Brachiosaurid skull comparison

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.