cryptospore
{{Short description|Fossilised primitive plant spore}}
Cryptospores are microscopic fossilized spores produced by embryophytes (land plants). They first appear in the fossil record during the middle of the Ordovician period, as the oldest fossil evidence for the colonization of land by plants. A similar (though broader) category is miospores, a term generally used for spores smaller than 200 μm. Both cryptospores and miospores are types of palynomorphs.{{Cite journal |last=Steemans |first=P |date=2000 |title=Miospore evolution from the Ordovician to the Silurian |url=https://linkinghub.elsevier.com/retrieve/pii/S0034666700000592 |journal=Review of Palaeobotany and Palynology |language=en |volume=113 |issue=1–3 |pages=189–196 |doi=10.1016/S0034-6667(00)00059-2|pmid=11164219 |bibcode=2000RPaPa.113..189S |url-access=subscription }}
Cryptospores, which occur as permanent tetrads, dyads, or hilate monads, sometimes with additional wall envelopes, dominated fossil assemblages for approximately 60 million years, first appearing around 470 million years ago during the Ordovician Period. They underwent rapid diversification during what Jane Gray (1993) called the Eoembryophytic epoch,{{Cite journal |last=Gray |first=Jane |date=1993-09-01 |title=Major Paleozoic land plant evolutionary bio-events |url=https://linkinghub.elsevier.com/retrieve/pii/0031018293901275 |journal=Palaeogeography, Palaeoclimatology, Palaeoecology |series=Event Markers in Earth History |volume=104 |issue=1 |pages=153–169 |doi=10.1016/0031-0182(93)90127-5 |issn=0031-0182|url-access=subscription }} but experienced an abrupt decline in diversity and abundance around 410 Ma during the latest Lochkovian (Early Devonian), with only a few forms persisting into the Emsian period. In contrast, trilete monads began diversifying around 430 Ma in the latter Silurian Period and eventually became the dominant element in dispersed spore assemblages. While trilete monads are generally associated with vascular plants, cryptospores lack close modern analogues (except possibly in some liverworts), making the identification of their parent plants one of evolutionary botany's significant unresolved problems.{{Cite journal |last=Edwards |first=Dianne |last2=Morris |first2=Jennifer L. |last3=Axe |first3=Lindsey |last4=Duckett |first4=Jeffrey G. |last5=Pressel |first5=Silvia |last6=Kenrick |first6=Paul |date=2022 |title=Piecing together the eophytes – a new group of ancient plants containing cryptospores |url=https://nph.onlinelibrary.wiley.com/doi/10.1111/nph.17703 |journal=New Phytologist |language=en |volume=233 |issue=3 |pages=1440–1455 |doi=10.1111/nph.17703 |issn=1469-8137|doi-access=free }}Wellman CH, Steemans P, Vecoli M. 2013. Chapter 29 Palaeophytogeography of Ordovician–Silurian land plants. Geological Society, London, Memoirs 38: 461–476.
Evidence that cryptospores derive from land plants
=Occurrence=
=Wall ultrastructure=
The walls of cryptospores consist of many lamellae (thin sheets). Liverworts, thought to be the most primitive land plants, also have this spore wall morphology.
=Chemical composition =
(Some) cryptospores are composed of sporopollenin and have the same chemical makeup as co-occurring trilete spores.{{cite journal|last=Steemans|first=P.|author2=Lepot, K. |author3=Marshall, C.P. |author4= Le Hérissé, A. and Javaux, E.J. |title=FTIR characterisation of the chemical composition of Silurian miospores (cryptospores and trilete spores) from Gotland, Sweden|journal=Review of Palaeobotany and Palynology|date=2010|volume=162|issue=4|pages=577–590|doi=10.1016/j.revpalbo.2010.07.006|bibcode=2010RPaPa.162..577S |url=https://hal-insu.archives-ouvertes.fr/insu-00558990/file/Organic_Geochem_Steemans.pdf}}
Other information
Recently, fossils of plant sporangia have been found in Oman with cryptospores showing concentric lamellae in their walls, similar to liverworts. The earliest known cryptospores are from Middle Ordovician (Dapingian) strata of Argentina.{{cite journal|last=Rubinstein|first=C.V.|author2=Gerrienne, P. |author3=de la Puente, G.S. |author4=Astini, R.A. |author5=Steemans, P. |s2cid=24070744|title=Early Middle Ordovician evidence for land plants in Argentina (eastern Gondwana)|journal=New Phytologist|date=2010|volume=188|issue=2|pages=365–369|doi=10.1111/j.1469-8137.2010.03433.x|pmid=20731783|doi-access=free|hdl=11336/55341|hdl-access=free}} Spores from the Lindegård Mudstone (late Katian–early Hirnantian) represent the earliest record of early land plant spores from Sweden and possibly also from Baltica and implies that land plants had migrated to the palaeocontinent Baltica by at least the Late Ordovician.{{cite journal|last=Badawy|first=A.S.|author2=Mehlqvist, K. |author3=Vajda, V. |author4= Ahlberg, P. and Calner, M. |title=Late Ordovician (Katian) spores in Sweden: oldest land plant remains from Baltica|journal=GFF|date=2014|volume=136|issue=1|pages=16–21|doi=10.1080/11035897.2014.899266|bibcode=2014GFF...136...16B |s2cid=22198834 |url=http://urn.kb.se/resolve?urn=urn:nbn:se:nrm:diva-1417}} This discovery reinforces the earlier suggestion that the migration of land plants from northern Gondwana to Baltica in the Late Ordovician was facilitated by the northward migration of Avalonia,{{cite journal|last=Steemans|first=P.|author2=Wellman, C.H. and Gerrienne, P. |title=Paleogeographic and paleoclimatic considerations based on Ordovician to Lochkovian vegetation|journal=Geological Society, London, Special Publications|date=2010|volume=339|pages=49–58|doi=10.1144/SP339.5|url=http://sp.lyellcollection.org/content/339/1/49.abstract|issue=1|bibcode=2010GSLSP.339...49S |s2cid=140195843 |url-access=subscription}} which is evidenced by the co-occurrence of reworked, Early–Middle Ordovician acritarchs, possibly suggesting an Avalonian provenance in a foreland basin system.
See also
References
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Further reading
- {{cite journal |last1=Edwards |first1=D. |last2=Morris |first2=J. L. |last3=Richardson |first3=J. B. |last4=Kenrick |first4=P. |year=2014 |title=Cryptospores and cryptophytes reveal hidden diversity in early land floras |journal=New Phytologist |volume=202 |number=1 |pages=50–78 |doi=10.1111/nph.12645|pmid=24410730 |url=https://orca.cardiff.ac.uk/57757/1/EdwardsD.EARTH3.pdf }}