Jaws and Radula of Baculites from the Upper Cretaceous (Campanian) of North America

Scaphites of the “Nodosus Group” from the Upper Cretaceous (Campanian) of the Western Interior of North America

“…cuneatus zones is similar to that of scaphite jaws described elsewhere by Landman and Waage (1993) and Kennedy et al (2002, and references therein). The terminology of the jaws is reviewed by Landman et al ( , 2007b. The upper jaw is U-shaped and consists of two narrow wings that converge anteriorly to a beaklike apex ( fig.…”

“…It may have served as reinforcement to strengthen the jaw for crushing or biting, but the layer is relatively thin (100-150 mm thick). In addition, the presence of a groove, rather than a thickening, along the middle of the lower jaw would have compromised any structural benefit from a mineralized layer (Landman et al, 2007b). Alternatively, the calcitic layer may have served as an operculum for protection against predators.…”

“…Alternatively, the calcitic layer may have served as an operculum for protection against predators. However, it is unclear how the lower jaw would have rotated into a position to fulfill this function (for a review of the various arguments, see Lehmann and Kulicki, 1990;Lewy, 2000;Engeser and Keupp, 2002;Landman et al, 2007b;and Kruta and Landman, 2008).…”

Description of the lower jaws of Baculites from the Upper Cretaceous U.S. Western Interior

“…Even in AMNH 66258 and RMDRC 07-025 in which the jaws are preserved inside the body chamber, the anterior end is missing, forming a notch. Landman et al (2007) noted this same feature in the rugaptychi from the Mooreville Chalk of Alabama, and suggested that it may be due to breakage. Alternatively, it is possible that a small gap is present at the apex between the two wings of the lower jaw, which is also mirrored in the aptychi.…”

“…This is similar to the position of the jaws inside the body chambers of Baculites sp. (smooth) from the Pierre Shale of South Dakota studied by Landman et al (2007). The lower jaws in AMNH 102517 are folded into a U-shape, which probably approximates the position of the lower jaws during life.…”