determination-of-the-settling-rate-of-claycyanobacterial-floccules

Determination of the Settling Rate of Clay/Cyanobacterial Floccules

The mechanisms underpinning the deposition of fine-grained, organic-rich sediments are still largely debated. Specifically, the impact of the interaction ...

Based on molecular clocks and biomarker studies, it is possible that bilaterian life emerged early in the Ediacaran, but at present, no fossils or trace fossils from this time have been reported. Here we report the discovery of the oldest bilaterian burrows in shallow-water glaciomarine sediments from the Tacuarí Formation, Uruguay. Uranium-lead dating of zircons in cross-cutting granite dykes constrains the age of these burrows to be at least 585 million years old. Their features indicate infaunal grazing activity by early eumetazoans. Active backfill within the burrow, an ability to wander upward and downward to exploit shallowly situated sedimentary laminae, and sinuous meandering suggest advanced behavioral adaptations. These findings unite the paleontological and molecular data pertaining to the evolution of bilaterians, and link bilaterian origins to the environmental changes that took place during the Neoproterozoic glaciations.

Bilaterian burrows and grazing behavior at >585 million years ago.

Gaucher et al. suggest that their field observations and petrographic analysis of one thin section do not support an Ediacaran age for the trace fossils-bearing strata of the Tacuarí Formation. We have strengthened our conclusion of an Ediacaran age for the Tacuarí Formation based on reassessment of new and previously presented field and petrographic evidence.

Article	Year
Bilaterian burrows and grazing behavior at >585 million years ago. Science (New York, N.Y.)\| PubMed ID: 22745427	2012
Response to comment on "Bilaterian burrows and grazing behavior at >585 million years ago". Science (New York, N.Y.)\| PubMed ID: 23430639	2013

Murray K. Gingras

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