Tommotiid

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Tommotiids
Temporal range: Terreneuvian–Drumian[1][2]
Scientific classification e
Kingdom: Animalia
Informal group: Lophophorata
Order: "Tommotiida"

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

The majority of tommotiids are mineralised with calcium phosphate rather than calcium carbonate.[5] although silicified examples hint that some species bore carbonate or carbonaceous sclerites.[6]

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.[7]

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.[8][9]

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.[10]

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.[8]

Taxonomy[edit]

Five families are recognized[11]:

  • 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?)

References[edit]

  1. ^ a b Skovsted, C. B.; Brock, G. A.; Topper, T. P.; Paterson, J. R.; Holmer, L. E. (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. ^ http://www.diva-portal.org/smash/record.jsf?pid=diva2%3A809326&dswid=-5399
  3. ^ Holmer, L.E., Skovsted, C.B, Brock, G.A., Valentine, J.L. , and Paterson,J.R. (June 2008). "The Early Cambrian tommotiid Micrina, a sessile bivalved stem group brachiopod". Royal Society: Biology Letters. 4 (6): 724–8. doi:10.1098/rsbl.2008.0277. PMC 2614141Freely accessible. PMID 18577500. Retrieved 2008-07-23.  There is a reconstruction of Micrina at "Catalogue of Organisms: Back to the Scleritome - Tommotiids Revealed!". Retrieved 2008-07-23. 
  4. ^ Skovsted, C.B, Brock, G.A., Paterson,J.R., Holmer, L.E., and Budd, G.E. (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. doi:10.1130/G24385A.1. Retrieved 2008-07-23. 
  5. ^ Bengtson, S. (2004). Lipps, J.H.; Waggoner, B.M., eds. "Neoproterozoic- Cambrian Biological Revolutions" (PDF). Paleontological Society Papers. 10: 67–78. Retrieved 2008-07-18.  |contribution= ignored (help)
  6. ^ (PDF) http://www.geology.cz/bulletin/fulltext/1609_Skovsted_161125.pdf.  Missing or empty |title= (help)
  7. ^ Holmer, L. E.; Skovsted, C. B.; Larsson, C.; Brock, G. A.; Zhang, Z. (2011). "First record of a bivalved larval shell in Early Cambrian tommotiids and its phylogenetic significance". Palaeontology. 54 (2): no. doi:10.1111/j.1475-4983.2010.01030.x. 
  8. ^ a b Skovsted, C. B.; Brock, G. A.; Paterson, J. R.; Holmer, L. E.; Budd, G. E. (2008). "The scleritome of Eccentrotheca from the Lower Cambrian of South Australia: Lophophorate affinities and implications for tommotiid phylogeny". Geology. 36 (2): 171. doi:10.1130/G24385A.1. 
  9. ^ (PDF) http://www.geology.cz/bulletin/fulltext/1609_Skovsted_161125.pdf.  Missing or empty |title= (help)
  10. ^ Skovsted, C. B.; Holmer, E.; Larsson, M.; Hogstrom, E.; Brock, A.; Topper, P.; Balthasar, U.; Stolk, P.; Paterson, R. (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 2660981Freely accessible. PMID 19203919. 
  11. ^ The tommotiid ~Kelanella~ and associated fauna from the early Cambrian of southern Montagne Noire (France): Implications for camenellan phylogeny