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The Triassic period was a time of recovery, transition, and diversification for much of the Earth's surviving life forms. A major global extinction, caused in part by changing continental positions and redirected ocean currents, had just occurred. The world was leaving an ice age, warming, and plant life was having to adapt to a predominantly warm, dry climate. Many once- dominant species faded to mere niche- holders. Others found new opportunity. The cycads and their allies seized the day. One of these new plants was Aricycas paulae, whose fossil leaves have been found in Arizona. Its leaves possessed a slender rachis and long narrow pinnae with a midrib. The tough epidermal structure and stomata more resistant to water loss mark it as a cycadale. There is a very strong resemblance to modern- day Cycas because of the highly visible midrib present in the pinnae. Some reproductive structures have also been found nearby that are similar to that of modern Cycadales, but it's not possible yet to attribute these fossils to Aricycas.
A Cycadeoid being enjoyed by |
Another possible precursor to Cycas was found in Triassic sediments in Antarctica: Antarcticycas schopfii consists of small fragments of stem, about 14 cm long; one stem is branched. The Cycadales had competition, of course. Cycadeoids and the Williamsonia both found this new warm climate equally to their liking. Judging from fossils found so far, they may have actually been more populous during the Mesozoic than the Cycadales.
Aricycas paulae
In foreground, Lyssoxylon grigsbyi, |
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