Bennettitales

Originally, Bennettitales were thought to be cycads for their strap-like leaves, however their flower-like reproductive parts separate the two groups. The two families of Bennettitales (Cycadeoidaceae and Williamsoniaceae) each have their own unique traits. Cycadeoidaceae had stout trunks and bisporangiate strobili (cones) serving as their reproductive structures and Williamsoniaceae either had bisporangiate or monosporangiate cones, and distinctly slender and branching woody trunks.[5] These bisporangiate cones consist of layers of protective bracts, a curved microsporophyll, and an ovulate receptacle.[6] The bisporangiate cones remained closed at maturation, and most likely were obligate self-fertilizers.[7]

In general, Bennettitales had leaves attached adaxially (toward the stem) with a distinct midrib. Veins stem from the midrib at an approximately 90 degree angle.[8] They have tough cuticles as well, as they were able to withstand high sulfur dioxide levels in the Triassic/Jurassic period for considerable time.[9] Some were characterized by thick trunks and pinnately compound leaves that bore a superficial resemblance to those of cycads, differing primarily in having a syndetocheilic stomatal arrangement.[10]

A study on members of Williamsoniaceae found that they had a divaricate branching habit, similar to that of Banksia, which was suggested to be an adaption to open habitats with poor soil nutrient conditions.[11]

The reproductive structures of some Bennettitales are flower like and were probably pollinated by insects. Several groups of Jurassic and Early Cretaceous insects possess long proboscis, and it has been suggested that these groups were feeders on nectar produced by bennettitalean reproductive structures. A specimen of the extinct long proboscis fly family Zhangsolvidae has been found directly associated with Bennettitales pollen, providing evidence that this family acted as pollinators for the group.[12]

Bennettitales were first identified by Engler in 1892 as separate from Cycadales, and were then further differentiated into the two groups Cycadeoidaceae and Williamsoniaceae by Caruthers. The Anthophyte hypothesis erected by Arber and Parking in 1907[13] posited that angiosperms arose from Bennettitales, as suggested by the wood-like structures and rudimentary flowers.[5] Based on morphological data, however, Bennettitales were classified as a monophyletic group when paired with Gnetales.[14] a study in 2006 suggested that Bennettitales, Angiosperms, and Gigantopteridales form a clade based on the presence of oleanane.[15] A 2007 study examining phase-contrast X-ray images of gymnosperm seeds suggested that the supported the Anthophyte hypothesis.[16] Evidence from seed coats suggest that Bennettitales form a clade with the gymnosperm orders of Gnetales and Erdtmanithecales.[17] Molecular evidence has consistently contradicted the Anthophyte hypothesis, finding that Angiosperms are the sister group to all living gymnosperms, including Gnetales.[18] It has been suggested that Williamsoniaceae are a paraphyletic assemblage of Bennettitales that do not belong to the Cycadeoidaceae.[11]

The affinities of Bennettitales to other seed plants remains uncertain, a phylogeny based on molecular signatures of fossilised cuticles found that Bennettitales were more closely related to the Ginkgo+Cycads clade than conifers, and were closely related to Nilssonia and Ptilozamites.[19] The oldest known remains of Bennettitales are from the Late Permian (likely Changhsingian) aged Umm Irna Formation in Jordan, assignable to the leaf morphogenus Pterophyllum.[1] Bennettitales became widespread during the Triassic Epoch. Bennettitales remained widespread during the Jurassic and Early Cretaceous, however Bennettitales severely declined during the Late Cretaceous, coincident with the rise of flowering plants, being mostly extinct by the end of the period, with the final known remains from the Northern Hemisphere being found in the polar latitude Kakanaut Formation in Chukotka, Russia, dating to the Maastrichtian, also assignable to Pterophyllum.[20] The latest known remains of the family are from the early Oligocene of Eastern Australia and Tasmania, assignable to the genus Ptilophyllum.[3]

• 
  A fossilised Bennettite, squashed by later compression.
• 
  Side view. Note embedded "flowers".
• 
  A flower-like structure.
• 
  Fossil leaf of Zamites mariposana from the Jurassic.

• Gymnosperms
• Lecture Notes on Mesozoic Mesophytic Communities
• Weblinks to articles about the Bennettitales