The Erniettomorphs are a form of Ediacaran

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

consisting of rows of airbed-like tubes arranged along a midline with a glide symmetry. Representative genera include '' Ernietta'', '' Phyllozoon'', ''

Pteridinium ''Pteridinium'' is an erniettomorph found in a number of Precambrian deposits worldwide. It is a member of the Ediacaran biota. Body plan The three-lobed body is generally flat such that only two lobes are visible. Each lobe consists of a number ...

'', ''

Swartpuntia ''Swartpuntia'' is a monospecific genus of erniettomorph from the terminal Ediacaran period, with at least three quilted, leaf-shaped petaloids — probably five or six. The petaloids comprise vertical sheets of tubes filled with sand. ''Swartp ...

''. Undisputed Erniettomorphs were Ediacaran, but the species '' Erytholus'', ''

Rutgersella ''Rutgersella truexi'' is a form species for problematic fossils of Early Silurian age in Pennsylvania. It has been of special interest because of its morphological similarity with the iconic Ediacaran fossil ''Dickinsonia'', and may have been ...

'', and ''

Protonympha ''Protonympha'' is a form genus for problematic fossils of Devonian age in New York. It has been of special interest because of its morphological similarity with the iconic Ediacaran fossil ''Spriggina'', and may have been a late surviving vend ...

'', who have by some been included in this group but are by no means clear members, are found through to the Late Devonian . Their affinity is uncertain; they probably form a clade and are most likely a sister group to the rangeomorphs, which bear a similar (though fractal) construction. Placements within the

metazoan Animals are multicellular, eukaryotic organisms in the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, and go through an ontogenetic stage in ...

crown-group have been rebutted, and it is most likely that these peculiar organisms lie in the

stem group In phylogenetics, the crown group or crown assemblage is a collection of species composed of the living representatives of the collection, the most recent common ancestor of the collection, and all descendants of the most recent common ancestor. ...

to the animals. There is no evidence that they possessed a mouth or gut. Because they may have been found in water which was too deep to permit photosynthesis – and in some cases, lived half-buried in sediment, it is speculated that they fed by

osmosis Osmosis (, ) is the spontaneous net movement or diffusion of solvent molecules through a selectively-permeable membrane from a region of high water potential (region of lower solute concentration) to a region of low water potential (region o ...

from the sea water. Such a lifestyle requires a very high surface area to volume ratio – higher than is observed in fossils. However, this paradox can be resolved if much of the volume of the organisms was not metabolically active. Many ''Pteridinium'' fossils are found completely filled with sand; if this sand were present ''within'' the organism while it was alive, this would reduce its metabolically active volume enough to make osmotic feeding viable.

References

Ediacaran life Petalonamae {{Ediacaran-stub

See also

References