Sagenopteris williamsii

Sagenopteris williamsii is an extinct pteridosperm (seed fern) that is known from the late Jurassic and Early Cretaceous 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.^[1] In 1956, it was referred to Sagenopteris by W.A. Bell based on additional specimens from western Canada.^[2]

Sagenopteris williamsii Temporal range: Late Jurassic-Early Cretaceous ~157–100 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Sagenopteris williamsii leaflet from the Early Cretaceous Grande Cache Member of the Gates Formation near Grande Cache, Alberta.
Scientific classification
Kingdom:	Plantae
Clade:	Tracheophytes
Division:	†Pteridospermatophyta
Order:	†Caytoniales
Family:	†Caytoniaceae
Genus:	†Sagenopteris
Species:	†S. williamsii
Binomial name
†Sagenopteris williamsii (Newberry) W.A. Bell

Description

Sagenopteris williamsii had four or more palmately arranged, ovate to obovate leaves, each up to 10 cm long and 10 cm wide. They had a petiole, anastomosing venation, and a midvein that thinned toward the apex.^[2]

Distribution and age

Leaves of S. williamsii have been reported (as Chiropteris williamsii)^[1] from the late Jurassic strata of the Morrison Formation in western Montana.^[3] In Canada, they are known from the Jurassic Hazelton Group of north-central British Columbia, the Early Cretaceous Blairmore and Luscar Groups of western Alberta, and the Early Cretaceous Bullhead Group of northeastern British Columbia.^[2]

References

1. 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.
2. Bell, W.A. 1956. Lower Cretaceous floras of western Canada; Geological Survey of Canada, Memoir 285, p. 80-81 and plates 31, 33, 34, and 36.
3. Harris, W.L. 1968. Stratigraphy and economic geology of the Great Falls - Lewiston coal field. M.Sc. thesis, University of Montana.