Browsing by Author "Lane, Jennifer A."
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Item Foldlike irregularities on the shell surface of Late Cretaceous ammonoids. American Museum novitates ; no. 3197(New York, N.Y. : American Museum of Natural History, 1997) Landman, Neil H.; Lane, Jennifer A.Item Impressions of the attachment of the soft body to the shell in late Cretaceous pachydiscid ammonites from the Western Interior of the United States. American Museum novitates ; no. 3273(New York, NY : American Museum of Natural History, 1999) Landman, Neil H.; Lane, Jennifer A.; Cobban, William A., 1916-2015.; Jorgensen, Steven D.; Kennedy, W. J. (William James); Larson, Neal L.Late Cretaceous pachydiscid ammonites Menuites oralensis Cobban and Kennedy, 1993 and Menuites portlocki (Sharpe, 1855) complexus (Hall and Meek, 1856) from the Western Interior of the United States show four kinds of markings on the phragmocone and body chamber. These markings are preserved on internal molds that retain traces of the original shell, mostly the inner prismatic layer. (1) Transverse lines appear on the surface of the inner prismatic layer and extend adorally as far as midway onto the adult body chamber. They consist of a sequence of regularly spaced iridescent lines that usually cross the venter with a marked adoral projection, forming a chev-ronlike pattern. The transverse lines do not follow the shape of the apertural margin. Viewed in close-up, these lines appear as narrow bands of nacre; the adoral edge of each band is ragged and the adapical edge thins out and disappears. (2) A longitudinal band occurs on the flanks and extends from the umbilicus to about two--thirds whorl height. It appears on the surface of the inner prismatic layer. (3) A mid-ventral band extends for several tens of millimeters adoral of the ultimate septum and terminates in an unpaired scar. It appears on the internal mold and is visible below the inner prismatic layer. (4) A pair of dorsal scars occurs on the internal mold several millimeters adoral of the ultimate septum. Each scar is boomerang-shaped and extends from the dorsal margin to just ventral of the umbilical shoulder. We hypothesize that the transverse line formed at the adapical margin of the zone of nacreous secretion in the middle of the body chamber. They may have represented narrow bands of mantle attachment. The longitudinal band demarcated a broad area of nacreous secretion on the flanks, which may have represented an additional area of mantle attachment. During growth, both the transverse lines and the longitudinal band were overlain by the inner prismatic layer (and are thus now visible on the surface of this layer on partially exfoliated shells). The mid-ventral scar and dorsal scars just adoral of the ultimate septum are the sites of attachment of the soft body at the adapical end of the body chamber. These sites developed on the inside surface of the inner prismatic layer (and are thus now visible on the internal mold below the inner prismatic layer, if present).Item Morphology of the braincase in the Cretaceous hybodont shark Tribodus limae (Chondrichthyes, Elasmobranchii), based on CT scanning. (American Museum novitates, no. 3681)(New York, NY : American Museum of Natural History., 2010) Lane, Jennifer A.The braincase of the Lower Cretaceous hybodont shark Tribodus limae is examined using high-resolution CT scanning, and its internal and external morphology is described based on three-dimensional digital reconstructions. This study represents the first in-depth examination of a hybodont braincase using CT scanning and digital imaging technology. The braincase of an additional Lower Cretaceous hybodont, Egertonodus basanus, is also digitally reconstructed and compared to Tribodus. A reconstruction of cranial nerves and blood vessels in Tribodus is presented on the basis of preserved foramina. The braincase of Tribodus shares many features with those of Egertonodus and neoselachians, providing further support for the sister-group relationship between hybodonts and extant elasmobranchs. CT scans confirm that in both Tribodus and Egertonodus the glossopharyngeal and vagus canals converge and exit from a common foramen (also found in Chlamydoselachus). In both of the hybodonts examined, the trochlear nerve exits the braincase anterior to the optic nerve, a possible hybodont synapomorphy. Separate foramina for the two rami of the octaval nerve are present in both Tribodus and Egertonodus, and may represent an additional hybodont synapomorphy. Also, both taxa have three separate foramina for the trigeminal, facial, and anterodorsal lateral line nerves, apparently including an individual foramen for the superficial ophthalmic complex. However, the basicranial arterial system in Tribodus differs considerably from that of Egertonodus in that in the former the internal carotid arteries enter the braincase much farther posteriorly and through paired foramina rather than a single median foramen. The median ventral basicranial process in Tribodus is similar in structure and position to median ventral processes seen in some extant neoselachians (e.g., Etmopterus) and in embryonic Torpedo (although in the latter this structure disappears during development), and thus may have had a similar ontogenetic origin.