Browsing by Author "Landman, Neil H."
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ItemAdditions to the ammonite fauna of the Upper Cretaceous Navesink Formation of New Jersey. American Museum novitates ; no. 3306(New York, NY : American Museum of Natural History, 2000) Kennedy, W. J. (William James); Landman, Neil H.; Cobban, William A., 1916-2015.; Johnson, Ralph O.New fossil collections provide additional information about the late Campanian and Maastrichtian ammonites from the Navesink Formation of New Jersey. Late Campanian ammonites include Pseudophyllites indra (Forbes, 1846), Nostoceras (N.) approximans (Conrad, 1855) (of which Nostoceras (N.) stantoni Hyatt, 1894, is a synonym), Nostoceras (N.) hyatti Stephenson, 1941, Nostoceras (N.) pauper (Whitfield, 1892), Didymoceras cf. D. draconis (Stephenson, 1941), Exiteloceras rude n. sp., Hoploscaphites pumilus (Stephenson, 1941), and Jeletzkytes cf. J. nodosus (Owen, 1852). Maastrichtian ammonites from the Navesink Formation include Pachydiscus (P.) neubergicas neubergicus (Hauer, 1858), Kitchinites sp., Nostoceras (N.) alternatum (Tuomey, 1854), Baculites sp., Eubaculites cf. E. labyrinthicus (Morton, 1834), Eubaculites sp.?, Jeletzkytes cf. J. plenus (Meek, 1876), Jeletzkytes criptonodosus Riccardi, 1983, and Discoscaphites gulosus (Morton, 1834). These faunas are correlated with those of Western Europe, the Gulf Coast, and the Western Interior of the United States. The older fauna from the basal phosphatic beds of the Navesink Formation at the classic Atlantic Highlands locality is referred to the Nostoceras (N.) hyatti zone. It is late Campanian in age and equivalent to the Nostoceras (N.) pozaryskii/Belemnella langei zone in Europe and the Baculites jenseni zone in the United States Western Interior. In addition, these beds contain ammonites that range into the early Maastrichtian, as well as Pachydiscus (P.) neubergicus, whose appearance marks the base of the Maastrichtian. Thus, these phosphatic beds represent a condensed sequence that spans the late Campanian to early Maastrichtian. Ammonites also occur at other localities in the Navesink Formation in New Jersey, and correspond to higher levels in the Maastrichtian. The youngest ammonite known from the Navesink Formation, Discoscaphites gulosus, from Sewell, New Jersey, indicates a correlation with the Hoploscaphites nicolletii or Jeletzkytes nebrascensis zone of the Western Interior. ItemAllostratigraphy and biostratigraphy of the Upper Cretaceous (Coniacian-Santonian) Western Canada Foreland Basin. (Bulletin of the American Museum of Natural History, no. 414)(American Museum of Natural History., 2017-06-26) Landman, Neil H.; Plint, A. Guy.; Walaszczyk, Ireneusz.; Hooper, Beth (Elizabeth A.); Grifi, Meriem D.; Gröcke, D. R. (Darren R.); Trabucho Alexandre, João P.; Jarvis, I. (Ian) ItemAmmonites from the upper part of the Pierre Shale and Fox Hills Formation of Colorado. American Museum novitates ; no. 3388(New York, NY : American Museum of Natural History, 2003) Landman, Neil H.; Cobban, William A., 1916-2015.The upper part of the Pierre Shale and Fox Hills Formation were deposited in the late Cretaceous (Maastrichtian) Western Interior Seaway. They crop out in a belt that roughly parallels the Front Range of the Rocky Mountains from Douglas to Weld County, Colorado. These rocks consist of sandy shales and sandstones and are overlain by the nonmarine Laramie Formation. A sparse assemblage of ammonites is present consisting of Coahuilites sheltoni Böse, 1928, Sphenodiscus pleurisepta (Conrad, 1857), Trachybaculites sp. cf. T. columna (Morton, 1834), Hoploscaphites birkelundae Landman and Waage, 1993, Hoploscaphites sp. cf. H. birkelundae, Jeletzkytes dorfi Landman and Waage, 1993, and Jeletzkytes sp. cf. J. dorfi. Hoploscaphites birkelundae and Jeletzkytes dorfi define the H. birkelundae Zone in the Western Interior, which represents the lower part of the Upper Maastrichtian. These rocks are thus equivalent in age to the Fox Hills Formation in Niobrara County, Wyoming, and older than the type Fox Hills Formation in north-central South Dakota. An analysis of the ratio of ⁸⁷Sr/⁸⁶Sr in a belemnite from this zone in Morgan County, Colorado, yields a value of 0.707790 ± 0.000008 (2-sigma SE), nearly identical to that of a bivalve from the same zone in Niobrara County, Wyoming (McArthur et al., 1994). The western shoreline of the seaway during the time of H. birkelundae extended as far west as northwestern Colorado and southwestern Wyoming. ItemAmmonites from the Weno limestone (Albian) in northeast Texas. American Museum novitates ; no. 3236(New York, NY : American Museum of Natural History, 1998) Kennedy, W. J. (William James); Cobban, William A., 1916-2015.; Gale, A. S.; Hancock, J. M.; Landman, Neil H.The Weno Limestone of northeast Texas is an upper Albian unit that has previously been imprecisely dated in terms of the European standard zonal sequence. Ammonite faunas, chiefly from the lower Weno, show it to be equivalent to a part of the lowest Mortoniceras (Subschloenbachia) rostratum Subzone of the highest Albian Stoliczkaia dispar Zone of Europe on the basis of the presence of M. (S.) rostratum (J. Sowerby, 1817), together with Engonoceras serpentinum (Cragin, 1900), Engonoceras aff. subjectum (Hyatt, 1903), Cantabrigites aff. subsimplex (Spath, 1933), Mortoniceras (Angolaites) drakei (Young, 1957), Mortoniceras (Angolaites) wintoni (Adkins, 1920), Stoliczkaia (Stoliczkaia) argonautiformis (Stoliczka, 1864), Neophlycticeras (Neophlycticeras) sp., Anisoceras armatum (J. Sowerby, 1817), Anisoceras perarmatum Pictet and Campiche, 1861, and Mariella (Wintonia) sp. Mortoniceras (Subschloenbachia) Spath, 1921, is regarded as the senior synonym of Durnovarites Spath, 1932, and Mortoniceras (Angolaites) Spath, 1932, as the senior synonym of Drakeoceras Young, 1957. Most previous studies have interpreted the ammonites of the Weno Limestone as predominantly endemic to Texas. However, Mortoniceras (Angolaites) was originally described from Angola, S. (S.) argonautiformis from southern India, and M. (S.) rostratum and the species of Cantabrigites, Neophlycticeras, and Anisoceras from western Europe. ItemCampanian ammonites from the Tombigbee Sand Member of the Eutaw Formation, the Mooreville Formation, and the basal part of the Demopolis Formation in Mississippi and Alabama. American Museum novitates ; no. 3201(New York, N.Y. : American Museum of Natural History, 1997) Kennedy, W. J. (William James); Cobban, William A., 1916-2015.; Landman, Neil H. ItemCephalopods from the Cretaceous-Paleogene (K-Pg) boundary interval on the Brazos River, Texas, and extinction of the ammonites (American Museum novitates, no. 3964)(American Museum of Natural History., 2021-01-13) Witts, James D.; Landman, Neil H.; Garb, Matthew P.; Irizarry, Kayla M.; Larina, Ekaterina; Thibault, Nicolas; Razmjooei, Mohammed J.; Yancey, Thomas E.; Myers, Corinne E.We report on new collections of cephalopods (ammonites and nautilids) from the Cretaceous-Paleogene (K-Pg) successions of the Corsicana and Kincaid formations exposed along the Brazos River in Falls County, Texas. An abundant fauna of eight species comprising four genera of ammonites is described from the Corsicana Formation, including Discoscaphites mullinaxorum n. sp. The presence of abundant aptychi (probably lower jaws) of Discoscaphites and Eubaculites, as well as juvenile specimens, indicates a living population that experienced little postmortem drift. The lytoceratid genus Gaudryceras is also reported for the first time from the Brazos River area. Presence of the index taxon Discoscaphites iris (Conrad, 1858) indicates that the fauna belongs to the D. iris Range Zone, the highest ammonite range zone in North America. Correlation with new and existing microfossil data indicates that the fauna represents the uppermost Maastrichtian, and comparison with published records further suggests that this is the most diverse D. iris Zone fauna yet reported from the Gulf and Atlantic Coastal Plains of North America. Three ammonite genera are recorded from the basal units of the K-Pg event deposit at Brazos, which likely represents deposition in the immediate aftermath of the Chicxulub impact event. A single specimen of the nautilid Eutrephoceras is reported from the Danian Kincaid Formation, less than 300 kyr after the K-Pg boundary. These data provide new information on the differing fate of these cephalopod groups during the K-Pg mass extinction and add to the picture of diverse and abundant Maastrichtian ammonite faunas prior to the Chicxulub impact event. ItemCephalopods from the Cretaceous/Tertiary boundary interval on the Atlantic Coastal Plain, with a description of the highest ammonite zones in North America. Part 1, Maryland and North Carolina. American Museum novitates ; no. 3454(New York, NY : American Museum of Natural History, 2004) Landman, Neil H.; Johnson, Ralph O.; Edwards, Lucy E.The sedimentary deposits on the Atlantic Coastal Plain in New Jersey, Delaware, Maryland, North Carolina, South Carolina, and Georgia span the Cretaceous/Tertiary boundary. We investigate the ammonites of the Severn Formation on the western and eastern shore of Chesapeake Bay, Maryland, and the Peedee Formation, North Carolina. We describe three ammonite assemblages from the Severn Formation and their associated dinoflagellates, defining three successive ammonite zones in the Upper Maastrichtian. The lowest ammonite zone is the Discoscaphites conradi Assemblage Zone. It occurs near the top of the Severn Formation in Prince Georges County, Maryland, just below the Paleocene Brightseat Formation. The ammonite fauna consists of Sphenodiscus pleurisepta (Conrad, 1857), Sphenodiscus lobatus (Tuomey, 1856), Discoscaphites conradi (Morton, 1834), Discoscaphites gulosus (Morton, 1834), Jeletzkytes nebrascensis (Owen, 1852), Glyptoxoceras rugatum (Forbes, 1846), Baculites vertebralis Lamarck, 1801, and Eubaculites latecarinatus (Brunnschweiler, 1966). Dinoflagellates from a sample of matrix include Isabelidinium aff. I. cooksoniae (Alberti, 1959) Lentin & Williams, 1977, which correlates with calcareous nannofossil Zone CC25b, indicating the lower part of the Upper Maastrichtian (68.2-67.4 MaBP). The D. conradi Zone is also present in parts of the Corsicana Formation, Texas, the Prairie Bluff Chalk, Alabama and Mississippi, the Peedee Formation, North Carolina, and the Navesink and New Egypt Formations, New Jersey. The next higher zone is the Discoscaphites minardi Assemblage Zone, which occurs in the Severn Formation approximately 6 m below the base of the Hornerstown Formation at Lloyd Creek, Kent County, Maryland. The ammonite assemblage is dominated by Discoscaphites minardi, n.sp., B. vertebralis, and S. pleurisepta, with rare specimens of Sphenodiscus sp., Discoscaphites iris (Conrad, 1858), and E. latecarinatus. A sample of dinoflagellates from the same bed as the ammonites includes Deflandrea galatea (Lejeune-Carpentier, 1942) Lentin & Williams, 1973 and Thalassiphora pelagica (Eisenack, 1954) Eisenack & Gocht, 1960, which correlate with the Neophrolithus frequens calcareous nannofossil Zone between Subzones CC26a and CC26b, indicating the middle part of the Upper Maastrichtian (66.4-66.0 MaBP). The D. minardi Zone is also present in the New Egypt Formation, New Jersey. The highest zone is the D. iris Assemblage Zone, which occurs near the top of the Severn Formation at its type locality at Round Bay, Anne Arundel County, Maryland. The ammonite assemblage is dominated by D. iris and E. carinatus, although elsewhere this zone also includes Pachydiscus (Neodesmoceras) mokotibensis Collignon, 1952, Pachydiscus (Pachydiscus) jacquoti jacquoti Seunes, 1890, S. lobatus, S. pleurisepta, Discoscaphites sphaeroidalis Kennedy and Cobban, 2000, and E. latecarinatus. Dinoflagellates from a sample of matrix surrounding one of the ammonites include Palynodinium grallator Gocht, 1970 and T. pelagica indicative of the P. grallator Zone, Tpe subzone, which correlates with the upper part of calcareous nannofossil Zone CC26b, indicating the upper part of the Upper Maastrichtian (65.6-65.0 MaBP). The D. iris Zone is also present in the upper part of the Corsicana Formation, Texas, the Owl Creek Formation, Mississippi, Tennessee, and Missouri, and the New Egypt and Tinton Formations, New Jersey. ItemCephalopods from the Cretaceous/Tertiary boundary interval on the Atlantic Coastal Plain, with a description of the highest ammonite zones in North America. Part 2, Northeastern Monmouth County, New Jersey. Bulletin of the AMNH ; no. 287(New York, NY : American Museum of Natural History, 2004) Landman, Neil H.; Johnson, Ralph O.; Edwards, Lucy E.The sedimentary deposits of the New Jersey Coastal Plain span the Cretaceous/Tertiary boundary and reveal a complex stratigraphy in the northeastern part of their outcrop belt. Newly discovered exposures of the New Egypt Formation in northeastern Monmouth County, New Jersey, indicate that a tongue of this formation, previously thought to be restricted in outcrop to southwestern Monmouth County, extends to the northeast. This formation is sandwiched between the Tinton Formation below and the Hornerstown Formation above. The upper contact is unconformable. Fossils occur in the upper part of the New Egypt Formation and the basal part of the Hornerstown Formation and are concentrated at the formational contact--this accumulation is known as the Main Fossiliferous Layer. The Discoscaphites minardi Assemblage Zone occurs in the New Egypt Formation approximately 2 m below the base of the Hornerstown Formation and contains Discoscaphites minardi Landman et al., 2004, Discoscaphites sp., Eubaculites carinatus (Morton, 1834), Eubaculites sp., and Eutrephoceras dekayi (Morton, 1834). Associated dinoflagellates include Deflandrea galatea (Lejeune-Carpentier, 1942) Lentin & Williams, 1973, and Thalassiphora pelagica (Eisenack, 1954) Eisenack & Gocht, 1960. The D. minardi Zone represents the middle part of the Upper Maastrichtian corresponding to the upper part of calcareous nannofossil Subzone CC26a and the lower part of Subzone CC26b. The Discoscaphites iris Assemblage Zone occurs at the top of the New Egypt Formation in an interval at least 20 cm thick and contains Discoscaphites iris (Conrad, 1858), Discoscaphites gulosus (Morton, 1834), D. minardi, Eubaculites latecarinatus (Brunnschweiler, 1966), E. carinatus, Sphenodiscus pleurisepta (Conrad, 1857), Sphenodiscus sp., and Eutrephoceras dekayi. Associated dinoflagellates include Palynodinium grallator Gocht, 1970, and T. pelagica. The D. iris Zone represents the uppermost Maastrichtian, corresponding to the upper part of calcareous nannofossil Zone CC26b. The basal beds of the Hornerstown Formation contain a mixed assemblage of Cretaceous and Paleocene fossils. Paleocene dinoflagellates include Carpatella cornuta Grigorovich, 1969, and Senoniasphaera inornata (Drugg, 1970) Stover & Evitt, 1978, and suggest that these beds correspond to planktonic foraminiferal zones PO-P[alpha]. There is no enrichment of iridium ([greater than or equal to]0.1 ppb) or layer of spherules at the formational contact but a dinoflagellate specimen with pockmarked damage consistent with melting is present in the top of the New Egypt Formation. The formational contact spans the Cretaceous/Tertiary boundary but probably contains a hiatus of approximately 100 k.y. All of the Cretaceous fossils in the Main Fossiliferous Layer are reworked from the upper New Egypt Formation and reflect a period of erosion and winnowing, perhaps related to changes in sea level as well as events associated with the bolide impact at the end of the Cretaceous. Subsequently and simultaneously, the sea floor experienced extensive bioturbation, which may have further reworked fossils. Elsewhere on the Gulf and Atlantic Coastal Plain, the D. iris Zone also occurs immediately below the K/T boundary and is truncated by an erosional unconformity, commonly with reworked material in the overlying beds. The geographic distribution of the D. iris Zone and cores spanning the K/T boundary on the Gulf and Atlantic Coastal Plains help approximate the coastline of North America at that time and indicate a broad Mississippi embayment. However, there is no firm evidence that the Western Interior Seaway persisted until the end of the Cretaceous. ItemCephalopods from the Cretaceous/Tertiary boundary interval on the Atlantic Coastal Plain, with a description of the highest ammonite zones in North America. Part 3, Manasquan River Basin, Monmouth County, New Jersey ; Bulletin of the American Museum of Natural History, no. 303(New York, NY : American Museum of Natural History, 2007) Landman, Neil H.; Johnson, Ralph O.; Garb, Matthew P.; Edwards, Lucy E.; Kyte, Frank Thomas, 1949-Geological investigations in the upper Manasquan River Basin, central Monmouth County, New Jersey, reveal a Cretaceous/Tertiary (= Cretaceous/Paleogene) succession consisting of approximately 2 m of the Tinton Formation overlain by 2 m of the Hornerstown Formation. The top of the Tinton Formation consists of a very fossiliferous unit, approximately 20 cm thick, which we refer to as the Pinna Layer. It is laterally extensive and consists mostly of glauconitic minerals and some angular quartz grains. The Pinna Layer is truncated at the top and is overlain by the Hornerstown Formation, which consists of nearly equal amounts of glauconitic minerals and siderite. The base of the Hornerstown Formation is marked by a concentration of siderite nodules containing reworked fossils. This layer also contains a few fossils of organisms that were living in the environment during the time of reworking. At some downdip sites, there is an additional layer (the Burrowed Unit), which is sandwiched between the top of the Pinna Layer and the concentrated bed of nodules. This unit is very thin and is characterized by large burrows piping down material from above. The Pinna Layer is abundantly fossiliferous and represents a diverse, nearshore marine community. It contains approximately 110 species of bivalves, gastropods, cephalopods, echinoids, sponges, annelids, bryozoans, crustaceans, and dinoflagellates. The cephalopods include Eutrephoceras dekayi (Morton, 1834), Pachydiscus (Neodesmoceras) mokotibensis Collignon, 1952, Sphenodiscus lobatus (Tuomey, 1856), Eubaculites carinatus (Morton, 1834), Eubaculites latecarinatus (Brunnschweiler, 1966), Discoscaphites iris (Conrad, 1858), Discoscaphites sphaeroidalis Kennedy and Cobban, 2000, Discoscaphites minardi Landman et al., 2004b, Discoscaphites gulosus (Morton, 1834), and Discoscaphites jerseyensis, n.sp. The dinoflagellates include Palynodinium grallator Gocht, 1970, Thalassiphora pelagica (Eisenack, 1954) Eisenack & Gocht, 1960, Deflandrea galeata (Lejeune-Carpentier, 1942) Lentin & Williams, 1973, and Disphaerogena carposphaeropsis Wetzel, 1933. These ammonites and dinoflagellates are indicative of the uppermost Maastrichtian, corresponding to the upper part of calcareous nannofossil Subzone CC26b. The mode of occurrence of the fossils in the Pinna Layer suggests an autochthonous accumulation with little or no postmortem transport. Many of the benthic organisms are preserved in life position. For example, specimens of Pinna laqueata Conrad, 1858, are oriented in a vertical position, similar to that of modern members of this genus. The echinoids also occur in aggregations of hundreds of individuals, suggesting gregarious feeding behavior. In addition, there are monospecific clusters of baculites and scaphites. These clusters are biological in origin and could not have been produced by hydraulic means. Scaphite jaws are also present, representing the first reports of these structures in the Upper Cretaceous of the Atlantic Coastal Plain. They occur both as isolated specimens and inside the body chamber, and indicate little or no postmortem transport. The Pinna Layer represents a geologically short interval of time. The fact that most of the animals are mature suggests that the community persisted for at least 5-10 years. If multiple generations of animals are present, perhaps reflecting multiple episodes of colonization and burial, then this unit probably represents more time, amounting to several tens of years. The fact that the Pinna Layer is truncated at the top implies a still longer period of time, amounting to hundreds of years. These age estimates are consistent with observed rates of sedimentation in nearshore environments. Iridium analyses of 37 samples of sediment from three sites in the Manasquan River Basin reveal an elevated concentration of iridium of 520 pg/g, on average, at the base of the Pinna Layer. The iridium profile is aymmetric with an abrupt drop off above the base of this unit and a gradual decline below the base. The elevated concentration of iridium is not as high as that recorded from some other Cretaceous/Tertiary boundary sections. However, it is sufficiently above background level to suggest that it is related to the global Ir anomaly documented at many other localities, and attributed to a bolide impact. The position of the iridium anomaly at the base of the Pinna Layer is inconsistent with the biostratigraphic data, because this anomaly occurs below the unit containing fossils indicative of the uppermost Maastrichtian. We present two alternative hypotheses: (1) If the enriched concentration of iridium is in place, it marks the Cretaceous/Tertiary boundary by reference to the global stratotype section and point at El Kef, Tunisia. The position of the iridium anomaly further implies that the Pinna community was living at the moment of impact and may even have flourished in its immediate wake. Subsequently, the community may have been buried by pulses of mud-rich sediment, possibly associated with enhanced riverine discharge following the impact. The Burrowed Unit may represent a subsequent pulse of riverine discharge that scoured the top of the Pinna Layer. (2) The iridium anomaly was originally located at the top of the Pinna Layer and was displaced downward due to bioturbation and/or chemical diffusion. This hypothesis implies that the Pinna Layer was deposited prior to the deposition of the iridium. The Pinna community may have died before or at the moment of impact. Erosion of the top of the Pinna Layer and deposition of the Burrowed Unit may have been associated with events immediately following the impact. In both hypotheses, the sea floor experienced an extended period of erosion and reworking in the early Danian, which may have lasted for several hundred thousand years, producing a concentrated lag of siderite nodules containing reworked fossils in the basal part of the Hornerstown Formation. This lag deposit is equivalent to the Main Fossiliferous Layer at the base of the Hornerstown Formation elsewhere in New Jersey. This period of erosion and reworking was probably associated with a transgression in the early Danian. The post-impact community was greatly reduced in diversity, with most of the species representing Cretaceous survivors. ItemDescription of the embryonic shell of Nautilus belauensis (Cephalopoda). American Museum novitates ; ; no. 2960.(New York, N.Y. : American Museum of Natural History, 1989) Landman, Neil H.; Arnold, John M.; Mutvei, Harry. ItemDescription 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. ItemDevelopment of the embryonic shell structure of Mesozoic ammonoids ; American Museum novitates, no. 3621(New York, NY : American Museum of Natural History, 2008) Tanabe, Kazushige.; Kulicki, Cyprian.; Landman, Neil H.Exceptionally well-preserved embryonic shells (ammonitellae) of the early Aptian ammonoid Aconeceras cf. trautscholdi Sinzov, 1870, preserved as coprolite remains from Symbirsk, Russia, were examined with scanning electron microscopy (SEM) to investigate the developmental sequence of the embryonic shell structure. Our SEM observations reveal that these shells can be classified into the following three groups with different wall microstructure: Group 1, with a thin (ca. 5 [micro]m), double-layered shell wall, consisting of inner prismatic and outer homogeneous layers, the former of which is absent in the adapical portion and becomes thicker adorally; Group 2, with a three-layered shell wall that consists of inner prismatic, middle homogeneous, and outer prismatic layers, with tubercles on the outer layer; and Group 3, with a thick nacreous swelling (primary varix) on the anteroventral side near the aperture. The middle homogeneous layer of the embryonic shells of Group 2 is the same as the outer homogeneous layer in shells of Group 1 and may be composed of amorphous calcium carbonate (ACC). In embryonic shells of Group 3, the middle homogeneous layer is absent and there are voids instead. It may have been transformed into the inner prismatic layer or else dissolved during diagenesis. In modern Nautilus and gastropods, embryonic or larval shell development is initiated by the secretion of a cap-shaped, fully organic shell prior to the deposition of calcium carbonate. This stage is not preserved in the material examined, but probably existed in the Ammonoidea. Based on our observations and data from extant Nautilus and gastropods, we propose a model for the development of the embryonic shell structure of Mesozoic ammonoids, starting from secretion of an organic primary shell, followed by deposition of ACC and its transformation into the inner prismatic layer, and terminating in the deposition of a primary varix on the inside of the ventral and ventrolateral position of the shell just adapical of the aperture. ItemEngonoceratid ammonites from the Glen Rose limestone, Walnut clay, Goodland limestone, and Comanche Peak limestone (Albian) in Texas. American Museum novitates ; no. 3221(New York, NY : American Museum of Natural History, 1998) Kennedy, W. J. (William James); Landman, Neil H.; Cobban, William A., 1916-2015.Ammonites of the family Engonoceratidae, commonly referred to as pseudoceratites because of their distinctive suture, are locally abundant in rocks of early to mid-Albian age in Texas, but have received little or no attention since their original description. Ten species are dealt with in the present publication in the following order: Engonoceras elegans, n. sp., Engonoceras gibbosum Hyatt, 1903, Engonoceras stolleyi Böhm, 1898, Engonoceras hilli Böhm, 1898, Engonoceras complicatum Hyatt, 1903, Parengonoceras roemeri (Cragin, 1893), Metengonoceras inscriptum Hyatt, 1903, Metengonoceras ambiguum Hyatt, 1903, Protengonoceras gabbi (Böhm, 1898), and Platiknemiceras flexuosum, n. sp. ItemExceptionally well-preserved ammonites from the Upper Cretaceous (Turonian-Santonian) of North America : implications for ammonite early ontogeny. American Museum novitates ; no. 3086(New York, N.Y. : American Museum of Natural History, 1994) Landman, Neil H. ItemFoldlike 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. ItemThe heteromorph ammonite Didymoceras cochleatum (Meek and Hayden, 1858), from the Pierre Shale of South Dakota and Wyoming. American Museum novitates ; no. 3268(New York, NY : American Museum of Natural History, 1999) Kennedy, W. J. (William James); Cobban, William A., 1916-2015.; Landman, Neil H.The middle Campanian (Upper Cretaceous) zone of Baculites gregoryensis Cobban, 1951 in south-central South Dakota and eastern Wyoming has yielded numerous fragments of a distinctive species of Didymoceras characterized by initial loose planispiral whorls followed by loose helical whorls, and finally by a slightly pendant body chamber. These fragments are referred to Didymoceras cochleatum (Meek and Hayden, 1858), a species based on one-half of a septate whorl from the helical growth stage. This species is abundant in the Gregory Member of the Pierre Shale along the Missouri River Valley in South Dakota, rare in the Red Bird Silty Member of the Pierre Shale in eastern Wyoming, and very rare in the Rock River Formation in southeastern Wyoming. ItemImpressions 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). ItemInquilinism 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. ItemInternal structures in the early whorls of Mesozoic ammonites. American Museum novitates ; no. 2823(New York, N.Y. : American Museum of Natural History, 1985) Landman, Neil H.; Bandel, Klaus."The first few septa and associated structures in the early whorls of Mesozoic ammonites were studied in a number of genera including Quenstedtoceras, Kosmoceras, Euhoplites, Hypacanthoplites, Baculites, and Scaphites and its related genera. Exceptionally well-preserved specimens with little obscuring matrix inside permitted observations of the spatial arrangement of the first few septa and were supplemented by sections polished parallel to the median plane. Our observations indicate that: 1. The proseptum is a single structure and does not consist of two septa. Prismatic attachment deposits of the caecum and siphuncle occur around the proseptal opening. 2. In all genera except Quenstedtoceras, the second septum is moderately distant from the proseptum and, in median section, is slightly convex, not concave, toward the aperture. In Quenstedtoceras, however, the second septum grows dorsally into the proseptum and is only conspicuous on the venter. These relationships are also expressed in the shape and spacing of the corresponding sutures on steinkerns of the initial whorls. 3. In all genera in which the original shell structure was preserved, the second septum is nacreous, not prismatic. Therefore, in agreement with Drushchits and Khiami (1970), we prefer the simpler terms second septum and third septum for primary septum and nacroseptum, respectively. 4. The development of a prismatic attachment ridge at the base of the proseptum, dorsal muscle scars just adoral of each septum, and wrinkles in the proseptum and prosiphonal attachment sheets support the model of early ammonite ontogeny proposed by Bandel (1982)"--P. . ItemIntraspecific variation through ontogeny in late Cretaceous ammonites. (American Museum novitates, no. 3922)(American Museum of Natural History., 2019-03-04) Klein, Carina.; Landman, Neil H.This project assesses intraspecific variation through the ontogeny of the ammonite Scaphites whitfieldi Cobban, 1951, from the Upper Cretaceous of the U.S. Western Interior. Our sample consists of 103 dorsoventral cross sections from nine localities that represent two lithofacies (shale and siltstone). We measured four shell parameters (ww/dm, ww/wh, uw/dm, and WER) to describe the ontogenetic changes in shell morphology. We investigated the variation at three growth stages: immediately after hatching (dm = 1 mm), the neanoconch (dm = 4 mm), and the submature stage (defined as at or near the base of the mature hooklike body chamber). In general, the shell becomes more discoidal through ontogeny with a narrower umbilicus and a more compressed whorl section. The results of the univariate analysis indicate that the variation is statistically significantly higher in the neanoconch than in either the hatchling or submature stage. This pattern is also apparent in the multivariate analysis in which the disparity increases markedly from the hatchling to the neanoconch and then decreases again at the submature stage. These results are consistent with the hypothesis that the neanoconch represents a transition in the life history of the animal to a more demersal mode of life followed by a canalization of morphology toward maturity. However, because the neanic transition occurs over a range of sizes, it is possible that some individuals may have already undergone these changes at dm = 4 mm, whereas others may not have, thus inflating the degree of variation. To resolve this issue in the future, it is critical to examine each ontogenetic trajectory individually to pinpoint the exact size at which the morphological changes occur. We also compared the values of ww/dm, ww/wh, uw/dm, and WER of the three growth stages for the sample from siltstone versus the sample from shale. The comparison reveals that the specimens from siltstone occupy lower regions of the morphospace, implying that these specimens are generally more compressed than those from shale. This difference may be related to selection pressures for improved hydrodynamic efficiency in the higher energy environment represented by siltstone.