Remarkable insights into the paleoecology of the Avalonian Ediacaran macrobiota

Abstract

Ediacaran macrofossils from the Avalon Terrane (primarily eastern Newfoundland and the central U.K.) record some of the earliest large and complex multicellular organisms on Earth.Perhaps the greatest unknown regarding these fossils is their relevance to the early evolutionary history of the Kingdom Animalia. In recent years, new data and discoveries have revealed insights into Ediacaran paleobiology, taxonomic relationships, paleoecology and taphonomy, significantly refining our understanding of Avalonian ecosystems. Here, we summarise recent observational and quantitative studies, and their bearing on the current understanding of Avalonian benthic marine ecosystems. A review of existing knowledge of the biological composition of Avalonian marine assemblages demonstrates that they recorddensely-populated ecosystems inhabited by a diverse range of organisms, likely representing multiple biological Kingdoms. Appreciation of this diversity, and of the complexities it introduces to paleoecological studies, is vital when considering the relationship between macroevolution and contemporaneous climatic, tectonic and geochemical events. We then summarise current understanding of Avalonian paleoecology. Studies into locomotion, reproduction, feeding strategies, and community structure and succession reveal that these ecosystems were considerably different to Phanerozoic settings. Furthermore, we suggest that Avalonian ecosystems witnessed the appearance of novel nutrient sources, offering new opportunities and niches for benthic organisms. The suggestion that the numerically dominant rangeomorphs were osmotrophic is reviewed and appraised in light of geochemical, morphological, and biological information. Finally, the use of modern ecological metrics in the study of Ediacaran fossil assemblages is assessed. Concerns regarding the interpretation of paleoecological data are outlined in light of current taphonomic and sedimentological understanding, and these cast doubt on previous suggestions that the Avalonian assemblages were largely composed of metazoans. Nevertheless, we emphasise that if treated with necessary caution, paleoecological data can play a significant role in assisting efforts to determine the biological affinities of late Ediacaran macroscopic organisms.

Ediacaran pre-placozoan diploblasts in the Avalonian biota: the role of chemosynthesis in the evolution of early animal life

“…Clapham et al 2003), but this has been shown to be inaccurate (Antcliffe & Brasier 2007); more recent computational models support passive suspension feeding in the enigmatic Tribrachidium (Rahman et al 2015). However, clear evidence for the presence of pores allowing the uptake of particulate matter is currently lacking (Liu et al 2015). Alternatively, DOM could be absorbed through cell surfaces, as has been proposed for Ediacaran forms with large surface areas such as rangeomorphs ).…”

“…The biological affinity of Ediacaran organisms remains enigmatic, but recent work tends to characterize them as stem-or crown-group metazoans (see Liu et al 2014Liu et al , 2015, potentially representing multiple clades that have been preserved under a common taphonomic regime ). Molecular clock data suggest that the origin of metazoans predates the late Ediacaran period, with many major clades radiating during the Cryogenian and early Ediacaran (dos Reis et al 2015;Erwin 2015).…”

Coprolites in mid-Cambrian (Series 2-3) Burgess Shale-type deposits of Nevada and Utah and their ecological implications

“…Similar observations have been made in the Ravens Throat River Lagerstätte, where coprolites preserve spreiten structures (unpublished observation). It is unlikely that the structures represent poorly preserved jellyfish, eldonids, or Ediacaran-like discoidal fossils, as no rays, ridges, or circular structures are preserved; typical features of such fossils (Liu et al 2015, Lieberman et al 2017, McMahon et al 2017, Sappenfield et al 2017.…”

Who Was the First Person Known to Have Discovered Fossils of the Precambrian (Ediacaran) Organism Aspidella terranovica?

“…Menon et al (2013Menon et al ( , 2014 controversially argued that A. terranovica fossils may suggest evidence of vertical and horizontal movement consistent with the behaviour of cnidarians, however Retallack (2014) disputed this argument. Liu et al (2015) argued the possibility "that Aspidella reflects several very different original entities, including holdfast discs, microbial colonies (cf. Grazhdankin and Gerdes, 2007), and discrete organisms (cf.…”

“…3) fossil Oldhamia flabellata (Hofmann et al 2008;Liu et al 2015). However, there is no evidence that Harvey's presumed Oldhamia fossils could have been referable to P. bonavistensis.…”