The
cycads are known to be an extremely ancient group of seed plants,
and are now recognized as the sister group to all other living seed
plants. Fossil cycads are known from the Lower Permian, of China,
270-280 million years ago, and the group is thought to have arisen
from within the ancient seed ferns, of the later Palaeozoic, era.
Strictly speaking, most fossil cycads are called cycadeoids and
are classified scientifically in the order Bennettitales
The
cycads widely radiated and spread in the Permian and early Mesozoic,
and have since continued as a separate lineage, still extant, and
considered to be living fossils. The Jurassic period is sometimes
referred to as the 'Age of Cycads'. During the Jurassic, cycads
and their kin along with conifers and Ginkgoales dominated the plant
kingdom. Fossil cycads are known from Mesozoic deposits on every
continent and latitude
from Siberia to the Antarctic. This perception of the cycads as
dominant plants of the Mesozoic Era is, however, somewhat misplaced,
resulting from past confusion of the cycads and a quite separate,
now extinct, group known variously as the Cycadeoids or the Bennettitales.
The
three extant cycad families are similar to fossils from the early
Tertiary, some 50-60 million years ago. There are also about 19
extinct cycad genera known only as fossils, all from the Paleozoic
and Mesozoic eras, excluding the form taxa, that is, isolated leaf
or stem fossils that are clearly cycads but cannot be placed in
a known family or genus.
Coming
from the famous Morrison Formation in Utah, this enormous an exceedingly
rare cycad fossil trunk is of the genus Bucklandia and dates to
the Jurassic. Climates of Jurassic Utah were mild and moist, as
attested by the rich fossil record of the Morrison Formation from
where this cycad fossil comes. Plant and dinosaurs fossils are typically
found in the Morrison Formation, including Cycads, ginkgoes, conifers,
horsetails and Allosaurus, Camptosaurus, Stegosaurus, and Camarasaurus.
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