Archaeopteris

Archaeopteris is an extinct genus of progymnosperm tree with fern-like leaves. A useful index fossil, this tree is found in strata dating from the Upper Devonian to Lower Carboniferous (383 to 323 million years ago), the oldest fossils being 385 million years old,^[1] and had global distribution.

Until the 2007 discovery of Wattieza, many scientists considered Archaeopteris to be the earliest known tree. Bearing buds, reinforced branch joints, and branched trunks similar to today's wood, it is more reminiscent of modern seed-bearing trees than other spore bearing taxa; It combines characteristics of woody trees and herbaceous ferns, and belongs to a group of extinct plants sometimes called the progymnosperms, plants with gymnosperm-like wood but that produce spores rather than seeds.

John William Dawson described the genus in 1871. The name derives from the ancient Greek ἀρχαῖος (archaīos, "ancient"), and πτέρις (ptéris, "fern"). Archaeopteris was originally classified as a fern, and it remained classified so for over 100 years. In 1911, Russian paleontologist Mikhail Dimitrievich Zalessky described a new type of petrified wood from the Donets Basin in nowadays Ukraine. He called the wood Callixylon, though he did not find any structures other than the trunk. The similarity to conifer wood was recognized. It was also noted that ferns of the genus Archaeopteris were often found associated with fossils of Callixylon.

In the 1960s, paleontologist Charles B. Beck was able to demonstrate that the fossil wood known as Callixylon and the leaves known as Archaeopteris were actually part of the same plant.^[2][3] It was a plant with a mixture of characteristics not seen in any living plant, a link between true gymnosperms and ferns.

The genus Archaeopteris is placed in the order Archaeopteridales and family Archaeopteridaceae. The name is similar to that of the first known feathered bird, Archaeopteryx, but in this case refers to the fern-like nature of the plant's fronds.

Archaeopteris is a member of a group of free-sporing woody plants called the progymnosperms that are interpreted as distant ancestors of the gymnosperms. Archaeopteris reproduced by releasing spores rather than by producing seeds, but some of the species, such as Archaeopteris halliana were heterosporous, producing two types of spores. This is thought to represent an early step in the evolution of vascular plants towards reproduction by seeds,^[4] which first appeared in the earliest, long extinct, gymnosperm group, the seed ferns (Pteridospermatophyta). The conifers or Pinophytaare one of four divisions of extant gymnosperms that arose from the seed ferns during the Carboniferous period.

A reconstruction of Archaeopteris macilenta from the Late Devonian, Walton Formation of Hancock, New York

A polished round of permineralised wood of Callixylon whiteanum from the Late Devonian Woodford Shale of Ada, Oklahoma

Archaeopteris sp. – reconstruction at MUSE - Science Museum in Trento

Archaeopteris notosaria fronds from the Waterloo Farm lagerstätte in the Eastern Cape, South Africa. These represent the only high latitude species of Archaeopteris as yet described.