facial muscles seen in mammals and the skin is pretty much attached directly to the skull and mandibles in most parts, especially the rostrum.

The jaw adductors visible in this phase are the M. adductor mandibulae externus (MAME) superficialis (MAMES) filling the lateral temporal fenestra, MAME medialis (MAMEM) occupying the supratemporal fenestra, an…

Be the Dinosaur: a travelling museum exhibit

For some time now, I have been working as a scientific consultant on a travelling museum exhibit called Be the Dinosaur. The main attraction to this exhibit is the virtual simulation of the Late Cretaceous Hell Creek Formation. Visitors can navigate through the environment as a Tyrannosaurus rex or a Triceratops and try and complete some tasks, such as gathering food, or crossing a river, etc. However, in order to survive these simulations, the visitor must be very keenly aware of what they need to do and where to look for necessary stuff such as energy-rich food - the dinosaurs have a virtual digestive system and need to stock up energy for severe tasks like fording rivers. These information are provided in the panel-based education kiosks located throughout the exhibit so you can't skip the kiosks and go straight into the simulator pods - because you won't be prepared to survive. I think this is a clever way to educate visitors in various fields of science associated with di…

Suchomimus tenerensis: colour

Phew...so this is an Adobe Illustrator version of the Suchomimus drawing from a few days ago. As always, I used Illustrator to trace out the outline and then use different layers to colour, shade, and add a bit of effect. The stripes took me forever to do...

DinoBase, 1 year anniversary coming up!

Well, it's almost a whole year since the launch of the new DinoBase. The actual one-year anniversary for the relaunch is the 17th of April (see here for my post on the launch day last year). I'm sure most of my readers are already aware, DinoBase is an online resource hosted by the Department of Earth Sciences, University of Bristol which I just happen to be the administrator of. The main feature of DinoBase is as the name suggests, its online database of dinosaurs. Visitors can search for dinosaurs using a number of search criteria such as genera, species, author, or year of description. I'll just go through the basic search function here.

Let's say we want to search for Tyrannosaurus rex but can't be bothered to spell out the whole name so we type in "tyranno".


Now we click on "search" and DinoBase will return the following list:


Note that DinoBase returns all records alphabetically, so the first few are the ones of interest, in this case, Tyrann…

Sinraptor dongi

Second drawing of the day...though the date has changed already. This is Sinraptor dongi an allosauroid from the Jurassic of Xinjiang, China. There are two recognised species of Sinraptor, S. dongi and S. hepingensis. S. hepingensis was initially described as the third species of Yangchuanosaurus after Y. shangyouensis and Y. magnus (Gao 1992 Vertebrata PalAsiatica30: 313-324) but was subsequently assigned to the genus Sinraptor (Currie and Zhao 1993 Canadian Journal of Earth Sciences30: 2037-2081). Compared to Yangchuanosaurus, Sinraptor has a relatively longer and lower skull. The two genera are united as Sinraptoridae. One of the distinchuishing features of sinraptorids is the high number (more than two) of accessory openings in the antorbital fossa. Another interesting feature of Sinraptor is the tall plate-like neural spines of the dorsal vertebrae. This is quite similar to Metriacanthosaurus such that Paul (1988 Predatory Dinosaurs of the World) synonymised Yangchuanosaurus with…

Suchomimus tenerensis

Ok. Back to my usual passion - drawing theropods. This time, it's Suchomimus tenerensis. As always, I ran out of paper but this time, I scotch-tapee another piece of paper to fit the tail...however, the extra length made it too big for my scanner so I had to scan it in twice and stitch them together using Photoshop...

Anyway, a bit about Suchomimus - though this dinosaur is really famous that I probably won't have anything unique to comment on. Suchomimus is a spinosaurid dinosaur from the Lower Cretaceous (Aptian) of Niger (Sereno et al. 1998). It is quite distinctly different from the other famous African spinosaur Spinosaurus in snout morphology and in the lack of the giant sail - although Suchomimus also has elongated neural spines along the posterior dorsal, sacral, and anterior caudal vertebrae. The elongation is most pronounced in the sacral vertebrae but it is nowhere as long as those seen in Spinosaurus.

Along with the slightly older Baryonyx from the UK and contemporar…

Evolutionary theories...hurt my head

It's been some time since my last post...

Anyway, I've been busy trying to write a manuscript on the evolution of bite forces using finches and cats as case studies. One thing I've found out through this process is that, it doesn't matter how sophisticated a method you use, nor does it matter how great you think your results look, what matters is your ability to tie that into a broader perspective of evolutionary theory. And I've sadly realised, that either I don't have the brains, or the imagination, or the creativity, to write anything remotely interesting in the grand scheme of evolutionary theory. Evolutionary theory's the interesting end-product of all this functional morphology and phylogenetic comparative methods anyway, and if you can't do that, then you're screwed...

But I don't intend to be lazy and give up. At the same time I've been trying to be greedy. So I've been trying to read as much evolutionary theories as I can...


....a…

The taxonomic status of Megalosaurus bucklandii

A new paper by Roger Benson of Cambridge University and colleagues discuss the taxonomic status of Megalosaurus bucklandii.

Every dinosaur fan knows of Megalosaurus, the first dinosaur to be named by William Buckland in 1824. Megalosaurus is also historically significant as being one of the taxa that Richard Owen based his Dinosauria in 1842, the other taxon obviously being Iguanodon. The type species M. bucklandii was erected by Gideon Mantell in 1827. Buckland's original description of Megalosaurus in 1824 is based on a series of syntypes, one of which is the famous dentary (fig). Over the years, many other large theropod specimens from the Middle Jurassic were "unjustifiably (Benson et al. 2008)" attributed to M. bucklandii. Over the years, many authors noted the possibility that the syntype series and all subsequent referred specimens may belong to different taxa all together. Thus M. bucklandii is suggested to only refer to the lectotype dentary.

According to Benson …

Happy birthday, Raptor's Nest!

March seems to be a popular month to be born...both my parents are born in March, my friends' birthdays are in March, Ask a Biologist just recently had its first year anniversary, and now, today (19 March) is a whole year from my first blog post on Raptor's Nest - Woohoo!

And coincidentally, it's actually my real birthday today as well - and I had only realised this coincidence last week! I've survived 28 years and been in school in one way or another for 25 of those years...As my name wich means "to learn" in Japanese suggests, I have so far led most of my life as a student (of science) and will probably do so for the rest of my life

Deinosuchus

I was recently asked a question about the possibility of Deinosuchus being in the Hell Creek and interacting with Tyrannosaurus rex. Since the Hell Creek is well-sampled and there are no Deinosuchus fossils it is safe to assume that it was absent from the Hell Creek. However, the person asking the question was fully aware of that so the question actually was, "if Deinosuchus were to be known from surrounding areas of the same age, would it be scientifically plausible to infer its presence in the Hell Creek?" To be perfectly honest, I had no idea of the temporal and geographic range of Deinosuchus and so it turned out to be an interesting afternoon of researching this.

As far as I can gather from the literature and also from colleagues that work on fossil crocs, there are no peer-reviewed scientific articles that ever state the presence of Deinosuchus in strata younger than the late Campanian. Lucas et al. (2006) include a review of Deinosuchus occurrences in one of their pap…

Velociraptor mongoliensis

I've been fooling around again toying with the idea of a Velociraptor mongoliensis perching atop a recently deceased carcass and intimidating its competitors, presumably other Velociraptor individuals. As a few of us have discussed here, according to Roach and Brinkman (2007), the evidence for pack-hunting behaviour in dromaeosaurs is pretty slim. The authors are casting doubt over Deinonychus regularly hunting large prey in a highly coordinated pack-hunting style, mainly based on the loose cooperative hunting styles seen in extant archosaurs (a couple of species of crocodiles and plenty of examples of predatory birds) and the komodo dragon.

Komodo dragons are known to solitarily take down prey as much as 10 times its own size. On this basis, the authors mention that it would be possible for a 70 - 100 kg Deinonychus to solitarily take down a Tenontosaurus anywhere between 700 - 1000 kg.

The fossil sites are reexamined as well. The Deinonychus skeleton(s) found with the Tenontosauru…

Happy birthday, Ask a Biologist!

Well, it's actually this coming Friday (the 14th) but since this is a good chance to promote the site, why not start early?







Ask a Biologistis a Q&A website started up by University of Bristol graduate, Dr. Dave Hone. The unique thing about AAB is that unlike many Q&A forums around the internet, AAB's answerers are all either qualified PhDs, PhDs in training, or have a similar level of experience or qualifications. So there is a certain level of quality and authenticity to the answers provided. The questions are either answered by someone in the field or someone decently knowledgeable in the field with proper scientific research and citations to back it all up.

As with many forums, absolutely anyone can ask questions on AAB, sometimes even the contributors ask the other experts for opinions. But it is primarily aimed towards children and young persons still in school. So if you know of any kids aching to get some of their burning questions regarding biology, then please u…

Torvosaurus 3

Following yesterday's pencil sketch and digital line tracings, I've digitally colored in my Torvosaurus using Illustrator. I like Illustrator as it allows me to store the image in vector format thus I can scale it to any size without losing any resolution. Plus, more importantly, I can use layers to add different tones and texture. I guess you can do the same in Photoshop but I'm more used to Illustrator.

This one turned out to be a lot better than my Allosaurus as I've been spending the last two weeks preparing figures for my manuscript in preparation basically using pretty much the same technique but on photographs of skulls and reconstructing jaw muscles on them.

Torvosaurus 2

Line tracing with shadows of the same Torvosaurus drawing from the previous post, using Adobe Illustrator.

Torvosaurus

I initially named this sketch Megalosaurus but then remembered that I've been relying on the proportions of Torvosaurus for the reconstruction, so it's been renamed to Torvosaurus.Torvosaurus is a North American "megalosaur" popularly used to aid in the reconstructions of the English Megalosaurus mostly because the long-held assumption that these two taxa are closely related. However, more recent phylogenetic analyses show that the traditional monophyletic Megalosauridae does not seem to exist anymore but rather a paraphyletic "Megalosauridae" with a paraphyletic grade of "megalosaurs" leading up to the Spinosauridae. Or something like that...there seems to be quite a lot of confusion in this area of the theropod phylogeny probably because of the lack of good specimens. Although, in a consensus tree of published trees, a fair chunk of the traditional "megalosaurs" still seem to come together in a smaller but yet monophyletic Megalosaurid…

Olfactory capabilities in T. rex and birds

I’ve recently had the chance to review the literature regarding olfaction in birds and to my surprise found that there is little research done on the olfactory functions (e.g. olfaction threshold) and their relations to the olfactory bulbs. The main reason I got into this was primarily for the claim that T. rex had an acute sense of smell because of its enlarged olfactory bulbs. Now the latter part of this statement is obviously true. According to Brochu (2000), the olfactory bulb is 1.5 times as wide as the cerebral region of the endocast in T. rex. Following Bang and Cobb’s (1968) simple method, the greatest diameter of the olfactory bulb is about 41% of the greatest diameter (in this case the longest length) of the total brain. That’s higher than the largest proportion of olfactory bulb in modern birds according to Bang and Cobb (1968), which is as follows:

37.0% - Snow Petrel
33.0% - Wilson’s petrel
30.0% - Wedge-tailed Shearwater
30.0% - Greater Shearwater
29.5% - Dove Prion
29.0% - Bl…