Buenaspis

''Buenaspis'' is a genus of small ( long) nektaspid arthropod, that lived during the early Cambrian period.Budd, G.E (1999).
A Nectaspid Arthropod from the Early Cambrian Sirius Passet Fauna, with a description of Retrodeformation based on Functional Morphology
. ''Palaeontology'', 42(1):99–122 Fossil remains of ''Buenaspis'' were collected from the Lower Cambrian Sirius Passet ''Lagerstätte'' of North Greenland. ''Buenaspis'' looks like a soft eyeless trilobite. It has a headshield (or cephalon) slightly larger than the tailshield (pygidium), and in between them six thoracic body segments (somites). The genus is monotypic, its sole species being ''Buenaspis forteyi''.

Etymology

The name of the genus is derived from the Buen Formation, the deposit where the species was collected, and the Greek word ''aspis'' (shield). The species was named in honor of Richard Fortey, a famed paleontologist.

Description

''Buenaspis forteyi'' is between 1 and 3 cm along the axis, approximately half a wide as long, in general outline shaped as a bar with parallel sides and rounded front and back ends. It is likely the animal was distinctly convex, considering the many concentric crush-marks found in many specimens. The dorsal exoskeleton consists of a cephalon, a pygidium and six thoracic somites with articulating half-rings, all non-calcified. The cephalon is sub-semicircular, broader than it is long, and with rounded genal angles. Eyes are absent. Antennas are not known. The six thoracic somites are extended into broad posteriorly directed pleural spines, which are free at their tips. The caudal shield is slightly smaller than the cephalic shield, and somewhat more rounded. Some specimens appear to have a lengthwise mid-ridge from the cephalon to the pygidium. Although Budd attributes this feature to deformations, since it does not occur in all specimens known, later authors seem to have accepted it as authentic.

Differences from Liwiidae

* ''Buenaspis forteyi'' differs from '' Liwia'' by having six thoracic somites instead of four. ''B. forteyi'' also has an oval pygidium with an entire margin, while ''Liwia'' has five pairs of modest marginal pygidial spines, a straight anterior border and a concave posterior border.
* ''B. forteyi'' differs from '' Tariccoia arrusensis'', that has a subcircular cephalon that is wider than the rest of its body, without a lengthwise mid-ridge, a broad doublure (about ¼× the cephalon length), three thoracic somites, and a pygidium that is longer than wide, with a straight anterior border. ''Buenaspis'' and ''Tariccoia'' have an entire margin in common.
* ''B. forteyi'' differs from '' Soomaspis splendida'', that has an oval cephalon that is wider than the rest of its body, without a lengthwise mid-ridge, a broad doublure (about ¼× the cephalon length), three thoracic somites, and a pygidium that is about as long as wide. ''Buenaspis'' and ''Soomaspis'' have an entire margin in common.

Distribution

''B. forteyi'' has been collected from the Lower Cambrian (Atdabanian) Buen Formation, Sirius Passet ''Lagerstätte'', Peary Land, North Greenland, on the south side of the broad valley known as Sirius Passet at its junction with J.P. Koch Fjord .

Habitat

''Buenaspis forteyi'' was probably a marine bottom dweller, that lived in deeper water. This may be deduced from the dominance of eyeless forms and the absence of seaweeds at the collection site.Peel, J.S. and M. Stein (2009).
A new Arthropod from the Lower Cambrian Sirius Passet Fossil-Lagerstätten of North Greenland
. ''Bulletin of Geosciences'' 84(4)

Taxonomy

The author that originally described ''Buenaspis'' and subsequent publications classified the genus as part of the family Liwiidae. Recently however, Paterson et al. propose to remove ''Buenaspis'' from the order Nektaspida entirely, on the argument that it lacks the 'waist' that is a common feature in ''Liwia'', ''Soomaspis'', ''Tariccoia'', ''Misszhouia'', ''Pseudonaraoia'' and ''Naraoia''. Also, they regard the ridge on cephalon and pygidium in ''Buenaspis'' an artifact, unlike the ridge on the pygidium only in ''Soomaspis'' and ''Tariccoia''. If Paterson et al. is followed, ''Buenaspis'' attains a position somewhere else in the Lamellipedia. Other authors have continued to consider ''Buenaspis'' a nektaspid, but have placed it outside Liwiidae or any other family.

References

External links

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{{Taxonbar, from=Q4985481

Nektaspida
Prehistoric arthropod genera
Cambrian arthropods
Cambrian Greenland
Fossils of Greenland
Sirius Passet fossils

Fossil taxa described in 1999