''Sagenopteris williamsii'' is an extinct

pteridosperm Pteridospermatophyta, also called pteridosperms or seed ferns, are a polyphyletic grouping of extinct Spermatophyte, seed-producing plants. The earliest fossil evidence for plants of this type are the Lyginopteridales, lyginopterids of late Devon ...

(seed fern) that is known from the late

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. ...

and

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 ...

strata of the western interior of North America. It was first described as ''Chiropteris williamsii'' by J.S. Newberry in 1891, based on specimens from the Great Falls coal field in

Montana Montana ( ) is a landlocked U.S. state, state in the Mountain states, Mountain West subregion of the Western United States. It is bordered by Idaho to the west, North Dakota to the east, South Dakota to the southeast, Wyoming to the south, an ...

.Newberry, J.S. 1891. The flora of the Great Falls Coal Field, Montana. American Journal of Science, 3rd series, vol. 41, p. 191-201 and plate 14. In 1956, it was referred to ''

Sagenopteris ''Sagenopteris'' is a genus of extinct seed ferns from the Triassic to late Early Cretaceous.Geological Survey of Canada The Geological Survey of Canada (GSC; , CGC) is a Canadian federal government agency responsible for performing geological surveys of the country developing Canada's natural resources and protecting the environment. A branch of the Earth Science ...

, Memoir 285, p. 80-81 and plates 31, 33, 34, and 36.

Description

''Sagenopteris williamsii'' had four or more

palmate The following terms are used to describe leaf morphology in the description and taxonomy of plants. Leaves may be simple (that is, the leaf blade or 'lamina' is undivided) or compound (that is, the leaf blade is divided into two or more leaflets ...

ly arranged,

ovate Ovate may refer to: * Ovate (egg-shaped) leaves, tepals, or other botanical parts *Ovate, a type of prehistoric stone hand axe * Ovates, one of three ranks of membership in the Welsh Gorsedd * Vates or ovate, a term for ancient Celtic bards ...

obovate The following terms are used to describe leaf morphology in the description and taxonomy of plants. Leaves may be simple (that is, the leaf blade or 'lamina' is undivided) or compound (that is, the leaf blade is divided into two or more leaflets) ...

leaves, each up to 10 cm long and 10 cm wide. They had a

petiole Petiole may refer to: *Petiole (botany), the stalk of a leaf, attaching the blade to the stem *Petiole (insect anatomy) In entomology, petiole is the technical term for the narrow waist of some hymenopteran insects, especially ants, bees, and ...

, anastomosing

venation Venation may refer to: * Venation (botany), the arrangement of veins in leaves * Wing venation, the arrangement of veins in insect wings See also * * Vernation Vernation or leafing is the formation of new leaves or fronds. In plant anatomy, it ...

, and a midvein that thinned toward the apex.

Distribution and age

Leaves of ''S. williamsii'' have been reported (as ''Chiropteris williamsii'') from the late Jurassic strata of the

Morrison Formation The Morrison Formation is a distinctive sequence of Upper Jurassic sedimentary rock found in the western United States which has been the most fertile source of dinosaur fossils in North America. It is composed of mudstone, sandstone, siltston ...

in western Montana.Harris, W.L. 1968. Stratigraphy and economic geology of the Great Falls - Lewiston coal field. M.Sc. thesis, University of Montana. In Canada, they are known from the Jurassic Hazelton Group of north-central

British Columbia British Columbia is the westernmost Provinces and territories of Canada, province of Canada. Situated in the Pacific Northwest between the Pacific Ocean and the Rocky Mountains, the province has a diverse geography, with rugged landscapes that ...

, the

Blairmore and

Luscar Group The Luscar Group is a geologic unit of Early Cretaceous age in the Western Canadian Sedimentary Basin, Western Canada Sedimentary Basin that is present in the foothills of southwestern Alberta. It is subdivided into a series of formation (stratigr ...

s of western

Alberta Alberta is a Provinces and territories of Canada, province in Canada. It is a part of Western Canada and is one of the three Canadian Prairies, prairie provinces. Alberta is bordered by British Columbia to its west, Saskatchewan to its east, t ...

, and the Early Cretaceous Bullhead Group of northeastern British Columbia.

References

Pteridospermatophyta Jurassic plants Early Cretaceous plants Fossil record of plants Mesozoic life of North America Prehistoric plants of North America Jurassic Canada Jurassic United States {{cretaceous-plant-stub