Anabarites is a genus of organisms known from thin mineralised tubes that commonly have three lobes in cross-section. It belongs to the earliest small shelly fossil assemblages and is especially important in Lower Cambrian strata. The soft body has not been found, so the animal’s appearance and relationships remain under discussion. In the Cambrian animal catalogue, Anabarites is presented as a useful fossil with an uncertain biological identity.
Quick facts
| Scientific name | Anabarites; type species A. trisulcatus |
|---|---|
| Named by | Vladimir Missarzhevsky, 1969 |
| Group | Anabaritidae; animal of uncertain placement |
| Age | Fortunian and younger Terreneuvian strata; some records extend into Stage 3 |
| Type locality | Kotuykan River mouth, Siberian Platform, Russia |
| Material | Tube fragments and phosphatic internal moulds |
| Diagnostic form | Three rounded lobes separated by shallow grooves |
| Soft body | Unknown |
What can the fossils tell us?
Missarzhevsky established A. trisulcatus in a 1969 monograph from material of the Anabar Uplift. The type locality lies near the mouth of the Kotuykan River, and the type horizon is in the lower Fortunian.
The tube gradually widened and curved irregularly. Its three lobes are divided by shallow longitudinal furrows; fine growth lines bend towards the open margin, which may form wedge-like projections.
Many fossils are phosphatic internal moulds left after the original tube wall dissolved. Other tubes are phosphatised, while related anabaritids can be replaced by celestine or barite. Diagenesis complicates identification of the original mineral.
Claims from the upper Ediacaran have been questioned because the fossils may be misidentified or the layer uncertain. The reliable record of the type species begins in the Early Cambrian.
The type species and its material
Vladimir Missarzhevsky established Anabarites trisulcatus in a collective monograph published in 1969, based on material from the Anabar Uplift of the Siberian Platform. The generic name refers to that region. The type locality is near the mouth of the Kotuykan River, and the type horizon belongs to the lower Fortunian Stage of the Cambrian.
A modern revision examined several hundred fragmentary tubes and internal moulds from the Manykay and Nemakit-Daldyn formations. Illustrated specimens SMNH X6002–X6007, X6009, X6010 and X6012 are housed in the Swedish Museum of Natural History. Some come from the original sample M419/12, allowing the type species to be compared with new material rather than relying only on an early drawing.
What the mineralised tube preserves
The tube of A. trisulcatus gradually widened and curved irregularly. In cross-section it had three rounded lobes divided by narrow, shallow grooves. Fine transverse growth lines within the grooves bent towards the open margin, where they may have formed wedge-shaped projections. The combination of cross-section, grooves and margin helps distinguish this species from related anabaritids.
Many specimens are phosphatic internal moulds left after the original wall dissolved. Other tubes were phosphatised; walls of some related anabaritids were replaced by celestine and barite. Microscopic structure points to a mineralised shell built in layers by an epithelium. The original mineral is often reconstructed as aragonite, but diagenesis altered the material, so its composition cannot be established equally well for each fossil.
Anabarites was not a cone-shaped shell like Conoteka, nor was it composed of separate star-shaped sclerites like the covering of Chancelloria. Its three-rayed tube was a continuous growing structure. That difference is visible in the form of the fossils, even though the soft animal that secreted the tube is unknown.
Age and geographic distribution
A. trisulcatus is widely reported from the Terreneuvian Series and locally extends into Cambrian Stage 3. Occurrences have been described on the Siberian Platform, in South China and on the Tarim block; related anabaritids are more widely distributed. On the Siberian Platform, the species gives its name to a biostratigraphic zone, although researchers do not correlate the lower and upper boundaries of that zone identically everywhere.
Reports of A. trisulcatus from the upper Ediacaran do exist, but authors and later revisions have highlighted uncertain identification or stratigraphic placement. Some similar pre-Cambrian tubes may belong to other organisms. The cautious conclusion is that the secure record of the type species begins in the Early Cambrian; crossing the formal period boundary remains disputed.
The organism inside the tube
Growth lines show that the shell lengthened at its open end. Internal projections in some anabaritids suggest close contact between soft tissues and the wall, but Anabarites has not yielded a mouth, gut, tentacles or an attachment organ. Its three-rayed symmetry prompted comparisons with cnidarians. Symmetry alone, however, is not enough to identify the genus as a coral.
The living orientation of the tube is also unknown for many finds. A vertical, stationary reconstruction is possible, but a stem, holdfast or soft body has not been directly preserved for the type species. Comparison with the two-walled cup of Nochoroicyathus shows an important difference: archaeocyaths preserve a porous filtering skeleton, whereas the feeding method of Anabarites remains unknown.
The fossils therefore provide stronger evidence for shell growth and early Cambrian occurrence than for behaviour. They preserve the mineralised tube and its changing cross-section, not the organs that produced it. Reconstructed colour, posture and feeding are artistic or functional hypotheses. The Cambrian animal catalogue places Anabarites among early marine fossils while leaving its affinities open.
Frequently asked questions
Did Anabarites definitely live before the Cambrian?
No. Upper Ediacaran identifications are disputed; secure records of A. trisulcatus are chiefly Early Cambrian.
Why is the tube called three-rayed?
Its cross-section has three rounded lobes separated by three longitudinal grooves, a key feature of the type species.
Has the soft body of Anabarites been found?
No confirmed soft body is known. Researchers study tubes, internal moulds and the microscopic structure of the mineralised wall.
Was Anabarites a coral?
That relationship has been proposed because of its three-rayed symmetry, but the genus remains among animals of uncertain placement. Calling it a true coral would go beyond the evidence.