Björn Kröger

The Origin and Initial Rise of Pelagic Cephalopods in the Ordovician

Background During the Ordovician the global diversity increased dramatically at family, genus and species levels. Partially the diversification is explained by an increased nutrient, and phytoplankton availability in the open water. Cephalopods are among the top predators of todays open oceans. Their Ordovician occurrences, diversity evolution and abundance pattern potentially provides information on the evolution of the pelagic food chain. Methodology/Principal Findings We reconstructed the cephalopod departure from originally exclusively neritic habitats into the pelagic zone by the compilation of occurrence data in offshore paleoenvironments from the Paleobiology Database, and from own data, by evidence of the functional morphology, and the taphonomy of selected cephalopod faunas. The occurrence data show, that cephalopod associations in offshore depositional settings and black shales are characterized by a specific composition, often dominated by orthocerids and lituitids. The siphuncle and conch form of these cephalopods indicate a dominant lifestyle as pelagic, vertical migrants. The frequency distribution of conch sizes and the pattern of epibionts indicate an autochthonous origin of the majority of orthocerid and lituitid shells. The consistent concentration of these cephalopods in deep subtidal sediments, starting from the middle Tremadocian indicates the occupation of the pelagic zone early in the Early Ordovician and a subsequent diversification which peaked during the Darriwilian. Conclusions/Significance The exploitation of the pelagic realm started synchronously in several independent invertebrate clades during the latest Cambrian to Middle Ordovician. The initial rise and diversification of pelagic cephalopods during the Early and Middle Ordovician indicates the establishment of a pelagic food chain sustainable enough for the development of a diverse fauna of large predators. The earliest pelagic cephalopods were slowly swimming vertical migrants. The appearance and early diversification of pelagic cephalopods is interpreted as a consequence of the increased food availability in the open water since the latest Cambrian.

On the origin of bactritoids (Cephalopoda)

There is a high probability that bactritoids represent a paraphylum or polyphylum. The initial chambers or protoconchs of the Early-Middle DevonianBactritesSandberger,DevonobactritesShimansky, andLobobactrites Schindewolf are elongated spheres with a diameter of 0.3–1.0 mm. The initial chambers are larger in diameter than the slender, smooth shaft located adorally to the initial chamber. Similar apices occur in a number of Late Silurian sphaerorthoceridans with central siphuncles. Sphaerorthoceridans with a bactritoid-like apex and an eccentric siphuncle are known from the Early Devonian. The earliest questionableBactrites occurs in the Pragian (middle Early Devonian). By Emsian time bactritoids are common elements of cephalopod faunas.Bactrites-like orthocones of the Middle Ordovician and Late Silurian are homeomorphs with clearly different early growth stages. Thus, the time interval between the first appearance ofBactrites and the origin of ammonoids can be narrowed down to the Pragian to Early Emsian. The placement of the siphuncle in a ventral marginal position has been used as one of the critical morphologic features in defining the bactritoids. However, the displacement of the siphuncle from subcentral or eccentric positions toward the conch margin occurred at least three times during the Ordovician — Early Devonian evolution of the Orthocerida. Thus, there is a high probability that a marginal shift of the orthocerid siphuncle occurred in post-Emsian times, too.KurzfassungDie Bactritida bilden mit hoher Wahrscheinlichkeit ein Para- oder Polyphylum. Die Anfangskammern oder Protoconche der Unter-Mitteldevonischen GattungenBactritesSandberger,DevonobactritesShimansky, undLobobactritesSchindewolf sind länglich sphäroidal mit einem Durchmesser von 0.3–1.0 mm. Die Anfangskammern haben einen größeren Durchmesser als der unmittelbar folgende, glatte, juvenile Gehäuseschaft. Ähnliche Apizes kommen in einer Reihe obersilurischer Sphaerorthoceriden vor, welche einen zentralen Sipho besitzen. Sphaerorthoceriden mit einem Bactriten-ähnlichen Apex und einem exzentrischen Sipho sind aus dem Unterdevon bekannt. Der älteste fraglicheBactrites kommt aus dem Pragium (mittleres Unterdevon). Während des Emsiums sind Bactriten bereits ein häufiges Element der Cephalopodenfauna.Bactrites-ähnliche Orthokone des Mittleren Ordoviziums und des Obersilurs sind Homöomorphe mit vonBactrites deutlich verschiedenen frühen Wachstumsstadien. Daher kann das Zeitintervall vom ersten Erscheinen der Bactriten bis zum ersten Erscheinen der Ammonoideen auf Pragium bis frühestes Emsium eingegrenzt werden. Die Verschiebung des Siphos zum Schalenrand wurde in der Vergangenheit als kritisches Merkmal herangezogen, um die Bactriten zu definieren. Es kann jedoch gezeigt werden, dass bei Orthoceriden eine Sipho Verschiebung vom Gehäusezentrum zum Schalenrand wenigstens dreimal im Zeitraum Ordovizium — Unterdevon stattfand. Es ist daher wahrscheinlich, dass eine Randverschiebung des orthoceriden Siphos auch im jüngeren Paläozoikum wiederholt stattfand.

Early growth-stages and classification of orthoceridan Cephalopods of the Darriwillian (Middle Ordovician) of Baltoscandia

Five apices of orthoceridan cephalopods from the early Middle Ordovician Holen Limestone of Oland, Sweden that where collected in the late 19th Century by G. Holm provide information on cephalopod evolution in the early Palaeozoic. The apices belong to specimens of the genus Hedstroemoceras Foerste, 1930 and Archigeisonoceras Chen, 1984. The apices are small in comparison with apices of other cephalopods of the Ordovician; the initial chambers of the shells of both genera are hemispherical and approximately 1 mm and 1.5 mm in cross-section diameter, respectively. The apical 2–3 mm of the shell are free from growth-lines and possess no cicatrix, though distinct longitudinal wrinkles are present. There is a slight variability of siphuncle position during early growth in Archigeisonoceras. It can be shown that the structure of the connecting ring of Hedstroemoceras is similar to that of other Orthocerida. Additionally, the hemispherical apex of Lituites perfectus Wahlenberg, 1821 gives evidence for the orthoceridan affinity of lituitidans. The investigation shows that early Middle Ordovician Orthocerida display a characteristic connecting ring structure, a characteristic apex morphology and variable siphuncular positions that differs significantly from other cephalopods of the Ordovician. Based on this evidence it is concluded that a small spherical apex is an autapomorphy of the Orthocerida. Moreover, this evidence supports a splitting of the order Orthocerida in two taxa of different affinities. The Orthocerida sensu stricto comprises orthocones with a tubular siphuncle nearly without endospiphuncular deposits, and a spherical apex. Embryonic shell, orthoceridan ancestry, orthoceridan classification.

Onset of the Ordovician cephalopod radiation – evidence from the Rochdale Formation (middle Early Ordovician, Stairsian) in eastern New York

The Rochdale Formation of eastern New York (= Fort Ann and lower Bascom formations, designations abandoned) is now recognized to record the earliest stages of the Great Ordovician Radiation of cephalopods. The earliest Bassleroceratidae, Tarphyceratidae and endoceridans on the east Laurentian shallow carbonate platform occur in the upper, thrombolite-bearing member of the Rochdale. This fauna demonstrates that the earliest radiation of Ordovician nautiloids took place in the late Tremadocian and is best recorded in tropical platform facies. Revision of this cephalopod fauna based on approximately 190 specimens collected along a 200 km, N–S belt in easternmost New York has provided new information on inter- and intraspecific variation of earlier described species. The ellesmerocerid Vassaroceras and the endocerids Mcqueenoceras and Paraendoceras are emended. New taxa include Bassleroceras champlainense sp. nov. and B. triangulum sp. nov., Mccluskiceras comstockense gen. et sp. nov., Exoclitendoceras rochdalense gen. et sp. nov. and Paraendoceras depressum sp. nov. A rank abundance plot of 146 specimens from a locality in the Lake Champlain lowlands provides information on the community structure of a nautiloid fauna in which the longiconic cyrtoconic Bassleroceras is shown to dominate strongly. The nautiloid community structure of the Rochdale Formation is similar to that of the underlying Tribes Hill Formation (late early Tremadocian) with respect to the depositional setting, diversity and evenness but displays a remarkably increased taxonomic distinctness.

The Oldest Cephalopods from East Laurentia

Cambrian cephalopods are presently reported only from tropical, carbonate platform successions that occur on a number of paleocontinents. Outside of West Gondwanan occurrences on the eastern Sino–Korean Platform in China, the record of Cambrian cephalopods is limited, and information on the early evolution and habitats of this molluscan class has grown slowly over the last century.nnPlectronoceras Ulrich and Foerste, 1933, from the Yenchou Member of the Fengshan Formation in Shantung Province and southern Manchuria, northeast China, was the first cephalopod described from the Upper Cambrian (Walcott, 1905; Kobayashi, 1935; see Mutvei et al., 2007). The occurrence of Plectronoceras with Tsinania-Ptychaspis Zone trilobites indicates a middle Late Cambrian age and means that it is generally regarded as the oldest known cephalopod (Chen and Teichert, 1983; Teichert, 1988). By contrast, a large number of named taxa (40 genera, 150 species) represented by brevicones, longicones, and straight to strongly cyrtoconic conchs are found in higher strata of the upper Fengshan Formation in east-central China (Chen and Teichert, 1983). Teichert (1988) regarded the upper Fengshan assemblage as showing a Late Cambrian “radiation” of cephalopods. These cephalopod-bearing strata include the upper 7–8 m of the Wanwankou Member of the Fengshan Formation in northern Anhui and Jiangsu Provinces and the Jiagou and Suxian Members of the Fengshan in southern Anhui (Chen et al., 1979a,b; Chen and Teichert, 1983, Lu and Lin, 1984; Mutvei et al., 2007). Further south in east-central China, approximately coeval cephalopods occur 4–7 m below the top of the Siyangshan Formation in western Zhejiang Province and define an Acaroceras-Antacaroceras Zone (Li, 1983). Although the high diversity Fengshan assemblage was considered lowest Ordovician in some older reviews (e.g., Flower, 1954, 1964; Yochelson et al., 1973, fig. 1), associated conodonts from the Wanwankou …

Cephalopods and Paleoenvironments of the Fort Cassin Formation (Upper Lower Ordovician), Eastern New York and Adjacent Vermont

Abstract The dramatic late Early Ordovician radiation of cephalopods on tropical paleocontinents is illustrated by the diverse fauna (21 genera, 30 species) of the Fort Cassin Formation (Floian and lower Blackhillsian Stage) in northeast Laurentia. Cephalopods occur through the thin (ca. 30–65 m) depositional sequence of the Fort Cassin but are most common and diverse in mollusk-rich, trilobite-poor parts of the formation that characterize the thrombolite-bearing intervals in the shoaling part of the highstand systems tract. This lithofacies-biofacies linkage persists from the Tribes Hill and Rochdale Formations (lower and lower upper Tremadocian, and upper Skullrockian and Stairsian Stages, respectively), and suggests that the Early Ordovician radiations of cephalopods took place in shallow-marine, thrombolite reef facies of tropical carbonate platforms. These habitats differed strongly from the near-shore, peritidal habitats of the older Cambrian evolutionary radiation. Genus-level diversity and absolute abundance changed little through the Skullrockian–Blackhillsian, but morphologic diversity and body size increased dramatically by the late Early Ordovician. The morphological diversification suggests cephalopods diversified into a wider variety of macropredators and more complex late Early Ordovician ecosystems. Anrangeroceras whitehallense n. gen. and n. sp. is proposed. The following are emended: the Protocycloceratidae, Centrotarphyceras and C. seelyi, Protocycloceras and P. lamarcki, and Rudolfoceras cornuoryx. The following are indeterminate and abandoned: Baltoceras? pusillum Ruedemann, 1906; Cameroceras annuliferum Flower, 1941; Cyptendoceras whitfieldi Ulrich et al., 1944; Endoceras? champlainense Ruedemann, 1906; Wolungoceras valcourense Flower, 1964. Beekmanoceras Ulrich and Foerste, 1936 is a gastropod.

THE EARLIEST ORDOVICIAN CEPHALOPODS OF EASTERN LAURENTIA— ELLESMEROCERIDS OF THE TRIBES HILL FORMATION, EASTERN NEW YORK

Abstract The Tribes Hill Formation (upper Skullrockian) of New York records the earliest Ordovician diversification of cephalopods, in particular ellesmerocerids, on the east Laurentian, shallow carbonate platform. Revision of this cephalopod fauna on the basis of approximately 430 specimens collected across eastern New York has led to new information on inter- and intraspecific variation of the taxa and extensive synonymization of species-level taxa. The Ellesmeroceratidae and Protocycloceratidae, Ellesmeroceras, and Eremoceras are emended, Eorudolfoceras n. gen. and Dakeoceras champlainense n. sp. are erected. A rank abundance plot of the 342 specimens at a locality in the Lake Champlain lowlands provides information on the community structure of the nautiloid fauna, where small orthoconic taxa are shown to dominate strongly. The small orthocone Ectenolites was the most common genus in terms of total occurrences, was the most paleogeographically widespread genus, and was the only genus to cross the Cambrian–Ordovician boundary.

Tribes Hill–Rochdale formations in east Laurentia: proxies for Early Ordovician (Tremadocian) eustasy on a tropical passive margin (New York and west Vermont)

Slow subsidence and tectonic quiescence along the New York Promontory margin of Laurentia mean that the carbonate-dominated Tribes Hill and overlying Rochdale formations serve as proxies for the magnitude and timing of Tremadocian eustatic changes. Both formations are unconformity-bound, deepening–shoaling, depositional sequences that double in thickness from the craton into the parautochthonous, western Appalachian Mountains. A consistent, ‘layer cake’ succession of member-level units of the formations persists through this region. The Tribes Hill Formation (late early Tremadocian, late Skullrockian, late Fauna B– Rossodus manitouensis Chron) unconformably overlies the terminal Cambrian Little Falls Formation as the lowest Ordovician unit on the New York Promontory. It was deposited during the strong early Tremadocian, or Stonehenge, transgression that inundated Laurentia, brought dysoxic/anoxic (d/a) slope water onto the shelf and led to deposition of the Schaghticoke d/a interval (black mudstone and ‘ribbon limestone’) on the Laurentian continental slope. The uniform lithofacies succession of the Tribes Hill includes a lower sand-rich member; a middle, dark grey to black mudstone that records d/a in eastern exposures; and an upper, shoaling-up carbonate highstand facies. A widespread (12000+ km 2 ) thrombolitic interval in the highstand carbonate suggests the New York Promontory was rimmed by thrombolites during deposition of the Tribes Hill. Offlap and erosion of the Tribes Hill was followed by the relatively feeble sea-level rise of the Rochdale transgression (new) in Laurentia, and deposition of the Rochdale Formation. The Rochdale transgression, correlated with the Kierograptus Drowning Interval in Baltica, marks a eustatic rise. The Rochdale Formation represents a short Early Ordovician interval (early late Tremadocian, middle–late Stairsian, Macerodus dianae Chron). It correlates with a depositional sequence that forms the middle Boat Harbour Formation in west Newfoundland and with the Rte 299 d/a interval on the east Laurentian slope. The Rochdale has a lower carbonate with abundant quartz silt (Comstock Member, new) and an upper, thrombolitic (Hawk Member, new) high-stand facies. Tribes Hill and Rochdale faunas are mollusc-rich, generally trilobite-poor, and have low diversity, Laurentian faunal province conodonts. Ulrichodina rutnika Landing n. sp. is rare in Rochdale conodont assemblages. Trilobites are also low in diversity, but locally form coquinas in the middle Tribes Hill. The poorly preserved Rochdale trilobites include the bathyurid Randaynia , at least two hystricurid species and Leiostegium .

Left behind – delayed extinction and a relict trilobite fauna in the Cambrian–Ordovician boundary succession (east Laurentian platform, New York)

Two completely dissimilar faunal changes occur between the Sunwaptan and Skullrockiann Stages (Ptychaspid and Symphysurid ‘Biomeres’) in the uppermostn Cambrian on the east Laurentian craton. An undolomitized section in the Little Fallsn Formation in Washington County, New York, shows a typical ‘biomere’n extinction, with highest Sunwaptan trilobites followed by the abrupt appearance ofn Cordylodus proavus Zone conodonts and the lowest post-extinctionn trilobites ( Parakoldinioidia Endo) 5.0 m higher. This stage boundaryn interval is very condensed by comparison with coeval Great Basin and Texas sections.n Approximately 70 km southwest, typical pre-extinction taxa (the catillicephalidn Acheilops Ulrich and several dikelocephalid species) are shown for then first time to persist well beyond the extinction as they occur with middle C.n proavus Zone conodonts ( Clavohamulus elongatus or, moren likely, Hirsutodontus simplex Subzone). The Ritchie Limestone member ofn the uppermost Little Falls Formation yields a succession of conodont faunas that spans then C. elongatus – H.n simplex – Clavohamulus hintzei Subzonesn (middle–upper C. proavus Zone). These data prove that then trilobites are a relict fauna that persisted into the Symphysurina Zonen of the Skullrockian Stage. The massive (burrow-churned), mollusc-dominated Ritchien Limestone, with the second Upper Cambrian cephalopod locality in east Laurentia,n represents an inner-shelf refugium for Sunwaptan trilobites that has not been previouslyn encountered. Final extinction of typical Sunwaptan clades is at least locally diachronous,n and a simple, genus-based approach to trilobite biostratigraphy in then Cambrian–Ordovician boundary interval is untenable. The relict fauna appears ton be distinct at the species level, so it is likely that a viable, species-basedn biostratigraphy can be developed. Teridontus gallicus Serpagli etn al . 2008 is a synonym of T. nakamurai (Nogami, 1967), andn T. ? francisi Landing sp. nov., with a large base andn tiny cusp, is a lower C. proavus Zone form. New trilobites aren Acheilops olbermanni Westrop sp. nov. and Parakoldinioidian maddowae Westrop sp. nov. The lowest Ordovician ‘Gailorn Dolomite’ is a junior synonym of the Tribes Hill Formation, and the Ritchien Limestone is assigned to the top of the terminal Cambrian Little Falls Formation.

CARBONIFEROUS ACTINOCERATOID NAUTILOIDEA (CEPHALOPODA)— A NEW PERSPECTIVE

Abstract New material from the Late Mississippian Fayetteville and Caney Formations of the south-central USA supports the taxonomic revision of the Mississippian actinoceroid cephalopods. New representatives of the previously poorly known Rayonnoceras solidiforme, Campyloceras striatulum, and Campyloceras imoense are described. Carbactinoceras procerum new species and Elmoceras graffhami new genus and species are described, and the genus Campyloceras is emended. Character evaluation suggests the shape of the endosiphuncular deposits in the Actinoceratida and Pseudactinocerida are homoplastic because similar patterns of endosiphuncular deposits occur in distantly related nautiloid clades. Apex shape, however, is shown to have previously unrecognized potential for taxon discrimination. Cladistic analysis of 13 actinoceroid and pseudorthocerid nautiloids supports the splitting of the Orthocerida and the creation of a sister group to the Actinoceratida which is identical with the largely neglected Pseudorthocerida.