Barbara Seuss

The Paleozoic evolution of the gastropod larval shell: larval armor and tight coiling as a result of predation-driven heterochronic character displacement

Early and middle Paleozoic gastropod protoconchs generally differ strongly from their corresponding adult morphologies, that is, most known protoconchs are smooth and openly coiled, whereas the majority of adult shells are ornamented and tightly coiled. In contrast, larval and adult shells of late Paleozoic gastropods with planktotrophic larval development (Caenogastropoda, Neritimorpha) commonly resemble each other in shape and principle ornamentation. This is surprising because habitat and mode of life of planktonic larvae and benthic adults differ strongly from each other.

Exceptional cameral deposits in a sublethally injured Carboniferous orthoconic nautiloid from the Buckhorn Asphalt Lagerstatte 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 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.

Bryozoan fauna of the Boggy Formation (Deese Group, Pennsylvanian) of the Buckhorn Asphalt Quarry, Oklahoma, USA

The Middle to Upper Pennsylvanian Buckhorn Asphalt Quarry (Boggy Formation, Deese Group) of Oklahoma, USA, is well known for its exceptionally preserved fauna of marine invertebrates, including conservation of original skeletal aragonite. Here, we describe for the first time the taxonomy of the Buckhorn bryozoans, recognising nine species, two of which are new: Stenophragmidium buckhornensis sp. nov. and Streblotrypa (Streblotrypa) heltzelae sp. nov. Two further species, Stenoporella sp. and Spinofenestella sp., are described in open nomenclature. The other species show relationships to the Pennsylvanian of the USA and Russia. The genera Shishoviclema and Shulgapora are identified for the first time in North America. Superior preservation of the Buckhorn bryozoans allows some new and poorly known skeletal characters to be described. These include nanoperforations, granule bands, mural spines, spinose hemiphragms and transverse fibrous wall fabric. Nanoperforations, found in the skeletal walls of several Buckhorn bryozoan species, are tiny holes around which laminae are deflected, indicating that they are not post-mortem structures. However, it is unclear whether they are features of the bryozoans or have resulted from the presence of microsymbionts. The primary wall layer of the fenestrate Septopora blanda Moore, 1929 is apparently composed of transverse fibrous crystallites, a skeletal fabric previously known only in post-Palaeozoic cyclostomes.

Microbial Bioerosion of Erratic Sub-Fossil Nautilus Shells in a Karstic Cenote (Lifou, Loyalty Islands, New Caledonia)

Abstract In a cenote formed in the limestone karst of Lifou (New Caledonia), more than 35 shells of Nautilus macromphalus were discovered in 35–40 m water depth. Seven shells were recovered and subsamples of two shells were used for a study on microbial bioerosion. Both shells were intensively bioeroded and SEM-analyses revealed a total of six ichnotaxa with a dominance of the cyanobacterial trace Scolecia filosa. Such a low diversity ichnocoenosis and the strong dominance of a single ichnotaxon indicate that the environment in the cenote was hostile for many euendolithic organisms. The unfavourable conditions were caused by (1) restricted water-mass exchange with the open ocean, limiting the chance of larvae being transported into the cenote; (2) intense fluctuations in fresh water influx in the karst system promoting traces of euryhaline euendoliths (Ichnoreticulina elegans, S. filosa, Scolecia serrata); and (3) very limited light availability, allowing the development of traces of organotrophs (S. serrata, Flagrichnus profundus) and the most effective among the photoautotrophs only (I. elegans, S. serrata, and ‘Conchocelis’-stages of bangiacean rhodophytes), indicating deep-euphotic to dysphotic conditions and leading to the observed low ichno-diversity. These results foster the knowledge on the environmental tolerance of microbioerosion trace makers, helping to draw conclusions regarding the characteristics of other extreme (palaeo)environments.

TAPHONOMY OF BACKSHORE VERSUS DEEP-MARINE COLLECTED NAUTILUS MACROMPHALUS CONCHS (NEW CALEDONIA)

Abstract The extant Nautilus nowadays exclusively lives in the Indo-Pacific Ocean along the slopes of coral reefs, mainly in water depths of 300–400 m. It possesses a complex gas-liquid combined system to regulate its buoyancy in the water column. After death this system is lost and the shells become either positively or negatively buoyant and float for some time or respectively sink to the seafloor where taphonomic processes strongly influence the shell’s condition. A major process in taphonomy is bioerosion. We present herein a detailed study of the influence of taphonomic pathways on bioerosion in backshore collected and deep-water dredged Nautilus shells from the New Caledonia region. Some bioerosion of Nautilus shells may take place during life but most occurs after death and deposition of the shell. The ichnocoenosis found in the shells collected in backshore settings indicates that these shells were positively buoyant after the death of the animals and were initially deposited in a nearshore environment (shallow euphotic zone III to deep euphotic zone) before they were transported ashore. Part of the deep-water dredged shells, in contrast, were initially deposited in the deep euphotic to dysphotic zone before being transported into aphotic depths. We demonstrate that bioerosion supports the reconstruction of taphonomic pathways of Nautilus shells and, following an actualistic approach, it can help to reconstruct taphonomic processes and depositional settings for fossil cephalopod shells.

Desmoinesian (Middle Pennsylvanian) Orthocerid Cephalopods from the Buckhorn Asphalt Lagerstätte in Oklahoma, Midcontinent North America

Abstract. Nine longiconic cephalopod species of Desmoinesian (Middle Pennsylvanian; upper Carboniferous) pseudorthoceratid orthocerids are described from the Buckhorn Asphalt Lagerstätte (Boggy Formation) in Southcentral Oklahoma, Midcontinent North America. The fauna consists of Pseudorthoceras knoxense (McChesney), Arbuckleoceras tricamerae (Smith), Bitaunioceras buckhornense (Smith), Cyrtothoracoceras? sp., Dolorthoceras boggyense sp. nov., Smithorthoceras unicamera (Smith), Sueroceras oklahomense (Smith), Sulphurnites taffi sp. nov. and Unklesbayoceras striatulum sp. nov. Bitaunioceras buckhornense represents the first Pennsylvanian and therefore the oldest record of this genus. Arbuckleoceras gen. nov. differs from a comparable genus, Shikhanoceras, in possessing a weak exogastric curvature with a circular cross section of the conch and in lacking a conspicuous inflation at the embryonic shell. Smithorthoceras gen. nov. resembles orthoceratids rather than pseudorthoceratids in characters of camerae and siphuncle; however it refers to the Pseudorthoceratidae by having endosiphuncular deposits. These similarities seem to be the result of convergent evolution. Endosiphuncular deposits in Sulphurnites gen. nov. initiate at apical and adoral junctions between septal neck and connection ring, whose characters are unique for pseudorthoceratids. Unklesbayoceras gen. nov. differs from Mitorthoceras in having the endogastric conch, longer camerae and a less eccentric siphuncle. Taxonomic status of these orthoceratids was uncertain in previous biogeochemical and morphological studies. Sediments in the Buckhorn Asphalt Lagerstätte were deposited in a tropical epeiric sea (the Midcontinent Sea). Small, restricted marine basins, like that in this Oklahoma occurrence, probably provided an orthocerid refuge habitat as indicated by the high diversity and provincialism in comparison with other Middle Pennsylvanian (= Moscovian) faunas in other regions of the world.

The fish assemblage from the Pennsylvanian Buckhorn Asphalt Quarry Lagerstätte (Oklahoma, USA)

A diverse assemblage of fishes (isolated teeth and scales) is reported from the Middle to Upper Pennsylvanian Buckhorn Asphalt Quarry Lagerstätte in Oklahoma, USA. The assemblage includes chondrichthyans such as the bransonelliform Bransonella lingulata, the xenacanthiform Xenacanthus, the symmoriiform Stethacanthus, ctenacanthiforms, an polyacrodontid euselachian, anachronistid neoselachians (Cooleyella amazonensis and C. sp.) and an iniopterygian paraselachian cf. Sibyrhynchidae. Moreover, the assemblage encompasses remains of acanthodians and various actinopterygians and a single specimen of an osteolepiform sarcopterygian. Most of the taxa are cosmopolitan during the Late Palaeozoic. The occurrence of bransonelliform and xenacanthiform species at the same locality is very rare in the Carboniferous. The assemblage yields the first Carboniferous occurrences of a polyacrodontid hybodontoid and an actinopterygian belonging to the Acropholidae. Bransonella lingulata from the Desmoinesian/Moscovian of the Buckhorn Asphalt Quarry in Oklahoma represents the youngest occurrence of this species.KurzfassungDie Ablagerungen des ‚Buckhorn Asphalt Quarry’ (mittleres-oberes Pennsylvanium, Oberkarbon – einer Fossil-Lagerstätte im Süden Oklahomas (USA) – enthalten eine diverse Fischfauna. Unter anderem wurden die Überreste (einzelne Zähne, Schuppen) verschiedenster Chondrichthyes (Bransonella lingulata (bransonelliform), Xenacanthus (xenacanthiform), Stethacanthus (symmoriiform)), sowie ctenacanthiformer Fische gefunden. Zusätzlich konnten Elemente eines polyacrodontiden Euselachii, von anachronistiden Neoselachii (Cooleyella amazonensis and C. sp.), sowie eines Paraselachii (cf. Sibyrhynchidae, Iniopterygii) nachgewiesen werden. Daneben wurden Überreste von Acanthodii und Actinopterygii und ein einzelnes Exemplar eines osteolepiformen Sarcopterygii gefunden. Der überwiegende Teil der Taxa tritt im späten Paläozoikum weltweit in Erscheinung. Ungewöhnlich ist jedoch das Auftreten bransonelliformer und xenacanthiformer Arten am gleichen Ort und in den selben Ablagerungen. Erstmalig im Karbon konnte ein polyacrodontider Hybodontoide sowie ein Strahlenflosser der Familie der Acropholidae nachgewiesen werden. Bransonella lingulata ist der jüngste Vertreter seiner Art.

A CHAETETID SPONGE ASSEMBLAGE FROM THE DESMOINESIAN (UPPER MOSCOVIAN) BUCKHORN ASPHALT QUARRY LAGERSTÄTTE IN OKLAHOMA, USA

The first detailed study on chaetetids from the Buckhorn Asphalt Quarry Lagerstatte is presented. Among the investigated specimens we found two samples (chaetetid specimens 2 and 6) that are different from all others in the quarry. Thin sections of these display a complex fragmentation of these Buckhorn chaetetids. Additionally, one of these samples contains two chaetetid morphotypes growing side by side, thus, in the same paleoenvironment. These specimens differ in their mode of growth (laminar and domical), which suggests that chaetetid growth was most likely influenced by genetic factors rather than by the paleoenvironment. We observed a feature, not hitherto reported as far as we are aware, on the surface of chaetetids; namely a regular clustering of seven tubules surrounding a central tubule. This feature could have had an exhalant function. Mineralogical analyses of the skeleton indicate primary high magnesian-calcite mineralogy, which is in accordance with reports in the literature. Cements precipitated during diagenesis are either calcite or dolomite and, where associated with microbial mats, they may contain a distinct amount of manganese. The comparison of the chaetetid skeletons from the Buckhorn Asphalt Quarry leads to the impression, that they represent various morphotypes or even species. Because of the lack of unique features, we have refrained however, from describing new species.