Mesozoic ammonites

21 p. : ill. ; 26 cm.Includes bibliographical references (p. 21)."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. [1]

Colorado ammonites

45 p. : ill., maps ; 26 cm.Includes bibliographical references (p. 42-44).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

Geographic and temporal morphological stasis in the latest Cretaceous ammonoid Discoscaphites iris from the U.S. Gulf and Atlantic Coastal Plains

We examine temporal and spatial variation in morphology of the ammonoid cephalopod Discoscaphites iris using a large dataset from multiple localities in the Late Cretaceous (Maastrichtian) of the United States Gulf and Atlantic Coastal Plains, spanning a distance of 2000 km along the paleoshoreline. Our results suggest that the fossil record of D. iris is consistent with no within species net accumulation of phyletic evolutionary change across morphological traits or the lifetime of this species. Correlations between some traits and paleoenvironmental conditions as well as changes in the coefficient of variation may support limited population-scale ecophenotypic plasticity, however where stratigraphic data are available, no directional changes in morphology occur prior to the Cretaceous/Paleogene (K/Pg) boundary. This is consistent with models of 'dynamic' evolutionary stasis. Combined with knowledge of life history traits and paleoecology of scaphitid ammonoids, specifically a short planktonic phase after hatching followed by transition to a nektobenthic adult stage, these data suggest that scaphitids had significant potential for rapid morphological change in conjunction with limited dispersal capacity. It is therefore likely that evolutionary mode in the Scaphitidae (and potentially across the broader ammonoid clade) follows a model of cladogenesis wherein a dynamic morphological stasis is periodically interrupted by more substantial evolutionary change at speciation events. Finally, the lack of temporal changes in our data suggest that global environmental changes (such as those possibly related to the emplacement of the Deccan Traps Large Igneous Province) had a limited effect on the morphology of North American ammonoid faunas during the latest Cretaceous prior to the K/Pg mass extinction event.Missing morphometric values are highlighted with NA in the dataset.Funding provided by: National Science FoundationCrossref Funder Registry ID: http://dx.doi.org/10.13039/100000001Award Number: 1924807Funding provided by: American Museum of Natural History and Richard Gilder Graduate School*Crossref Funder Registry ID: Award Number:We assembled a large morphometric dataset consisting of 328 individual fossil specimens of the scaphitid ammonoid cephalopod Discoscaphites iris collected from nine localities in Texas, Missouri, Mississippi, and New Jersey, representing a ~2000 km transect from SW to NE and encompassing the full geographic range of this species. Morphometric parameters were measured on well-preserved adult specimens of two dimorphs (Macroconchs - presumably the female, and microconch, presumably the male). We took up to seven morphometric measurements, and calculated ratios that captured the size, shape, and degree of compression of each of these ammonoid shells from each different locality. We evaluated the coefficient of variation (the standard deviation divided by the mean) for size and shape ratios as well as compression ratios at each locality. We used non-parametric statistical tests [Mann-Whitney U] to evaluate the significance of changes in mean morphological trait values between localities. To correct for multiple comparisons we applied a Bonferroni correction and also controlled for the false discovery rate. We also explored relationships between morphological traits and several environmental variables using linear modelling. All analyses were conducted in the R programming environment

New discovery of rhyncholites and conchorhynchs (cephalopod jaw elements) from the Upper Cretaceous Mount Laurel Formation of Delaware (American Museum novitates, no. 3998)

20 pages : illustrations (some color), map ; 26 cm.Rhyncholites and Conchorhynchs are the calcitic elements of upper and lower jaws of cephalopods, respectively. Rhyncholites and conchorhynchs occur in relatively high abundance and are widely distributed, with a long geological range, extending from the Triassic to the Miocene. While rhyncholites and conchorhynchs are relatively common in Europe, there are only a few reports from North America. Here, we document 24 specimens of rhyncholites and 12 specimens of conchorhynchs from the Upper Cretaceous Mount Laurel Formation in Delaware. The specimens were found in isolation and, thus, identifying the taxon to which the rhyncholites and conchorhynchs belong is difficult. However, the Cretaceous nautilid Eutrephoceras occurs in the same formation, suggesting that the rhyncholites and conchorhynchs may belong to this taxon. We performed a morphometric analysis of these structures based on linear measurements. Our results reveal that some morphological parameters in rhyncholites are correlated with size. Additionally, our specimens exhibit high intraspecific variation, which may have been overlooked in previous studies

Late Cretaceous ammonoids show that drivers of diversification are regionally heterogeneous

Palaeontologists have long sought to explain the diversification of individual clades to whole biotas at global scales. Advances in our understanding of the spatial distribution of the fossil record through geological time, however, has demonstrated that global trends in biodiversity were a mosaic of regionally heterogeneous diversification processes. Drivers of diversification must presumably have also displayed regional variation to produce the spatial disparities observed in past taxonomic richness. Here, we analyse the fossil record of ammonoids, pelagic shelled cephalopods, through the Late Cretaceous, characterised by some palaeontologists as an interval of biotic decline prior to their total extinction at the Cretaceous-Paleogene boundary. We regionally subdivide this record to eliminate the impacts of spatial sampling biases and infer regional origination and extinction rates corrected for temporal sampling biases using Bayesian methods. We then model these rates using biotic and abiotic drivers commonly inferred to influence diversification. Ammonoid diversification dynamics and responses to this common set of diversity drivers were regionally heterogeneous, do not support ecological decline, and demonstrate that their global diversification signal is influenced by spatial disparities in sampling effort. These results call into question the feasibility of seeking drivers of diversity at global scales in the fossil record

Ammonites of New Jersey

30 p. : ill., map ; 26 cm.Includes bibliographical references (p. 27-30).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

Cretaceous/Tertiary boundary cephalopods.

122 p. : ill. (some col.), maps (some col.); 26 cm.Includes bibliographical references (p. 111-122).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

Heteromorph ammonites

88 p. : ill., maps ; 26 cm.Includes bibliographical references (p. 80-85).Heteromorh ammonites of the families Nostoceratidae Hyatt, 1894, and Diplomoceratidae Spath, 1926, are common to abundant in sediments deposited in the western and central parts of the U.S. Western Interior Seaway during the early late Campanian. The indices of successive zones of Didymoceras nebrascense (Meek and Hayden, 1856a) (oldest), Didymoceras stevensoni (Whitfield, 1877), Exiteloceras jenneyi camacki, n. subsp., Exiteloceras jenneyi jenneyi (Whitfield, 1877) and Didymoceras cheyennense (Meek and Hayden, 1856a) are revised, as are Nostoceras monotuberculatum Kennedy and Cobban, 1993a (D. nebrascense and D. stevensoni zones), Oxybeloceras crassum (Whitfield, 1877) (D. stevensoni and E. jenneyi zones), and Spiroxybeloceras meekanum (Whitfield, 1877) (D. cheyennense zone). Solenoceras elegans, n. sp. (D. stevensoni and E. jenneyi zones), Solenoceras bearpawense, n. sp. (D. nebrascense zone), and Solenoceras larimerense, n. sp. (E. jenneyi zone) are also described