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Duck-billed dinosaurs at the Royal Ontario Museum. A Maiasaura skeleton is visible on the foreground, with two Maiasaura juveniles at the foot of the skeletal mount. On the background, flushing with the wall, there's the two-dimensional mount of a Gryposaurus specimen. The unidentified skull of another duck-billed dinosaur is visible on the low right corner of the photograph.

Duck-billed dinosaurs at the Royal Ontario Museum. A Maiasaura skeleton is visible on the foreground, with two Maiasaura juveniles at the foot of the skeletal mount. On the background, flushing with the wall, there's the two-dimensional mount of a Gryposaurus specimen. The unidentified skull of another duck-billed dinosaur is visible on the low right corner of the photograph.

Restoration of the spinosaurid dinosaur Siamosaurus in the Sao Khua Formation palaeoenvironment, with Sunosuchus in the middle left and a herd of Phuwiangosaurus in the background. References: Siamosaurus based on tooth specimens [1] and the neural spine of a possibly referable skeleton[2], with other missing elements filled in with relatives (Suchomimus[3], Baryonyx[4], IchthyovenatorFile:Ichthyovenator_laosensis_skeletal_reconstruction_by_PaleoGeek.png). Phuwiangosaurus based on skeletal by Suteethorn et al. (2009)[5] and missing elements of skull of EuhelopusFile:Euhelopus.png. Sunosuchus based on Suteethorn and Ingavat (1983)[6] and missing elements based on Goniopholis[7].

Diagram of the skull of Haya griva in lateral view, reconstructed from IGM 100/2017

Skull cast of Liaoceratops yanzigouensis on display at the Baoding Natural History Museum.

Skeleton of Yamaceratops dorngobiensis (MPC-D 100/553) in right dorsolateral view. (A) Photograph; (B) Interpretive drawing. Bones are bounded by solid lines and colored beige; the matrix is gray. Shaded areas represent the broken surface of bones. Abbreviations: cd, caudal vertebrae; dr, dorsal ribs; dv, dorsal vertebrae; f, femur; fi, fibula; h, humerus; L, bone on the left side; p, isolated parietal; pp, pedal phalanges; R, bone on the right side; ra, radius; sk, skull; sv, sacral vertebrae; ti, tibia; u, ulna; il, ilium; is, ischium.

Reconstructions of diplodocoid skulls used in this analysis. Reconstructions of Nigersaurus and Diplodocus modified from [10] and [34], respectively. All other reconstructions based on material listed in Table S1. Skulls scaled to equivalent anteroposterior lengths.

Partial skull of Manidens condorensis from the Middle Jurassic Cañadón Asfalto Formation of Argentina. Skull reconstructions in lateral view. Dashed lines indicate estimated edges. Abbreviations: a angular antfo antorbital fossa asaf anterior surangular foramen be buccal emargination bo basioccipital bt basal tubera d dentary d1, 2, 11 dentary tooth 1, 2, 11 emfo external mandibular fossa f frontal gl glenoid gr groove j jugal jfl jugal flange jh jugal horn m maxilla m1, 11 maxillary tooth 1, 11 n nasal pd predentary pm premaxilla po postorbital pof postorbital fossa popr paroccipital process q quadrate qj quadratojugal ri ridge sa surangular sq squamosal.

Achelousaurus horneri skull, collected in Glacier County, Montana, at the Museum of the Rockies in Bozeman, Montana. The Ceratopsidae are those dinosaurs with head frills. There are three large subgroups of Ceratopsidae: Centrosaurinae, Ceratopsinae, and Chasmosaurinae. The Triceratopsini are a "tribe" of the Chasmosaurinae -- a genus so vast that it gets the special name "tribe". The Pachyrhinosaurini are a "tribe" within the Centrosaurinae. Achelousaurus is a genus within the Pachyrhinosaurini. So far, only three skulls and some limited skeletal remains have been collected anywhere in the world -- and all of them in Montana. Their bony frills are quite similar to the Styracosaurus albertensis, although their other skull features (such as big bony bosses on the nose and behind the eyes) are not.

a Skeletal reconstruction of A. greppini. Elements preserved in the material and therefore providing information for the skeletal reconstruction are marked in blue. Because much information is missing from the incomplete skeletal material, the dorsal vertebrae, the proportions and morphology of the cervical vertebrae and the skull were modified from Camarasaurus. b Scaled silhouette drawings of Cetiosauriscus stewarti (in black) and A. greppini (in grey) demonstrating the significant size difference between the two taxa. Scale bar is 1 m

The palatal view of the skull of NMS G.2021.6.2 and comparative assessment of the pterygoid region. The palatal region of NMS G.2021.6.2, A as seen in the ventral view. The comparative, to scale, pterosaur palatine and palatal regions in the ventral view. From left to right: B Cacibupteryx (IGO-V 208); C Parapsicephalus (GSM 3166); D Dearc (NMS G.2021.6.2); E Rhamphorhynchus (NHM R 2786); F Rhamphorhynchus (CM 11434). Abbreviations: bsp—basipterygoid; cho—choana; ec -, ectopterygoid; ipv—interpterygoid vacuity; pal—palatine; pf—posterior palatine fenestra; pte—pterygoid; stf -subtemporal fenestra; sof – suborbital fenestra; vm—vomer. Scale bar 10 mm

Selmasaurus johnsoni mounted skull in the Rocky Mountain Dinosaur Resource Center in Woodland Park, Colorado

Skull of Yulong mini. The horizontal line projected through the posterodorsal corner of the antorbital fenestra is parallel to the line linking the articular end of the quadrate and the ventral margin of the premaxillae.

Cast of the skull of Parapsicephalus purdoni (specimen AMNH 1694) in the American Museum of Natural History.

Sarahsaurus aurifontanalis, referred skull (MCZ 8893), in (a) lateral, (b) occipital, (c) dorsal and (d) ventral views. an, angular; ar, articular; bo, basioccipital; bs, basisphenoid; ec, ectopterygoid; f, frontal; h, hyoid; j, jugal; l, lacrimal; ls, laterosphenoid; m, maxilla; n, nasal; op, opisthotic-exoccipital; p, parietal; po, postorbital; prf, prefrontal; pm, premaxilla; pt, pterygoid; q, quadrate; qj, quadratojugal; so, supraoccipital; sq, squamosal. Scale bar, 5 cm.

Holotype skull of Plesiotylosaurus crassidens (LACM 2759) on display at the Natural History Museum of Los Angeles County.