Caytoniales

The first fossils identified in this order were discovered in the Middle Jurassic Gristhorpe bed of the Cloughton Formation in Cayton Bay, Yorkshire, with the name of the bay giving the name to the group. They have since been found in Mesozoic rocks all over world. It is likely that Caytoniales flourished in wetland areas, because they are often found with other moisture-loving plants such as horsetails in waterlogged paleosols. The first fossil Caytoniales were preserved as compressions in shale with excellent preservation of cuticles allowing study of cellular histology. ==Description==

The woody nature of associated stalks and preserved short shoots are evidence that Caytoniales were seasonally deciduous shrubs or trees. The ovules were located inside fleshy cupules with tough outer cuticle. Individual ovules had an apical tube called a micropylar canal, that allowed pollen to pass into the pollen chamber. The outer layers of the cupules were fleshy and fruit-like; it is possible this was to aid in animal dispersal. (Fig 1-2), The most common and widespread part found fossilized are leaves of Sagenopteris (Fig. 3). These are compound leaves consisting of, usually, 4 leaflets (two pairs of two) arrayed in a palmate manner, with the leaflets having a prominent midrib and a generally lanceolate shape. The bases of the four leaflets were attached to the apex of a petiole, which at its other end joined a woody stem. The individual leaflets are up to 6 cm in length. The leaflets have anastomosing veins, like those of some ferns, but lacking orders of venation found in angiosperm leaves. ==Relationship to other seed plants==

Caytonia was first described by Hamshaw Thomas in 1925. His close examination of the cupules led him to believe this was one of the earliest examples of angiosperms. He mistakenly thought the entire ovule was enclosed in the cupule, unlike typical gymnosperms. He worked meticulously, collecting and cleaning specimens to get the best understanding. He spent weeks boiling fruits in different solutions to try to make them resemble their living states. He proposed that the fruits contained a stigma with a funnel-shaped opening in the center in which the pollen grains would get lodged.), among other groups (see Evolutionary history of plants). Beyond flowering plants, some authors have suggested that they may be related to the glossopterids and the corystosperms, possibly as part of a broader clade including flowering plants. == Evolutionary history ==

As recorded by fossils of Sagenopteris leaves, the most common fossils of Caytoniales, the earliest fossils of the group are from the Anisian stage of the Middle Triassic of what is now Europe. In the Late Triassic, the Caytoniales expanded their distribution to become widespread across Pangaea. Caytoniales were apparently not significantly effected by the end-Triassic mass extinction, and remained widespread during the entirety of the Jurassic epoch, reaching the apex of their abundance during this period. The group declined during the Late Jurassic and Early Cretaceous, likely due at least in part to the rise of flowering plants during the Cretaceous period. During the Late Cretaceous, they were primarily confined to high latitudes in the Northern Hemisphere, mirroring the decline and geographic contraction of other prominent Mesozoic seed plant groups such as the Bennettitales. The youngest records of Sagenopteris, and more broadly of Caytoniales, date to the Campanian stage towards the end of the epoch. ==Gallery==

File:Morphology of Caytoniales.jpg|Fig. 2 A) leaf structure B) Venation C) Pollen sacs D) Pollen grain E) Seed structure F) Cupule G) Cupule from side H) Ovule File:Sagenopteris phillipsi Natural History Museum v18596 Retallack 1980.jpg|Fig. 3 Fossil leaves of Sagenopteris phillipsii from the Gristhorpe Bed at Cayton Bay. Natural History Museum specimen photographed by G.J.Retallack File:Caytonia nathorsti Natural History Museum v18582 photo Retallack 1980.jpg|Fig. 4 Fossil Caytonia nathorstii, the reproductive structure that encloses ovules. Natural History Museum specimen photographed by G.J. Retallack. File:Reproductive structures of Caytoniales and Glossopteris.jpg|Fig. 5 Diagram comparing ovulate structures in Caytoniales, Glossopteridales, and Angiospermae. The upper illustrations show Caytoniales as angiosperm ancestors, and the lower illustrations show glossopterid ancestors. ==References==