Burykhia

''Burykhia hunti'' is an Ediacaran fossil from the White Sea region of Russia dating to . It is considered of possibly ascidian affinity, due to the sac-like morphology and a series of distinctly perforated bands reminiscent of a tunicate pharynx. If ''B. hunti'' is a tunicate, it could be the oldest ascidian fossil known as of its publication in 2012. It is also possibly related to the slightly younger '' Ausia'', another putative ascidian from the Vendian biota in Namibia.

Discovery and Naming

The fossil material of ''Burkyhia'' was found in the Syuzma River of the Ustʹ Pinega Formation, in Arkhangelsk Oblast of Northwestern Russia in 1995 and 2003, and described in 2012.

The generic name ''Burykhia'' derives from the Latinised surnames of Andreevna and Timofey Antonovich Burykh, residents who lived near the fossil site that helped with the expedition. The specific name ''hunti'' derives from the surname of Nathan Hunt, who has contributed to the study of Neoproterozoic rocks in Russia.

Description

''Burykhia hunti'' is possibly the earliest, and oldest, known ascidian tunicate, alongside ''Ausia'' from the younger Nama Group.

It has a sac-like form, which grew up to in height, and a width of . The body itself is made up of bands, which contain evenly spaced openings, which are also equal in size. There is also a longitudinal zig-zag ridge running down the length of the body, supporting a possible affinity with the suborder Phlebobranchia, and was most likely sessile. The fossil material of ''Burykhia'' also clearly shows that it was highly elastic, due to the deformation of the bands and fossils themselves. It has also been noted that in all material, there is preserved a spherical feature within or adjacent to ''Burykhia'', which could be infilled internal structures, such as a digestive tract.

It has been noted to share many similarities with Ausia, although it is much bettered preserved, and has a few key details which differentiate it as its own genus. Even when taking deformational processes into account, openings of ''Burykhia'' are set further apart than the openings seen in ''Ausia'', and are not as elongated. The longitudinal ridge seen in ''Burykhia'' is also a lot more distinct than in ''Ausia''. Although it has been noted that if more better material of ''Ausia'' or ''Burykhia'' is found that shows both are the same, there is a likely chance ''Burykhia'' could be synonymized with ''Ausia'', but until then, they remain as separate genera.

Affinities

Due to the preservation of ''Burykhia'', thanks to the possible rapid infilling of its internals from sand, something common to the area ''Burykhia'' was found, it was possible to do an in depth look at to what ''Burykhia'' may have affinities to, unlike the possibly related ''Ausia'', which has been though many reinterpretations.

It has already been noted that the longitudinal ridge that runs down the length of ''Burykhia'' suggest affinities with the Phlebobranchia, a suborder with in class Ascidiacea, which itself sits within subphylum of Tunicata. The arrangement of the openings is also similar to that of the gill sacs seem in adult tunicates. Although, it must be noted that the banding that runs around ''Burykhia'' joins the longitudinal ridge with a noticeable glide reflection, similar to other Ediacaran forms like the Proarticulata or Petalonamae, although the paper also notes that it is known that some chordates do show glide reflection during developmental stages, like hemichordates, which show a glide reflection in their gill apparatus during growth. ''Burkhia'' also has a similar size range to most tunicates.

If ''Burykhia'' is indeed an tunicate, alongside ''Ausia'', both would also lend credence and help calibrate the debated molecular clock estimates of chordates, with one molecular clock study estimating that protochordates separated some 900 million years ago, although some have disputed this, putting the time-interval of separation at 794 million years ago.

See also

* List of Ediacaran genera

References

{{Taxonbar, from=Q5001149

Enigmatic prehistoric animal genera
Ediacaran life
Precambrian fossils
Ediacaran Europe
White Sea fossils
Taxa named by Patricia Vickers-Rich