Mongolitubulus is a genus of small shelly fossil. It is potentially a synonym with Rushtonites, and owing to the similarity of the two genera they are both dealt with herein.

Morphology

The fossils consist of round, slender, pointed, spines with a slight curvature, and are covered with short triangular processes.
Spines very from sub-millimetric up to two centimetres in length, but do not show any growth lines, suggesting that they were moulted and replaced.
Species are defined on the basis of the ornamentation, which may of course be convergent

Convergent evolution

Convergent evolution describes the acquisition of the same biological trait in unrelated lineages.The wing is a classic example of convergent evolution in action. Although their last common ancestor did not have wings, both birds and bats do, and are capable of powered flight. The wings are...

.

Affinity

M. henrikseni has been shown to be part of the carapace of a bivalved bradoriid

Bradoriid

Bradoriids are small marine arthropods with a bivalved carapace, and were globally distributed, forming a significant portion of the Cambrian and early Ordovician soft-bodied communities.- Affinity :...

 arthropod. However, the affinity of M. squamifer is still unresolved; the genus may transpire to be a form taxon

Form taxon

Form classification is the classification of organisms based on their morphology, which does not necessarily reflect their biological relationships...

, which would require M. henrikseni to be re-classified into a new genus. Unlike the spines of M. henrikseni, which flare out at the base where they attach to the cuticle, the spines of M. squamifer are more parallel-sided, with the fossil material becoming thinner towards the base: consistent with their attachment to non-mineralized cuticle. M. squamifer spines appear to have formed in pairs, owing to their symmetry; on this basis they have been likened to the spines of certain armoured lobopods known from Burgess shale-type deposits.

Preservation

The spines often comprise layers of phosphate, with a central void often infilled with diagenetic phosphate.
Similar spines have been recovered from acid maceration

Acid maceration

Acid maceration is a technique to extract organic microfossils from a surrounding rock matrix using acid.Hydrochloric acid or acetic acid may be used to extract phosphatic fossils, such as the small shelly fossils, from a carbonate matrix....

s, where they are preserved as films of organic carbon.

Distribution

The fossils are known from the Botomian to the lower strata of the Middle Cambrian, and have a worldwide distribution.