Topological analysis of graphoglyptid trace fossils, a study of macrobenthic solitary and collective animal behaviors in the deep-sea environment

Abstract

Graphoglyptids are biogenic structures commonly found in deep-sea flysch deposits and occasionally detected on the modern deep-sea floor. They extend principally horizontally and take a variety of geometric patterns, whose functional morphology remains an enigma in ichnology and paleoceanography. Based on published materials from 1850 to 2017 (79 ichnotaxa from 28 ichnogenera of graphoglyptids) and systematic observations of one of the largest deep-sea trace fossil collections in the world, this paper proposes that topological analysis is an important ingredient in the taxonomy and functional interpretation of graphoglyptids. Accordingly, graphoglyptids are classified into line, tree, and net forms by their key topological architecture, and are further attributed to 19 topological prototypes by detailed secondary topological features. Line graphoglyptids are single-connected structures with uniform tunnel width, representing primarily the feeding patterns of solitary animals. Tree graphoglyptids, the most diverse architectural group of graphoglyptids, are ascribed to 11 topological prototypes according to the connectivity features of burrow segments and the number and distributional pattern of the branching points. Net graphoglyptids are subdivided into three topological prototypes on the basis of the connectivity features and/or the regularity of the meshes. Multiconnected net forms are considered as a continuous morphological spectrum with different levels of complexity in the net formation. The various connected components in multiconnected tree and net graphoglyptids generally exhibit small and uniform tunnel diameter in a given structure (suggesting a tiny trace maker[s]). The whole structure shows relatively extensive linear or surface coverage and overall good preservation, indicating sustained processes of burrow construction. It is highly probable that certain multiconnected tree and net graphoglyptids represent some emergent patterns from self-organized collective behaviors of conspecific animals. Graphoglyptids thus provide us with a new perspective on the study of solitary and collective behaviors of macrobenthos in the deep-sea environment.

Were the First Trace Fossils Really Burrows or Could They Have Been Made by Sediment-Displacive Chemosymbiotic Organisms?

“…Recent work has divided the Graphoglyptida into three topological groups (Fan et al 2018): 1) "line graphoglyptids" (mostly meanders and spirals) which are common in the Fortunian lower Cambrian worldwide (Fig. 5a, b); 2) "tree-form (mainly sympodiallybranching) graphoglyptids" (including Treptichnus; Uchman et al 1998) which are locally common in lower shoreface settings (Fig.…”

“…Most authors have considered the mode of life of the graphoglyptid-making organisms to include a combination of: 1) intensive [near]surficial bulk-sediment detritus feeding in meanders and spirals (Seilacher 1977;Fan et al 2018); and 2) the creation of open sub-surface branching burrows and networks that were maintained for the purpose of "farming" microbes on the burrow wall (Seilacher 1977).…”

“…worms and some arthropods. Some authors have argued that sharp corners could be maintained in networks if burrowed by a trace-maker that is about as long as the burrow is wide (Fan et al 2018).…”

Unravelling Phanerozoic evolution of radial to rosette trace fossils

“…Recently, Capodistria has been regarded as a graphoglyptid based on a reconstruction of its three‐dimensional structure (Fan et al . ); it is here considered as a radial to rosette ichnogenus until further studies resolve its affinity.…”

“…Some deepmarine recent traces (Bell et al 2013) may be analogs of Capodistria, extending the record to the Holocene. Recently, Capodistria has been regarded as a graphoglyptid based on a reconstruction of its three-dimensional structure (Fan et al 2018); it is here considered as a radial to rosette ichnogenus until further studies resolve its affinity.…”