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Brachiosaurid skull comparison by Paleo-King Brachiosaurid skull comparison by Paleo-King
Skull material for nearly all the brachiosaurs for which there are currently known extant skulls*, along with some scaled estimates of skulls for larger subadult/adult specimens (which unfortunately were not found with skulls).

Yes, there is another putative B. altithorax skull originally discovered by Marsh back in the 1800s, besides the Felch Quarry skull reassembled by Carpenter and Tidwell (1998). Ironically, flawed reconstructions both of these fragmentary skulls (and not Camarasaurus) were used by Marsh in his two published Brontosaurus skeletal drawings (in 1883 he used the YPM skull and in 1891 he used the Felch skull). In both cases he got the shape of the skulls wrong and stuck them on the same wrong (diplodocid) body. The horrible Yale Brontosaurus skull model of the 20th century was yet a further distortion of Marsh's second drawing. svpow.com/2014/11/14/how-did-t…; However the Field Museum and the Carnegie museum did use sculpted skulls based on Camarasaurus rather than the Marsh brachiosaur skulls.

Of course the most interesting thing is that these skulls were found before Brachiosaurus itself was described. Luckily neither skull was designated as type specimen for Marsh's Brontosaurus... otherwise based on naming precedence, Brachiosaurus would have to be called Brontosaurus today, brachiosauridae would be brontosauridae, and the diplodocid we know as Brontosaurus excelsus would need to be renamed, and to something other than Apatosaurus... in an even worse taxonomic mess than we already had with Brontosaurus as it was.

The Giraffatitan skulls are also very interesting, and they indicate that the skull proportions changed substantially as the animal grew (or at least in one of the sexes). The nose and upper face became enormous, while the lower jaw retailed its modest proportions. This isn't the first time that the large HMN S116/SII skull has been figured, but previous restorations fail to reflect just how bizarre the proportions were getting relative to the less mature (and far more famous) HMN t1. If Giraffatitan was sexually dimorphic (as Europasaurus appears to be) then the high-crested HMN S116 may be a subadult male, with t1 as an immature female and S66 as an immature male (both S116 and S66 have larger, more robust postnasal struts and thus higher-rooted nasals compared to t1, despite S66 being slightly smaller than t1). The skulls shown here are based pretty much directly on Janensch (1935-36). There is also another braincase figured by Janensch in his skull paper, HMN Y1, which isn't figured here as it is basically the same size and pretty much the same shape as the braincase of HMN t1 (indeed it may even be a misprint of t1, as there is not much other information on it).

The Abydosaurus skull material, other than the smallest skull, is based on the quarry maps in Chure, et. al. (2010) and there are no available photos of the larger skulls, so their images here may not be completely true to form.

The Atlasaurus material necessitated a fair bit of speculation but the extant skull bones do appear to be from a primitive brachiosaur or stem-brachiosaur (and the dorsals and arms look extremely close to Europasaurus and Brachiosaurus, respectively). And yes, the skull really is that big. The rest of the body, though, was unusually short and stocky for a brachiosaur, not much longer than 50 feet. As there is no skull material for more "mainline" basal brachiosaurs like Lapparentosaurus, there is a clear morpho-evolutionary gap in skull shape between Atlasaurus and the more derived forms seen here, which we will for now have to tolerate. Somebody go down to Madagascar and dig up a skull or two... we already have the teeth!

*There are multiple juvenile skulls known from Europasaurus which for the sake of brevity are not listed here. They do not differ greatly from the subadult skulls here, other than having less developed nasal arches. The "male" and "female" skulls differ mainly in the size of the nasal crest, though there may be patterns of dimorphic variance in eye sockets and other elements too.


REFERENCES:

Carpenter, K. and Tidwell, V. (1998). "Preliminary description of a Brachiosaurus skull from Felch Quarry 1, Garden Park, Colorado." Pp. 69–84 in: Carpenter, K., Chure, D. and Kirkland, J. (eds.), The Upper Jurassic Morrison Formation: An Interdisciplinary Study. Modern Geology, 23:1-4.

Chure, Daniel; Britt, Brooks; Whitlock, John A.; Wilson, Jeffrey A. (2010). "First complete sauropod dinosaur skull from the Cretaceous of the Americas and the evolution of sauropod dentition" (PDF). Naturwissenschaften 97 (4): 379–391. doi:10.1007/s00114-010-0650-6.

Janensch, W. 1935-36. Die Schädel der Sauropoden Brachiosaurus, Barosaurus und Dicraeosaurus aus den Tendaguru-Schichten Deutsch-Ostafrikas. Palaeontographica, Supplement 7 1(2):147-298.

Marpmann, J. S.; Carballido, J. L.; Sander, P. M.; Knötschke, N. (2014-03-27). "Cranial anatomy of the Late Jurassic dwarf sauropod Europasaurus holgeri (Dinosauria, Camarasauromorpha): Ontogenetic changes and size dimorphism". Journal of Systematic Palaeontology: 1–43.

Monbaron, D.; Russell,D.; Taquet, P. (1999). "Atlasaurus imelakei n.g., n.sp., a brachiosaurid-like sauropod from the Middle Jurassic of Morocco". Comptes Rendus de l'Academie des Sciences. Science de la terre and des planetes (329): 519–526.
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:iconevodolka:
Evodolka Featured By Owner Feb 23, 2017  Hobbyist Artist
love brachiosaurus
and it's super interesting to see just how little of the skull we have actually discovered
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:iconpaleosir:
paleosir Featured By Owner Dec 25, 2016  Hobbyist Traditional Artist
Giraffatitan has a really weird skull.
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:iconpaleo-king:
Paleo-King Featured By Owner Dec 25, 2016  Professional Traditional Artist
Yes and it kept on getting weirder. We don't have a fully adult skull yet.
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:iconpaleosir:
paleosir Featured By Owner Dec 26, 2016  Hobbyist Traditional Artist
Yeah
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:iconkazuma27:
Kazuma27 Featured By Owner Jul 1, 2016  Hobbyist General Artist
Wait!
You're telling me we don't have adult Brachiosaurus and Giraffatitan skulls?!

Frankly, this... Well, i didn't expect it!
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:iconpaleo-king:
Paleo-King Featured By Owner Edited Jul 2, 2016  Professional Traditional Artist
Nope. The skulls are all from individuals that are not done growing. You should have known they never find adult skulls! LOL.

The biggest Giraffatitan skull (HMN S116) was found close to the SII skeleton and is probably the same individual. This animal was around 75 feet long or maybe a bit longer. The associated scapula classed as specimen HMN Sa9 (possibly also from the same individual, or at least cross-scales well with it) is not fused to a coracoid. SII's coracoid is also not fused to a scapula. This animal was not done growing. And remember, HMN XV2 was around 15% larger. Maybe even bigger than that, since we only have the tibia, and as sauropods reach adulthood the legs slow their growth allometrically relative to the body as a whole. HMN Fund no. is also bigger than SII, since its tail scales up about 12% bigger than than HMN Aa, which is almost certainly past of the same individual as SII (I know, their cataloging system was crazy. oh well).

Fund no. (tail) and XV2 (tibia) may be parts of the same animal. It was probably around 95-100 ft. long which means a skull around 1m long. No telling if THIS beast was an adult either, since there's no shoulder material!

The two referred Brachiosaurus skulls are definitely not from adult individuals, they scale up considerably smaller than the holotype animal (unfused coracoid again!) assuming similar estimated proportions (and guess who estimated those proportions? :XD:). The Felch Quarry skull is not that big, if you visit the Cleveland Museum you will see how small it is next to their cast of the AMNH T. rex skull. The Potter Creek Brachiosaurus, the biggest referred specimen we know of, would have had a skull roughly around 1m, that rivals many T. rex skulls in size. And again, no shoulder material for that one either, so whether it was still immature is anyone's guess.
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:iconornithopsis:
Ornithopsis Featured By Owner Jul 7, 2016  Hobbyist Traditional Artist
Of course, it's worth considering that full fusion of all synostoses and sutures can occur very late in life--the human skull, for example, often still has open sutures into its owner's 30s or 40s. Sexual maturity in dinosaurs appears to have occurred long before 'adult' morphology, skeletal fusion, or size were all necessarily reached--so defining 'adult' precisely can be difficult. When you consider that truly 'adult' individuals, as defined by skeletal fusion, were probably extremely rare, the fact that their fossils are so uncommon is less surprising!
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:iconpaleo-king:
Paleo-King Featured By Owner Jul 9, 2016  Professional Traditional Artist
That's true. How do you really define what is 'adult'? Even human definitions of adult age have changed over time and depending on culture and rulers. It was not uncommon to get married around age 13 or 14 in medieval times in many places. Technically if you go by gray matter density, 25 is the minimum adult age. But fertility-wise it's already "past prime". Different measures.

It's known that sexual maturity for sauropods (in females at least) happened at around 50% of maximum known size, based on medullary bone. So what we consider "immature" for skeletal ontogeny was likely fully mature when it came to banging out egg caches.

So for all we know HMN t1 could have been mature for reproductive purposes, but was hardly mature skeletally. The huge-nosed SMN SII/S116 (assuming it was male) may or may not have been sexually mature. There really isn't a good way to test for that in male skeletons. We could also have a case of dimorphic development rates where females mature much faster, like in sperm whales today. On the other hand if t1 was a female and S116 and the smaller S66 were both males, as the nasals and maxillae indicate may be the case, then possibly even S66 was reproductively mature since it was already showing "mature" male face proportions.

It's hard to tell if Giraffatitan had sexual dimorphism in skull shapes, but I've seen some convincing arguments that Europasaurus did, since a lot of skulls for it have been found. Most of these still have yet to be published, but there was a detailed presentation in SVP 2011.
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:iconkazuma27:
Kazuma27 Featured By Owner Jul 2, 2016  Hobbyist General Artist
Man, one meter long skull for a sauropod... It's something i'd def want to see!
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:iconpaleo-king:
Paleo-King Featured By Owner Jul 3, 2016  Professional Traditional Artist
Me too. Maybe someday the Humboldt Museum will reconstruct HMN S116 and put it on display, at least that would be a start. HMN t1 is already pretty large in person, but seeing a bigger skull next to it will really get some attention.
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:iconcomixqueen:
comixqueen Featured By Owner Jun 25, 2016  Professional Digital Artist
Really cool!!

Shit, those are huge skulls! O_O
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:iconpaleo-king:
Paleo-King Featured By Owner Jul 2, 2016  Professional Traditional Artist
Yeah a lot of people assume sauropods had tiny heads, but that just isn't so. When you realize how huge they got, the big skulls make sense, scale-wise. Also brachiosaurs were high-browsers so they needed a big mouth full of teeth to hack through branches. A head approaching 1m is no joke, that's comparable to many big tyrannosaur heads. The teeth are pretty big too, once you get close to them. They put wimpy diplodocid teeth to shame.
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:iconsameerprehistorica:
SameerPrehistorica Featured By Owner Aug 25, 2016  Hobbyist
yes,lot of people think their heads are small. Their heads are small compared to their bodies but generally the large sauropods don't have tiny heads.
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:iconbricksmashtv:
bricksmashtv Featured By Owner Jun 25, 2016  Hobbyist Traditional Artist
Super cool! The skulls look so awesomely detailed!
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:iconleopold002:
Leopold002 Featured By Owner Jun 25, 2016  Hobbyist Writer
Very interesting!!!
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