Abstract
The Recent planktonic larvae of the polychaete spionids are some of the most widespread and abundant group of coastal meroplankton worldwide. To study the possible co-migration of biotic partners and determine whether they were host-specific, the type of biotic relationship between hosts and borers of an Upper Ordovician Peruvian brachiopod collection from the Proto-Andean margin of Gondwana was re-exanimated and compared with material from Wales (Avalonia). The species list studied is composed of Colaptomena expansa (41%), Heterorthis retrorsistria (24%), Horderleyella chacaltanai (19%), Drabovinella minuscula (13%), and Dinorthis cf. flabellulum (3%) and coincides closely with that of the Dinorthis community described in the Caradoc series of North Wales. The borings attributed to these spionids have been identified as Palaeosabella prisca only present in the valves of Colaptomena expansa and Heterorthis retrorsistria. All the studied valves are disarticulated, with very low fragmentation and are randomly oriented in a context below the fair-weather wave base. The settling larvae would feed on their brachiopod host soft parts at an early stage, being the biotic interaction initially of the parasitic type. Since Palaeosabella borings from Peru and Wales are identical, as well as the species specificity of their producers with their brachiopod hosts, it can be concluded that the same spionid annelid species produced them. The Southern Westerlies current that connected the Proto-Andean margin of Gondwana with Avalonia must have been responsible for transporting the larvae of annelids and brachiopods in what had to be a successful biotic relationship over a great transoceanic distance.
Highlights
The Recent spionid polychaetes are receiving great attention in present oceanographic research due to their boring activities on bivalve and gastropod shells of commercial interest for shellfisheries (Díaz-Díaz and Liñero-Arana, 2009; Skeel, 2009; Diez et al, 2011)
This paper revises the systematic assignment of Vermiforichnus to Palaeosabella, which along with Trypanites, are two of the characteristic ichnogenera of the Ordovician Bioerosion Revolution (OBR; Wilson and Palmer, 2001, 2006)
The traces attributed to these spionids have been identified as Palaeosabella prisca consisting of a long, unbranched, tubular or cylindroclavate macroboring that expand distally as an acute cone
Summary
The Recent spionid polychaetes are receiving great attention in present oceanographic research due to their boring activities on bivalve and gastropod shells of commercial interest for shellfisheries (Díaz-Díaz and Liñero-Arana, 2009; Skeel, 2009; Diez et al, 2011). This paper revises the systematic assignment of Vermiforichnus to Palaeosabella, which along with Trypanites, are two of the characteristic ichnogenera of the Ordovician Bioerosion Revolution (OBR; Wilson and Palmer, 2001, 2006) This event marked the beginning of Phanerozoic diversity for macroborings, which involved a critical ecological change being the first borings that provide secondary niche space for cryptic organisms (Tapanila and Copper, 2002), among others for the annelids. The studied ichnofossils occur about 50 km northwest of Lake Titicaca in the morphotectonic region of the Altiplano (high plains) of the Puno Department, southwestern Peru, belonging to the northern part of the Central Andean Palaeozoic Basin They have been collected at the same fossiliferous locality of Calapuja from where Villas et al (2015; Figure 1) studied several brachiopod assemblages, Vinn and Gutiérrez-Marco (2016; Figure 1) described new cornulitids and Ebbestad and GutiérrezMarco (2000; Figure 1) a new bellerophontoid gastropod. These authors found two brachiopod species known from the British Burrellian Stage of the Caradoc Series, allowing them to indirectly correlate the fossiliferous horizon with the upper Sandbian global stage (Sa2 of Bergström et al, 2009)
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