Dianulites(Trepostomata, Bryozoa) from the Early Ordovician of Severnaya Zemlya, Arctic Russia

Abstract

Trepostome bryozoan Dianulites borealis Astrova, 1965, the earliest known member of this genus, has been identified from the Early Ordovician of Severnaya Zemlya, Arctic Russia. This species developed hemispherical colonies which indicate that it lived on a relatively soft substrate with moderately low rates of sedimentation and erosion. The new record from Severnaya Zemlya expands the palaeogeographical distribution of Dianulites, known before from the Early Ordovician of Novaya Zemlya, Arctic Russia.

Fossil evidence unveils an early Cambrian origin for Bryozoa

“…The miniaturized body-plan, much thinner, unmineralized cuticles (compared to arthropods and ‘worms’) and hard substrate habitat of early bryozoans such as P. gatehousei explain the poor fossil record and cryptic history of bryozoan stem taxa in the Cambrian 11 , 14 , 28 . However, the rapid diversification of the Bryozoa 6 , 7 , 30 during the Ordovician probably coincides with calcite seas 5 , increasing hardground development and more robust biomineralization, leading to increased bryozoan colony size (centimetre to decimetre scale) and enhancing fossilization potential 4 , 5 , 8 , 11 , 20 . Thus, the recognized sequence of appearance for bryozoan taxa over geological time probably does not fully convey the real evolutionary history and may not provide a comprehensive understanding of bryozoan phylogeny 2 , 7 .…”

“…Bryozoans (also known as ectoprocts or moss animals) are aquatic, dominantly sessile, filter-feeding lophophorates that construct an organic or calcareous modular colonial (clonal) exoskeleton [1][2][3] . The presence of six major orders of bryozoans with advanced polymorphisms in lower Ordovician rocks strongly suggests a Cambrian origin for the largest and most diverse lophophorate phylum 2,[4][5][6][7][8] . However, a lack of convincing bryozoan fossils from the Cambrian period has hampered resolution of the true origins and character assembly of the earliest members of the group.…”

The oldest known bryozoan: Prophyllodictya (Cryptostomata) from the lower Tremadocian (Lower Ordovician) of Liujiachang, south‐western Hubei, central China

“…; Gorjunova and Koromyslova ; Koromyslova ; Ernst et al . ). All of these colony forms may have been derived from an unmineralized, ctenostome‐grade bryozoan with a simple, uniserial, encrusting colony form (Taylor and Ernst ; Taylor et al .…”

Chapter 12 A review of the Early Palaeozoic biogeography of bryozoans

“…The oldest known unequivocal bryozoans are of Late Tremadoc age from China (Hu & Spjeldnaes 1991;Xia et al 2007;Zhang et al 2009;Cuffey et al 2012) and Severnaya and Novaya Zemlya (Astrova 1965;Ernst et al 2013). They are not known from any other location at this time.…”