Siphonotretida
Temporal range: Cambrian Stage 4–Ludlow
"Schizambon" [sic] perspinosum, a siphonotretid from the Upper Ordovician of Oklahoma
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Brachiopoda
Class: Lingulata
Order: †Siphonotretida
Kuhn, 1949
Superfamily: †Siphonotretoidea
Kutorga, 1848
Family: †Siphonotretidae
Kutorga, 1848

Siphonotretida is an extinct order of linguliform brachiopods in the class Lingulata. The order is equivalent to the sole superfamily Siphonotretoidea, itself containing the sole family Siphonotretidae. Siphonotretoids were originally named as a superfamily of Acrotretida, before being raised to their own order.[1]

Evolution

Spihonotretids were most abundant in the late Cambrian and Early Ordovician (Furongian to Floian), and were traditionally considered to have gone extinct in the Upper Ordovician ("Ashgill").[1] More recently, new siphonotretids have been described as early as Cambrian Stage 4 (Schizambon)[2][3] and as late as the Ludlow Epoch of the Silurian (Orbaspina).[4][5] Isolated fragments are even known from the Emsian stage of the Lower Devonian.[3] Archaic Cambrian-style siphonotretids such as Schizambon and Helmersenia, with basic forms of ornamentation, populated the shores of Baltica, Laurentia, and Gondwana by the start of the Ordovician. In the late Tremadocian, advanced Ordovician-style spiny siphonotretids spread out from temperate waters around Gondwana and mostly replaced their older relatives.[6][7]

Anatomy

Siphonotretids had simple, rounded shells, with an ornamentation of hollow spines[1] or rarely pointed tubercles.[3] The shell is usually ventribiconvex (both valves convex, the ventral valve moreso) and composed of microscopic granules of apatite. The inner surface of the shell tends to be weakly mineralized, so many aspects of the musculature and other soft anatomy are difficult to estimate in most species. Available data supports comparison to the internal structures of lingulids.[1] Siphonotretids may be related to the linguloid families Lingulellotretidae or Dysoristidae.[8]

Similar to acrotretides, the pedicle foramen was set at the apex of the ventral valve, though it is often elongated into a tubular groove opening forwards. This groove lies on a triangular extension of the ventral valve, known as a pseudointerarea, which overhangs the dorsal valve. Unlike acrotretides, the adult shell is spinose while the larval shell lacks a pitted texture.[1]

The possible siphonotretid Acanthotretella is known from several exceptionally-preserved specimens which reveal lingulid-like traits such as setae, a spirolophous lophophore and U-shaped gut. However, the shell was poorly mineralized and sends out a very long, stalk-like pedicle, which in one specimen was attached to a fragment of algae. Combined with a lightweight shell, the pedicle likely helped to suspend the body above the seabed, an epibenthic lifestyle dissimilar to the infaunal (burrowing) lingulids.[9][2][10]

List of genera

References

  1. ^ a b c d e Holmer, Lars E.; Popov, Leonid E. (2000). "Chapter 1 (part): Lingulata". In Kaesler, Roger L. (ed.). Part H, Brachiopoda (Revised). Volumes 2 & 3: Linguliformea, Craniiformea, and Rhynchonelliformea (part). Treatise on Invertebrate Paleontology. Boulder, Colorado; Lawrence, Kansas: Geological Society of America; University of Kansas. pp. 136–146. ISBN 0-8137-3108-9.
  2. ^ a b c Hu, S.; Zhang, Z.; Holmer, L.E.; Skovsted, C.B. (2010). "Soft−part preservation in a linguliform brachiopod from the lower Cambrian Wulongqing Formation (Guanshan Fauna) of Yunnan, South China". Acta Palaeontologica Polonica. 55 (3): 495–505. CiteSeerX 10.1.1.729.8220. doi:10.4202/app.2009.1106. S2CID 59439966.
  3. ^ a b c d e Holmer, Lars E.; Popov, Leonid E.; Bassett, Michael G. (2007). "Chapter 3 (part): Siphonotretida". In Selden, Paul A. (ed.). Part H, Brachiopoda (Revised). Volume 6: Supplement. Treatise on Invertebrate Paleontology. Boulder, Colorado; Lawrence, Kansas: Geological Society of America; University of Kansas. pp. 2575–2577. ISBN 978-0-8137-3136-0.
  4. ^ a b Mergl, M. (2003). "Orbaspina chlupaci sp. nov., a new siphonotretid brachiopod from the Silurian of the Barrandian area, Bohemia" (PDF). Bulletin of Geosciences. 78 (4): 419–421.
  5. ^ Mergl, M.; Fryda, J.; Kubajko, M. (2018). "Response of organophosphatic brachiopods to the mid-Ludfordian (late Silurian) carbon isotope excursion and associated extinction events in the Prague Basin (Czech Republic)" (PDF). Bulletin of Geosciences. 93 (3): 369–400. doi:10.3140/bull.geosci.1710.
  6. ^ Popov, Leonid E.; Bassett, Michael G.; Holmer, Lars E.; Ghobadi Pour, Mansoureh (2009-08-01). "Early ontogeny and soft tissue preservation in siphonotretide brachiopods: New data from the Cambrian–Ordovician of Iran". Gondwana Research. 16 (1): 151–161. Bibcode:2009GondR..16..151P. doi:10.1016/j.gr.2009.01.009. ISSN 1342-937X.
  7. ^ Popov, Leonid E.; Holmer, Lars E.; Bassett, Michael G.; Pour, Mansoureh Ghobadi; Percival, Ian G. (2013). Harper, D.A.T.; Servais, T. (eds.). "Chapter 10: Biogeography of Ordovician linguliform and craniiform brachiopods". Geological Society, London, Memoirs. Early Palaeozoic Biogeography and Palaeogeography. 38 (1): 117–126. doi:10.1144/M38.10. ISSN 0435-4052.
  8. ^ a b Valentine, James L.; Brock, Glenn (2003). "A new siphonotretid brachiopod from the Silurian of central-western New South Wales, Australia" (PDF). Records of the Australian Museum. 55 (2): 231–244. doi:10.3853/j.0067-1975.55.2003.1378.
  9. ^ a b Holmer, L. E.; Caron, J. B. (2006). "A spinose stem group brachiopod with pedicle from the Middle Cambrian Burgess Shale". Acta Zoologica. 87 (4): 273. doi:10.1111/j.1463-6395.2006.00241.x.
  10. ^ "Acanthotretella spinosa". Burgess Shale Fossil Gallery. Virtual Museum of Canada. 2011. Archived from the original on 2020-11-12.
  11. ^ Streng, Michael; Mellbin, Barbro B.; Landing, Ed; Keppie, J. Duncan (2011). "Linguliform brachiopods from the terminal Cambrian and lowest Ordovician of the Oaxaquia microcontinent (Southern Mexico)". Journal of Paleontology. 85 (1): 122–155. Bibcode:2011JPal...85..122S. doi:10.1666/10-074.1.


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