Ediacaran Relative of Bryozoans and Brachiopods Found

Ediacaran skeletal metazoan interpreted as a lophophorate

Authors:

Zhuravlev et al

Abstract:

While many skeletal biomineralized genera are described from Ediacaran (635–541 million years ago, Ma) strata, none have been suggested to have an affinity above the Porifera–Cnidaria metazoan grade. Here, we reinterpret the widespread terminal Ediacaran (approx. 550–541 Ma) sessile goblet-shaped Namacalathus as a triploblastic eumetazoan. Namacalathus has a stalked cup with radially symmetrical cross section, multiple lateral lumens and a central opening. We show that the skeleton of Namacalathus is composed of a calcareous foliated ultrastructure displaying regular concordant columnar inflections, with a possible inner organic-rich layer. These features point to an accretionary growth style of the skeleton and an affinity with the Lophotrochozoa, more specifically within the Lophophorata (Brachiopoda and Bryozoa). Additionally, we present evidence for asexual reproduction as expressed by regular budding in a bilateral pattern. The interpretation of Namacalathus as an Ediacaran total group lophophorate is consistent with an early radiation of the Lophophorata, as known early Cambrian representatives were sessile, mostly stalked forms, and in addition, the oldest known calcareous Brachiopoda (early Cambrian Obolellida) and Bryozoa (Ordovician Stenolaemata) possessed foliated ultrastructures.

Giant Bryozoan Reef Mounds From Eocene Paleogene Australia

Giant middle Eocene bryozoan reef mounds in the Great Australian Bight

Authors:

Sharpies et al

Abstract:

This paper reports the discovery of extensive middle Eocene bryozoan reef complexes along the paleoshelf edge of the Great Australian Bight (GAB). The complexes form the earliest carbonate deposit in the GAB, which is the largest Cenozoic cool-water carbonate province on Earth. The bryozoan reef mounds, previously misidentified as volcanic bodies, were deposited parallel to the shelf margin for more than 500 km along strike. Individual reef mound complexes are 60–150 km long, as wide as 15 km, and as thick as 200 m, and dwarf all previously described examples. Superimposed on the distal margin of an underlying Paleocene to mid-Eocene siliciclastic delta complex, the reef mounds provide a critical insight into changing paleoenvironments of the Australo-Antarctic Gulf ca. 43 Ma, coinciding with global and continent-wide climatic and tectonic events. The rapid growth and demise of reef mound-building bryozoans raises new questions regarding the interplay of Southern Ocean opening, ocean currents, and biosphere interactions.

Tales from the KT Boundary: Dead Clades Walking?

Survival, but…! New Tales of ‘Dead Clade Walking’ from Austral and Boreal Post-K–T Assemblages

1. J Stillwell (a,*)
2. E Håkansson


a. Applied Palaeontology and Basin Studies Group, School of Geosciences, Monash University, Clayton, Vic 3800, Australia Centre for Evolutionary


*. Author to contact: Jeffrey.Stilwell@sci.monash.edu.au

Abstract:

Our knowledge of postmass extinction biotic trajectories is at the mercy of available data and detailed research on the governing factors of differential extinction/survivorship patterns of fossil biotas. Some taxa managed—barely—to survive major extinction events, but only for the short-term, becoming extinct at variable times in the following geologic stage, having succumbed to myriad natural forces generated by severe paleoenvironmental perturbations. These ‘Dead Clade Walking’ (DCW) organisms should be included in investigations on the resultant effects of the extinction bottleneck and subsequent rebound phase(s). Significantly, even though the ‘big five’ mass extinctions of the Phanerozoic are distinguished primarily by their overwhelming intensities, their magnitudes—and thus importance for shaping the present-day biosphere—have been systematically underestimated, when time frames including immediate, post-apocalyptic DCW taxa are included in survivorship/extinction analyses. Our research from recent studies of Austral and Boreal invertebrates and vertebrates in relation to the Cretaceous–Tertiary (K–T) boundary provides alluring new evidence of the DCW phenomenon, including the short-term survivorship of ammonoid cephalopods and possible non-avian dinosaurs into the dawn of the Cenozoic.

Link. Cenozoic dinosaurs live on.