An unusual occurrence of Nautilus macromphalus in a cenote in the Loyalty Islands (New Caledonia)

Exploration of a landlocked cenote on Lifou (Loyalty Islands) revealed 37 shells of the cephalopod Nautilus macromphalus Sowerby, 1849, in saltwater on the cenote floor, approximately 40 m below the water surface. The occurrence of these shells is unusual because N. macromphalus is restricted to the open marine waters surrounding the island. All of the shells are mature, and nearly all of them are unbroken, with faded red-brown color stripes. We analyzed seven shells to determine their age. Radiocarbon dating yielded ages of 6380¡30 to 7095¡30 y BP. The 238U-series radionuclides 210Pb (half-life 522.3 y) and 226Ra (half-life 51600 y) also were measured. Two of the samples showed radioactive equilibrium between the nuclides, consistent with the old radiocarbon dates, but the other five samples showed excess 210Pb. When corrected for radioactive decay, the 226Ra activities were much greater than those found in living Nautilus. We conclude that exposure to high activities of 222Rn and 226Ra in the salty groundwater of the cenote altered the activities originally incorporated into the shells. Human placement of the shells in the cavity is rejected based on their radiocarbon age and the geometry of the cenote. The most probable explanation is that the animals entered the flooded karstic system through a connection on the seaward side at approximately 7,000 y BP, during an interval of slowly rising sea level. Unable to find an exit and/or due to anoxic bottom waters, the animals were trapped and died inside. The open connection with the sea persisted for ,700 y, but after ,6400 y BP, the connection was lost, probably due to a roof collapse. This is a rare example of Nautilus in a karstic coastal basin and provides a minimum age for the appearance of N. macromphalus in the Loyalty Islands

Palaeocological and evolutionary significance of anatomically preserved terrestrial plants in Upper Carboniferous marine goniatite bullions

Anatomically preserved plants are described from marine goniatite bullions of Marsdenian age (Namurian B, Upper Carboniferous) from Star Wood, Oakamoor, Staffordshire, England. They comprise stems and petioles, up to 15 cm long, predominantly of cordaites (Mesoxylon) and pteridosperms (Sutcliffa), with rare calamites, ferns and lycopsids, and are preserved as calcareous permineralizations. Rare fusainized plant fragments are also found. The flora is similar, although comprising fewer species, to the roof nodule floras of Langsettian (Westphalian A) age from Lancashire which occur above coal seams yielding calcareous coal balls. The plants preserved in these roof nodules probably grew in well-drained, slightly elevated lowlands, not inundated during marine transgression, and contrast in botanical composition to the boras of lowland peat-forming mires represented in typical coal ball floras. The Oakamoor assemblage likewise probably represents an assemblage living in well-drained elevated areas which drifted into the sea and was preserved in sediment-starved carbonates during the height of the marine transgression. These species of plants appear not to have become part of lowland mire ecosystems until later in the Carboniferous. The occurrence of this flora pre-dates that previously described From the Westphalian Coal Measures, and extends the range of several important Upper Carboniferous plant taxa

Chaetognath grasping spines from the Upper Mississippian of Arkansas [USA]

Previously unidentified tiny (about 0.5 mm in length), hollow, gently curved, serrated spines probably originally composed of horny, organic fibers from the Upper Mississippian (Middle Chesterian = Namurian A equivalent or lower Serpukhovian) of Arkansas (USA) are described, and their probable chaetognath affinities are discussed. The specimens are preserved in an oval accumulation (about 15 mm long and 6 mm wide) of approximately 200 specimens within a small (about 25 mm in length) phosphatic concretion. For comparison, the grasping spines of the Recent chaetognath Eukrohnia hamata were examined. The Arkansas specimens are named Eoserratosagitta serrata gen. et sp. nov., and this genus is assigned to the Phylum Chaetognatha. The Upper Mississippian spines are also compared with protoconodonts. This comparison supports the hypothesis that the chaetognaths may have existed in the Cambrian

Paleozoic cumaceans (Crustacea, Malacostraca, Peracarida) from North America

Thiee new species of malacostracans are described from North America in the Upper Mississippian Into Formation of Arkansas, and the Pennsylvanian Eudora Shale of southeastern Kansas. These appear to be the oldest fossils attributed to the Cumacea and are only the third collection of fossil cumaceans anywhere to be described. Previously depicted forms occur in the Permian and Jurassic of Europe. We herein double the number of described fossil cumacean species and suggest some necessary adjustments to the higher taxonomy of the group to accommodate apomorphic features of the fossil and Recent forms

Dorsal shell wall in ammonoids

In ammonoids, a soft body organ (possibly a supracephalicmantle fold), extending from the conch aperture secreted aragonitic wrinkles, forming a layer on the surface of the preceding whorl. The dorsal shell wall consists of the outer and inner components which were deposited sequentially, beginning at the aperture of the living chamber inwards. The dorsal wall attains its full thickness near the last septum. The outer component is visible in the apertural region and is smooth or wrinkled; it is called the wrinkled layer in the latter case. The wrinkles may be continuous, interrupted, or form isolated patches arranged in rows. The wrinkles are usually triangular in cross section. A further stage of dorsal wall development involves filling in the space between the apices of triangles, and then adding one or more inner prismatic layers from the inside of the living chamber. This pattern occurs at least in the postembryonic stage of all genera studied, belonging to five suborders of Ammonoidea ranging from Late Carboniferousto Late Cretaceous. In many genera, the outer component of the dorsal shell wall exhibits remarkable ontogenetic change in its ultrastructure and microornament. It may be compared with the black film of Recent Nautilus shells with respect to place of formation. The outer component of the ammonoid dorsal shell wall is regarded as a product of organic secretion and carbonate precipitation in the area of the supracephalic mantle fold.U planispiralnie skręconych amonoidów, u których ścianka grzbietowa styka się bezpośrednio ze ścianką poprzedniego skrętu, mamy do czynienia z modyfikacją strukturalną ścianki grzbietowej w obszarze styku obu ścianek. Wymienione modyfikacje dotyczą w głównej mierze zewnętrznego składnika ścianki grzbietowej tzw. wrinkle-layer, położonego bezpośrednio na peryostrakum poprzedniego skrętu. Strefa zmarszczek (wrinkle-layer) znana była początkowo jedynie u amonoidów paleozoicznych, dopiero Senior (1971) i Kulicki (1979) odnotowali jej występowanie u amonoidów mezozoicznych. Na podstawie przebadanego materiału obejmującego 12 rodzajów należących do pięciu podrzędów Ammonoidea i występujących od późnego paleozoiku do późnej kredy nie stwierdzono występowania strefy zmarszczek poza ścianką grzbietową. Podobne suuktury, obserwowane u paleozoicznych amonoidów w ściankach bocznej i brzusznej nosza nazwę „Ritzstreifen” i nie są homologiczne do zmarszczek „wrinkle-layer”. Typowa zmarszczka „wrinkle-layer” w przekroju podłuznym zbudowana jest z elementu centralnego, organicznego lub organo-mineralnego, oraz pryzmatycznych warstewek, w których długie osie pryzm są prostopadłe do boków trójkąta skierowanych do wnętrza komory mieszkalnej. Obok typowych elementów strefy zmarszczek, opisano tzw. elementy dwurożne o zarysie okrągłym, lub owalnym u triasowych rodzajów Subolenekites i Sibirites, a także u wczesnokredowego Aconeceras. Te elementy były błędnie interpretowane (Doguzhaeva & Mutvei 1986) jako pory związane z przyczepami miękkich tkanek płaszcza do muszli. Typowa strefa zmarszczek wytwarzana przez fałd nadgłowowy płaszcza, została stwierdzona we wszystkich badanych podrzędach za wyjątkiem Phylloceratina. W wymienionym rzędzie opisano powszechnie występujące rytmiczne modyfikacje peryostrakum wbudowywane do ścianki grzbietowej. We wczesnych stadiach rozwojowych modyfikacje te mogą przypominać elementy strefy zmarszczek, lecz ich pochodzenie i budowa są różne

Piggyback whorls: A new theoretical morphologic model reveals constructional linkages among morphological characters in ammonoids

A new theoretical morphological model is proposed for the analysis of growth, form and morphospace of ammonoid shells. In this model, the shape of a radial cross section through the shell is simulated by “piggybacking” of successive whorls. The “piggyback whorls model” is defined in terms of the enlarging rate of the perimeter and the proportion of the dorsal wall to the whorl periphery, if an isometric relationship is assumed between perimeter and area of the cross−sectioned whorl. Allometric coefficients on these growth parameters determine how compressed and evolute shells are formed. The present model successfully reproduced some correlations among purely geometric variables that have been reported in previous works and were also observed in our biometric analyses. This model yields a hypothesis of “constructional linkages” between aperture shape and coiling geometry that might provide a functional coupling between hydrostatic and hydrodynamic characters. The model may partly explain Buckman’s Law of Covariation between rib features and shell shapes

Modern Nautilus (Cephalopoda) taphonomy in a subtidal to backshore environment, Lifou (Loyalty Islands)

Thirty-two samples of submerged Nautilus macromphalus shells were recovered in 2008 from Lifou, Loyalty Islands in the South Pacific Ocean. Specimens were collected from carbonate-dominated sediment in water depths of 1-3 m. Some specimens were partly buried, whereas others rested on the seafloor. The majority of the specimens (66%) were recovered in a horizontal position, whereas 34% of the specimens were oriented vertically. Some specimens were pristine, with sharp color stripes and little encrustation by algae, cyanobacteria, or epizoans. The majority of specimens have substantial algal and cyanobacterial overcoats with some epizoans. In some specimens, the overcoats also trapped substantial amounts of carbonate sediment. Comparison of the 2008 collection of subtidal specimens to 43 beached Nautilus shells collected in 2002 from the same location reveals that the nearshore taphonomic pathways for drift cephalopod shells can be more complicated than published theoretical models suggest. Nautilus shells may or may not float directly to the beach. Shells not immediately deposited on the beach sink in the shallow water in a vertical position. Weight added by attached organisms and water infiltration, causes the submerged shells to eventually assume a horizontal position. Waves, currents, and bioturbation can then flip the shells over from side to side. Eventually submerged shells are buried, broken apart, or transported onto the beach. Beached shells that follow this taphonomic pathway have conspicuous algal coatings compared to those that simply float to shore. The Lifou subtidal population represents the first substantial modern externally shelled cephalopod collection from a shallow water environment to be analyzed to determine its taphonomic pathways. Conclusions from this analysis can be applied to nearshore deposits that contain externally shelled, fossilized cephalopods

Exceptional cameral deposits in a sublethally injured Carboniferous orthoconic nautiloid from the Buckhorn Asphalt Lagerstätte in Oklahoma, USA

The cameral and intrasiphonal deposits of a Pennsylvanian straight nautiloid (Pseudorthoceratidae) are studied in order to understand the formation of these deposits. The specimens from the Buckhorn Asphalt deposit (Oklahoma) are exceptionally preserved including original aragonite and microstructures. The specimen investigated survived a predation attempt and shows bite marks on the phragmocone. This is the second report of an ectocochleate cephalopod and first report of an orthoconic nautiloid which survived massive damage of conch and siphuncle. For the first time, a high-magnesium calcitic (HMC) mineralogy of cameral deposits is documented. These deposits were formed in alternation with aragonite in a chamber which was perforated during the unsuccessful predation attempt. The animal formed the chamber deposits throughout its entire lifetime and the siphuncle played a major role in formation of the cameral deposits