The skull of Kaatedocus siberi

In 2013 Emanuel Tschopp and Octávio Mateus described a new species of diplodocid sauropod. The specimen was excavated in the famous Howe Quarry near Shell in Wyoming in 1990 and 1991. This is the same quarry in which Barnum Brown made some of his most numerous findings. A team of the Sauriermuseum Aathal (SMA) reopened it in 1989, 57 years after he had abandoned the quarry.

Quarry map of the holotype of Kaatedocus siberi, SMA 0004. Grey elements represent disarticulated skull elements. Drawing by Esther Premru. Scale bar = 50 cm. Modified from Tschopp & Mateus. 2012.
Quarry map of the holotype of Kaatedocus siberi, SMA 0004. Grey elements represent disarticulated skull elements. Original drawing by Esther Premru. Scale bar = 50 cm. (Modified from Tschopp & Mateus 2013) Used with permission.

The skull was found disarticulated next to the neck and a few other bones, including ribs, the right pes and some caudal vertebrae. SMA 0004, bearing the field name ‘H.Q. Zwei’, was long thought to be a juvenile Diplodocus (Ayer 2000) or Barosaurus (Michelis 2004), due to it’s relative small body size. But it has a few unique features which clearly distinguishes it from any other flagellicaudatan or diplodocid taxa. (Tschopp & Mateus 2012; Tschopp et al. 2015)

Drawing of the reconstructed skull of the holotype of Kaatedocus siberi (SMA 0004) in right (A) and left (B) lateral views. Light grey areas are reconstructed parts. The right surangular is mistakenly mounted as left angular. Scale bar = 5 cm. For anatomical abbreviations see below. (Modified from Tschopp & Mateus 2013) Used with permission.
Drawing of the reconstructed skull of the holotype of Kaatedocus siberi (SMA 0004) in right (A) and left (B) lateral views. Light grey areas are reconstructed parts. The right surangular is mistakenly mounted as left angular. Scale bar = 5 cm. For anatomical abbreviations see below. (Modified from Tschopp & Mateus 2013) Used with permission.

As the skull fell into its individual bones during the deposition, they were compressed and deformed irregulary through the overlaying rock layers. A few bones are lacking huge parts and there are even some which are entirely missing (see above). The braincase however is completely preserved. The deformation and the missing elements made the reassembling and mounting of the skull extremely difficult. Below you can see my drawing of the mounted skull of the SMA 0004 holotype.

Some parts are slightly reconstructed, for example the sutures or the mirrored surangular.
Some parts are slightly reconstructed, for example the sutures or the mirrored surangular.

Emanuel Tschopp gave me some very useful information about the deformations on the skull. The caudal end of the left maxilla, where it touches the lacrimal, is compressed and bent downwards. It should have been straight in the living animal. The braincase and skullcap are deformed irregularly. It was nearly impossible for Ben Papst, the preparator of the SMA, to mount them correctly due to the deposit-related deformation and compression. The sutur on top of the orbitosphenoid should match with the one on the frontal. The basypterigoid processes were bent backwards, normaly they protrude in about 45 degrees relative to the skullcap, so that they are hidden behind the quadrate and the pterygoid in lateral view. The occipital condyle was deformed and rotated a bit upwards as well. The parasphenoid rostrum and palate aren’t preserved. The ‘palatal region’ in the mount was somewhat inspired by the palate of diplodocids and serves as a support structur for the rostral parts of the skull without claiming to be exact.

The reconstructed skull of the <em>Kaatedocus siberi</em> holotype SMA 0004
The reconstructed skull of the Kaatedocus siberi holotype SMA 0004

With the information provided by Emanuel Tschopp and by looking at some related taxa, I was able to reconstruct the skull of Kaatedocus as it would have been ‘in vivo’. The braincase was moved upwards to match the sutures and was slightly modified according to Galeamopus hayi HMNS 175 (formerly CM 662) (Tschopp et al. 2015). The parasphenoid rostrum was borrowed from Diplodocus longus CM 11161 (Young et al. 2012). The palate was reconstructed after the juvenile Diplodocus skull CM 11255 (Whitlock et al. 2010) and the CM 11161 specimen (Young et al. 2012; Holliday 2009). The size and position of the scleral ring was derived from the CM 11161 specimen (Tschopp et al. 2015) as well.

For those of you who are not familiar with the Sauriermuseum Aathal:

The SMA is a privately run dinosaur museum based in Aathal, Switzerland. They are excavating their finds according to common scientific method and documenting the findings carefully in photographic and graphic manner. All discoveries made by the Sauriermuseum Aathal are accessible to science.

Dr. Heinrich Mallison, researcher at the Museum für Naturkunde Berlin, has written about digging with the SMA here.

The Sauriermuseum has made some spectacular findings. Hans-Jakob ‘Kirby’ Siber and his team found the world’s famous and remarkably well preserved Allosaurus ‘Big Al’, which became state property and was later confiscated by the American authorities (Ayer 2000). It was then put in to the Museum of the Rockies, where it is on display and cataloged as MOR 693. You can find the whole story about ‘Big Al’ here. A few years later, in 1996, Siber found an even better preserved (97% complete) Allosaurus: The SMA 0005 specimen, also known as ‘Big Al Two’.

The SMA holds now more than 10 specimens from own excavations in the Howe Quarry, which are all on display, these are: Camarasaurus sp. ‘E.T.’ (SMA 0002), Diplodocus sp. ‘H.Q. Eins’ (SMA 0003), Kaatedocus siberi ‘H.Q. Zwei’ (SMA 0004), Allosaurus fragilis ‘Big Al Two’ (SMA 0005), sauropod baby ‘Toni’ (undefined species but might belong to the Diplodocidae) (SMA 0009), Othnielosaurus consors ‘Barbara’ (SMA 0010), Galeamopus sp. ‘MaX’ (SMA 0011), Stegosaurus sp. ‘Victoria’ (SMA 0017 and SMA 0018) Hesperosaurus mjosi ‘Moritz’ (VFSMA 0001 (previously SMA 0122)) and ‘Lilly’ (SMA 0092), Camptosaurus dispar ‘Arky’ (SMA 0249).

Anatomical abbreviations:

a: articular; aof: antorbital fenestra; bpr: basipterygoid process; bt: basal tuber; d: dentary; f: frontal; la: lacrimal; ls: laterosphenoid; ltf: laterotemporal fenestra; m: maxilla; o: orbit; os: orbitosphenoid; p: parietal; paof: preantorbital fossa; pm: premaxilla; po: postorbital; popr: paroccipotal process; pra: proatlas; pro: prootic; q: quadrate; qj: quadratojugal; sq: squamosal

Refereces:

Ayer, J. 2000. The Howe Ranch Dinosaurs. Sauriermuseum Aathal, Aathal, 96 pp.

Holliday, C. M. 2009. New Insights Into Dinosaur Jaw Muscle Anatomy. The Anatomical Record 292:1246-1265.

Michelis, I. 2004. Taphonomie des Howe Quarry’s (Morrison-Formation, Oberer Jura), Bighorn County, Wyoming, USA. Unpublished PhD thesis, Institute of Palaeontology, University of Bonn, 41 pp.

Tschopp, E. & Mateus, O. 2013. The skull and neck of a new flagellicaudatan sauropod from the Morrison Formation and its implication for the evolution and ontogeny of diplodocid dinosaurs. Journal of Systematic Palaeontology 11:853–888.

Tschopp, E., Mateus, O. & Benson, R. B. J. 2015. A specimen-level phylogenetic analysis and taxonomic revision of Diplodocidae (Dinosauria, Sauropoda). PeerJ 3:e857.

Whitlock, J. A., Wilson, J. A. & Lamanna, M. C. 2010. Description of a nearly complete juvenile skull of Diplodocus (Sauropoda: Diplodocoidea) from the Late Jurassic of North America. Journal of Vertebrate Paleontology 30:442-457.

Young, M. T., Rayfield, E. J., Holliday, C. M., Witmer, L. M., Button, D. J., Upchurch, P. & Barrett, P. M. 2012. Cranial biomechanics of Diplodocus (Dinosauria, Sauropoda): testing hypotheses of feeding behaviour in an extinct megaherbivore. Naturwissenschaften 99:637-643.

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