''Ctenis'' is a genus of fossil foliage attributable to the

Cycadales Cycads are seed plants that typically have a stout and woody (ligneous) trunk with a crown of large, hard, stiff, evergreen and (usually) pinnate leaves. The species are dioecious, that is, individual plants of a species are either male or ...

, being one of the most common genera of cycad fossil leaves in the

Mesozoic The Mesozoic Era is the Era (geology), era of Earth's Geologic time scale, geological history, lasting from about , comprising the Triassic, Jurassic and Cretaceous Period (geology), Periods. It is characterized by the dominance of archosaurian r ...

Taxonomy

The genus was first erected by Lindley and

Hutton Hutton may refer to: Places ;Antarctica * Hutton Cliffs, Ross Island * Hutton Mountains ;Australia * Hutton Sandstone Formation ;Canada * Hutton, Alberta, a locality * Hutton, British Columbia, a railway point * Hutton railway station, Brit ...

in "''The fossil flora of Great Britain''", based on material of ''Ctenis falcata'' from the

Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately 143.1 Mya. ...

Yorkshire Yorkshire ( ) is an area of Northern England which was History of Yorkshire, historically a county. Despite no longer being used for administration, Yorkshire retains a strong regional identity. The county was named after its county town, the ...

. This species was later synonymized with '' Cycadites sulcicaulis,'' leading to the new combination ''Ctenis sulcicaulis'.'' Later, Seward

Florin The Florentine florin was a gold coin (in Italian ''Fiorino d'oro'') struck from 1252 to 1533 with no significant change in its design or metal content standard during that time. It had 54 grains () of nominally pure or 'fine' gold with a pu ...

, and

Harris Harris may refer to: Places Canada * Harris, Ontario * Northland Pyrite Mine (also known as Harris Mine) * Harris, Saskatchewan * Rural Municipality of Harris No. 316, Saskatchewan Scotland * Harris, Outer Hebrides (sometimes called the Isle ...

added details of the

cuticle A cuticle (), or cuticula, is any of a variety of tough but flexible, non-mineral outer coverings of an organism, or parts of an organism, that provide protection. Various types of "cuticle" are non- homologous, differing in their origin, structu ...

to the

diagnosis Diagnosis (: diagnoses) is the identification of the nature and cause of a certain phenomenon. Diagnosis is used in a lot of different academic discipline, disciplines, with variations in the use of logic, analytics, and experience, to determine " ...

of the genus. Due to the leaves of ''Ctenis'' possessing characters unknown in any living cycad, ''Ctenis'' is thought to belong to an extinct lineage distinct from modern cycads, with a 2023 analysis finding that the genus was

paraphyletic Paraphyly is a taxonomic term describing a grouping that consists of the grouping's last common ancestor and some but not all of its descendant lineages. The grouping is said to be paraphyletic ''with respect to'' the excluded subgroups. In co ...

with respect to the genera '' Dioonopsis'' and '' Pterostoma,'' with this group suggested to be the

sister group In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and ...

to Cycadaceae, from which they diverged in the

Permian The Permian ( ) is a geologic period and System (stratigraphy), stratigraphic system which spans 47 million years, from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.902 Mya. It is the s ...

period.

Description

The leaves of ''Ctenis'' are once

pinnate Pinnation (also called pennation) is the arrangement of feather-like or multi-divided features arising from both sides of a common axis. Pinnation occurs in biological morphology, in crystals, such as some forms of ice or metal crystals, and ...

, and the pinnae have multiple parallel

veins Veins () are blood vessels in the circulatory system of humans and most other animals that carry blood towards the heart. Most veins carry deoxygenated blood from the tissues back to the heart; exceptions are those of the pulmonary and fetal c ...

that often anastomosize (i.e. fuse together). The cuticle of ''Ctenis'' has

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

with

guard cell Guard cells are specialized cells in the epidermis of leaves, stems and other organs of land plants that are used to control gas exchange. They are produced in pairs with a gap between them that forms a stomatal pore. The stomatal pores are lar ...

s arranged in a random fashion, and the stomatal apparatus has often a cuticular ring surrounding the stomatal pit. The cuticular surface is usually

striate In geology, a striation is a groove, created by a geological process, on the surface of a rock or a mineral. In structural geology, striations are linear furrows, or linear marks, generated from fault movement. The striation's direction revea ...

Distribution

Though ''Ctenis''-like leaves are known from the

Late Permian Late or LATE may refer to: Everyday usage * Tardy, or late, not being on time * Late (or the late) may refer to a person who is dead Music * ''Late'' (The 77s album), 2000 * Late (Alvin Batiste album), 1993 * Late!, a pseudonym used by Dave Groh ...

Umm Irna Formation The Umm Irna Formation is a geological formation in Jordan. It is found in several outcrops in Jordan in the area around the eastern shore of the Dead Sea. It is Late Permian (likely Changhsingian) in age, and is the oldest unit in the succession, ...

Jordan Jordan, officially the Hashemite Kingdom of Jordan, is a country in the Southern Levant region of West Asia. Jordan is bordered by Syria to the north, Iraq to the east, Saudi Arabia to the south, and Israel and the occupied Palestinian ter ...

, ''Ctenis'' fossils becomes more common from the

Late Triassic The Late Triassic is the third and final epoch (geology), epoch of the Triassic geologic time scale, Period in the geologic time scale, spanning the time between annum, Ma and Ma (million years ago). It is preceded by the Middle Triassic Epoch a ...

onwards. In the

, many ''Ctenis'' species are retrieved from Europe, North America, and Asia. In the

Early Cretaceous The Early Cretaceous (geochronology, geochronological name) or the Lower Cretaceous (chronostratigraphy, chronostratigraphic name) is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 143.1 ...

, ''Ctenis'' is still found in Europe (i.e. in the

Wealden Group The Wealden Group, occasionally also referred to as the Wealden Supergroup, is a group (stratigraphy), group (a sequence of rock strata) in the lithostratigraphy of southern England. The Wealden group consists of wiktionary:paralic, paralic to c ...

) and Asia, but from the Late Cretaceous its

range Range may refer to: Geography * Range (geographic), a chain of hills or mountains; a somewhat linear, complex mountainous or hilly area (cordillera, sierra) ** Mountain range, a group of mountains bordered by lowlands * Range, a term used to i ...

seems to retreat to more Northern Latitudes in the

Siberia Siberia ( ; , ) is an extensive geographical region comprising all of North Asia, from the Ural Mountains in the west to the Pacific Ocean in the east. It has formed a part of the sovereign territory of Russia and its predecessor states ...

n region and North America and Southern latitudes in Australia. The last members of this genus are found in the

Eocene The Eocene ( ) is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene'' comes ...

of North America.

Paleoecology

Little is known about the ecology of the ''Ctenis''-producing plants. However, in the Big Cedar Ridge locality in

Wyoming Wyoming ( ) is a landlocked U.S. state, state in the Mountain states, Mountain West subregion of the Western United States, Western United States. It borders Montana to the north and northwest, South Dakota and Nebraska to the east, Idaho t ...

(

Campanian The Campanian is the fifth of six ages of the Late Cretaceous epoch on the geologic timescale of the International Commission on Stratigraphy (ICS). In chronostratigraphy, it is the fifth of six stages in the Upper Cretaceous Series. Campa ...

), ''Ctenis'' is found in the fern

wetland A wetland is a distinct semi-aquatic ecosystem whose groundcovers are flooded or saturated in water, either permanently, for years or decades, or only seasonally. Flooding results in oxygen-poor ( anoxic) processes taking place, especially ...

together with ferns from the families

Dipteridaceae The Dipteridaceae is a family of ferns in the order Gleicheniales of the class Polypodiopsida. They are commonly known as umbrella ferns and contain two genera, '' Cheiropleuria'' and '' Dipteris'', with a total of nine species confined to Asia, ...

Gleicheniaceae The forked ferns are the family Gleicheniaceae, which includes six genera and about 160 known species. The formerly independent families Dicranopteridaceae and Stromatopteridaceae are generally included in the Gleicheniaceae, whereas the Dipteri ...

, and

Matoniaceae Matoniaceae is one of the three families of ferns in the Gleicheniales order of the Polypodiopsida class. Fossil records reveal that Matoniaceae ferns were abundant during the Mesozoic era (about 250-million to 66-million years ago), during which ...

. This suggests that at least some members of the genus inhabited wet environments with

peat Peat is an accumulation of partially Decomposition, decayed vegetation or organic matter. It is unique to natural areas called peatlands, bogs, mires, Moorland, moors, or muskegs. ''Sphagnum'' moss, also called peat moss, is one of the most ...

y soils.

References

{{Taxonbar, from=Q60898408 Cycads Prehistoric gymnosperm genera Mesozoic plants Cenozoic plants Clarno Formation