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Genus Parvancorina


Abstract

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Keywords: yyy

Introduction

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Morphology

Phylogeny and Evolution

Affinities

This form may be a stem group or other very early arthropod.

“Glaessner (1980) concluded that Parvancorina could be assigned to the Arthropoda on the basis of its interpreted carapace, but considered it to have no direct relationship to any extant groups. Glaessner (1980) dismissed the positive comparison, made by Della Cave and Simonetta (1975), of Skania fragilis Walcott, 1931 and Parvancorina as speculative, on the basis of the poor preservation of material ascribed to Skania. However, from study of the specimens available in the Smithsonian Institution Museum of Natural History in Washington D.C., and the Royal Ontario Museum, Toronto, it appears that there may be good grounds for systematic comparison between these forms. While many specimens labelled as Skania are indescribable, a small number preserve sufficient characters to suggest an organism of the same three dimensional form and size as Parvancorina. Both taxa have a strong axial ridge, and an arcuate structure parallel to the frontal margin. Parvancorina is known from hundreds of specimens, most less than 10 mm long. Originally described as a flat, shield-shaped arthropod (Glaessner, 1980), Parvancorina is now known to have a highly convex profile (Gehling. 1987). From a deeper water subfacies of the Ediacara Member, numerous small specimens are preserved with a median ridge that is as high as the animal is wide .... Their profile matches that of the “1aterally flattened” specimen of Skania figured by Della Cave and Simonetta (1975, figure 17). It seems likely that not just the flattened impressions of Parvancorina, but many other taxa may have been previously reconstructed as two dimensional organisms” (Gehling 1991, pp. 206-207).

Fossil Record

Origins

Evolution

Extinction

Systematics

?Phylum Arthropoda Siebold & Stannius ????

 

Incertae Sedis

Genus Parvancorina Glaessner 1958, p. ??

<synonymy>

Type: Parvancorina minchami Glaessner 1958, p. 187

Original Diagnosis: xxx

Description: xxx

?Habit: xxx

Occurrence: xxx

Discussion: xxx

Parvancorina minchami Glaessner 1958, p. 187

Fig. 1

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1958 Parvancorina minchami Glaessner, p. 187, pl. 1, fig. 4

1966 Parvancorina minchami Glaessner 1958, Glaessner & Wade, p. 625

<synonymy>

Type: xxx

Original Diagnosis: xxx

Description: Small sub-circular to circular, shield-shaped fossils with an elevated, anchor-shaped, antero-median ridge bearing curved, linear postero-lateral appendages on its anterior arms and finer transverse appendages on its median bar (after Glaessner & Wade 1966, p. 625).

Dimensions of undeformed specimens ranging from 3 mm long < 2 mm wide up to 25 mm long 21 mm wide. Some specimens are approximately circular or slightly wider than long such as one quoted by Glaessner & Wade 1966 at 22 mm long 23 mm wide.

?Habit: xxx

Occurrence: Glaessner & Wade 1966 note "about 60 specimens" form the Ediacara locality.

Discussion: Glaessner & Wade 1966 note that the integument "was pliable and possibly chitinous. It is not clear whether some feeble ridges on the inverted anterior portion of one specimen are reflected dorsal or independent ventral structures" (p. 625).

thmParvancorinaminchami.gif (38329 bytes)

Fig. 1: Parvancorina minchami – A candidate arthropod, possibly a trilobite (see Fortey et al. 1996). In this scenario, the central axial ridge and the strongly arched anterior ‘lobes’ may be analogous to the midgut and gastric diverticulae. The scale bar is in centimetres. [Image and interpretation courtesy of Chris Nedin, Department of Industry, Science and Resources, Canberra.]

Conclusion

Further Information

Chris Nedin's web site

References

Della Cave, L.; Simonetta, A.M. 1975: Notes on the Morphology and Taxonomic Position of Aysheaia (Onychophora?) and of Skania (Undetermined Phylum). Monitore Zool. Ital. (N.S.) 9: 67-81.

Gehling, J.G. 1991: The Case for Ediacaran Fossil Roots to the Metazoan Tree. Geological Society of India Memoir 20: 181-224.

Glaessner, M.F. 1958: New Fossils from the Base of the Cambrian in South Australia. Trans. Roy. Soc. S. Aust. 81: 185-188.

Glaessner, M.F. 1980: Parvancorina - an Arthropod from the Late Precambrian of South Australia. Ann. Naturhist. Mus. Wein, 83: 83-90.

Glaessner, Martin F.; Wade, Mary 1966: The Late Precambrian Fossils from Ediacara, South Australia. Palaeontology 9 (4), pp. 599-628.


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