Metasequoia occidentalis

Metasequoia occidentalis is an extinct redwood species of the family Cupressaceae that is found as fossils throughout the Northern Hemisphere. It is one of three extinct species of Metasequoia that are currently recognized as valid.[2][3]

M. occidentalis cone with long, leafless stalk; Ypresian, Klondike Mountain Formation

Metasequoia occidentalis
Temporal range: Late Cretaceous–Pliocene
Metasequoia occidentalis foliage; early Paleocene, Alberta, Canada
Scientific classification
Kingdom: Plantae
Clade: Tracheophytes
Division: Pinophyta
Class: Pinopsida
Order: Pinales
Family: Cupressaceae
Genus: Metasequoia
Species:
†M. occidentalis
Binomial name
†Metasequoia occidentalis
Synonyms

History

The species was first described in 1863 from fossils found in the outcrops of the Late Paleocene-Middle Eocene Chuckanut Formation around Birch Bay, Washington. The species was originally described as Taxodium occidentale by John Strong Newberry. Fossilized Metasequoia-like remains were noted in Europe and North America from the 1800s on, but were assigned to the cupressaceous genera Sequoia (redwoods) and Taxodium (bald cypresses). It was not until the living species Metasequoia glyptostroboides was discovered and described from a remote area of China during the 1940s, that the affinity of many of the fossils became apparent.[4][5] In 1951, the species was reassigned to Metasequoia as M. occidentalis by Ralph Works Chaney based on the close resemblance to living Metasequoia.[1] It has been said that, with few exceptions, the bulk of the fossils described in the literature indicate that M. occidentalis was indistinguishable from living Metasequoia glyptostroboides.[6]

Description

Like living Metasequoia, M. occidentalis was deciduous. The foliage consists of branchlets with oppositely arranged leaves. The leaves are ovate to linear in shape, ranging from 6–25 mm (0.24–0.98 in) in length and 1–2 mm (0.039–0.079 in) in width, with a distinct midvein, a petiolate base, and an acute tip. The seed-bearing cones are globose to ovoid, 11–40 mm (0.43–1.57 in) long and 6–34 mm (0.24–1.34 in) wide, with decussately arranged triangular scales, and are borne on long, leafless stalks. The seeds have two wings, are ovoid to cordate in shape, and are up to 5 mm (0.20 in) long and 4 mm (0.16 in) wide. The pollen-bearing cones are small, globose to ovoid, 1–5 mm (0.039–0.197 in) long and 0.5–4 mm (0.020–0.157 in) wide, and oppositely arranged on specialized stalks with one terminal cone.[2][3]

Age and distribution

Metasequoia occidentalis appeared in fossil record during the Late Cretaceous epoch (Cenomanian stage). By the Tertiary period, it had become a major constituent of lowland and swampy forests in the northern circum-Pacific and polar regions, where it commonly coexisted with Glyptostrobus europaeus. Fossils assignable to M. occidentalis have been reported from parts of the United States, Canada, Russia, China, Japan, Greenland and Svalbard, but Metasequoia appears to have been rare or absent in much of Europe.[6]

References
  1. Chaney, R.W. (1951). "A revision of fossil Sequoia and Taxodium in western North America based on the recent discovery of Metasequoia". Transactions of the American Philosophical Society. 40 (3): 231.
  2. Stockey, R.A., Rothwell, G.W. and Falder, A.B. 2001. Diversity among taxodioid conifers: Metasequoia foxii sp. nov. from the Paleocene of central Alberta, Canada. International Journal of Plant Sciences, v. 162, p. 221-234.
  3. Liu, Y-J, Li, C-S, and Wang, Y-F, 1999. Studies on fossil Metasequoia from north-east China and their taxonomic implications. Botanical Journal of the Linnaean Society, v. 130, p. 267-297.
  4. Chaney, R. W. (1948). "Redwoods around the Pacific basin". Pacific Discovery. 1 (5): 4–14.
  5. Fulling, E. H. (1976). "Metasequoia – fossil and living". The Botanical Review. 42: 215–315.
  6. LePage, B. A., Yang, H., and Matsumoto, M. 2005. The evolution and biogeographic history of Metasequoia. In: The geobiology and ecology of Metasequoia, pp. 3-114. Springer, Netherlands.
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