Jakub Witkowski

Life in a temperate Polar sea: a unique taphonomic window on the structure of a Late Cretaceous Arctic marine ecosystem

As the earth faces a warming climate, the rock record reminds us that comparable climatic scenarios have occurred before. In the Late Cretaceous, Arctic marine organisms were not subject to frigid temperatures but still contended with seasonal extremes in photoperiod. Here, we describe an unusual fossil assemblage from Devon Island, Arctic Canada, that offers a snapshot of a ca 75 Myr ago marine palaeoecosystem adapted to such conditions. Thick siliceous biogenic sediments and glaucony sands reveal remarkably persistent high primary productivity along a high-latitude Late Cretaceous coastline. Abundant fossil faeces demonstrate that this planktonic bounty supported benthic invertebrates and large, possibly seasonal, vertebrates in short food chains. These ancient organisms filled trophic roles comparable to those of extant Arctic species, but there were fundamental differences in resource dynamics. Whereas most of the modern Arctic is oligotrophic and structured by resources from melting sea ice, we suggest that forested terrestrial landscapes helped support the ancient marine community through high levels of terrigenous organic input.

A rare double skeleton of the silicoflagellate Corbisema

Silicoflagellates are usually associated with simple skeletons made of a domal latticework of rod-shaped elements, known as the apical structure, which is attached to a polygonal basal ring. Silicoflagellate reproduction is poorly understood (Moestrup & Thomsen, 1990) but they are known to divide mitotically associated with the construction of a double skeleton. Such double skeletons connected at the abapical face of the basal ring are observed from Recent and fossil material. Double skeletons of Dictyocha and Distephanus noted in Cenozoic sediments (Dumitricǎ, 1973, pl. 4, fig. 8; Boney, 1976) show basal rings positioned with their corners in close proximity. Ling & Takahashi (1985, pl. 1, fig. 5) and Takahashi et al . (2009, pl. 2, figs 3, 5) illustrate Distephanus with the spines of the two skeletons in exact alignment with one another. Recent work in a Campanian sequence of strata near Horton River, District of Mackenzie in the Northwest Territories, Canada …

Rutilariaceae redefined: a review of fossil bipolar diatom genera with centrally positioned linking structures, with implications for the origin of pennate diatoms

We present four genera of bipolar centric diatoms with linking structures located on the valve face: Rutilaria (including two new species from the Cretaceous), Spinivinculum, Pseudorutilaria and Kisseleviella, which are commonly classified in the family Rutilariaceae. Functional comparison of their linking structures and modes of chain formation shows considerable diversity and does not support a close phylogenetic relationship among them. In order to reflect the probable phylogeny of this group, the Rutilariaceae is retained as a monotypic family, while Kisseleviella is transferred to the Cymatosiraceae. Rymariopsis gen. nov. is proposed as a possible link between the Hemiaulaceae and the Rutilariaceae. Based on the comparison of the stratigraphic ranges of these taxa with other diatoms, we explore the possibility of a close phylogenetic relationship between bipolar centric diatoms with centrally located linking structures and pennate diatoms, as suggested by recent molecular phylogenies. As a consequence, the Rutilariaceae is suggested as a possible sister taxon of the pennate diatoms.

Two rare silicoflagellate double skeletons of the Star-of-David configuration from the Eocene

Two, rare double skeletons of Corbisema silicoflagellates have been observed from Early and Middle Eocene sediments. Both specimens are in the Star-of-David configuration, with the basal corners of each skeleton aligned with the middle of sibling basal sides. These specimens are of a species that has an elongate basal ring, which shows that skeletons are flipped 180° with respect to one another, rather than simply rotated.

BLOCHIA AND NIKOLAEVIA: NEW CRETACEOUS DIATOM GENERA RELATED TO STELLARIMA HASLE & SIMS

Two new genera of fossil diatoms, Blochia gen. nov. and Nikolaevia gen. nov., are proposed from Kanguk Formation (Upper Cretaceous) outcrops on Devon Island, Canadian Arctic margin. Both genera display morphological features suggesting a relationship with Stellarima Hasle & Sims. Nikolaevia is unusual in having an external opening of the rimoportula in the form of an arcuate canal. Blochia is a genus of large diatoms that are ornamented with spines, and bear a centrally positioned rimoportula with a prominent external tube. Inferred vegetative and resting stages are presented for Nikolaevia symbolica sp. nov., while Blochia magna sp. nov. is considered a resting spore. Observations summarized in the present paper further document the diversity of the Stellarimaceae in one of the oldest available fossil localities providing well-preserved material.

Cenozoic silicoflagellate skeletal morphology: a review and suggested terminology

Silicoflagellate skeletons are made up of siliceous components that interconnect through triple-junctions to form a basket-shaped design made of basal and apical structures. The skeletal framework has a domal shape that can be paired with another to form a double skeleton. For Cenozoic skeletal morphologies, the basal structure consists of a ring of polygonal shape that often includes spines at the basal corners that are directed radially away from the double-skeleton central point, and pikes that point towards the apical axis. The apical structure is made up of elements of less thickness that are connected to the basal ring by struts. The skeletal components of the silicoflagellate conform to a consistently applied set of rules. There is a need to standardize silicoflagellate descriptive terminology in light of recent studies and detailed examination of the elements, spines and pikes that comprise Cenozoic skeletons. Here we review established and recently defined terminology that relates to silicoflagellate skeletons and suggest terminology to standardize future descriptive work.

Generic limits within the Eupodiscaceae: I. Observations on three unusual species of Cerataulus, with reference to the type species, C. turgidus

Scanning electron and light microscope observations are presented of Biddulphia brittoniana Kain & Schultze, B. heteroceros Grunow and B. multicornis Grunow. All these species possess unusual modes of chain formation, including entangling spines and clasping of the external tubes of the rimoportulae. The three species are transferred to Cerataulus Ehrenberg based on their loculate valve structure, rows of areolae with internal foramina and external groups of fine pores interrupted by spinules and locular walls, the presence of ocelli pointing away from the apical axis, and of a sipho marginalis. Observations on C. turgidus (Ehrenberg) Ehrenberg, the type species of this genus, are also provided, and the generic description is emended. Morphological features that separate Cerataulus from Pleurosira (Meneghini) Trevisan, Odontella C. Agardh and Zygoceros Ehrenberg are discussed. The overall good preservation of the materials examined here also provides new insights into the structure of the sipho marginalis.

Typification of Eocene–Oligocene diatom taxa proposed by Grove & Sturt (1886–1887) from the Oamaru Diatomite

The so-called Oamaru Diatomite dates from approximately the Eocene–Oligocene Transition (∼34 million years ago), which is widely regarded as one of the most important climatic events of the entire Cenozoic era due to global cooling and the onset of continental-scale Antarctic glaciations. It also represents one of the richest fossil diatom deposits ever known and was first made famous owing to a series of diatom papers by Grove & Sturt. Based primarily on the collection of Sturt, supplemented by slides mounted by Grove, all curated in The Natural History Museum, we consider all 108 diatom taxa from the Oamaru Diatomite that were proposed in these seminal papers by Grove & Sturt and designate type specimens for 87 taxa that were not typified by previous workers, and for which nomenclatural types could be established. Light photomicrographs of all specimens interpreted as types are presented next to reproductions of the line drawings from Grove & Sturt publications to aid future workers on the Oamaru Diatomite, and on diatom evolution across this critical climatic phase of the Palaeogene period.