Diversity in early animal communities of the Ediacaran, Avalon assemblage

Diversity is an emergent property of macroecological and macroevolutionary processes. The Avalon assemblage preserves near-census snapshots of Ediacaran communities, enabling tests of the drivers of diversity. However, it remains unclear how alpha diversity varied among surfaces or whether variation reflected uneven sampling, abiotic context or biotic processes. We analysed diversity for 11,342 specimens across 22 surfaces and examined abiotic and biotic correlates. Despite compositional variation, most surfaces fell into four community types dominated by Fractofusus andersoni, F. misrai and/or Pectinifrons, Bradgatia, or upright fronds, with potential substructure within the upright-frond type, whereas Clapham's Pigeon Cove and Shingle Head communities, from the oldest and youngest formations, respectively, may indicate greater community differentiation near the sampled stratigraphic limits. Sampling effort varied widely, yet taxon-area curves showed richness was well captured on 12 of 22 surfaces, and Shannon and Simpson diversity remained consistent across sampling completeness and taxonomic treatments. Diversity showed no clear associations with locality or stratigraphic affiliation, but differed among community types and declined with increasing vertical segregation. Overall, these results suggest that, among the predominantly Newfoundland communities sampled, Avalon alpha diversity may have been shaped more by local community assembly and organisation than by broader geographic, environmental and temporal context.