''Equisetum thermale'' is an extinct

horsetail ''Equisetum'' (; horsetail, snake grass, puzzlegrass) is the only living genus in Equisetaceae, a family of ferns, which reproduce by spores rather than seeds. ''Equisetum'' is a "living fossil", the only living genus of the entire subclass ...

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriat ...

in the family Equisetaceae described from a group of whole plant

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

s including rhizomes, stems, and leaves. The species is known from Middle to Late Jurassic sediments exposed in the province of Santa Cruz, Argentina. It is one of several extinct species placed in the living genus ''Equisetum''.

History and classification

''Equisetum thermale'' is represented by a series of fossil specimens preserved in

hot spring A hot spring, hydrothermal spring, or geothermal spring is a spring produced by the emergence of geothermally heated groundwater onto the surface of the Earth. The groundwater is heated either by shallow bodies of magma (molten rock) or by circ ...

s deposits preserved in the

Callovian In the geologic timescale, the Callovian is an age and stage in the Middle Jurassic, lasting between 166.1 ± 4.0 Ma (million years ago) and 163.5 ± 4.0 Ma. It is the last stage of the Middle Jurassic, following the Bathonian and preceding the ...

Tithonian In the geological timescale, the Tithonian is the latest age of the Late Jurassic Epoch and the uppermost stage of the Upper Jurassic Series. It spans the time between 152.1 ± 4 Ma and 145.0 ± 4 Ma (million years ago). It is preceded by ...

aged

La Matilde Formation La Matilde Formation is a Jurassic geological formation in the Austral Basin of Santa Cruz Province, Patagonia, Argentina. It is dated to the Middle to Late Jurassic. From the Bathonian age (164.7 to 167.7 million years ago) to the Kimmeridgian ...

. The group is part of the Bahía Laura Group exposed in the northwestern region of the Deseado Massif. The formations is the result of Jurassic age fault generated valleys filled by lacustrian infilling and

hydrothermal Hydrothermal circulation in its most general sense is the circulation of hot water (Ancient Greek ὕδωρ, ''water'',Liddell, H.G. & Scott, R. (1940). ''A Greek-English Lexicon. revised and augmented throughout by Sir Henry Stuart Jones. with th ...

activity represented by epithermal deposits. One such hot spring deposit, the San Agustín hot spring complex was reported in 2010 and is noted for the preservation of plants growing around the complex by silicification. Along with the other fossils found at the site specimens of ''Equisetum thermale'' are highly detailed and complete. The species was described from a part and counterpart pair of specimens, the

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of seve ...

, number "MPM-PB 2029" which is currently preserved in the paleobotanical collections housed at the

Museo Provincial Padre Jesús Molina Museo may refer to: * Museo, 2018 Mexican drama heist film *Museo (Naples Metro) Museo is a station on line 1 of the Naples Metro. It was opened on 5 April 2001 as the eastern terminus of the section of the line between Vanvitelli and Museo. O ...

Río Gallegos, Santa Cruz Río Gallegos (Local ) is the capital and largest settlement of the Patagonian province of Santa Cruz in Argentina. Located in the department of Güer Aike, it has a population of about 98,000, according to the , a 24% increase from the 79,000 ...

, Argentina. The specimens were studied by a group of four Welsh and Argentinian

paleobotanist Paleobotany, which is also spelled as palaeobotany, is the branch of botany dealing with the recovery and identification of plant remains from geological contexts, and their use for the biological reconstruction of past environments (paleogeogr ...

s led by Alan Channing of the School of Earth and Ocean Sciences,

Cardiff University , latin_name = , image_name = Shield of the University of Cardiff.svg , image_size = 150px , caption = Coat of arms of Cardiff University , motto = cy, Gwirionedd, Undod a Chytgord , mottoeng = Truth, Unity and Concord , established = 1 ...

, Wales. Channing and his team published their 2011

type description A species description is a formal description of a newly discovered species, usually in the form of a scientific paper. Its purpose is to give a clear description of a new species of organism and explain how it differs from species that have be ...

for ''E. thermale'' in the ''

American Journal of Botany The ''American Journal of Botany'' is a monthly peer-reviewed scientific journal which covers all aspects of plant biology. It has been published by the Botanical Society of America since 1914. The journal has an impact factor of 3.038, as of 2019 ...

''. The

etymology Etymology () The New Oxford Dictionary of English (1998) – p. 633 "Etymology /ˌɛtɪˈmɒlədʒi/ the study of the class in words and the way their meanings have changed throughout time". is the study of the history of the form of words ...

of the chosen specific name ''thermale'' is in recognition of both the geology of the type location and as a reference to the original habitat of a hot spring.

Description

''Equisetum thermale'' shows a combination of morphological characters found in both of the living ''Equisetum'' subgenera, ''E.'' subgenus ''Hippochaete'' and ''E.'' subgenus ''Equisetum''. As with members of ''Equisetum (Equisetum)'', ''E. thermale'' has

stoma In botany, a stoma (from Greek ''στόμα'', "mouth", plural "stomata"), also called a stomate (plural "stomates"), is a pore found in the epidermis of leaves, stems, and other organs, that controls the rate of gas exchange. The pore is bo ...

, occasionally paired, placed on the surface of the stem on both irregular horizontal bands and in vertical files. ''E. thermale'' also show infrequent branching of the stems, a feature found only in ''Equisetum (Hippochaete)''. This combination is to the modern species ''

Equisetum bogotense ''Equisetum bogotense'', the Andean horsetail, is a herbaceous perennial that reproduces through spores. It has thicker less bushy whorled branches, and a silica rich rhizomatous stem, which roots grow out of, under ground. This stem is a dull ...

'' which is generally placed as a sister species to the subgenera. Overall the stems of ''E. thermale'' grew up to long and in diameter with between six and twelve ridges to the stem. Each of the nodes on the stem have up to twelve single veined leaves which correspond to the number of ridges on the stem.

References

{{Taxonbar, from=Q5384609 thermale Jurassic plants Prehistoric plants of South America Jurassic Argentina Flora of Argentina Fossils of Argentina Fossil taxa described in 2011 Plants described in 2011