Erniettomorph
Encyclopedia
The Erniettomorphs are a form of Ediacaran
fossil
consisting of rows of airbed-like tubes arranged along a midline with a glide symmetry. Representative genera include Ernietta
, Phyllozoon
, Pteridinium
, Swartpuntia
and possibly Dickinsonia
.
There is no record of Erniettomorphs after the end of the Ediacaran period. 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 crown-group have been rebutted, and it is most likely that these peculiar organisms lie in the stem group to the animals. There is no evidence that they possessed a mouth or gut. Because they are often 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
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 was present within the organism while it was alive, this would reduce its metabolically active volume enough to make osmotic feeding viable.
Ediacaran
The Ediacaran Period , named after the Ediacara Hills of South Australia, is the last geological period of the Neoproterozoic Era and of the Proterozoic Eon, immediately preceding the Cambrian Period, the first period of the Paleozoic Era and of the Phanerozoic Eon...
fossil
Ediacara biota
The Ediacara biota consisted of enigmatic tubular and frond-shaped, mostly sessile organisms which lived during the Ediacaran Period . Trace fossils of these organisms have been found worldwide, and represent the earliest known complex multicellular organisms.Simple multicellular organisms such as...
consisting of rows of airbed-like tubes arranged along a midline with a glide symmetry. Representative genera include Ernietta
Ernietta
Ernietta is a bag-shaped erniettomorph genus that lived half-buried in sediment, and probably fed by osmosis. It had chambered walls. It was from shale in the Dabis Formation in Namibia dated from 549 to 543 mya. The name has also been misspelled as Ernettia in some papers...
, Phyllozoon
Phyllozoon
Phyllozoon 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 making organism moved....
, Pteridinium
Pteridinium
Pteridinium is an erniettomorph found in a number of Precambrian deposits worldwide. It is a member of the Ediacaran biota.-Body plan:It has a three-lobed body which is generally smashed flat such that only two lobes are visible. Each lobe consists of a number of parallel ribs extending back to the...
, Swartpuntia
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. Swartpuntia specimens range in length from 12 to 19 cm, and...
and possibly Dickinsonia
Dickinsonia
Dickinsonia is an iconic fossil of the Ediacaran biota. It resembles a bilaterally symmetrical ribbed oval. Its affinities are presently unknown; most interpretations consider it to be an animal, although others suggest it may be fungal, or a member of an "extinct kingdom".-Species variety:A...
.
There is no record of Erniettomorphs after the end of the Ediacaran period. Their affinity is uncertain; they probably form a clade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
and are most likely a sister group to the rangeomorphs, which bear a similar (though fractal) construction. Placements within the metazoan crown-group have been rebutted, and it is most likely that these peculiar organisms lie in the stem group to the animals. There is no evidence that they possessed a mouth or gut. Because they are often 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
Osmosis is the movement of solvent molecules through a selectively permeable membrane into a region of higher solute concentration, aiming to equalize the solute concentrations on the two sides...
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 was present within the organism while it was alive, this would reduce its metabolically active volume enough to make osmotic feeding viable.
See also
- Rangeomorpha, a probable sister clade
- ProarticulataProarticulataProarticulata is a proposed extinct phylum of very early bilateral animals known from fossils found in the Ediacaran fauna. Mikhail A. Fedonkin describes animals in Proarticulata as having a "shield-like" shape, an unmineralized, thin, flexible carapace and a thick, segmented body...
, sharing similar 'glide symmetry' - Ediacara biotaEdiacara biotaThe Ediacara biota consisted of enigmatic tubular and frond-shaped, mostly sessile organisms which lived during the Ediacaran Period . Trace fossils of these organisms have been found worldwide, and represent the earliest known complex multicellular organisms.Simple multicellular organisms such as...
, for an overview of the bizarre late Ediacaran organisms. - List of Ediacaran genera