DECIPHERING EARLY CAMBRIAN LOPHOTROCHOZOAN RELATIONSHIPS USING TOMMOTIID SCLERITE MICROORNAMENT AND ULTRASTRUCTURE

Tommotiids are a group of enigmatic early Cambrian animals characterized by accretionary organophosphatic biominerals (sclerites), which formed part of a larger external skeleton. Their taxonomic and phylogenetic relationships remain uncertain, complicating understanding of relationships at the root of the stem lophoptrochozoan tree. Tommotiids are informally subdivided into two groups: mobile, slug-like camenellans and sessile, tubiform eccentrothecimorphs. Both groups are found in abundance in lower Cambrian carbonate deposits across the Arrowie and Stansbury basins, Flinders Ranges, South Australia, which provide the raw material for novel investigations. Previous research has shown that some eccentrothecimorph taxa (e.g. Kulparina rostrata and Paterimitra pyramidalis) share external morphological similarities, but have disparate microornamental textures.

This project provides a detailed comparison of the micro-ornament, internal structures and some geochemical composition of key tommotiids, primarily eccentrothecimorphs, at different scales and across sclerite types. High resolution SEM imaging of morphological traits are compared with detailed description of internal ultrastructure from a wide range of sclerite morphotypes. Elemental composition of varying laminae and other structures across sclerite interiors (and between species) is compared for the first time using EDXS elemental mapping. This project’s goal is to uncover homologous traits shared among eccentrothecimorphs and phosphatic shelly fossil groups, better constraining the position of Tommotiids within early Lophotrochozoa.