Mickwitzia

Mickwitzia Temporal range: Cambrian
Scientific classification
Kingdom:	Animalia
Phylum:	Brachiopod Duméril, 1806
Family:	Mickwitziidae Goryanskii, 1969
Genus:	Mickwitzia Schmidt, 1888
Species
M. monilifera (Linnarsson, 1869) M. formosa (Wiman, 1902) M. muralensis Walcott, 1913 M. lochmana McMenamin, 1992 M. multipunctata McMenamin, 1992

Mickwitzia is a genus of stem group brachiopods with punctate shells from the Cambrian period. Mickwitziid shells are composed of apatite (calcium phosphate). Punctae or tubes penetrate through multiple shell wall layers, and individual punctae often develop a single, axial phosphatic tube. Members of the genus appear to share characteristic shell microstructure in common with halkieriids such as Micrina^[1], and like the halkieriids, mickwitziids may not have been able to enclose their entire body within a bivalved shell.^[2] As such, mickwitziids represent a potentially critical intermediate fossil taxon linking Phylum Brachiopoda to another animal phylum, with both higher taxa appearing rather suddenly near the beginning of the Cambrian. The origins and functions of the tubes that penetrate mickwitziid shells are controversial. One hypothesis considers the tubes to represent marginal setae that became surrounded by phosphatic shell material.^[3] Another hypothesis suggests that the tubes represent conduits for the delivery of anti-predation or anti-fouling toxins to the shell surface.^[4] The two hypotheses are not necessarily mutually exclusive.

References

1. ^ McMenamin, M. A. S. (1992). "Two new species of the Cambrian genus Mickwitzia". Journal of Paleontology 66 (2): 173–182. 
2. ^ Holmer, L. E.; Skovsted, C. B.; Williams, A. (2002). "A stem group brachiopod from the Lower Cambrian: Support for a Micrina (halkieriid) ancestry". Palaeontology 45 (5): 875–882. 
3. ^ Skovsted, C. B.; Holmer, L. E. (2003). "The Early Cambrian (Botomian) stem group brachiopod Mickwitzia from Northeast Greenland". Acta Palaeontologica Polonica 48 (1): 1–20. 
4. ^ McMenamin, M. A. S. (1987). "The emergence of animals". Scientific American 256 (4): 94–102.