''Pterophyllum'' is an extinct form genus of leaves known from the

Carnian The Carnian (less commonly, Karnian) is the lowermost stage of the Upper Triassic Series (or earliest age of the Late Triassic Epoch). It lasted from 237 to 227 million years ago (Ma). The Carnian is preceded by the Ladinian and is followed by t ...

to the

Maastrichtian The Maastrichtian () is, in the ICS geologic timescale, the latest age (uppermost stage) of the Late Cretaceous Epoch or Upper Cretaceous Series, the Cretaceous Period or System, and of the Mesozoic Era or Erathem. It spanned the interval from ...

, belonging to the

Bennettitales Bennettitales (also known as cycadeoids) is an extinct order of seed plants that first appeared in the Permian period and became extinct in most areas toward the end of the Cretaceous. Bennettitales are among the most common Mesozoic seed plants ...

(family

Williamsoniaceae ''Williamsoniaceae'' is a family within the Bennettitales, an extinct group of seed plants within the Cycadophyta subdivision. Members of this family are believed to have been around two meters tall and with widely serrate leaves along a central ...

). It contains more than 50

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 appropriate s ...

, and is mainly found in

Eurasia Eurasia (, ) is the largest continental area on Earth, comprising all of Europe and Asia. Primarily in the Northern and Eastern Hemispheres, it spans from the British Isles and the Iberian Peninsula in the west to the Japanese archipelago a ...

and

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...

Description

''Pterophyllum'' are characterized by their completely segmented leaves, with slender leaflets more than twice as long as they are high. The leaflets are regularly spaced, arranged opposite to each other, and have nearly parallel edges, only slightly broader at their bases and narrower at their tips. They are covered with fine longitudinal veins with minor bifurcation. The leaflets slightly lengthen towards the middle of the leaf and shrink towards its tip, for an overall lanceolate (long and tapered) or oblong shape to the leaf. At the tip of the leaf sits a terminal leaflet which can vary in shape from the rest. Like other bennettitaleans, the leaf's cuticle was syndetocheilic (with guard and subsidiary cells of the

stomata 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 bor ...

having the same mother cells) and hypostomatic (with stomata located entirely underneath the leaf). In the

Mesozoic Era The Mesozoic Era ( ), also called the Age of Reptiles, the Age of Conifers, and colloquially as the Age of the Dinosaurs is the second-to-last Era (geology), era of Earth's Geologic time scale, geological history, lasting from about , comprising ...

, the ''Pterophyllum'' thrived and could be found in great abundance together with the rest of the

order. ''Pterophyllum'' plants would have likely looked similar to modern

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

plants, which are found in a different order.

Taxonomy

''Pterophyllum filicoides'', a species named by Schlotheim in 1822, was established as the

type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specimen ...

of ''Pterophyllum'' by Zeiller in 1906. The name ''Pterophyllum'' was first introduced in 1825 by Brongniart, who described two species from the

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

found in

Sweden Sweden, formally the Kingdom of Sweden,The United Nations Group of Experts on Geographical Names states that the country's formal name is the Kingdom of SwedenUNGEGN World Geographical Names, Sweden./ref> is a Nordic country located on ...

. These species were ''P. minus'' and ''P. majus''. At this time, what now is the type species was thought to be an alga, but later Brongniart expanded his diagnosis to include more species, including the type species. Later, the two originally described species were moved to the genus '' Anomozamites'', resulting in the illegitimatization of the name. Since ''Pterophyllum'' as a name had been widely used, the new type species ''P. filicoides'' was assigned to the name to retain legitimacy. Species of ''Pterophyllum'' are generally separated by the shape of their leaves as well as other features on the leaves such as vein density, anatomy of the stomata and epidermal cell shape.

Difficulties in classification

''Pterophyllum'' can at times be very similar to ''Anomozamites'', and the need to review the diagnostics of these genera has been raised, since both genera has no distinct characteristics from one another in regards to their cuticles or epidermal cells. This means that the morphology of their leaves are the only method to differentiate between the two: the fossil is classified as a ''Pterophyllum'' if the leaf has a length which is at least twice its width, and as an ''Anomozamite'' if it does not. This can be difficult at times, and there are several examples where plants have been erroneously placed in one genus, before being correctly placed in the other. The similar form genus ''Ctenophyllum'' from the Late Triassic of Germany (as well as misattributed North American leaves) is likely a

junior synonym The Botanical and Zoological Codes of nomenclature treat the concept of synonymy differently. * In botanical nomenclature, a synonym is a scientific name that applies to a taxon that (now) goes by a different scientific name. For example, Linna ...

of ''Pterophyllum''.

Significance

''Pterophyllum'' can be used as a

proxy Proxy may refer to: * Proxy or agent (law), a substitute authorized to act for another entity or a document which authorizes the agent so to act * Proxy (climate), a measured variable used to infer the value of a variable of interest in climate ...

to reconstruct past climates using the stomatal method to estimate CO₂ concentrations. Due to the similarities between ''Pterophyllum'' and ''Anomozamites'', these can be used interchangeably to increase the amount of data. Considering the abundance of these plants during the Mesozoic era, this can be of great value for scientists reconstructing the Mesozoic climate.

References

{{Taxonbar, from=Q47527940 Bennettitales Prehistoric plant genera Fossil taxa described in 1828