scholarly journals Surfing in and on microbial mats: Oxygen-related behavior of a terminal Ediacaran bilaterian animal

Geology ◽  
2019 ◽  
Vol 47 (11) ◽  
pp. 1054-1058 ◽  
Author(s):  
Shuhai Xiao ◽  
Zhe Chen ◽  
Chuanming Zhou ◽  
Xunlai Yuan
Keyword(s):  
Microbial Mats ◽  
Trace Fossil ◽  
Redox Conditions ◽  
Animal Distribution ◽  
Close Relationship ◽  
Bilaterian Animal ◽  
Burrowing Behavior ◽  
Thin Section Analysis ◽  
Section Analysis ◽  
Redox Dynamics

Abstract Geochemical evidence suggests that terminal Ediacaran (ca. 551–539 Ma) oceans experienced expansive anoxia and dynamic redox conditions, which are expected to have impacted animal distribution and behaviors. However, fossil evidence for oxygen-related behaviors of terminal Ediacaran animals is poorly documented. Here, we report a terminal Ediacaran trace fossil that records redox-regulated behaviors. This trace fossil, Yichnus levis new ichnogenus and new ichnospecies, consists of short and uniserially aligned segments of horizontal burrows that are closely associated with microbial mats. Thin-section analysis shows that the trace-making animal moved repeatedly in and out of microbial mats, with mat-burrowing intervals interspersed by epibenthic intermissions. This animal is hypothesized to have been a bilaterian exploring an oxygen oasis in microbial mats. Such intermittent burrowing behavior reflects challenging and dynamic redox conditions in both the water column and microbial mats, highlighting the close relationship between terminal Ediacaran animals and redox dynamics.

Ediacaran scavenging as a prelude to predation

2018 ◽  
Vol 2 (2) ◽  
pp. 213-222 ◽  
Author(s):  
James G. Gehling ◽  
Mary L. Droser
Keyword(s):  
Microbial Mats ◽  
South Australia ◽  
Trace Fossil ◽  
Localized Source ◽  
Oxygen Levels ◽  
Stem Group ◽  
Ediacara Biota ◽  
Ecological Innovation ◽  
Large Predators ◽  
Ancient Ecosystems

Predation is one of the most fundamental ecological and evolutionary drivers in modern and ancient ecosystems. Here, we report the discovery of evidence of the oldest scavenging of shallowly buried bodies of iconic soft-bodied members of the Ediacara Biota by cryptic seafloor mat-burrowing animals that produced the furrow and levee trace fossil, Helminthoidichnites isp. These mat-burrowers were probably omnivorous, stem-group bilaterians that largely grazed on microbial mats but when following mats under thin sands, they actively scavenged buried Dickinsonia, Aspidella, Funisia and other elements of the Ediacara Biota. These traces of opportunistic scavengers of dead animals from the Ediacaran of South Australia represent a fundamental ecological innovation and a possible pathway to the evolution of macrophagous predation in the Cambrian. While the Ediacaran oceans may have had oxygen levels too low to support typical large predators, the Helminthoidichnites maker lived in and grazed on microbial mats, which may have provided a localized source of oxygen.

Details of Thin Section Analysis of Pottery Fabrics

1987 ◽  
Vol 53 (S3) ◽  
pp. 53-59
Author(s):  
Carol Allen
Keyword(s):  
Thin Section ◽  
Clay Matrix ◽  
Thin Section Analysis ◽  
Maximum Measurement ◽  
Section Analysis

Terms usedGrog relates to clay inclusions within the pottery which appear as discrete pieces of varying sizes. Usually such entities are assumed to be crushed parts of pre-existing pots.Sizes of quartz, grog, shell or other inclusions referred to in the analysis concern measurements taken on the longest axis of the grain or piece. In each case the maximum measurement stated is the longest observed in that particular section, and does not infer that other grains in the sample were all of this size, unless stated.Percentages of materials shown as included in the clay matrix are estimates expressed by area using comparison charts (Terry and Chilingar 1955, and Flugel 1982, 247-257).

The Holmes effect and the lower limit of modal analysis

1956 ◽  
Vol 31 (234) ◽  
pp. 276-281 ◽  
Author(s):  
F. Chayes
Keyword(s):  
Modal Analysis ◽  
Lower Limit ◽  
Thin Section ◽  
Transmitted Light ◽  
Apparent Area ◽  
Measurement Surface ◽  
Areal Measurement ◽  
Thin Section Analysis ◽  
Measurement Area ◽  
Section Analysis

SummaryThin-section analysis is essentially an areal measurement, the measurement area usually being the upper surface of the section. If transmitted light is used for the measurement, the apparent areas of opaque grains will in general be somewhat larger than their true areas on the measurement surface. For strictly spherical opaque particles in a transparent matrix the expected excess of apparent over true area is shown to be (πr2k)/(2r + k) where r is the spherical radius and κ is the thickness of the thin section. A table shows the relation between true and apparent area as a function of r/k.

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