Microdictyon

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Microdictyon
Temporal range: Cambrian Stage 3–Middle Cambrian
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Microdictyon model.JPG
Model of Microdictyon on display at the Chengjiang fossil site museum
Microdictyon Chengjiang.JPG
Microdictyon Fossil
Scientific classification Red Pencil Icon.png
Kingdom: Animalia
Stem group: Onychophora
Genus: Microdictyon
Bengtson, Matthews & Missarzhevsky, 1986
Type species
Microdictyon effusum
Bengtson, Matthews & Missarzhevsky, 1986
Species

See text

Microdictyon is an extinct "armored worm" coated with net-like scleritic scales, known from the Early Cambrian Maotianshan shale of Yunnan China. Microdictyon is sometimes included in a somewhat ill-defined Phylum Lobopodia that includes several other odd worm-like and segmented free-swimming animals that do not appear to be arthropods or worms. The phylum includes Microdictyon, Onychodictyon , Cardiodictyon , Luolishania , and Paucipodia . The isolated sclerites of Microdictyon are known from other Lower Cambrian deposits. Microdictyon sclerites appear to have moulted; one sclerite seems to have been preserved during ecdysis. [1]

Microdictyon sinicum (Chen, Hou and Lu, 1989) is typical. The wormlike animal has ten pairs of sclerites (suggestions that these may be eyes or eye-like structures have no weight [2] ) on the sides, matched to a pair of tentacle-like feet below. The head and posterior are tubular and featureless.

Species composition

In addition to the type species, 13 species: [3]

A picture can be found at https://web.archive.org/web/20030730043530/http://paws.wcu.edu/dperlmutr/earlyfauna.html.


The name Microdictyon is also used for a genus of green algae.

Related Research Articles

Lobopodia group of animals

The lobopodians, members of the informal group Lobopodia are worm-like taxa with stubby legs.

Halkieriid Family of molluscs

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The Chancelloriids are an extinct family of animal common in sediments from the Early Cambrian to the early Late Cambrian. Many of these fossils consists only of spines and other fragments, and it is not certain that they belong to the same type of organism. Other specimens appear to be more complete and to represent sessile, bag-like organisms with a soft skin armored with star-shaped calcareous sclerites from which radiate sharp spines.

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<i>Yunnanocephalus</i> genus of trilobites

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<i>Tsunyidiscus</i> genus of trilobites

Tsunyidiscus is a genus of eodiscinid agnostid trilobites. Tsunyidiscus occurs near the end of the Lower Cambrian, during the late Atdabanian stage period and some collections suggest it may have survived into the Botomian. They are very small, have eyes, and equal sized head and tail shields, with a narrow dome-shaped glabella and a narrow bullet-shape pygidial axis. It has a thorax of three segments. Tsunyidiscus is the only genus currently attributed to the family Tsunyidiscidae.

The small shelly fauna, small shelly fossils (SSF), or early skeletal fossils (ESF) are mineralized fossils, many only a few millimetres long, with a nearly continuous record from the latest stages of the Ediacaran to the end of the Early Cambrian Period. They are very diverse, and there is no formal definition of "small shelly fauna" or "small shelly fossils". Almost all are from earlier rocks than more familiar fossils such as trilobites. Since most SSFs were preserved by being covered quickly with phosphate and this method of preservation is mainly limited to the Late Ediacaran and Early Cambrian periods, the animals that made them may actually have arisen earlier and persisted after this time span.

Xenusiid subset of lobopodian worms that fall in the stem-lineage of Onychophora

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Allonnia is a genus of coeloscleritophoran known as complete scleritomes from the Middle Cambrian Burgess Shale. It is also a constituent of the small shelly fauna.

Mongolitubulus is a form genus encapsulating a range of ornamented conical small shelly fossils of the Cambrian period. It is potentially synonymous with Rushtonites, Tubuterium and certain species of Rhombocorniculum, and owing to the similarity of the genera, they are all dealt with herein. Organisms that bore Mongolitubulus-like projections include trilobites, bradoriid arthropods and hallucigeniid lobopodians.

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Rhombocorniculum is a species of small shelly fossil comprising twisted ornamented cones. It has been described from the Comely limestone and elsewhere. R. cancellatum straddles the Atdabanian/Botomian boundary. The structure of its inner layer suggests that its phosphatic fibres formed within a flexible organic matrix.

<i>Delgadella</i>

Delgadella is a diminutive trilobite that lived during the late Lower Cambrian and has been found in Russia, Mongolia, Spain, Italy (Sardinia), Portugal, Morocco and Canada (Newfoundland). It can be recognized by its strongly effaced headshield and tailshield, with narrow but distinct furrows and borders along its margins, and three thorax segments.

The genus Milaculum was erected to contain isolated plates that have since been identified as components of palaeoscolecid worms. They are adorned with regularly arranged humps that recall the arrangement of holes in Microdictyon. The plates are sometimes found in association with palaeoscolecid cuticle.

Protoconodonts are an extinct taxonomic group of conodonts or, possibly, Chaetognaths.

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References

  1. Figured in Dzik, J. (2003). "Early Cambrian lobopodian sclerites and associated fossils from Kazakhstan" (PDF). Palaeontology. 46: 93. doi:10.1111/1475-4983.00289.
  2. 1 2 Zhang, X. -G.; Aldridge, R. J. (2007). "Development and Diversification of Trunk Plates of the Lower Cambrian Lobopodians". Palaeontology. 50 (2): 401. doi:10.1111/j.1475-4983.2006.00634.x.
  3. 1 2 Demidenko, Yu. E. (2006). "New Cambrian lobopods and chaetognaths of the Siberian Platform". Paleontological Journal. 40 (3): 234–243. doi:10.1134/S0031030106030026.
  4. 1 2 Thomas Wotte; Frederick A. Sundberg (2017). "Small shelly fossils from the Montezuman–Delamaran of the Great Basin in Nevada and California". Journal of Paleontology. 91 (5): 883–901. doi:10.1017/jpa.2017.8.