The Erniettomorphs are a form of

Ediacaran The Ediacaran ( ) is a geological period of the Neoproterozoic geologic era, Era that spans 96 million years from the end of the Cryogenian Period at 635 Million years ago, Mya to the beginning of the Cambrian Period at 538.8 Mya. It is the last ...

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 preserve ...

consisting of rows of airbed-like tubes arranged along a midline with a

glide symmetry In geometry, a glide reflection or transflection is a geometric transformation that consists of a reflection across a hyperplane and a translation ("glide") in a direction parallel to that hyperplane, combined into a single transformation. Bec ...

, vaguely resembling plant leaves in shape. Representative genera include '' Ernietta'', ''

Phyllozoon ''Phyllozoon'' (lit. "Leaf animal" in Greek) is an Ediacaran imprint that resembles a proarticulatan and has been interpreted as a feeding trace. It usually occurs in long chains of imprints formed, presumably as the organism that made it move ...

'', '' Pteridinium'', '' Swartpuntia'', and '' Tulaneia''. Undisputed Erniettomorphs were Ediacaran, but the species '' Erytholus'', '' Rutgersella'', and '' Protonympha'', who have by some been included in this group but are by no means clear members, are found through to the

Late Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era during the Phanerozoic eon, spanning 60.3 million years from the end of the preceding Silurian period at million years ago ( Ma), to the beginning of the succeeding ...

. Their affinity is uncertain; they probably form a

clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...

and are most likely a sister group to the rangeomorphs, which bear a similar (though

fractal In mathematics, a fractal is a Shape, geometric shape containing detailed structure at arbitrarily small scales, usually having a fractal dimension strictly exceeding the topological dimension. Many fractals appear similar at various scale ...

) construction. Placements within the

metazoan Animals are multicellular, eukaryotic organisms in the biological kingdom Animalia (). With few exceptions, animals consume organic material, breathe oxygen, have myocytes and are able to move, can reproduce sexually, and grow from a ho ...

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, selectively-permeable membrane from a region of high water potential (region of lower solute concentration) to a region of ...

from the

sea water Seawater, or sea water, is water from a sea or ocean. On average, seawater in the world's oceans has a salinity of about 3.5% (35 g/L, 35 ppt, 600 mM). This means that every kilogram (roughly one liter by volume) of seawater has approximate ...

. 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