Microconchida
The order Microconchida is a group of small, spirally-coiled, encrusting fossil "worm" tubes from the class Tentaculita found from the Upper Ordovician to the Middle Jurassic (Bathonian) around the world. They have lamellar calcitic shells, usually with pseudopunctae or punctae and a bulb-like origin. Many were long misidentified as the polychaete annelid Spirorbis until studies of shell microstructure and formation showed significant differences. All pre-Cretaceous "Spirorbis" fossils are now known to be microconchids. Their classification at the phylum level is still debated. Most likely they are some form of lophophorate, a group which includes phoronids, bryozoans and brachiopods. Microconchids may be closely related to the other encrusting tentaculitoid tubeworms, such as Anticalyptraea, trypanoporids and cornulitids. Their habitat is more controversial. While there is a consensus that they were present in the seas and in brackish water, there is a debate about their presence in freshwater. Some studies suggested that they colonised freshwater in the Early Devonian, whereas others suggest that microconchids never colonised that environment. A recent review of the associated fauna failed to find reliable occurrences of microconchids in the Middle Devonian to Early Permian time interval because microconchids seem to co-occur with other signs of marine influence, such as xiphosurans and chondrichthyan egg capsules.
| Microconchida Temporal range:
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|---|---|
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| Palaeoconchus angulatus (Hall, 1861) on a brachiopod from the Middle Devonian (Givetian) of Michigan | |
Scientific classification 
| |
| Kingdom: | Animalia |
| Clade: | Lophophorata |
| Class: | †Tentaculita |
| Order: | †Microconchida Weedon 1991 |
| Genera | |
The order Microconchida is a group of small, spirally-coiled, encrusting fossil "worm" tubes from the class Tentaculita found from the Upper Ordovician to the Middle Jurassic (Bathonian) around the world.[1][2][3][4][5] They have lamellar calcitic shells, usually with pseudopunctae or punctae and a bulb-like origin. Many were long misidentified as the polychaete annelid Spirorbis until studies of shell microstructure and formation showed significant differences.[6] All pre-Cretaceous "Spirorbis" fossils are now known to be microconchids.[6] Their classification at the phylum level is still debated. Most likely they are some form of lophophorate, a group which includes phoronids, bryozoans and brachiopods. Microconchids may be closely related to the other encrusting tentaculitoid tubeworms, such as Anticalyptraea, trypanoporids and cornulitids.[3] Their habitat is more controversial. While there is a consensus that they were present in the seas and in brackish water, there is a debate about their presence in freshwater. Some studies suggested that they colonised freshwater in the Early Devonian,[7][8] whereas others suggest that microconchids never colonised that environment.[9][10] A recent review of the associated fauna failed to find reliable occurrences of microconchids in the Middle Devonian to Early Permian time interval because microconchids seem to co-occur with other signs of marine influence,[11] such as xiphosurans and chondrichthyan egg capsules.[12]
References
[edit]- ^ Weedon, M.J. 1991. "Microstructure and affinity of the enigmatic Devonian tubular fossil Trypanopora". Lethaia 24:227-234 doi:10.1111/j.1502-3931.1991.tb01471.x.
- ^ Vinn, O. 2006. "Two new microconchid (Tentaculita Bouček 1964) genera from the Early Palaeozoic of Baltoscandia and England". Neues Jahrbuch für Geologie und Paläontologie 2006:89-100.
- ^ a b Vinn, O. 2010. "Adaptive strategies in the evolution of encrusting tentaculitoid tubeworms". Palaeogeography, Palaeoclimatology, Palaeoecology 292:211–221.
- ^ Vinn, O. & Mutvei, H. 2009. "Calcareous tubeworms of the Phanerozoic". Estonian Journal of Earth Sciences 58:286-296.
- ^ Zaton, M. & Vinn, O. 2011. "Microconchids and the rise of modern encrusting communities". Lethaia 44:5-7 doi:10.1111/j.1502-3931.2010.00258.x
- ^ a b Taylor, P.D. & Vinn, O. 2006. "Convergent morphology in small spiral worm tubes ("Spirorbis") and its palaeoenvironmental implications". Journal of the Geological Society, London 163:225-228 doi:10.1144/0016-764905-145.
- ^ Zatoń, Michał; Vinn, Olev; Tomescu, Alexandru M. F. (1 November 2012). "Invasion of freshwater and variable marginal marine habitats by microconchid tubeworms – an evolutionary perspective". Geobios. 45 (6): 603–610. doi:10.1016/j.geobios.2011.12.003. ISSN 0016-6995.
- ^ Zatoń, Michał; Wilson, Mark A.; Vinn, Olev (1 January 2016). "Comment on the paper of Gierlowski-Kordesch and Cassle "The 'Spirorbis' problem revisited: Sedimentology and biology of microconchids in marine–nonmarine transitions" [Earth-Science Reviews, 148 (2015): 209–227]". Earth-Science Reviews. 152: 198–200. doi:10.1016/j.earscirev.2015.11.012. ISSN 0012-8252.
- ^ Gierlowski-Kordesch, Elizabeth H.; Cassle, Christopher F. (1 September 2015). "The 'Spirorbis' problem revisited: Sedimentology and biology of microconchids in marine-nonmarine transitions". Earth-Science Reviews. 148: 209–227. doi:10.1016/j.earscirev.2015.04.010. ISSN 0012-8252.
- ^ Gierlowski-Kordesch, Elizabeth H.; Falcon-Lang, Howard J.; Cassle, Christopher F. (1 January 2016). "Reply to comment on the paper of Gierlowski-Kordesch and Cassle "The 'Spirorbis' problem revisited: Sedimentology and biology of microconchids in marine–nonmarine transitions"". Earth-Science Reviews. 152: 201–204. doi:10.1016/j.earscirev.2015.11.011. ISSN 0012-8252.
- ^ Laurin, Michel (30 December 2024). "Habitat of early stegocephalians (Chordata, Vertebrata, Sarcopterygii): a little saltier than most paleontologists like?". Fossil Record. 27 (3): 299–332. doi:10.3897/fr.27.123291. ISSN 2193-0074.
- ^ Lomax, Dean R.; Robinson, Peter; Cleal, Christopher J.; Bowden, Alistair; Larkin, Nigel R. (2016). "Exceptional preservation of Upper Carboniferous (lower Westphalian) fossils from Edlington, Doncaster, South Yorkshire, UK". Geological Journal. 51 (1): 42–50. doi:10.1002/gj.2602. ISSN 1099-1034.
- Wilson, M.A., Yancey, T.E. and Vinn, O. 2011. "A new microconchid tubeworm from the Lower Permian (Artinskian) of central Texas, USA". Acta Palaeontologica Polonica 56:785-791 doi:10.4202/app.2010.0086.
- Zaton, M., Wilson, M.A. and Vinn, O. 2012. "Redescription and neotype designation of the Middle Devonian microconchid (Tentaculita) species ‘Spirorbis’ angulatus Hall, 1861". Journal of Paleontology 86:417-424 doi:10.1666/11-115.1.