Vendobionta

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Vendobionta
Temporal range: Ediacaran–Middle Cambrian
Diorama of the Ediacaran biota at the Field Museum in Chicago.jpg
Interpretation of the Ediacaran biota.
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Superphylum:† Vendobionta
Seilacher (1992) [1]
Subtaxa
Synonyms

Vendobionts or Vendozoans (Vendobionta) are a proposed very high-level, extinct clade of benthic organisms that made up of the majority of the organisms that were part of the Ediacaran biota. It is a hypothetical group and at the same time, it would be the oldest of the animals that populated the Earth about 580 million years ago, in the Ediacaran period (formerly Vendian). They became extinct shortly after the so-called Cambrian explosion, with the introduction of fauna formed by more recognizable groups and more related to modern animals. [2] [ full citation needed ] It is very likely that the whole Ediacaran biota is not a monophyletic clade and not every genus placed in its subtaxa is an animal.

This biological group is not widely recognized; credibility is limited by the expansive speculation needed to establish phylogenetic relationships between such ancient extinct groups. The hypothesis was formulated by the German geologist Adolf Seilacher, who even doubts its relationship with the animal kingdom, or its multicellular nature — the group might have originated independently, and could be large unicellular forms. It has also been proposed that they could have been cnidarians, or articulates; perhaps a fungus, colonial protist, algae, or lichen; or a group divergent from all current animals. The only current consensus is that they could not have been photosynthetic. In any case, like the acritarchs, they are considered evolutionary enigmas, and probably an independent and extinct kingdom. [1]

Features

Dickinsonia, a proarticulate. Dickinsonia costata.jpg
Dickinsonia , a proarticulate.

Within the description of this hypothetical group, characteristics have been proposed that could have been common in all the first groups of Ediacaran organisms:

Structure

Relatively soft body, without hard parts such as armor or skeletons. In appearance, they have been compared to thin inflatable mattresses generally flat and filled with a liquid which has been called plasmodial fluid. Internally they could contain a single compartment (the syncytium) [3] and externally they presented several types of folds or segments (parallel, radial, or concentric) in addition to, probably, some type of cell wall (such as plants or fungi) that offered resistance to contraction or compaction, thus promoting fossilization. [4]

Habitat

All were marine and probably also benthic, inhabiting the seabed, from shallow to deep subtidal environments. Even medusoids, which were thought to be swimmers, were actually later concluded to be like polyps [5] or benthic discs anchored to the seabed, or semi-buried endobentonics. This habitat influenced the popular name of "The garden of Ediacara".

The Ediacarans' abundant preservation is surprising, despite having soft bodies; this nearly surely indicates the absence of burrowing creatures in their home sediments. [6]

Tribrachidium, a trilobozoan. Tribrachidium heraldicum.jpg
Tribrachidium , a trilobozoan.

Mobility

Most lacked locomotion. The oldest groups did not have any capacity for movement, as evidenced by the complete lack of ash and sediment disturbance during fossilization. [4] It is believed that there were no musculature or nervous system, given their simplicity, and many were sessile. However, it is considered that the movement would have appeared in Proarticulata and would have been slow and sliding; presumably, mobile representatives such as Spriggina grazed on a lawn of microorganisms (epifaunal grazing). This characteristic of Proarticulata is the main argument to consider that vendobionts, if they were a clade, would be ascribed to the animal kingdom; although the development of its own nervous system would have been independent of the other animals. [7]

Diet

There is no definitive evidence of the presence of the mouth, anus or a digestive system, although internal structures have been identified.It is believed that the feeding could have been by osmosis, [8] just as fungi or bacteria do. The presence of numerous streaks, folds or segments considerably increases the total surface area necessary for the osmotic absorption of nutrients. It was also proposed that they were photosynthetic organisms, however, they lived at different depths, even under 200 meters where light does not reach for photosynthesis. Due to the absence of bite marks in the Ediacaran fossils, it was concluded that the vendobionts were not predators nor were they exposed to them; which could then have made them easy victims of Cambrian predators.

Growth

They grow preserving their shape and maintain the same number of segments regardless of size, although the segments are subdivided more and more. It is believed that they did not have an embryonic stage. If so, they would be a different group from the other animals. [7]

Reproduction

Vendozoan reproduction would apparently have been asexual. No sex organs or gonads have been recognized.

Age and distribution

Charnia, a frondomorph. Charnia.JPG
Charnia , a frondomorph.

The first to appear were frondomorphs (Petalonamae) and simple medusoids 578 Ma (millions of years) ago and are considered the oldest complex life forms. The Ediacaran biota is chronologically divided into three associations:

  1. The Avalon association is the oldest fossil bed. It is found in the cliffs of the Avalon Peninsula, Newfoundland (578–560 Ma), and shows a postglacial, deep-water habitat. The Avalonian organisms are completely benthic, with a predominance of rangeomorphs, well below the photic zone, at a depth of one kilometer, which rules out that they were algae or lichens. [4] The Avalon biota achieve great distribution in all marine niches, worldwide: There was an abrupt appearance of macroscopic organisms in what was called the Avalon explosion, 37 million years before the Cambrian explosion. These same organisms – frondomorphs and medusoids – were the last to disappear during the extinction of all Vendobionts in the Cambrian.
  2. The bilateralomorphs (Proarticulata) appeared 555 Ma ago and had more environmental restrictions, being found in tropical seas. [9] The White Sea association (560–550 Ma, Russia and Australia), showed a great variety of new fossil footprints and the greatest diversity occurs in rocks that were deposited in well-lit and energetically active shallow waters. [10]
  3. The last Ediacaran association is that of Nama (550–541 Ma, Namibia), where a decrease in biodiversity is observed, as a preamble to the massive extinction of the Ediacaran biota. Before the end of the Ediacaran period, proarticulates and trilobozoans would have already become extinct; and the last vendobionts disappear with the arrival of the animals of the Cambrian explosion. [11]

Systematic

The classification is very controversial. As a unified group they have been placed primarily in Animalia, but are considered by others to be protists, fungi, terrestrial lichens, or an independent kingdom. Those who see here different unrelated groups, place the proarticulates in Bilateria basally (this opinion is the most upheld among these alternative theories) or as pre-arthropods, the petalonams with cnidarians such as sea pens or as ctenophores, and the trilobozoa and medusoids are considered jellyfish without cnidoblasts and classified in Cnidaria or Coelenterata. Finally, given their antiquity, others consider it speculative to develop a phylogeny or to directly relate these organisms to modern animals.

Comparison with protists

It has been suggested that vendobionts may come from amoeboid protozoa or protists, and be, for example, similar to xenophiophores, [12] which are unicellular foraminifera that have developed large size, reaching 20 cm. They could therefore have been unicellular organisms that developed macroscopic size thanks to the absence of predators, since all the groups have a size that ranges from a few millimeters to exceeding a meter in length, favored by the increase in oxygen; in such a way that the opportunity is opened to consider that they were not animals, fungi or plants, but an independent and extinct kingdom. [1] However, structural studies of these fossils have so far revealed no traces of a shell, testa or carapace organic material (sclerotized), agglutinated or mineralized, the presence of which is implicit in this hypothesis. [13]

It has also been suggested that the Ediacaran biota could be formed by colonial organisms, as an intermediate degree between protists and animals. [14] However, the morphological complexity and the absence of layers of stromatolites or other microbial structures, [15] in addition to indications that they were multicellular as seen in discoid forms like Aspidella ; would indicate that they were not colonial. [4]

Comparison with coelenterates

All vendobionts, except proarticulates, have been classified in Cnidaria by some on the basis of morphological similarities, although differences have also been described.

Similarities

Petalonamae shares basic structural characteristics with sea pens cnidarians (Pennatulacea). Similarly, the extant jellyfish impressions and the Proterozoic (Ediacaran) medusoid circular impressions show general similarities in the arrangement and position of radial and concentric structures, as well as a central raised axis.

Differences

Recent sea feathers have produced fossil impressions that are more misshapen and irregular than Proterozoic fossils. While in medusoids, concentric rings and radial grooves are more numerous in Proterozoic fossils, as strongly folded or deformed fossils are rare compared to modern jellyfish prints. This could mean that Ediacaran organisms, despite not having hard parts, had stiffer or firmer bodies than many modern cnidarians of comparable size. Many Ediacaran fossils have no counterpart among existing forms. The structural simplicity of the impressions of existing Ediacaran and cnidarians suggests that their mutual similarities may be due to convergence; however, possible phylogenetic affinities between them cannot be completely ruled out. [16]

Difference with Petalonamae

There are important morphological differences. The current sea feathers are actually a colony of polyps, they grow from a polyp that after losing its tentacles becomes the axis of the colony and from which the other tentaculated polyps grow, they are also quite capable of certain movements . On the other hand, the petalonamos are immobile, they do not seem to be a colony and could rather be closer to the proarticulated ones due to their simple and flat shape, because of their segmentation and because of the lack of a mouth, anus and tentacles, in addition, instead of a axis there is usually a middle suture that can be zigzagging if the segments are alternate. An analysis of the growth and development of Charnia fossils through laser imaging of the holotype reveals that it cannot be related to modern cnidarians such as sea feathers, with which it has been compared for so long, because they have opposite growth polarities. [17]

Cyclomedusa, a medusoid. Cyclomedusa cropped.jpg
Cyclomedusa , a medusoid.

Differences with medusoids

There are morphological differences between the jellyfish and their globose and gelatinous shape, compared to the flat, discoid medusoids, with relief that is greater on the dorsal side and firmer due to the indications that would reveal the existence of a rigid wall surrounding the body . It can be suggested that there is no evidence that medusoids share biological characteristics with coelenterates; there is no mouth, no two-layered body wall enclosing a single cavity. This, and the evidence for a rigid outer wall, adds to recent doubts about the concept of an Ediacaran fauna that would have been dominated by soft-bodied coelenterates. [18]

Comparison with articulates

Spriggina, a proarticulate of the group Cephalozoa. Spriggina floundersi Ediacara.jpg
Spriggina , a proarticulate of the group Cephalozoa.

Proarticulata have been compared to modern articulated animals such as arthropods or annelids. However, other anatomical features of the proarticulates, mainly the absence of truly complete segmentation, articulated limbs, and any other lateral processes, do not agree with this interpretation. The body of the proarticulates consisted of two rows of identical 'semi-segments' (the isomers), right and left, located along their longitudinal axis, which does not correspond to the articulated ones. This type of symmetry is not typical in animals; instead, it has been observed in other vendobionts, protists, multicellular colonies and frequently in plants. [19]

In general, Vendobionta is being defined as a group apart from animals, with no proven common origin. However, those in favor of considering them animals, see in the discovery of trails left by some proarticulates that would have locomotion, a decisive argument of the relationship with the metazoans. [19]

Comparison with fungi

It has been hypothesized that Ediacaran organisms such as frondomorphs or medusoids, could be related to fungi (Fungi) or to some other fungal organism (slime molds), due to certain characteristics such as multicellularity, lack of movement, indeterminate growth, osmotrophic feeding and resistance to taphonomic shrinkage (ease of fossilization given by the presence of a cell wall). [4] However, there is no evidence of mycelial development, nor presence of sporangia or fruiting bodies. For other Ediacaran fossils, a fungal model is clearly inappropriate.

Related Research Articles

<span class="mw-page-title-main">Ediacaran</span> Third and last period of the Neoproterozoic Era

The Ediacaran is a geological period of the Neoproterozoic era that spans 96 million years from the end of the Cryogenian period at 635 Mya to the beginning of the Cambrian period at 538.8 Mya. It is the last period of the Proterozoic eon as well as the last of the so-called "Precambrian supereon", before the beginning of the subsequent Cambrian period marks the start of the Phanerozoic eon, where recognizable fossil evidence of life becomes common.

<span class="mw-page-title-main">Neoproterozoic</span> Third and last era of the Proterozoic Eon

The Neoproterozoic Era is the unit of geologic time from 1 billion to 538.8 million years ago.

The cloudinids, an early metazoan family containing the genera Acuticocloudina, Cloudina and Conotubus, lived in the late Ediacaran period about 550 million years ago. and became extinct at the base of the Cambrian. They formed millimetre-scale conical fossils consisting of calcareous cones nested within one another; the appearance of the organism itself remains unknown. The name Cloudina honors the 20th-century geologist and paleontologist Preston Cloud.

<span class="mw-page-title-main">Proterozoic</span> Geologic eon, 2500–539 million years ago

The Proterozoic is the third of the four geologic eons of Earth's history, spanning the time interval from 2500 to 538.8 Mya, the longest eon of the Earth's geologic time scale. It is preceded by the Archean and followed by the Phanerozoic, and is the most recent part of the Precambrian "supereon".

<i>Dickinsonia</i> Extinct genus of early animals

Dickinsonia is a genus of extinct organism, most likely an animal, that lived during the late Ediacaran period in what is now Australia, China, Russia and Ukraine. It is one of the best known members of the Ediacaran biota. The individual Dickinsonia typically resembles a bilaterally symmetrical ribbed oval. Its affinities are presently unknown; its mode of growth has been considered consistent with a stem-group bilaterian affinity, though various other affinities have been proposed. The discovery of cholesterol molecules in fossils of Dickinsonia lends support to the idea that Dickinsonia was an animal, though these results have been questioned.

<i>Ausia fenestrata</i> Genus of marine filter feeders

Ausia fenestrata is a curious Ediacaran period fossil represented by only one specimen 5 cm long from the Nama Group, a Vendian to Cambrian group of stratigraphic sequences deposited in the Nama foreland basin in central and southern Namibia. It has similarity to Burykhia from Ediacaran (Vendian) siliciclastic sediments exposed on the Syuzma River of Arkhangelsk Oblast, northwest Russia. This fossil is of the form of an elongate bag-like sandstone cast tapering to a cone on one end. The surface of the fossil is covered with oval depressions ("windows") regularly spaced over the surface in the manner of concentric/parallel rows. The taxonomic identity of Ausia is unresolved.

<i>Kimberella</i> Primitive Mollusc-like organism

Kimberella is an extinct genus of bilaterian known only from rocks of the Ediacaran period. The slug-like organism fed by scratching the microbial surface on which it dwelt in a manner similar to the gastropods, although its affinity with this group is contentious.

<span class="mw-page-title-main">Rangeomorph</span> Form taxon of frondose Ediacaran fossils

The rangeomorphs are a form taxon of frondose Ediacaran fossils that are united by a similarity to Rangea. Some researchers, such as Pflug and Narbonne, suggest that a natural taxon Rangeomorpha may include all similar-looking fossils. Rangeomorphs appear to have had an effective reproductive strategy, based on analysis of the distribution pattern of Fractofusus misrai, which consisted of sending out a waterborne asexual propagule to a distant area, and then spreading rapidly from there, just as plants today spread by stolons or runners.

<i>Spriggina</i> Extinct genus of annelid worms

Spriggina is a genus of early animals whose relationship to living animals is unclear. Fossils of Spriggina are known from the late Ediacaran period in what is now South Australia. Spriggina floundersi is the official fossil emblem of South Australia; it has been found nowhere else.

<i>Yorgia</i> Extinct proarticulate animal

Yorgia waggoneri is a discoid Ediacaran organism. It has a low, segmented body consisting of a short wide "head", no appendages, and a long body region, reaching a maximum length of 25 cm (9.8 in). It is classified within the extinct animal phylum Proarticulata.

Chondroplon bilobatum is a medusoid Ediacaran fossil. It has sand-filled tubes, although these may not have been sand-filled in life. It has a shield-like shape, with one end different from the other, and bilateral symmetry, and although it has been suggested that it possesses glide reflection symmetry, such suggestions are based upon a taphonomic effect deforming some specimens. Chondroplon was originally described by Mary Wade in 1971 from fossils found in South Australia. It was named after chondrophores — chitinous floats found on some kinds of colonial floating hydroids.

<span class="mw-page-title-main">Ediacaran biota</span> All organisms of the Ediacaran Period (c. 635–538.8 million years ago)

The Ediacaranbiota is a taxonomic period classification that consists of all life forms that were present on Earth during the Ediacaran Period. These were enigmatic tubular and frond-shaped, mostly sessile, organisms. Trace fossils of these organisms have been found worldwide, and represent the earliest known complex multicellular organisms. The term "Ediacara biota" has received criticism from some scientists due to its alleged inconsistency, arbitrary exclusion of certain fossils, and inability to be precisely defined.

<i>Albumares</i> Extinct genus of soft-bodied Trilobozoan

Albumares brunsae is a tri-radially symmetrical fossil animal that lived in the late Ediacaran seafloor. It is a member of the extinct group Trilobozoa.

The end-Ediacaran extinction is a mass extinction believed to have occurred near the end of the Ediacaran period, the final period of the Proterozoic eon. Evidence suggesting that such a mass extinction occurred includes a massive reduction in diversity of acritarchs, the sudden disappearance of the Ediacara biota and calcifying organisms, and the time gap before Cambrian organisms "replaced" them. Some lines of evidence suggests that there may have been two distinct pulses of the extinction event, one occurring 550 million years ago and the other 539 million years ago.

The Cambrian explosion is an interval of time approximately 538.8 million years ago in the Cambrian period of the early Paleozoic when there was a sudden radiation of complex life, and practically all major animal phyla started appearing in the fossil record. It lasted for about 13 to 25 million years and resulted in the divergence of most modern metazoan phyla. The event was accompanied by major diversification in other groups of organisms as well.

Ediacaran type preservation relates to the dominant preservational mode in the Ediacaran period, where Ediacaran organisms were preserved as casts on the surface of microbial mats.

<span class="mw-page-title-main">Erniettomorph</span> Extinct clade of fossils

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. 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. Their affinity is uncertain; they probably form a clade and are most likely a sister group to the rangeomorphs, which bear a similar 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 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 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.

<span class="mw-page-title-main">Avalon explosion</span> Proposed evolutionary event in the history of metazoa, producing the Ediacaran biota

The Avalon explosion, named from the Precambrian faunal trace fossils discovered on the Avalon Peninsula in Newfoundland, eastern Canada, is a proposed evolutionary radiation of prehistoric animals about 575 million years ago in the Ediacaran period, with the Avalon explosion being one of three eras grouped in this time period. This evolutionary event is believed to have occurred some 33 million years earlier than the Cambrian explosion, which had been long thought to be when complex life started on Earth.

<span class="mw-page-title-main">Precambrian body plans</span> Structure and development of early multicellular organisms

Until the late 1950s, the Precambrian was not believed to have hosted multicellular organisms. However, with radiometric dating techniques, it has been found that fossils initially found in the Ediacara Hills in Southern Australia date back to the late Precambrian. These fossils are body impressions of organisms shaped like disks, fronds and some with ribbon patterns that were most likely tentacles.

<span class="mw-page-title-main">Petalonamae</span> Proposed extinct group of animals

The petalonamids (Petalonamae) are an extinct group of archaic animals typical of the Ediacaran biota, also called frondomorphs, dating from approximately 635 million years ago to 516 million years ago. They are benthic and motionless animals, that have the shape of leaves, fronds (frondomorphic), feathers or spindles and were initially considered algae, octocorals or sea pens. It is now believed that there are no living descendants of the group, which shares a probable relation to the Ediacaran animals known as Vendozoans.

References

  1. 1 2 3 Seilacher, A. (1992). "Vendobionta and Psammocorallia: Lost constructions of Precambrian evolution". Journal of the Geological Society (abstract). 149 (4). London, UK: Geological Society: 607–613. Bibcode:1992JGSoc.149..607S. doi:10.1144/gsjgs.149.4.0607. S2CID   128681462 . Retrieved 21 June 2007.
  2. ↑ Martínez Chacón, María Luisa. Invertebrate paleontology (Report). Spain: Paleontology, Geological, and Mining Institute.
  3. ↑ Seilacher, A.; Grazhdankin, D.; Legouta, A. (2003). "Ediacaran biota: The dawn of animal life in the shadow of giant protists". Paleontological Research. 7 (1): S. 43–54. doi: 10.2517/prpsj.7.43 . S2CID   85146476.
  4. 1 2 3 4 5 Peterson, Kevin J.; Waggoner, Ben; Hagadorn, James W. (1 February 2003). "A fungal analog for Newfoundland Ediacaran fossils?". Integrative and Comparative Biology . 43 (1): 127–136. doi:10.1093/icb/43.1.127. PMID   21680417.
  5. ↑ Smith, Dave (1999). "Cyclomedusa". Vendian. UC Museum of Paleontology. UC Berkeley.
  6. ↑ Stanley, S.M. (1973). "An ecological theory for the sudden origin of multicellular life in the Late Precambrian". Proceedings of the National Academy of Sciences . 70 (5): 1486–1489. Bibcode:1973PNAS...70.1486S. doi: 10.1073/pnas.70.5.1486 . PMC   433525 . PMID   16592084 . Retrieved 21 June 2007.
  7. 1 2 McMenamin, M.A.S. (1998) [1986]. The Garden of Ediacara: Discovering the first complex life. Columbia University Press. ISBN   9780231500302. ISBN   9780231105590
  8. ↑ Laflamme, Marc; Shuhai, Xiao; Kowalewski, Michał (2009). "Osmotrophy in modular Ediacara organisms". Proceedings of the National Academy of Sciences . 106 (34): 14438–14443. doi: 10.1073/pnas.0904836106 . PMC   2732876 . PMID   19706530.
  9. ↑ Waggoner, Ben (1 February 2003). "The Ediacaran biotas in space and time". Integrative and Comparative Biology . 43 (1): 104–113. CiteSeerX   10.1.1.491.4910 . doi:10.1093/icb/43.1.104. PMID   21680415.
  10. ↑ Dornbos, Stephen Q.; Clapham, Matthew E.; Fraiser, Margaret L.; la Flamme, Marc (2012). "Chapter 5: Lessons from the fossil record: The Ediacaran radiation" (PDF). In Solan, Martin; Aspden, Rebecca J.; Paterson, David M. (eds.). Marine Biodiversity and Ecosystem Functioning (1st ed.). Oxford University Press. Retrieved 18 December 2022.
  11. ↑ The Ediacara biota and first mass extinction of metazoan life (video). National Museum of Natural History. Smithsonian Institution. 2016 – via YouTube.
  12. ↑ Zhuravlev, A.Y. (1993). "Were Ediacaran Vendobionta multicellulars?". Neues Jahrbuch für Geologie und Paläontologie. 190: 299–314.
  13. ↑ Waggoner, B.M. (1998). Three-dimensional anatomy and microstructure of some simple "medusoids" from the Vendian of Siberia. Geological Society of America (abstract). Prog. 3034.
  14. ↑ Bergström, J. (1991). "Metazoan evolution around the Precambrian-Cambrian transition". In Simonetta, A.M.; Conway Morris, S. (eds.). The Early Evolution of Metazoa and the Significance of Problematic Taxa. Cambridge, UK: Cambridge University Press. pp. 25–34.
  15. ↑ Hagadorn, J.W.; Bottjer, D.J. (1 November 1997). "Wrinkle structures: Microbially mediated sedimentary structures common in subtidal siliciclastic settings at the Proterozoic-Phanerozoic transition". Geology . 25 (11): 1047–1050. Bibcode:1997Geo....25.1047H. doi:10.1130/0091-7613(1997)025<1047:WSMMSS>2.3.CO;2 . Retrieved 18 December 2022– via ResearchGate.com.
  16. ↑ Norri, Richard D. (October 1989). "Cnidarian taphonomy and affinities of the Ediacara biota". Lethaia . 22 (4): 381–393. doi:10.1111/j.1502-3931.1989.tb01439.x.
  17. ↑ Antcliffe, Jonathan B.; Brasier, Martin D. (January 2008). "Charnia at 50: Developmental models for Ediacaran fronds". Palaeontology . 51 (1): 11–26. doi: 10.1111/j.1475-4983.2007.00738.x . S2CID   83486435.
  18. ↑ Crimes, T.P.; Insole, A.; Williams, B.P.J. (June 1995). "A rigid-bodied Ediacaran biota from Upper Cambrian strata in Co. Wexford, Eire". Geological Journal . 30 (2): 89–109. doi:10.1002/gj.3350300202.
  19. 1 2 Ivantsov, A.Yu. (2013). "Trace fossils of precambrian metazoans "Vendobionta" and "Mollusks"". Stratigr. Geol. Correl. 21 (3): 252. Bibcode:2013SGC....21..252I. doi:10.1134/S0869593813030039. S2CID   128638405.
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