Tommotiid

Tommotiids are Cambrian (Terreneuvian) shelly fossils thought to belong to the Brachiopod + Phoronid lineage (Brachiozoa).[3][4][5]

Tommotiids
Temporal range: Terreneuvian–Drumian[1][2]
Scientific classification
Kingdom: Animalia
Clade: Lophophorata
Order: †"Tommotiida"

The majority of tommotiids are mineralised with calcium phosphate rather than calcium carbonate.[6] although silicified examples hint that some species bore carbonate or carbonaceous sclerites.[7]

Micrina and Paterimitra possess bivalved shells in their larval phases, which preserve characters that might position them in the Linguliformea and Rhynchonelliformea stem lineages respectively. This would indicate that the brachiopod shell represents the retention of a larval character.[8]

For a long part of their history, the tommotiids were only known from disarticulated shells - a complete organism had not been found. The 2008 discovery of Eccentrotheca offered the first insight into a complete organism, and permitted a reconstruction of the animal as a sessile, tube-like animal made up of a spiral of overlapping plates.[5][7]

Articulated specimens of Paterimitra, discovered a year later, suggest a similar form and lifestyle - it is possible that many tommotiids need redescribing as sessile tube-dwellers.[9]

These discoveries have produced an alternative model for the origin of the brachiopods; it suggested that they evolved by the reduction of sessile tube-like organisms, until only two shells were left. This contrasts with the brachiopod fold hypothesis which suggests that they formed by the folding of a halkieriid-like organism.[5]

Taxonomy

Five families are recognized:[10]

  • Tommotiidae Missarzhevsky in Rozanov et al., 1969
  • Tannuolinidae Fonin and Smirnova 1967
  • Sunnaginiidae Landing, 1984
  • Kennardiidae Laurie, 1986
  • Lapworthellidae Missarzhevsky in Rozanov and Missarzhevsky, 1966
Taxon Relationship[1]
Kulparina Paterinid stem-group
Paterimitra Paterinid stem-group
Askepasma Paterinid stem- (or crown-?) group
Tannuolina Linguliform stem-group
Micrina Linguliform stem-group
Mickwitzia Linguliform stem- (or crown-?) group
Camenella Stem-group to {Brachiopods + Phoronids}
Dailyatia Stem-group to {Brachiopods + Phoronids}
Lapworthella Stem-group to {Brachiopods + Phoronids}
Eccentrotheca Stem-group to Phoronids? (or perhaps Brachiopods?)
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References
  1. Skovsted CB, Brock GA, Topper TP, Paterson JR, Holmer LE (2011). "Scleritome construction, biofacies, biostratigraphy and systematics of the tommotiid Eccentrotheca helenia sp. nov. from the Early Cambrian of South Australia". Palaeontology. 54 (2): 253–286. doi:10.1111/j.1475-4983.2010.01031.x.
  2. Skovsted, Christian; Bassett-Butt, Lewis (2015). "Discovery of the youngest known tommotiid from the middle Cambrian (Drumian) Nelson Limestone of Antarctica". Diva.
  3. Holmer LE, Skovsted CB, Brock GA, Valentine JL, Paterson JR (June 2008). "The Early Cambrian tommotiid Micrina, a sessile bivalved stem group brachiopod". Biology Letters. 4 (6): 724–728. doi:10.1098/rsbl.2008.0277. PMC 2614141. PMID 18577500.
  4. Taylor, Christopher (2008-06-27). "Back to the Scleritome - Tommotiids Revealed!". Catalogue of Organisms. Retrieved 2008-07-23.
  5. Skovsted CB, Brock GA, Paterson JR, Holmer LE, Budd GE (February 2008). "The scleritome of Eccentrotheca from the Lower Cambrian of South Australia: Lophophorate affinities and implications for tommotiid phylogeny". Geology. 36 (2): 171–174. Bibcode:2008Geo....36..171S. doi:10.1130/G24385A.1.
  6. Bengtson, S. (2004). "Early skeletal fossils". In Lipps, J.H.; Waggoner, B.M. (eds.). Neoproterozoic-Cambrian Biological Revolutions (PDF). The Paleontological Society Papers. 10. pp. 67–78. doi:10.1017/S1089332600002345. Archived from the original (PDF) on 2008-10-03. Retrieved 2008-07-18.
  7. Skovsted CB (2016). "A silicified tommotiid from the lower Cambrian of Greenland" (PDF). Bulletin of Geosciences. 91 (3): 553–559. doi:10.3140/bull.geosci.1609. ISSN 1214-1119.
  8. Holmer LE, Skovsted CB, Larsson C, Brock GA, Zhang Z (2011). "First record of a bivalved larval shell in Early Cambrian tommotiids and its phylogenetic significance". Palaeontology. 54 (2): 235–239. doi:10.1111/j.1475-4983.2010.01030.x.
  9. Skovsted CB, Holmer LE, Larsson CM, Högström AE, Brock GA, Topper TP, Balthasar U, Stolk SP, Paterson JR (May 2009). "The scleritome of Paterimitra: an Early Cambrian stem group brachiopod from South Australia". Proceedings of the Royal Society B: Biological Sciences. 276 (1662): 1651–1656. doi:10.1098/rspb.2008.1655. ISSN 0962-8452. PMC 2660981. PMID 19203919.
  10. Devaere L, Clausen S, Monceret É, Vizcaïno D, Vachard D, Genge M (2014). "The tommotiid Kelanella and associated fauna from the early Cambrian of southern Montagne Noire (France): Implications for camenellan phylogeny". Palaeontology. 57 (5): 979–1002. doi:10.1111/pala.12098.
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