Of Time and Taphonomy: Preservation in the Ediacaran

Abstract

The late Neoproterozoic witnessed a revolution in the history of life: the transition from a microbial world to the one known today. The enigmatic organisms of the Ediacaran hold the key to understanding the early evolution of metazoans and their ecology, and thus the basis of Phanerozoic life. Crucial to interpreting the information they divulge is a thorough understanding of their taphonomy: what is preserved, how it is preserved, and also what is not preserved. Fortunately, this Period is also recognized for its abundance of soft-tissue preservation, which is viewed through a wide variety of taphonomic windows. Some of these, such as pyritization and carbonaceous compression, are also present throughout the Phanerozoic, but the abundance and variety of moldic preservation of body fossils in siliciclastic settings is unique to the Ediacaran. In rare cases, one organism is preserved in several preservational styles which, in conjunction with an increased understanding of the taphonomic processes involved in each style, allow confident interpretations of aspects of the biology and ecology of the organisms preserved. Several groundbreaking advances in this field have been made since the 1990s, and have paved the way for increasingly thorough analyses and elegant interpretations.

Modularity and Overcompensatory Growth in Ediacaran Rangeomorphs Demonstrate Early Adaptations for Coping with Environmental Pressures

“…The preservation of rangeomorphs as external molds [22] has necessarily meant that many aspects of their biology and ecology are inferred from indirect evidence, particularly from their growth and developmental characteristics [2]. A modular organization has been assumed based on their self-similar branching architecture [17,20,23], but supporting evidence for their branches (modules) having had developmental or physiological independence from one another [24,25] has been lacking.…”

“…Both mechanisms indicate a greater level of control and complexity to the rangeomorph growth program than previously assumed: while locally controlled production of growth factor would suggest greater module autonomy, targeted delivery would suggest a high level of physical interconnectedness between modules. Based on the available specimens of H. fordi, there is currently no way to distinguish between these two alternatives, and previous reports of an unspecified internal, semi-rigid, organic skeleton within rangeomorphs [23] have subsequently been dismissed as taphonomic artifacts (see [22]). Consequently, the degree to which resources may have been shared between modules within a frond remains unknown.…”

The Beothukis/Culmofrons problem and its bearing on Ediacaran macrofossil taxonomy: evidence from an exceptional new fossil locality

“…The preservation of rangeomorphs in the manner typical of Avalonian (eastern Newfoundland and the southern UK) Ediacaran macrofossils, on siliciclastic bedding planes as external moulds and casts (cf. Kenchington and Wilby ), contributes to a dearth of diagnostic morphological characters with which to constrain their phylogenetic affinities.…”

Revealing rangeomorph species characters using spatial analyses

“…Random labelling analyses hold the positions of the specimens constant so that if taphonomic processes (cf. Kenchington and Wilby 2014) impact all groups similarly, as might reasonably be expected for mutually aligned and simultaneously buried specimens (see Wilby et al 2011, then they are independent of the RLAs. This property of RLAs means that a subsample of the total population can be analysed.…”

“…The preservation of Avalonian macrofossil communities may be exceptional, with notable examples of thousands of these organisms preserved in-situ on successive bedding planes (Wood et al 2003, Kenchington and Wilby 2014. Their sessile habit and their preservation in life position means that their position on a bedding plane encapsulates their lifehistory: that is, their position is a combined record of the abiological, biological and ecological processes that impacted them during their life.…”