Spriggina

''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.

The organism reached in length and may have been predatory. Its bottom was covered with two rows of tough interlocking plates, while one row covered its top; its front few segments fused to form a "head."

The affinity of ''Spriggina'' is unknown; it has been variously classified as an annelid worm, a rangeomorph-like frond, a variant of '' Charniodiscus'', a proarticulatan, an arthropod (perhaps related to the trilobites), or even an extinct phylum. The lack of known segmented legs or limbs, coupled with the presence of glide reflection instead of symmetric segments, suggests that an arthropod classification is unlikely despite some superficial resemblance.

The genus ''Spriggina'' originally contained three different species—''S. floundersi'', ''S. ovata'', and ''S. borealis''—but ''S. ovata'' is now considered a junior synonym of '' Marywadea ovata'', while the phylogenetic status of ''S. borealis'' remains a subject of active debate.

Description

''Spriggina'' grew to in length and was approximately oblong. The organism was segmented, with no fused segments; the segments were sometimes curved. The upper surface of the organism was covered by one row of overlapping cuticular plates, the underside with paired plates.

The first two segments formed a "head". The front segment had the shape of a horseshoe with a pair of depressions on its upper surface; these may have represented eyes. The second segment may have borne antennae. Subsequent segments bore annulations.

Some fossils have what may be a circular mouth at the centre of the semicircular head, although interpretation is hampered by the small size of the creature relative to the large grains of sandstones in which it is preserved. Legs are not preserved.

The symmetry observed is not exactly bilaterian but appears to be a glide reflection, where opposite segments are shifted by half an interval. In some specimens the body segments tilt backwards, making roughly chevron patterns; while in others they are more or less straight. There appear to be fairly complex variations between these two extremes.

Discovery and naming

The genus was named after Reg Sprigg who discovered the fossils of the Ediacara Hills—part of the Flinders Ranges in South Australia—and was a proponent of their recognition as multicellular organisms.
''Spriggina floundersi'' is at present the only generally accepted species in this genus. The specific name "''floundersi''" refers to amateur South Australian fossil hunter Ben Flounders. ''Spriggina ovata'' has now been moved into its own genus, '' Marywadea''.

''Spriggina'' is known only from beds of Ediacaran age.
Fossils from the Vindhyan basin, reliably dated to around , have been classified as ''Spriggina'', but in all likelihood represent microbial artifacts.

''Spriggina'' possessed a tough, though uncalcified body, evident from the fossils' preservation: always as a mould in the lower surface of the fossiliferous bed.

Classification

Like many of the Ediacara biota, the relationship of ''Spriggina'' to other groups is unclear. It bears some similarity to the living polychaete worm '' Tomopteris'' and Amphinomidae, but its lack of chaetae, along with other lines of evidence, suggests that it cannot be placed in this phylum. It was also compared to the rangeomorphs, frondose members of the Ediacara biota that may represent a separate kingdom. While its glide symmetry may suggest otherwise, some researchers like Mark McMenamin suggested ''Spriggina'' would be an arthropod; its superficial resemblance to the trilobites may suggest a close relationship to this class and even suggested to be predatory. However, later studies do not consider such Ediacaran biota like it and '' Parvancorina'' to be stem-arthropods, as they do not share compelling characters with arthropods, and there are no definite proof to make them related to arthropods or other extant bilaterians. This similarity to trilobites could also be an example of convergent evolution.

Affinity

At first, ''Spriggina'' was thought to resemble a polychaete worm such as '' Nereis'', but a close look at the segmentation reveals that the segments do not match across the midline, just as in '' Dickinsonia''. In 1989 Seilacher turned the interpretation upside-down, suggesting that ''Spriggina'' could be another type of sea-pen, and that the ‘head’ was actually a holdfast.

A relationship with arthropods has also been suggested because of superficial similarities with the Cambrian trilobite, but the lack of limbs and exoskeleton casts profound doubt on an arthropod affinity. Furthermore, the broad pleural lobes of trilobites served primarily as a rigid hood under which the legs could process the sediment for food.

South Australia’s fossil emblem

In 14 February 2017 the ''Spriggina'' was adopted as South Australia’s fossil emblem, due the fact it hasn’t been found anywhere else. The uniqueness of this Ediacaran fossil has led it to become the official fossil emblem of South Australia, the 550-million-year-old fossil was chosen for best representing the state’s geological and scientific prowess. More than 3500 South Australians cast their vote for a fossil to become the state’s new emblem in an online poll.

See also

* '' Yorgia''
* '' Dickinsonia''
* List of Ediacaran genera

References

External Links

Google Image Search
''Spriggina''
Ediacara Foundation
''Ediacaran Fossils''

{{Taxonbar, from=Q132927

Sprigginidae
Prehistoric bilaterian genera
†Spriggina
Emblems of South Australia