Borings in trepostome bryozoans from the Ordovician of Estonia: two ichnogenera produced by a single maker, a case of host morphology control

Abstract

Key, M.M., Jr. 2007: Borings in trepostome bryozoans from the Ordovician of Estonia: two ichnogenera produced by a single maker, a case of host morphology control. Lethaia , Vol. 40, The evolution of borings has shown that the morphology of borings is a function of both the borer and its substrate. This study investigated the effect of bryozoan internal skeletal morphology on the dimensions and distribution of borings. One hundred and forty-three trepostome colonies from the Middle and Upper Ordovician strata of northern Estonia were examined. Of these, 80% were matrix entombed, longitudinally sectioned ramose and hemispherical colonies, and 20% were matrix-free hemispherical colonies that allowed examination of the colony surfaces. Seventy-one percent of the ramose colonies were bored, whereas 88% of the hemispherical colonies were bored. On average, only 8% of colony surface areas were bored out. Borings were more randomly oriented in the hemispherical colonies. In contrast in the ramose colonies, the borings tended to more restricted to the thin-walled endozone and thus parallel to the branch axis. This is interpreted to be a function of the thick-walled exozones controlling to some extent where the borer could bore. Based on morphology, the borings in the hemispherical colonies are referred to Trypanites and those in the ramose colonies to Sanctum . Sanctum is revised to include two possible openings and to recognize that boring shapes were inherently constrained by the thick-walled exozones of the host bryozoan colonies. Both trace fossils were probably produced by a boring polychaete that used the tubes as domiciles. ᮀ Estonia, Ichnotaxa, Ordovician, Sanctum, trace fossils, Trypanites. Patrick N. Wyse Jackson [wysjcknp@tcd.ie],

Symbiotic interactions in the Ordovician of Baltica

“…The 'worms' may have acquired protection from predators by this embedment in a massive skeleton (Vinn et al, 2014b). The 'worms' may have had negative effect on the bryozoan colony by competing with it for nutrients (Wyse Jackson and Key, 2007; see also Ernst et al, 2014).…”

“…Soft-bodied 'worms' (as inferred in the trace fossil Sanctum) sometimes bored into living bryozoan colonies, which is indicated by skeletal tissue repair (Wyse Jackson and Key, 2007). The 'worms' may have acquired protection from predators by this embedment in a massive skeleton (Vinn et al, 2014b).…”

“…Associations with bryozoans were most common (40% of associations). Bryozoans hosted the most diverse fauna of endobiotic symbionts; these symbionts were all non-colonial (Anoigmaichnus, Sanctum, 'Hicetes', and Conularia; Männil, 1959;Wyse Jackson and Key, 2007;Vinn et al, 2014b). Some bryozoans were epibionts themselves on living crinoid stems.…”

SHORT COMMUNICATION: First record of the trace fossilOikobesalonfrom the Ordovician (Darriwilian) of Baltica

“…Previously only amphora-shaped traces of Amphorichnus Männil, 1966 and conical traces of Conichnus Männil, 1966 have been described from the Darriwilian and Sandbian of Estonia (Männil 1966). The record of hard substrate trace fossils is much more complete, comprising Trypanites borings in brachiopods (Vinn 2005) and bryozoans (Wyse Jackson & Key 2007). Recently bioclaustrations have also been described from the Ordovician of Estonia (Vinn & Mõtus 2012).…”

First description of rare Teichichnus burrows from carbonate rocks of the Lower Paleozoic of Estonia

“…Recently, several traces have been described from the Ordovician and Silurian limestones of western and northern Estonia (VINN & WILSON, 2013;VINN & TOOM, 2015, 2015VINN et al, 2014VINN et al, , 2015c. Bioerosional trace fossils (ORVIKU, 1960(ORVIKU, , 1961DRO-NOV et al, 2000;WYSE JACKSON & KEY, 2007;VINN et al, 2015b) and various bioclaustrations (VINN et al, 2015a) have the best record among trace fossils in the Ordovician and Silurian of Estonia. Soft bottom trace fossils of the Ordovician and Silurian of Estonia deserve to be studied in more detail in order to use their full potential as paleoenvironmental indicators.…”