Paleoecology of the earliest skeletal metazoan communities: Implications for early biomineralization

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Abstract

The oldest skeletal metazoans (similar to 550-543 Ma) are probably of diploblast grade, i.e., stem- or crown-group cnidarians or basal stem-group bilaterians, sessile benthos, and found in shallow marine carbonate settings. The abundant ions in carbonate environments made the formation of carbonate exoskeletons within preexisting organic matrices physiologically inexpensive. Individuals also reached the largest sizes within reefs, further suggesting that growth in settings conducive to rapid carbonate precipitation promoted skeletonization. Likewise, the preferential precipitation of aragonite and high-Mg calcite mineralogies was thermodynamically-favored by ambient seawater Mg:Ca ratios/pCO(2). Finally, the sessile habit of the earliest skeletal metazoans may be due to the fact that it is energetically far less costly to mineralise immobile rather than mobile organisms.

The morphological and paleoecological characteristics of this biota occupation of progressively younger skeletal parts (Cloudina and Sinotubulites), aggregating behavior and possession of a stalk or holdfast (Namacalathus), and the ability to encrust, a modular habit, and large size (Namapoikia) as well as general attachment to thrombolitic substrates, are all consistent with competitive strategies and anti-predation traits. Together, these observations support the view that skeletonization was promoted by the rise of substrate competitors and bilaterian predators, in predominately carbonate platform and reef environments. (C) 2011 Elsevier B.V. All rights reserved.

Original languageEnglish
Pages (from-to)184-190
Number of pages7
JournalEarth-Science Reviews
Volume106
Issue number1-2
DOIs
Publication statusPublished - May 2011

Keywords

  • biomineralization
  • Ediacaran
  • Cambrian
  • reefs
  • competition
  • predation
  • MINERALIZED BIOLOGICAL-MATERIALS
  • PROTEROZOIC NAMA GROUP
  • SHELLY FOSSILS
  • CARBONIC-ANHYDRASE
  • SEAWATER CHEMISTRY
  • SOUTHERN SHAANXI
  • CLOUDINA
  • NAMIBIA
  • CHINA
  • FAUNA

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