Mickwitzia

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Mickwitzia
Temporal range: Terreneuvian–mid Cambrian
Scientific classification e
Kingdom: Animalia
Clade: Brachiozoa
Stem group: Brachiopoda
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

Mickwitziids are a Cambrian group of shelly fossils with originally phosphatic valves, belonging to the Brachiopod stem group, and exemplified by the genus Mickwitzia – the other genera are Heliomedusa (a possible junior synonym of Mickwitzia?) and Setatella.[1]

Shell microstructure[edit]

Punctae or tubes penetrate through multiple shell wall layers, and individual punctae often develop a single, axial phosphatic tube. The shell comprises multiple phosphatic laminae; the region closest to the edge of the shell was presumably more organic-walled than phosphatized as it tends to be more flimsily preservevd.[2]

Members of the genus appear to share characteristic shell microstructure in common with Tommotiids such as Micrina,[3] and like this taxon, mickwitziids may not have been able to enclose their entire body within a bivalved shell.[4]

The shells are punctuated with inward-directed hollow cones, conceivably associated with setae – though intact setae are exceptionally preserved along the margin of mickwitziid shells yet not found emanating from the cones, which have no evidence of ever incorporating setae.[2]

Affinity[edit]

Mickwitziids are stem-group brachiopods, with links to the tommotiid grade. Mickwitzia itself is conceivably synonymous with Heliomedusa.[2]

Distribution[edit]

The oldest mickwitziid dates to the Terreneuvian.[5]

References[edit]

  1. ^ 1 Butler, A. D., Streng, M., Holmer, L. E. & Babcock, L. E. 2015 Exceptionally preserved Mickwitzia from the Indian Springs Lagerstätte (Cambrian Stage 3), Nevada. J. Paleontol. 89, 933–955. (doi:10.1017/jpa.2016.8)
  2. ^ a b c Butler, Aodhán D.; Streng, Michael; Holmer, Lars E.; Babcock, Loren E. (2016). "Exceptionally preserved Mickwitzia from the Indian Springs Lagerstätte (Cambrian Stage 3), Nevada". Journal of Paleontology. 89 (6): 933–955. doi:10.1017/jpa.2016.8. 
  3. ^ McMenamin, M. A. S. (1992). "Two new species of the Cambrian genus Mickwitzia". Journal of Paleontology. 66 (2): 173–182. doi:10.1017/S0022336000033680. JSTOR 1305903. 
  4. ^ 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. doi:10.1111/1475-4983.00265. 
  5. ^ Devaere, Léa; Holmer, Lars; Clausen, Sébastien; Vachard, Daniel (2014). "Oldest mickwitziid brachiopod from the Terreneuvian of southern France". Acta Palaeontologica Polonica. doi:10.4202/app.00021.2013.