Browsing by Author "Larson, Neal L."
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Item Description of two species of Hoploscaphites (Ammonoidea, Ancyloceratina) from the Upper Cretaceous (Lower Maastrichtian) of the U.S. Western Interior. (Bulletin of the American Museum of Natural History, no. 427)(American Museum of Natural History., 2019-02-22) Landman, Neil H.; Kennedy, W. J. (William James); Larson, Neal L.; Grier, Joyce C.; Grier, James W.; Linn, Tom.Two species of scaphitid ammonites (Ammonoidea: Ancyloceratina) from the Upper Cretaceous (lower Maastrichtian) of the Western Interior of North America are described. Hoploscaphites macer, n. sp., is medium size, with coarse ribs on the phragmocone, which become finer on the body chamber, and closely spaced ventrolateral tubercles. It occurs in the upper part of the Baculites baculus Zone and lower part of the overlying B. grandis Zone in the Pierre Shale in Montana, Wyoming, and Colorado, and in the Bearpaw Shale in Montana. Hoploscaphites criptonodosus (Riccardi, 1983) is larger and more coarsely ornamented, including one or two rows of lateral tubercles on the flanks of the phragmocone. It occurs in the upper part of the Baculites baculus Zone and overlying B. grandis Zone in the Pierre Shale in Montana, Wyoming, Colorado, and possibly South Dakota, and in the Bearpaw Shale in Montana and Saskatchewan, Canada. Both species form part of an evolving lineage of Hoploscaphites that first appears in the Western Interior of North America in the middle Campanian.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 Inquilinism of a baculite by a dynomenid crab from the Upper Cretaceous of South Dakota. (American Museum novitates, no. 3818)(American Museum of Natural History., 2014-11-06) Landman, Neil H.; Fraaije, René H. B.; Klofak, Susan M.; Larson, Neal L.; Bishop, Gale A.; Kruta, Isabelle.We describe a small crab inside the phragmocone of a heteromorph cephalopod Baculites sp. smooth from the Gammon Ferruginous Member (lower Campanian) of the Pierre Shale in Butte County, South Dakota. The crab Ferricorda kimberlyae (Bishop, 1987) is well preserved with its carapace and pereiopods parallel to and between two septa of the phragmocone. Because of its superb preservation, the specimen is unlikely to have been washed into the phragmocone. The crab probably retreated into the phragmocone chamber to avoid predation or to molt and was subsequently buried by an influx of rapid sedimentation. This is the first instance of inquilinism by a crab in a heteromorph ammonite. Despite the rarity of such fossils, the occurrence of crabs inside ammonite shells was probably not uncommon on sea floors during the Mesozoic. Morphological details of the specimen reveal that Ferricorda is a dynomenid crab.Item Jaws of late Cretaceous placenticeratid ammonites : how preservation affects the interpretation of morphology. American Museum novitates ; no. 3500(New York, NY : American Museum of Natural History, 2006) Landman, Neil H.; Tsujita, Cameron J.; Cobban, William A., 1916-2015.; Larson, Neal L.; Tanabe, Kazushige.; Flemming, Roberta L.We describe upper and lower jaws of Placenticeras Meek, 1876, from the Upper Cretaceous (Upper Campanian) Bearpaw Shale and Pierre Shale of the Western Interior of North America and lower jaws of the related ammonite Metaplacenticeras Spath, 1926, from the Campanian Yasukawa Formation of Hokkaido, Japan. One lower jaw is preserved inside the body chamber of Placenticeras costatum Hyatt, 1903. The other jaws are isolated but are generally associated with fragments of placenticeratid shells. The jaws from North America are attributed to Placenticeras meeki Böhm, 1898, and P. costatum, while those from Japan are attributed to Metaplacenticeras subtilistriatum (Jimbo, 1894). All of the jaws are presumed to be from adults. The jaws of Placenticeras attain lengths of up to 95 mm. They are preserved as steinkerns with a thin film of black material, representing diagenetically altered chitin. X-ray diffraction analysis of samples of this material indicates that it consists of magnesium-rich calcite, pyrite, and amorphous material (organic compounds). The upper jaw is approximately the same length as the lower jaw and is U-shaped, with narrow wings that converge anteriorly to a dome-shaped hood. The lower jaw is composed of two lamellae. The outer lamella is broad and consists of two wings terminating in a bilobate posterior margin. The inner lamella is one-half the length of the outer lamella. The two lamellae are separated except in the apical region and along the sides. The junction between the lamellae appears as a U or V-shaped outline on the anterior portion on the ventral surface of the jaw. This junction is especially conspicuous in specimens in which part of the inner lamella has eroded away. In crushed specimens, the lower jaw is subquadrate in shape. In specimens that retain some or all of their original curvature, the central portion is gently convex and the sides bend steeply dorsally. The rostrum projects slightly anteriorly and dorsally and there is a thickened rim of chitin along the anterior margin where the two lamellae are doubled over. A small indentation appears at the apical end and, in most specimens, develops into a midline slit that extends posteriorly 10-15 mm. However, as shown in well-preserved specimens and based on comparisons with the jaws of closely related ammonites, this slit represents the remnants of a narrow ridge on the ventral side of the inner lamella. This ridge is surrounded by an elongate boss of thickened chitin, which corresponds to a depression on the dorsal side. The ventral surface of the outer lamella bears a midline ridge with a central groove, which essentially forms a continuation of the ridge on the inner lamella. The ventral surface of the outer lamella is ornamented with thin, radial striations and irregular broad undulations paralleling the posterior margin. The posterior end is generally incomplete, probably as a result of predation or postmortem degradation, and the lateral margins are commonly creased, indicating postmortem plastic deformation. The lower jaws of Metaplacenticeras subtilistriatum are much smaller than those of Placenticeras but are otherwise similar in morphology. However, they retain pieces of a very thin, fibrous outer layer comprising two plates. X-ray diffraction analysis of samples of this layer indicates that it consists of calcite enriched in magnesium. Each plate covers the ventral surface of one of the wings and terminates at the midline ridge. Based on the close affinity of Metaplacenticeras and Placenticeras, and in comparison with published descriptions of placenticeratid jaws from elsewhere, we hypothesize that similar plates covered the lower jaws of all placenticeratids, although these plates have not been found in any Placenticeras material from North America. The thin nature and fibrous microstructure of this layer would have made it susceptible to mechanical breakage and chemical dissolution. Furthermore, jaws are internal structures embedded in the buccal bulb. The micro-environment within this bulb may have promoted dissolution of the outer calcitic layer of the lower jaw. The presence of a pair of calcitic plates (aptychi) and a midline ridge with a central groove on the outer lamella of the lower jaw are unique features of the lower jaws of the Aptychophora Engeser and Keupp, 2002. Although differences in preservation obscure this similarity, the lower jaws of placenticeratids conform to the description of aptychus-type jaws. However, unlike the thick calcitic aptychi of other Ammonitina, the thin calcitic aptychi of placenticeratids probably did not function as opercula and would have served simply to strengthen the lower jaw. The jaws of placenticeratids were probably designed for biting and cutting food rather than for passively collecting and straining plankton. Other data about the habitat and mode of life of placenticeratids are consistent with this interpretation. These ammonites probably inhabited surface waters and were capable of pursuing and attacking sluggish prey. An ecological analog of placenticeratids may be the modern ocean sunfish Mola mola (Linnaeus, 1758), which inhabits surface waters and feeds on gelatinous zooplankton.Item Large scaphitid ammonites (Hoploscaphites) from the Upper Cretaceous (upper Campanian-lower Maastrichtian) of North America : endless variation on a single theme. (Bulletin of the American Museum of Natural History, no. 441)(American Museum of Natural History., 2020-09-14) Landman, Neil H.; Kennedy, W. J. (William James); Grier, Joyce C.; Larson, Neal L.; Grier, James W.; Linn, Tom; Tackett, Lydia; Jicha, Brian R.We describe three species of large scaphitid ammonites (Ammonoidea: Ancyloceratina) from the Upper Cretaceous (upper Campanian-lower Maastrichtian) of the Western Interior of North America. Each species occurs as two dimorphs, referred to as macroconch and microconch. All three species share a similar pattern of ornamentation consisting of long, thin, nonbifurcating ribs on the adoral part of the phragmocone, suggesting that they constitute a single monophyletic clade. Macroconchs of Hoploscaphites crassus (Coryell and Salmon, 1934) are characterized by a globose whorl section, with closely spaced ventrolateral tubercles on the body chamber, usually persisting to the aperture. Macroconchs of Hoploscaphites plenus (Meek and Hayden, 1860) differ from those of H. crassus in having a more subquadrate whorl section with flatter flanks, and fewer, larger, and more widely spaced ventrolateral tubercles. Macroconchs of Hoploscaphites peterseni, n. sp., closely resemble those of H. crassus, but differ in being nearly circular in side view with a more compressed whorl section. All three species lived at approximately the same time in the same general area and depositional environment. They are abundant in the Baculites baculus Zone but also occasionally occur in the B. eliasi Zone and possibly lower part of the B. grandis Zone. They are present in the Pierre Shale of east-central Montana and east-central Wyoming, the Lewis Shale of south-central Wyoming, and the Bearpaw Shale of northeast Montana. It is possible that these three species represent subspecies within a single species or a "flock" of very closely related species, similar to the "species flocks" observed in modern cichlid fishes.Item A new species of Hoploscaphites (Ammonoidea, Ancyloceratina) from cold methane seeps in the Upper Cretaceous of the U.S. Western Interior. (American Museum novitates, no. 3781)(American Museum of Natural History., 2013-09-23) Landman, Neil H.; Kennedy, W. J. (William James); Cobban, William A., 1916-2015.; Larson, Neal L.; Jorgensen, Steven D.We describe Hoploscaphites gilberti, n. sp. (Ammonoidea: Ancyloceratina), from the Upper Cretaceous (middle-upper Campanian) Pierre Shale spanning the zones of Baculites scotti and Didymoceras nebrascense in Colorado, Wyoming, Montana, and South Dakota. This species is strongly dimorphic and is characterized by a compressed whorl section, with a rounded to elongate outline in lateral view. The apertural angle is approximately 50° in macroconchs. The body chamber is ornamented with fine flexuous ribs, umbilicolateral bullae, and ventrolateral tubercles. Hoploscaphites gilberti, n. sp., most closely resembles H. gilli Cobban and Jeletzky, 1965, but differs from this species in several important features: (1) the flanks of the body chamber are nearly subparallel rather than steeply convergent toward the venter, (2) the ventrolateral tubercles are larger and more numerous, and (3) the ribs are more widely spaced. Hoploscaphites gilberti, n. sp., is abundant at "tepee buttes" in the Pierre Shale, which are now interpreted as cold methane seeps.Item A new species of scaphitid ammonite from the Lower Maastrichtian of the Western Interior of North America, with close affinities to Hoploscaphites constrictus Sowerby, 1817. (American Museum novitates, no. 3833)(American Museum of Natural History., 2015-04-30) Landman, Neil H.; Kennedy, W. J. (William James); Larson, Neal L.We describe a new species of scaphitid ammonite from the Upper Cretaceous (Lower Maastrichtian) of North America. Hoploscaphites sargklofak, n. sp., is endemic to the U.S. Western Interior, but closely resembles H. constrictus Sowerby, 1817, from the Maastrichtian of northern Europe.Item Scaphites of the "nodosus group" from the Upper Cretaceous (Campanian) of the Western Interior of North America. (Bulletin of the American Museum of Natural History, no. 342)(American Museum of Natural History., 2010) Landman, Neil H.; Kennedy, W. J. (William James); Cobban, William A., 1916-2015.; Larson, Neal L.Scaphitid ammonites (scaphites) are common in the Upper Cretaceous Pierre Shale and Bearpaw Shale of the Western Interior of North America. We redescribe Hoploscaphites nodosus (Owen, 1852) and H. brevis (Meek, 1876) from the Baculites compressus–B. cuneatus zones of the upper Campanian. The types of both of these species were collected in the mid-19th century in what was then called Nebraska Territory, and included parts of present-day South Dakota, North Dakota, and Montana. Based on our present knowledge of the distribution of these species, the type material was probably collected from the B. compressus–B. cuneatus zones in the Pierre Shale at Sage Creek, a tributary of the Cheyenne River, Pennington County, South Dakota. Traditionally, the more robust, more coarsely ornamented scaphites (comprising the "nodosus group") from the Pierre Shale and Bearpaw Shale were assigned to Jeletzkytes Riccardi, 1983, and the more slender, more finely ornamented scaphites were assigned to Hoploscaphites Nowak, 1911. However, our large collections of these scaphites from the Baculites compressus–B. cuneatus zones reveal a complete intergradation between the two morphological extremes, and for many specimens, the choice of genus is arbitrary. In addition, our studies of other biostratigraphic zones in the Pierre Shale and Bearpaw Shale reveal that cooccurring species of these two "genera" share more in common with each other than they do with congeneric species from other horizons. Furthermore, contrary to earlier assumptions, Jeletkytes is not endemic to the Western Interior Basin of North America and occurs, for example, in the U.S. Atlantic Coastal Plain and Europe. We thus provisionally treat Jeletzkytes as a junior subjective synonym of Hoploscaphites. This expanded definition of Hoploscaphites is consistent with present-day concepts of other scaphitid genera such as Discoscaphites Meek, 1876, and Trachyscaphites Cobban and Scott, 1964...Item Supplemental Material for 'Large scaphitid ammonites (Hoploscaphites) from the Upper Cretaceous (upper Campanian-lower Maastrichtian) of North America : endless variation on a single theme. (Bulletin of the American Museum of Natural History, no. 441)'(American Museum of Natural History., 2020-09-14) Landman, Neil H.; Kennedy, W. J. (William James); Grier, Joyce C.; Larson, Neal L.; Grier, James W.; Linn, Tom; Tackett, Lydia; Jicha, Brian R.Supplemental Material for 'Large scaphitid ammonites (Hoploscaphites) from the Upper Cretaceous (upper Campanian-lower Maastrichtian) of North America : endless variation on a single theme. (Bulletin of the American Museum of Natural History, no. 441)'