Australia: The Land Where Time Began

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Nectocaridid Ecology - Cephalopod-like Body Plan, Early Origin, Diversity and Affinity

Nectocaridids, soft-bodied organisms that are known from Burgess Shale-like deposits of Early to Middle Cambrian age in China, the earliest known, Australia, the Emu Bay site on Kangaroo Island, dated to between the site in China and Canadian site, the youngest of the 3. According to Smith1 they have recently been interpreted as a clade, though they were originally interpreted as unrelated species. They have flexible tentacles, camera-type eyes, lateral fins, internal gills, axial cavity and funnel, this suite of features now seen as pointing to a relationship with cephalopods. Some authors have called some aspects of this interpretation into question, including the relevance of the group to cephalopod evolution.

In this paper the Smith1 examines new and existing Nectocaridid fossils, including a large new form that has been suggested to possibly be a sexual dimorph of Nectocaris pteryx. When considering existing taxa differences largely represent taphonomic variation between sites and specimens, which provides further constraint on the anatomy of the organism. Smith1 revises the morphology of the tentacles and fins, as well as describing the mouthparts and gills for the first time. The presence of the earliest known camera-like eyes is supported by a mathematical analysis, and the funnel is suggested by fluid mechanical considerations to have been optimised for efficient jet propulsion in a low Reynolds number flow regime.

Nectocaridids bear a close similarity to coleoid cephalopods but fewer stratigraphic challenges are raised by a deeper position within cephalopods. The body plan of Nectocaris adds substantially to the Cambrian disparity, demonstrating the rapid colonisation of nektobenthic niches following the Cambrian Explosion, whether or not common ancestry of profound convergence is reflected in its coleoid-like construction.

Sources and further reading

  1. Smith, Martin R. "Nectocaridid Ecology, Diversity, and Affinity: Early Origin of a Cephalopod-Like Body Plan." Paleobiology 39, no. 2 (March 1, 2013 2013): 297-321.
Author: M. H. Monroe
Last Updated 12/02/2014
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