File:Bulletin (1970) (20238677580).jpg

Title: Bulletin
Identifier: bulletin34351970peab (find matches)
Year: 1926 (1920s)
Authors: Peabody Museum of Natural History
Subjects: Natural history
Publisher: New Haven, Peabody Museum of Natural History, Yale University
Contributing Library: Smithsonian Libraries
Digitizing Sponsor: Smithsonian Libraries

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CLOVERLY FORMATION, STRATIGRAPHY AND PALEONTOLOGY 87 tion and growth changes. The present report does not seem an appropriate place, how- ever, and I defer this to a later contribution. Skull. Several partial skulls are present in the collections of Tcnontosaurus, but the best by far is the complete paratype skull YPM 5456 (Plate 16: A; Plate 17: A). In fact, this skull is probably the best skull in existence of a pre-Late Cretaceous ornitho- pod from the Western Hemisphere. The following description is based almost en- tirely on that specimen, with occasional comparisons with the sub-adult skull of YPM 5458 and several other fragmentary skulls. Some comparisons are made with skull fragments of Camptosaurus and the restorations of that genus given by Gilmore (1909), as well as with certain other ornithopods (Laosaurus, Dryosaurus, Parkso- saurus, Dysalotosaurus, Heterodontosaurus, Thescelosaurus and Iguanodon). In lateral view, the the skull is long and deep, in pronounced contrast to the low profile of Camptosaurus (Fig. 8). It has a large subrectangular orbit, a smaller oval lateral temporal fenestra and large external nares. A small oval subsidiary lateral tem- poral fenestra is situated between the jugal and quadratojugal near the lower margin of the lower temporal arch, and a long narrow slitlike antorbital fenestra descends obliquely across the maxilla from the lacrimal. The greatest skull length is approxi- mately twice the skull height. In dorsal aspect, the skull is narrowly wedge shaped with stout, rostrally rounded premaxillae and a sharply concave occipital outline. The greatest breadth is in the temporal region. The supratemporal fenestrae are oval and of moderate size. The snout is dominated by the stout, edentulous premaxillae which flare out broadly below into a rounded, spatula-like beak. Dorsally, they extend backward as long, narrow, parallel-sided processes that interpose between the nasals for a distance of about 9 cm. This is well preserved in YPM 5456 and 5459. Similar interposition of
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FIG. 8. Reconstructed lateral view of the skull and mandibles of Tenontosaurus tilletti. Abbreviations: an = angular; de = dentary; f =: frontal;ju = jugal; la rr lacrimal; mx = max- illa; na =z nasal; p = parietal; pd =: predentary; pmx := premaxilla; po = postorbital; poc = paroccipital process (exoccipital &/or opisthotic) ; prf = prefrontal; qj = quadratojugal; qu =z quadrate; s = supraorbital; sq ^ squamosal; sur =z surangular.

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